A multi-sensor approach to improve interpretability of the 6-min walk test as an outcome in muscular dystrophies: an observational study

The 6-min walk test (6MWT) is commonly used to assess physical function and endurance. The purpose of this observational study was to test a newly developed biomechanical system, Ephion Mobility system, and establish whether these biomechanical measures can improve the objectivity and interpretability of the 6MWT as an outcome measure. Fifty-eight participants took part in this study: 20 participants with myotonic muscular dystrophy (DM1), 18 with Becker muscular dystrophy (BMD) and 20 healthy controls for comparison. Every DM1 participant was classified using Muscular Impairment Rating Scale, and every BMD participant was classified using the Vignos scale. Each participant performed the 6MWT while wearing the Ephion Mobility system sensors, which recorded walking distance, surface electromyography (sEMG), heart rate (HR), ground reaction force (GRF), trunk vertical acceleration and joint kinematics. Both patient groups exhibited significantly shorter walking distance, lower cadence and shorter step length. Lower HR was found in both patient groups; this increased as disease severity increased. Limited range of motion was observed during the entire walk test in both patient groups. The DM1 group showed gait alterations during toe-off with reduction in hip and knee extension and a delayed and reduced plantar flexion. As disease severity increased, visual interpretation of sEMG in the DM1 group exhibited lower amplitude in the proximal muscles. The BMD group exhibited gait alterations during contact, stance and toe-off phases. Flat foot landing was observed in the BMD group along with reduced hip flexion and ankle dorsiflexion. During stance, they were unable to extend the hip and flex the knee and muscle activity increased, and reduced plantarflexion was observed during toe-off. The GRF was lower during heel strike and higher during mid-stance, and trunk vertical acceleration was close to zero during the contact phase in both patient groups. A visual interpretation of the gait patterns showed differences among disease severity levels. Our findings show that the Ephion Mobility system can determine biomechanics during walking and is coupled with distinct patterns of walking in BMD and DM1. Ephion Mobility system is useful in obtaining observational differences among disease severities and may be responsive to progression or treatment-induced improvement. The system adds value to improving interpretability of the 6MWT and additionally be used in assessing other functional capabilities, such as sit-to-stand and stair climbing.