Speed Is King
Team and field sports are punctuated by high-intensity efforts—the moments that matter most happen at top speed. Whether it be chasing a through ball in football before a goal being scored (Faude et al., 2012), a length of the field try in rugby, or a stolen base in baseball, speed affords athletes the opportunity to break open the game. Speed also clouds coaches’ and administrators’ perceptions of an athlete’s worth—faster athletes earn more money (Treme and Allen, 2009)—regardless of whether or not this is necessarily associated with performance. Whether it’s in creating a team of athletes better prepared to take advantage of their perceptual-motor landscape or in helping a private client get paid, strength and conditioning coaches should be highly concerned with speed development.
As previously discussed on Complementary Training, the agile periodization approach aims to address uncertainty in training by implementing robust training planning strategies. Traditional undulating or block periodization models tend to overly rely on an industrial age mechanistic understanding of physiological training responses. For example, Kiely (2012) argues most periodization theory is based on the work of Taylor (1919) concerned with management strategies for factories and production lines to formalize systems of efficiency following the industrial revolution. This model purports that outcome A must be achieved prior to outcome B, outcome B before outcome C, and so forth, much like the process required for Henry Ford’s Model T to roll off the production line. In training, this is akin to block periodization’s assertion that for any realization of training to occur, first an accumulation and transmutation (scientism vs. scientific—just because something sounds scientific, doesn’t make it so) phase must be completed (Issurin, 2008).
However, we now appreciate that physiology, biomechanics, sports psychology, and motor learning and skills acquisition all form part of a complex, dynamic system—where no single change can be made in isolation without countless unknown cascading butterfly effects that influence performance. Training cannot target a single system or quality in isolation. There is no such thing as ‘maximal strength’, ‘anaerobic power’, or ‘maximum velocity speed’. These are just models or concepts that we use to help us simplify and understand reality. That’s not to say we can’t or shouldn’t use models, however, we must understand and appreciate their limitations when building training programs that target vague or theoretical components of performance.
“All models are wrong, but some are useful.”
Problems Faced by Strength and Conditioning Coaches Delivering Speed Programs
Contemporary physical preparation leans heavily on the experiences of track and field coaches to inform speed development programming. Personally, I have used resources like Altis, followed coaches online like Mike Young, and shadowed six-time New South Wales athletics coach of the year, Roger Fabri, to learn the science and practical application of linear speed development. This is where I learned about different drills, elements of technique, how fatigue can affect training and the prescription of sprint training. However, I continue to wonder how well straight-line speed, in a sterile environment, transfers to the chaos of sports.
I’m not the first coach to search for improved transfer in speed training. Many have followed a similar journey. Unfortunately, for too many coaches this leads to the fads and gimmicks of eyewash agility ladder footwork patterns, knee bungees, and cone drills. None of these adequately replicate the dynamics of movement to overload training in such a way that creates positive training adaptations (Weyand et al., 2000). In my experience, most athletes would still be better off working on straight-line speed with a track coach.
Video 1 – Eyewash training video
Sprint training volume is a controversial topic. Even among track and field coaches, there is much disagreement regarding how much sprint work is appropriate. Haugen et al. (2019) note that the general best practice for acceleration training is 100 – 300 m per session and for maximal velocity sprint sessions is 50 – 150 m top speed volume. It is worth considering that these recommendations are for sprint specialists. These athletes don’t also need to worry about skills and conditioning. Thus, it’s safe to assume our team and field sport athletes are better suited to working at the lower end of these spectrums.
However, elite sprinters have a long history of technique development, operate at much higher maximal outputs, and have extensive sprint focussed training histories. Does this mean our field sport athletes need more work to get them up to speed (da dum – see what I did there…)? Further, what are the sprint-related demands of their specific sport/position? The training must prepare the athlete for worst-case scenarios—train hard, play easy. With this being the case, perhaps our field sport athletes should train at the upper end of the Haugen et al. (2019) sprint training volume parameters.
To further complicate the sprint training program, if you’re like me you’ve got 15 minutes to get the athletes warmed up, complete the sprint training program, and provide enough time for a quick drink before handing over to skills. So how do we jam so much in with so little time? And what if so and so the athlete is always too sore on game day +2 for high-speed running? You need a robust planning strategy. Remember, you’ll always hit acceleration when you hit max velocity – but not always the other way around—how can this form part of your planning strategy?
Components of Effective Speed Programming
In a recent Twitter ‘ask me anything’, Altis CEO and sprints coach Stuart McMillan discussed his ‘know, think, guess (KTG) model’ for decision making in training planning. McMillan frames his training philosophy around what he knows to be true, what he thinks to be true, and finally what he guesses to be true. In much the same way agile periodization relies on the barbell strategy (Jovanović, 2019, Taleb, 2007), McMillan doubles down on robust components of training—what he knows to be true makes up ~75% of the program. He also makes a small but consequential investment in the upside, what he thinks to be true is 20% and the final 5% of his training are guesses, experimentation, and novelty for novelty’s sake.
So, with respect to straight-line speed and training for sprint performance in team and field sports, what do we know to be true?
- Regular sprinting is required to condition for top speed (Oakley et al., 2018, Edouard et al., 2019, Malone et al., 2017)
- Longer recoveries improve training outputs (Haugen et al., 2019)
- Strength and power training supports speed development in less trained athletes (McBride et al., 2009)
- Faster sprinters have a higher proportion of fat-free mass (Barbieri et al., 2017)
- Muscle actions and kinetic sequencing is specific to movement velocity with phase transitions occurring from acceleration to top speed (Higashihara et al., 2018)
- Resisted sprints improve acceleration in less trained athletes (Cross et al., 2017, Cross et al., 2018, Morin et al., 2017)
- Large and abrupt changes in sprint volume increase the risk of injury (Carey et al., 2017)
- Sprints approaching top speed are relatively uncommon in field sports but are often associated with scoring situations (Gabbett, 2012, Faude et al., 2012)
- Plyometrics and horizontally orientated jumps improve sprint performance in less trained athletes (de Villarreal et al., 2012)
- Higher level sprinters demonstrate greater levels of stiffness (Haugen et al., 2019)
- During acceleration, higher level performers better orientate their ground reaction forces in the global horizontal vector (Morin et al., 2011)
- Faster top running speeds are achieved with greater ground reaction forces, not more rapid leg movements (Weyand et al., 2000)
Figure 1: Top speed and acceleration gait patterns are different. During upright sprinting (top), the swing leg lever is shortened during the recovery phase whereas, in acceleration (bottom), the foot recovers low to the ground—these differences result in contrasting mechanical forces applied at the hamstrings during the late swing phase. Therefore it is important to expose athletes to these specific stimuli for both development of performance and to mitigate injury risk
Knowledge of these factors should form the basis for 75% of our speed development program. Therefore, if working with younger, less developed athletes, we should dedicate more time, energy, and effort to supplemental general training in the weights room. Additionally, our speed sessions need to be completed regularly—at least once per week—and should use long recoveries. We should also train both acceleration and top speed. And our exercises, drills, and coaching cues should help athletes develop the ability to achieve orientate and deliver ground reaction forces in the most efficient and effective way possible. It will also be beneficial to layer game-like scenarios over speed development to allow for exploration of the perceptual-motor landscape, variation of fluctuations, and challenging/stabilization of attractors.
Think to be true is where personal opinions will differ, so for the purposes of this exercise, these are simply my own personal beliefs regarding training for speed development:
- Constraints led learning and the application of variation creates more robust attractor states in team and field sports athletes
- The crossed extensor reflex (sometimes referred to as switching or limb exchange), whereby hip, knee, and ankle flexion on the swing leg side is reciprocated by a powerful extension of the hip, knee, and ankle on the support leg, is a trainable and transferable skill for improving sprinting
- Mini hurdle wickets drills improve front side dominant sprint mechanics(Take a look at the Mini Hurdle Wicket Drill video below)
- Running mechanics drills (A skips, dribbles/ankling and paw backs) +/- variations with plates/perturbations, etc. transfer to sprint performance by conditioning and priming the neuromuscular system, improving the number of affordances for economical, emergent movement solutions(Watch the Running Mechanics video below)
- Isometric muscle actions are used—and can be trained—to decrease degrees of freedom, improving the rate of force development and energy transfer in running
- Recovery periods should be 30 – 60 seconds per every 10 m of sprinting
- Designated speed development time is better invested in top speed training as athletes generally get plenty of exposure to acceleration in general skills training
- Traditional strength and power training ceases to transfer to sprint performance in intermediate and advanced athletes—however, it remains an important part of physical preparation to retain resilience and robustness and increase work capacity
- Sprinting straight after heavy strength training or in an excessively fatigued state may increase the risk of injury
Video 2: Mini Hurdle Wicket Drill
Video 3: Running Mechanics Drills
Finally, we arrive at guesses. In this instance, my guesses are the best way to practice much of what I think to be true. For example, drill selection, specific accessory exercises in the weights room, and cues I use day-to-day are the thin layer of guessing that lies atop the underlying known knowns.
As stated by Taleb (2007), investments should first and foremost protect from the downside—play it safe, act conservatively and make sure we’re not going to get hurt. In training, this is focussing on athlete health, wellbeing, robustness, and general physical conditioning. The resilient athlete is prepared to take off for a sprint at any given time and we don’t fear them pulling a hamstring. Therefore, one of the key things we know to be true, that must be part of our game speed program is regular exposure to very high-speed running. Sprinting is the vaccine (Edouard et al., 2019) and avoiding it starts the merry-go-round, self-fulfilling prophecy of persistent and recurring hamstring injuries. In my program, injury-free athletes are required to hit >90% of maximum velocity at least once per week in a sterile, sprint focussed environment (excluding the first few weeks of pre-season when we’re building back into things).
Next, it is essential that we use general strength training to improve tissue quality. The precise details regarding exercise selection remain less clear, but it’s safe to say that ‘doing the strength training is non-negotiable. The evidence seems to indicate that a mixed approach is likely the most robust strategy for covering our bases when it comes to hamstring strength training. Supramaximal eccentrics, isometrics, and traditional concentric muscle actions targeting the distal, mid-belly, and proximal portions of the hamstrings should all be trained for injury prevention (Oakley et al., 2018). I like to hit the posterior chain in one way or another during every strength session. It’s important to get the timing of this training right though—an overzealous strength coach who is determined to get Nordics done may regret it if they’ve not realized that this afternoon’s field session involves many repeated, long, high-intensity sprint efforts.
View this post on Instagram
Video 4 – Hamstring robustness
Fat doesn’t fly. While a potentially touchy subject depending on your athlete cohort, body composition is undoubtedly causative of relative sprint performance. All else being equal, a leaner athlete will always outperform one carrying more adipose tissue in a sprint. Needs assessments must be undertaken to determine how important this is for your sport/position. For example, collision-based sports like rugby or American football will have far more tolerance for non-contractile mass due to the inherent advantage of greater momentum in a tackle (F=MA, thanks again Newton). However, if your athlete’s position is speed reliant, getting body composition in check is a fundamental component of adequate preparation.
Most athletes’ untrained perception of what constitutes good running mechanics/technique is wrong. It is imperative that we demystify and educate. Many athletes I’ve worked with will put their lack of speed down to ‘poor technique’. However, running form is an emergent property. Our own internal anatomy and physiology create the affordances through which we self-organize. The biological organism and, in particular, the nervous system is incredibly clever problem solvers and always find the most efficient and effective way to perform the task, given the constraints placed upon it. The key here is the constraints—tissue quality, pennation angles, tendon stiffness, mobility, rate coding etc. We as coaches need to do a better job of empowering our athletes to just run so they’re not chasing red herrings and creating overly mechanical, cognitively confusing, biologically inefficient movement solutions.
Let the drill be the teacher!
Figure 2: Nassim Taleb’s Barbell Strategy
In contrast, the right side of the barbell is concerned with potential gains. Small, aggressive investments in the upside. Once we have bedded down our key fundamentals, we’re free to experiment with advanced training methods, unique variations, and chaotic game-based speed scenarios. This part of the program is engaging and novel for athletes, increasing buy-in and fostering intensity and training culture. A skillful coach can use this part of the training session to give the athletes both what they want, and what they need.
Some examples from my own practice include game speed drills like simulated defensive kick-chase in rugby league, through ball shooting drills in football, boundary fielding in cricket, etc.; running with a tailwind as often as possible (over speed methods); use of dowels, plates and aqua bags to overload sprint specific coordination/strength exercises; specialized strength training exercises in the weights room such as Alex Natera’s run specific isometrics and Frans Bosch’s integrated strength and coordination exercises; and finally, a culture of speed—creating leader boards and competition that revolves around speed metrics and the underlying components (stiffness via reactive strength index) rather than focussing exclusively of repetition maximums in the gym.
View this post on Instagram
Video 5: Bosch clean
View this post on Instagram
Video 6: Aqua bag
Superfluous Elements of the Speed Program
Via negativa or addition via subtraction are heuristics or rules of thumb we can use to make decisions about what should be included in the program. When we apply a heuristic like via negativa, we are attempting to create sophistication through simplicity. Narrowing down the training menu options to the most potent, time-efficient, and bang for your buck exercises or drills to attain the desired outcomes.
Speed training is rife with fitness fad gimmicks like the agility ladder, knee bungees, and wearable loads. These are the first, a most obvious layer of training tools we can remove. They are not supported by a body of scientific literature, they’re aggressively marketed, and they’re not widely used by elite-level performers (success leaves clues). Next, we should be hyper-critical of advanced or specialized strength training and drills. I’m a big fan of the dynamic systems theory and have a lot of time for pioneers like Frans Bosch who’ve brought widespread attention to the science and practice of motor learning and skill acquisition to strength and conditioning practitioners. However, if we’re truly scientific in our approach to training, we must be able to question everything. Let’s talk about drills.
To drill or not to drill, that is the question.
- Do drills make athletes faster? Probably not
- Does an inadequate warm-up negatively affect training outputs and performance? Yes, often this can be the case
- Can running mechanics drills like ankle dribbles, A-skips, exchanges, and straight leg runs improve blood flow, potentiate working muscles, and strengthen sprint-specific anatomical structures? Affirmative
- Should you do drills? Yes, but understand their purpose and their limitations. Sprinting is the stimulus that drives the adaptations. The drills serve to prepare the body to perform the main thing and generate the highest outputs
A basic series of warm-up exercises that can target the ankles, hips, and posterior chain is likely all we need in the armory to get our athletes prepared to run fast. I like to use exercises like those shown above such as ankle dribbles, pogos, and hops to get the intrinsic muscles of the feet and calves fired up. Some basic exchange drills, skips, and high knee runs will loosen up the hips and wake up the glutes and quads. And finally, some B skips or straight leg runs serve as a nicely posterior chain primer before we go full noise at top speed. However, athletes who can do nice-looking drills are just that—athletes who can do nice-looking drills. When it comes to running fast, there will never be a substitute for running fast.
Minimal Viable Program
To borrow another concept from agile periodization, we should always have the minimal viable program (MVP) for speed development in our back pocket, ready to roll out when the plan goes down the drain. The minimal viable program is the most basic, simple session design framework that will ensure we address our key performance indicators for the speed session. For example, the MVP should include a basic general dynamic warm-up that the coach knows will prepare athletes to run fast, whether it be a beautiful day in the tropics or a cold rainy night in Stoke. Next, the MVP should provide a couple of basic options for skill development. This is where our prior knowledge of constraints-led learning theory becomes powerful. What are our go-to constraint manipulations that provide overload which can positively influence mechanics? Finally, we need a system for making effective decisions regarding the sprint program itself—we’re talking sets and reps.
The MVP can be used by any coach short of time, mental planning energy or to fill gaps due to uncertainty—like when the coach decides last minute that they don’t have a session plan so you get to entertain the players. For the best part of the last five years, I’ve used an adapted version of Mike Young’s sprint training for team and field sport athletes’ recommendations (see table 1). To date, this has served me extremely well.
From this table, I only have to address four questions in my head—with simple decision-making trees attached at each layer.
- How many times are we doing speed this week?
- Seven or more days turn-around, twice
- b. Fewer than seven days, once
- Do we consolidate sprint volume onto one, or separate out over two days?
- Short turn around, consolidate
- Longer turn-around, break it up
- Do I want to focus more on acceleration or top speed?
- Players are sore, fatigued, low mood etc., acceleration
- Players feel good, refreshed, excited to train, top speed
- Do we have time to assign for longer recoveries?
- Always try and assign the longest recoveries possible within the parameters of other logistical elements—time assigned by coaches for warm up/speed development at start of session
Table 2 below is a real-world example of the MVP template I use for speed development. There will be times where we advance to more complex or novel scenarios, but if all else fails, I’m working with a new athlete/cohort, plans change last minute or an athlete needs a top-up of high-speed running, this is where I start.
Table 2: Minimal viable program template for speed development (20 minutes)
|General dynamic warm up (2 minutes)
|Hamstring sweeps, lunges, arabesques, choose your own adventure etc.
|10 m each
|Running mechanics (3 minutes)
|2 x 30 m
|2 x 10 m
|High knee run
|2 x 10 m
|Straight leg scissor bounds
|2 x 30 m
Hills or sleds (3 minutes)
|75, 85, 95%
|2 x 10m, 20m, 30m each
|3-5 x 20 m
|~30° or 30-50% BW
|3-5 x 20 m
|Sprints (12 minutes)
|Once per week
|6 x 40 m
|Twice per week
|3 x 40 m
Table 2: Minimal viable program template for speed development (20 minutes)
Heuristics for a Robust Speed Development Training Plan
As mentioned above, heuristics serve as rules of thumb. Yes, there will be exceptions, but exceptions don’t make the rule. When chaos or uncertainty strikes or you’re unsure of what is ‘optimal’, we should fall back on what is robust. Some simplified models or concepts I apply to help improve decision making in speed training include:
- Short to long periodization
- Bias towards maximal velocity
- Run downwind where ever possible
- <1.5 ACWR for high-speed running volume
- Modify, don’t miss
Short to long periodization is a model for increasing the length of sprint efforts in a chronological manner. Because we know the hamstrings muscles are at a particularly high risk of injury during sprinting, we need to appreciate the stimulus, recovery, and adaptation cycle that corresponds with exposure to our program. Athletes without an extensive speed development training history will not be able to tolerate large sprint volumes. In fact, they may not be able to tolerate any sprint volumes in the beginning. To mitigate risk, focussing on shorter sprints over reduced distances in the early phases of the program respects the phase transition between the acceleration or drive phase and upright running—during which hamstring muscle activation changes dramatically (Higashihara et al., 2018). In the first month or so of pre-season, my all-out sprint efforts are over distances of 10, 20, or 30 m. To build capacity in the hamstrings I use extensive tempo running, float-stride-float drills, and constraints like wickets or dowel run to cap movement velocity.
Video 7: Note how the various constraints limit movement speed, allowing for maximal intent with reduced mechanical load
The program should always bias towards maximal velocity sprinting. Remember, the game and regular skills training does not provide a speed development stimulus. However, key game-defining moments are often punctuated by sprints in excess of 36 km/h. In order to provide the necessary overload, we must be willing to sacrifice specificity. The game already provides countless opportunities to be exposed to short, sharp accelerations, cuts, and changes of direction. Therefore, where ever possible I look to prescribe sprints towards the longer end of the recommendations in table 1. This guarantees athletes can get up into top speed mechanics, get comfortable in these postures and positions and build the specific capacity and qualities to not only tolerate but thrive in high-velocity environments.
Running downwind provides a unique type of overload and can facilitate supramaximal sprint speeds for your athletes. Expensive towing systems are increasingly popular, however, simply orientating your speed work downwind further exacerbates the bias towards maximal velocity in the program. As mentioned before, we already get plenty of short accelerations in the field sports training session. Combine this with hills, sled work, prowlers pushes in the gym, and strength and power training and there’s a huge volume of work already being conducted at submaximal speeds. So, every once in a while, when mother nature serves you up a gift—take advantage.
We can also use the acute: chronic work ratio (ACWR) to help monitor changes in weekly high-speed and very high-speed running volumes. While the ACWR has been the perennial whipping boy of the strength and conditioning Twittersphere over the last year or two (Impellizzeri et al., 2020), it can serve as a useful model for understanding the relative distribution of week-to-week training load. The ACWR loosely models Bannister’s fitness fatigue model. Acute load (fatigue) is often represented by the previous seven days of training and chronic load (fitness) by the weekly average of the past 28 days. We can sum high-speed (26 – 30 km/h) and very high-speed (30 – 36 km/h) running volumes using GPS wearable devices like the Catapult system to create an ACWR. It’s a safe bet that a large discrepancy in acute and chronic workload—particularly acute spikes, will augment injury risk. Living and dying by the numbers isn’t my thing, but planning for and reflecting upon speed development training practice is a sound strategy for removing the guesswork in the program.
Figure 3: Wearable devices can be used to create acute: chronic workload ratios for high speed, very-high-speed, and sprint exposure volume to monitor training progression and mitigate injury risk. Take note of the progressive overload applied during the preparatory phase from weeks 25 – 38.
Modify, don’t miss. If there’s a reason an athlete can’t participate in full training, first ask yourself, how much regular training can they still complete—then get them involved in this. The last thing the player wants is to be ostracised on the sideline by the physio who’s labeled them unfit to train when really the only thing they can’t do is the full live sprint component of the session. The drills, constraints-led exercises, some strides can all accelerate the recovery process from an injury by reconditioning tissues and reducing apprehension and sensitivity to movement. Work sequentially back from plan A, to plan B, and then C. Don’t immediately jump to plan F without first exhausting the other options.
Speed kills. While recruiters and the back office will focus on buying it, the performance coaches’ job is to build it. The most robust speed development programs will ensure regular exposure to maximum velocity sprinting, supplement with a well-rounded strength and power training program, maximize inter-repetition recoveries, focus on improving technique to optimize ground reaction forces, and plan and monitor weekly sprint volumes. Basic speed development guidelines and the MVP and heuristics can improve decision-making by reducing uncertainty and provide robust options for coaches. At its heart, speed development relies on sprinting fast, recovering slowly and repeating as often, and at the highest outputs possible.
- Barbieri, D., Zaccagni, L., Babić, V., Rakovac, M., Mišigoj-Duraković, M. & Gualdi-Russo, E. 2017. Body composition and size in sprint athletes. The Journal of sports medicine and physical fitness 57, 1142-1146.
- Carey, D. L., Blanch, P., Ong, K.-L., Crossley, K. M., Crow, J. & Morris, M. E. 2017. Training loads and injury risk in Australian football—differing acute: chronic workload ratios influence match injury risk. British Journal of Sports Medicine, 51, 1215-1220.
- Cross, M. R., Brughelli, M., Samozino, P., Brown, S. R. & Morin, J.-B. 2017. Optimal loading for maximizing power during sled-resisted sprinting. International Journal of Sports Physiology and Performance, 12, 1069-1077.
- Cross, M. R., Lahti, J., Brown, S. R., Chedati, M., Jimenez-Reyes, P., Samozino, P., Eriksrud, O. & Morin, J.-B. 2018. Training at maximal power in resisted sprinting: Optimal load determination methodology and pilot results in team sport athletes. PLoS One, 13.
- De Villarreal, E. S., Requena, B. & Cronin, J. B. 2012. The effects of plyometric training on sprint performance: A meta-analysis. The Journal of Strength and Conditioning Research, 26, 575-584.
- Edouard, P., Mendiguchia, J., Guex, K., Lahti, J., Samozino, P. & Morin, J.-B. 2019. Sprinting: a potential vaccine for hamstring injury. Journal of Sport Performance Science Reports, 48, v1.
- Faude, O., Koch, T. & Meyer, T. 2012. Straight sprinting is the most frequent action in goal situations in professional football. Journal of Sports Sciences, 30, 625-631.
- Gabbett, T. J. 2012. Sprinting patterns of national rugby league competition. The Journal of Strength & Conditioning Research, 26, 121-130.
- Haugen, T., Seiler, S., Sandbakk, Ø. & Tønnessen, E. 2019. The training and development of elite sprint performance: an integration of scientific and best practice literature. Sports medicine-open, 5, 1-16.
- Higashihara, A., Nagano, Y., Ono, T. & Fukubayashi, T. 2018. Differences in hamstring activation characteristics between the acceleration and maximum-speed phases of sprinting. Journal of sports sciences, 36, 1313-1318.
- Impellizzeri, F., Woodcock, S., Coutts, A. J., Fanchini, M., Mccall, A. & Vigotsky, A. 2020. Acute to random workload ratio is ‘as’ associated with injury as acute to actual chronic workload ratio: time to dismiss ACWR and its components. SportRxiv.
- Issurin, V. 2008. Block periodization: breakthrough in sports training, Ultimate athlete concepts.
- Jovanović, M. 2019. Strength training manual: The agile periodization approach, Belgrade, Serbia, Complimentary training.
- Kiely, J. 2012. Periodization paradigms in the 21st century: evidence-led or tradition-driven? International journal of sports physiology and performance 7, 242-250.
- Malone, S., Roe, M., Doran, D. A., Gabbett, T. J. & Collins, K. 2017. High chronic training loads and exposure to bouts of maximal velocity running reduce injury risk in elite Gaelic football. Journal of Science and Medicine in Sport, 20, 250-254.
- Mcbride, J. M., Blow, D., Kirby, T. J., Haines, T. L., Dayne, A. M. & Triplett, N. T. 2009. Relationship between maximal squat strength and five, ten, and forty yard sprint times. The Journal of Strength and Conditioning Research, 23, 1633-1636.
- Morin, J.-B., Edouard, P. & Samozino, P. 2011. Technical ability of force application as a determinant factor of sprint performance. Medicine & Science in Sports & Exercise, 43, 1680-1688.
- Morin, J.-B., Petrakos, G., Jiménez-Reyes, P., Brown, S. R., Samozino, P. & Cross, M. R. 2017. Very-heavy sled training for improving horizontal-force output in soccer players. International Journal of Sports Physiology and Performance, 12, 840-844.
- Oakley, A. J., Jennings, J. & Bishop, C. J. 2018. Holistic hamstring health: not just the Nordic hamstring exercise. Middlesex University.
- Taleb, N. N. 2007. The black swan: The impact of the highly improbable, Random house.
- Taylor, F. W. 1919. The principles of scientific management, Harper & brothers.
- Treme, J. & Allen, S. K. 2009. Widely received: Payoffs to player attributes in the NFL. Economics Bulletin, 29, 1631-1643.
- Weyand, P. G., Sternlight, D. B., Bellizzi, M. J. & Wright, S. 2000. Faster top running speeds are achieved with greater ground forces not more rapid leg movements. Jounral of Applied Physiology, 89, 1991-1999.