Training the equine respiratory muscles: Ultrasonographic measurement of muscle size

Abstract

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

“…The results presented here indicate that both conventional race training and high‐load IMT appear to increase the strength of the equine diaphragm, in line with results in human subjects 8,10 . A linked investigation also demonstrated an increase in diaphragm thickness, measured ultrasonographically, in association with training 1 . Although the results of the linked investigation did not show an increase in the size of the muscles of the upper airway with IMT, previous studies have indicated the potential use of IMT for the management of dynamic upper airway obstruction in both equine and human athletes 22,27 .…”

“…Finally, the association between IMT, IMSi, and race performance were not assessed in this investigation as the number of horses included in the study, and the time between examinations, were both deemed too small to obtain a meaningful difference. This study was performed alongside a linked investigation conducted in a larger population of horses which did explore the association between ultrasound measurement of respiratory muscle size and performance ratings 1 …”

“…Based on this information, with power β = 0.8 and type 1 error α = 0.05, a minimum of 10 horses were to be recruited. As this investigation was conducted alongside ultrasound measurement of the respiratory muscles, which required a larger sample size, additional horses were recruited 1 . Inclusion criteria required horses to be considered ‘race fit’ by the trainer and to continue in training and competition in National Hunt races for the 10 weeks of the study period.…”

“…In human athletes there is a training‐induced adaptation of the respiratory muscles 1 , 2 with an increase in the inspiratory muscle strength following both non‐specific strength training and specific inspiratory muscle training (IMT). 1 , 2 , 3 IMT has been used as an ergogenic aid in healthy human subjects, with investigations demonstrating an improvement in athletic performance 4 and a change in a range of physiological parameters 5 , 6 but most importantly attenuation of inspiratory muscle fatigue.…”

“…In human athletes there is a training‐induced adaptation of the respiratory muscles 1 , 2 with an increase in the inspiratory muscle strength following both non‐specific strength training and specific inspiratory muscle training (IMT). 1 , 2 , 3 IMT has been used as an ergogenic aid in healthy human subjects, with investigations demonstrating an improvement in athletic performance 4 and a change in a range of physiological parameters 5 , 6 but most importantly attenuation of inspiratory muscle fatigue. 7 In addition, there is a correlation between diaphragm thickness and inspiratory muscle strength in people, 8 , 9 , 10 with an increase in diaphragm thickness and inspiratory muscle strength (measured by maximal inspiratory pressure) following IMT.…”