Morphometric analysis of the capillary supply in skeletal muscles of trained and untrained subjects — Its limitations in muscle biopsies

Abstract

Muscle fiber area, capillary density, and capillary to fiber ratio were determined in needle biopsy samples ofM. vastus lateralis processed for electron microscopy from 9 untrained men (average$\dot V_{{\text{O}}_{\text{2}} }$max = 61.3 ml/min kg), 3 untrained women ($\dot V_{{\text{O}}_{\text{2}} }$max = 43.7 ml/min kg) and 5 well trained orienteers ($\dot V_{{\text{O}}_{\text{2}} }$max = 76.1 ml/min kg). The volume density of mitochondria was previously reported to be significantly higher in orienteers (7.32%) than in untrained men (5.19%) and in untrained women (4.08%) in the same material (Hoppeler et al. 1973).

The mean fiber area was found to be somewhat larger in orienteers (6,410 μm² than in untrained men (5,350 μm², not significant), but significantly smaller values were found in untrained women (3,390 μm²). The capillary density was almost identical in the three experimental groups, it ranged from 416 to 431 mm⁻². The absolute values reported for both of the above variables are subjected to a bias due to fiber shrinkage, fiber shortening and fiber kinking occurring during the needle biopsy procedure and the subsequent steps of tissue preparation. The capillary to fiber ratio is much less affected by tissue handling and significantly higher values were found in orienteers (2.70) than in untrained men (2.07) and in untrained women (1.37). There was a significant linear relationship between the capillary to fiber ratio and both$\dot V_{{\text{O}}_{\text{2}} }$max and the volume density of mitochondria for all subjects analysed, suggesting an adjustment of the capillary supply to the maximal aerobic capacity as well as to the mitochondrial content inM. vastus lateralis.