Figure 2. Electron micrographs of longitudinal sections illustrating muscle damage following eccentric exercise in human skeletal muscle.

All muscle sections were obtained from the same subject. Normal ultrastructural profiles were observed in control (a) and in day 14 muscle biopsies (b). Eccentric muscular contractions gave rise to extensive disorganization of the myofibrillar ultrastructure immediately after exercise (c) and at day 1 post exercise (d, e and f). Overall, eight subjects experienced muscle damage (n = 2, post exercise; n = 8, day 1). Streaming, disruption and dissolution of the Z-disk were frequently observed. Severe Z-disk damage was associated with A-band disruption and misalignment of myofibrils (c, d, e and f). Disturbances of the cross-striated band pattern were focalized along the longitudinal sections (c). Scale bars: 1 μm.