CJ. Aerobic exercise capacity at sea level and at altitude in Kenyan boys, junior and senior runners compared with Scandinavian runners.

The study comprises data on 12 Scandinavian runners who had either trained for two weeks in Kenya (n= 6; ∼2000 meters above sea level (m.a.s.l.)) or in Portugal (n= 6; sea level (s.l.)) and on 13 Kenyan runners (9 junior and 4 senior) living and training at ∼2000 m.a.s.l. Muscle biopsies were taken before and after the training camps in the Scandinavian runners and once on the Kenyan runners from the vastus lateralis (v.l.) and the gastrocnemius muscles. Muscle fiber size and composition were similar in the various groups (4.6–5.1 × 103μm2; ST ∼60–70%; FTa 30–40%; FTb < 6.0%) with a tendency for some more (∼5%) FTa fibers in the gastrocnemius muscle. Mean number of capillaries in v.l. varies between 405–493 cap · (mm2)−1, 2.0–2.7 cap · fiber−1, and 4.4–6.2 cap around the various fiber types, with the Kenyan seniors having the highest and the Kenyan juniors the lowest values. All runners had 10–20% more capillaries in their gastrocnemius muscle. Similar levels for citrate synthase (CS) activity were found in the v.l. of the Kenyan seniors and Scandinavian runners, whereas the Kenyan juniors were 10–15% lower. The 3‐hydroxyacyl‐CoA‐dehydrogenase (HAD) activity was 20% higher in the Kenyan than in the Scandinavian runners. In the gastrocnemius muscle, both enzyme activities were 20–50% higher in Scandinavian and Kenyan runners. The ratio for lactate dehydrogenase (LDH) isoform1–2 and isoform4–5 was increased when training at altitude due to a lowering of LDH4–5 and became close to what was observed in the Kenyan runners. Also muscle buffer capacity became increased in the altitude training groups. It is concluded that muscle morphology is quite similar in Scandinavian and Kenyan runners with no effect of training at altitude. Mitochondrial enzyme activities are also unaltered at altitude, but the Kenyan runners have markedly higher HAD activity. Muscle buffer capacity is elevated in the Scandinavian runners training at altitude, and it appears to be an effect of altitude, as no change was observed in the Scandinavian runners training at s.l., which was also the case for the LDH1–2: LDH4–5 ratio as a result of a lowering of LDH4–5 activity.