Is the intended or actual movement velocity more important for velocity-based training?
The development of speed and power are desirable adaptations for a variety of athletes. Researchers have suggested that general strength training alone may be adequate for inexperienced trainees to improve high-velocity specific training adaptations (33,39) (e.g. improving maximum squat strength transfers to improved vertical jump performance). As athletes generally become “stronger,” it’s been noted that they typically require increased training specificity to attain targeted adaptations (19) (e.g. improving maximum squat strength may not transfer to improved vertical jump performance). However, there is a debate for high-velocity adaptations as to whether the intent or the movement velocity must be specific to maximize adaptations from training.
On the one side of the debate, there’s an argument to be made that the actual movement velocity is not as crucial for driving high velocity-specific training adaptations, but rather the intent is what drives these adaptations. Let’s use a (crude) example to illustrate this point. Imagine that two separate experimental groups used a squat exercise to improve their vertical jump. The intent side of the debate would argue that there would be no differences in the improvement of vertical jump performance if one group trained their squats with 45% of their 1RM or the other trained with 90% of their 1RM so long as both intended to move as fast as possible. In other words, it would argue that adaptations are intent specific, and since tasks performed at a maximum velocity require maximum intent, the actual movement velocity is irrelevant. Even though the group training with 90% of their 1RM would be moving at a slower velocity, since the intent to move as fast as possible is the same between groups there wouldn’t be any expected difference in resulting adaptations. Further, some may argue that motor unit recruitment may be more significant when training with heavier loads (i.e. 90%1RM). Thus it would result in perhaps even superior improvements in vertical jump performance than being velocity specific.
On the other side of the debate, some have posited that the actual movement velocity does drive velocity-specific training adaptations. Suppose we continue using our example from the previous paragraph. In that case, the velocity side of the debate will hypothesize that there would be a difference in the resulting adaptations between the two groups. Since the group training with 45% of their 1RM would attain faster movement velocities, they would improve their vertical jump significantly since it is a high-velocity task.
As I will argue in this article, both sides of the argument have merit, and both can perhaps be made “less wrong” by finding a middle ground. It is my (perhaps unremarkable) contention that both the actual and the intended movement velocity contribute to the development of velocity-specific training adaptations. The purpose of this article is to briefly highlight both sides of this debate (hereafter referred to as “Intent-Specific” and “Velocity-Specific”) and provide a rationale for the contention that both are responsible for driving velocity-specific adaptations. In the next section, this article will outline the existing literature, and the final section will conclude with practical recommendations for exercise professionals.
Debate position- intent specific
The premise behind the argument that training adaptations are intent specific rather than velocity specific is grounded in two main ideas: 1) the size-theory of motor unit recruitment, which suggests that lifting large loads with a maximum effort recruits the maximum number of motor units, and 2) an article published in 1993 by Behm and Sale titled “Intended rather than actual movement velocity determines velocity-specific training response” (4). Therefore, it is essential to dissect both the theory and this landmark study in more detail.
Size theory of motor unit recruitment
First, it is crucial to recognize that some in-vivo studies suggest that surface EMG activity decreases as velocity increases (and thus load decreases) (3), suggesting that large loads are best to maximize the recruitment of a maximum number of motor units. It is essential to highlight that EMG activity is not analogous to motor unit recruitment (although they may be related, we cannot infer one from the other. This would require a post on its own, but see (15,36,37) for more information). Essentially, without other methods such as spike-trigger averaging or advanced wavelet & statistical analyses to assess motor unit recruitment, it is perhaps unfair to extrapolate the findings from studies using surface EMG to motor unit recruitment. Furthermore, and perhaps more importantly, the initially proposed size theory may be overly simplistic and reductionist for in-vivo analyses. Since the formulation of this theory, there has been more emphasis highlighting that factors such as the mechanics, sensory feedback, and central control may also influence motor recruitment (see Hodson-Tole & Wakeling’s 2009 paper for a review on the topic (20)). To summarize, we should be careful of the data analysis procedures used in studies and move beyond the initial size-theory of motor unit recruitment to understand whether the intended vs actual movement velocity is driving velocity-specific training adaptations.
Empirical evidence
Moving on to Behm and Sale’s study, eight males and females performed a 16-week training program whereby on one leg they performed high-velocity ankle dorsiflexion movements and on the other performed a low-velocity training program with the same movement. The researchers then compared the resulting adaptations between legs to determine if the training adaptations were velocity specific. They found no difference in the resulting high-velocity adaptations between groups, suggesting that low-velocity and high-load training is just as practical as high-velocity and load-load training (i.e. high-velocity adaptations were not specific to the movement velocity, but rather the intent).
There are a couple of limitations, though, if trying to extrapolate these findings to applied settings. The first is that more recent data has suggested that using the opposite limb as a control may be inappropriate because the contralateral limb can benefit from unilateral strength training (7,13,22,28). Therefore, adaptations from one limb were perhaps “crossing over” into the other, clouding any velocity-specific adaptations. The other limitation is that a high level of performance in sport-related tasks is critically dependent on the skilled coordination of several joints. There is data suggesting that lower extremity strength and coordination are independent contributors to maximum vertical jump height (35) and that the coordination of an arm swing, for example, can influence the proximal-to-distal sequencing of the lower extremity (which in turn influence the net joint moments and height attained during the jump) (8). Just as we cannot discount the structural adaptations that occur from training (e.g. changes in muscle fibre type), we cannot ignore the coordinative adaptations that may emerge from high-velocity training. This consideration is especially relevant from the dynamical systems theory of motor control perspective since data suggests that increasing load and velocity have unique influences on movement behaviour (16). Therefore, we cannot assume the multi-joint coordinative adaptations from lifting heavy loads with maximal intent to positively transfer to the multi-joint coordination patterns that improve the performance of high-velocity activities.
Although this subsection has only focused on theoretical limitations and Behm & Sale’s landmark paper, it is also essential to review the existing empirical data. Another commonly cited study by Cronin et al. compared high- vs. low-velocity training and its transfer to netball throwing velocity (10). The authors suggested that high-velocity specific training may not improve throwing velocity any more than low-velocity strength training. Although this appeases the abovementioned concern about extrapolating Behm and Sale’s findings from single-joint to multi-joint movements, they used an untrained female population in their study. Therefore, these results are perhaps unsurprising given that generally “weaker” athletes don’t require the same level of specificity in their training as “stronger” athletes.
Debate position- velocity specific
A relatively larger proportion of the literature seems to support the contention that training adaptations are velocity-specific. Various studies using single-joint “isokinetic” devices have consistently shown training adaptations to be specific to the trained movement velocity (5,6,9,14,17,21,27,31) (please see references for particular study details), even after controlling for the intent to move as fast as possible. However, for reasons mentioned in the previous subsection, it is perhaps inappropriate to extrapolate these findings to multi-joint movements that exercise professionals are more interested in improving.
For example, lifting lighter loads in the jump squat (30% squat 1RM) elicited superior adaptations in 20m sprint performance than jump squats with heavier loads (80% 1RM) (25). In another investigation that compared training protocols that prioritized high velocity vs. high load (i.e. slow-velocity), high-velocity training showed significantly greater improvements in initial acceleration, maximum running velocity, and 100m sprint times than the high load training (11). In a training study with experienced sprint kayakers, researchers have found that athletes’ training velocity was more likely to improve parts of the race specific to those adaptations (i.e. high-load training was superior for improving the initial acceleration where velocities were low whereas high-velocity training was superior at improving the high-velocity portions of the race) (23).
In addition to this empirical data, research has demonstrated there are other coordinative (2,19,25,31,33) and muscle fibre [i.e. fibre type (12,24,30), number of sarcomeres/fascicle length (1,38)] characteristics that may also be responsible for explaining high-velocity specific adaptations. However, the minutiae of these studies are beyond the scope of this article.
Alternative Perspective- both intended and actual movement velocity specific
Based on the data presented in the preceding subsections, it may be tempting to conclude that adaptations are clearly velocity specific. However, the answer is still a little more complicated than just that. Take, for example, the findings of Gonzalez-Badillo et al.’s 2014 study (18). In their investigation, they compared velocity-prioritized training programs that instructed athletes to perform a bench press in two different ways: 1) participants performed each repetition at 100% of the highest movement velocity that participants could attain with a given load (MaxV group); and 2) participants performed each repetition at 50% of the fastest movement velocity that participants could attain with a given load (HalfV group). After six weeks of training, the MaxV group had a greater increase in their 1RM bench press strength and the average velocity they could attain when bench pressing heavy and light loads compared to the HalfV group. The same research group conducted a similar study with the back squat (29) and found that the MaxV group improved their countermovement jump height significantly more than the HalfV group. Since the HalfV group did not attempt to lift as fast as possible, likely, both the intent to move as fast as possible and the actual movement velocity contribute to the development of velocity-specific adaptations. If adaptations were solely velocity-specific, we should have seen the slow velocity group increase their maximum strength to a similar extent since 1RM lifts are performed at slow velocities. Therefore, adaptations cannot solely be velocity-specific and must also be intent-specific to a certain extent.
Practical Applications
In conclusion, the current research suggests that advanced trainees may benefit from prioritizing faster movement velocities during training while also imparting maximum intent.
I want to be very explicit, though, and highlight that this DOES NOT suggest that maximum strength training (i.e. lifting heavy loads at slow velocities) cannot or would not improve high-velocity specific training adaptations in a well-designed training program for advanced athletes—quite the contrary. Moving at high velocities necessitates that athletes produce large forces in short periods, and maximum strength training is a fantastic way to improve the maximum force capabilities of athletes. Instead, the emphasis of this article is to challenge the contention that only maximum strength training is not the best way to improve high-velocity specific adaptations, even if athletes intend to move as fast as possible. Although you could probably get advanced athletes to move faster by having them train only with maximum loads, according to our available data, this probably isn’t the best way to structure training.
Conversely, this does not suggest that maximum velocity training cannot improve maximum strength either. As we’ve seen in the data cited in previous sections, people can still improve their 1RM by prioritizing fast movement velocities during training. Improving one’s rate of force development through high-velocity training may also improve 1RMs as well. Again, though, this probably isn’t the best way to train if one wanted to improve an athlete’s maximum strength.
With this in mind, I will modify the first sentence of this section by claiming that advanced trainees may stand to benefit from primarily prioritizing training at faster movement velocities with maximum intent. The distribution of “how much” time to prioritize maximum velocity vs maximum loads to elicit specific adaptations is another discussion all on its own. It is dependent on factors such as the total experience of the trainee, the amount of time they have to train, the length of their training season, etc. We’ll possibly highlight this in more detail in a future article, but I’d love to know what you have found in your practice and to hear your arguments for or against my interpretations of the literature as well!
Note: I derived much of this post from my Master’s thesis, "Instrument, Analysis, and Coaching Considerations with Velocity-Based Training," located on the T-Space thesis repository or ResearchGate.
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