BACKGROUND: In patients with peripheral arterial disease and presenting intermittent claudication (PAD-IC), the pain due to ischemia impacts gait parameters, particularly in cases of unilateral disease. Deterioration of gait parameters in a pathological context is frequently associated with increased coactivation (simultaneous activation of agonist and antagonist muscles around a joint). RESEARCH QUESTION: Does unilateral PAD-IC affect the coactivation pattern during walking? Does the coactivation pattern change with increasing pain intensity? METHOD: We evaluated symptomatic and asymptomatic legs in 17 subjects with unilateral PAD-IC and 16 without PAD-IC (control group), during walking. Tibialis anterior (TA) and gastrocnemius medialis (GM) electromyographic activity, and peaks of vertical ground reaction force were recorded in this prospective study. We analyzed the coactivation index (CI(GM/TA)) during three periods (pain-free, pain and maximum pain) and phases of the gait cycle. Statistical analysis was carried out using the ANOVA procedure. RESULTS: During single support, CI(GM/TA) increases in the symptomatic leg during the pain period (+28 %) and in the asymptomatic leg during the maximum pain period (+29 %). During second double support, CI(GM/TA) increases in the symptomatic leg only (+49 %). In these gait phases, pain elicits differences in CI(GM/TA) between legs (p < 0.05). Second peak force decreases in the symptomatic leg only (-9%) and is negatively correlated with CI(GM/TA) during the three periods (r = -0.57; -0.76 and -0.78 respectively, p < 0.05). No difference is found in the control group. SIGNIFICANCE: The appearance and development of pain in the lower limbs is associated with a higher level of CI(GM/TA), revealing a compensatory gait pattern in PAD-IC patients. Optimal prevention, rehabilitation and re-training strategies for PAD-IC patients should take into consideration neuromuscular compensatory mechanisms between asymptomatic and symptomatic legs.