Acute Effects of Isometric Conditioning Activity with Different Rest Intervals Between Sets on Countermovement Jump Performance in Resistance-Trained Participants

This study investigated the acute effects of different rest intervals between sets of isometric conditioning activity (ICA) on countermovement jump (CMJ) performance. Fifteen resistance-trained males completed four conditions: three ICA protocols with 1, 2, or 3 min rest intervals between sets and a control condition (CTRL). ICA was performed in the half-squat position at a 90° knee angle against an immovable barbell, with each protocol consisting of three sets of short maximal voluntary isometric contractions (3 × 3 s per set). CMJ performance was assessed before and at 3, 6, 9, and 12 min after ICA or CTRL. The results showed no significant effects of the ICA or rest interval on CMJ height or relative peak power. However, independent of rest duration, ICA induced transient alterations in jump mechanics, characterized by decreased stiffness at 9 min and reduced eccentric peak velocity at 6–12 min post-ICA. Similar fluctuations were observed in the CTRL condition, suggesting that these changes may reflect time-dependent variability rather than specific potentiation effects. In conclusion, the studied ICA protocols did not enhance CMJ height or power output, and the length of the rest interval did not influence the outcomes, indicating limited applicability of this approach in resistance-trained males.