Training the equine respiratory muscles: Inspiratory muscle strength

Background Little is known about the response of the equine respiratory muscles to training. Objectives To measure an index of inspiratory muscle strength (IMSi) before and after a period of conventional exercise training (phase 1) and inspiratory muscle training (IMT), comparing high-load (treatment) and low-load (control) groups (phase 2). Study design Prospective randomised controlled trial. Methods Phase 1: Twenty National Hunt Thoroughbred racehorses performed an inspiratory muscle strength test (IMST) twice on two occasions; when unfit at timepoint A (July), and when race fit at timepoint B (October). Phase 2: Thirty-five Thoroughbred racehorses at race fitness were randomly assigned into a high-load (treatment, n = 20) or low-load (control, n = 15) IMT group. The high-load group followed an IMT protocol that gradually increased the inspiratory pressure applied every 4 days. The low-load group underwent sham IMT with a low training load. The IMT was performed 5 days/week for 10 weeks. The IMST was performed twice on two occasions, timepoint B (October) and timepoint C (January). Conventional exercise training and racing continued during the study period. The peak IMSi values obtained from the different groups at timepoints A, B and C were compared using a Wilcoxon Signed Rank Test. Results Phase 1: There was a significant increase in IMSi from timepoint A: 22.5 cmH(2)O (21-25) to timepoint B: 26 cmH(2)O (24-30) (p = 0.015). Phase 2: From timepoint B to C there was a significant increase in IMSi for the high-load group 34 cmH(2)O (28-36) (p = 0.001) but not the low-load group 26 cmH(2)O (24-30) (p = 0.929). The peak IMSi at timepoint C was significantly higher for the high-load than low-load group (p = 0.019). Main limitations Single centre study with only National Hunt horses undergoing race-training included. Conclusions In horses undergoing race training there is a significant increase in IMSi in response to conventional exercise training and high-load IMT.