Changes in maximum oxygen uptake during prolonged training, overtraining, and detraining in horses

Tyler, Catherine M., Lorraine C. Golland, David L. Evans, David R. Hodgson, and Reuben J. Rose. Changes in maximum oxygen uptake during prolonged training, overtraining, and detraining in horses. J. Appl. Physiol. 81(5): 2244–2249, 1996.—Thirteen standardbred horses were trained as follows: phase 1 (endurance training, 7 wk), phase 2 (high-intensity training, 9 wk), phase 3 (overload training, 18 wk), and phase 4 (detraining, 12 wk). In phase 3 , the horses were divided into two groups: overload training (OLT) and control (C). The OLT group exercised at greater intensities, frequencies, and durations than group C. Overtraining occurred after 31 wk of training and was defined as a significant decrease in treadmill run time in response to a standardized exercise test. In the OLT group, there was a significant decrease in body weight ( P < 0.05). From pretraining values of 117 ± 2 (SE) ml ⋅ kg−1 ⋅ min−1, maximal O2 uptake (V˙o 2 max) increased by 15% at the end of phase 1 , and when signs of overtraining were first seen in the OLT group,V˙o 2 max was 29% higher (151 ± 2 ml ⋅ kg−1 ⋅ min−1in both C and OLT groups) than pretraining values. There was no significant reduction inV˙o 2 max until after 6 wk detraining whenV˙o 2 max was 137 ± 2 ml ⋅ kg−1 ⋅ min−1. By 12 wk detraining, meanV˙o 2 max was 134 ± 2 ml ⋅ kg−1 ⋅ min−1, still 15% above pretraining values. When overtraining developed,V˙o 2 max was not different between C and OLT groups, but maximal values for CO2 production (147 vs. 159 ml ⋅ kg−1 ⋅ min−1) and respiratory exchange ratio (1.04 vs. 1.11) were lower in the OLT group. Overtraining was not associated with a decrease inV˙o 2 max and, after prolonged training, decreases inV˙o 2 max occurred slowly during detraining.