This study investigated for the first time maximum force production, shortening velocity (Vmax) and power output in permeabilised single muscle fibres at 12 ˚C from lion (Panthera leo) and caracal (Caracal caracal), and compared the values to that of single fibres from human cyclists. Additionally, the use and validation of previously frozen tissue for contractile experiments is reported. Only type IIx muscle fibres were identified in the caracal sample, whereas type IIx and only two type I fibres in the lion sample. Only pure type I and IIa, and hybrid type IIax fibres were identified in the human samples, but no pure type IIx fibres. Nevertheless, compared to all the human fibre types, the lion and caracal fibres were smaller (P < 0.01) in cross-sectional area (in µm2: human: 6194 ± 230, lion: 3008 ± 151, caracal: 2583 ± 221). On average, the felid type IIx fibres produced significantly greater force (191 – 211 kN·m-2) and ~3x more power (29.0 – 30.3 kN·m-2·FL·s-1) than the human IIax fibres (100 – 150 kN·m-2, 4 – 11 kN·m-2·FL·s-1). Vmax values of the lion type IIx fibres were also higher than human type IIax fibres. The findings suggest that the same fibre type may differ substantially between species and potential explanations are discussed.

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