Electrical muscle stimulation improves vastus medialis quality: A single-case experimental design

Background & Aims Studies have shown that qualitative changes, such as ectopic fat accumulation, are associated with muscle weakness and degeneration of the articular cartilage. This study aimed to investigate the effects and timing of electrical muscle stimulation on the vastus medialis using a single-case experimental design to evaluate improvement in muscle quality. Methods Three healthy males participated in this study. An "ABAB design" was employed over a 14-week period, alternating between baseline phases without electrical muscle stimulation (3 weeks each) and intervention phases with electrical stimulation (4 weeks each). Electrical muscle stimulation was applied to the vastus medialis for 30 min three times per week during the intervention phases. The intensity was adjusted to a tolerable level of discomfort. Sonographic echo intensity of the vastus medialis, reflecting intramuscular fat content, and body fat percentage were measured. Results During the first electrical muscle stimulation phase, the effect size based on the percentage of non-overlapping data in echo intensity was 0% for all three subjects compared to the baseline. However, during the second baseline phase, subjects A and C achieved 100% (indicating very effective changes). In the second electrical muscle stimulation phase, all subjects exhibited 100%. No significant changes in body fat percentage were observed during the study. Conclusions These findings suggest that electrical muscle stimulation must be sustained for at least 4 weeks to effectively reduce intramuscular fat and improve vastus medialis muscle quality.