# Effects of Post-Activation Performance Enhancement on Jump Performance in Elite Volleyball Players
## 2 Materials and Methods  
### Study Design  
Twelve elite male volleyball players took part in the study. The following inclusion criteria were used: (a) professional level of competition (Polish Volleyball League (PLS--Polska Liga Siatkowski) divisions); (b) valid medical examination; and (c) lack of injuries or other health contraindications in the last 6 months. Initially, fourteen players were supposed to participate in the study, but two participants were excluded from taking part in the study due to low back pain in prior weeks. CMJ was performed by all twelve participants; one participant did not perform SJ due to an ankle injury during a volleyball session. Participants were instructed to follow their normal dietary, supplement and sleeping habits during the study. All participants were informed about the study protocol, voluntarily took part in the experiment and signed informed consent. The study protocol was approved by the Bioethics Committee (Regional Medical Chamber in Krakow, Poland; opinion no: 1/KBL/OIL/2022) and performed according to the ethical standards of the Declaration of Helsinki (2013).  
Before the main part of the study, on day 1, somatic parameters were measured, and one repetition maximum (1 RM) was determined. In the main part of the study, for four days, the participants performed a standardized warmup, baseline CMJ or SJ (depending on the day), two experimental sessions (one for CMJ and one for SJ) with CA (PAPE condition) and two control conditions (one for CMJ and one for SJ) without CA (CNTR condition) (Figure 1). Four conditions were performed in a random order; on days 2 and 3, participants performed PAPE and CNTR conditions of the same jump, and on days 4 and 5, PAPE and CNTR of the second jump (e.g., on day 2, SJ) PAPE; on day 3, SJ CNTR; then, on day 4, CMJ CNTR; on day 5, CMJ PAPE). Six participants performed SJ conditions first, and the other six performed CMJ conditions first. The conditioning activity used in the study comprised 3 repetitions of a trap bar deadlift with a load of 80% 1 RM and an accommodating resistance of approximately 25 kg provided by an elastic band (yellow band, Corength, Domyos) (18 \(\pm\) 2% of 1 RM); the remainder of the load was provided by traditional resistance. There was no familiarization session, as the players were familiar with a trap bar deadlift with accommodating resistance and jumping tests. All daily sessions were performed at the same time of day (from 9 a.m. to 11 a.m.). Apart from experimental days, players participated in their volleyball training schedule (afternoon training sessions).  
As the magnitude of the response to CA may be individual, after completing all tests, for further statistical analysis, based on the obtained data, players were divided into two groups: positive responders to the CA and non-responders. Because Optojump has an 0.8 cm standard error of measurement [27], positive responders were defined as athletes exhibiting improvement in absolute values by \(\geq\)0.8 cm between baseline and post-CA jumps, whereas non-responders were defined as players whose changes between baseline and post-CA jumps were \(<\)0.8 cm. Statistical analysis was performed for all subjects and separately for positive responders and non-responders.