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Recovery 1%er’s

In a previous post about recovery (Recovery Essentials), we spoke about the importance of recovery after competition/training, and the fundamentals of recovery. Recovery is a key component of every athlete’s performance, having the ability to recover effectively after a training session or competition means that they are able to reduce the effects of fatigue and therefore perform better in subsequent training or competition. There are 4 main aims of recovery for an athlete:

  • Repair muscle damage (with every bout of physical activity performed by an athlete they create micro-tears within the muscle – the muscle’s then need adequate rest and protein stores to re-synthesise / repair the muscle).
  • Reduce muscles soreness (due to the build-up of metabolic waste and the muscle damage created during activity this can lead to delayed onset muscle soreness – DOMS, this can last anywhere from 24 to 48 hours after exercise).
  • Clear metabolic waste (during physical activity there is an increase in the production of blood lactate, an excess build-up of this can result in impaired muscle function)
  • Refuel energy stores (after exercise there is a depletion of fuel stores such as glycogen, fat and protein, it is therefore important that these stores are replenished after exercise).

As spoken about in our previous post the most crucial components to an athlete’s recovery include:

  • Sleep
  • Nutrition
  • Hydration

It is important that we target these areas of our recovery first prior to looking for alternate recovery options. It is well known however that there are many alternate recovery options on the market that can be used to potentially further aid the effects of recovery. Throughout this blog post, we will be discussing the use of what we like to call the 1% er’s of recovery, what are they, what effect they have and how you can effectively use them to aid your recovery.

Cold water immersion/Hydrotherapy and hot/cold showers:

Hot and cold-water therapy (otherwise known as contrast water therapy) is a form of recovery many will know about as it is widely used across many sports. The idea behind contrast water therapy is that it creates a ‘muscular pump,’ whereby it causes the blood vessels within the muscles to dilate (vasodilation) when in hot water and then constrict (vasoconstriction) when in cold water (8). Doing this creates a pump-like action within the muscles aiding in pumping the blood back to the heart and lungs to be re-oxygenated and pumped back around the body (8). The idea is that in doing this you can remove any metabolic waste products from the muscles reducing the effects of DOMS and aiding in a faster recovery. Research has found that simple CWI or CWT can result in improved recovery from high-intensity activity (8).

An example protocol for CWT may look like 1 min in cold (15 degrees) and 1 min spent in hot water (38 degrees) repeating this seven times with a short transition between temperatures (8).

Coldwater immersion (CWI) is another method commonly used by athletes for recovery. This method involves the athlete submerging themselves into cold water (15 degrees) for 14 minutes. CWI cause vasoconstriction of the blood vessels, this consequently reduces blood flow to the muscles this reduction in blood flow to the damaged muscles can result in a reduction in inflammation and oedema within the muscles (8). There can also be an analgesic effect caused by CWI whereby there is decreased nerve conduction and excitability, thus reducing communication with the sympathetic nervous system leading to a reduction in perceived pain (8). Overall research has shown that CWI can reduce the effects of DOMS 24, 48 and 96 hours post-exercise (8).

Contrast water therapy, switching between hot and cold baths.

Pneumatic Compression Devices (Normatec):

Pneumatic Compression (PC) devices such as the Normatec Boots have been marketed to aid in removing metabolic waste from the muscles. The theory behind these devices is that through intermittent compression they create or mimic a muscular-venous pump consequently circulating blood from the muscles towards the heart and lungs to be re-oxygenated and back to the heart to be pumped back around the body (2). The mechanical ‘squeezing’ of the muscle is thought to push swelling out of the extremity and promote blood flow back to the heart and lungs (2). The actual effectiveness of this device is similar to that of active recovery, it has been found that similar blood lactate removal has been found for athletes after an active recovery versus a 20-minute session using a pneumatic compression device (2). Due to this evidence, it is possible that PC devices could have an effect on reducing DOMS by reducing the level of blood lactate within the muscles. Some research has found that it could result in recovering from DOMS at a more rapid rate, however, this is no significant difference when compared not using a PC device (2).

It has been thought that the use of PC devices could aid in glycogen resynthesis post-exercise. Glucose is the bodies main fuel source for activity and after approximately 90 minutes of continuous exercise, it is said that an individual’s glycogen stores will be depleted, if not replenished during activity. It is therefore important that athletes performing this type of exercise look to replenish their glycogen stores within the first 60 minutes after activity. It is thought that the aid of the PC device creating a muscular pump may lead to a more rapid replenishment of glycogen stores. It has however been found that this is not the case and that the rate of glycogen resynthesis does not change with or without the use of PC devices (2).  

Overall, the consensus is that PC devices may provide some reduction in DOMS through the reduction in blood lactate levels aiding a quicker return to homeostasis. It is important to note however that this device will not improve performance.

Normatec recovery boots.

Massage:

Massage is a widely used recovery strategy however the effects of it on improved subsequent performance is debated widely in the research. The idea behind massage is that it creates a squeezing like action of the muscles similar to that of PC devices pushing any swelling and metabolic by-products away from the peripheral muscles and back to the heart and lungs allowing for the blood to be re-oxygenated and pumped back around the body (10). In some studies, it has been found that this can have a positive impact on DOMS as well as improved muscle flexibility post-exercise (10). This may provide the athlete with some relief from post-exercise fatigue, however, it’s impact on subsequent performance has not been proven (3).

Athlete receiving massage.

Stretching:

Flexibility is the range of motion (ROM) of a joint or related series of joints such as the spine (7). There are various types of flexibility that an athlete can use such as flexibility for ROM enhancement whereby the joints are taken through excessive ROM placing muscles and tendons under unaccustomed tensile stress, an example of someone using this type of stretching would include dancers and gymnasts (7). Another form of stretching can be used prior to a session commonly called dynamic stretching where the joint is taken through a ROM in a gentle active manner, this forms part of many athlete’s warm-ups prior to commencing their sport (7). Stretching for recovery however, is used to reduce stiffness and soreness after a training session this is generally performed via static stretching (7).

Stretching can be categorised into several different forms including active or passive, static or dynamic, and acute or chronic. For the sake of this article, we will be focusing on the use of static stretching for recovery. Static stretching involves taking a joint through its ROM to a point of resistance a holding it there for a given period (7). It has been found that static stretching via pain-free ROM with minimal resistance may reduce post-exercise DOMS and improve post-exercise ROM (7). It, however, has not been found if stretching post-exercise can improve subsequent performance, it may, however, reduce post-exercise fatigue and soreness (7).  

Stretching for recovery.

Thera-guns:

Thera-gun is a massage device that looks like a drill. It uses percussive massage therapy to treat muscle soreness post-exercise. Percussion therapy is s form of soft tissue manipulation that is intended to reduce muscle soreness and increase ROM (5). It is said to do this via delivering rapid long vertical strokes to the muscles resulting in a neuromuscular response (5). Through this impact on the neuromuscular system, it is said to have effects on improving ROM after exercise (5). The percussive therapy is believed to improve muscular blood flow resulting in a reduction of DOMS through the aid in the removal of metabolic by-products (5). There is however limited research on this recovery modality making it unclear on the true effects it may have, leading to the presumption that it may have more of a placebo effect. It is clear however that the Thera-gun has limited to no effect on subsequent performance (5).  

Thera-guns.

Foam rollers and massage balls both normal and vibrating:

Now we have all heard of the humble foam roller to use for recovery, well how about a foam roller or massage ball that vibrates. Seems like a great idea, so let’s delve a little deeper and determine just how effective they are in aiding recovery after exercise. When using a foam roller an individual uses their own body weight to apply pressure and produce friction over a muscle or group of muscles, increasing muscle temperature and decreasing pain associated with DOMS (6). The way the foam roller works is that it works to release tension in the facial lining of the muscles as it increases muscle temperature (6). Massage balls, however, can be used to target trigger points within the muscle (think of this as a knot in the muscle), when pressure is placed on this point for a period it can lead to a relaxation in the muscle tissue (6). Using a vibrating foam roller or massage ball combines this pressure and friction-based therapy with percussion therapy in an effort to achieve the same results. It has been found that vibrating foam rollers and massage balls can have a slightly enhanced effect on recovery over a conventional foam roller and massage ball (6). The effect that both devices have is on a reduction in post-exercise perception of pain as well as increased ROM shortly after treatment (6). Again, foam rollers and massage balls have not been shown to have a positive effect on subsequent performance (6).   

Vibrating Foam Roller.

Float tanks:

A relaxing form of recovery where an individual lies face up in a quiet dark environment, in a tank of Epsom salt and water heated to approx. skin temperature (4). The level of Epsom salt (magnesium sulphate) within the water is considerably higher than that of the dead sea allowing an athlete to effortlessly float within the tank (4). It is believed that the Epsom salts within the water promote the removal of blood lactate from the muscles having a significant impact on perceived pain post-exercise (4). As with all other recovery modalities mentioned this does not appear to have an impact on athlete subsequent performance not impacting muscle strength, or blood glucose levels, factors important for improved subsequent performance (4).  

Float Tank.

Summary

So, what is to come from all these different recovery modalities?

The key take a ways are:

  • The best form of recovery for improved performance comes from sleep, nutrition and hydration.
  • These modalities can be used as supplements to the above however they should not be relied upon.
  • These recovery modalities may have an impact on muscle blood lactate levels and perceived soreness post fatiguing exercise, however, they won’t have an impact on an individual’s subsequent performance.
  • Through the research these recovery strategies have not been found to significantly improve performance…… however, if you find there is a strategy that aids in your recovery, and you find it super beneficial to use, then use it – every little bit helps to make sure you are recovered and ready for the next game/competition.

References:

  1. Eston, R. & Peters, D. Effects of cold-water immersion on the symptoms of exercise-induced muscle damage. Journal of Sports Science. 17: 231-238, 1999.
  2. Hanson, E. Stetter, K. Li, R. & Thomas, A. An intermittent Pneumatic Compression Device reduces blood lactate concentrations more effectively than passive recovery after Wingate testing. Journal of Athletic Enhancement. 2(3): 20-24, 2013.
  3. Hemmings, B. Smith, M. Graydon, J. & Dyson, R. Effects of massage on physiological restoration, perceived recovery, and repeated sports performance. Journal of Sports Medicine. 34: 109-115, 2000.
  4. Morgan, P. Salacinski, A. & Stults-Kolehmainen, M. The acute effects of flotation restricted environmental stimulation technique on recovery from maximal eccentric exercise. Journal of Strength and Conditioning Research. 27(12): 3467-3474, 2013.
  5. Pournot, H. Tindel, J. Testa, R. Mathevon, L. & Lapole, T. The acute effect of local vibration as a recovery modality from exercise-induced increased muscle stiffness. Journal of Sports Science and Medicine. 15: 142-147, 2016.
  6. Romero-Moraleda, B. Gonzalez-Garcia, J. Cuellar-Rayo. Balsalobre-Fernandez. Munoz-Garcia. & Morencos, E. Effects of vibration and non-vibration foam rolling on recovery after exercise with induced muscle damage. Journal of Sports Science and Medicine. 18: 172-180, 2019.
  7. Sands, W. McNeal, J. Murray, S. Ramsey, M. Sato, K. Mizuguchi, S. & Stone, M. Stretching and its effects on recovery: A review. National Journal of Strength and Conditioning. 35(5): 30-36, 2013.
  8. Vaile, J. Halson, S. Gill, N. & Dawson, B. Effect of hydrotherapy on recovery from fatigue. International Journal of Sports Medicine. 29: 539-544, 2008.
  9. Winke, M. & Williamson, S. Comparison of pneumatic Compression Device to a compression garment during recovery from DOMS. International Journal of Exercise Science. 11(3): 375-383, 2018.
  10. Zainuddin, Z. Newton, M. Sacco, P. & Nosaka, K. Effects of delayed-onset muscle soreness, swelling, and recovery of muscle function. Journal of Athletic Training. 40(3): 174-180, 2005.

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Running Phases Part 3: Speed Endurance:

Now that we have spoken about both acceleration and maximal speed running it is time to turn our focus to speed endurance. Speed endurance, when spoken about in its standard form, is the ability for an individual to maintain a near maximal velocity for an extended period (3). This will range between anywhere from 10 to 40 seconds or 100 to 400 meters. The ability for an individual to hold a near-maximal speed will be greater in those that are highly trained than those that are not (3, 4). Speed endurance is referred to most when speaking about events ranging from 200m to 800m on the track. It is rare that a team sport athlete would run further than 100m in a single effort, however, commonly, they would perform multiple short sprint efforts with little rest between referred to as repeat sprint ability (RSA) (1, 3). The ability of a team sport athlete to do this is underpinned by the same physiological systems as that of speed endurance (1, 3).

AUSTRALIA – SEPTEMBER 25: Track & Field: 2000 Summer Olympics, Australia Cathy Freeman in action, winning 400M final at Olympic Stadium, Sydney, AUS 9/25/2000 (Photo by Bill Frakes/Sports Illustrated/Getty Images) (SetNumber: X61190 TK11 R7 F24)

What exactly is it that affects our speed endurance and repeat sprint ability? As with acceleration and maximal speed running our strength power and technique are all paramount to our performance outcome. Now, however, we also have a greater impact from our energy systems. Throughout this article we will take a close look at the energy system contributions during speed endurance running and how we can manipulate them in training to further improve our speed endurance capabilities.

Energy systems:

To begin we have three ways in which our body can produce and utilize energy during exercise, that being the ATP-CP system, the anaerobic glycolysis system and the aerobic glycolysis system. The ATP-CP system is when the body uses already stored energy in the muscles to produce energy at a rapid rate, this however only lasts for approximately 10 seconds (5, 6). The anaerobic glycolysis system is when glucose is turned into energy with limited amounts of oxygen, unfortunately, this does result in the production of some fatiguing by-products such as lactate and hydrogen ions (5, 6). It is for this reason that we can only rely on this energy system for a short period (10-40 seconds). The aerobic glycolysis system is when glucose is converted into energy in the presence of oxygen (5, 6). This energy system has no fatiguing by-products and can, therefore, be relied upon for and extended period (40 seconds to 90 minutes) (5, 6). It is, however, a slow way of producing energy and therefore if you are wanting to move fast your body will place greater reliance on the ATP-CP and anaerobic glycolysis systems. It is important to note that these systems do not work in isolation, rather working simultaneously with one energy system being dominant at any one time (5, 6).  Speed endurance and RSA are heavily reliant on the anaerobic glycolysis system so let’s break it down a little further.

A diagram showing the energy system interplay during activity.

When we use our anaerobic glycolysis system glycogen is converted into glucose which is converted into a molecule called pyruvic acid (6). Due to the insufficient amounts of oxygen in the muscles, two fatiguing by-products are produced, lactic acid and hydrogen ions. The lactic acid and hydrogen ions can then be converted to produce more energy (6).

Sounds like there is no issue right?

However, when there becomes a greater production of these by-products compared to the muscles ability to utilize and clear these products, they build up in the muscles inhibiting chemical processes that ultimately lead to energy production (5, 6). When this occurs we have a greater reliance on the aerobic system (where oxygen is available) and ultimately slow down due to the greater reliance on oxygen for energy production (5, 6). This is evident when watching a 400-meter race, at the elite level the athletes may be able to hold their speed for 300 to 350 meters, while after that point they inevitably begin to slow down (5, 6). It has been stated that for a 400-meter runner the anaerobic glycolysis system will be the predominant energy system used for 60% of the race while the aerobic energy system will become dominant over the last 30% of the race (5, 6). In a team sport, however, this may seem a little more difficult to see, rather than seeing them slow down on one continual effort you may see then perform less high-intensity efforts and/or have a reduced intensity during those efforts.

Fatigue setting in towards the end of a 400m race.

Then we ask the question of how are we best to train this energy system to allow ourselves or our athlete to run faster for longer or perform high-intensity efforts for a longer period?

One of the big factors when attempting to train any energy system is that you have the right work to rest ratios. This is referring to the amount of time you are working compared to the amount of time you are resting. When looking to target the anaerobic glycolysis system we want our rest period to be the same, double or half that of the work period so a 1:1, 1:2 or 2:1 ratios (5, 6). By doing this we are not allowing the body enough time to fully recover and replenish energy stores before performing the next high-intensity effort (5, 6). This means that as the efforts (or reps) continue there is an increased build-up of lactic acid and hydrogen ions in the muscles, again causing us to fatigue and slow down.

However, the more you train this system the greater ability you gain to be able to buffer the fatiguing effects of hydrogen ions and lactic acid (5, 6). This allows you to maintain a high velocity for an extended period, or continue to perform repeated high-intensity reps (1, 2). It is important to note that this does not mean that there is a decreased build-up of hydrogen ions and lactic acid within the muscle, rather just that you can with stand their fatiguing effects for a longer period before it causes you to slow down (2, 5, 6).

The following are some potential sessions that you could perform to improve your speed endurance:

4 x 150m [walk back recovery]

5 x 80m fly’s (30m build up in acceleration) [1min recovery between reps]

1 x 30 seconds (run as far as possible) [1min rest] run the remaining 400m distance

The following are some example sessions you could perform to improve your RSA:

10 x 100m leaving every 30 seconds

6 x 30m leaving every 10sec

8 x 60m leaving every 20 seconds

References:

  1. Dawson, B. Repeated-sprint ability: Where are we? International Journal of Sports Physiology and Performance. 7: 285-289, 2012.
  2. Lockie, R. Murphy, A. Schultz, A. Knight, T. & Janse De Jonge, X. The effects of different speed training protocols on sprint acceleration kinematics and muscle strength and power in field sport athletes. Journal of Strength and Conditioning Research. 26(6): 1539-1350, 2012.
  3. Marcello Iaia, F. Fiorenza, M. Perri, E. Alberti, G. Millet, G. & Bangsbo, J. The effects of two speed endurance training regimes on performance of soccer players. PLOS One. 10: 100-116, 2015.
  4. Miguel, P. & Reis, V. Speed strength endurance and 400m performance. New Studies in Athletics. 19(4): 39-45, 2004.
  5. Ohkuwa T. & Miyamura, M. Peak blood lactate after 400m sprinting in sprinters and long-distance runners. Japanese Journal of Physiology. 34: 553-556, 1984.
  6. Plevnik, M. Vucetic, V. Sporis, G. Fiorentini, F. Milanovic, Z. & Miskulin, M. Physiological responses in male and female 400m sprinters. Croatian Journal of Education. 15: 93-109, 2013.

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Running Phases Part 2: Max Speed:

Following on from our acceleration post we move into maximum speed or velocity. Maximum velocity is reached after our acceleration phase (after 4-6 seconds) where velocity is maximal and is maintained for only a short period of time (generally 3-5 seconds) (4). In lower level athletes this phase will be reached sooner, while in higher level athletes it will take longer for them to reach their maximum velocity, of which will also be far greater than that of lower level athletes (4). For some sports such as tennis, netball or basketball, maximum speed is somewhat irrelevant as players will never cover enough distance to be able to reach their maximum speed (4). For field sports such as AFL, soccer and hockey and track and field where there are greater distances that can be run, maximum velocity becomes important (4). It is argued that because in field-based sports it is often that sprints are started from a walk, jog or running start that they may be more likely to reach their maximum velocity earlier (4). This can occur as a field sport athlete’s maximum velocity is generally slower than that of a track and field athlete (4).

Daniel Rioli running at max speed.

What exactly is maximum velocity and how can we train for it? Maximum velocity is the highest possible velocity you can achieve and maintain for a short period of time before muscular deceleration and fatigue slow you down (4). As we increase our running velocity our stride length will also increase until a moderate speed, while stride frequency will increase until we reach our maximum velocity (4). As we increase our running velocity our muscles must shorten and lengthen at increasingly rapid rates (4). There are a few mechanical properties that allow us to do this including, strength, power and technique (4).

Strength:

Just like with acceleration there are various types of strength that can affect our maximal speed and all of these need to be considered when training to improve our maximal speed (1, 2, 6). It has been found that maximum speed running has a greater reliance on maximum strength and reactive strength (1, 2, 6).

Maximum Strength:

As stated in our previous acceleration article maximum strength is the maximum amount of force you can apply to an object or how strong you are (1, 2, 6). It has been stated that one of the single best predictors of maximal sprint velocity is that of maximal force relative to body weight (1, 2, 6). Ways that this can be measured include through a 1 repetition maximum (RM) or through an Isometric Mid-thigh Pull Test (1, 2, 6). From this measure it can be determined how much force an individual can apply to the ground with each stride during their maximal velocity phase.

Isometric Mid-thigh Pull test – assessing maximum strength.

Reactive Strength:

As stated in our previous article on acceleration, reactive strength is our ability to rapidly change from an eccentric to a concentric muscle contraction (1, 2, 6). This type of strength uses the stretch shortening cycle (SSC). This relates to our ability to store and utilize elastic energy within our tendons allowing them to act like a spring (where they are stretched to their maximum potential, before rapidly releasing energy as they recoil back to their resting state) (1, 2, 6). This means that we can have faster ground contact times (GCT) increasing our stride frequency and the velocity at which we are travelling (1, 2, 6). This form of strength is commonly measured through a countermovement jump test (assessing the slow SSC) or a drop jump test (assessing the fast SSC) (1, 2, 6). It has been found that the drop jump test has a greater correlation to maximum speed sprinting due to the shorter contact time and the smaller knee flexion angles produced (6).

Countermovement Jump is a powerful exercise using the slow SSC.

Power:

Power is the change in force being applied with respect to time, this means that the amount of force that is applied is proportional to the speed at which force is applied (1, 2). During maximum velocity running power is just as important as during the acceleration phase. As stated, stride frequency is at its greatest during the maximum velocity stage of running, this also means that out GCT is also at its greatest (1, 2). Therefore power is important as the greater amount of force you are able to apply to the ground over a short period of time, the shorter the GCT you will have (1, 2).

Technique:

We know the 2 biggest factors affecting an athlete’s maximum velocity include stride rate and stride length (3). An athlete however can only run as fast as their technique will allow them (3, 5). Poor technique will lead to poor body position, poor leg turn over, over striding (creating braking forces) and collapsing at the hips (3, 5). So, how can we improve our technique to improve our maximum velocity and reduce our risk of injury? There are 3 technique factors that we will talk about below.

Triple extension/slight forward lean:

Triple extension is the ideal position we can form at toe off during all phases of running. This is when we form a straight line from the shoulder to the ankle, linking the whole of the posterior kinetic chain together (erector spinae, glutes, hamstrings and calves) (2, 5). This allows the big power house muscle groups to work together in a synergistic manner, allowing you to apply greater force to the ground with every step (5). When we break this chain the end resultant force that we are able to apply to the ground is reduced. Reducing our stride frequency and ultimately slowing us down (3, 5). This can lead to technique faults such as over striding (creating breaking forces), collapsing at the hips and poor leg turn over (3, 5).

Active clawing action:

This means that with every step your forefoot actively lands on the ground and pushes the ground behind you (3, 5). Doing this will mean that you are able to achieve the next technique point. It will also help to prevent you from overstriding (creating a breaking force), and/or have poor body position as it forces you to lean forward (3, 5). The best way to think of running and especially running at high velocity, is that it is just falling forward and catching yourself with every stride (3, 5). However, if we are able to turn that catch phase into a positive clawing action this will lead to the propulsive phase of the gait cycle efficiently (3, 5).

Negative shin angle:

When the foot lands behind the knee on ground contact, doing this will mean that you are not over striding and will force you into a forward lean position (3, 5). This foot positioning and shin angle also allows us to have a greater use of our SSC with every stride, one of the fastest ways for us to produce and utilize energy within our muscles and tendons (3, 5). Leading to shorter GCT and a faster stride rate, ultimately increasing your maximum velocity (3, 5).

Usain Bolt at max speed.

Some ways that we can teach these technique points include:

A March/Skip:

Ankling:

Bounding:

Butt Kicks:

References:

  1. Barr, M. Agar-Newman, D. Sheppard, J. & Newton, R. Transfer effect of strength and power training to the sprinting kinematics of International rugby players. Journal of Strength and Conditioning Research. 28(9): 2585-2596, 2014.
  2. Lockie, R. Murphy, A. Schultz, A. Knight, T. & Janse De Jonge, X. The effects of different speed training protocols on sprint acceleration kinematics and muscle strength and power in field sport athletes. Journal of Strength and Conditioning Research. 26(6): 1539-1550, 2012.
  3. McFarlane, B. Developing maximum running speed. National Strength and Conditioning Association Journal. 18: 24-28, 1984.
  4. Miller, R. Umberger, B. & Caldwell, G. Limitations to maximum sprinting speed imposed by muscle mechanical properties. Journal of Biomechanics. 45: 1092-1097, 2012.
  5. Nagahara, R. Matsubayashi, T. Matsuo, A. & Zushi, K. Kinematics of transition during human accelerated sprinting. Biology Open. 3: 689-699, 2014.
  6. Young, W. McLean, B. Ardagna, J. Relationship between strength qualities and sprinting performance. The Journal of Sports Medicine and Physical Fitness. 35: 13-19, 1995.