Capillarity, fibre types and fibre morphometry in different sampling sitesacross and along the tibialis anterior muscle of the rat

Capillarity, fibre types, fibre cross-sectional areas and perimeters were s tudied along and across the rat tibialis anterior muscle. The muscle was se ctioned at three different levels (proximal, equatorial and distal) choosin g five sampling fields for measurements at each level (from anterior to pos terior and lateral to medial zones). Significant differences were found in the percentage of fibre types and capillarity between different fields of t he same muscle section. Slow oxidative fibres were confined to the posterio r muscle zone with a maximum of 3.7%. The posterior fields also had a great er percentage of fast oxidative glycolytic fibres at proximal (72.3%) and e quatorial (61.3%) levels, but a lower value at the distal level (44.8%) and lower capillary density counts in total cross-section means (758 vs. 1,069 capillaries/mm(2) in equatorial and 1,035 capillaries/mm2 at proximal leve ls). The uneven distribution of both fast fibre types and the different deg rees of capillarisation along the muscle are statistically significant and may be due to different biomechanical performances along the rat tibialis a nterior. Fibre size was significantly larger at the distal level, but no mo rphometric differences were found across the section of the same level. At the distal level, the mean total fibre area of fast glycolytic fibres (5,13 0 mu m(2)) and fast oxidative glycolytic fibres (2,493 mu m(2)) contrasted with values at the proximal (fast glycolytic: 4,070 mu m(2), fast oxidative glycolytic: 1,970 mu m(2)) and equatorial (fast glycolytic: 3,535 mu m(2), fast oxidative glycolytic: 1,714 mu m(2)) levels. The differences along an d across the muscle show the need to design a standardised procedure for sa mple location when performing comparative studies of morphofunctional adapt ive changes in skeletal muscle. A significant difference between individual s (animals) in all parameters was evident and should be taken into consider ation when analysing the variability: the factor 'animal' should be conside red in multiway ANOVAs, especially when low sample sizes are used. Copyrigh t (C) 2000 S. Karger AG,Basel.