MITOCHONDRIAL VOLUME DENSITY IN HUMAN SKELETAL-MUSCLE FOLLOWING HEAVY RESISTANCE TRAINING

Abstract

Needle biopsies were taken from triceps brachii of 6 healthy males before and after a 6 mo. intensive weight training program. The tissue was sectioned, photographed under a Philips EM200 and subjected to sterological analysis. Cross sectional fiber areas were also calculated from cryostat sections stained for ATPase activity. Morphometric analysis indicated that training resulted in a significant 26% reduction in mitochondrial volume density and a 25% reduction in the mitochondrial volume to myofibrillar volume ratio. These changes were accompanied by significant increases in fiber area for both FT [fast-twitch, 33%] and ST [slow-twitch, 27%] fibers as determined from the light microscope. There was a significant correlation between the reduction in mitochondrial volume density and the increase in FT fiber area following training (r = 0.845). Heavy resistance training leads to a dilution of the mitochondrial volume density through an increase in myofibrillar size with hypertrophy.