Balancing training load, rest and musculoskeletal injury risk: a mathematical modelling study in Thoroughbred racehorses.

Musculoskeletal injuries (MSI) in Thoroughbred racehorses are a leading cause of death and premature retirement, and are heavily influenced by training practices. Greater distances of high-speed galloping accumulated during racing campaigns are associated with MSI. Bone injury is the most common MSI, and understanding how training practices influence bone damage accumulation is critical for improving both horse welfare and racing outcomes. This study builds on an existing mathematical model of bone adaptation and damage to investigate the impact of different training programmes on bone injury risk. Several training programmes (three progressive, four race-fit, six rest programmes and two with rest replaced by low-intensity training) were constructed to reflect representative practices undertaken by professional trainers in Victoria, Australia. Training programmes varied in training volume, rest frequency and programme duration. Lower-volume training programmes that included high-speed training achieved sufficient bone adaptation with less accumulation of bone damage, and subsequently lower risk of bone failure. In addition, incorporating more frequent rests (minimum of two per year) and/or longer rest periods (minimum of six weeks) reduced bone damage owing to the extended opportunity to remove and repair bone damage. These results provide an in silico mathematical model of the bone's response to training, demonstrating the effects of training programmes on bone adaptation, damage formation and repair. The findings can guide the design of training programmes that balance both bone adaptation and bone health throughout a horse's racing career.