Purpose: Sprint interval training (SIT), involving brief intermittent bursts of vigorous exercise within a single training session, is a time-efficient way to improve cardiorespiratory fitness (CRF). It is unclear whether performing sprints spread throughout the day with much longer (≥ 1 h) recovery periods can similarly improve CRF, potentially allowing individuals to perform "sprint snacks" throughout the day to gain health benefits.
Methods: Healthy, young, inactive adults (~ 22 years, peak oxygen uptake [VO2peak] ~ 35 ml kg- 1 min- 1) were randomly assigned to one of two groups and performed 18 training sessions over 6 wks. Sprint snacks (SS) involved 3 × 20-s 'all out' cycling bouts separated by 1-4-h rest (n = 12, 7 females). Traditional SIT involved 3 × 20-s bouts interspersed with 3-min rest within a 10-min training session (n = 16, 7 females). The primary outcome was CRF determined by a VO2peak test conducted before and after training. Secondary outcomes included a 150 kJ cycling time trial and exercise enjoyment.
Results: Absolute VO2peak increased by ~ 6% after SIT and ~ 4% for SS (main effect of time P = 0.002) with no difference between groups (group × time interaction, P = 0.52). 150 kJ time trial performance improved by ~ 13% in SIT and ~ 9% in SS (main effect of time, P < 0.001) with no difference between groups (group × time interaction, P = 0.36).
Conclusion: CRF was similarly increased by a protocol involving sprint snacks spread throughout the day and a traditional SIT protocol in which bouts were separated by short recovery periods within a single training session.
Keywords: Exercise performance; HIIT; High-intensity interval training; Maximal oxygen uptake; Physical activity.