This study aims to clarify the effectiveness of electrical stimulation-induced muscle contractions during immobilization in reducing skeletal muscle pain and to understand the underlying mechanisms.
Twenty-nine Wistar rats were divided into the following three groups: Control group (CON; normal housing without intervention), Immobilization group (Im; immobilization of bilateral ankle joint only), and Electrical muscle stimulation group (EMS; Muscle contraction induced via electrodes during immobilization). The conditions of electrical stimulation were as follows: the intensity was 4.7 mA, the frequency was set at 50 Hz, and the duty cycle was 1:1 (2 seconds of contraction/2 seconds of rest), performed for 15 minutes, 6 days a week, for 2 weeks.
Behavior tests as the pressure pain threshold was performed during the experiment, and after that the lateral gastrocnemius muscle was collected for analysis. Then, the pressure pain threshold test was conducted, followed by the collection of the lateral gastrocnemius muscle for analysis. Pressure pain thresholds are believed to be primarily influenced by the superficial layer of the lateral gastrocnemius muscle, therefore all analyses of muscle samples were focused on this layer of skeletal muscle.
The pressure pain thresholds in the IM and EMS groups were significantly lower than in the CON group, but the EMS group had significantly higher thresholds than the IM group. The number of myonuclei and macrophages in the EMS group was significantly higher than in the IM group, with no significant differences compared to the CON group. The cross-sectional area (CSA) of muscle fibers in the EMS group was significantly larger than in the IM group but smaller than in the CON group.
Muscle contraction through the electrical muscle stimulation would be effective in preventing immobilization-related muscle pain in the rat gastrocnemius muscle. It is suggested that the mechanism involves the prevention of muscle fiber atrophy, muscle nuclei apoptosis and accumulation of macrophage.
Immobilization is one of the unavoidable conditions throughout the medical procedures in the acute phase. One of the symptoms of disusing the skeletal muscle is muscle pain. It is important to prevent the muscle pain in physiotherapy. This study’s findings provide important insights into therapeutic interventions to prevent immobilization-related muscle pain.
Muscle pain
Muscle contraction
