Summary: A thorough knowledge of the horse's back and limb movements at different speeds is important in the design of training programmes and the prevention of speed‐related injuries. The objective of this study was to investigate changes in muscle activity and kinematics of the trot with increased speed. To evaluate these effects, 4 Saddlehorses were recorded while trotting on a horizontal treadmill at speeds ranging from 3.5–6.0 m/s. The 3‐D trajectories of skin markers on the left side of the horse and the dorsal midline of the trunk were established. Electrical activity was obtained simultaneously from 6 muscles using surface electrodes. Ten consecutive strides were analysed for each horse at each of the 5 velocity steps. The increase in speed resulted in a decrease in stride and stance phase duration, increased muscle activity and range of motion of the limbs, but a decrease in back movements. During the stance phase, the limbs appeared more loaded, which resulted in more flexion of the joints and higher excentric muscle activity. During the swing phase, the higher concentric activity of the muscles was responsible for an increased shortening of the limbs. Understanding the effects of speed on equine locomotion is a prerequisite for the development of training programmes.

Horses revolutionized human history with fast mobility¹. However, the timeline between their domestication and their widespread integration as a means of transport remains contentious^2–4. Here we assemble a collection of 475 ancient horse genomes to assess the period when these animals were first reshaped by human agency in Eurasia. We find that reproductive control of the modern domestic lineage emerged around 2200 bce, through close-kin mating and shortened generation times. Reproductive control emerged following a severe domestication bottleneck starting no earlier than approximately 2700 bce, and coincided with a sudden expansion across Eurasia that ultimately resulted in the replacement of nearly every local horse lineage. This expansion marked the rise of widespread horse-based mobility in human history, which refutes the commonly held narrative of large horse herds accompanying the massive migration of steppe peoples across Europe around 3000 bce and earlier^3,5. Finally, we detect significantly shortened generation times at Botai around 3500 bce, a settlement from central Asia associated with corrals and a subsistence economy centred on horses^6,7. This supports local horse husbandry before the rise of modern domestic bloodlines.