Changes in maximal aerobic capacity, body composition, and running capacity with prolonged training and detraining in Standardbred horses

This study tested the hypothesis that 12 weeks of training would significantly alter maximal aerobic capacity (VO₂max), running capacity, and body composition in mature Standardbred horses, and that these alterations would be maintained over an additional 60 weeks of training. It was also hypothesised that there would be a reversal of the training-induced adaptations with 20 weeks of detraining. Eight rested Standardbred horses (n=4 mares, n=4 geldings, 3-8 years) were trained for 72 weeks and then undertook 20 weeks of detraining in groups of four per two-acre paddocks. Body composition, VO₂max, run time to fatigue, and distance completed were assessed before training, at 12 and 72 weeks of training, and after 20 weeks of detraining (92 weeks). VO₂max (P<0.05), run time to fatigue (P<0.05), and distance completed (P<0.05) increased in both sexes after 12 weeks of training. Geldings, however, had a greater run time to fatigue (P<0.05) and total work completed (P<0.05) during incremental exercise. Aerobic and running capacities were subsequently maintained over the 72-week training period, as well as the 20- week detraining period, with no significant sex differences. Body compositions were altered in both sexes (P<0.05) between 12 and 72 weeks of training and were subsequently maintained with 20 weeks of detraining. Geldings were leaner at 12 weeks and at 92 weeks compared to the mares (P<0.05). Fat-free mass remained unchanged after 72 weeks of training but decreased (P<0.05) after 20 weeks of detraining. These results document that aerobic and running capacities can be improved with training and then maintained after a prolonged training and detraining period. Further, given a long enough training period, moderate fat gain may not hinder running performance.