Diagram of the experimental setup. The cheetahs and greyhounds both chased a mechanical lure across eight Kistler force plates. A set of two AOS cameras filmed the subject from each side of the run and each set was synchronised to global positioning system (GPS) time.
A representative example of stance timing during strides at various speeds. Red bars represent the stance periods of each limb of the cheetah and blue bars those of the greyhound during a complete stride at different speeds. The dashed vertical lines represent the end of the stride. Both animals use a rotary gallop whereby the non-lead forelimb (NLFL) contacts first followed by the lead forelimb (LFL). This is followed by the gathered aerial phase when the feet are pulled together prior to the non-lead hindlimb (NLHL) contact. Last to contact is the lead hindlimb (LHL); this is followed by the extended aerial phase where the feet are extended away from the body before the stride cycle starts again. Slow: 8 to <12 m s–1; medium: 12 to <14 m s–1; fast: >14 m s–1.
Variation in stride frequency (left) and stride length (right) with increasing speed in the cheetah (red +) and greyhound (blue x). Stride length significantly increased with speed (P<0.01) and cheetahs used significantly longer strides than greyhounds (P<0.01). Stride frequency showed a gradual increase with speed in the cheetah (P<0.01) but no significant change in the greyhound. Across the whole speed range the greyhound used significantly higher stride frequencies than the cheetahs (P<0.01). Lines represent predicted means from the linear mixed models (LMM) ± s.e.m.
Variations in stance time (left), swing time (middle) and duty factor (right) with increasing speed in the cheetah (red +) and greyhound (blue x) for the NLFL. Both stance time and duty factor showed a curvilinear decrease with speed (P<0.01). In the cheetah, swing time decreased with increasing speed, but a weak increase with increasing speed was observed in the greyhound. Cheetahs used significantly longer swing times (P<0.01) and significantly lower duty factors (P<0.01) than the greyhounds. This pattern was observed on all limbs except the LHL, for which cheetahs used significantly longer stance times and swing times, and there were no significant species differences in duty factor. Lines represent predicted means from the LMM ± s.e.m.
Mean vertical and cranio-caudal ground reaction force (GRF) curves (±s.e.m.) for stances of each limb for cheetahs (red) and greyhounds (blue) within various speed ranges: slow: 8 to <12 m s–1; medium: 12 to <14 m s–1; fast: >14 m s–1.
Variations in limb peak vertical force (BW, body weight) and limb vertical impulse with increasing speed in the cheetah (red +) and greyhound (blue x). Variations are shown for each of the limbs, whereby lines represent predicted means from the LMM ± s.e.m. Both forelimbs showed a significant decrease in vertical impulse with increasing speed (P<0.01), and the vertical impulse applied by the cheetah's LHL was significantly larger than that applied by the greyhound's. The NLHL showed a significant increase in peak vertical force with speed (P<0.01), but no significant species variation in peak force was apparent.
GRF curves for the greyhound whilst on a concrete surface (A,B) and an artificial grass surface (C,D). Red line, vertical GRF; green line, cranio-caudal force; black line, medio-lateral force. When little body weight is being supported in the later part of stance, the greyhound is still able to apply large propulsive forces on the artificial grass, but not on the concrete surface. B and D represent the ratio of horizontal (Fx) to vertical (Fz) forces, providing an estimate of the coefficient of friction, which is large at the end of stance whilst on the artificial grass surface.