Hind limb extensor muscle activation timing during trotting in Beagles shows limb-specific variability and can be referenced to kinematic events swing vertical moment and stance vertical moment.

Limb-specific EMG assessment using kinematic reference events improves interpretation of hind limb neuromuscular activation in dogs.

This observational study characterized hind limb extensor muscle activation timing during trotting in four clinically normal Beagles using synchronized surface electromyography (EMG) and 3-D motion capture. Four muscles were evaluated bilaterally: the middle gluteal, vastus lateralis, biceps femoris, and gastrocnemius. Two novel kinematic reference events were introduced—the swing vertical moment (SwV) and the stance vertical moment (StV)—to anchor EMG timing data to meaningful biomechanical events rather than fixed gait-cycle percentages. Results revealed substantial inter- and intraindividual variability, including asymmetry between contralateral hind limbs, suggesting that population-based normative references may be inadequate for individual assessment. Despite this variability, consistent intermuscle patterns emerged: the vastus lateralis most frequently showed delayed activation onset, while the middle gluteal tended to cease activity earlier during stance. Muscle onset clustering was observed within the SwV-to-touchdown interval across most limbs, and activity termination generally occurred after the StV. The authors conclude that event-based kinematic references provide a more physiologically meaningful framework for interpreting EMG data compared to traditional gait-cycle proportion methods. The study supports limb-specific neuromuscular assessment strategies and highlights the importance of individualized baseline data in canine gait evaluation. These findings have practical implications for veterinary rehabilitation planning, post-surgical recovery monitoring, and biomechanics research, particularly in conditions affecting hind limb neuromuscular function such as hip dysplasia, cruciate ligament disease, and lumbosacral disorders.

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