Background Previous studies on players with jumper's knee (cross-sectional studies and case-control studies) have found that symptomatic athletes were training more strength and more workouts per week compared with healthy asymptomatic players. Registration of training volume as risk factor for the development of jumper's knee is to our knowledge not previously done.

Aim Study training volume as a risk factor for the developing jumper's knee.

Design Cohort study.

Participants Elite volleyball players at junior high school (Top Volley Norway) at Sand, Norway.

Method Registration of training volume through weekly training diary on the internet, and interviews with the player and the coach. The jumper's knee diagnosis was based on a standardised clinical examination.

Results A total of 140 symptom-free students were included (69 boys and 71 girls), with an mean observation time of 1.8 years. Of these, 28 developed jumper (22 boys and 6 girls). The jumper's knee group trained 20.1 ± 6.9 (SD) h per week, compared with the asymptomatic athletes 16.9 ± 6.9 h (p<0.001). The difference in the training workload was primarily related to indoor volleyball training, where the jumper's knee group trained 15.0 ± 3.0 h and the asymptomatic players 11.9 ± 3.8 h (p<0.001). The volume for other forms of training (volleyball, strength training, flexibility training and other training) were similar. For further analysis, the total training exposure (average hours per week) were divided into four groups. The training group 4 (21–28 h per week) have a significantly increased risk of developing jumper's knee. χ² test=8.57 gives p=0.01.

Conclusion We find that athletes who developed jumper's knee significantly trained more than athletes who remain asymptomatic. High training loads in the form of indoor volleyball training will therefore be an important risk factor for the developing jumper's knee.