Our aim was to clarify the relationship between power output and the different mechanical
parameters influencing it during squat jumps, and to further use this relationship
in a new computation method to evaluate power output in field conditions. Based on
fundamental laws of mechanics, computations were developed to express force, velocity
and power generated during one squat jump. This computation method was validated on
eleven physically active men performing two maximal squat jumps. During each trial,
mean force, velocity and power were calculated during push-off from both force plate
measurements and the proposed computations. Differences between the two methods were
not significant and lower than 3% for force, velocity and power. The validity of the
computation method was also highlighted by Bland and Altman analyses and linear regressions
close to the identity line (P<0.001). The low coefficients of variation between two
trials demonstrated the acceptable reliability of the proposed method. The proposed
computations confirmed, from a biomechanical analysis, the positive relationship between
power output, body mass and jump height, hitherto only shown by means of regression-based
equations. Further, these computations pointed out that power also depends on push-off
vertical distance. The accuracy and reliability of the proposed theoretical computations
were in line with those observed when using laboratory ergometers such as force plates.
Consequently, the proposed method, solely based on three simple parameters (body mass,
jump height and push-off distance), allows to accurately evaluate force, velocity
and power developed by lower limbs extensor muscles during squat jumps in field conditions.