Muscle function in Turner syndrome: normal force but decreased power.

ObjectiveAlthough hypogonadism and SHOX gene haploinsufficiency likely cause the decreased bone mineral density and increased fracture rate associated with Turner syndrome (TS), the exact mechanism remains unclear. We tested the hypothesis that muscle dysfunction in patients with TS contributes to increased fracture risk. The secondary aim was to determine whether menarche, hormone therapy duration, positive fracture history and genotype influence muscle function parameters in patients with TS. DesignA cross-sectional study was conducted in a single university hospital referral centre between March 2012 and October 2013. PatientsSixty patients with TS (mean age of 13745years) were compared to the control group of 432 healthy girls. MeasurementsA Leonardo Mechanograph((R)) Ground Reaction Force Platform was used to assess muscle force (F-max) by the multiple one-legged hopping test and muscle power (P-max) by the single two-legged jump test. ResultsWhile the F-max was normal (mean weight-specific Z-score of 011 +/- 077, P=027), the P-max was decreased in patients with TS (Z-score of -093 +/- 15, P<0001) compared with healthy controls. The muscle function parameters were not significantly influenced by menarcheal stage, hormone therapy duration, fracture history or genotype (linear regression adjusted for age, weight and height; P>005 for all). ConclusionF(max), a principal determinant of bone strength, is normal in patients with TS. Previously described changes in bone quality and structure in TS are thus not likely related to inadequate mechanical loading but rather represent a primary bone deficit. A decreased P-max indicates impaired muscle coordination in patients with TS.