The Relationship Between Dolphin Kick Movement And Underwater EMG Of Lower Leg Muscles In Competitive Swimmers

Abstract

Improvement in swimming performance is not only associated with stroke technique but also with the gliding movement during the start and turn phases. The underwater dolphin kick movement during the start and turn phases is important for improving total race time in modern swimming. PURPOSE: The study was designed to analyze the findings of underwater electromyography of lower limb muscles during the underwater dolphin kick movement in competitive collegiate swimmers. METHODS: Six healthy male collegiate swimmers volunteered to participate in this study. The subjects performed underwater gliding movement at maximum speed after pushing off from the start wall. In addition, three types of underwater dolphin kick movement [Control (C): maximum effort kick; Build-up (BU): small-to-large kick; and Dynamic (D): large kick) were performed with maximum effort. The subjects were monitored through an underwater video camera with a sampling frequency of 60 Hz in the sagittal plane to measure the angular displacement of their different joints. A wireless electromyography system (Biolog DL-5000, S&ME, Japan) was used to collect the muscle activities from the vastus lateralis, hamstrings, tibialis anterior, and gastrocnemius. Speed Meter (Vine Co., Japan) was used to measure swimming speed, and a motion analysis system (Frame-DIAS4; DKH, Japan) was used to digitize body landmarks. RESULTS: Among the underwater dolphin kick movement types, the BU kick was the fastest (BU: 1.67 m/s; C: 1.65 m/s; and D: 1.65 m/s). The rectified EMG findings showed that gastrocnemius and hamstrings muscle activities of elite swimmers were higher than non-elite swimmers during these movements. However, elite swimmers had no muscle activity in the tibialis anterior. CONCLUSIONS: The present study results suggested that the angular displacement of the knee joints gradually increases during underwater dolphin kick movement. In addition, the muscle activity of the hamstrings and gastrocnemius increase during underwater dolphin kick movement. However, the muscle activity of tibialis anterior was inhibited during these movements. Our results also suggested that swimmers experienced a large propulsion force and a small resistance force with the help of these movements.