Self-paced HIIT is less physiologically demanding than traditional HIIT

BACKGROUND: High-intensity interval training (HIIT) has been shown to elicit similar or superior cardiovascular and muscular adaptions to moderate-intensity continuous training. The majority of the literature has examined the acute responses to HIIT using traditional (TRAD) HIIT protocols. Few studies have investigated the metabolic and physiologic response to self-paced (SP) HIIT protocols, that may improve exercise adherence. The purpose of this study was to investigate the central, peripheral, and subjective responses to an acute SP and TRAD HIIT protocol.METHODS: Sixteen recreationally trained individuals (M=8, F=8, 20.6±1.3 years; 68.2±11.6 kg; 1.72±0.08 m; 42.3±7.6 mL/kg/min) were recruited for participation in this repeated-measure, counterbalanced crossover design study. Subjects performed a maximal cycle ergometer test followed by two HIIT (SP and TRAD) protocols matched for work duration. The TRAD HIIT protocol consisted of ten bouts of a 1:2 work to rest ratio (30:60 seconds), while the SP protocol consisted of ten-30 second work bouts followed by a self-paced recovery. During both HIIT sessions, central (oxygen consumption [VO2], heart rate [HR]), peripheral (muscle oxygenation [SmO2], blood lactate [BLa-]), and subjective (ratings of perceived exertion [RPE], enjoyment) responses were assessed.RESULTS: Peak HR, average work intensity, postexercise BLa-, and SmO2 were significantly different between TRAD and SP protocols (P<0.05). No significant differences were observed in RPE, enjoyment scores, or mean recovery time between TRAD and SP.CONCLUSIONS: TRAD HIIT protocols appear to provoke a greater physiological and metabolic demand in recreational exercisers. Future research should investigate the chronic effect of SP and TRAD HIIT programs.