Are Self-Selected Intervals as Effective as Fixed Intervals in Controlling Acute Responses in High-Intensity Interval Resistance Training?

Physical conditioning programs often apply high-intensity resistance training (HIRT), but there is a lack of research investigating the effects of using fixed or self-selected resting intervals between exercises on the performance, relative intensity, and affective perception during this modality of training. This study compared fixed versus self-selected rest intervals in HIRT sessions on cardiorespiratory responses, number of repetitions, and enjoyment perception in trained young men. Sixteen trained males (27.1 ± 3.9 years; 56.6 ± 7.5 mL.kg.min) performed HIRT circuits with 30-s and self-selected recovery interval. The duration of resting intervals was longer in HIRT performed with fixed than self-selected intervals (14.04 ± 5.82 s; < 0.0001; ES = 3.2). Both sessions elicited similar relative HRR (79.4 ± 6.2 % . 81.6 ± 4.2 %; = 0.14), VOR (43.0 ± 12.2% . 47.7 ± 9.6%; = 0.10), and enjoyment reflected by scores in the PACES questionnaire (107.9 ± 15.1 . 109.2 ± 12.8; = 0.65). The total number of repetitions (403.4 ± 45.5 . 353.1 ± 27.4; < 0.01, ES = 1.3) and caloric expenditure (154.4 ± 28.6 kcal . 121.4 ± 21.6 kcal; < 0.001, ES = 0.13) were greater in HIRT performed with fixed . self-selected intervals. In conclusion, HIRT performed with fixed and self-selected rest intervals elicited similar relative intensity and enjoyment perception. However, the number of repetitions and caloric expenditure were greater in sessions performed with fixed 30-s.