High-density surface electromyography as biomarker of muscle aging.

Sarcopenia is a muscle disease with adverse changes that increase throughout lifetime, but with different chronological scale between individuals. Addressing "early muscle aging" is becoming a critical issue for prevention. Through the CHRONOS study, we demonstrated the ability of the high-density surface electromyography (HD-sEMG), a non-invasive, wireless, portable technology, to detect both healthy muscle aging and accelerated muscle aging related to sedentary lifestyle, one of the risk factors of sarcopenia. The HD-sEMG signals were analyzed in 91 healthy young, middle-aged and old subjects (25-75yrs) distributed according to their physical activity status (82 active and 9 sedentary; IPAQ) and compared with current methods for muscle evaluation including muscle mass (dual-energy X-ray absorptiometry, ultrasonography), handgrip strength, physical performance. The HD-sEMG signals were recorded from the rectus femoris during sit-to-stand trials, and two indexes were analyzed: Muscular Contraction Intensity and Muscle Contraction Dynamics. The clinical parameters did not differ significantly across the aging and physical activity levels. Inversely, the HD-sEMG indexes were correlated to age, and were different significantly through the age categories of the 82 active subjects. They were significantly different between sedentary subjects aged 45-54 years and active ones at the same age. The HD-sEMG indexes of sedentary subjects were not significantly different from those of older active subjects (≥55years). The Muscle thicknesses evaluated using ultrasonography were different significantly between the 5 age decades, but did not show a significant difference with physical activity. The HD-sEMG technique can assess muscle aging and physical inactivity-related "early aging" outperforming clinical and DXA parameters.