Evaluation of the EMG activity of the long back muscle during induced back movements at stance.

The study evaluates the activity of Musculus longissimus, the main back muscle of horses, during induced extensions and lateral flexions using surface electromyography (EMG). It essentially provides insights on appropriate location of EMG’s application in clinical practice for effective detection of spinal reflexes.

Research Design and Methodology

• The research included 15 horses of ages between 5 and 20 years and weighing 450 to 700 kg in a symptom-free state with no signs of back pain.
• Reflecting markers were placed on the head, T5, T12, T16, L3 spinous processes, and 2 sacral bones for the purpose of tracking movements.
• The surface EMG electrodes were positioned on the Musculus longissimus on both sides of the dorsal spinous processes of T12, T16, and L3.

Results and Findings

• In all horses and movements, the EMG activity was the highest on both sides of the dorsal spinous process of T12 and the lowest on both sides of the L3 spinous process.
• The amplitude of the EMG signal at T16 was identified to be 60% of that at T12 while the amplitude at L3 was found to be 30% of T12.
• There was no observed time shift between the EMG signals at different locations (T12, T16, L3), indicating an immediate response across the measured regions.
• A high correlation (0.78 at L3, 0.80 at T16 and 0.75 at T12) was observed between the amplitude of the EMG signal and motion during extension movements.
• However, during lateral flexion, the correlation between EMG and motion was lower (0.38 at L3, 0.43 at T16 and 0.39 at T12).

Research Implications

• This study confirms that for clinical purposes, the best location for placing surface EMG is on both sides of the T12 region when assessing spinal reflexes in horses. This is due to it having the highest activity during induced movements.
• The differences in signal amplitudes across different parts of the spinous process provide important information for understanding the functioning of back muscles during various motion activities.
• Finding a high correlation between signal amplitude and extension motion but a low correlation with lateral flexion could influence treatment strategies for horses and potentially lead to more targeted therapies.