Inspiratory muscle training in young, race-fit Thoroughbred racehorses during a period of detraining

Training the equine respiratory muscles: Ultrasonographic measurement of muscle size

BACKGROUND

Limited information exists regarding changes in the size of respiratory and locomotor muscles in response to exercise training in the Thoroughbred racehorse.

OBJECTIVES

To describe and compare the responses of the respiratory and locomotor muscles to conventional exercise training and inspiratory muscle training (IMT).

STUDY DESIGN

Prospective randomised controlled trial.

METHODS

Thoroughbred racehorses, in training for competition in National Hunt races, were recruited from two training establishments. Ultrasonographic images were obtained for selected muscles of the upper airway, diaphragm, accessory respiratory, and locomotor systems and their sizes measured. Examinations were performed at three timepoints: (A) when unfit, (B) following 12 weeks of conventional exercise training and (C) following 10-12 weeks continued training at race fitness. In addition, horses at yard 1 performed IMT, between timepoint B and C, and were randomly assigned into high-load (treatment) or low-load (control) group. Repeated measures models were constructed to compare the change in muscle measurements over time, and to investigate the effects of yard, previous airway surgery and IMT on the change in ultrasonographic size measurements obtained.

RESULTS

Upper airway muscle size increased in response to conventional race training between timepoints A-C, and B-C. Diaphragm size increased in response to conventional exercise training between timepoints A and B. The diaphragm size of horses that undertook high-load IMT was either maintained or increased, whereas diaphragm size decreased in horses that undertook low-load IMT or no IMT between timepoints B and C. A significant interaction between gluteal muscle size and airway surgery status was observed, with greater gluteal muscle thicknesses measured in horses that had not previously undergone airway surgery (left gluteal 3.9%, p < 0.001; right 4.5%, p = 0.04).

MAIN LIMITATIONS

Low number of horses underwent IMT.

CONCLUSIONS

Respiratory and locomotor muscles increase in size in response to conventional exercise training, with a further change in diaphragm size in response to inspiratory muscle training.

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 cmH₂ O (21-25) to timepoint B: 26 cmH₂ 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 cmH₂ O (28-36) (p = 0.001) but not the low-load group 26 cmH₂ 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.