Structural and ultrastructural changes in skeletal muscle associated with long-distance training and running

The histological and ultrastructural features of 21 males and 8 females were monitored during an 18- to 20-month training period, during which the training distance was gradually increased. The training period was divided into three periods of 6, 5, and 7 months, respectively. The first, second, and third periods were concluded with a 15-, 25-, 42-km road race, respectively. The competitive distance always exceeded the maximal distance covered in any previous training session. Percutaneous biopsies were taken from the vastus lateralis muscle 5 days before each contest as well as 0.5-6 h post-contest and 8-9 days post-contest. No shift in fiber type was observed during the training period from the 15-km contest until the 42-km contest nor were any changes in fiber diameter observed. Histological examination demonstrated a gradual increase in degenerative changes during the training period, which occurred in type I as well as in type II fibers. Ultrastructural examination revealed irregular Z-lines and hypercontraction immediately after exercise. No damage to the sarcolemma was detected. The number of degenerative changes after each contest was not higher than before each race. It is concluded that long-distance running is associated with transient minor pathological changes in skeletal muscle, which are related to the total distance covered per week rather than the intensity of the exercise.