Olympic Lifting: Just a Sport or Key in the development of Power?

Dmitry Klokov of Russia competes in the men's 105kg weightlifting competition during the World Weightlifting Championships at Disney Village in Marne-la-Vallee outside Paris

What is Olympic lifting?

Olympic lifting is the aim to lift the most amount of weight in the two competition lifts of the Snatch and Clean & Jerk. However, what makes the movements difficult is the technique used which requires a high amount of explosiveness and strength to be successful. The sport of Olympic weightlifting has been in many forms but the modern version has been around since 1972.

How does it affect performance?

Due to short explosive nature of the Olympic lifts and their variations it is evident that the anaerobic ATP-PC energy system is key to effect performance and use of these movements. The use of Olympic lifts develops the neuromuscular patter in multiple joint partners known as triple extension ie: the hip, knee and ankle when jumping or sprinting. The triple extension process begins with the closing of the joints, followed by a fast opening of the joints. By developing this neuromuscular pattern it allows for faster recruitment of muscle and so increasing the speed of the contractile force.

Using Olympic lifts to develop power

Over the years different training methods have been used to develop power (Hoffman, 2004) due to its vital importance in all sports. The difference in the best athletes/players in the world is their ability to generate power whether this is to beat an opponent or to force an opponent to the ground from a tackle. To help develop this differentiating feature in sport Research (Johnson, et al, 2008) suggest that with the use of the Olympic lifts in training, Power output, increased force development and efficient neuromuscular patterns can all be developed.

 Even though power consists of force x velocity, the contribution to the physical demands of power in training is not so equal. There have been two trains of thought when considering the development of power. The development of strength and then subsequent practice in the sporting activity or the development of explosive power, which seems the most effective due to explosive power being a learned skill from the neuromuscular system (Gamble, 2010, pg 79)

Traditional methods such as Power lifting  can produce strength however, this method of developing strength, can be characterized as being of slow speed and have a negative effect on the explosive power of athletes (Johnson Sabatini, Sparkman, 2008). To account for this need to develop speed-strength as opposed to speed-strength, which is defined by Athlepedia to be “the ability of the neuromuscular system to produce the greatest amount of force in the shortest possible time and is characterised in 3 components. Starting strength, Explosive strength and reactive strength”.

Hoffman’s 2004 study, conducted a study with 20 College Level American footballers to show the differences between powerlifting and Olympic lifting in the development of power. What was found was both groups developed significant gains in their strength, measured through a 1RM Back Squat however, those who had used Olympic lifting in their training developed a greater improvement in their Vertical Jump (VJ) This was supported further by Channel and Barfield (2008) who showed that both methods increased VJ however Olympic lifting was produced greater gains.

However, Hakkinen et al (1987) found that after observing a years training with elite weightlifters that the development of the Stretch shortening cycle had improved but it had become slower in its application of force. Hakkiken et al put this down to the concretion dominance involved in the Olympic lifts. There is also uncertainty surrounding the bi-lateral nature of the lifts that their application to uni-lateral events such as sprinting are debatable (Youngs, 2006). Therefor it may be more beneficial to consider the split variations of the Olympic lifts.

Technical Breakdown and my own use of Olympic lifts

In the following section I will demonstrate the Olympic lifts in their different variations for each lift. So for the Snatch, I will be showing the Full Snatch, Power Snatch and hang power snatch. For the Clean & jerk I will be demonstrating, the full clean and jerk, power clean, hang clean and the full split clean.

 For each exercise I will attempt to highlight the technical demands of each lift, with links to people more experienced than me in the field to better explain the process. As a minor detail for those wanting to know more about how to perform the lifts, “the hook grip” is used as to prevent a weak grip effecting how much a person can lift.

Snatch

For an example of a powerful snatch see the video below of Russian Weightlifter Dimity Klokov lifting 205kg.


 

Full Snatch

The bar starts over the middle of the foot, not too close to the body, with shoulders slightly in front of the bar. There should be space a significant space between the hip, arm and chest to know if this is correctly set up. As the first pull begins, the back angle of the athlete should remain the same as the original set up angle, with the bar being pushed up by the legs rather than pulled by the arms and upper body. On the second pull, the bar does not go around the knees; rather the knees are sent back to be in the correct position. Once past the knee, you want the hips to open up and be ready in the power position, however shoulders still need to remain over the bar. Once past knee, the triple extension begins, with a violent extension of hips, knees and ankles and done efficiently should result in the bar being overhead. During this phase of the lift the bar will become ‘weightless’. At this point the athlete should drop underneath the bar and be in the catch position, with arms turned out and core tight to maintain strength throughout the movement. The athlete can then stand with the bar still overhead to complete the lift.

Power Snatch

The power snatch is the same as the full snatch, however during the catch phase the athlete must not go below 90 degrees knee angle. This variation can allow for more focus on the power development of the lower joints.

Hang Snatch

The hang snatch allows for those with weak technique o begin to understand the triple extension required to efficiently lift the bar. The bar is brought up to the ‘hip pocket’; the gap between the pubic bone and waist and from this position the athlete violently extends hips, knees and ankles to move the bar from the hip to the catch position overhead at either the power or full depth position.

Clean

For an example of an elite clean and jerk, look no further than Pyrro Dimas

 Full clean and Jerk

The starting position of the clean involves the bar over the middle of the foot, a nice flat back, with hips way below the shoulders with those shoulders over the bar. The grip width should be just outside of the knees as to allow the athlete to lift without connecting with those knees. To begin the first pull, the back remains at the same angle as set up with bar being pushed up to mid thigh level from the legs, with knees being sent back and out rather than going around the knee. From the mid thigh position, the athlete then enters the transition or 2nd pull, the athlete extends the hip create a vertical back, with shoulders back and to shove the knees under the bar with knees still bent. This allows for a strong power position for the final part of the clean portion. From this position the athlete will engage the triple extension and include a shrug and drop underneath the weight at the moment of weightlessness. If done effectively then the athlete will jump from the ground and the bar will land on the shoulders. When catching the bar in the front rack position it is important to catch in only a few fingers grip as due to flexibility it is difficult to do so.

Jerk

In the Jerk part of the lift, the hook grip is released to a normal grip. The athlete dips and drives up to full extension with bar overhead, over the middle position of the body. The legs split front and back with the back leg acting as support and the front providing the drive the complete the lift overhead in full extension with straight legs.

Power Clean

This follows the same pattern as the full clean however the bar is caught above 90 degrees knee angle in the front rack position.

Hang clean

The hang clean variation involves starting from the ground and bringing to the hip or starting from blocks to high hang position. The athlete then finds their position and drives through their triple extension of the hip, knee and ankle to finish in the from track position.

Summary

Olympic weightlifting can be beneficial for training power in athletes, if the sport of participation reflections the specific adaptations which will because. However, the lifts can be manipulated to suit uni-lateral events in such exercises as the split snatch or the split clean and jerk. The teaching of technique to the athletes allows for the better development of the triple extension patterns in the athletes when performing in their sport of choice. So it is down to the coach or player to ensure that the exercises are safe and do not increase the risk of injury.

Reference:

  • Channell, B.T & Barfield, J.P. (2008). Effect of Olympic and traditional resistance training on vertical jump improvement in high school boys.Journal of strength and conditioning research. 22 (1), 1522-1527
  • Gamble, P (2010). Strength and conditioning for team sports: Sport Specific physical preparation for high performance. London, UK: Routledge. 79
  • Hakkinen, K & Komi, PV & Alen, M & Kauhanen, H. (1987). EMG, Muscle Fibre and force production characteristics during a one year training period in elite weightlifters. Europen Journal of Applied Physiology. 56, 419-427
  • Hoffman, J & Cooper, J & Wendell, M & Kang, J. (2004). COMPARISON OF OLYMPIC VS. TRADITIONAL POWER LIFTING TRAINING PROGRAMS IN FOOTBALL PLAYERS. Journal of strength and Conditioning Research. 18 (1), 129-135
  • Johnson, J.B, Sabatini, P.L & Sparkman, M.R. (2008). A debate between power lifting and Olympic lifting as the main athletic training method.Virginia Journal. 29 (4), 19-23.
  • Young, B. (2006). Transfer of strength and power training to sports performance. International Journal of Sports Physiology and Performance. 1, 74-83
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Complex training: Key training tool or Detrimental to performance?


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What is Complex training?

Similarly to plyometric training, complex training originated from the Soviet Union with the first journal article being written about it by Fleck and Kontor in 1986. Complex training, or Post activation Potentiation (PAP) is the combination of a high intensity exercise with a heavy load, such as a Back Squat, to a speed strength or explosive training method such as plyometrics or a sport specific explosive movement (Beachle & Earl, 2008; Gamble, 2010).

Post-activation potentiation is the correlate between fatigue and performance where, muscular force is improved as a result of previous contractions (Tillin et al 2009). The previous contractions cause an increase in potential contraction force due to the increased level of neurones sent through the synaptic nerves. This is similar to the effect of the Stretch shortening cycle mentioned in this Plyometric training blog. Due to a higher force of contraction being in the muscle, neurones are sent to the muscle that fire up the Central Nervous System (CNS) pattern associated with the performed movement. The issue for the coach and athlete is finding the balance between the fatiguing of the muscles and the optimal time for an increased training stimulus after a heavy lift.

Movement combinations can include:

  • Heavy Back squat and Vertical Jump
  • Bench Press and Power push up
  • Deadlift and a sprint
  • Barbell Lunge and one-legged Vertical jump.

Factors affecting the use of Complex training

 Athlete strength

Baker (2003) demonstrated with 16 rugby players, who had at least 1 year of resistance training experience, that the strongest members of the group bettered the improvement made by those who had low levels of strength. So it is recommended that athlees don’t engage in complex training until they have a recommended level of strength (Ebben and Watts, 1998). Beachle and Earle (2008) also suggest that despite it’s enhancing evidence it may inappropriate for novies and youths.

Rest intervals

A very important consideration when carrying out complex training is the rest period between the heavy lift and the explosive exercise (Ensen and Ebben, 2003). As carter and Greenwood (2014) demonstrate, research has shown ranges of complex training rest intervals to range from 30 seconds to 24 minutes. Comyns et al (2006) suggests a 4-minute rest interval is optimal for exploiting the PAP response with 1 to 4 minutes or less showing no improvement in muscle force output. However, studies have also shown 8-12 minutes to be effective for taking advantage of the PAP response. (Bevan et al, 2009). However, due to the training environment it may be necessary to find a balance between the two as athletes will not want to be waiting around to continue with exercise, so it may be necessary to find a compromise of 4-8 minutes for the athlete, however individual differences will play a role so therefor it is important to test to see how best the athlete responds to the stimuli.

Weight of the Heavy Lift

Carter and green wood (2014) suggest that a weight no less than 85% of 1RM should be used during this phase of complex training, so based upon Beachle and Earles (2008) table of reps, no more than 5 repetitions should be done of the exercise.

My experiences of Complex training

My sport is Football, so therefor I had to find a suitable complex pair, which matched the movement of kicking a ball, so it had to be unilateral and have a follow through type action. I decided to use the complex pair of a Forward lunge and a one legged box jump

As part of the load phase, I perform a forward lunge with the bar in the front rack position with a weight above 85%  of my 1RM, in this circumstance, 5 reps. I then wait 5 minutes to perform the explosive movement phase, which is the one legged box jump.

Application to practice

Complex training attempts to increase the training stimuli encountered by the athlete as to increase performance and with effective recovery (see here for my recovery blog) it can increase have a greater long-term effect. However, if an athlete can become accustomed to it’s uses and can control the variables of complex training there is no reason why the athlete cannot use prior to short burst of explosive type activities as the final part of their warm up ie: 100m, Long jump or even in situations such as the NFL Combine where athletes are tested for their physical abilities.

References:

  • Baechle, T & Earle, R (2008). Essentials of strength and conditioning. 3rd ed. Leeds, UK: Human Kinetics. 394-395.
  • Baechle, T & Earle, R (2008). Essentials of strength and conditioning. 3rd ed. Leeds, UK: Human Kinetics. 422-423.
  • Baechle, T & Earle, R (2008). Essentials of strength and conditioning. 3rd ed. Leeds, UK: Human Kinetics. 460-461
  • Baker, D (2003). Acute effect of alternating heavy and light resistances on power output during upper-body complex power training. Journal of Strength and Conditioning Research. 17, 493-497.
  • Bevan, HR & Owen, NJ & Cunningham, DJ & Kingsley, MIC & Kilduff, LP. (2009). Complex training in professional rugby players: Influence of recovery time on upper-body power output. Journal of Strength and Conditioning Research. 23, 1780-1785
  • Carter, J & Greenwood, M. (2014). Complex Training Reexamined: Review and Recommendations to Improve Strength and Power. Strength and Conditioning Journal. 36 (2), 11-19
  • Comyns, T & Harrison, A & Hennesey, L & Jensen, R. (2006). The optimal complex training rest interval for athletes from anaerobic sports. . Journal of Strength and Conditioning Research. 20, 471-476.
  • Ebben, W & Watts, P. (1998). A review of combined weight training and plyometric training modes: Complex training. Journal of Strength and Conditioning Research. 20, 18-27
  • Ensen, R & Ebben, W. (2003). Kinetic analysis of complex training rest interval effect on vertical jump performance. Journal of Strength and Conditioning Research. 17 (.), 345-349
  • Gamble, P. (2010). Strength and conditioning for team sports: Sport specific physical preparation for high perfomance.. New York: Routledge. 139-157
  • Fleck S and Kontor K. Soviet strength and conditioning: Complex training. Strength Cond J 8: 66–68, 1986.
  • Tillin, N.A & Bishop, D. (2009). Factors Modulating Post-Activation Potentiation and its Effect on Performance of Subsequent Explosive Activities. Sports Medicine. 39 (2), 147-166
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Small Sided Games as metabolic conditioning.

The above video shows a Small Sided Game from the pre-season training of Bayern Munich. It is evident that the players have different physical demands depending on their role in the session structure. The method of using SSG as Fitness training instead of traditional fitness training is becoming a key point in the training of physical attributes in football players. This means that the development of fitness factors can be carried out in a more soccer specific way than plain running (Hoff et al, 2002)

 What are Small sided games?

 Small Sided Games (SSG) is one of the most frequently seen methods of play in coaching sessions or on the street with children playing 5v5. When used by Coaches during their training sessions, it means that players can repeatedly experience situations that happen in the game (Owen et al, 2004). SSG have been developed to become a popular strategy for improving the aerobic fitness for football players (Impellizzeri, 2006) and by affecting the variables of SSG such as pitch size and player numbers, it can influence the physical demands of the session (Aguiar, 2012) and if carried out effectively exceed match intensities (Hill-Hass, 2011)

 What Factors affect the physical demands of Small Sided Games?

 There are numerous factors that coaches must be aware of when designing sessions for their players, and understand how to manipulate these variables to elicit the desired physical demands (Clement, 2012).

 Player numbers

With decreased numbers in small sided games, it can mean that players have more involvement with game activity and the amount of high intensity efforts during play increases (Jones & Durst, 2007). This means that recovery time between these high intensity efforts is reduced and can therefore, improve the aerobic capacity of the players involved (Hill-Hass, 2011).

 Area size

The manipulation of area size is one of the key factors in the use of Small Sided Games. In Koklu et al (2013) research they demonstrate that with the variation of area sizes, certain demands of gameplay are altered. What was found was that, with smaller area sizes came reduced levels of heart rate, decreased frequency of higher intensity runs and a more anaerobic demand to those small-sided games played in larger areas. Similarly to this research, Harrison (2013) found that with more room for the players to execute technical ability that the intensity of practice increased. Consequently, it can be said, depending on the amount of players and the aim of the small-sided games, coaches can manipulate area dependent on player numbers and what they want the physical demands of the session to be.

 Conditions and rules

During coach sessions it is typical to see a coach or players recommend, the use of different conditions and constraints to be put on an individual or the group. Certain conditions have significant effects upon the physical demands of the session.

 Firstly, this can include the use of limiting touches compared to free play (Dellal, 2011), as with a 1 or 2 touch condition set by the coaches the physical demands include an increase in the intensity of the players movements however, this did cause a decrease in their technical success in passes and losses of possession. With free play being allowed by the coach the difference was that, high intensity movements where still frequent but with no touch limitations, the players technical ability improved. So, the balance between creating physical demands and the tactical and technical success must be considered.

 Secondly, the use of a defensive man-marking tactic can cause an increase in the heart rate and in the Rate of Perceived Exertion (RPE), a perception for the players of how hard the session was for them (Ngo, 2012). This study also found that with the inclusion of goals in the session, that intensity of practice was also increased. So this suggests that the motivation of the players in the session can affect the physiological demands. So it may seem that by doing less, pure possession game where 5 passes may equal a goal, it can be more beneficial to include goals to elicit a greater aerobic response due to increased motivation to score.

 Along similar lines, the use of a ‘multi-ball’ system where balls are not our of play for long periods of time being collected by payers, can cause effect players physical output. By remaining continuous rather than an interval practice, heart rate remains higher (Franchini, 2011) and maintaining these intensities over a period of time is key to physical development.

 By understanding the different physical outputs demanded by certain session coaches can recognise when and when not to do a certain session or adapt to suit the situation. This could be beneficial for when players need to have more focus on tactical understanding or for when player need to recover well and be provided with a session of decreased intensity.

 With the use of Small sided games to improve player’s physical capabilities, it allows for reduced time to be spent performing traditional interval training methods (Hill-Hass, 2011). This could be extremely effective for those at grassroots level who are there to play with the football. The use of Small sided games to increase fitness levels can increase levels of motivation and maintain participation.

 My own experiences of Small Sided Games

As I’ve been coaching through the years, I’ve become more aware of why I do what I do in terms of putting on sessions for the players involved. With the university team I coached last season, our training sessions where the day before our games and from my own perspective the balance between improving players abilities and being careful of tiring out the players was a difficult balance. One session in particular I coached seemed to be extremely strenuous and the following game I saw a drop in their physical abilities.

Below you will see a basic explanation of this session with the university group.

From the session below you can see that players are engaged and so motivated to make those high intensity runs to the opposite side of the field where they can then score. No touch limitations where put on the session and balls that went out where replaced with another as soon as possible.

Further examples of Small-sided games being used for metabolic conditioning go to this youtube channel

https://www.youtube.com/user/sfield13

Summary

Small-sided games can be used instead of traditional metabolic conditioning by manipulating the variables of the practice to suit the required demands of the team, player and coach. This can include reducing area size to work the anaerobic systems, increasing area size with smaller numbers to force a higher frequency of intensity by the players and so working the aerobic system.

For those at the elite end of performance the use of GPS and heart rate data can be used to monitor player load and the influence of different sessions on players physical output. However, for those at grassroots level, the RPE scale previously mentioned allows coaches to see player’s perceptions of ‘work’ during practice. So at the end of practice just ask players on a scale of 6-20, how hard they thought that session was physically. Store this information with the session plan to allow yourself as a coach to know how your session with affect the players involved.

Hopefully from this blog you’ve developed an appreciation of the effect that conditions can have on the physical demands you would like to come from the session. As always feedback is welcome in the comments.

References:

  1. Aguiar, M & Botelho, G & Lago, C & Macas, V. (2012). A review on the effects of Soccer Small-Sided Games. Journal of Human Kinetics. 33 (1), 103-113
  2. Clementa, F & Couceiro, M & Martins, F & Mendes, R. (2012). The usefulness of Small sided games on soccer training. Journal of Physical Education and Sport . 12 (1), 93-102
  3. Dellal, A & Lago-Penas, C & Wong, D & Chamari, K. (2011). Effect of the number of ball contacts within bouts of small-sided soccer games. International journal of sports physiology and performance. 6, 322-333
  4. Fanchini, M & Azzalin, A & Castagna, C & Schene, F & Mcall, A & Impellizzeri, F. (2011). Effect of bout duration on exercise intensity and technical performance of small-sided games. Journal of Strength and Conditioning Research. 25, 453-458
  5. Harrison, C & Andrew, Kidling, A & Gill, N & Kinugasa. (2013). Small-sided games for young athletes: is game specificity influential?. Journal of Sports Sciences. 32 (4), 336-344.
  6. Hill-Hass, S & Dawson, B & Impelizzeri, F & Coutts, A. (2011). Physiology of Small-Sided Games Training in Football: A Systematic Review. Sports Med. 41 (3), 199-220
  7. Hoff, J & Wisloff, U & Engen, LC & Kemi, OJ & Helgrund, J. (2002). Soccer specific aerobic endurance training. Br J Sports Med. 36. 218-221
  8. Impellizzeri, FM & Rampinini, E & Marcora, SM. (2005). Physiological assessment of aerobic training in soccer. Journal of Sports Sciences. 23 (6), 583-592
  9. Jones, S & Drust, B . (2007). Physiological and technical demands of 4v4 and 8v8 games in elite youth soccer players. Kinesiology. 39 (2), 150-156.
  10. Koklu, Y & Albayrak, M & Keysan, H & Alemdaroglu, U & Dellal, A. (2013). IMPROVEMENT OF THE PHYSICAL CONDITIONING OF YOUNG SOCCER PLAYERS BY PLAYING SMALL-SIDED GAMES ON DIFFERENT PITCH SIZE – SPECIAL REFERENCE TO PHYSIOLOGICAL RESPONSES. Kinesiology. 45 (1), 41-47.
  11. Ngo, J & Tsui, MC & Smith, A & Carling, C & Chan, GS & Wong, DP. (2012). The effects of man-marking on work intensity in small-sided soccer games. Journal of Sports Science and Medicine. 11, 109-114
  12. Owen, A. (2004). Physiological and technical analysis of small sided condition training games within professional soccer. Soccer J. 49 (5),
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A change of direction for plyometric training

In the video below you can see Lionel Messi Scoring vs Real Madrid one of the great El Classico goals. From a purely physical view,alongside his outstanding dribbling ability, the changes of direction from slow to fast were incredible.

Now, football is a sport with frequent changes of direction, which involve slowing down to deceleration and accelerating away. The use of plyometric training can be therefor be beneficial for decreasing the time it takes to change direction in games. The best players in the world, even those from previous generations, all share the ability to beat their opponent with changes of direction ie: Messi, Cryuff, Ronaldo, Maradona, Iniesta. So Surely to be as good if not better than them it would be beneficial to train the body to suit. A method of doing so is through plyometric training.

What is Plyometric Training?

Plyometric training is aimed at producing a greater amount of force generating from a pre-stretch of the muscles involved in a movement that is influenced by the Stretch-Shortening Cycle.

History of Plyometric training

Plyometric training originates from the notorious Soviet Union and stem from a Russian scientist named Yuri Verkhoshansky, who had originally called this form of training “Shock training” due to the shock of the landing phase involved. The term ‘Plyometric’ came from an American athlete called Fred Wilt who had seen the Soviet Union athletes prepare for track and field events. Plyometric training began to gather great attention due to the Eastern European countries domination in power related events.

The Science.
(Baechle & Earle, 2008)

Plyometric training refers to the manipulation of the performance of the Stretch Shortening Cycle (SSC). This is what produces a high intensity concentric contraction (to shorten the muscle) resulting from a powerful eccentric (lengthening of the muscle) contraction. The key factors in the SSC responsiveness are the Spindles and Golgi Tendon Organs (GTOs) inside of the muscles.

The spindles inside the muscle act as proprioceptors that feed the Central Nervous System (CNS) and relays message to the brain about the length of a muscle. When muscles are stretched, so are the spindles, this therefor causes a heightened neuron response in the muscles via the CNS. This increases the potential contractile force from a future concentric movement.

Similarly to muscle spindles, the Golgi Tendon Organs (GTOs) act as proprioceptors, however GTOs respond to the tension of the muscle compared to length. Upon activation, they cause an impulse to be sent to the muscle, that inhibits motor neuron activity in the muscle, which causes the muscle to relax. This is done to prevent the muscle becoming injured, however the consequence is a decreased amount of force production due to the muscle losing tension.

The contribution of Muscle spindles and Golgi Tendon Organs are vital in the manipulation of the stretch shortening cycle. Through plyometric training, the inhibiting response of the GTOs can be overcome and tension in the muscle can be increased to produce a more powerful concentric contraction from an eccentric contraction, which encompasses the Stretch-shortening cycle.

How the stretch shortening cycle works
(Baechle & Earle, 2008)

The SSC contains 3 phases of action but not all 3 are equal in time, as some may not need to last as long as others.

Phase 1 is the eccentric phase, where the kinetic energy from the agonist (a muscle which causes its own contraction) muscle or muscle group is pre-loaded with elastic, kinetic energy. If we consider a change of direction to be a plyometric movement, then phase 1 would be the time from touch down of the foot to the bottom of the movement. This is where the amortization phase begins.

Phase 2 is the amortization phase or transition phase and is the transition time between the eccentric and the response of the concentric contraction. It is at this point the Muscle spindles play their role to fire neurons into the muscle to generate force. If the amortization phase lasts too long, kinetic energy is released as heat and reaction force is decreased (Cavagna, 1977).

The Concentric phase, phase 3, is the reaction of kinetic energy in the muscles combined with the pure muscle contraction force. This means the movement response is more of the muscle group’s previously achievable force (Cavagna & Dusman & Margaria, 1968; Svantesson & Grimby & Thomme, 1994). Following the change of direction example this would be the push off from the original leg to another direction to get past an opponent.

What is the research saying?

Unknown

Bruce-low and Smith (2007) review explosive training methods in sport and they conclude that due to the lack of sport specificity of the movements, specifically the vertical jump (Carpinnelli et al, 2004), that it is better to do slow, controlled power movements in combination with sport specific training to improve sporting performance. More recent research however, has attempted to justify its use during training.

In Villeral et al (2010) research review of 56 studies, it attempts to find themes and conclude upon an optimal approach towards plyometric training. It demonstrates that Plyometric training significantly improved Vertical Jump Height and found that those who used a combination of exercises such as Squat Jumps (SJ), Depth Jumps (DJ) or Counter movement Jumps (CMJ) generate greater gains than those who only use 1 type. The research also found that those with greater experience in sport had the best improvement in VJH performance.

Specifically to Football, Thomas, French and Hayes (2009) demonstrate that both Counter movement jumps and depth jumps both can cause an improvement in explosiveness and agility, with no significant difference between the two methods. Vaczi et al (2013) demonstrates similar finding showing the use of uni-lateral and bi-lateral exercises together increase power and football specific agility in the Illinois agility test and T-Test.

Applying theory to training with specific focus on football

Taking a critical view of the research, it can be said that plyometric can improve the testing of the explosive attributes of participants, however with further specificity to a specific sport such as the football specific agility tests, it can be even more beneficial. Therefore I have attempted to replicate the situations that occur in football and create plyometric training exercises that attempt to improve performance.

Bi-Lateral Methods
Counter-movement jump + Header of a ball

Uni-Lateral Method
1 leg depth jump + sprint

Summary

By using plyometric training football players can decrease the time it takes to change direction in a 1v1 situation, improve their leaping ability and their power over a short distance, but what is key is knowledge of how best to achieve those. By manipulating the variables of training to suit your individual attributes of recovery and ability, while maintain the football specific or even position nature of training, plyometric training can be extremely beneficial.

Additional information and examples:

Arjen robben and Sebastian Schweinsteiger plyometric training

http://athletics.wikia.com/wiki/Plyometrics

Lionel Messi using plyometrics in his recovery from injury

 

References

1. Baechle, T & Earle, R (2008). Essentials of strength and conditioning. 3rd ed. Leeds, UK: Human Kinetics. 415-417
2. Bruce-Low, S & Smith, D. (2007). Explosive exercises in sports training: A Critical Review. Journal of Exercise Physiology. 10 (1), 21-33
3. Carpinelli, R.N & Otto, RM & Winnet, R.A. (2004). A critical analysis of the ACSM position stand on resistance training: insufficient evidence to support recommended training protocols. Journal of Exercise Physiology. 7 (3), 1-60
4. Cavagna, G.A & Dusman, B & Margaria, R. (1968). Positive work done by a previously stretched muscles. Journal of Applied Physiology. 24, 21-32
5. Cavagna, G.A. (1977). Storage and Utilisation of elastic energy in skeletal muscleq. Exercise and Sport Science Reviews. 5 (,), 80-129
6. Svantesson, U & Grimby, G & Thomme, R. (1994). Potentiation of concentric plantar flexion torque following eccentric and isometric muscle actions. Acta Physiol Scand. 152 (1), 287-293
7. Thomas, K & French, D & Hayes, P. (2009). The effect of two plyometric training techniques on muscular power and agility in youth soccer players. Journal of Strength and Conditioning Research. 23 (1), 332-335
8. Vaczi, M & Tollar, J & Meszler, B, Juhasz & Karsai, I. (2013). Short‐Term High Intensity Plyometric Training Program Improves Strength, Power and Agility in Male Soccer Players. Journal of Human Kinetics. 36 (1), 17-26
9. Villarreal, E.SD, Requena, B & Newton, R.U. (2010). Does plyometric training improve strength performance? A meta-analysis. Journal of Science and Medicine in Sport. 13 (1), 513-522.

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Altitude Training

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The effects of altitude on performance came to the forefront of athletics during the 1968 Olympics in Mexico City, when the performance of endurance athletes dramatically dropped. Those athletes from higher altitude environments did not seem to suffer as much as others in the competition, where the stadium had an altitude of 2239 meters. This was the catalyst for research into the effects of altitude on performance.

ImageThe effects of altitude become a factor around 1,000 to 2,000 meters above sealevel (Wilmore, Costill & Kenney, 2008) with less than 500m being considered sea level. Moderate altitude levels range from 2,000 to 3000 meters and it is at this level that performance is significantly affected, with the higher ranges of altitude 3,000m plus showing severe effects health as well as on performance. Due to the air reducing pressure and being thinner at these higher altitudes, it can actually disrupt the sensory control of athletes and influence their balance and co-ordination. This decreased air resistance can play an advantage in sporting contexts such as ball-orientated sports such as football or American Football. Could this be why Peyton Manning, the QB of the Denver Broncos, who plays at 1732 meters above sea level broke the passing yards record in the NFL this season?

The science

As altitude increases the percentage of oxygen in the air, actually remains constant at 21% regardless of the altitude a person is at. The physiological effects occur due to there being less oxygen particles in each breath a person takes (Smoliga, 2009). These conditions are known as Hypoxic and the low-pressure environment of high altitude is known as hypobaric (Smoliga, 2009). The main physiological advantage of training at higher altitudes is that it can cause an increased level of Erythropoietin (EPO). This triggers the bone marrow to produce more red blood cells, which therefor increase the amount of hemoglobin in the blood. This means that more that more oxygen molecules can be carried in the blood to the muscles in use (Smoliga, 2009). Now, there have been suggestions that due the similarities to blood doping, made famous from the Lance Armstrong scandal, that altitude training is a form of cheating. However, Wilber (2011) shows that it acceptable to be used by all athletes, due its natural occurrence in the environment and is just another variable to take into consideration when training for sport.

Training methods

The ways in which altitude training can be used can vary. These include living high and training high (LH/TH); living high and training low (LH/TL) or living low and training high (LL/TH).

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The most obvious example of living high and training high can be the consistent domination of endurance sport athletes coming from East Africa in counties such as Ethiopia and Kenya (Wilber, 2011). The environment in this area is perfect for the development of long distance runners as the high altitude forces an adaption to occur. Runners such as Mo Farah have taken this on board and have moved away from their families to high altitude environments, in his case the famous Rift valley, in Kenya.  For those not born into high altitude conditions, Wilber (2011) showed that living high and training low may be the best option. This can allow for a higher training stimulus in training and therefor better performance when at sea level.

The live low, train high method has some advantages also. It can allow for increased recovery time after training due to the increased oxygen intake. However, due to training high, the training stimulus will be lower and consequently have a detrimental effect on performance. Brutsaert al (2000) shows that those who live at a lower altitude and train in high altitude conditions suffer lactate build up much earlier than those who live high, train high or train low.

Examples of the use of altitude training include the England rugby union team preparing for the rugby world cup in South Africa by doing interval training using masks, which fed through air simulating conditions of 2,000m. However, the Fitness coach of England at the time explained its use to be to “experience the conditions” and “suffer together”. So, despite its weak physiological application, it’s possible that it can have a significant psychological effect. Many athletes and teams choose different methods of using altitude training in their practice, with athletes such as the triathletes, the Brownlee brothers, sleeping in hypobaric tents, simulating the artificial version Live high, train low conditions or fighters in the UFC using Big bear, California, a live high train high approach, to prepare for fights.

 Implications

ImageWith South America being a continent with some severe altitude variations, the 2014 FIFA world cup will be one where the effects of altitude will be noticeable throughout. Stadium altitudes will be ranging from 0 at sea level in Rio de Janiero to over 1,172 meters in the capitol city of Brasilia. It will be vital how team prepare for the tournament. This has happened previously with world cups held in Mexico in 1986 and more recently South Africa in 2010. Prior to the 2010 world cup in South Africa, England spent 2 weeks in the Austrian Alps attempting to acclimate to South African conditions. However, this produced a questionable result with England going out in the last 32 with a 4-1 defeat to Germany.

Research (Duke, Chapman & Levine 2012; Millet & Roels & Schmidt et al. 2010; Igor et al, 2011) has recommended that teams involved in high altitude conditions, go through an acclimating process ranging from 2 to 4 weeks to gain the benefits. However, due to the short period of time between the seasons in Europe finishing, it may be necessary to short this to 1-2 weeks to allow for recovery and other factors, which can occur (Billaut et al 2012). The acclimation effects will apply, but their influence will mostly be on health with small benefits for performance.

Further research (Billaut et al 2012) has shown that the effects of altitude in team sports can affect different positions in different ways. Due to the higher longer sprints of the wide players in the team such as fullbacks or wingers, it is harder for them to recover. This may mean a change in tactics by the coach to focus play through the middle as to alleviate the stress or even take more of players in these positions and rotate where possible. Rotation can allow for the maintenance of intensity in play, and allow for better recovery over the competition period. 

Summary

Understanding the role that altitude training can have on performance is vital, as it will allow athletes to compete and train at higher levels and gain the edge they need. The use of a live high/Train Low approach has been shown to generate the greatest gain. It will be a tough task to overcome the East African dominance on endurance sport while their environment at high altitude. However, the  live high  approach could be achieved through artificial means such as chambers, tents or even hyperbaric houses depending on access and commitment. If an athlete the can reach the level hours needed in a day to acclimatise to the artificial altitude then there is no reason why a person at sea level cannot feel the benefits. 

It will be interesting over the summer to see how international teams deal with the effects of altitude on performance and whether those countries who are used to higher altitudes can succeed. Acclimation, Combined with an effective recovery process, may just give those teams unaccustomed to it a chance at success. 

 

 

 

References

Billaut, F & Gore, C & Aughey, R. (2012). Enhancing Team-Sport Athlete Performance. Sports Med. 42 (9), 751-767.

Brutsaert, T et al. (2000). Performance Of Altitude Acclimatized And Non-Acclimatized Professional Football (Soccer) Players At 3,600 M. Journal of Exercise Physiology. 3 (2), 28-37

Costill, L & Wilmore, H & Kenney, L. (2008). Physiology of sport and exercise. Human Kinetics.

Duke, J & Chapman, R & Levine, B. (2012). Live-High Train-Low Altitude Training on Maximal Oxygen Consumption in Athletes: A Systematic Review and Meta-analysis. International Journal of Sports Science & Coaching. 7 (1), 15-19

Igor, R et al. (2011). New tendencies in the application of altitude training in sport preparation. Journal of Physical Education and Sport . 11 (2), 200-204

Millet, G & Roels, B & Schmidt, L et al. (2010). Combining hypoxic methods for peak performance. sports Med. 40 (1), 1-25

Smoliga, J. (2009). Altitude And Beyond: The Science Of Hypobaric Training. To Train Or Not To Train At Altitude.

Wilber, RL. (2011). Application of altitude/hypoxic training by elite athletes. Journal of human sport and exercise science. 6 (2), 271-286

 

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Recovery strategies: Build on the basics

Recovery

Recovery in sport is a vital consideration for athletes, players and coaches. By controlling the variables of recovery, it causes a decreased recovery time in the training process which means an increase in the level of super-compensation or adaption, which is  vital to reaching athletic potential. Image

Recovery however, is not only of physical benefit, it can also have a mental effect (Tessitore & Meeusen & Cortis 2007) therefor it is important to monitor fatigue in the short and long term. A method of monitoring fatigue and consequently recovery from performance is to ask the player how they are feeling and using the RPE (rate of perceived exerction) scale to do so. This can be done after training sessions or throughout the season. This can allows for coaches to recognize how different sessions affect a player’s continual physical condition. At the elite level of performance with access to expensive technology, monitoring recovery can be taken further. Twist & Highton (2013) show by drawing fluids from the body through blood and/or saliva it can allow coaches to monitor how well the player has recovered or if the player needs more time to do so.

Application 

Recovery after performance has multiple levels of application, regardless of an athlete or player’s participation level. The key aspects of nutrition, stretching and sleep are vital. Furthermore, there are more advanced methods such as of cold-water immersion and the increasingly popular use of compression garments.

Nutrition

Those involved in all areas of sport need to give consideration to the basics of recovery strategies. No matter what level athletes can control their diet, rehydration and sleep (Tessitore & Meeusen & Cortis 2007). Nedlec et al, (2013) show that 1.2 g carbohydrate every hour post exercise for up to 5 hours (Jentjens & Jeukendrup, 2003) and 9 grams of (Beelen, Burke, Gibala et al, 2010) protein consumption after a match are effective recovery strategies for replenishing the body and repairing the muscles. Carbohydrates allow for the replenishment of glycolytic stores in the body, where for those sports lasting longer than 30-90 minutes are vital. Protein allows for the muscles to reduce soreness through muscle synthesis after previous muscle fiber breakdown. Remaining hydrated before, during and after performance is vital as cognitive and physical ability both suffer as a consequence.

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So a recommendation to aid recovery, is to reach a form of hyper-hydration ‘post exercise’ as to never get in a dehydrated state. This would be 200% of the total body weight lost during activity, so it requires a pre and post game screening by people weighing themselves to determine these numbers.

Sleep

Sleep is vital to the recovery process and vital for optimal performance. Despite sleep being one of key aspects of sleep Walters (2002) outlines athletes often neglect this aspect and in some circumstances sleep less than those who do not exercise, which can therefore lead to a decrease in performance (Davenne, 2009). . Bompa and Haff (2009) suggest 9-10 hours of sleep for those over the age of 18. This can include naps during the day and the recommended 8 hours of sleep during the night, which would make up 80-90% of this. By having sufficient sleep it allows the body to rest, recover and repair the body’s systems to be prepared for the next training session or game.

Stretching

The use of stretching is rife in sport with Dabedo et al (2004) showing that English football clubs use 40% of their total training time doing so with a major focus on static stretching, with over 50% of French football teams using it as a method for recovery (Nedlec et al, 2013), even though there is no scientific evidence to prove this. Lund, et al, (1998), Show that it actually causes a reduction in physical performance, especially when combined with eccentric loading such as slowing down or sports which involve High intensity changes of direction. Due to the other methods of recovery mentioned in this blog, which can speed up the recovery process but maintain physical ability, using static stretching after exercise is ineffective.

Is it a lack of knowledge at the elite level or is It an unwillingness to change as that’s what always been done? For athletes to be at their optimal levels they need to be at the top of their game and stretching will not provide that.

Compression Garments

Frequently, we see players in multiple sports wearing Nike, Under Armour or Adidas compression garments under their standard playing kit, with (Nedlec, et al 2013) showing 22% of French professional football teams using them. Compression garments in sport come in such forms as under shirts, and short and long pants.

The benefits of wearing compression garments in sports with sprinting and agility characteristics have been shown to have no significant benefits on the physical attributes of players (Nedlec, et al 2013). However, there may be a perceived mental boost in wearing such items, which can be called the placebo effect, as players believe themselves to be better with them even though there are minimal benefits. Bernhardt and Anderson (2005) show that while wearing compression shorts 93% of participants in their study felt they had performed better while wearing them.

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Compression garments were originally used medically, to reduce swelling and inflammation (Kraemer, et al, 2001) in those with blood flow issues as to increase oxygenation to those damaged areas, so the leap to help recovery from sports performance was granted. By increasing Oxygenation to the damaged muscles it allows for the increased rate of flushing of waste products from the muscles and so repairing them at a faster rate. Nedlec et al (2013) suggest they have particular benefits for highly trained athletes with Kraemer et al (2001) shows there is a lower perceived muscled soreness after wearing them post exercise. So consequently, despite the lack of evidence for the physiological benefits of wearing compression garments, the perception that they do increase recovery, or the placebo effect shows their potential benefit for recovery .

Cold Water immersion

In a recent blog post on pre-cooling, cold-water immersion was shown to have benefits for cardiovascular performance. It can also have further benefits on athletic performance.

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Nedlec et al (2013) shows that Cold-water immersion, specifically water of 9–10 °C used immediately post exercise for 10-20 minutes can have dramatic effects on anaerobic performance and perceived muscle soreness (Bailey, Erith & Griffin, 2007). Vaile, O’Hagan, Stefanovic et al (2011) suggest a whole-body immersion approach as to bring heat away from the skin to the core to allow for increased blood flow to the muscles for repair.

Despite this evidence, consistent use of cold-water immersion can have a negative impact on the long term adaptions caused by exercise, specifically in elite athletes. However, when athletes have a congested period of events, over a few days, Cold-water immersion can be a key tool. Used in the short-term process it can allow for a fast recovery process, specifically in the higher intensity sports such as football.

Key points for recovery

To perform optimally all athletes need to control their diet, hydration and sleep. This will allow for a higher level of training volume or rest when needed. Once the basics of recovery are consistent then it is time to use further recovery methods such as the effect of compression garments on muscle damage. When in a congested period of exercise, use Cold-water immersion to raise the level of fitness quickly to be nearer those optimal levels of performance.

References:

Bailey DM, Erith SJ, Griffin PJ, et al (2007). Influence of cold-water immersion on indices of muscle damage following prolonged intermittent shuttle running. J Sports Sci.;25 (11):1163–70.

Beelen M, Burke LM, Gibala MJ, et al (2010). Nutritional strategies to promote postexercise recovery. Int J Sport Nutr Exerc Metab.;20(6):515–32.

Bernhardt T, &Anderson GS (2005). Influence of moderate prophy- lactic compression on sport performance. Journal of Strength Conditioning Res. 2005;19:292–297.

BOMPA, T.O. & HAFF, G.G. (2009). Periodization: Theory and methodology of training (5th ed.). Champaign, IL: Human Kinetics.

Dadebo B, White J, George KP (2004). A survey of flexibility training protocols and hamstring strains in professional football clubs in England [published erratum appears in Br J Sports Med  38 (6): 793

DAVENNE, D. (2009). Sleep of athletes: Problems and possible solutions. Biological Rhythm Research, 40(1): 45-52.

Hausswirth C & Mujika, I (2013). Recovery for performance in sport. Leeds: Human Kinetics Ltd

Jentjens R, Jeukendrup A. (2003) Determinants of post-exercise glycogen synthesis during short-term recovery. Sports Med.;33(2): 117–44.

Kraemer, WJ et al. (2001). “Influence of compression therapy on symptoms following soft tissue injury from maximal eccentric exercise”. The Journal of orthopaedic and sports physical therapy 31 (6): 282–90

Lund H, Vestergaard-Poulsen P, Kanstrup IL, et al (1998). The effect of passive stretching on delayed onset muscle soreness, and other detrimental effects following eccentric exercise. Scand J Med Sci Sports.;8(4):216–21.

Nedlec, M et al . (2013). Recovery in soccer: Part 2 – Recovery strategies. Sports Med. 43 (.), 9-22

South African Journal for Research in Sport, Physical Education and Recreation, (2012)

Tessitore, A & Meeusen, R & Cortis, C . (2007). EFFECTS OF DIFFERENT RECOVERY INTERVENTIONS ON ANAEROBIC PERFORMANCES FOLLOWING PRESEASON SOCCER TRAINING. Journal of strength and conditioning research. 21 (3), 745-750

Twist, C & Highton, J. (2013). Monitoring fatigue and recovery in rugby league players. International Journal of Sports Physiology and Performance. 8, 467-474.

Vaile J, O’Hagan C, Stefanovic B, et al (2011). Effect of cold-water immersion on repeated cycling performance and limb blood flow. Br J Sports Med.;45(10):825–9.

WALTERS, P.H. (2002). Sleep, the athlete, and performance. National Strength & Conditioning Association, 24(2): 17-24.

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Pre-cooling: key to success in hot and humid conditions?

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Having an increased body temperature during exercise is commonly referred to being prepared and ready for whatever the activity is. It is a standard procedure for a warm up, when following the RAMP protocol. This means that muscles can become more pliable and that sweat evaporates from the skin more efficiently therefor regulating the temperature in the body. However, when in hot and/or humid conditions the necessity to raise the body temp even more can be detrimental to performance.

When in hot and/or humid conditions the body’s ability to control its temperature and muscle blood flow around the body (Thermoregulation) is compromised and so the ability of the athlete to continue performing optimally is jeopardised. This is due to the specific influence heat has on the cardiovascular system due to its regulatory control of the body’s level of physical homeostasis (Taylor and cotter, 2008). When body temp is particularly higher than usual, then an ‘Oxygen Debt’ is produced where the body cannot fulfil the demands of the skin and blood flow to the muscles. Sweating remains functional, but the core temperature of the body accelerates. For those taking part in longer distance events, combined with hot and/or humid conditions an athlete will have to reduce their exercise intensity or risk heat- related injury (Maughan, 2010).

The combination of long distance events and hot conditions can be a volatile mix with issue arising when in hot and/or humid conditions when taking part in events longer than 5 minutes. Tyler and cotter (2006) show that the longer distance and time an event goes the greater increase in body temperature. For those events under 5 minutes and in the anaerobic (ATP-PC and glycolytic systems), regulating body temperature is less of an issue due to its minimal involvement of the cardiovascular system.

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Studies (Quod et al, 2006;Sunderland and Neil, 2008) show a 6% decrease in performance in hot (32°C) conditions compared to moderate (23°C) with levels of RPE (Rate of Perceived Exertion) and perceived thirst being higher compared to moderate temperature conditions. So by reducing body temperature of an athlete in hot conditions it can cause a more optimal performance and prevent a negative influence of the conditions.

Pre cooling

A strategy to reduce body temperature, prior and between events is that of Pre cooling. This involves the reduction of body temperature to allow the body to perform in an optimal state by allowing the body increased time to reach the critical core temperature, which is so detrimental to performance. Quod et al (2006) outlines methods of doing so which are Internal cooling (Core) and External cooling (Skin). The methods that will be analysed will be Cold-water immersion, the use of cooling garments and cold-water ingestion.

Cold water immersion involves an athlete placing there whole body into cold water or a temperature lower than the bodies, with an aim to cause a reduction in heat production and increase heat storage capacity (Booth, 1998). Marino and Booth (1998) suggest reducing the temperature of the water of a 30-60 minute period as to prevent ‘shivering’.

Jones et al (2012) shows the practical and successful application in wider research, however, for those in the sub-elite this method may be unrealistic. To take an ice bath or the equipment necessary to carry this out can be unrealistic for those weekend participants in cycling, running or other cardiovascular demanding sports. A compromise for the sub-elite could be that of cold showers, as most facilities would have this option.

Cold-water ingestion causes lower skin surface and intramuscular temperatures due to heat energy being transferred to melt the ‘ice slush’ inside the body. Jones et al (2012) show the wider research showing the success of this type of pre-cooling method.  With it’s cheap an easy attributes and supported research this is a viable option for those at elite and/or sub-elite levels.

Cooling garment (towel/jacket). This may include such items as an ice vest as used by the AIS in 1996 for the Olympic games in Atlanta, with athletes feeling a higher perceived effort after wearing it during their warm up. However Jones et al (2012) show that there is no significant evidence to show that this is an effective pre-cooling method.

I have conducted a small investigation at university into its application with myself and another student rowing 2x2000m on a rower separated with a 15-minute rest period between attempts. 2 Methods of pre-cooling were attempted with me using an external strategy of a cold towel to the back of the neck and the other person using an internal strategy of drinking iced water.  The Results showed that the external towel had a greater effect on recovery between 2000m row efforts. The application that this could have to wider research is limited but as with all sport science investigations it can vary per individual.

Consequently, the use of pre-cooling for those in cardiovascular activity can be great. The research shows the most effective method is that of Cold-water, whole body immersion but it may not be the most realistic. So, it is therefor up to the athlete to determine their creativity in doing so. Whether this be a cold shower before activity or the use of cold-water ingestion, which is easy to make and to use due it, s cheap an practical attributes.

For a summer, where sport is prevalent within hot climates such as the World Cup in Brazil and many middle to long distance races, the application of these methods could be vital. As football can be seen as a cardiovascular activity with variating levels of intensities it can be applicable. This could be done by using cold-water ingestion during games around sides of the pitch, with a previous history of stoppages during play, to allow for fluid intake. By combining the need for hydration with thermoregulation, it can give teams that edge on other teams who don’t use it.

References:

Marino, F & Booth, J. (1998). Whole body cooling by immersion in water at moderate temperature. Journal Sci Med Sport. 1, 73-82.Jones et al. (2012). Pre-cooling for endurance exercise performance in the heat: a systematic review. BMC medicine. (10), 1-20

Maughan, RJ. (2010). Distance running in hot environments: a thermal challenge to the elite runner. Scandinavian journal of medicine science and sports. 20, 95-102

Qoud, MJ et al . (2008). Practical precooling: effect on cycling time trial performance in warm conditions. Journal of sports Sciences. 26, 1477-1487.

Sunderland, C., & Nevill, M. E. (2005). High-intensity intermittent running and field hockey skill performance in the heat. Journal of sports sciences, 23(5), 531-540.

Taylor, N & Cotter, J. (2006). Heat adaptation: Guidelines for the optimisation of human performance. International SportMed Journal. 7 (1), 33-57

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