Abstract
Muscle soreness that has a delayed onset is a common feature among both athletes and
untrained individuals who engage in unusual exercises. This study was designed to
provide additional morphological data to assess the relevance and significance of
our previous findings that the sore muscles contain fibers with disorganized myofibrillar
material, Muscle biopsies were obtained from 12 males (mean age 25 ± 7 years), who
suffered from severe soreness in their thigh muscles 18-72 h following eccentric bicycle
exercise. Their strength performances were tested in parallel. Knee extensor strength
was decreased at all angular velocities soon after exercise but gradually increased
over the subsequent days although slower at the fastest contractions. Disturbances
of the cross-striated band pattern were constantly observed. They originated from
the myofibrillar Z-band, which showed marked streaming, broadening and, at places,
total disruption. The disturbances were found in every second to every third fiber
up to 3 days after exercise and in one tenth of the fibers 6 days following the exercise.
Type 2 fibers were predominantly affected. Thus, this eccentric exercise gives rise
to muscle soreness and influences, on mechanical basis and selectively with regard
to fiber type, the fine structure of the contractile apparatus.
Key words
human - muscles - myofibrils - muscle proteins - histocytochemistry - ultrastructure
- exertion - fatigue
