Glenohumeral Dynamic Stability
The shoulder complex features the greatest range of motion of any joint in the human body, sacrificing skeletal congruity for dynamic mobility. Dynamic muscular stability is maintained by the rotator cuff musculature. Isokinetic testing evaluates the strength ratio between external rotators (infraspinatus, teres minor) and internal rotators (subscapularis, pectoralis major, latissimus dorsi).
Key Shoulder Metrics & Normative Ratios
Concentric ER:IR Ratio
Under concentric conditions at 60°/s, the normative external-to-internal rotation peak torque ratio is typically 65% to 75% (0.65–0.75). Ratios below 60% indicate external rotator weakness relative to internal rotator dominance.
Functional Deceleration Ratio (ERecc:IRcon)
In throwing and serving sports (tennis, cricket, rugby passing), the external rotators must contract eccentrically to decelerate the rapidly internalizing arm. The functional ERecc:IRcon ratio should approach or exceed 1.0 at higher angular velocities.