Electromyographic changes in hind limbs of Thoroughbreds with fatigue induced by treadmill exercise.

The research explores how fast-paced treadmill exercise induces fatigue in Thoroughbreds (horse breed), particularly focusing on changes in the hind limb muscles. The study found that high-speed galloping led to a reduction in integrated electromyographic (iEMG) values in the gluteus medius and biceps femoris muscles, potentially affecting the horse’s speed.

Study Design

• The research involved eight Thoroughbreds. Key muscles in the horses’ hind limbs (longissimus dorsi, tensor fasciae latae, gluteus medius, and biceps femoris) were fitted with instruments for surface electromyography – a technique that measures muscle response to nerve’s stimulation.
• Horse strides were tracked using hoof strain gauges. The horses were put to gallop on a treadmill at a constant speed, aiming to induce fatigue after about 360 seconds.
• Before and after the fatigue-inducing exercise, the horses were made to trot at a moderate speed.
• At 30-second intervals during galloping, the integrated electromyography (iEMG) value for a stride and the median frequency of muscle discharge in each limb were recorded.
• Strides frequency, iEMG value, and median frequency of five consecutive strides at the start and end of galloping for both the lead and trailing limbs were compared.
• For trotting, these same variables were compared 60 seconds before and after galloping.

Results

• The research observed a decrease in stride frequency over time.
• Furthermore, fatigue caused a decrease in iEMG values of the gluteus medius and biceps femoris muscles in both the lead and trailing limbs. However, the longissimus dorsi and tensor fasciae latae muscles’ iEMG values remained unchanged.
• There was no noticeable change in the median frequency of any muscle during the high-speed galloping with fatigue.
• Additionally, when the horses were trotting, there was no change in stride frequency, iEMG value or median frequency even with fatigue.

Conclusions

• The research concluded that high-speed galloping-induced fatigue decreases iEMG values of the gluteus medius and biceps femoris muscles in Thoroughbreds.
• Fatigue of these hind limb muscles, which are appreciably less resistant to fatigue, could significantly impact a horse’s speed. This insight might have implications for equestrian sports and training strategies.