It is unknown whether muscle damage at the level of the sarcomere can be induced without lengthening contractions. To investigate this, we designed a study where 7 young, healthy men underwent 30 minutes of repeated electrical stimulated contraction of m. gastrocnemius medialis, with the ankle and leg locked in a fixed position. Two muscle biopsies were collected 48 hours later, one from the stimulated muscle and one from the contra-lateral leg as a control. The biopsies were analysed immunohistochemically for inflammatory cell infiltration and intermediate filament disruption. Ultra-structural changes at the level of the z-lines were investigated by transmission electron microscopy (TEM). Blood samples were collected for measurement of creatine kinase (CK) activity and muscle soreness was assessed in the days following stimulation. The biopsies from the stimulated muscle revealed macrophage infiltration and desmin-negative staining in a small percentage of myofibres in 5 and 4 individuals, respectively. Z-line disruption was evident at varying magnitudes in all subjects and displayed a trend towards a positive correlation (r=0.73, p=0.0663) with the force produced by stimulation. Increased muscle soreness in all subjects combined with a significant increase in CK activity (p<0.05) are indirectly suggestive of muscle damage, and the novel findings of the present study, i.e. 1) macrophages infiltration, 2) lack of desmin staining, and, 3) z-line disruption, provide direct evidence of damage at the myofibre and sarcomere levels. These data support the hypothesis that muscle damage at the level of the sarcomere can be induced without lengthening muscle contractions.