Ageing is associated with reduced transport and utilization of O2, diminishing exercise tolerance. Reductions may occur in cardiac output (delivery), and skeletal muscle oxidative capacity (utilization). To determine the reversibility of the declines in the muscular determinants of these limitations, skeletal muscle morphological, angiogenic and biochemical responses to acute exercise and endurance training were investigated in female Fischer 344 rats (n = 42; seven groups of six rats) aged 6 (Y) and 24 (O) months compared with resting untrained controls (YC, OC). Treadmill training lasted 8 weeks (10 deg incline, 1 h per day, 5 days per week). Two groups ran at maximum tolerated speeds (YTR, OTR), while an additional Y group (YTM) trained at OTR speed. There was no effect of age on vascular endothelial growth factor gene expression in gastrocnemius muscles after acute exercise. Similarly, age did not impair the effects of training, with increases (P < 0.05; ±S.E.M.) occurring in all of the following: 1 h exercise running speed (YTR 92 ± 4% versus OTR 140 ± 25%); citrate synthase (YTR 37 ± 8% versus OTR 97 ± 33%) and β-hydroxyacyl-CoA-dehydrogenase (YTR 31 ± 7%, versus OTR 72 ± 24%) activities; and capillary-to-fibre ratio (YTR 5.2 ± 0.2% versus OTR 8.1 ± 0.2%). However, YTM muscle was unchanged in each measure compared with YC. In conclusion, these muscular responses to training were (1) not reduced by ageing, but (2) dependent on relative and not absolute work rate, since, at the same speed, OTR rats showed greater changes than YTM. Therefore, increases in exercise tolerance and muscle adaptations are not impaired in female rats up to 24 months of age, and require a smaller absolute exercise stimulus (than young) to be manifest.
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