Résumé :
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Unless neuromuscular maturation during growth is a key element, it has been poorly documented with respect to the biological development of children. The strength generation capacity of the muscles is one of the main maturation features. Most of the time, maximal voluntary isometric contraction (MVIC) was measured to provide normative data from healthy children. This has particularly performed for the handgrip function, probably because its assessment appears simple and straightforward in children. For other muscle functions, it has been mainly performed by handheld dynamometry and isokinetic/isometric dynamometers. The method denominated as Quantitative Muscle Testing (QMT) has rarely been used in healthy children although muscle strength assessed by QMT has been chosen as a primary or secondary criterion in several therapeutic trials (for instance, in Duchenne muscular dystrophy or in amyotrophic lateral sclerosis). The main goal of the study was to establish a normative database of muscle strength assessed by QMT for children aged from 5 to 16 years and to propose practical predictive models for the muscle functions tested. The secondary goal was to test if any learning effect occurred on strength measured at two successive visits for children.This study involved 96 healthy children aged from 5 to 16 years. Strength was assessed for 5 muscle functions bilaterally: handgrip, elbow flexion and extension, knee flexion and extension. The measurements were performed with a QMT system. To ensure that MVIC was really measured, a second measurement session was proposed to test if reliability of the measurement was good and if any learning effect occurred. Fifty-five subjects participated to this retest session.No learning effect was detectable between the first and the second sessions for none of the muscle functions tested (all p>0.05). Paediatric norms for Quantified Muscle Testing were built. Predictive equations for strength are proposed for hand grip, elbow flexion and extension and knee flexion and extension. The models suggest the strong influence of height on muscle strength.This work provides normative data for the strength of several muscle function and underline the particular role of body height, hence maturation, in the generation force capacity of children. Chronological age should not be used as a single variable to compute normal strength due to the strong effect of children maturation on muscle strength. Norms may be applied to compute composite indicators of strength in children to help situating their strength with respect to normal values. This is in use in children under long-term corticoid therapy in an ongoing work.
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