Effect of speed and leading or trailing limbs on surface muscle activities during canter in Thoroughbred horses

Abstract

Given that Thoroughbred horses’ canter is an asymmetric gait, not only speed but also leading or trailing limbs could affect muscle activities. However, the muscle activity during a canter remains poorly understood. Hence, we aimed to investigate speed and lead-side (leading or trailing) effects on surface electromyography (sEMG) during a canter. The sEMG data were recorded from left Musculus brachiocephalicus (Br), M. infraspinatus (Inf), long head of M. triceps brachii (TB), M. gluteus medius (GM), M. semitendinosus (ST), and M. flexor digitorum longus of seven Thoroughbreds with hoof-strain gauges at the left hooves. Horses cantered on a flat treadmill at 7, 10, and 13 m/s for 25 s each without lead change. Subsequently, the horses trotted for 3 min and cantered at the same speed and duration in the opposite lead side (“leading” at the left lead and “trailing” at the right lead). The order of the lead side and speed was randomized. The mean of 10 consecutive stride durations, duty factors, integrated-EMG values (iEMG) for a stride, and muscle onset and offset timing were compared using a generalized mixed model (P < 0.05). Stride durations and duty factors significantly decreased with speed regardless of the lead side. In all muscles, iEMG at 13 m/s significantly increased compared with 7 m/s (ranging from +15% to +134%). The lead-side effect was noted in the iEMG of Br (leading > trailing, +47%), Inf (leading > trailing, +19%), GM (leading < trailing, +20%), and ST (leading < trailing, +19%). In TB, GM, and ST, muscle onset in trailing was earlier than the leading, while offset in the leading was earlier in Br. In conclusion, different muscles have different responses to speed and lead side; thus, both the lead side and running speed should be considered during training and/or rehabilitation including canter or gallop.

Changes in muscle activation with graded surfaces during canter in Thoroughbred horses on a treadmill

“…Our results in TB align with these findings. We observed that the normalized iEMG values during the swing phase on an 8% grade significantly increased compared to a 0% grade, indicating that TB may play an important role in decelerating the forelimb [36]. Contrary to Hodson-Tole's findings [20], the activity of Br was not affected by grade in our study.…”

“…These muscles may play an important role in decelerating the limb and redirecting it from protraction to retraction in the late swing phase. This function is similar to the role of the long head of TB, where a shorter swing duration necessitates faster limb protraction [35,36]. This indicates that not only passive properties, such as the biceps brachii tendon unit's catapult mechanism, but also an increase in muscle activity, could facilitate faster limb movements on an uphill grade [10,37].…”

“…We measured muscle activity in the leading limb side because the leading hindlimb may be more important than the trailing hindlimb in generating potential energy, especially since an increase in potential energy on 8%-12% inclines compared to 0%-2% inclines was observed during the leading hindlimb stance phase [10]. However, considering that canter and gallop are asymmetric gaits, wherein muscle activity and kinematics significantly differ between leading and trailing limbs [36,40,55,56], our approach may overlook important aspects of equine locomotion. Further, some studies have shown that an interaction between graded surfaces and speed affected muscle activity and range of motion in human running [33,57].…”