Muscle mass and maximal isometric force in elite volleyball players

Abstract

The influence of knee angle on the maximal isometric strength (MIS) during a squat exercise at 90°, 12° y 140° knee angle was assessed in elite volleyball players (21 males and 9 females) and Physical Education Students (12 males and 11 females). Force measurements were obtained using a force plate. Simultaneously, the superficial electromyographic activity (EMG) of the vastus lateralis was recorded while and the muscle mass of the legs determined by dual-energy X-ray absorptiometry (DXA). Male volleyball players had a greater MIS tha the Physical Education students, while similar values of MIS were observed in the females regardless of volleyball participation. After accounting for the effect of leg muscle mass, however, MIS was similar in all subjects. The time needed to reach the maximal force was also similar without any significant effect of sex and volleyball participation. The MIS was, on the other hand, attained 1-1.7 s faster at 90° knee angle than at 120° or 140° (p<0.05). No significant differences were observed in the integrated EMG (iEMG) between volleyball players and Physical Education students. A greater iEMG activity was, however, recorded at 90° knee angle than at 120° or 140° (p < 0.05). In addition, the iEMG peak preceded by 0.8 s the force peak. In summary, maximal isometric during a squat extension exercise is similar in volleyball players and Physical Education students, when the values are adjusted depending on the leg muscle mass. The knee angle at which force measurements are performed has a marked influence on the values of force and iEMG.