Author(s): ITO, R., YAMASHITA, N., OSAKABE, J., YAMAMOTO, M., TAKAHASHI, K., Institution: DAIDO UNIVERSITY, Country: JAPAN, Abstract-ID: 1215

INTRODUCTION:
Moderate hypoxia and local muscle cooling are environmental stressors that influence oxygen delivery, muscle metabolism, and neuromuscular activation during exercise. Moderate hypoxia reduces arterial oxygen availability and may increase reliance on anaerobic metabolism even during submaximal exercise. Local muscle cooling alters muscle temperature and contractile function, potentially modifying motor-unit recruitment and metabolic demand. Although both factors independently affect physiological responses to exercise, their combined influence during low-intensity exercise remains unclear. Therefore, this study investigated the interaction of moderate hypoxia and local thigh cooling on metabolic, neuromuscular, and cardiovascular responses during prolonged cycling.
METHODS:
Twelve healthy young men (20.4 ± 2.3 years) performed 30 min of cycling at 40% VO₂max under four randomized conditions: normoxia without cooling (CON), normoxia with cooling (ICE), hypoxia (FiO₂ ≈ 15.5%) without cooling (HYPO), and hypoxia with cooling (ICEHYPO). For cooling conditions, phase-change material sleeves (≈5–8 °C) were applied to both thighs for 30 min prior to exercise and removed immediately before cycling. Heart rate, arterial oxygen saturation (SpO₂), rectal and skin temperature, oxygen uptake (VO₂), respiratory exchange ratio (RER), blood lactate concentration, electromyographic activity (%RMS), rating of perceived exertion, and thermal sensation were measured throughout exercise.
RESULTS:
Blood lactate concentration during exercise (10–30 min) was significantly higher in ICEHYPO than in CON, ICE, and HYPO (p < 0.05). Neuromuscular activation (%RMS) was greater in ICEHYPO than in CON and HYPO (p < 0.05). Heart rate was significantly lower in ICEHYPO than in HYPO (p < 0.05). No significant differences were observed in VO₂ or RER among conditions.
CONCLUSION:
These findings indicate that combining moderate hypoxia with local muscle cooling increases lactate accumulation and neuromuscular activation even during low-intensity cycling while reducing heart rate compared with hypoxia alone. Simultaneous oxygen and thermal stress may induce distinct metabolic and cardiovascular adjustments during submaximal exercise.