Arnold Huurnink

Chapter 4 4 50 Abstract Coordination of corrective motor actions is considered important for soccer performance and injury prevention. A single-leg stance test (SLS) assesses the integrity and proficiency of the sensorimotor control system, quantified by center of pressure averaged speed (COPspeed). We aimed to provide age-matched z-scores for COPspeed in elite male youth soccer players. Secondly, we assessed a threshold for abnormal long-term change in performance, i.e., critical difference (CD). In a youth academy program, 133 soccer players of 9 to 18 years were tested twice for both legs (two repetitions) and one repetition follow- up was conducted at 5.8 months (SD 2.7). Linear regression between age and COPspeed was performed to provide age-matched z-scores. Variance of differences in z-scores at baseline and between sessions were used to estimate the CD up to five repetitions. Intraclass correlation coefficients (ICC) were assessed within and between sessions. The age significantly affected COPspeed (p<0.0001), with lower values in older players (95% CI; 3.45–9.17 to 2.88–5.13 cm∙s -1 , for 9 and 18 years, respectively). The z-score CD ranged from 1.72 (one repetition) to 1.34 (five repetitions). The ICC of z-scores was 0.88 within session and 0.81 between sessions. In conclusion, the SLS performance in elite male youth soccer players improves with age. We determined age-matched z-scores of COPspeed, which reliably determined performance according to age. The CD allows detection of abnormal variations in COPspeed to identify players with a (temporary) deterioration of sensorimotor function. This could be applied to concussion management, or to detect underlying physical impairments.