By Chris Beardsley
Chris Beardsley graduated from Durham University with a Masters Degree in 2001. He since contributed to the fields of sports science and sports medicine by working alongside researchers from Team GB boxing, the School of Sport and Recreation at Auckland University of Technology, the Faculty of Sport at the University of Ljubljana, the Department of Sport at Staffordshire University, and the College of Health Solutions at Arizona State University. He is also a Director at Strength and Conditioning Research Limited
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For any athlete, we can establish a force-velocity (FV) profile in the vertical jump. This FV profile can be found by measuring mean force exerted into the ground and the mean velocity of the center of mass in jump squats with a range of loads.
Plotting all of these values on a graph provides a line. The gradient of this line is the FV profile.
Since strength is velocity-specific, not everyone automatically has an optimal FV profile for producing peak power output in a vertical jump. The difference between the optimal and the actual FV profile can be expressed by the FV imbalance.
Having a FV imbalance means either that high-velocity strength is small compared with low-velocity strength, or that low-velocity strength is small compared with high-velocity strength. This is important, because having a FV imbalance means that the athlete is more likely to perform poorly at the vertical jump.
Since strength is velocity-specific, training with a light load and a faster bar speed leads to preferentially greater gains in high-velocity strength. In contrast, training with a heavy load and a slower bar speed leads to preferentially greater gains in low-velocity strength.
This suggests that training to reduce a FV imbalance could be a very effective way of improving vertical jump performance in athletes.
Indeed, this very recent long-term study showed that training specifically using either high-velocity (ballistic) exercises or low-velocity (strength) exercises according to the individual FV needs was superior to a general training program.
Interestingly, the data reported in these studies showed that athletes from different sports tended to center around different FV profiles for the vertical jump.
Soccer players seem to have a force-deficit, sprinters seem to have a fairly optimum profile, and rugby players seem to have a velocity-deficit. It would be interesting to see a large cross-sectional study performed in this area, as it would reinforce the need for strength training for high-level soccer athletes, and power training for high-level rugby players.
Even so, it is important to bear in mind that the FV profiling relates to the vertical jump, and not to sprinting or change of direction, which may be quite different.