Surface electromyography (EMG) amplitude during resistance exercise performed to task failure does not reliably reflect muscle fiber activation or anabolic signaling, indicating that EMG is an inadequate surrogate for underlying muscle physiological responses under these conditions.

When you lift weights until you can't do another rep, your body forces all muscle fibers to work hard, no matter how heavy the weight is. This full effort builds up waste products in the muscle, which turn on growth signals inside the cells. The electrical signal measured on the skin doesn't match what's happening inside because it can't capture how all fibers are being used or how the waste products trigger growth.