REASONS FOR PERFORMING STUDY: Reference values for quantitative electromyography (QEMG) in shoulder and hindlimb muscles of horses are limited. OBJECTIVES: To determine normative data on QEMG analysis of supraspinatus (SS), infraspinatus (IS), deltoideus (DT) and biceps femoris (BF) muscles. STUDY DESIGN: Experimental observational study and retrospective case series. METHODS: Seven adult healthy Royal Dutch sport horses underwent quantitative motor unit action potential analysis of each muscle using commercial electromyography equipment. Measurements were made according to published methods. One-way ANOVA was used to compare quantitative motor unit action potential variables between muscles, with post hoc testing according to Bonferroni, with significance set at P15% polyphasic motor unit action potentials in SS and IS muscles. CONCLUSIONS: Differences between muscles should be taken into account when performing QEMG in order to be able to distinguish normal horses from horses with suspected neurogenic or myogenic disorders. These normal data provide the basis for objective QEMG assessment of shoulder and hindlimb muscles. Quantitative electromyography appears to be helpful in diagnosing neuropathies and discriminating these from myopathies.