| Keywords |
Lactate ; Anaerobic metabolism ; Ventilatory response ; Heart rate ; HDT |
| Abstract |
This studies examined the combined effects of normobaric hypoxic breathing and heat exposure during leg cycling at 6o Head Down Tilt (HDT) on thermoregulatory, body fluid, and metabolic responses. Ten healthy men (23 ±2 yrs, 69±6 kg, 174±5 cm) participated in three experimental sessions; 1) breathing normal air in ambient temperature (23.7±0.5oC) (N21), 2) breathing normal air in heat (38.8±0.5oC) (H21), and 3) breathing 13% oxygen in heat (H13). In each session, subjects rested for 30 min followed by leg cycling at 50~60% of VO2max for 30 min, then recovered 30 min while maintaining HDT throughout. Blood oxygen saturation was lower in H13 (77%) than N21 (98%) and H21 (97%). Subjects lost 0.1±0.2, 0.8±0.3, and 0.6±0.2 kg in N21, H21, and H13, respectively (P<0.05). During exercise in all sessions, blood pressure was elevated for about 10 mmHg than resting state, but not statistically significant. Minute ventilation was not changed within trials and between conditions (P>0.05). During H21 and H13, rectal, skin, and body temperature as well as heart rate were significantly higher than N21 (P<0.05). No differences were found between conditions in hemoglobin, plasma protein, plasma osmolality, and aldosterone, and blood electrolytes including, sodium, potassium, and chloride. However, blood lactate was significantly higher at 30 min of exercise in H13 than other two conditions (P<0.05) while no other marginal differences were noticed in metabolic parameters such as glucose, creatine phosphokinase and lactate dehydrogenase. Based on the results, heat exposure resulted in marginal body temperature changes and body fluid loss, while did not induce any changes of metabolic responses. Hypoxic effect was evidence in H13 conditions showing anaerobic metabolism during exercise in heat while maintaining HDT. |