Objective To analyze shoulder strength and function in patients presenting with possible supraspinatus pathology and to ascertain if these clinical findings are associated with severity of supraspinatus pathology on MRI. Materials and methods In total, 171 patients with presumptive rotator cuff pathology and with preserved strength on standard rotator cuff examination were prospectively recruited. Patients were subjected to bilateral shoulder strength testing employing dynamometry; this included isometric strength testing at 90° of abduction, followed by eccentric assessment of isotonic strength from full abduction through the full range of motion until the arm rested at the patient’s side. We calculated absolute strength and symptomatic-to-asymptomatic arm (S/A) strength ratios. On subsequent shoulder MRI, supraspinatus pathology was designated into one of seven categories. The association between strength measurements and MRI findings was analyzed. Results Increasing lesion severity on MRI was associated with both decreasing absolute strength (no tear 59.9 N to full-thickness tear 44.2 N; P  = 0.036) and decreasing S/A strength ratios during isotonic testing (no tear 91.9% to full-thickness tear 65.3%; P  = 0.022). In contrast, there were no significant relationships between imaging severity and absolute strength or S/A strength ratios on isometric testing. Conclusion Severity of supraspinatus pathology on MRI was associated with dynamic clinical function. These results validate the clinical correlation between MRI designations of supraspinatus pathology and function and suggest the need for future work to investigate utility of dynamic (versus isometric) rotator cuff physical examination maneuvers.