The bigger, the stronger? Insights from muscle architecture and nervous characteristics in obese adolescent girls.

BACKGROUND: Young obese youth are generally stronger than lean youth. This has been linked to the loading effect of excess body mass, acting as a training stimulus comparable to strength training. Whether this triggers specific adaptations of the muscle architecture (MA) and voluntary activation (VA) that could account for the higher strength of obese subjects remains unknown. METHODS: MA characteristics (that is, pennation angle (PA), fascicle length (FL) and muscle thickness (MT)) and muscle size (that is, anatomical cross-sectional area (ACSA)) of the knee extensor (KE) and plantar flexor (PF) muscles were evaluated in 12 obese and 12 non-obese adolescent girls (12-15 years). Maximal isometric torque and VA of the KE and PF muscles were also assessed. RESULTS: Results revealed higher PA (P<0.05), greater MT (P<0.001), ACSA (P<0.01), segmental lean mass (P<0.001) and VA (P<0.001) for KE and PF muscles in obese girls. Moreover, obese individuals produced a higher absolute torque than their lean counterparts on the KE (224.6±39.5 vs 135.7±32.7 N m, respectively; P<0.001) and PF muscles (73.3±16.5 vs 44.5±6.2 N m; P<0.001). Maximal voluntary contraction (MVC) was correlated to PA for the KE (r=0.46-0.57, P<0.05-0.01) and PF muscles (r=0.45-0.55, P<0.05-0.01). MVC was also correlated with VA (KE: r=0.44, P<0.05; PF: r=0.65, P<0.001) and segmental lean mass (KE: r=0.48, P<0.05; PF: r=0.57, P<0.01). CONCLUSIONS: This study highlighted favorable muscular and nervous adaptations to obesity that account for the higher strength of obese youth. The excess of body mass supported during daily activities could act as a chronic training stimulus responsible for these adaptations.

Isokinetic muscle strengthening for knee osteoarthritis: A systematic review of randomized controlled trials with meta-analysis.

OBJECTIVE: To assess the level of scientific evidence and the place in the rehabilitation framework of isokinetic muscle strengthening (IMS) for knee osteoarthritis (OA). METHODS: A systematic review of the English literature in MEDLINE via PubMed, the Cochrane Library, and PEDro databases for only randomized comparative trials. Data that were sufficiently homogeneous underwent comprehensive meta-analysis. Methodological assessment was done by using the CLEAR scale for non-pharmacologic trials. RESULTS: We identified articles for 9 trials (696 patients). All trials were of low to moderate quality. Tolerance of IMS was considered good. Improvement in muscle strength was better with an IMS program than no treatment or an isometric exercise but did not differ with an aerobic program. We found an important effect for pain (standardized mean difference 1.218 [95% CI 0.899-1.54], P<0.001) and functional Lequesne index (1.61 [0.40-2.81], P=0.009) and a moderate effect for the Western Ontario and McMaster Universities Osteoarthritis Index subscore C for disability (0.58 [0.04-1.11], P=0.03). CONCLUSIONS: IMS is an effective way to propose dynamic muscle strengthening for knee OA rehabilitation and has a significant effect on pain and disability. Because of the weak methodology and the great heterogeneity of studies, particularly in IMS protocol and outcome measures, insufficient data are available to provide guidelines about efficacy and strategy. Future clinical trials are needed, but more attention should be paid to the methods of such studies to clarify the role of IMS in the therapeutic armamentarium of knee OA.