Motions of the Running Cheetah and Horse

1. What they did

The horse is perhaps the most efficient running animal there is, built for running a long way without tiring. The cheetah is the fastest of all animals over a short dash but has little endurance. The author compared how the two run, to find out what gives the cheetah its speed.

• The cheetah. Walt Disney Productions supplied film strips of a running male cheetah from the film “African Lion”. The author traced 155 successive frames and redrew them as a composite, with each image in its correct position relative to the others. The film was not sharp and low plants often hid the feet, but there were enough near-identical frames to fix a ground line.
• The horse. He analysed the same way the 1948 film of the racehorse “Citation” winning the American Derby, and Muybridge’s 1899 photographs of galloping horses.
• Records. He also gathered published speed and endurance records for horses, people, the pronghorn, the Mongolian wild ass and the cheetah.

2. What they found

Speed and endurance

• Cheetah speeds are widely quoted but poorly documented. One reported test of a trained cheetah at about 71 mph had to be disregarded: the enclosure was only about 65 yards long, the timing was inexact, and the arithmetic was wrong. The general consensus is that cheetahs can run at least 70 mph.
• The filmed cheetah was running at an estimated 37½ to 49 mph, among shrubs 6 to 24 inches high. The longer of its two dashes was about 325 yards.
• The horse has run ¾ mile at 43.27 mph and could probably average 44 mph for 300 yards. Horses also have great endurance; the Mongolian wild ass appears to have even more, with one animal running 29 miles before it stopped from exhaustion.
• The cheetah seldom runs more than ¼ mile. It almost always overtakes its prey, but often gives up if the prey gets up and runs again.

Footfalls and stride

• The horse uses the transverse gallop: the leading forefoot is followed by the hind foot on the other side of the body. The cheetah uses the rotary (lateral) gallop: the leading forefoot is followed by the hind foot on the same side. The cheetah must swing its hind legs outside its forelegs, because both hind feet pass ahead of both forefeet when the body is flexed.
• The horse has all four feet off the ground once in each stride, for about a quarter of the stride. The cheetah is airborne twice (when bunched up and when stretched out), and the author believes sometimes a third, brief time between the two front footfalls. Altogether it is off the ground for about half of each stride.
• At about 35 mph the horse takes about 2¼ strides per second; at about 45 mph the cheetah takes about 2½.
• The horse’s leading legs carry it longer than its trailing legs, so it changes lead to spread the strain. The cheetah’s legs share the work more evenly, and it changes lead often to follow dodging prey: three times in 33 strides and nine times in 34 strides in the film. It can change lead quickly and smoothly at the moment its front and hind feet pass each other.
• Horse strides recorded by Muybridge ranged from nearly 19 to nearly 23 ft (average 22.8 ft). Assuming the cheetah was 7 ft long, its strides were 21 to 26 ft (average 23 ft). So the much smaller cheetah covers at least as much ground per stride: about 8½ to 11½ times its shoulder height, against 4½ to 5 times for the horse.

Body and back

• The horse’s forelegs mostly support it. They lift its forequarters slightly, but this slows it by only about 0.034 mph. The cheetah’s forelegs give little support, and its shoulders fall the whole time its front feet are on the ground.
• The cheetah bends and straightens its back strongly; the heavy horse keeps its back nearly rigid. The angle between pelvis and shoulder blade changes by about 130° in the cheetah and about 60° in the horse. Bending shortens the cheetah’s body by about 16 inches, the horse’s by about 9.
• Because the cheetah bends its back while its front feet hold the forequarters still, and stretches out while its hind feet hold the hindquarters, its body moves forward like a measuring worm (inchworm). This adds nearly 15 inches per stride, worth about 2 to 2¾ mph at around 40 mph, and probably at least 3 mph at 60 mph.
• The cheetah lifts its feet high (about one-third higher than the horse’s for the front feet and the trailing hind foot), so they travel farther and gather more backward speed before striking the ground.

Body size

At about 125 lbs, the cheetah is about one-ninth the weight of a horse and about 14 times that of a red fox. Heavy animals must run economically to avoid impossible strain on their muscles, so the horse keeps its body steady. The cheetah only needs to run 400 to 600 yards, so it can use every means of gaining speed without regard to efficiency.

3. What they concluded

• The cheetah’s speed comes mainly from its very long stride, helped by a faster rate of stride.
• Its stride is long because it has two main airborne periods instead of one, spends more of each stride airborne, swings its legs further, and bends and straightens its back in time with its legs so that it moves forward like a measuring worm.
• Its stride is fast because its smaller muscles contract faster, its back muscles and leg muscles move the legs at the same time, its feet gather speed before landing, its forelegs do little supporting, its legs fold more as they swing forward, and its shoulders and hips move slightly slower than the rest of the body while their legs push.
• The cheetah is about the best size for top speed: small enough to be built for speed with little regard for efficiency, but large enough for a long, rapid stride, a wide view, independence from small bumps in the ground, and enough weight to bring down its prey.

6. Other technologies, skills or innovations

• Frame-by-frame tracing of motion-picture film with a Recordak Film Reader, with registration points used to rebuild each run as one composite picture in correct spatial relationship.
• Footfall diagrams showing how long each foot is on the ground during one stride (Fig. 3), and plots relating body length and the height of shoulders and hips to each footfall (Fig. 7).