Effects of Short Term Endurance Training on VO2, HR, and StO2 Kinetics

Abstract

Previous studies have reported faster oxygen uptake (VO2) kinetics following short term endurance training. PURPOSE: This study investigated whether short term training also affects heart rate (HR) or muscle oxygen saturation (StO2) kinetics. METHODS: Seven untrained subjects (23.4 ± 1.5 yr; 73.9 ± 7.8 kg; 3.303 ± 0.618 L ? min−1) completed a 2 week training program by cycling at 70% of maximal HR for 30 min on alternate days. Before and after training, subjects completed a 6-min cycling bout at 50% between ventilatory threshold (VT) and maximal VO2 (VO2max). VO2, HR, and StO, data were averaged into 10-s bins and modeled using non-linear regression. To maintain consistency with the length of phase II, the StO2 data were modeled from 10 to 120 s and from 20 to 120 s for VO2 and HR. The slow component was estimated as the difference between minutes 6 and 3 (e.g., ΔVO2 6–3). RESULTS: The VO2max and VT were unaffected by the short-term training. The VO2 time constant (τ) for phase II was unchanged by training, but the post-training ΔVO2 6–3 was smaller (0.344 ± 0.034 and 0.255 ± 0.029 L · min−1 for pre- and posttraining, respectively; P = 0.03). Likewise, the phase II τ for StO2 also was unaffected by training. However, training speeded the phase II τ for HR (P = 0.03). This adaptation was likely the result of either faster sympathetic innervation to the heart or increased sensitivity to the sympathetic innervation.TableCONCLUSION: These findings suggest that HR kinetics are a more sensitive marker of training adaptations than are VO2 or StO2 kinetics.