The study was aimed at investigating if endurance training of moderate intensity and
longer duration, intended to promote health rather than performance, evokes ultrastructural
changes in skeletal muscle tissue comparable to those observed after high-intensity
protocols. Twenty healthy, middle-aged men enrolled in a 6-month, home-based jogging
program of 120 min/wk at 75 % VO2max. Only 12 men showed a sufficient exercise adherence over the 6 months (> 60 min/wk
on average) and were included into statistical analysis. Their average training activity
was 105 ± 31 min/wk. The results revealed significant increases in VO2max (± 8.4 %, p < 0.01) and submaximal power output (± 18.1 %, p < 0.01). Total mitochondrial
volume density in M. vastus lateralis increased by 20 % (p < 0.05) with a larger increase
in subsarcolemmal volume compared to central volume (50 % vs 15 %). No changes in
volume of intracellular lipid droplets, capillary density, capillary per fiber ratio,
fiber mean cross-sectional area and muscle fiber type could be observed. Body composition
analysis showed a decrease in trunk fat mass (- 7.3 %, p < 0.05) and an increase in
trunk lean mass (± 1.7 %, p < 0.05), while changes in the legs were not significant.
It can be concluded that a moderate-intensity, health oriented endurance training
beneficially affected cardiovascular and muscle oxidation capacity as well as body
composition in the trunk area. No adaptations in capillaries or lipid metabolism could
be demonstrated. The results support the hypothesis of thresholds for induction of
adaptation processes in muscle skeletal tissue depending on the intensity of the exercise
stimulus.
Key words
Jogging - morphological adaptations - cardiovascular capacity - body composition
