Reduced Leg Muscle Oxygenation During Underwater Treadmill Walking

Abstract

Central circulation and whole body metabolism adjustments, in particular, have been investigated using respiratory gas analysis and heart rate (HR) measurement. However, local muscle circulation and oxidative metabolism have never been investigated during underwater walking. PURPOSE: The purpose of this study was to determine muscle oxygenation in the lower extremities during underwater walking on a treadmill. METHODS: Eight healthy men (age 25 ± 3 y.r., height 175 ± 4 cm, weight 69.6 ± 5.7 kg, BMI 23 ± 2, VO2max 56.7 ± 5.9 ml/kg/min) performed a treadmill walking test twice, once in water and once on land. Each subject began underwater treadmill walking at 1.0 km/h in 0.5 km/h increments at intervals on 2 minutes until 3.5 km/h. Each subject also began land-treadmill walking at 2.0 km/h in 1.0 km/h increments at intervals of 2 minutes until 7.0 km/h. The HR was continuously monitored by a telemeter. Muscle electromyographic (EMG) activity was monitored in the vastus lateralis (VL) and the medial head of the gastrocnemius (MG). The muscle oxygenation level was continuously monitored in the VL and the MG using near-infrared spectroscopy (NIRS). RESULTS: Muscle oxygenation decreased greater during underwater walking than during land walking both in the VL and in the MG. There is no significant difference in the EMG activity between the two conditions in both muscles. The combination of EMG and NIRS results indicate that the greater decrease in the muscle oxygenation is due to reduced muscle perfusion resulting from the facilitated venous return to central circulation during underwater walking. CONCLUSIONS: The results of this study indicate that the greater decrease in the muscle oxygenation is due to reduced muscle perfusion resulting from facilitated venous return to central circulation during underwater walking. Supported by the Mizuno Sports Foundations (2006) and by the twenty-first century COE program, Ministry of Education, Culture, Sports, Science and Technology (2002-2006 Nishihira Project), Japan.