Effects of Duchenne muscular dystrophy on muscle stiffness and response to electrically-induced muscle contraction: A 12-month follow-up

•DMD patients exhibit a progressive impairment of muscle force transmission.•Electromechanical delay is sensitive to quantify degenerative effects of DMD.•Increase in muscle stiffness indicates tissue changes over 12 months in DMD.•Electromechanical delay and elastography may help detect muscle impairments for research purposes.

The present study aimed to assess the ability of muscle stiffness (shear modulus) and response to electrically-induced muscle contraction to detect changes in muscle properties over a 12-month period in children with Duchenne muscular dystrophy (DMD). Ten children with DMD and nine age-matched healthy male controls participated in two experimental sessions (T0 and T+12months) separated by 12.4 ± 0.9 months. Two contractions of the biceps brachii were electrically-induced during which an ultrasound probe was placed over the muscle. The resting shear modulus was measured using elastography from six muscles. Evoked maximal torque was increased at T+12months in controls (+11.2 ± 7.6%, P <0.001) but was not modified in children with DMD (P = 0.222). Electromechanical delay (+12.9 ± 11.3%, P <0.001) and its force transmission component (+10.1 ± 21.6%, P = 0.003) were significantly longer at T+12months than T0 for children with DMD. The results revealed an increase in muscle stiffness at T+12months in children with DMD for tibialis anterior (+75.1 ± 93.5%, P = 0.043), gastrocnemius medialis (+144.8 ± 180.6%, P = 0.050) and triceps brachii (+35.5 ± 32.2%, P = 0.005). This 12-month follow-up study demonstrates that electromechanical delay and elastography may help detect subtle muscle impairments in patients with DMD. These sensitive outcomes may improve the follow-up of innovative therapeutic interventions within the field of DMD.