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.

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.

Inspiratory muscle training for the treatment of dynamic upper airway collapse in racehorses: A preliminary investigation.

Exercise-induced upper airway collapse (UAC) probably occurs when the stabilising muscles of the upper airway are unable to withstand the dramatic changes in airflow and pressure that occurs during exercise. In racehorses, the mainstay of treatment is surgical intervention. In human athletes, exercise-induced laryngeal obstruction has been treated successfully with inspiratory muscle training (IMT). The aims of this study were: (1) to assess the feasibility of IMT in racehorses; and (2) describe the exercising endoscopy findings pre- and post-IMT in racehorses diagnosed with dynamic UAC. Horses undergoing IMT wore a mask with an attached threshold-valve to apply an additional load during inspiration, creating a training stimulus with the purpose of increasing upper airway muscle strength. Each horse underwent IMT once daily, while standing in the stable, 5-6 days/week for 10 weeks. Endoscopy recordings were analysed in a blinded manner using an objective grading scheme and subjective pairwise analysis. Seventeen horses successfully completed the IMT protocol, with full information available for 10 horses. Objective grading analysis showed a lower grade of vocal fold collapse (6/9 horses), palatal instability (7/10 horses) and intermittent dorsal displacement of the soft palate (5/7 horses) post-IMT. Pairwise subjective analysis suggested better overall airway function post-IMT in 3/10 horses. The main limitations of this preliminary investigation were the low number of horses examined and lack of a control population. Further research is required to investigate the effects of IMT on upper airway muscle strength and to evaluate its efficacy for prevention and treatment of UAC.

Inspiratory muscle training and testing: Rationale, development and feasibility.

BACKGROUND: Inspiratory muscle training applies a training stimulus directly to the inspiratory muscles and is distinct from whole-body training. The potential benefits of inspiratory muscle training have yet to be explored in horses. OBJECTIVES: The objectives were as follows: (a) to develop an equine-specific method of testing and training inspiratory muscles; (b) to assess tolerance and feasibility in a pilot study in a commercial Thoroughbred training establishment. STUDY DESIGN: Field study. METHODS: A mask was used to interface commercial human inspiratory muscle training equipment. Ten horses undertook inspiratory muscle training once daily while stood in the stable approximately 5 days/wk over a 9-week period. Inspiratory muscle strength testing employed a continuous incremental inspiratory loading protocol alternating two loaded and two minimally loaded breaths until failure to tolerate the load occurred or the maximum 60 breaths were completed. The inspiratory muscle strength testing was undertaken twice; firstly, in 10 horses with minimal acclimatisation and secondly, in eight horses experienced with the inspiratory muscle training programme. RESULTS: The 10 horses undertook inspiratory muscle training for a median of 42 days, reaching a median peak training load of 32.5 cm H2 O. One horse did not tolerate the mask with repeated snorting and was replaced. All horses completed the inspiratory muscle strength testing. The median peak value in inspiratory muscle strength testing protocol 1 was 27 cm H2 O and in inspiratory muscle strength testing protocol 2 was 41 cm H2 O. Two of 10 horses reached the maximum possible value in inspiratory muscle strength testing protocol 1; therefore, the test was adapted to permit a higher maximum value, despite this 3/8 horses reached the maximum possible value in inspiratory muscle strength testing protocol 2. MAIN LIMITATIONS: A small number of horses were assessed. The inspiratory muscle strength testing protocol was refined during the study and requires additional refinement. CONCLUSION: Inspiratory muscle testing and training were feasible and tolerated in horses. Further research is required to understand whether the inspiratory muscle strength testing values obtained correlate with other physiological/performance outcomes. The potential benefits and/or adverse effects of inspiratory muscle training warrant further investigation.