A novel method to monitor lower limb muscles flexibility in elite youth soccer players
The International Olympic Committee consensus on elite child athlete recognized this population as exclusive in many aspects and requires appropriate supervision to insure a healthy athletic development (Mountjoy et al., 2008). Philippaerts et al. (2006) presented the longitudinal change in youth soccer players including the trunk flexibility pattern during the growth period and the rapid modification of this physical factor during this critical phase was emphasized. Witvrouw et al. (2003) reported that an increased tightness or length imbalance of the hamstring or quadriceps muscles in professional players may increase the risk of injury. Recently de Lucena et al. (2011) stated on Brazilian adolescent a prevalence of 9.8% of Osgood-Schlatter’s disease, the factors associated were practising regular sport and the shortness of the rectus femoris muscle (odds ratio, 7.15; 95% CI 2.86, 17.86). Nevertheless, while there is no definitive consensus regarding the possible benefit of stretching on athletic performance or injury prevention (Ben and Harvey, 2010), the development or maintenance of optimal flexibility has become very popular in the past years to prevent injury. An accurate monitoring of the primary lower limb muscle groups performed on a regular basis in youth elite soccer players may, however, help to identify flexibility imbalance of players in order to prescribe specific exercises, to reduce injury risks and football development time loss. The accuracy and the reliability of flexibility measures is of primary interest for clinicians working with elite youth soccer players (i.e., screening, prevention, rehabilitation programmes). Today there is a large body of literature about flexibility assessments. The most common methods rely either on the subject’s tolerance to stretch (Law et al., 2009) or on the patient’s voluntary activation (Folpp et al., 2006), which likely limits the accuracy of these methods. In an attempt to overcome these weaknesses a new method has recently been developed using a standardized stretch force (Fourchet et al., 2011). This novel procedure is an extension of a previous method using a standardized stretch force on hamstrings (Fredriksen et al., 1997) to the main lower limb muscles groups. The aim of the present study was therefore to, 1) evaluate the reliability of this novel digital video
analysis method to assess the flexibility of the lower limb muscles groups in youth elite soccer players, and 2) examine whether changing the operators and/or the video analysers was likely to affect the reliability of the measures. 2. METHOD
Ten healthy male adolescents from a sports academy (15.3 ± 1.6 years, 65.4 ± 26.2 kg, 171.7 ± 8.8 cm and +1.5 ± 1.5 years from peak height velocity (Mirwald et al., 2002) were tested. All participants were without history of musculoskeletal injuries of the lower limbs the previous two months before the study. Prior to testing, informed consent was obtained from all participants and their parents. The study was approved by the local research ethics committee and conformed to the recommendations of the Declaration of Helsinki.