The Effects of Muscle Strengthening on Neuro-Musculo-Skeletal Dynamics in A Squat Jump: A Simulation Study

Abstract

Purpose. The aim of this study was to quantitatively investigate the effects of muscle strengthening in a vertical squat jump based on a neuro-musculo-skeletal model and a forward dynamics simulation. Methods. During simulation trials, 16 major muscle groups of the lower extremities were gradually strengthened up to 20%. Results. Complex yet systematic deviations in body kinematics, kinetics and the neural control pattern were observed as a result of gradual muscle strengthening. Conclusions. based on the generated results it was concluded that: (i) the pattern of kinematical changes depends on which muscles are strengthened, while the magnitude of the changes depends on how much the muscles are strengthened. (ii) Adjustment of muscle coordination, in some cases, can be performed without adjustment of neural control. (iii) The adjustment of neural control is done in an adaptive manner. (iv) Inter-segmental coordination is further altered if a smaller number of muscles are strengthened. (v) The main effect of equally strengthening all the muscles is an increase in joint torque, which is proportional to the increase in muscle strength.

Effects of Repeated Jump Testing and Diurnal Changes on Subsequent Countermovement Jump and Squat Jump Output and Force-Time Characteristics

“…Repeated jump testing involving 5 assessments occurred before an additional rested baseline test in the afternoon was completed and following a 3-6 days of recovery period. As such, learning effects and possibly diminished fatigue induced by repeated jump testing may have positively influenced mechanisms associated with a heightened SJ performance (i.e., timing of muscle activation (1,3,4,26)) during the subsequent afternoon test. Data indicate that proficiency in technically demanding tasks (i.e., SJ test ( 29)) may remove its potential masking effect on diurnal changes in performance (28).…”

“…The period of inactivity separating the repeated jump testing protocol and completion of the afternoon test may also have positively influenced intermuscular coordination and thus SJ performance (26), possibly because of diminished fatigue (2). Findings from previous research have indicated that residual fatigue after repeated jump testing separated by limited recovery periods may obscure possible diurnal variation (28).…”

“…Findings from previous research have indicated that residual fatigue after repeated jump testing separated by limited recovery periods may obscure possible diurnal variation (28). Therefore, although cumulative fatigue likely did not alter diurnal patterns of performance rhythms (28), the rest period separating the baseline tests may have enabled improvements in SJ performance (2,26). These observations suggest that although SJ metrics may have demonstrated small increases between morning and afternoon baseline values, considerations other than diurnal effects influenced the results.…”