Muscle fibre type composition in untrained and endurance-trained Andalusian and Arab horses.

This research article investigates the muscle fibre composition of Andalusian and Arab horses, noting contrasts between untrained horses and those that have undergone endurance training. The study showed that the proportions of type I and II fibres were largely stable across breed, but the influence of training results in changes to the contractile properties and oxidative capacity of type II subgroups.

Study Design and Participants

• The research utilized muscle biopsies from the middle gluteal muscle in 68 stallions. The horses studied were categorized into two breed groups: 52 Andalusian (AN) and 16 Arab (AR).
• The age of the horses involved in the study ranged from six to 12 years.
• Out of 68 stallions, seventeen AN horses and eight AR horses were untrained while the rest underwent an endurance training program for six months.
• The endurance training was of two levels: 15 AN horses undertook moderate endurance training while the remaining sequence of 20 AN horses and eight AR horses were part of a rigorous endurance training.

Results

• The percentages of type I and type II muscle fibres were found to be similar across groups. This means that the muscle fibre composition is largely stable within a particular breed or group.
• However, horses that underwent the more rigorous endurance training had notable differences in muscle fibre composition. Specifically, these horses had a higher percentage of type IIA fibres and a lower percentage of type IIB fibres as compared to the untrained horses.
• This discrepancy was valid for both the AN and AR horses involved in the study suggesting a more universal result.
• All endurance-trained horses, regardless of their breed, displayed a higher percentage of type IIB oxidative fibres and a lower percentage of type IIB non-oxidative fibres when compared to untrained horses.

Conclusion

• The research concludes that the muscle fibre composition, especially regarding type I and type II fibres, is steadfast in a given breed. However, exposure to training particularly influences type II subgroups. This effectuated change is seen in both the contractile properties and, more explicitly, in the oxidative capacity.