The influence of exercise on bone morphogenic enzyme activity of immature equine subchondral bone.

The research explores the impact of exercise on bone morphogenic enzyme activity in young horses and compares this data to other bone-related characteristics. The study found that continuous, evenly distributed exercise, like that in the pasture group, seemingly leads to an overall increase in bone mass, and that the ratio of two enzymes – ALP and TRAP – appears to be related to this process.

Study Methods

• 43 foals were reared until 5 months of age under identical conditions, except for the type and scale of exercise. They were divided into three groups:
  • The Pasture group (and also control group) comprised of 15 foals that remained at pasture
  • The Box group had 14 foals that were kept in box stalls
  • The Training group contained 14 foals housed similarly to the Box group but were subjected to increasing daily gallop sprints
• Post weaning, eight foals from each group were euthanized. The remaining 19 animals were housed together with access to a small paddock to study the possible reversal of exercise-induced effects
• Post-mortem bone samples were collected from the femoropatellar joint and analyzed for bone morphogenic enzymes, namely alkaline phosphatase (ALP), tartrate resistant acid phosphatase (TRAP), and lysyl oxidase (LO)
• The enzymatic data was compared with calcium content, number of collagen cross-links, bone mineral density (BMD), and cross-sectional area (CSA), all of which are parameters collected in other bone-related studies from the same group of experimental animals.

Findings

• At five months, ALP levels were significantly lower, and TRAP levels were higher, in the Box and Training groups, reversing the ALP:TRAP ratio compared to the Pasture group. LO levels were lower specifically in the Box group
• Comparatively, ALP and TRAP data corresponded with modifications in CSA, but not with calcium and BMD; the latter two were the same in both the Training and Pasture groups
• The LO levels corresponded well with hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP) cross-links
• By the age of 11 months, ALP and TRAP levels normalized in most groups, except that TRAP levels in the previous Training group lagged a bit. The LO levels, meanwhile, were significantly lower in the former Box group

Conclusion

• An overall increase in bone mass, defined by the alteration in CSA, seems to be related to consistent, evenly distributed exercise, as experienced by the Pasture group
• This process seems to be related to the levels and ratio of ALP and TRAP
• Short heavy bouts of exercise superimposed on a basic rest regimen (as demonstrated by the Training group) seem sufficient for normal cross-link levels and BMD
• However, results from this study and previous studies suggest that the aforementioned exercise regimen might have a detrimental effect in the long run.