We aimed to investigate joint coordination of lower limbs in dancers during tiptoe standing and the relationship between joint coordination and muscle coactivation. Seven female ballet dancers performed tiptoe standing with six leg positions (fi e classical dance positions and one modern dance position) for 10 s. The kinematic data of the metatarsophalangeal (MP), ankle, knee, and hip joints was collected, and surface electromyography (EMG) of over 13 lower limb muscles was conducted. Principal component analysis was performed to determine joint coordination. MP–ankle and ankle–knee had in-phase coordination, whereas knee–hip showed anti-phase coordination in the sagittal plane. In addition, most EMG–EMG coherence around the MP and ankle joints was significant up to 50 Hz when these two joints swayed with in-phase. This suggests that different joint coordination patterns are associated with neural processing related to different muscle coactivation patterns. In conclusion, ballet dancers showed in-phase coordination from the MP to knee joints, which was associated with muscle coactivation to a higher frequency domain (up to 50 Hz) in comparison with anti-phase coordination.
Hiroko Tanabe, Keisuke Fujii and Motoki Kouzaki
Kohei Watanabe, Motoki Kouzaki and Toshio Moritani
In some muscles, nonuniform surface electromyography (EMG) responses have been demonstrated within a muscle, meaning that the electrode location could be critical in the results of surface EMG. The current study investigated possible region-specific EMG responses within the human biceps femoris (BF) muscle. Surface EMG was recorded from various regions along the longitudinal axis of the BF muscle with 20 electrodes. Ten healthy men performed maximal isometric contractions of hip extension and knee flexion, which involve the BF muscle. The ratio of the EMG amplitude between hip extension and knee flexion tasks (HE/KF) was calculated and compared among the regions. There were no significant differences in HE/KF among the regions along the BF muscle (P > .05). This suggests that the entire superficial region of the BF muscle is equally regulated in the 2 different tasks. We suggest that the electrode location is not critical in estimating the activation properties and/or functional role of the superficial region, which corresponds with approximately 50% of the muscle length of the BF muscle, using surface EMG during maximal contraction.