Contrast Training and Volleyball Players' Jumping Ability

Volleyball is a sport in which the ability to perform repeated vertical jumps plays an important role in the effectiveness of actions such as attacking, blocking, and jump serving. Therefore, developing lower-limb strength-speed capabilities is an important component of volleyball players' physical preparation. One of the methods used for this purpose is contrast training, in which exercises performed with high external loads are combined with high-velocity exercises such as jumps. Complex training is also used in practice, in which resistance exercises and high-velocity exercises are performed in separate parts of the training session.

The aim of the study was to evaluate the effectiveness of three 10-week training programs and to determine whether the use of elastic bands to assist plyometric exercises could enhance the effectiveness of contrast training compared with traditional contrast training and complex training. Assistance provided by elastic bands partially reduces the load resulting from the athlete's body mass during jumping. This allows the movement to be performed at a higher velocity than during a traditional bodyweight jump. The study examined whether regular exposure to such a stimulus could lead to different training adaptations and influence the athletes' ability to generate high power during jumping.

Forty-two male volleyball players were recruited for the study. The inclusion criteria were: age between 17 and 22 years, at least 12 months of regular high-intensity resistance training, and at least 12 months of technical volleyball training. Participants were excluded if they had sustained an injury within the three months preceding the study or had experienced a training absence longer than four weeks during the previous year. Ultimately, 38 players completed the full study protocol. Four participants were excluded from the final analysis due to injury or insufficient training attendance. Only participants whose attendance during the intervention exceeded 80% were included in the analysis.

The study protocol was approved by the Bioethics Committee (approval no. KB-11/23). Before participation, each athlete was informed about the study procedures and the potential benefits and risks associated with participation and subsequently provided written informed consent. For underage participants, consent was provided by their legal guardians. Participants were free to withdraw from the study at any stage.

Three volleyball teams participated in the study. The teams were randomly assigned to one of three training interventions, meaning that entire teams rather than individual players were randomized. The first group performed contrast training in which selected high-velocity exercises were assisted using elastic bands (G-CNT). The second group performed the same program without elastic-band assistance (CNT). The third group performed complex training (CTRL), in which high-intensity resistance exercises were performed during the first part of the training session and high-velocity exercises during the second part. Training volume was designed to be comparable across the three interventions. In addition to resistance training sessions performed on Tuesdays and Thursdays, all groups participated in volleyball training from Monday to Friday, lasting approximately 2 hours per session. On Tuesdays and Thursdays, a 5-hour recovery period was maintained between the resistance training session and the technical volleyball session. Saturday and Sunday were rest days.

All interventions were conducted during the off-season period and lasted 10 weeks. The program included high-intensity resistance exercises and high-velocity exercises. In accordance with the principle of exercise pairing, exercises with similar biomechanical movement patterns were combined. Therefore, both the conditioning activity (CA) and the post-conditioning activity (post-CA) were intended to involve the same muscle groups, be performed through a similar range of motion, and generate force in a similar direction. Resistance exercise intensity was individualized on the basis of maximal strength tests performed before the intervention. Across successive stages of the program, the number of sets, repetitions, and the magnitude of external load were progressively modified.

The main difference between the G-CNT and CNT groups was the way selected high-velocity exercises were performed. In the G-CNT group, athletes performed selected jumps with elastic bands providing assistance, whereas in the CNT group the same exercises were performed without assistance. In the CTRL group, both high-intensity and high-velocity exercises were also included in the program, but they were not alternated in contrast pairs. Resistance exercises were performed first, followed by high-velocity exercises later in the session. This design allowed three different methods of training organization to be compared while maintaining a similar overall type and volume of training load.

Before the start of the main training program, participants completed two familiarization sessions. The purpose of these sessions was to familiarize the athletes with the testing procedures and the exercises used in the study and to determine individualized training loads. Maximal strength was assessed in selected resistance exercises involving both the lower and upper limbs. Participants were also familiarized with the jump tests subsequently used during the testing sessions and with jumps performed using resistance-band assistance.

Training effects were assessed by comparing results obtained before and after the 10-week intervention. Testing sessions were conducted three to five days before the start of the training program and within the same time interval after its completion. Participants were instructed to refrain from resistance exercise for 48 hours before each testing session. All measurements were conducted in the Exercise Physiology Laboratory of the Gdansk University of Physical Education and Sport.

Three types of vertical jumps were used to assess jumping performance. Because all three groups consisted of experienced volleyball players, with an average volleyball training experience of 7.4 years, the countermovement jump with arm swing (CMJ+AS) was used. The remaining tests consisted of drop jumps from heights of 20 cm and 60 cm (DJ20, DJ60). The use of two drop heights allowed the athletes' responses to be assessed under different mechanical conditions.

All measurements were performed using a Kistler 9286BA force platform. During the CMJ+AS, participants were instructed to jump as high as possible while using an arm swing. During the drop jump, the athlete initiated the trial by stepping off the box and, after ground contact, was instructed to jump as quickly and as high as possible. The order of the 20-cm and 60-cm drop jump conditions was randomized. Participants performed two trials of each test, and the trial with the greatest jump height was retained for statistical analysis.

During the CMJ+AS, jump height (JH), relative peak power (RPP), countermovement time (CMT), and modified reactive strength index (RSImod; calculated as the ratio of jump height to countermovement time) were assessed. During the DJ20 and DJ60, jump height (JH), relative peak power (RPP), ground contact time (CT), and reactive strength index (RSI) were assessed.

In addition to comparing mean changes between groups, individual responses to the training interventions were also assessed. This was considered important because athletes may respond differently to the same training program, and the mean group response does not necessarily reflect the response of each individual participant. Based on the magnitude of changes in the analyzed variables and the predefined smallest worthwhile change (SWC) threshold, participants were classified as positive responders, non-responders, or negative responders to the intervention. Subsequently, it was assessed whether the frequency of the different response categories differed between the training methods.