OBJECTIVE: To describe the activity pattern of the vastus lateralis muscle in dogs at walk measured by surface electromyography (EMG) in relation to kinematics and kinetics of the pelvic limb. STUDY DESIGN: Experimental. ANIMALS: Malinois dogs (n=11). METHODS: Dogs (mean +/- SD age, 5.5 +/- 2.9 years; weight, 27.3 +/- 3.8 kg; shoulder height, 62.7 +/- 3.3 cm) walked on a treadmill system with integrated force plates, which allowed simultaneous analysis of kinematics, kinetics, and EMG data from all limbs. The maxima, minima, and their time of occurrence in the motion cycle of the EMG and the pelvic limb kinematics and kinetics were calculated; correlations between joint movement patterns, ground reaction forces (GRF), and activity pattern of the muscle group were investigated. RESULTS: The vastus lateralis muscle had an activity pattern with 2 peaks and a close positive correlation with GRF. The 1st peak occurred in early stance, followed by a decrease in activity during mid-stance. The 2nd peak occurred directly before the quick activity decrease in late stance phase, reaching its minimum early in swing phase. CONCLUSIONS: These results suggest that the vastus lateralis muscle supports the vertical position and elevation of the pelvis during stance and push-off. During early stance, the muscle acts as a coantagonist to the hamstring muscle group and the gastrocnemius muscle, and restrains flexion during the late stance. CLINICAL RELEVANCE: Results of this study could enhance diagnosis of locomotor system disorders and facilitate monitoring effects of treatments (e.g., therapeutic exercises) on gait ability and muscle function.