Physiological and blood biochemical variables in horses exercising on a treadmill submerged in water.
Authors: Lindner A, Wäschle S, Sasse H H L
Journal: Journal of animal physiology and animal nutrition
Summary
# Editorial Summary Lindner and colleagues investigated how water immersion depth affects cardiovascular and metabolic responses in horses exercising on a submerged treadmill, measuring blood lactate concentration and heart rate across two standardised exercise protocols. Ten horses were tested at water depths of 10%, 50% and 80% of withers height during incremental exercise, followed by a second protocol where depth increased progressively (20–77% of withers height) whilst speed remained constant at 5.5 m/s. Blood lactate plateaued at approximately 1.9 mm after the third exercise step at shallow and moderate water depths (10–50% withers height), but notably decreased after the fourth step when submerged to 80%—suggesting a buoyancy-mediated reduction in metabolic demand—whilst heart rate similarly plateaued after the first or second step depending on water depth. These findings demonstrate that deeper water immersion does not produce the expected linear increase in physiological stress; instead, buoyancy effects appear to reduce lactate accumulation and attenuate heart rate escalation despite continued exercise intensification. For practitioners utilising aquatic conditioning programmes, this suggests that water depth represents a significant training variable capable of modulating workload independently of speed or duration, with deeper immersion potentially offering lower-impact exercise options for rehabilitation or conditioning without proportional increases in anaerobic metabolism.
Read the full abstract on PubMed
Practical Takeaways
- •Water treadmill therapy at deeper depths (80% withers height) may provide cardiovascular training stimulus at lower physiological intensity, useful for rehabilitation or conditioning of compromised horses
- •Progressive immersion depth rather than speed increase modulates exercise intensity in water, allowing practitioners to customize workload based on individual patient tolerance
- •Heart rate monitoring alone may not accurately reflect exercise intensity in aquatic environments due to buoyancy effects—blood lactate or other biomarkers provide more reliable assessment
Key Findings
- •Blood lactate concentration plateaued around 1.9 mm at 10-50% water height but decreased at 80% water height during standardized exercise test
- •Heart rate response was blunted at higher water depths, reaching plateau at step 1 with 80% water height (134 ± 10 beats/min) compared to step 3 at 10% water height
- •Increasing both water height and exercise speed does not produce continuous linear increases in blood lactate and heart rate responses
- •At maximal speed of 5.5 m/s with progressively deeper water, blood lactate peaked after step 2 then declined, suggesting buoyancy effects reduce physiological demand