Oxygen consumption (VO2) during trotting on a 10% decline

Although there have been reports of oxygen consumption measurements of horses running on the level and incline, there are no measurements during decline locomotion. This may be due, in part, to the potential for muscle damage produced by eccentric contractions. In man, running on a 10% decline, VO2 decreased by 35% and stride frequency (SF) decreased by 3% when compared to level locomotion.

The rate of O2 consumption and SF would be decreased in horses on a 10% decline when compared to the level.

Six horses (average 467 +/- 68 kg) were acclimated to trotting on the level and decline prior to data collection. VO2 under moderate conditions was measured (using open flow respirometry) during trotting between 2.25 and 4.0 m/sec (at 0.25 m/sec increments) on a treadmill on the level and declined 10%. Stride frequencies were counted manually.

VO2 decreased (P<0.009) on the decline by an average of 45% (range 42-47%), and SF was 2.7% slower. The speed at which the minimum Cost of Transport occurs on the decline was faster than on the level. SF was reduced on the decline. No evidence of muscle soreness was noted in response to the downhill running.

Downhill trotting, eccentric exercise, can be done safely in the horse and requires almost half the energetic costs as trotting on the level. It is not known whether this is the optimum downhill gradient or if the horse adjusts its preferred speed to accommodate downhill trotting.