Effect of hiking training at high-altitude on V'O2 and Q' kinetics in healthy sedentary women

Aim: Previous studies have shown faster pulmonary oxygen uptake (V’O2) kinetics in men after moderate intensity exercise performed either in normoxia [2] or in hypobaric hypoxia [1]. We tested the hypothesis that 2 weeks of trekking performed at sea level and at high-altitude can induce a significant acceleration of the V'O2 and cardiac output (Q’) kinetics in adult women as compared to a similar training performed at the sea level (normoxia). Methods: 7 moderately active women (25±7 yy; 68±11 kg, 165±8 cm) were recruited by the Department of Basic and Applied Medical Sciences of the University ‘G.d’Annunzio’-Chieti-Pescara. A sea level (SL) the training program consisted in trekking on irregular and undulating terrain for 2weeks (3 to 6h every day) with absolute altitudes ranging from 160m to 800 asl (SL). The same training program was repeated after 5 months at high altitude (HA) (>5000m) (Ama Dablam, Nepal) with the same absolute variations of altitude. Before and immediately after trekking, breath-by-breath V’O2 and beat-by-beat Q’ were measured. These were evaluated during: i) an incremental ramp cycling test up to exhaustion, to calculate V’O2max, and; ii) three consecutive square wave tests (separated by 6 min of recovery) performed at approximately 50 % of V’O2max. V’O2 and Q’ values of each test were 1-s normalized, aligned and ensemble-averaged. Then, a bi-exponential models was iteratively fitted to the data in order to describe V’O2 and Q’ kinetics during square-wav exercise transitions. Friedman’s test was applied to evaluate the differences of the selected parameter in the various conditions. Results: Absolute and relative V’O2max (PRE-SL 32,90±6,27ml/kg/min; POST-SL 33,45±4,64ml/kg/min; PRE-HA 33,43±4,10ml/kg/min; POST-HA 35,26±4,53ml/kg/min) and Q’max (PRE-SL 13,1±2,2l; POST-SL 13,3±1,9l; PRE-HA 12,8±1,5l; POST-HA 13,3±1,8) values did not increase as a result of training at SL and HA. τ2of V’O2 kinetics (PRE-SL 25,43±5,29s; POST-SL 17,76±4,58s; PRE-HA 17,78±3,60s; POST-HA 13,84±4,70s) were significantly smaller after each training (P < 0.05). τ2 of Q’ kinetics (PRE-SL 23,97±6,47s; POST-SL 18,99±3,66s; PRE-HA 22,97±12,74s; POST-HA 18,82±7,67s) were unaffected by training. Conclusion: 2 weeks of trekking, at SL and at HA do not modify V’O2max and Q’max, confirming that this sort of moderate intensity exercise, either in normoxia or hypobaric hypoxia, does not affect the responses to maximal exercise [2]. At the contrary [3], this kind of training is able to elicit a substantial acceleration of V’O2 kinetics