Musculoskeletal responses of 2-year-old Thoroughbred horses to early training. 4. Morphometric, microscopic and biomechanical properties of the digital tendons of the forelimb.

The study examined the impact of early training on the physical properties of digital tendons in young Thoroughbred horses, finding that the volume and cross-sectional area of specific tendons were larger in trained horses, and the density of one particular tendon was reduced in the trained group, with these changes assumed to be adaptive and induced by training.

Objective and Methodology

• The goal of the research was to understand the impact of early training on the weight, volume, density, and cross-sectional area (CSA) of various digital tendons and ligaments in the forelimbs of two-year-old Thoroughbred horses. Also, to examine the response of superficial digital flexor tendon (SDFT) tissue to a known set of training parameters.
• In the study, the corresponding tendons of seven trained horses were inspected, segmented, and compared with those from seven untrained horses matched for age, sex, and breed.
• Biophysical and histological properties such as weight, volume, density, and CSA were determined. Other factors assessed include crimp angle, histological features, and biomechanical ultimate stress and stiffness of tendon samples from the mid-metacarpal region of the SDFT.

Findings

• On visual inspection, there was no macroscopic evidence of swelling or discoloration in any of the tendon segments.
• The volumes of SDFT and common digital extensor tendon (CDET) segments were found to be significantly larger in the trained horses compared to the untrained horses.
• A greater increase in volume than weight resulted in a lower density in the SDFT but not in the CDET of trained horses, compared to the untrained ones.
• The cross-sectional area of these two tendons was also significantly larger in the trained group.
• The number of tenocytes or tendon cells was found to be less in trained horses indicating a possible adaptive response in these cells due to training.
• No histological evidence of inflammation was observed, and there was no difference in crimp angle between groups.
• There was no significant difference in stiffness or ultimate stress levels of tendon strips between the two groups.

Conclusions

• The study concluded that the volume and CSA of the SDFT and CDET were larger in trained than untrained horses.
• This research found that the SDFT was less dense in the trained group.
• As there was no evidence of tendonitis and the crimp angle and biomechanical properties of tendon strips seemed unchanged by training, the observed changes in size and density were deemed to be adaptive and induced by the training.
• However, the researchers noted that detecting these adaptations from initial pathological increases in the size of the SDFT in in vivo settings would likely be challenging.