SPEEDING OF V’O2 KINETICS IN RESPONSE TO HIGH-INTENSITY-INTERVAL TRAINING IN OLDER, HEALTHY MEN

Introduction Experimental evidence suggests that High Intensity Interval Training (HIT, high intensity - low volume exercise) may be effective in accelerating the dynamic response pulmonary O2 uptake (V’O2) in older subjects through an improvement of the matching between local O2 delivery and uptake (Williams et al., 2013). This study explores the effect of HIT on V’O2 kinetics and muscle deoxygenating during step transitions of moderate intensity, cycling exercise in older, healthy men. Methods 12 moderately active older adults (68-yy ± 4) were exposed to 8 weeks of HIT training with 7 two-minute repetitions at 40 and 90% of V ̇O2max, 3 times a week. Before and after training we measured: i) V’O2 peak (V’O2p), gas exchange threshold (GET) and respiratory compensation point (RCP) during an incremental test up to exhaustion; ii) breath-by-breath V’O2 and change of fractional muscle O2 extraction (ΔHHb) of vastus lateralis by quantitative NIRS during three step-exercise transitions performed at a workload corresponding to 90% of GET. V’O2 kinetics was modeled, after synchronization and overlapping of the three series, by means of a double - exponential function so that we estimated the time constant (Tau) of the primary component of VO2 kinetics. Finally, the normalized ΔHHb to ΔV’O2 ratio was obtained as index of the matching between muscular O2 delivery and uptake (De Roia et al., 2012; Murias et al., 2011). Results V’O2max increased by 9% (29.9 mL min-1 kg-1 ±4.3 - 32.6 mL min-1 kg-1± 6.0, p<0.01, ES 0.51) after 8 weeks of HIT. RCP (respiratory compensation point, per cent of V’O2max) significantly improved by 10% (76.4 % ± 8.3 - 82.9 % ± 4.9, p<0.05, ES 0.97); Tau decreased by about 26% (26.97 s ± 5.54 - 19.63 s ± 4.31, p<0.001, ES 1.48), suggesting a substantial acceleration of V’O2 kinetics; peak value of ΔHHb to ΔV’O2 ratio was smaller after HIT (∼ 29%) (1.83 ± 0.63 - 1.23 ± 0.37, p<0.01, ES 1.17). Discussion This study shows that 8 weeks of HIT were sufficient to induce a significant acceleration of V’O2 kinetics during moderate intensity exercise and to improve the matching between muscular O2 delivery and uptake in older, healthy men. These results suggest that the acceleration of the dynamic response of aerobic metabolism was due to an improved matching of O2 utilization to microvascular delivery. References Williams AM, Paterson DH, Kowalchuk JM. (2013) J Appl Physiol 114, 1550–1562. De Roia G, Pogliaghi S, Adami A, Papadopoulou C, Capelli C. (2012) Am J Physiol Regul Integr Comp Physiol. 302, R1158- R1166. Murias JM, Spencer MD, DeLorey DS, Gurd BJ, Kowalchuk JM, Paterson DH. (2011) J Appl Physiol 111, 1410–1415.