THU0623-HPR Joint Hypermobility – is There a Correlation Between Muscle Cross Sectional Area and Muscle Strength?
Authors: G. Luder, M. Haehni, C. Mueller Mebes, M.L. Verra, D. Aeberli, J.-P. Baeyens
Journal: Annals of the Rheumatic Diseases (2015)

<h3>Background</h3> Generalized Joint Hypermobility (GJH) is often underestimated and little is known about clinical implications and optimal treatment. Hypermobile persons are often restricted in performing sports or leisure activities, as well as during work, due to pain and disability (1). Adequate muscle strength for movement control might be an important issue to overcome these restrictions. However, little is known about muscle properties of women with GJH. Although it is commonly recognized that strength and muscle cross-sectional area (CSA) are related, the exact relationship seems complex and remains unclear. <h3>Objectives</h3> The aim of the study was to analyze the correlation between muscle strength and muscle CSA in women with GJH. <h3>Methods</h3> This cross-sectional study included 52 hypermobile women (mean age 26.7±4.7 years, weight 62.4±10.8 kg, BMI 22.8±3.6 kg/m<sup>2</sup>) with a Beighton-score of six or more (2). Maximum isometric muscle strength for knee extensors and flexors was measured and calculated as maximal voluntary contraction (MVC) and rate of force development (RFD). Muscle CSA of thigh was measured at one third above knee using peripheral quantitative computer tomography (pQCT). Parameters were calculated as absolute values and related to body weight. Correlation coefficients according to Pearson (r) were calculated, as well as the coefficient of determination (r<sup>2</sup>) in percent. Significance level was set at p=0.05. <h3>Results</h3> For the absolute values significant correlations were found between MVC and muscle CSA with r=0.46 (r<sup>2</sup>=21%, p&lt;0.001) for knee extensors and r=0.29 (r<sup>2</sup>=9%, p=0.035) for flexors. Values related to body weigh showed comparable correlations for MVC and additional significant correlation between RFD of knee extensors and CSA with r=0.31 (r<sup>2</sup>=9%, p=0.028). Regarding strength, the correlation between MVC and RFD for extensors was significant at a middle level (r=0.52, r<sup>2</sup>=27%, p&lt;0.001), as well as for flexors (r=0.56, r<sup>2</sup>=32%, p&lt;0.001). Between flexors and extensors correlations were middle, with r=0.69 (r<sup>2</sup>=48%, p&lt;0.001) for MVC and r=0.51 (r<sup>2</sup>=26%, p&lt;0.001) for RFD. Finally, body weight was correlated with muscle CSA (r=0.52, r<sup>2</sup>=27%, p&lt;0.001), only weak with MVC of extensors (r=0.26, r<sup>2</sup>=7%, p=0.059), but not with RFD of extensors (r=0.009). <h3>Conclusions</h3> Maximum strength of knee extensors and flexors was correlated with muscle CSA of thigh, with values comparable to studies with healthy or exercising people (3). Correlations were highly significant, but on a low level with r<sup>2</sup> from 9 to 21%. This indicates that muscle CSA is not solely responsible for the determination of adequate muscle strength. The fact that RFD of knee extensors was only correlated when related to body weight, may point to the importance of fibre type distribution and neuromuscular control (4). In contrast MVC is more dependent on muscle CSA. To conclude, muscle strength is a complex phenomenon, especially RFD and depends on various factors, not solely on muscle CSA. <h3>References</h3> Simmonds &amp; Keer, Manual Therapy 2007:298-309. Remvig et al. The Journal of Rheumatology 2007:798-803. Remvig et al. The Journal of Rheumatology 2007:798-803. Jones et al. Sports Med 2008:987-994. Andersen &amp; Aagard, Eur J Appl Physiol 2006:46-52. <h3>Acknowledgements</h3> The study was approved by the Ethics Committee of Canton Bern (222/12). <h3>Disclosure of Interest</h3> None declared