Does sex matter in the cheetah? Insights into the skeletal muscle of the fastest land animal.

The cheetah is considered the fastest land animal, but studies on their skeletal muscle properties are scarce. Vastus lateralis biopsies, obtained from male and female cheetahs as well as humans, were analysed and compared for fibre type and size, and metabolism. Overall, cheetah muscle had predominantly type IIX fibres, which was confirmed by the myosin heavy chain isoform content (type I: 17±8%, type IIA: 21±6%, type IIX: 62±12%), whereas humans contained predominantly type I and IIA fibres (type I: 49±14%, type IIA: 43±8%, type IIX: 7±7%). Cheetahs had smaller fibres than humans, with larger fibres in the males compared to their female counterparts. Citrate synthase (16±6 vs. 28±7 µmol/min/g prot, P<0.05) and 3-hydroxyacetyl co-enzyme a dehydrogenase (30±11 vs. 47±15 µmol/min/g prot, P<0.05) activities were lower in cheetahs, whereas lactate dehydrogenase activity was 6 times higher in cheetahs (2159±827 vs. 382±161 µmol/min/g prot, P<0.001). The activities of creatine kinase (4765±1828 vs. 6485±1298, P<0.05 µmol/min/g prot) and phosphorylase (111±29 vs. 216±92 µmol/min/g prot) were higher in humans, irrespective of higher type IIX fibres in cheetahs. Superoxide dismutase and catalase, markers of antioxidant capacity, were higher in humans, but overall antioxidant capacity was higher in cheetahs. To conclude, fibre type, fibre size and metabolism differ between cheetahs and humans, with limited differences between the sexes.