Measurement bias in estimates of system power during a vertical jump

This study sought to determine the level of measurement agreement in measures of force, velocity and power during a CMJ between three separate assessment techniques.

At a glance:

• Alternative measurement and computation techniques will alter force, velocity and power values captured between jump conditions.
• If using a single linear optical encoder, confine the bar to vertical axis, jump with relative heavy barbell loads, or avoid barbell estimated of system power.
• Practitioners should be mindful of the level of measurement variability associated with force plate estimates of power and velocity.

Full reference and abstract:

Williams, K. J., Chapman, D. W., Phillips, E. J. & Ball, N. (2019). Measurement bias in estimates of system power during a vertical jump. Sports Biomechanics. Epub ahead of print.

This investigation sought to quantify the level of measurement agreement in system force, velocity and power values derived across three commonly applied assessment techniques during a countermovement jump (CMJ).

Twenty-five male national representative athletes completed three CMJs under unloaded (0%1RM) and loaded (40%1RM) jump conditions. Associated values of force, velocity and power were captured simultaneously from either a linear optical encoder (LOE) or force plate (FP) and then compared to the gold-standard reference values derived from a combined force plate and three-dimensional motion capture system (FPMC).

The LOE significantly (p < 0.001) overestimated and failed to meet the minimum level of relatedness (<0.80) for measures of peak velocity, peak force, peak power and mean power across both conditions compared to the FPMC reference values. A reduction in measurement dispersion and bias was, however, evident during the loaded condition. The FP significantly (p < 0.05) underestimated mean and peak power across both conditions, yet measurement bias and dispersion remained consistent.

These findings highlight a disparity in measurement agreement in force, velocity and power values across alternative assessment techniques and loads. Such variance in measurement agreement will uniquely alter derived force-velocity profiles, and thus the prescription of training loads to maximise system power during unrestricted CMJs.