Background Male gender, training volume (# of hours per week) and match exposure (# of games played per week) have been documented as risk factors for jumper's knee among young elite volleyball players (Visnes & Bahr, 2012). However, it is not known whether jump frequency differs between intra-squad players.
Objective To examine inter-individual and gender differences in jump frequency during training and matches in young elite volleyball players.
Design Observational study.
Setting Norwegian elite volleyball boarding school training program.
Participants Student-athletes (26 boys and 18 girls, 16–18 yrs).
Main outcome measures Individual jump counts were recorded based on video recordings obtained from one week of volleyball training (9 training sessions for boys and 10 for girls, 14.1 h and 17.8 h of training, respectively) and 10 matches (5.9 h for boys (16 sets) and 7.7 h for girls (21 sets).
Results A total of 7805 jumps were recorded during training, 4993 among boys and 2812 among girls. As training attendance and jump frequency varied substantially between players, the total exposure in training ranged from 50 to 666 jumps/week among boys and from 11 to 251 jumps/week among girls. On average, this corresponded to 35.7 jumps/h for boys and 13.7 jumps/h for girls (t-test, P=.002). Total jump exposure ranged between 1 to 339 jumps among boys and between 0 to 379 jumps among girls. Player jump frequency averaged 62.2 jumps/h for boys and 41.9 jumps/h for girls (t-test, P<.039). The inter-individual differences seen in jump frequency were substantially more pronounced than any differences observed between player functions.
Conclusions Substantial inter-individual and gender differences were observed in jump frequency during training and matches in young elite volleyball players. Thus, jump frequency may represent a more important risk factor for jumper's knee than total training volume and warrants further research attention.
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