Category Archives: Sport Specific Training

Muscles Cannot Change Size Without Changing Shape

Let me lay down the groundwork for this guest article from Andrew Vigotsky. On March 3rd, I posted THIS thread on Facebook. It’s a before/after pic of Casey Bergh, which I used to illustrate my point that muscles can indeed change shape. Many fitness professionals chimed in, stating that muscles don’t change shape, they just grow. Before I entered the S&C scene, I was a high school Algebra and Geometry teacher, so I know my mathematics. I kept stating repeatedly throughout the thread that muscles don’t just grow proportionately larger, and that since the fixed endpoints don’t grow as much as the muscle belly, the shape must necessarily change. In addition, some regions grow more than other regions depending on which portion of the muscle is most highly activated, but that’s not as important.

My colleague Andrew and I were discussing this one night, and in typical fashion, he sent me this guest article a few hours later. Andrew is the smartest kid I’ve ever known, and when his mind is fixed on something, he gets to the bottom of it very quickly. You might be thinking, “who gives a shit?,” in which case we wouldn’t blame you. But this is the sort of thing that biomechanics geeks love to contemplate. We’re not saying that resistance training turns triangles into rectangles, we’re simply stating that muscles cannot grow without changing shape. Hopefully at least a few of you geeky meatheads will appreciate the article. 

Muscles Cannot Change Size Without Changing Shape
By Andrew Vigotsky

Last week, Bret posted a rant on Facebook describing how muscles can change shape. Many say this is impossible, but to be frank, they’re wrong. The purpose of this piece is to show, mathematically, that a muscle cannot change size without changing shape.

Firstly, it is important that we understand how shapes are comparable. Shapes can be compared in three ways.

  1. Congruency – congruent shapes can be made identical and superimposable by translating, rotating, or reflecting.
  2. Similarity – similar shapes can be made identical and superimposable by translating, rotating, reflecting, or proportional
  3. Isotopy – isotopic shapes can be made identical and superimposable by deforming a shape in such a way that does not “break” it (think tying a knot).

When it comes to muscle, the most appropriate measure of comparing its shape is similarity, as it changes size, so scaling may be necessary.

In order to do this, we will assume muscle has a hyperbolic cosine (my favorite function) shape, which does have a strong correlation with a muscle’s actual architecture. Next, we know points of muscle attachment cannot change, so let’s say the muscle before and following hypertrophy is modeled by the following function, where x is a position and α is the coefficient of hypertrophy.

1Graphically, it looks like this. Of course, these numbers are arbitrary, but the principles of this model still hold true.


Let’s say the muscle doubles in size, α = 2.


Traditionally, shapes are compared using Procrustes analysis, which is when the shapes are optimally scaled, rotated, and superimposed to best match. Then, Procrustes distance is calculated by

4Of course, this is an approximation, as, in reality, there are an infinite number of points that can be analyzed. Nevertheless, I used MATLAB to find the Procrustes distance between these two functions. If a distance exists (d > 0), then these functions are dissimilar.

Using 4585 points, a distance of .0070 was found. Using 5 points, a distance of .0074 was found. These functions are not similar; therefore, these shapes are different.

A muscle cannot change size without changing shape, as the attachments of a muscle remain constant, but the size of the muscle changes. In order for a muscle to remain the same shape, the attachments would need to shift with changes in size. Lastly, this model assumes uniform growth, but in reality, this does not occur, and non-uniform growth would make d even larger (more dissimilarity).

Four Reasons Why Athletes Must Sprint

Robert A. Panariello MS, PT, ATC, CSCS
Professional Physical Therapy
Professional Athletic Performance Center
New York, New York 

The athlete’s ability to sprint at high velocities is an integral component in the related fields of Sports Rehabilitation and the Performance Enhancement Training of athletes. A principal objective of the rehabilitation process is to restore the athlete to their previous level of athletic performance including the athlete’s pre-injury running velocity. With regard to the athlete’s performance enhancement training, a necessary component of training, when appropriate, would be to enhance the athlete’s abilities in linear velocity. The review of the various rehabilitation and/or performance enhancement training program designs often leads to the inquiry, as well as reveals the lack of an appropriate programmed sprinting volume as often the focus of the running volume prescription is “tempo” in nature. The Rehabilitation and Strength and Conditioning (S&C) Professional must ensure that the athlete incorporates an appropriate and proficient amount of sprinting volume into their rehabilitation and performance enhancement training program designs. Based on the athlete’s medical history, demonstrated physical quality levels, biological age, training history, etc., these appropriately prescribed sprinting volumes will vary from athlete to athlete. Nonetheless it is essential to incorporate appropriate high velocity sprinting volumes into the athlete’s rehabilitation and performance training program design.

The following are some of the simple explanations for prescribing suitable sprinting volumes for the athlete:

  1. Speed Enhancement – The obvious reason for the incorporation of appropriate sprinting volumes is for the athlete to increase their linear velocity. Speed is a dangerous weapon in the world of sport and the fastest athletes will have a distinct advantage over their slower opponent in the arena of athletic competition.
  1. Improve the co-activation index of the lower extremity musculature – An additional benefit of performing high sprinting velocity training is the positive effect upon the body’s co-activation index. A simple example of the co-activation index transpires during slower velocity body weight (as well as applied weight intensity) activities resulting in the stabilization of a joint via the agonist and antagonist muscle groups working together as these slower movement velocities result in an applied stress application over a prolonged period of time. Thus the co-activation index of the agonist and antagonist muscle groups working together during a prolonged slow activity performance is close to or at a 1:1 ratio.

High velocity sprinting movements are dependent upon a brief factor of ground contact time. The performance of high velocity sprinting activities requires a prominent contribution from the agonist muscle group(s) while the antagonist muscle group(s) has a lower level of contribution. This emphasized contribution of the agonist muscle group results in a shift in the co-activation index in favor of the agonist. This emphasized contribution of the agonists result in optimal high speed propulsion, as well as a fluid motion of the body in the desired direction of movement. Charlie Francis and Tudor Bompa have indicated that the highest skilled athlete’s are those with the ability to completely relax their antagonist muscle groups during high velocity movement and that ridged and rough movements are a result of poor coordination between the agonists and antagonists.

  1. Speed Endurance – It’s one thing for the athlete to perform at top sprinting speed for a few repetitions, but a necessity of many athletic contests is for the athlete to perform at top velocity frequently throughout the length of the competition. If the athlete does not have the speed endurance to perform at maximum velocity repeatedly over time, excessive fatigue will occur resulting in a loss of force output, technical proficiency, possible risk of injury, and neuromuscular inefficiency during the sprinting performance. The athlete must perform an adequate volume of sprinting to establish an appropriate level of speed endurance.
  1. Neuromuscular timing – The literature has demonstrated that the hamstring muscle most often injured during athletic competition is the biceps femoris (BF). One possible mechanism that may result in the injury of this muscle is poor neuromuscular timing. The BF muscle is comprised of a long head and a short head with different nerve innervations. The tibial nerve innervates the long head of the BF while the short head is innervated by the common peroneal nerve (Figure 1). If the neuromuscular “timing” of the BF muscle innervation is poorly coordinated, this may result in a hamstring injury.
Figure 1: The Biceps Femoris Muscle

Figure 1: The Biceps Femoris Muscle

An analogy of the significance of applicable neuromuscular timing of the shoulder occurs during the rehabilitation of the rotator cuff musculature in a baseball pitcher. During this shoulder rehabilitation process a neuromuscular timing must be established between the musculature of the gleno-humeral (GH) and scapula-thoracic (ST) joints of the shoulder for optimal throwing performance to occur. During the final stages of rehabilitation the initiation and progression of a post-operative rotator cuff repair tossing/throwing program may be prescribed as follows: Short Toss to Long Toss to Pitching on Flat Ground to Pitching from a Pitchers Mound.

This throwing progression requires the shoulder/arm to travel at higher throwing velocities during each progressive throwing phase of the athlete’s rehabilitation. Thus the neuromuscular efficiency, or timing, of the GH&ST musculature that is required for optimal throwing performance is enhanced via a progression of higher throwing velocities. Therefore wouldn’t the efficient timing of the dual innervation of the biceps femoris require the same high speed program design for optimal performance as well as the prevention of injury?

Optimal running velocities are imperative for success in many athletic endeavors. Appropriately prescribed sprinting volumes at the applicable times will not only enhance an athlete’s sprinting velocity, but maintain that linear velocity throughout the course of athletic competition while assisting in the prevention of lower extremity injury as well.

Sprint mechanics in world-class athletes: a new insight into the limits of human locomotion

JB Morin

JB Morin

JB Morin is a man on a mission – to unravel the science and discover the practices behind what best makes athletes sprint faster. He has amassed an incredible team of researchers who are equally as interested in advancing speed training science and methodology. I urge athletes and coaches to read through this interview carefully, as the information is cutting edge and highly insightful. 

Hi JB (follow JB on Twitter HERE), thanks for agreeing to do another interview. Your LAST INTERVIEW was very well received in the strength coaching and track & field communities. You’ve been very busy, and your BRAND NEW PAPER is getting some great attention. But let’s back up a bit. Over the past several years, your lab has published some incredible research on sprint mechanics. Why should we care about sprinting forces – how can it help us improve upon our training methods?

Thanks Bret, it’s always a pleasure to share views and research conclusions with you and your followers. Initially, the labs and collaborators involved in these studies were performed by the research group at the University of Saint-Etienne on the sprint instrumented treadmill, but then we extended and basically confirmed our results in the recent paper using track embedded force plates at the French National Institute of Sports INSEP. Even though I personally moved to a new position at the University of Nice, our multi-center research group still has projects under review, and in preparation. 

As to your question, our approach is considering the overall mechanical output of the neuro-musculo-tendinous system and the resulting forces applied onto the ground to propel the center of mass (CoM), and in turn the entire body. So in this “dynamics” context, ground reaction forces (GRF) in relation to subjects’ body mass are the main determinants of the motion of the athlete’s body, and in turn of his sprint performance.

This is a “macroscopic” approach in that we only measure and study the overall output of the system, i.e. the magnitude of resultant GRF produced, and the orientation of its application, from its horizontal, vertical and lateral components. So here is one limit of this approach in terms of training, it tells us how much force is produced and how effectively it is oriented onto the ground but it does not go into further details as to the muscles involved, their respective contributions to the total (resultant) GRF, and their timing of activation (coordination). Still, these two “basic” elements: magnitude of GRF and orientation of the GRF vector are very interesting from a training perspective to quantify both the muscular capabilities of the sprinter, and the effectiveness of GRF application. I usually refer to “technique” for the latter concept, but it is also a matter of muscle action.

In the 2011 paper, and then in a 2012 paper involving top level individuals, both using the instrumented treadmill technique, and now with this force-plate 2015 study, we basically show that the sprinters who are able to produce the highest acceleration and 40-m or 100-m performance are not those who produce the highest amounts of resultant GRF during the acceleration, but those who are able to orient their push with the highest horizontal component step after step. To make things simple, if I train and produce a resultant GRF of 100 arbitrary units per body mass, and orient this push with a high versus low effectiveness, the horizontal component of this GRF, i.e. the component that will propel my CoM forward, will be high or low, and my forward acceleration of the CoM will directly follow. So in terms of training, our studies consistently show that for the acceleration phase performance, horizontally-orienting the GRF produced is of higher importance than trying to develop a higher GRF production capability. Of course, training to both produce more force AND orient it more forward will be the ideal, but for sure at a given same level of force output capability, the highest acceleration will be produced by the athlete able to orient his push the most horizontally…

The main training challenges now are to find out how to best train this ability. As your readers know, training science has gone into much detail as to how to increase the lower limbs’ “total” force, now the idea is to increase the athlete’s ability to apply this force with effectiveness. Our aim in this series of studies was to investigate what mechanical factors differ between non-specialists, good and world-class sprinters during their acceleration. Now our challenge (ours and coaches’) is to investigate and test the best solutions to develop these factors through practice. Training implies time, money, sometimes pressure for performance, and risk of injury, so you want to know what to work on and how.

I am excited for future research to emerge elucidating the best methods for improving the horizontal orientation of GRF production. Now I ask you to please discuss the pros and cons of your previous lab’s methods.

Our previous methods were based on having the subjects sprint on a motorized treadmill that accurately and instantaneously responds to the subjects’ motor actions. Every Newton of propulsive or braking ground reaction force was associated with an acceleration or a deceleration of the device. To see this in detail, watch this video. The obvious limit of this device is that subjects do not sprint overground, and a serious familiarization session is needed before undertaking any sound measurements. Furthermore, the top speed reached and the overall sprint performance is around 20% lower than what subjects could typically do on the field. However, we showed in a 2011 paper that treadmill and field performances were correlated and the fastest sprinters on the treadmill were also the fastest sprinters on the track, and thus inter-individual comparisons were possible.

For the pros, first and foremost, this device allows measurement of the three components of the GRF, at the sampling rate of 1000 Hz, and for any type of duration (for instance we simulated 400-m efforts for a fatigue study, or repeated sprints in another one). It is totally safe, and even highly skilled sprinters told us that the acceleration feeling was very close to what they experienced on the track. So it’s virtually like having a force plate under the feet for the entire sprint. In addition, this device allows athletes to perform a typical acceleration phase (from zero to high speed), which was hitherto not possible with other devices on which subjects typically had to drop themselves onto the fast rolling belt. Last, the motor torque is adjustable so we can do resisted or assisted sprints (data in process). Only 2 motorized treadmills of this kind exist in the world; one is at the Laboratory of Exercise Physiology at the University of Saint-Etienne in France, and the other one is at ASPETAR Sports Medicine Hospital in Doha, Qatar. 

Sounds like the pros of using the motorized treadmill for research far outweigh the cons. To your knowledge, how many published studies on sprinting forces (or impulse or power) to date examine elite sprinters?

If by elite sprinters you mean sub-10 second guys, very few scientists were lucky enough to specifically and directly study such a population, and publish the results in peer-review Journals. Peter Weyand and Ken Clark did recently, Bezodis et al., and Japanese colleagues who published a congress proceedings’ abstract showing the GRF traces of top Jamaican sprinters. I like to remember that Archibald V Hill, the famous physiologist, also did field experiments on top-level sprinters in the 1920’s (see this fascinating tribute paper):

My favorite sport science picture. Archibald Hill during field sprint measurements.

My favorite sport science picture. Archibald Hill during field sprint measurements.

By the way, Hill and others showed the exponential decay of sprint velocity as a function of time in papers from 1927 and 1928 (see below).

Of the published papers that currently examine sprinting forces (or impulse or power) what is the major drawback of every single one of the papers?

Studying sprint mechanics is a “pick your poison” game: either researchers like Peter Weyand or our group used instrumented force treadmill and studied treadmill sprinting rather than overground sprinting, or researchers used force plates and studied “real” sprinting mechanics, but over a very limited number of steps (typically 1 or 2). The treadmill modality allows you to measure GRF continuously but either at realistic top speeds only (Weyand’s studies) or the entire acceleration phase but until top speeds that are lower than reality (our studies).

The main drawback of the force-plate approach is that you get accurate but really narrow “pictures” of the sprinting mechanics, since you have data measured over one or two steps in the blocks, at 8, 12, 25 or 40-m of the sprint. It does not allow you to have a broad knowledge of the GRF production over the entire performance, and there is a risk that the data you collect do not represent the entire sprint. 

Well put JB. When I was in New Zealand at AUT University, I told my supervisor John Cronin that we should have built an entire 100 meter track lined with force plates embedded into the ground. I don’t think it would be that hard to do, and it would have allowed for some incredible research. There currently aren’t any Universities to my knowledge that have anything like this. What was your solution to overcome this problem?

Should money and logistics allow you to build it, this kind of track is possible, however, empowering the plates, setting filters, gains in the signals, time-synchronizing the different plates, digitizing the data and eventually getting smooth and treatable GRF data will be a huge challenge. In our recent paper, the INSEP engineer, Antoine Couturier, had a really hard time getting final data for us to process and study, and the force plate setting in Paris is only about 7-m long! In fact, Figure 1 in our recent paper (see image below) is one of the most impressive Figures I’ve ever inserted in a publication, and there were many hours of work behind these data.

GRF traces over time and the corresponding positions of the force-plate system.

Vertical, horizontal, and lateral GRF traces over time and the corresponding positions of the force-plate system.

So it might take a little while until longer installations than the currently existing 10-m to 15-m force plate systems are available for human performance research. But at the time of Hill’s research on sprint running in the 1920’s they used magnets and coils along the track, so we can definitely anticipate that such instrumented tracks will exist in the future.

In our most recent study, we virtually re-constructed a complete 40-m by having athletes perform several 10, 15, 20, 30 and 40-m sprints, and placing the starting blocks at various distances from the force plates, so that we collected data for almost all the steps of a 40-m sprint in each of the subjects. Because these highly skilled sprinters have very reproducible kinetic and kinematic patterns, we assume that, should this have been possible, the data collected over a continuous 40-m measurement would not have been different from those we present here.

Below is a schematic representation of the protocol design:

Schematic representation of the protocol, by Pierre Samozino.

Schematic representation of the protocol, by Pierre Samozino.

This is a great step up from previous research! Does this mean it’s perfect?

Perfection does not exist in science, and we always struggle to limit drawbacks and biases, and use the “least worst” solution, method, design, device, etc. Sometimes it is frustrating, but my view is that when nothing better exists, you must do with what’s available to you, and just be conscious of the limits floating above your results and conclusions. Refutability and debate is the basis of the scientific game, and what is accepted as true now will be adjusted/refuted/confirmed in the future. You have to be humble and accept the inherent limitations of the current methods, and try to put sound knowledge forward. Otherwise, you just stay at your desk waiting for perfection. This is for sure easier as there is no risk of having to say, “we were wrong”, but it is unproductive and hopeless.

Amen JB! Let’s talk about what we learned from this latest research. Please discuss the relationship with stride rate and stride frequency throughout the entire 40 meter sprint.

Our results show that while step length increases regularly over the acceleration phase (from the blocks push-off to the 40-m line), step frequency is almost instantaneously leveled at the maximal value athletes can reach: 80% at the first step and about 90% after the third step, and then remained constant thereafter. This is basically what Sofie Debaere et al. also reported in 2013: high-level sprinters develop in the 0-to-10-m phase a step frequency higher than 95% of the step frequency they reach at maximal speed. As a consequence, the speed increase of high-level athletes is afterwards quasi-exclusively caused by the increase in step length.

Fascinating! Do faster sprinters produce more total force into the ground in the blocks and during the 40 meter sprint, or is vertical or horizontal force more important? What about the ratio of forces?

In the blocks, elite sprinters produce much more (about 25% more) horizontal force and power than less skilled sprinters.

When averaging data from all the steps of the 40-m sprints after the blocks push-off, we observe that faster sprinters produce 10% higher horizontal force (Effect Size of 1.75). Contrastingly, they produce less vertical force (2% on average, Effect Size of 0.59). Note that our comparison is based on the data of 4 elite sprinters (best 100-m times ranging from 9.95 to 10.29) and 5 sub-elite sprinters (10.4 to 10.6 s). Sorry we could not recruit more athletes of the same level to perform more detailed stats than just % difference and Effect Size analyses.

Ratio of force data (the “ratio of force” in our approach is the ratio, for each contact phase, of the horizontal component to the resultant GRF) show that elite athletes are more efficient both in the blocks (+13%, ES of 1.46) and on average over the 40-m (+10%, ES of 2.31). In other words, since elite sprinters produce around 10% more horizontal force and around 2% less vertical force than their sub-elite counterparts, their ratio of horizontal to total force ends up being around 13% greater.

Does this validate your previous findings using the sprint treadmill?

Overall, yes, clearly. The horizontal force production during the acceleration is significantly and highly related to field sprint performance, whereas the vertical and resultant GRF production are not. This is better expressed through the paramount importance of the “ratio of force”, and in summary, the fastest sprinters at the end of the acceleration phase are not those who produce the highest amounts of total force with their lower limbs, but those who orient their push the most effectively, and in turn produce the highest horizontal force. In both our treadmill and overground studies, acceleration and 40-m or 100-m performances are significantly and highly correlated to the average horizontal force produced per unit body mass, and not to the average vertical force produced. Note that the vertical force produced per unit of body mass was only related to the value of top speed reached, as previously observed by Weyand et al.

Our new study supports the fact that the importance of horizontal versus vertical force production to sprint performance basically depends on what phase of the sprint you are interested in: whole acceleration versus top-speed phase only. However, even in top speed sprinting, horizontal force is critical.

If we look at Figure 1 from the study (shown above), we see that throughout the 40 meter sprint, vertical force rises and horizontal propulsive force diminishes. Many track & field specialists infer this to mean that vertical force is more important than horizontal force. Why is this outlook unacceptable?

Yes, this is true if you look at the force peak only, but what is really important is to look at impulses (i.e. force-time integral). The vertical impulse increases and the horizontal net impulse decrease over the acceleration, respectively because the CoM height increases from the starting-blocks to the classical running position and because as you know (muscle’s force-velocity relationship), our bodies can’t help producing lower and lower amounts of force as moving velocity increases.

We recently submitted a study focusing specifically on impulses in which the vertical impulse per unit body mass is not correlated to 40-m performance, whereas horizontal net impulse is. So definitely, to accelerate in the early phase of a sprint (typically a 20 or a 40-m sprint), what is a key determinant is the amount of net horizontal, not vertical impulse you produce. So although speed and vertical impulse increase concomitantly over the acceleration, the amount of speed produced (i.e. sprint performance) is not correlated to the amount of vertical impulse produced.

That said, our data (treadmill and track) clearly and consistently show that only the average vertical force produced AT TOP SPEED is well correlated to the amount of top speed reached, and not to the amount of acceleration produced beforehand. So maybe here is the main confusion made, you should not extrapolate what is important for top speed running only to what is important for acceleration. Our paper, currently in review, shows that vertical impulse tends to be negatively related to 40-m acceleration performance in very high-level sprinters (when its influence on performance is tested independently from that of the horizontal impulse, by means or multiple regression analyses).

Many coaches (such as myself) seem more interested in maximum speed sprint mechanics. Why should we be more interested in acceleration sprint mechanics for sports? 

To me this is paradoxical, if you look at the descriptive time-motion data published in various sports, you see that in fact, only in track and field 100 and 200-m is top speed running a key factor. In all other sports where sprinting is a major physical ability (soccer, football, rugby, etc.), only much shorter distances represent most of the demands of the game, and very rarely do players actually reach their individual top speed. A simple reason for this is that in order to run at your top speed, you need an acceleration of 30 to 50-m depending on your level, in a straight line, with no opposition (tackle, change of direction, etc.). This almost never happens, and when it does, it occurs in situations that are not key situations for a defensive or offensive action. Take a rugby player (except maybe in Rugby 7s) who is able to slalom between defenders and sprint towards the try line, the decisive action will be his ability to accelerate and change direction over the first 5-20-m, afterwards, his top speed (once again, reached after 30 to 50-m) might not be a determinant anymore. Last, studies show that in soccer or rugby, most sprints and decisive sprints are shorter than 20 or even 10-m, so no top speed is involved here – just “top acceleration” capability.

So to me, if you list all sports involving sprinting and sub-list only those involving pure top speed (reached after a complete acceleration) versus those involving maximal acceleration over distances too short to allow players to reach top speed, there might be only 100-m and 200-m events concerned versus a plethora of other sports. Not to mention that if you think, from a training perspective, about the number of athletes concerned in the world (i.e. 100/200-m sprinters versus all the other sports), then top speed capability might be considered as a really minor capability compared to shorter distances acceleration capability. Take the famous NFL combine 40-yard dash. It is clearly an acceleration test. Even if in fine, a high acceleration on the field will result in a high running speed, the typical constraints of the rugby, soccer, and football codes do not often allow players enough time and space to reach their absolute maximal speed. From the tenths of sprint acceleration files we’ve processed in elite athletes and soccer and rugby (all codes) players, I think 90% of all players reach their top speed between 30 and 40-m. However, we observed that in young players (below 18), top speed is reached before 30-m. So these might be exceptions to the aforementioned general observation. Some authors observed very short distances to reach top speed in college football players, during specific short sprint tests, but we may wonder whether this top speed could have been actually higher in a longer sprint acceleration context. This is the difference between the “absolute” top speed of an athlete or a team sport player and his “top speed” in the context of the shorter-than-necessary distances that the demands of his sport allow (see discussion here). So when talking about “top speed” in sports, we should definitely clarify between absolute top speed and top speed in a specific sport context.

Last, even though some acceleration sprints are “flying start” sprints, the durations still rarely allow players to reach their absolute top speeds. Nota: for numerous and detailed references in all the above-mentioned sports, look for “time-motion analysis” or “physical demands” of these sports in PubMed.

I see that you were also able to calculate horizontal power overground. How did you pull this off? Previously we needed a specialized treadmill in order to enable us to do this? 

Yes, one of our recent aims was to propose and validate a field method to get horizontal net force, and mechanical power output in sprinting from either time-distance (photocells split times) or time-speed (radar or laser) measurements. The idea was to allow many more coaches, scientists and athletes to assess and monitor the mechanical power, force-velocity profile and even effectiveness of force application (ratio of forces), and use these variables in their practice (training load, follow-ups, effects of fatigue, etc.).

The theoretical basis of this simple method, first authored by Pierre Samozino, is that when humans (whatever their level) accelerate from null to maximal speed, the change in speed over time superbly follows an exponential decay. So we fit the speed-time curve with this simple exponential function, and then derivate the speed-time curve to get the acceleration-time curve. Then, using the laws of motion in the forward direction and estimating the air friction on the runner from body mass, height, wind speed and air temperature and pressure, we obtain the net horizontal force output, and when multiplying by speed (since power equals force times velocity), we obtain the mechanical power output produced in the horizontal direction. The validation was made by comparing our computations to the force plate data we’ve mentioned earlier, and basically, it works very well. The validation results were first presented in an abstract at the International Society of Biomechanics in Brazil in 2013, and the full paper is currently under review. Many coaches in various sports currently use this approach, in collaboration with us, and we’ve already published a couple of studies about soccer players acceleration versus top speed performance, hamstring injuries and how injured players differ in their mechanical output from non-injured players, at the return to sport and after 2 months of full practice, and a comparison between elite players from different rugby codes.

See below for instance the computations we did of Usain Bolt’s force-velocity profile and power-velocity relationships over his World Record 100-m sprint. The cool thing is that our computations are based on the published 10-m splits of the World Record, but should force plates have been installed under the track in Berlin, our validation results show that we would have obtained values within 2-3% of what Bolt exactly produced…

For a detailed explanation, see this video of a workshop I did at Auckland University of Technology SPRINZ institute in 2013 (second part, sprint force-velocity-power profile).

Force-Velocity (FV) Profile of Usain Bolt's World Record Performance

Force-Velocity-Power Profile of Usain Bolt’s World Record Performance

This is incredible! Thanks JB. Moving on, horizontal power was the most highly correlated marker of maximum sprint speed and 40 meter performance in your study. Do we know how to best increase horizontal power in training? What are your ideas?

I think that for historical reasons (use of weights and weightlifting for S&C) and for obvious mechanical reasons (gravity and loads apply a vertical constraint), it has been overall easier to work on vertical than horizontal power development. And if I agree that there might be a transfer between gains in vertical power through training and gains in horizontal power, I am convinced it is the case in lower level and heterogeneous populations, but not above a certain level. In collaboration with researchers Matt Brughelli (see an interview with Matt HERE) and Pedro Jimenez-Reyes, we recently collected a ton of data in various sports and for levels ranging from leisure to world-class, and our first results (paper writing in process) show that jumping power in elite rugby players for instance is not correlated at all to sprint power as we measure it with our method.

In pro rugby players, sprint power and 30-m sprint time are highly correlated (bottom left), but not sprint FV profile and jump FV profile (top left), not sprint max power and jump max power (top right), and not jump max power and 30-m sprint time (bottom right)

In pro rugby players, sprint power and 30-m sprint time are highly correlated (bottom left), but not sprint FV profile and jump FV profile (top left), not sprint max power and jump max power (top right), and not jump max power and 30-m sprint time (bottom right)

I like to illustrate this by the “toothpaste tube” theory: when the toothpaste tube is full (low skill level), no matter how you press the tube (no matter how you train) you’ll get some toothpaste (performance improvements). So any kind of force training might result in sprint performance gains. But after a certain skill level, when the toothpaste is almost empty (very narrow margins for improvement), you’ll have to press the tube with very specific and well-designed gestures. In a sprint acceleration training context, this might relate to the horizontal force training, when vertical force does not transfer to sprint performance anymore.

So I really think there is an interest in specifically targeting horizontal force and power development to train for sprint acceleration – especially with highly skilled athletes. One of the best ways is probably resisted sprinting using sled and additional loads, or elastic bands, or uphill sprinting. As to sled training, some studies recently confirmed the higher effectiveness of high loads compared to low loads. Kawamori showed that heavy load sled training resulted in a higher sprint acceleration performance, not because more resultant force was applied after training, but because heavy loads led subjects to push with more effectiveness and apply similar amounts of resultant GRF, but with a more horizontal orientation (and thus higher horizontal component of the GRF and in turn forward acceleration). So the key is in coaches’ hands, I think they should systematically think about finding exercises and training modalities that stimulate the forward push, in addition to or instead of the vertical push, whenever possible.

I concur! Thanks again JB, one last question. Do you have any other interesting research in the works?

Yep, our main current project is a one-season follow-up of tenths of well-trained athletes, soccer, rugby players’ force-velocity and power profiles in sprinting, using our simple radar method. Our focus is to seek whether power output and force-velocity profile in sprinting (or an unexpected change in these variables) is related to a higher risk of injury, and could be an objective variable to focus on in the prevention, rehabilitation and return to sport process. Other projects are in the works about the role of hip extensors in the horizontal GRF production, the so-called “transfer” between vertical and horizontal power (now that we can assess the latter precisely and specifically in sprinting), and the best training methods to develop this horizontal power output in many sports such as athletics, rugby or soccer. So I guess we’ll have new and exciting things to share for the next interview.



The Most Under-Utilized Exercises for Developing Devastating Power

Today I have a guest blog for you by my former intern Joey Percia. I vouch for all of these exercises; they’re my favorite for improving power. Great stuff right here!

The Most Under-Utilized Exercises for Developing Devastating Power
By Joey Percia

‘Olympic lifting is terrible, heavy barbell training is useless, sprinting sucks’.

Sound familiar?

Training to maximize power output becomes a very interesting topic when discussed amongst strength coaches. Some coaches swear by Olympic lifts and its variations, while others use a variety of approaches when seeking out maximal power development.

What is power?

Power is work divided by time ( P = work / time) and is a product of strength and speed. Research has shown that the optimum load for maximizing power production in a particular exercise depends on the movement being performed. Some studies show very little significant difference between loads (the Olympic lifts), while others have a much more obvious load that maximizes power (jump squats).

Someone that tells you that power is only developed at a certain percentage of your 1RM (for example, at 30% of 1RM), no matter what the exercise being performed, is misinformed. Some lifts are maximized at 0% of 1RM (jump squat), others at 30-70% of 1RM (bench throw, bench press, leg press, half squat, split jump squat), and others at 80% of 1RM and above (Olympic lift variations).

Considerations for Exercise Selection

Here are some important variables to account for when choosing exercises to develop devastating power.

1. Training Age

Choose exercises that coincide with an athlete’s training age — referring to the number of years they have been strength training. Those with a younger training age tend to show greater difficulty properly executing complicated exercises, in which case these should be avoided. Athletes spend a limited amount of time with a strength coach, which is why it is of great importance to perform exercises that will elicit the greatest gains (‘the most bang for your buck’).

Time is precious. It is a waste to prescribe frustrating and difficult tasks to athletes whose time spent with a strength coach is limited and valuable. Choose movements that are significantly easier to learn and perform yet are still highly beneficial.

2. Coach to Athlete Ratio

Monitor the athlete. Make sure form is correct and exercises are being performed safely and effectively. This is critical because the job of a coach depends on the athlete’s safety. Advanced movements and technical lifts which require different equipment and more coaching may not be optimal for settings other than one-on-one and small-group training. There is nothing wrong with performing these lifts if the proper amount of coaching is dedicated to each athlete.

3. Equipment Availability

Equipment is not just a common problem in commercial gyms. With larger groups of athletes, equipment can become an issue as well. When choosing an exercise make sure the athlete is able to perform it in the manner in which it was designed to increase maximal power output, specifically in relation to recovery time between sets and the optimal loading being used. It would be foolish to try to manage a group of 15 athletes doing barbell jumps squats with only 2 barbells .

4. Movement Specificity

To ensure you choose the most beneficial exercises to improve power in a particular sporting movement or event, look at the movement and ask these simple questions:

  • What is the direction of the movement?
  • What joints are involved?
  • What are the muscles that cross those joints?
  • What is the speed of the movement?
  • What is the duration of the movement?
  • How intense are the muscular contraction?

Pick exercises that best fit the answers to these questions. When answering these questions appropriately you will see the best carry-over to improving maximal power potential in a particular movement.

Movement Execution

“Bad Intentions”

You can’t just grab a kettlebell, do half-hearted swings and say you are training power. Well you can, but that doesn’t mean you are going to achieve the desired training adaptations you are seeking.

One of the key aspects for developing power that demands respect is intent. The intent to move the bar, object or body as fast and hard as humanly possible while maintaining proper technique. When the load is higher, speed will necessarily decrease, but the intent to move as fast as possible must remain. This is a very important component to developing power.

In this case, violence is acceptable — often encouraged. Perform the movement with ‘controlled chaos’ as I like to call it.

Quality over Quantity

Speed must be maintained throughout the set. If it starts to decrease the set or exercise should be terminated. This is critical. Speed may drop off because the intent has decreased or fatigue has set in because rest in between sets was too short or due to the accumulation of volume.

Make sure you allow adequate rest in between sets to fully recover and keep those bad intentions flowing.

The Exercises

Here’s a video you can check out before delving into the individual exercises:

Band Resisted Swing or Heavy Kettlebell Swing

Heavy kettlebell swings have a noticeably different feeling than using a lighter kettlebell. Pilot research shows that heavy swings compared to lighter swings elicit higher glute and hamstring activity. To get the most out of the heavy kettlebell swing for a power exercise, make sure you focus on the ‘hip snap’ by violently contracting the glutes. This makes a huge difference opposed to coasting through the end of the movement, especially when it comes to developing serious power.

When I worked with Bret at the Glute Lab we liked to perform heavy kettlebell swings with the 203lb kettlebell. For males with a 450lb+ deadlift this is a good goal weight.

band resisted swing

Unfortunately the largest kettlebell I have access to is the 106lb, that is shown. I attach bands to the kettlebell to add resistance. This doesn’t have the exact same feeling of swinging the 203lb’er but it is very similar and teaches a powerful hip extension. I actually prefer the band resisted swing over the heavy kettlebell swing because it is easier for most to control the movement but still must be performed violently because of the added band resistance.

how to setup band

How to set it up (right image first, then left)

Prescription : 5-8 sets of 8 explosive repetitions

Hex Bar Jump Squat

The hex bar jump squat looks similar to the traditional barbell jump squat except weight is held in the hands. This makes it a hip dominant movement compared to the barbell jump squat being more quad dominant. Research has shown that you can achieve greater power outputs with the hex bar jump squat compared to the back loaded barbell jump squat.

hex bar jump squat

Most feel more comfortable with the weight in the hands as opposed to the weight placed on the back, especially if something ‘doesn’t feel right’. It is easier to let go and release the weight rather than trying to dump the bar off your back.

Jump as high as possible on each rep, absorb the impact during landing, and minimize the time you spend in contact with the ground in between each rep.

Prescription: 3-5 sets of 3 explosive repetitions with 50-60% of 1RM hex bar deadlift

Explosive Back Extensions

The explosive back extension should be performed with a slightly rounded upper back and posterior pelvic tilt compared to the traditional back extension with a neutral spine. Perform explosive back extensions with a lighter load or against resistance bands — preferably monster mini band for males and mini band for females.

explosive back ext

The main focus should be maintaining posterior pelvic tilt, keeping the upper back rounded, driving the hips into the pad as hard as possible and then reversing the movement as quickly as possible.

Prescription: 3-5 sets of eight explosive repetitions with 50% load used for a hard set of 20 reps

Jumping Lunges

Jumping lunges are a great movement to develop power when space and equipment is limited to only bodyweight. The jumping lunge is great because technique can be dialed in to ensure the athlete’s safety. The movement is very easy to learn compared to other single leg plyometrics activities and in most cases very similar to positions found in common field sports.

split squat jumps

An external load can be used by holding dumbbells or wearing a weight vest if need be. I prefer the weight vest (typically 10-20lbs) compared to dumbbells since the weight vest still allows the use of an arm swing, which is a important component in improving jumping ability.

Prescription: 5-8 sets of 4 repetitions per foot

Sled Sprints

Sled sprints are an amazing movement to include for the development of tremendous lower body power. The sled allows the athlete to strengthen the sprinting muscles while decreasing the overall loading as well as wear and tear on the joints.

sled push

Two common ways to perform sled sprints include:

  • Lighter weights which moves quickly
  • Very heavy weights which moves slowly

Both must be performed with the intent of moving the sled as fast as humanly possible. The idea behind these two methods is it allows us to train two different parts of the strength continuum. The lighter weights train more speed strength/explosive strength and the heavy weights will train more strength speed/absolute strength.

Prescription: 5-8 sets of 10-20 yards sprints

Putting it all together

When the goal of training is to increase maximal power production it is important to perform these movements in a well-recovered state. This can be accomplished by placing power exercises at the beginning of training or training these movements at a separate time after allowing adequate time for refueling and recovery — For example:

  • AM Session – Heavy sled sprints of 5 x 10 yards
  • PM Session – Normal strength training regimen later that day with decrease in normal volume

Allow proper time in between sets to ensure full recovery. Training to increase maximal power output is not meant to be performed during a state of fatigue.


Whether you are training for looks, fun or an athletic event it never hurts to be more powerful. Using the movements listed in this article will allow you to train harder while feeling better. Give your body a break and give these joint-friendly power exercises a shot.


Author Bio



Joey is a strength coach and personal trainer. He is a performance specialist at ‘Soho Strength Lab’, a boutique training studio in New York City and runs an online training business where he helps clients crush their goals. Joey has his Masters degree in Exercise Science and has received his CPPS, CSCS and is Westside Barbell Certified. He is a competitive powerlifter and has been mentored by Louie Simmons at Westside Barbell as well as Bret Contreras at ‘The Glute Lab’.

He provides free content related to all things strength, fitness, health and life on his YouTube Channel ‘Percia Performance‘. Connect with him via Facebook, Instagram, Twitter for a cyber high five. SUBSCRIBE to his free newsletter and receive his 23 page E-book ‘Damage Control for Special Occasions‘ a complete guide for managing fat gain while enjoying special events.