Seven High-Intensity Interval Training Sessions Increases Aerobic Capacity and Blunts the Metabolic and Hormonal Responses to Intense Exercise

Abstract

Numerous studies have shown that traditional endurance exercise (∼55–70% VO2peak) improves aerobic capacity. Alternately, a recent study reported that 2 wk of sprint interval training (>100% VO2peak) also improved aerobic capacity and exercise performance. Interval training at an intermediate, but still intense power output (∼90% VO2peak), may offer a more practical training protocol to improve aerobic capacity and high intensity performance for the general population. PURPOSE: Our aim was to investigate the effects of a short term, high intensity interval training (HIT) program on aerobic capacity and to quantify the short-term changes in the cardiovascular, metabolic and hormonal responses to exercise at ∼90% VO2peakM METHODS: Eight females participated in the study (mean ± SE: 22.1 ± 0.2 yrs, 65.0 ±0.8 kg, 2.36 ± 0.17 VO2peak). Subjects performed a VO2peak test prior and following training. Training consisted of 7 HIT sessions over 2 wk. Subjects trained every other day performing ten 4 min bouts at 90% VO2peak with 2 min of rest between bouts. On the 2nd and 7th training session, heart rate (HR) and respiratory and blood samples were collected before and after bouts 1, 3, 5 and 10. The 7th training session was at the same absolute power output as the 2nd session. RESULTS: On average, subjects reached 90% VO2peak by the end of each exercise bout (session 2 (S2): 90.3 ± 3.6, session 7 (S7): 90.5 ± 4.0% VO2peak). Exercising workloads increased throughout training, with an average increase of 10% from the 1 * to 6th training session. VO2peak significantly increased (p < 0.05) following training (2.36 ± 0.17 to 2.66 ± 021 l/min). Lactate decreased with training following the 3rd bout (S2: 3.37 ± 0.08 vs. S7: 2.96 ± 0.18 mM) and following the 5th bout (S2: 3.63 ±0.12 vs. S7: 3.27 ± 0.18 mM). Plasma epinephrine significantly decreased with training following the 3rd bout (S2: 1.80 ±0.08 vs. S7: 0.95 ± 0.06 nM) and the 10th bout (S2: 3.11 ±0.24 vs. S7: 1.39 ±0.03 nM). The highest HR reached during exercise significantly decreased following training (S2: 179.6 ± 1.4, S7: 173.9 ± 1.7 beats/min). HR recovery during rest periods decreased on average from 128.1 ± 3.0 to 122.8 ± 3.5 beats/min. Plasma free fatty acids (S2: 0.38 ±011 vs. S7: 0.27 ± 0.03 mM) and glycerol(S2: 127.7 ± 13.5 vs. S7: 97.6 ± 5.9 mM) following bout 10 were significantly decreased following training. CONCLUSION: Aerobic capacity was increased and cardiovascular, hormonal and metabolic responses to high intensity exercise were blunted with 2 wk of HIT. HIT at ∼90% VO2peak may offer a realistic and practical training protocol to improve aerobic capacity and high intensity performance for the general population.