Lion (Panthera leo) and caracal (Caracal caracal) type IIx single muscle fibre force and power exceed that of trained humans

This study investigated for the first time maximum force production, shortening velocity ( V max) and power output in permeabilised single muscle fibres at 12°C from lion, Panthera leo (Linnaeus 1758), and caracal, Caracal caracal (Schreber 1776), and compared the values with those 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 were found in the lion sample. Only pure type I and IIa, and hybrid type IIax fibres were identified in the human samples – there were no pure type IIx fibres. Nevertheless, compared with all the human fibre types, the lion and caracal fibres were smaller ( P <0.01) in cross-sectional area (human: 6194±230 μm2, lion: 3008±151 μm2, caracal: 2583±221 μm2). On average, the felid type IIx fibres produced significantly greater force (191–211 kN m−2) and ~3 times more power (29.0–30.3 kN m−2 fibre lengths s−1) than the human IIax fibres (100–150 kN m−2, 4–11 kN m−2 fibre lengths s−1). V max values of the lion type IIx fibres were also higher than those of human type IIax fibres. The findings suggest that the same fibre type may differ substantially between species and potential explanations are discussed.