Activity modulations of trunk and lower limb muscles during impact-absorbing landing.

This study aimed to investigate the activity patterns of trunk and lower limb muscles during impact-absorbing landing. Electromyogram activities of the trunk and lower limb muscles along with kinematic and ground reaction forces were measured while subjects (n=17) performed 10 landings from a height of 35 cm. Landing motions were divided into three phases: 100 ms preceding ground contact (GC) (PRE phase), from GC through 100 ms (ABSORPTION phase), and from the end of the ABSORPTION phase until the vertical position of the center of mass was minimized (BRAKING phase). During the PRE phase, the rectus abdominis, external oblique, and medial gastrocnemius were highly activated. Upon GC, the hip and knee joints were in a flexed position; the ankle joints, in a plantarflexed position. After GC, peak timings of muscle activities and lower limb joint rotations were characterized by distal-to-proximal sequential patterns. The peak vertical ground reaction force in the ABSORPTION phase relative to body weight positively correlated with the activity levels of the vastus lateralis and gluteus maximus in the PRE phase and that of rectus abdominis in the ABSORPTION phase. These findings indicate that the intensities and peak timings of muscle activities in the trunk and lower limb are coordinated to absorb landing impact.