Evaluation of oxygen uptake kinetics on subthreshold and supra threshold CYCLE exercise

The aim of this study is to determine the physiological responses of sub-threshold and supra-threshold exercise on cardiovascular and metabolic parameters, oxygen uptake kinetics and muscle activity. Subjects were divided to groups as a sub–threshold (n=12) and supra-threshold (n=12). Exercise test protocols were applied to two groups before and after the six-weeks exercise period. Maximal cycle ergometer ramp test was applied for to determine anaerobic threshold and maximal oxygen uptake. After this test, subjects return to the laboratory on a different day to perform 6 min constant load moderate intensity that elicited a VO2 corresponding to a 90% anaerobic threshold and 8 min constant load 8 min heavy intensity that elicited Δ%80. Oxygen uptake, lactate and electromyography (EMG) of tibialis anterior, gastrocnemius medialis, biceps femoris, vastus lateralis, vastus medialis and rectus femoris muscles were measured in the test periods. Physiological parameters were not statistically different between two groups before the exercise periods. Cardiovascular and metabolic parameters (VO2maks, hearth ratemax, VO2 at anaerobic threshold (%VO2maks), lactatemax) were increased after two-exercise periods (p<0.05). Oxygen uptake kinetics were changed after the two-exercise protocols. O2 gain (ml.dk-1.W-1) was decreased after two exercise protocol similarly (p<0.05). Although the ratio was not statistically different after supra-threshold exercise O2 gain (ml.dk-1.W-1) was more decreased than after sub-threshold exercise (%7-%4) (p<0.05). Time constant τ1 (s) was also decreased statistically significant after sub-threshold and supra-threshold exercises in similarly ratios (%16-%20) (p<0.05). Second time constant τ2 (s) as slow component kinetics was also decreased after two exercise protocols (p<0.05). But supra-threshold exercise was more effect on τ2 (s) than sub-threshold exercise (%23-%33) (p<0.05). Before and after the six week exercise period there is no statistically significant differences in EMG activity. In conclusion, this study demonstrates that 6-weeks of subthreshold and supra-threshold exercise resulted cardiovascular and metabolic adaptation and faster VO2 kinetics. But this acceleration was not explained with the neuromuscular adaptation. Key Words: Anaerobic threshold, oxygen uptake kinetics, EMG