A healthy horse can produce significantly more than 1 horsepower for short bursts. Studies and anecdotal data suggest with a sprint or jump, a horse can generate up to 10–15 horsepower during intense, short efforts (e.g., a gallop or pulling a heavy load briefly). This is based on calculations of muscle force in Thoroughbreds or draft horses during maximal exertion, where peak forces can exceed 2,000 pounds for a few seconds.
Draft horses (e.g., Clydesdales, Percherons) can sustain about 0.8–1.5 horsepower over hours when pulling loads. Historical data from agricultural work shows a draft horse can pull around 10–12% of its body weight (e.g., 180–240 pounds for a 2,000-pound horse) at a steady pace of 2–3 mph for 6–8 hours.
James Watt’s original estimate of 1 horsepower was based on observing horses lifting coal or turning mill wheels, averaging their sustained effort. He estimated a horse could lift 330 pounds 100 feet per minute (33,000 foot-pounds/min), but this was conservative.
Modern tests (e.g., dynamometer studies) show horses can exceed this briefly. For example, a horse pulling a sled with 1,000 pounds of force at 4 mph generates about 2.7 hp (1 hp = 375 pound-feet/second).
Horses risk injury or exhaustion if pushed beyond their aerobic threshold for too long. Safe daily work typically stays below 70–80% of max capacity. Overloading (e.g., pulling >15% of body weight for long periods) can cause lameness or metabolic issues like colic.
Note: Copied from Grok.