Strength as a Velocity-Dependent Concept

The following is an exclusive excerpt from the book NSCA’s Essentials of Sport Science, published by Human Kinetics. All text and images provided by Human Kinetics.

Beyond the task or muscle groups involved in testing, what does it mean to be a “strong athlete”? First and foremost, a central pillar of exercise physiology dictates that muscle force output depends on the movement velocity. In sprint cycling, for example, “being strong” while producing high levels of force when pushing on a pedal during the very first down-stroke is not the same as “being strong” a few seconds later, when the highest possible levels of force onto the pedal are still needed, this time at a pedaling rate above 200 rotations per minute. However, in order to perform successfully, the objective of the cyclist should be to apply the highest amount of force in all possible velocity conditions throughout the sprint. The same line of thinking may be applied to many other sports or movements, like pushing a 200-kg bench press bar (very high force output, likely low velocity) versus a shot-put action (relatively lower force output, very high velocity output). Therefore, although strength is associated in the collective thinking with the maximal level of force output an athlete can produce (against very high resistance and in a very low-velocity context), it is critical to understand that maximal force, and therefore the strength capability, depends on the movement velocity. This pillar of human skeletal muscle physiology has been verified at the isolated muscle fiber level (15), during single-joint movements (3), and during multi-joint sporting movements like vertical jumps and bench press, as well as cycling and running sprints (17). In complex tasks such as vertical jumping or sprinting, there is a linear decrease in the force output capability with increasing movement velocity (29).

The force–velocity capabilities of several hundred male and female athletes (from leisure to elite level) have been compared in 14 sports, and it was clearly shown that the maximal force capability at low velocities was, overall and within each sport, poorly correlated to the maximal force capability at high velocities (here termed velocity capability), especially in highly trained athletes (21). An illustration of this experimental result is shown in figure 13.1. Although exceptional athletes display very high levels of both force and velocity, the two ends of the force–velocity spectrum are not highly and systematically correlated, and being strong in a low-velocity context does not necessarily mean being strong in an intermediate- or high-velocity context. In addition, the higher the training and practice level, the lower the overall correlation between maximal force and velocity outputs, in both vertical jumping and sprinting modalities (21). For example, the authors of this chapter directly studied sub-10-second elite sprinters who were not able to produce a high level of force when performing a half squat (1RM below 120 kg), but could apply more force onto the ground than their peers when running faster than 10 m/s. They were definitely strong, but at the very high-velocity end of the force–velocity spectrum (maximal velocity phase of sprinting), not at the low-velocity end of the spectrum (i.e., half-squat 1RM test).

Consequently, coaches should avoid the unsubstantiated belief that a strong athlete (as quantified in classical maximal strength tests) will be de facto strong, that is, able to produce high amounts of force throughout the force–velocity spectrum. Instead, coaches should seek to assess and monitor the entire force–velocity spectrum of the athlete in order to get the big picture of the athlete’s strength within all the possible velocity conditions. In turn, since physical performance in specific tasks (e.g., sprint acceleration, upper-body push, vertical jumps) generally occurs within quantifiable velocity bandwidths, training could be based on the individual comparison between the sport task demands (in terms of velocity) and the athlete’s force production capability (both outside and within this specific velocity zone).

Modern training, based on the physiological, neuromuscular, and biomechanical principles of force and velocity production, should include the assessment, analysis, and long-term monitoring of the force–velocity spectrum on an individual basis. Indeed, another clear research finding is that large interindividual differences in the force–velocity profile or spectrum orientation can be observed within heterogeneous groups of athletes from different sports, position, and level of practice (14, 21). This can help improve training practice, but also the prevention and rehabilitation process and the long-term physical development of young athletes. Finally, how this force–velocity profile changes in fatigue conditions (sport-specific or not) is key additional information for a more comprehensive description of the athlete’s strength capabilities.

NSCA’s Essentials of Sport Science provides the most contemporary and comprehensive overview of the field of sport science and the role of the sport scientist. It is a primary preparation resource for the Certified Performance and Sport Scientist^™ (CPSS^™) certification exam. The book is available in bookstores everywhere, as well as online at the NSCA Store.