Resistance Training Improves Muscle Strength But Not Echo Intensity In Older Adults

Longitudinal aging studies have shown that the gradual loss of muscle strength is closely associated with changes in muscle quality, but not muscle mass. Skeletal muscle echo intensity (EI) obtained via B-mode ultrasonography reflects intramuscular adiposity and/or fibrous tissue content and shows promise as a simple measure of muscle quality among older adults. Many cross-sectional studies have shown significant relationships between EI and muscle strength, but little is known about whether resistance training enhances EI among older adults. PURPOSE: We sought to examine the effects of short-term resistance training on muscle strength, size, and EI among older adults. METHODS: Twelve older adults (2 males, 10 females, mean ± SD age = 71 ± 5 years, BMI = 25.8 ± 4.0 kg/m2) performed a supervised, lower-body resistance training program twice per week for 6 weeks. The exercises included the trap bar deadlift, leg press, leg extension, and leg curl. All exercises were performed with a full range of motion using loads corresponding to 85% of the estimated one-repetition maximum (1RM) until failure. We assessed 5RM leg extension strength, knee extensor maximal voluntary isometric contraction (MVIC) force, and vastus lateralis (VL) cross-sectional area (CSA) and EI before and after the training intervention. EI was corrected for subcutaneous adipose tissue thickness using published equations. RESULTS: Large improvements were observed for 5RM strength (+28.3%, p < .001, d = 2.09) and knee extensor MVIC force (+10.7%, p = .006, d = 0.97). The increase in VL CSA was modest (+6.0%, p = .209, d = 0.39). Corrected VL EI did not change (+0.52%, p = .804, d = 0.07). CONCLUSION: Resistance training among older adults resulted in large and modest improvements in muscle strength and size, respectively, but EI did not change. Our findings are in opposition to cross-sectional investigations showing significant associations between EI and muscle strength among older adults. This project was funded by a Learning Institute for Elders (LIFE) at UCF Gerontology Research Grant. We are appreciative of the LIFE at UCF group's support of the UCF Institute of Exercise Physiology and Rehabilitation Science.