Self-selected or fixed: is there an optimal rest interval for controlling intensity in high-intensity interval...

This study investigated the effects of different rest interval strategies during high-intensity interval resistance training (HIRT) on cardiorespiratory, perceptual, and enjoyment responses among trained young men.

Sixteen men experienced with HIRT underwent cardiopulmonary exercise testing and were familiarized with the exercises and HIRT protocol. On the subsequent three visits, interspaced 48-72 h, participants performed HIRT sessions with different rest intervals in a randomized order: 10 s and 30 s fixed rest intervals (FRI-10 and FRI-30), and self-selected rest interval (SSRI). Oxygen uptake (VO2), heart rate (HR), and recovery perception (Total Quality Recovery Scale) were measured during HIRT, while enjoyment responses (Physical Activity Enjoyment Scale) were assessed immediately after the sessions.

The VO2 during exercise was greater in FRI-10 than FRI-30 (55% VO2max and 47% VO2max, respectively, p = 0.01), while no difference occurred between SSRI and bouts performed with fixed intervals (52% VO2max vs. FRI, p > 0.05). HR, excess post-exercise oxygen consumption (EPOC), recovery perception, and enjoyment responses were similar across conditions (p > 0.05).

Exercise intensity was not affected by the rest interval strategy. High exercise intensity was maintained in sessions performed with FRI or SSRI, without negative repercussions on the duration of training sessions and enjoyment responses after exercise sessions.