Acute Physiological, Metabolic and Perceptual Responses to different High-Intensity Interval Training formats

Purpose: The aim of this study was to compare the acute cardiorespiratory and metabolic effects induced by a High-Intensity Continuous Training (HI-CT) and three High-Intensity Interval Training regimes (HIITs) in young active students. The assessment of internal training load through the rate of perceived exertion (RPE) at iso-time was also a focus. Methods: Fifteen active university students (age: 21.0±1.1 ys, height: 1.74±0.9 m, weight: 64.8±12.9 kg, VO2max 48.1±7.5 mL∙kg-1∙min-1) performed an incremental treadmill test to assess VO2max and maximal aerobic speed (MAS). Then, each participant performed, on testing sessions, separated by a minimum of 72 h and in a randomized order, one HI-CT session at 95% MAS for 8 minutes and three different HIIT sessions (10s-20s, 30s-30s, 50s-30s) with a work phase at 95% MAS and an active recovery at 40% MAS for 16 minutes. Oxygen consumption (VO2), heart rate (HR), time spent near or above 90%VO2max (T@90%VO2max) and blood lactate concentration ([La]+) were measured. The rating of perceived exertion (RPE), by the Borg’s CR 10 scale, was used to assess the subjective level of fatigue experienced at the end of each testing session. Results: The statistical analysis revealed that VO2peak, HRpeak, T@90%VO2max, and RPE values in 10-20 HIIT were significantly lower compared to 30-30 and 50-30 HIIT regimes (p always <0.001). In HI-CT session VO2peak, HRpeak, T@90%VO2max were significantly higher than in 10-20 and 30-30 sessions (p<0.0001 and p<0.05). Blood lactate values were significantly higher in HI-CT and in 50-30 and 30-30 HIITs, compared to 10-20 protocol. Finally, internal workload in HI-CT and 50-30 HIIT was significantly higher than those in 30-30 (p<0.01) and 10-20 (p<0.0001) HIIT sessions. Conclusions: Our results show that in active young subjects a HI-CT and a long work interval HIIT regime (50-30) represent an optimal training stimulus to elicit higher physiological and metabolic responses compared to short work interval HIIT regimes (30-30 and 10-20), being the most effective for stressing both the aerobic and anaerobic energy systems. Coaches can choose and balance the level of aerobic/anaerobic energy requirements and neuromuscular engagement associated with the three HIIT regimes and a HI-CT protocol based on the expected physiological and metabolic adaptations as well as neuromuscular characteristic and ability level of the athlete/subject individual profile.