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

Abstract

Musculoskeletal injuries (MSI) in Thoroughbred racehorses are a leading cause of death and premature retirement in racehorses 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 programs on bone injury risk. Several training programs (three progressive, four race-fit, six rest programs and two with rest replaced by low-intensity training) were constructed to reflect representative practices undertaken by professional trainers in Victoria, Australia. Training programs varied in training volume, rest frequency and program duration. Lower volume training programs 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 (at least 2 per year) and/or longer rest periods (at least 6 weeks) reduced bone damage due to the extended opportunity to remove and repair bone damage. These results provide an in-silico mathematical model of the bone response to training, demonstrating the effects of training programs on bone adaptation, damage formation and repair. The findings can guide the design of training programs that balance both bone adaptation and bone health throughout horses racing career.

Figures (7)

• Figure 1: Schematic of a typical training preparation in Victoria, Australia. Speeds ($s_i$) are expressed in metres/second and corresponding distances ($d_i$) are expressed in metres/week. During each phase (coloured column), the indices $i$ are ordered from the fastest to slowest speed. For a typical training preparation, the durations of each training phase (in days) are $T_\text{rest} = 44$, $T_\text{pre-train} = 28$, $T_\text{slow} = 28$, $T_\text{fast} = 38$, $T_\text{prog} = T_\text{slow} + T_\text{fast} = 66$ and $T_\text{race} = 56$. The duration of the entire training program is $T_\text{total} = 194\ days$ with a rest frequency of 1.9 per year.
• Figure 2: A comparison of progressive training programs. (a--c) Simulation of bone volume fraction (blue lines) and damage (pink lines) for training programs incorporating (a) fast and light; (b) moderate; and (c) high volume progressive training preparations, as defined by MorriceWest2020Mar. The damage $D^*$ is a normalised variable, where bone failure occurs at $D^*=1$. Backgrounds are coloured based on the phase of training during preparation. (d--e) A comparison of the evolution of (d) bone volume fraction and (e) bone damage for different progressive training programs. The grey dashed line indicates the threshold at which the bone is considered to have failed. (f--g) A comparison of net changes in damage over different phases of preparation. (f) First preparation; (g) final (fourth) preparation. Changes are defined as the difference between the final value relative to the initial value within a phase of training preparation.
• Figure 3: A comparison of race-fit training programs. (a--d) Simulation of bone volume fraction (blue lines) and damage (pink lines) for training programs incorporating (a) low; (b) medium; (c) medium-high and (d) high volume race-fit training program, as defined by MorriceWest2020Mar. The damage $D^*$ is a normalised variable, where bone failure occurs at $D^*=1$. Backgrounds are coloured based on the phase of training preparation. (e--f) A comparison of the evolution of (e) bone volume fraction and (f) bone damage for different race-fit training programs. The grey dashed line indicates the threshold at which the bone is considered to have failed. (g--h) A comparison of changes in damage over different phases of a preparation. (g) First preparation; (h) final (fourth) preparation. Changes are defined as the difference in final value relative to the initial value within a phase of training.
• Figure 4: The effect of rest duration on damage accumulated during training. (a--c) Simulations of racehorse training programs are run with rest durations of (a) 4 weeks; (b) 6 weeks; and (c) 8 weeks. Horses are rested two times per year. The damage $D^*$ is a normalised variable, where bone failure occurs at $D^*=1$. Backgrounds are coloured based on the phase of training during a preparation. (d--e) A comparison of the evolution of (d) bone volume fraction and (e) bone damage for different rest durations. The grey dashed line indicates the threshold at which the bone is considered to have failed. (f--g) A comparison of changes in damage over different phases of a preparation. (f) First preparation; (g) final (fourth) preparation. Changes are defined as the difference in final value relative to the initial value within a phase of training.
• Figure 5: The effect of rest frequency on damage accumulated during training. (a--c) Simulation of bone volume fraction (blue lines) and damage (pink lines) for training programs with (a) 1 rest per year; (b) 2 rests per year; and (c) 3 rests per year. The damage $D^*$ is a normalised variable, where bone failure occurs at $D^*=1$. Backgrounds are coloured based on the phase of training during a preparation. (d--e) A comparison of the evolution of (d) bone volume fraction and (e) bone damage for different rest frequencies. The grey dashed line indicates the threshold at which the bone is considered to have failed. (f--g) A comparison of changes in damage over different phases of a preparation. (f) First preparation; (g) final preparation, preceding the end of the second year. Changes are defined as the difference in final value relative to the initial value within a phase of training.