Effect of detraining on cardiorespiratory variables in young Thoroughbred horses

Abstract

Reasons for performing study: Thoroughbred racehorses often experience interruptions to their training. Identifying the effects of these changes and how they alter athletic performance might provide an insight on to how to prevent these changes from occurring. Hypothesis: Training and detraining young Thoroughbreds alters their aerobic capacities with correlated changes in circulatory capacities; if horses remained spontaneously active in a pasture during their detraining period, their decreases in aerobic capacity during detraining would be reduced. Methods: We trained 6 Thoroughbred yearlings for 6 months using a conventional yearling race training programme. They were then detrained for 10 weeks with free range on pasture for 8 h/day and stall rest at night. Treadmill measurements of O2 transport variables were made before training (PRE), after training (TR) and after detraining (DT). A step-test protocol identified each horse's aerobic capacity (VO2max) and speed to attain it, and a steady-state run at VO2max was used to quantify O2 transport variables at each time period. Results: The mass-specific and whole-body VO2max, cardiac output (Q) and stroke volume (Vs) increased from PRE to TR. All mass-specific values decreased significantly from TR to DT; however, because body mass increased by 8.3% from TR to DT, none of the variables changed significantly from TR to DT on a whole-body basis. Conclusions: Changes in aerobic capacity are highly correlated with changes in Vs and circulatory capacity during training and detraining. Exercise activity of trained young horses free at pasture for 8 h/day is sufficient to maintain VO2max, Q and Vs during 10 weeks of DT. Potential relevance: Aerobic and cardiovascular fitness may be maintained in young Thoroughbred horses during at least 10 weeks of detraining by maintaining modest spontaneous exercise activity. © 2006 EVJ Ltd.