Formation of unique vacuoles in tenotomized rat soleus muscle fibers

Low-frequency fatigue as an indicator of eccentric exercise-induced muscle injury: the role of vitamin E

This study investigates whether vitamin E can attenuate eccentric exercise-induced soleus muscle injury as indicated by the amelioration of in situ isometric force decline following a low-frequency fatigue protocol (stimulation at 4 Hz for 5 min) and the ability of the muscle to recover 3 min after the termination of the fatigue protocol. Adult male Wistar rats were divided into vitamin E-supplemented or placebo-supplemented groups studied at rest, immediately post-exercise or 48 h post-exercise. Daily dl-α-tocopheryl acetate intraperitoneal injections of 100 mg/kg body mass for 5 consecutive days prior to exercise doubled its plasma levels. Fatigue index and recovery index expressed as a percentage of the initial tension. FI at 0 h post- and 48 h post-exercise respectively was 88% ± 4.2% and 89% ± 6.8% in the vitamin E groups versus 76% ± 3% and 80% ± 11% in the placebo groups. RI was 99% ± 3.4% and 100% ± 6% in the vitamin E groups versus 82% ± 3.1% and 84% ± 5.9% in the placebo groups. Complementally to the traditionally recorded maximal force, low-frequency fatigue measures may be beneficial for assessing injury-induced decrease in muscle functionality.

Recent advances in the understanding of skeletal muscle fatigue

Prolonged or repeated contractions of skeletal muscles lead to impaired muscle function, fatigue develops. Fatigue may be caused by factors within the muscle cells (peripheral fatigue) and diminished activation from the central nervous system (central fatigue). The relative importance of peripheral central fatigue depends on the type of physical activity. Central fatigue may be more prominent in elderly subjects. Increased concentration of inorganic phosphate seems to be of major importance for acute peripheral fatigue. There is frequently a long-lasting depression of force production after fatiguing muscle activity, especially at low stimulation frequencies. This low-frequency fatigue seems to be due to "structural" changes in proteins involved in intracellular Ca handling. Contractions in which the muscle is stretched (eccentric contractions) cause muscle weakness and damage. The initial defect induced by eccentric contractions is overstretched sarcomeres, but these appear to cause localized membrane tears that subsequently contribute to muscle weakness and damage.