Author(s): SAYAKA, K., SHINCHI, K., INOGUCHI, T., OYABE, S., KOZUMA, A., NAKAMURA, S., KAMIYA-SAITO, M., MOCHIZUKI, Y., HOMMA, H., KIKUCHI, N., Institution: NIPPON SPORT SCIENCE UNIVERSITY, Country: JAPAN, Abstract-ID: 1827

INTRODUCTION:
Rest intervals during sprint interval exercise (SIE) represent a crucial variable influencing physiological stress, including metabolic responses, cardiovascular responses, and local muscle oxygen dynamics (Shi et al., 2018; Çabuk et al., 2025). In this study, we aimed to examine the effects of rest redistribution, identical total exercise time per set and total rest time, on oxygen consumption (VO2), tissue oxygen index (TOI) and power output during SIE.
METHODS:
Four healthy male university students (age: 25.5 ± 2.4 years, VO2max: 41.9 ± 2.9 mL·kg⁻¹·min⁻¹) in this randomized crossover study. Participants completed three SIE conditions with different rest period allocations. The SIE protocol consisted of six sets of 10-s all-out cycling bouts against a resistance corresponding to 7.5% of body mass, with a total rest duration of 400 s. In the rest interval distributions, we implemented the following protocols: a condition where all rest periods per set were 80 s (CON), a condition where rest periods decreased progressively with each set: 120-100-80-60-40s (DEC), and a protocol where rest periods gradually increased (INC): 40-60-80-100-120s. Measurements included VO2, TOI, heart rate (HR) and power output during SIE, as well as blood lactate concentration (La) and rated perceived exertion (RPE) after SIE. The power metrics used in SIE were peak power output (PPO), mean power output (MPO), minimum power output (min PO), and fatigue index (FI). FI was calculated as [(PPO − min PO) / PPO] × 100.
RESULTS:
During SIE, the FI for PPO and MPO was lowest in INC (PPO: -13.3±6.2%, MPO: -15.7±6.4%), followed by CON (PPO: -16.9±9.9%, MPO: -20.1±10.0%) and DEC (PPO: -19.9±15.3%, MPO: -23.9±18.1%). Mean VO2 during SIE (INC : 31.9±2.4 mL·kg⁻¹·min⁻¹, CON : 30.3±4.1 mL·kg⁻¹·min⁻¹, DEC : 31.6±1.3 mL·kg⁻¹·min⁻¹), and the minimum TOI(INC : 42.9±4.5%, CON :44.0±5.0 %, DEC :45.1±5.6 %), also remained comparable across conditions. HR, La and RPE showed similar values across conditions.
CONCLUSION:
Redistributing rest intervals during SIE may attenuate the decline in power output, while physiological responses related to oxygen uptake and muscle oxygenation appear to remain unaffected.