Adaptation and overtraining in horses subjected to increasing training loads.
Level 5 - mechanism / opinion, no new human data
Animal physiology study (CEBM Level 5)
PubMed 8063649 · doi:10.1152/jappl.1994.76.5.1908
What was done
Seven male racehorses underwent a 272-day progressive training program comprising alternating daily bouts of endurance running (target heart rate 140 beats/min) and interval training (maximal heart rate). Incremental exercise tests were conducted every four weeks, increasing to every two weeks from day 187. Researchers measured muscle glycogen, muscle lactate, energy-rich phosphates, adrenal response to adrenocorticotropic hormone, plasma and red blood cell volumes, and various blood chemical variables.
What was found
Increasing endurance exercise intensity induced weight loss, irritability, and an inability to complete training sessions. Incremental exercise test performance did not decrease. Adrenal response to adrenocorticotropic hormone was unchanged during overtraining. Muscle ATP concentration decline during maximal exercise was less during staleness, whereas plasma volume, red blood cell volume, and blood chemical variables showed no change. The abstract reports no numerical values.
Why it matters
The study demonstrates that behavioral staleness and functional exercise intolerance can develop without decrements in laboratory exercise test performance. It suggests that isolated physiological or blood chemical parameters are inadequate for detecting early overtraining.
Limits
The sample was small (n = 7) and limited to male racehorses without a non-exercising control group. Abstract results are entirely qualitative without reporting exact numerical values, effect sizes, or confidence intervals.
Cited by
- contradicts Harm Kuipers conducted a study on racehorses showing that increasing the intensity of recovery sessions caused signs of overtraining, including reduced performance and elevated resting heart rate, within one week.