LOPEZ, C.M.*; GORTON, M.J.; HOYT, D.F.; COGGER, E.A.; WICKLER, S.J.: The energetic cost and time of contact with added limb mass in trotting horses.

Although the metabolic cost of accelerating and decelerating the limbs during terrestrial locomotion appears to be minimal, studies on humans and quadrupeds (dogs and horses) demonstrate a disproportionate increase in the rate of oxygen consumption (VO₂) when weights are added to the distal limb. One explanation for this increased VO₂ could be changes in time of contact (t_c). Because VO₂ is proportional to 1/t_c, a higher VO₂ in animals with additional mass on their distal limbs could be explained by a shorter t_c. Four horses (average mass = 486 kg) were run at two speeds, 2.5 and 4.5 m/s, with and without weight boots. Each boot averaged 708 g and was attached over the hoof (2.83 kg total = 0.58% of body mass). VO₂ was measured using open-flow respirometry. Time of contact was measured using an accelerometer placed on the lateral wall of the right hind hoof. Speeds and treatment (boots or no boots) were randomized. At 2.5 m/s, VO₂ (ml/g h, mean &plusmn SD) was increased 8% (p = 0.008) with weight boots (1.21 &plusmn 0.16 vs 1.12 &plusmn 0.12). At 4.5 m/s VO₂ was increased 5.3% (p=0.006) with weight boots (1.97 &plusmn 0.20 vs 1.87 &plusmn 0.24). At 2.5 m/s, t_c (seconds) with and without boots (0.345 &plusmn 0.019 vs 0.368 &plusmn 0.019) was not different (p=0.22). At 4.5 m/s, t_c with and without boots (0.228 &plusmn 0.009 vs 0.231 &plusmn 0.0119) was not different (p=0.34). The relatively large increase in VO₂ cannot be explained by changes in t_c. Supported by NIH# S06 GM53933.