Workload and spirometry associated with untethered swimming in horses.
Authors: Leguillette R, McCrae P, Massie S, Filho S Arroyo, Bayly W, David F
Journal: BMC veterinary research
Summary
# Workload and Spirometry Associated with Untethered Swimming in Horses Swimming's use as a rehabilitation and conditioning tool in equine practice has largely been based on empirical observation, partly because the challenges of recording physiological data in an aquatic environment have left the actual metabolic intensity of free swimming poorly characterised. Leguillette and colleagues equipped five fit Arabian endurance horses with modified ergospirometry facemasks and underwater electrocardiography to measure oxygen consumption, detailed ventilatory parameters, heart rate, and postexercise blood lactate and ammonia during unrestricted swimming in a 100 m indoor pool. Free swimming elicited a median oxygen consumption of 43.2 ml/(kg·min) with heart rates averaging 178 bpm—confirming submaximal aerobic exercise—whilst blood lactate remained modest at 1.5 mmol/L. Notably, horses exhibited a distinctive breathing pattern characterised by initial bradypnea (12 breaths/min for the first 30 seconds), followed by an elevated respiratory rate of 31 breaths/min, with expiration times nearly twice as long as inspiration and marked oscillations in expiratory flow coinciding with audible vibrations. For practitioners, these findings validate swimming as a genuine aerobic training stimulus without excessive lactate accumulation, whilst the unique respiratory mechanics—including the prolonged expiratory phase and unusual flow patterns—warrant consideration when assessing respiratory function or stress in horses transitioning to or recovering via aquatic work.
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Practical Takeaways
- •Swimming can be used safely for aerobic conditioning without pushing horses into anaerobic metabolism, making it suitable for rehabilitation and fitness work
- •The unique breathing pattern with prolonged expiration suggests horses naturally coordinate breathing with limb movements in water—do not force horses to hold their breath or rush their natural rhythm
- •Monitor heart rate during swimming (expect ~178 bpm in fit horses) as a practical guide to exercise intensity, since lactate remains low even at this workload
Key Findings
- •Free swimming in horses produces submaximal aerobic exercise with VO₂ of 43.2 ml/(kg·min) and heart rate of 178 bpm
- •Horses display unique breathing patterns during swimming with initial bradypnea (12 breaths/min) followed by elevated respiratory frequency (31.4 breaths/min) with expiration lasting 2.4 times longer than inspiration
- •Blood lactate (1.5 mmol/L) and ammonia (41.0 µmol/L) levels remained low, confirming primarily aerobic metabolism during untethered swimming