EFFECTS OF MUSCLE ACTION TYPE WITH EQUAL IMPULSE OF CONDITIONING ACTIVITY ON POSTACTIVATION POTENTIATION GREGORY C. BOGDANIS,ATHANASIOS TSOUKOS,PANAGIOTIS VELIGEKAS,CHARILAOS TSOLAKIS, AND GERASIMOS TERZIS Faculty of Physical Education and Sports Science, University of Athens, Athens, Greece ABSTRACT Bogdanis, GC, Tsoukos, A, Veligekas, P, Tsolakis, C, and Terzis, G. Effects of muscle action type with equal impulse of conditioning activity on postactivation potentiation. J Strength Cond Res 28(9): 2521–2528, 2014—This study investigated the effects of muscle action type during conditioning activity (half-squat) on subsequent vertical jump performance. Fourteen track and field athletes (relative half-squat of 2.3 6 0.3 times their body weight) completed 4 main trials in a randomized and coun- terbalanced order 5–7 days apart: (a) concentric (CON) half- squats: 7.5 6 1.2 repetitions against 90% of 1 repetition maxi- mum (1RM), (b) eccentric (ECC) half-squats: 9.3 6 1.5 repeti- tions against 70% of 1RM, and (c) 3 sets of 3-second maximal isometric (ISO) half-squats, (d) a control (CTRL) trial, where sub- jects rested for 10 minutes. The number of repetitions in CON and ECC was adjusted so that the impulse of the vertical ground reaction force was similar to ISO. Countermovement vertical jump (CMJ) performance was evaluated for 21 minutes after each main trial. Countermovement vertical jump performance in ISO was higher than CTRL from the second to the 10th minute of recovery, whereas CMJ performance in ECC was higher than CTRL from the sixth and 10th minute of recovery. Analysis of the peak indi- vidual responses revealed an increase in CMJ performance com- pared with baseline only in ISO (3.0 6 1.2%; p = 0.045), whereas no significant increases were observed in ECC and CON. Peak CMJ performance for all subjects in ISO and ECC was achieved within 2–10 minutes after the conditioning muscle actions. Iso- metric were more effective than CON and ECC muscle actions in increasing explosive leg performance when the impulse of the ground reaction force of the conditioning exercise was equated. KEY WORDS complex training, fatigue, countermovement vertical jump, concentric, eccentric, isometric INTRODUCTION C omplex training is a method that combines a high- load conditioning exercise that stimulates the neuromuscular system, followed by a plyometric exercise of the same muscle groups, in which power output is augmented (12). Both acute and chronic gains in muscle power may be further enhanced by performing an explosive exercise, while the muscle groups involved are in this potentiated state (10,37). Enhancement of muscle power output in the second exercise is termed as postactivation potentiation (PAP) and has been attributed to increased phos- phorylation of regulatory myosin light chains, acute changes in the pennation angle of muscle fascicles (11,16), and increased recruitment of motor units (34). However, the conditioning muscle action also causes fatigue, and the interaction between fatigue and PAP determines whether muscle explosive perfor- mance will be enhanced in the exercise that follows (23). Several factors affect the balance between fatigue and PAP, such as volume, intensity and type of the conditioning muscle action, as well as the recovery period between the condition- ing and the plyometric exercise (33). Many studies have examined PAP following different types of exercise (13,20,24,33,35,36). The improvement of muscle performance ranged from 1 to 17% (8,9,14,24,25) and was observed 4–12 minutes after the conditioning exercise (9,19). One of the possible sources for this variability may be the type of muscle action during the conditioning exercise because the magni- tude of potentiation and muscle fatigue may differ between isometric (ISO), eccentric (ECC), and concentric (CON) ex- ercises. However, only few studies have compared the effects of muscle action type on subsequent performance. Rixon et al. (24) compared the effects of maximal ISO (3 3 3 seconds) and dynamic half-squat exercise (3 repetitions at 90% of 1 repetition maximum [1RM]) on countermovement vertical jump (CMJ) performed 3 minutes after the conditioning exer- cise. They concluded that the ISO condition evoked greater muscle PAP than the dynamic condition (2.7 vs. 1.7%; p , 0.01), only in men. In contrast, Tsolakis et al. (35) found a decrease in CMJ performance 8 and 12 minutes after a 3 3 3-second maximal ISO leg press exercise and no change in CMJ height after plyometric exercise (3 3 5 tuck jumps). In Address correspondence to Gregory C. Bogdanis, gbogdanis@phed.uoa.gr. 28(9)/2521–2528 Journal of Strength and Conditioning Research Ó 2014 National Strength and Conditioning Association VOLUME 28 | NUMBER 9 | SEPTEMBER 2014 | 2521 Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.