Muscle fibre composition and glycogen depletion in horses competing in an endurance ride.

The study explores the muscle fibre composition and how glycogen gets depleted in the middle gluteal muscle of horses undertaking an 80 km endurance ride. The findings suggest that horses with a high proportion of slow twitch high oxidative fibres tend to perform better, and prevalent glycogen depletion was generally noticed in these fibres post the ride.

Study Participants and Methods

• The study was undertaken on 16 horses who participated in an 80 km endurance ride. The muscle fibre composition and glycogen depletion patterns in the middle gluteal of these horses were studied.
• The researchers focused on the proportion of slow twitch high oxidative (ST) fibres, fast twitch low oxidative (FT), and fast twitch high oxidative (FTH) fibres, which are the main types of muscle fibres found in horses.

Findings on Muscle Fibre Composition and Race Performance

• The researchers observed that the proportion of ST fibres in horses varied between 7 and 38 per cent. The horses possessing the highest proportion of ST fibres generally had superior performance records, suggesting a possible correlation between high ST fibre count and better endurance.
• Among the other muscle fibres, FT fibres had the largest cross-sectional area, while ST and FTH were similar in size.

Observations on Glycogen Depletion

• Investigation into glycogen depletion after the ride showed significant histological evidence of depletion in ST fibres, which appeared to be completely depleted of glycogen.
• However, the depletion of glycogen was found to be variable in FTH and FT fibres, indicating that not all muscle fibres were similarly affected.
• The biochemical measurement of muscle glycogen showed a notable decrease in content—around 56 +/- 7.2 per cent (mean +/- SEM).

Implications of the Study

• This study’s findings point towards a considerable role of ST fibres and their glycogen depletion patterns in the performance of endurance races by horses.
• It also indicates a potential strategy for race training and horse selection based on the muscle fibre composition, particularly the ratio of ST fibres.