High speed galloping in the cheetah (Acinonyx jubatus) and the racing greyhound (Canis familiaris): spatio-temporal and kinetic characteristics

1. What they did

Cheetahs and racing greyhounds are about the same size and build, yet cheetahs are far faster: the fastest recorded cheetah averaged 29 m/s (about 104 km/h) over 200 m, while greyhounds top out at about 17 m/s. Earlier anatomical studies found no clear reason for the difference. The authors compared how the two species gallop, to see how cheetahs reach such speeds and to test three proposed limits to top speed: how fast a leg can be swung forward, how much force a leg can take, and muscle power.

• The animals. Nine captive-bred cheetahs (three at ZSL Whipsnade Zoo in the United Kingdom and six at the Ann van Dyk Cheetah Centre near Pretoria, South Africa) and six retired racing greyhounds. All were adults, fit and regularly exercised.
• The runs. Each animal chased a mechanical lure along a track of about 90 m. About 50 m along the track, four high-speed cameras filmed both sides of the animal.
• Measuring forces. For two cheetahs at Whipsnade and all six greyhounds, the animals also ran over eight force plates set under artificial grass, which measured how hard each foot pushed on the ground in each direction.
• Analysis. From the video they measured stride length, stride frequency (strides per second), how long each foot was on the ground (stance time) and in the air (swing time), and the share of the stride each foot was on the ground (duty factor). From the force plates they worked out how much of the body weight each leg carried. They used statistical models to see how each measure changed with speed and between species.

2. What they found

The gallop

• Cheetahs ran at 8.7 to 17.8 m/s and greyhounds at 9.9 to 19.0 m/s, so the cheetahs ran far below their known top speed.
• Both species used a rotary gallop, in which the feet land in a circular sequence around the body: the non-lead forefoot, the lead forefoot, then a “gathered” airborne phase with the back flexed, the non-lead hindfoot, the lead hindfoot, and an “extended” airborne phase with the legs stretched out.
• Cheetahs often changed their lead leg in response to the bouncing lure, so they often completed the footfall pattern of the other type of gallop (the transverse gallop).
• Cheetahs spent longer in the gathered airborne phase than greyhounds. The extended airborne phase got longer with speed in both species.

Stride length and stride frequency

• In both species, stride length increased steadily with speed, and cheetahs took longer strides than greyhounds at any speed. Once stride length was adjusted for back or leg length, the difference between species disappeared.
• Cheetahs also increased their stride frequency with speed (mean 2.4 to 3.2 strides per second). Greyhounds did not, though they used higher stride frequencies than cheetahs across the speed range. Both species reached a maximum of 3.9 strides per second.

Foot timing

• Stance time got shorter with speed for all four legs.
• Cheetahs swung their legs forward more slowly on average than greyhounds (mean 0.27 against 0.24 seconds for the non-lead foreleg), but the fastest swing times were similar (0.20 and 0.19 seconds). So cheetahs seemed to have room to speed up their strides further, while the greyhounds at 19 m/s seemed to be at their limit.
• Cheetahs had lower duty factors than greyhounds on every leg except the lead hindleg.

Forces and body weight

• In the hindlegs, peak force rose with speed. In the forelegs, peak force stayed level (about 500 to 900 newtons, up to about three times body weight) while the push they gave fell as stance time shortened.
• Over a full stride, the cheetahs carried about a quarter of their body weight on each leg. The greyhounds carried 56% on the forelegs and split the rest unevenly between the hindlegs, with the lead hindleg carrying only about 18%.
• As speed rose, weight shifted onto the hindlegs. At 18 m/s, by the model, cheetahs carried 70% of their body weight on the hindlegs and greyhounds 62%.
• Both species gave strong forward pushes at the end of each stance while carrying little weight. On roughened concrete in early trials, the greyhounds’ feet slipped forward on landing and backward at push-off.

3. What they concluded

• Several differences may explain why cheetahs are faster. Their longer legs and back give a longer stride at any speed, and they can shorten their swing times to those of greyhounds, which should let them reach higher top speeds.
• Neither species often used its shortest possible swing time, so cheetahs in particular may reach even higher stride frequencies at greater speeds.
• The forelegs kept a constant peak force as speed rose. A simple foreleg force limit seems unlikely, though, because turning, braking and swiping at prey probably load the forelegs more than straight running.
• Carrying more weight on the hindlegs at speed may reduce the risk of slipping and free the forelegs for catching prey. The authors suggest the cheetah’s very flexible back lets them place their hindlegs further forward, under their centre of mass.
• Claws dug into the surface for grip, letting both species push off hard and probably accelerate faster.
• The data say nothing about the muscle power limit. Top speed is probably limited by several factors, both mental and physical; the authors believe the captive cheetahs ran slower than wild ones mainly through lack of motivation, not ability.

6. Other technologies, skills or innovations

• A laboratory method taken into the field: force plates and high-speed video used together at a zoo, with a hole dug in the track, a steel frame on compacted sand, and eight Kistler force plates under artificial grass.
• Four AOS high-speed cameras, two on each side of the track, synchronised to Global Positioning System (GPS) time; video analysed in VirtualDub and custom Matlab software, with corrections for lens distortion and parallax.
• Body mass calculated from the force plate records themselves.