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

Abstract

SummaryStudy 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.

Application of Leg, Vertical, and Joint Stiffness in Running Performance: A Literature Overview

“…The speculations concerning a desirable value “leg-spring” stiffness that is the most advantageous for the accumulation of potential elastic energy and most favours reaching maximal sport performance have already been addressed in many previous studies [ 1 , 3 , 22 , 24 – 28 , 31 – 35 ]. However, no studies have provided unequivocal evidence for the presence of a desired “leg-spring” stiffness value.…”

“…The reason for this may be the lack of longitudinal studies that have investigated the effects of strength or power training on mechanical stiffness and consequently the relative lack of concrete recommendations that would allow to improve the speed-strength abilities of an athlete and their competitive sport results. The speculations concerning a desirable value of “leg-spring” stiffness that is the most advantageous for the accumulation of potential elastic energy and most favours reaching maximal sport performance have been partially examined [ 1 , 3 , 22 , 24 – 28 , 31 – 35 ]. However, no studies have provided unequivocal evidence for the presence of a desired value of “leg-spring” stiffness.…”

Assessment of Countermovement Jump: What Should We Report?

“…The acceptable reliability of the RSI modified is in line with the findings of previous studies [ 18 , 20 , 33 ] (CV ≤ 10%). The only performance variable that presented a questionable reliability was the leg stiffness (CV = 11%), a variable that is considered as a quantitative measure of the elastic properties of lower body muscles [ 9 ]. Although several studies reported similar findings [ 17 , 19 , 34 ], Heishman et al [ 21 ] argued that leg stiffness cannot be considered a reliable CMJ-derived variable because they obtained CV values that exceeded 20%.…”

“…One variable that stands out from all performance metrics is jump height, due to its direct association with the performance on a variety of sport-specific tasks and physical preparedness of the athletes [ 3 , 8 ]. Moreover, some complex metrics, such as leg stiffness (i.e., ratio of vertical ground reaction force to minimal centre of mass displacement) and modified reactive strength index (RSI modified; i.e., quotient of jump height and push-off duration), are gaining massive popularity in terms of being considered as indirect measures of elastic/reactive properties of lower body muscles [ 9 , 10 , 11 ]. Kinetic variables (e.g., mean force, peak force, impulse) have been frequently computed by sports scientists and practitioners due to their ability to provide in-depth insight into the mechanics of the CMJ execution [ 12 ].…”

The Physical Fitness Effects of a Week-Long Specialist Tactical Police Selection Course

“…There were decreases in both power output and jump velocity after the completion of the selection course, these were not deemed to be significant. Interestingly and unexpectedly, vertical jump increased by 23.1% over the selection course, potentially due to an increase in passive stiffness, and decrease in active stiffness in the lower limb and consequent increased ability to store elastic potential energy [ 23 ]. Evidence of this ability to redirect energy through the hysteresis loop may be highlighted by the increases in joint stiffness as measured by the sit-and-reach assessment.…”