Leg stiffness and potential energy in the countermovement phase and the CMJ jump height

Study aim: The elastic potential energy accumulated in the musculotendinous units during the countermovement phase of a jump adds up to the energy supplied by the contracting muscles used in the take-off phase. Consequently, the total mechanical energy used during the jump may reach higher values. Stiffness represents a quantitative measure of a body’s elastic properties. Therefore, the aim of this study was to establish the relationship between leg stiffness and the countermovement jump height.

Material and methods: 24 basketball players from the II Division participated in the study. The measurements employed a Kistler force plate and a BTS SMART system for the motion analysis. Each study participant performed three countermovement jumps with arm swings. Leg stiffness in the countermovement phase was determined from the slope of the ground reaction forces curve, with respect to the coexisting height of the greater trochanter of the femur. The decline in the gravitational potential energy of the centre of mass during the countermovement phase is partially accumulated in the form of potential elastic energy through the stretched musculotendinous units, and consequently contributes to the jump height.

Results: We found a statistically significant relationship between leg stiffness and a decline in the potential energy during the countermovement phase. The relationship between leg stiffness and the jump height was not statistically significant.

Conclusions: The distribution of measurements may suggest the presence of local maximums, with their locations representing a value of leg stiffness that allows for high values of changes in the potential energy and the jump height to be obtained. Therefore, the presence of a specific value for leg stiffness that would be the most favourable for the accumulation of potential elastic energy is likely. However, this study cannot unequivocally confirm this fact, and the confirmation of the above statement will require further experimentation.