Background A 3-year prospective cohort study has been initiated in Japanese young female handball and basketball players to identify risk factors for non-contact ACL injuries. Although we examined the baseline data of the players at their first year of high school, it raises concern about the use of the individual baseline data as the characteristics of the players (might be identified as a risk factor) in cases where the players get injured during their senior year of high school.

Objectives To compare the player's data examined at the first year and the senior year of high school.

Design Case-control study.

Participants 21 of 84 high school female players (handball: 4 players, basketball: 17 players) who participated in our prospective cohort study.

Methods Body compositions, static balance (locus length per unit area examined by stabilometer), dynamic balance (star excursion balance test; SEBT), isokinetic hamstrings/quadriceps strength, isometric hipabduction strength, hamstrings flexibility, knee laxity (KT1000), navicular drop, generalized joint laxity (Beighton index), and psychological-competitive ability (DIPCA-3) were examined.

Results Significantly better result of isokinetic hamstrings/quadriceps strength, isometric hip abduction strength, and hamstrings flexibility were found at the senior. Significantly lower result of navicular drop was found at the senior. No significant differences were found between the groups in body compositions, static and dynamic balance, and DIPCA-3. Generalized joint laxity in the senior was significantly higher level of the index than that at the first.

Conclusions During two years after baseline evaluation, the players increased their hip and knee strength without matching increases of static and dynamic balance ability. Considering that even generalized joint laxity which assumed to be consistent had changed, careful interpretation is needed to use the baseline data as a risk factor in a prospective cohort study.