The locomotor kinematics of Asian and African elephants: changes with speed and size

1. What they did

How elephants move has long been argued over. Do they only walk, or do they run? How fast can they go? Writers have claimed speeds of up to 11 or even 13 metres per second (m/s) for African elephants, with little evidence. Without good data on normal elephant movement, it is also hard to spot when a captive elephant is moving abnormally, which can be an early sign of disease in the limbs or feet.

The authors filmed elephants moving freely over level trackways about 30 m long:

• The elephants. 60 elephants (46 Asian and 14 African bush elephants), from a 119 kg baby to adults of over 4600 kg, at zoos and facilities in the USA, England and Germany, and 42 working elephants in Thailand. They added published data for two more Asian elephants, for 62 in all.
• Getting different speeds. Most elephants were led by trainers; some were ridden by their mahouts or moved on their own. For fast trials they were encouraged with playful chasing, friendly elephants waiting at the end of the track, food rewards, noise and cheering, never with pain.
• Measuring each stride. Joints on the right side were marked with paint or reflective markers. Video of the central 10 m was used to time each foot’s touch-down and lift-off and to follow the hip and shoulder. Altogether about 2400 strides from 621 trials were measured.
• Analysis. They looked at how footfall pattern, the share of each stride a foot is on the ground (duty factor), stance and swing times, stride length and stride frequency change with speed and body size, compared the two species, and compared elephants with predictions for other animals.

2. What they found

Footfall pattern

• Every elephant, at every speed, used the same lateral sequence footfall pattern: left hind, then left front, then right hind, then right front. None ever trotted, paced, galloped or switched to another pattern.
• As speed rose, the four footfalls became more evenly spaced in time, moving toward a “singlefoot” where each foot lands a quarter of a stride after the last.
• Elephants never had all four feet off the ground at once. At slower speeds at least two feet were always down; above a Froude number of about 1 there were growing periods with only one foot on the ground.

Duty factor and timing

• The share of each stride a foot spent on the ground fell with speed, levelling off at the fastest speeds. The lowest value was 0.37, in a young elephant, well below earlier published values for elephants (0.49 and above).
• Front feet stayed on the ground slightly longer than hind feet in over 90% of trials, so the hindquarters reached a brief airborne phase (both hind feet off the ground) at slower speeds than the forequarters.
• Stance and swing times dropped steeply at first, then levelled out. Elephants sped up mainly by taking quicker strides, but at the fastest speeds they relied more on longer strides.

Speed and size

• The fastest elephant was a large Asian bull in Thailand (about 2790 kg) at 6.8 m/s (about 15 mph). The Thai elephants, trained for speed, were the fastest overall.
• The fastest African elephant, being chased by another, reached 5.9 m/s, close to many Asian elephants.
• Top speed did not change obviously with body size: even young elephants of about two years could move as fast as adults. But smaller elephants were relatively more athletic, with relatively longer and quicker strides and lower duty factors.
• At any given speed, smaller elephants took shorter, quicker strides.

Hip and shoulder movement

At slow speeds the hip and shoulder rose then fell during each footfall, like a stiff-legged walk. At fast speeds (around a Froude number of 1) the hip instead dipped then rose, with more bending at the hip and knee, while the shoulder kept its walking motion. Vertical movements stayed small, about 4% to 9% of hip height.

Asian versus African elephants

The two species differed statistically in several stride measures, but the differences were very small. Their footfall timing did not differ.

3. What they concluded

• Elephants never switch to a trot or gallop and never have all four feet off the ground, so in the classical sense they do not run. But several lines of evidence suggest their limb mechanics change near a Froude number of 1, toward a springier, more compressed hind limb, with the hindquarters and then forequarters gaining brief airborne phases. They prefer not to call fast elephants truly running until force-plate data are available.
• The claimed speeds of 9.5 to 11 m/s for African elephants are probably exaggerations, from speedometer and parallax errors and the excitement of a charging elephant. African elephants’ near-maximal speed is most likely about the same as Asian elephants’.
• Earlier estimates of bone stress in fast-moving elephants are probably too low, because elephants reach lower duty factors than previously thought.
• Very large elephants (over 4000 kg) might lose the ability to reach their fastest gait; more study of the largest elephants is needed.
• Elephants match many scaling predictions for other four-legged animals, but are unusual in keeping a walking footfall pattern at fast speeds. Mammoths and other extinct elephants probably moved in a similar way.
• These data set out what normal elephant movement looks like, which can help keepers spot abnormal movement and early limb disease in captive elephants.

6. Other technologies, skills or innovations

• Video at 50 to 200 frames per second, digitised in Peak Motus or SiliconCOACH software, with thigh length used to scale the images.
• White tempera paint markers (outlined in black) or infrared-reflective motion capture markers on the joints.
• Foot-on was scored when the foot stopped moving forward and foot-off when it began moving forward or upward, supported by preliminary foot-mounted accelerometer data.

7. Implications for conservation (from the paper)

• Knowing normal elephant kinematics allows abnormal movement to be identified, which could aid early diagnosis of musculoskeletal disorders in captive elephants, some of which end in euthanasia.