Muscle Oxygenation after Downhill Walking- Induced Muscle Soreness

Abstract

Prolonged downhill walking exercise may result in delayed onset muscle soreness (DOMS) and/or muscle damage. PURPOSE: This study investigated the hypothesis that evoking DOMS via downhill walking might impair muscle oxygenation and muscle blood flow in healthy adults. METHODS: The study employed a 5-day prospective time-series design. Nine healthy males performed 40-min walking on a motorised treadmill at a gradient of-25%, and an average speed of 6.4km·h-1, whilst carrying an additional load equivalent to 5% of their body mass. Before exercise on day 1, and over the next four days, maximum voluntary contraction (MVC), plasma creatine kinase and myoglobin concentrations, subjects' perception of muscle soreness, resting muscle oxygenation and on-transient exercise kinetics (using near infrared spectroscopy; NIRS) within vastus lateralis of both legs were assessed. RESULTS: Repeated-measures ANOVA revealed that MVC had decreased (by 26% on day 1 post exercise, and by 18% on days 2 and 3), while muscle soreness and myoglobin were significantly increased (p<0.05) until day 4, consistent with downhill walking's effectiveness to evoke DOMS. Resting muscle oxygen saturation, total haemoglobin and oxyhaemoglobin were significantly decreased. Muscle blood flow at rest averaged 37% higher (p<0.05) on day 2 compared to pre-downhill walking on day 1, and then gradually returned towards original values. During isometric knee extension at 30%, 50% and 80% of MVC, significant increases were observed in oxygen desaturation and re-saturation kinetics (p<0.05). These changes in NIRS-related measures of muscle oxygenation and kinetics were persistent for up to 4 days after exercise. CONCLUSION: This study was the first to demonstrate alterations in muscle oxygenation at rest and oxygenation kinetics during exercise in humans following a prolonged session of downhill walking. Further investigation is warranted to identify the underlying mechanisms supporting changes in muscle oxygenation kinetics after DOMS, and to elucidate whether these are affected by or affecting DOMS.