| Keywords |
Stretch-shortening cycle exercise ; EMG ; Muscle stiffness |
| Abstract |
The purpose of this study was to investigate the behavior of gastrocnemius muscle-achilles tendon complex (MTC) and lower limb joint work during rebound drop jumps on slanted contact surfaces. Nine male subjects executed a rebound drop jump from heights of 30 cm (RDJ30) and 50 cm (RDJ50) on three surface gradient conditions. Surfaces were 8 degree uphill gradient, 8 degree downhill gradient and level type. Force plate data, limb position and EMG of the medial head of m. gastrocnemius and m. tibialis anterior data were recorded simultaneously during all jumps. The length change of MTC during eccentric phase were calculated according to the model of Grieve et al. (1978). The main results were as follows; In RDJ30 on slanted contact surface conditions, Integrated EMG (IEMG) of m. gastrocnemius (IEMGGAS) during eccentric phase were lower, and IEMG of m. tibialis anterior (IEMGTA) were higher than those on level conditions. In RDJ50, there was no clear difference between slanted contact surface conditions and level conditions in IEMGGAS and IEMGTA. However, there was a tendency of a higher in IEMGGAS during eccentric phase as the landing direction changed from downhill type conditions to uphill type conditions. Stretch velocity of MTC in RDJ30 and RDJ50 on slanted contact surface conditions were lower than those on level conditions. Achilles tendon force at midpoint (ATFMID) in RDJ30 and RDJ50 on slanted contact surface conditions were the same or lower than those under level conditions. Joint work around the hip and knee joint during eccentric phase in RDJ30 and RDJ50 on downhill type conditions were higher, and joint work around the ankle joint was lower than those on level and uphill type conditions. From these results, RDJ on slanted contact surface conditions compared to level conditions causes a reduction of muscle stiffness and elastic energy utilization in order to protect the tendomuscular system and to maintain jumping balance. |