Purpose:
The objective of the study was to analyse the effects of post-activation potentiation induced by single- and multijoint maximal voluntary isometric contractions (MVIC) on squat jump performance.

Methods:
Overall, 13 resistance-training males volunteered to participate in the study. Isometric knee extension exercise was chosen to represent single-joint MVIC (MVIC_SJ) and isometric squat to represent multi-joint MVIC (MVIC_MJ). Four experimental protocols were implemented in a randomized order on different days as follows: P1: squat jump performed before and 3 minutes after MVIC_MJ; P2: squat jump performed before and 7 minutes after MVIC_MJ; P3: squat jump performed before and 3 minutes after MVIC_SJ; P4: squat jump performed before and 7 minutes after MVIC_SJ. Jump height, mean power output, peak power output, net impulse, and electromyographic activity of lower limbs were analysed in squat jump before and after the interventions.

Results:
ANOVA showed that peak power output increased in P1 (p = 0.04). No difference was found for electromyographic activity in any of the protocols.

Conclusions:
We concluded that MVIC_MJ performed 3 minutes before the main task (P1) was more effective than MVIC_SJ in optimizing squat jump performance and that the changes in performance were unrelated to muscle activation.