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When a new weightlifter admires her bulging biceps or developing deltoids, she might assume larger muscles mean new muscle cells. In reality, skeletal muscle cells—those attached to the skeleton that enable voluntary movement—have a surprisingly long life span.
Skeletal muscle, also called striated muscle, is one of the three primary muscle tissues in the body, alongside cardiac and smooth muscle. Research suggests that, like neurons, skeletal muscle cells do not divide after birth. Instead, they can increase in size by adding more muscle fibers and organelles.
Carbon‑14 dating of muscle cells near the rib cage revealed ages up to 15.1 years, a finding reported by Dr. Jonas Frisén and colleagues at the Karolinska Institute in Stockholm. This demonstrates that most muscle fibers persist for many years.
Professional bodybuilders therefore do not possess more muscle cells than the average person. Their cells contain a higher density of fibers and mitochondria—the cellular “powerhouses”—which contribute to increased strength and hypertrophy.
