INTRODUCTION: Maximal sprinting velocity influences performance in many sports. Despite the variety of training methods developed to enhance sprinting, a key question remains: is muscle coordination related to performance gains? To deal with the well-known "degrees of freedom problem" [1], movement coordination is organized into muscle synergies [2], meaning that there are synergistic neural components of movement. The present study aimed to analyse the relationships between muscle coordination and functional performance during sprinting running. METHODS: 14 elite athletes in rugby sevens and track and field (10 men and 4 women, age: 27.0±3.4 years, height: 181.8±11.9 cm, mass: 81.3±17.6kg) performed two trials of 40-m maximal sprint acceleration. EMG activity of eight ipsilateral muscles from the hamstring, quadriceps and gluteal muscle groups was recorded. Step length, step frequency, stance and flight times as well as maximal speed (Vmax) were measured with an optoelectronic measurement system. Muscle synergies were extracted from the EMG signals over the entire sprint by non-negative matrix factorization and divided into motor modules (i.e., relative muscle contribution) and motor primitives (i.e., temporal coefficients). Each synergy was characterized by their center of activity (CoA), their width of activity, their complexity within the running cycle (Higuchi`s fractal dimension) as well as their irregularity between the running cycles (Hurst exponent). Spearman rank correlations were assessed between the muscle synergies and functional parameters. RESULTS: Three muscle synergies were extracted (R2 = 0.85±0.05). The first synergy referred to the pre-activation and braking phases with a major contribution of the vastus lateralis and the gluteus muscles. The second synergy corresponded to the early swing phase showing a high contribution of the rectus femoris. The third synergy was in the late swing and early stance with large hamstrings contribution. Step frequency and the CoA of the braking synergy were negatively correlated (* = -0.59, p
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