Contrast Training and Volleyball Players' Jumping Ability

Volleyball is a sport in which the ability to perform repeated vertical jumps plays animportant role in the effectiveness of actions such as attacking, blocking, and jumpserving. Therefore, developing lower‐limb strength‐speed capabilities is an importantcomponent of volleyball players' physical preparation. One of the methods used for thispurpose is contrast training, in which exercises performed with high external loads arecombined with high‐velocity exercises such as jumps. Complex training is also used inpractice, in which resistance exercises and high‐velocity exercises are performed inseparate parts of the training session.The aim of the study was to evaluate the effectiveness of three 10‐week training programsand to determine whether the use of elastic bands to assist plyometric exercises couldenhance the effectiveness of contrast training compared with traditional contrasttraining and complex training. Assistance provided by elastic bands partially reduces theload resulting from the athlete's body mass during jumping. This allows the movement tobe performed at a higher velocity than during a traditional bodyweight jump. The studyexamined whether regular exposure to such a stimulus could lead to different trainingadaptations and influence the athletes' ability to generate high power during jumping.Forty‐two male volleyball players were recruited for the study. The inclusion criteriawere: age between 17 and 22 years, at least 12 months of regular high‐intensityresistance training, and at least 12 months of technical volleyball training.Participants were excluded if they had sustained an injury within the three monthspreceding the study or had experienced a training absence longer than four weeks duringthe previous year. Ultimately, 38 players completed the full study protocol. Fourparticipants were excluded from the final analysis due to injury or insufficient trainingattendance. Only participants whose attendance during the intervention exceeded 80% wereincluded 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 thepotential benefits and risks associated with participation and subsequently providedwritten informed consent. For underage participants, consent was provided by their legalguardians. Participants were free to withdraw from the study at any stage.Three volleyball teams participated in the study. The teams were randomly assigned to oneof three training interventions, meaning that entire teams rather than individual playerswere randomized. The first group performed contrast training in which selectedhigh‐velocity exercises were assisted using elastic bands (G‐CNT). The second groupperformed the same program without elastic‐band assistance (CNT). The third groupperformed complex training (CTRL), in which high‐intensity resistance exercises wereperformed during the first part of the training session and high‐velocity exercisesduring the second part. Training volume was designed to be comparable across the threeinterventions. In addition to resistance training sessions performed on Tuesdays andThursdays, all groups participated in volleyball training from Monday to Friday, lastingapproximately 2 hours per session. On Tuesdays and Thursdays, a 5‐hour recovery periodwas maintained between the resistance training session and the technical volleyballsession. Saturday and Sunday were rest days.All interventions were conducted during the off‐season period and lasted 10 weeks. Theprogram included high‐intensity resistance exercises and high‐velocity exercises. Inaccordance with the principle of exercise pairing, exercises with similar biomechanicalmovement patterns were combined. Therefore, both the conditioning activity (CA) and thepost‐conditioning activity (post‐CA) were intended to involve the same muscle groups, beperformed through a similar range of motion, and generate force in a similar direction.Resistance exercise intensity was individualized on the basis of maximal strength testsperformed before the intervention. Across successive stages of the program, the number ofsets, 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‐velocityexercises were performed. In the G‐CNT group, athletes performed selected jumps withelastic bands providing assistance, whereas in the CNT group the same exercises wereperformed without assistance. In the CTRL group, both high‐intensity and high‐velocityexercises were also included in the program, but they were not alternated in contrastpairs. Resistance exercises were performed first, followed by high‐velocity exerciseslater in the session. This design allowed three different methods of trainingorganization to be compared while maintaining a similar overall type and volume oftraining load.Before the start of the main training program, participants completed two familiarizationsessions. The purpose of these sessions was to familiarize the athletes with the testingprocedures and the exercises used in the study and to determine individualized trainingloads. Maximal strength was assessed in selected resistance exercises involving both thelower and upper limbs. Participants were also familiarized with the jump testssubsequently used during the testing sessions and with jumps performed usingresistance‐band assistance.Training effects were assessed by comparing results obtained before and after the 10‐weekintervention. Testing sessions were conducted three to five days before the start of thetraining program and within the same time interval after its completion. Participantswere instructed to refrain from resistance exercise for 48 hours before each testingsession. All measurements were conducted in the Exercise Physiology Laboratory of theGdansk University of Physical Education and Sport.Three types of vertical jumps were used to assess jumping performance. Because all threegroups consisted of experienced volleyball players, with an average volleyball trainingexperience of 7.4 years, the countermovement jump with arm swing (CMJ+AS) was used. Theremaining tests consisted of drop jumps from heights of 20 cm and 60 cm (DJ20, DJ60). Theuse of two drop heights allowed the athletes' responses to be assessed under differentmechanical 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. Duringthe drop jump, the athlete initiated the trial by stepping off the box and, after groundcontact, was instructed to jump as quickly and as high as possible. The order of the20‐cm and 60‐cm drop jump conditions was randomized. Participants performed two trials ofeach test, and the trial with the greatest jump height was retained for statisticalanalysis.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 jumpheight 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 thetraining interventions were also assessed. This was considered important because athletesmay respond differently to the same training program, and the mean group response doesnot necessarily reflect the response of each individual participant. Based on themagnitude of changes in the analyzed variables and the predefined smallest worthwhilechange (SWC) threshold, participants were classified as positive responders,non‐responders, or negative responders to the intervention. Subsequently, it was assessedwhether the frequency of the different response categories differed between the trainingmethods.