Histochemical and metabolic changes in lower leg muscles in exercise-induced pain.

Intramuscular pressure, fiber type distribution, relative cross-sectional area of slow-twitch muscle fibers, muscle lactate, and water content were studied in eight patients with medial tibial syndrome and in eight patients with chronic anterior compartment syndrome. The variables were determined before and after standardized exercise that provoked lower leg pain. In patients with medial tibial syndrome, the intramuscular pressures in the deep posterior compartment were not elevated before or 10 min after exercise. In patients with chronic anterior compartment syndrome, there was a significant post-exercise increase from 9 +/- 9 to 48 +/- 35 mmHg (P less than 0.01) in the anterior tibial compartment. The patients with medial tibial syndrome and chronic anterior compartment syndrome had a predominance of slow-twitch fibers in the deep posterior (69% and 77%, respectively) as well as in the anterior tibial (69% and 80%, respectively) compartments. The slow-twitch muscle fibers covered less cross-sectional area than could be expected from the fiber composition. Muscle lactate concentration did not increase after exercise in any of the patient groups in contrast to the healthy controls in whom there was an increase (P less than 0.05). The lactate change ratio (post-exercise/pre-exercise) correlated negatively to the percentage of slow-twitch muscle fibers (P less than 0.05) in the patients but not in the healthy controls. Muscle water content increased for both patient groups in the anterior tibial but not in the deep posterior compartment. The findings indicate that the chronic anterior compartment syndrome is related to changes on the muscle fiber level and to a subsequently changed anaerobic metabolism and fluid infiltration.(ABSTRACT TRUNCATED AT 250 WORDS)