The myotonic dystrophy type 1 (DM1) is the most common adult muscular dystrophy. DM1 is clinically characterized by a decrease of muscle strength during adolescence and adulthood, resulting in a decrease of functional capacity. In this population, gait is characterized by a lack of hip and knee range of motion, as well as lower ankle power generation during the push-off phase. Distal muscle weakness can be suspected as a key parameter resulting in such gait adaptation in people with DM1. The aim of this study was to explore the relationship between lower limb muscle strength and spatiotemporal gait parameters in adults with DM1.

An instrumented gait analysis, including kinematic and kinetic measurements was performed in 17 adults with DM1. All participants were asked to walk at their comfortable speed along a 13-meter walkway. Maximal isometric muscle strength was measured at the hip and knee joints by an experimented assessor using hand held dynamometer. Ankle power generation during walking was used as plantar strength indicator.

Ankle peak power generation was correlated with stride length (r=0.64) and walking speed (r=0.76, P<0.01). Stride length was also correlated with maximal contralateral (r=0.64) and ipsilateral (r=0.68) knee extensors strength (P<0.01) and maximal contralateral (r=0.59) and ipsilateral (r=0.53) hip abductors strength (P<0.05). Linear regression models were fitted using a forward stepwise model selection procedure to explain the variance of spatiotemporal gait parameters. Maximal isometric lower limb muscle strength and ankle peak power generation were considered as independent variables. Ankle peak power generation accounted for 57% of the walking speed variance (P<0.001). Ankle power, knee extension and hip flexion account for 72% of the step length variance (P<0.05).

The present study highlighted the key role of ankle power generation and knee extensor strength on gait pattern adaptation in people with DM1.