Force, speed, and oxygen consumption in Thoroughbred and draft horses

Thoroughbred (TB) and draft horses (DH) havelong been selected for tasks of very different intensities andforce-speed relationships. To study their adaptations, we measuredO₂ consumption and related variables in three TB and four DH during progressive exercise tests ona level treadmill. The horses exerted a draft force of 0, 5, 10, 15, or20% of their body weight at speeds that increased by 2 m/s every 3 minuntil they could not maintain that speed. We found that TB could exertthe same draft forces as DH and, at each force, TB achieved about twicethe speed, twice the external power, and twice theO₂ consumption as DH; thus the twobreeds had the same gross efficiencies. We also found maximalO₂ consumption of TB to be abouttwice that of DH (134 vs. 72 ml · kg¹ · min¹,respectively), suggesting adaptations to high-intensity exercise. Peakefficiency was reached at lower speeds in DH than in TB, suggestingadaptations to high-force, low-speed exercise. These differencesbetween TB and DH in force-speed and aerobic capacities and in speedfor peak efficiency likely reflect different contraction velocities inlocomotor muscles.