Author(s): FRANCINI, L., RIBOLI, A., MAURELLO, F., SALVADOR, S., BOLDRINI, L., MAZZONI, S., Institution: AC MILAN, Country: ITALY, Abstract-ID: 2188

INTRODUCTION:
Several studies (1) suggested eccentric peak force (PF) and inter-limb asymmetry during Nordic hamstring exercise (NH) as factors possibly affecting hamstring injury risk (2). However, the information about PF and asymmetry during NH in top-class women soccer players are still lacking. Therefore, the current study aims to describe the PF and asymmetry during NH in adult and young female soccer players.
METHODS:
One hundred and thirty-two female soccer players were involved (n=24 PRO, n=38 U19, n=33 U17, n=37 U15). After a standardized warm-up, NH were performed using a dedicated dynamometer (NordBord VALD, Australia). The injured players were excluded from data collection for at least 1 month after their return to team training; players with a severe hamstring injury during the previous 2 seasons were excluded. A total of 515 NH with ~7 (range: 5 to 19) NH for each player were collected. The PF was measured for each leg and for determining the weaker and the stronger leg. The inter-limbs asymmetry was calculated for both absolute (Newton, N) and relative (percentage, %) values using the following formula [absolute asymmetry = (strong leg - weak leg)] and [relative asymmetry = ((strong leg - weak leg) / (strong leg + weak leg)) * 100], as suggested in previous studies (3). The PF and asymmetry distributions are presented in terms of centiles (i.e. which describe the typical variation in the population). In a Gaussian distribution, some centiles correspond to the standard deviations of the sample (4). Therefore, the 50th (median), 84.13th (+1 SD), 97.72nd (+2 SD), 99.87th (+3 SD) percentiles were calculated (4). A t-test was used for comparisons between PF in weak vs strong leg; statistical significance was set at P < 0.05.
RESULTS:
The 50th, 84.13th, 97.72nd and 99.87th percentiles for PF and asymmetries were calculated. The 50th percentile for PF and asymmetries were ~287 to ~312 N with 17.1 N (~2.8%) asymmetry in PRO, ~266 to ~281 N with 15.5 N (~2.9 %) asymmetry in U19, ~241 to ~364 N with 17.5 N (~3.5%) asymmetry in U17, ~204 to ~219 N with 13.7 N (~3.3 %) asymmetry in U15. The average PF was higher in strong than weak leg (P<0.001) in PRO (320±76 vs 295±70 N for strong vs weak leg, respectively), in U19 (283±41 vs 264±40 N), in U17 (260±36 vs 240±35 N) and in U15 (218±36 vs 203±35 N).
CONCLUSION:
The present study describes the PF and asymmetry during NH in PRO, U19, U17 and U15 female soccer players. This information may help coaches and performance scientists for NH players’ profiling and hamstring exercise prescription during training routine. The current results might be considered as a descriptive analysis of PF and asymmetries during NH exercises in elite women soccer population across different age-categories. The current results may open to further investigation about the association between PF and asymmetry during NH and hamstring injury risk in women’s soccer.

1.Rudisill, et al (2003) 2. Ekstrand, et al (2023) 3. Parkinson, et al (2021) 4. Brook, et al (1982)