Effect of an Injury Prevention Program on the Lower Limb Stability in Young Volleyball

A sample of 29 players were included in this study. The experimental group was formed by 18 players, while the control group was formed by 11 players. Sample characteristics for both groups are shown in Table 1. The inclusion criteria for the sample selection were: 1) to be aged between 14 and 18 years old; 2) to train in volleyball twice or three times a week, for at least an hour and a half per session; 3) to take part in federated competitions regularly; 4) to have been competing in volleyball for at least two seasons. The exclusion criteria were: 1) to leave the training or the competition during the study; 2) to suffer an injury at the beginning of the intervention program or during its implementation; 3) to miss more than 25% of the training sessions during the intervention program. Lastly, three players from the experimental group were excluded from the statistical analysis because they interrupted their volleyball practice.

The study was approved for the institutional ethics committee. An explanatory letter was given to the participants and their parents and an informed consent form was signed by the parents of the participants.

The intervention program consisted of 16 sessions, performed for eight weeks, twice per week. The intervention group performed 20-minute sessions before their habitual volleyball training. The structure of the prevention program consisted in a warm up, a lower limb strength exercise; two core exercises; a lower limb plyometric exercise, and a lower limb stability exercise. While the injury prevention program was being performed, both groups continued with their regular volleyball training sessions. The sessions designed for each day can be observed in Figure 1.

Strength training was oriented to increase the strength-endurance capacity of the players. It was focused on the quadriceps, hamstrings, gluteus maximus and gluteus medius, spinal erectors, transverse abdominal, obliques and rectus abdominis. These muscles perform flexion and extension of the knee and the hip, and stabilize the spine, hip and knee. A range of 10-20 repetitions were performed of each exercise, or 15-30 seconds in the case of isometric exercises. Plyometric training was focused on the lower limbs. A total volume of 40 jumps and landings were performed in each session, so volume was controlled by the number of jumps performed according to the guidelines published by the National Strength Conditioning Association (NSCA). Stability training was divided into three groups depending on if they were performed without equipment, with a volleyball ball, or after a landing.

Two measurements were carried out. The first one, a week before the intervention (pre-test) and, the second one a week after the 8 weeks of the injury prevention program (post-test). The participants answered a questionnaire about previous sport injuries of the lower limbs in the pre-test. A laterality test was performed to confirm the dominant side of the subjects. After that, some anthropometric variables and stability with a force platform and the Y-Balance test were taken randomly.