Several muscle diseases are traditionally named after the topography of muscle affection. Attention to the involvement of the axial musculature, however, is scarce, possibly due to the difficulties in assessing strength in these muscles compared with muscles of the limbs and face. Consequently, the involvement of the axial musculature is largely unexplored in muscle diseases [1]. Recently, several magnetic resonance imaging (MRI) studies have described significant involvement of the paraspinal musculature in patients with facioscapulohumeral dystrophy (FSHD) [2], and limb-girdle muscular dystrophy (LMGD) types R1 [3], R2 [4] and R3 [3, 5]. However, no

ObjectiveTo investigate intrarater reliability and concurrent and construct validity of muscle strength, balance, and functional mobility measures in individuals with noncongenital myotonic dystrophy type 1 (DM1).MethodsSeventy-eight adults with noncongenital DM1 participated in visit 1, and 73 of the them participated in visit 2 separated by 1 to 2 weeks. The assessments consisted of muscle strength tests with handheld dynamometry (HHD) and stationary dynamometry in the lower limb. The balance tests consisted of the step test, Timed Up and Go test, feet-together stance, tandem stance, 1-leg stance, and modified Clinical Test of Sensory Integration and Balance on a balance platform. The functional mobility tests consisted of the 10-m walk test (10mWT) and 10-times Sit-to-Stand test.ResultsThe HHD and stationary dynamometry had sufficient intrarater reliability for most muscle groups on a group (SEM% ≤15%) and individual (minimal detectable difference [MDD95%] ≤30%) level, but the HHD was most reliable. Stationary dynamometry measured a higher torque than HHD for all extensor muscles, but for single individuals, none of the devices were favored. Overall, intrarater reliability and validity were sufficient only for the dynamic balance tests, not the static balance tests. Both functional mobility tests were sufficiently reliable and valid, but the 10mWT was most reliable.ConclusionOverall, HHD is recommended as a reliable and valid tool for single individuals and for flexor muscles on a group level. For balance assessments, the dynamic balance tests are recommended as the most valid and reliable balance tests. Both functional mobility tests are recommended for valid and reliable outcomes, but the 10mWT was superior for reliability.