Response-Methodological issues associated with the use of force plates when assessing push-ups power.

We read with interest the article by Wang et al. (5). The authors calculated the peak power and mean power of ballistic push-ups as the highest and average power output using similar methods as for lower-body jump squats assessment (i.e., force-plate technique). We believe that the evaluation of power in Wang et al.'s (5) study is based on a misinterpretation of the articles cited in their study. Specifically, Hogarth et al.'s (4) study performed measures which indicate the performance of the exercises but did not actually evaluate power. However, Cormie et al.'s (1) study compared different methods of estimating peak power output. There are sufficient and necessary conditions that have to be respected in order to be able to correctly estimate the power on lower-limb dynamic exercises. We believe that Wang et al. (5) have in appropriately applied this method to the upper-limbs, for the following reasons: Cormie et al. (1) demonstrated that the force-plate technique underestimates the velocity and power output. In addition, this approach assumes linear kinetics, whereas the push-up movement involves rotation of the body about the toes. Moreover, in the push-ups, contrary to the vertical jump where the hands are “free,” both the hands and feet are in contact with the ground so all ground reaction forces should be measured. Nevertheless, only one part of the external forces were measured (hand-related forces) in the experimental protocol in the study of Wang et al. (5). The power provided in lower-limb vertical jump articles (1,3) is linear as the body moves upward in a linear motion. However, the trajectory of the center of mass of the body in the longitudinal plane when performing jump/ballistic push-ups is a circular arc around the toes (fixed point). A kinematic analysis is therefore needed to verify the path of the push-up and quantify the errors in power estimated when it is assumed that the push-up jump movement is perfectly vertical. We believe that this “transposed” technique used with the lower-limb to the upper-limbs is inappropriate. This takes on assumptions and can cause large measurement errors. We therefore suggest either (a) using some indices that are related to components of power without actual measurement of power (2), such as rate of force development, impulse, and flight-time, or (b) using 2 synchronized force-plates, which allow supporting the whole body in push-up position. We hope our concern be taken as constructive.