Recruitment pattern of muscle fibre type during flat and sloped treadmill running in thoroughbred horses.

The research studied the use of different muscle fibers in Thoroughbred horses during treadmill running on flat and uphill inclines. The sample involved 13 subjects and the study found that exercise intensity and duration control muscle fiber recruitment, not running speed, suggesting that uphill running can result in the same training effect as faster flat track running.

Study Objective and Methodology

• The main aim of this research was to understand the pattern of muscle fibre usage during sloped and flat treadmill running in Thoroughbred horses.
• The intensity of training was determined by VO2max percentages.
• A total of 13 thoroughbred horses were used as subjects in this experiment.
• The horses were made to undergo incremental treadmill tests on flat (0%) and sloped (10%) inclines.
• For each horse, running speed was measured at 90% and 60% of maximum oxygen usage (VO2max).
• Post exercise, biopsy samples were taken from the middle gluteal muscle for testing.
• The muscle fibers were then categorised into four types – I, IIA, IIA/IIX, and IIX – based on their biochemical properties.
• The analysis phase involved identifying the glycogen content in these sample muscle fibres using Periodic Acid Schiff staining and then comparing the results against exercise intensity.

Results

• The study found no significant differences in glycogen depletion patterns between different muscle fibre types after exercise bouts at the same intensity on different inclines.
• The researchers found consistent fibre type recruitment across all exercise bouts.
• The results suggested that the pattern of muscle fibre usage in horses was mainly determined by the exercise’s intensity and duration rather than the speed at which they were running.
• Moreover, no significant differences were found in the utilisation patterns of each muscle fibre type between the flat and the inclined treadmill exercises.

Conclusions

• This study’s findings suggest a new understanding of muscle adaptation in racehorses, mainly that muscle fibre recruitment is not dictated by running speed but rather by the intensity and duration of exercise.
• Another key conclusion drawn was that uphill running could serve as a feasible alternative to increase training intensity as it exhibited the same muscle adaptation effect as running at higher speeds on a flat track.