Objective

Shoulder internal (IR) and external rotator (ER) muscles play an important role in the stability of glenohumeral joint. The ratio between the peak torque of ER and IR in concentric (ER/IRPT) and mixed (ER-ECC/IR-CONPT) are usually measured to evaluate the effects of muscle weakness, sport activities, injury and treatment (Greenfield et al., 1990; Scoville et al., 1997). However, ER/IRPT and ER-ECC/IR-CONPT failed to provide some indication on the evolution of the ER/IR torque ratio (ER/IRTorque) and mixed torque ratio (ER-EC/IR-COTorque) during the range of motion (ROM).

The aim of this study was to examine the ER/IRTorque and ER-EC/IR-COTorque during ROM in regard to the ER/IRPT and ER-ECC/IR-CONPT values.

Patients and methods

Twenty-one healthy trained (23.0 ± 2.7 y) underwent an isokinetic concentric IR and ER strength test on a Cybex Norm ^® dynamometer in a seated position (45° shoulder abduction in scapular plane), at 60°.s ⁻¹ for both sides. ER/IRTorque and ER-EC/IR-COTorque were continuously recorded (PowerLab ^® ) then averaged per range of 10° throughout 110°. ER/IRPT and ER-ECC/IR-CONPT were calculated according conventional method.

Results

Repeated Anova test revealed that ER/IRT significantly increased during internal rotation ( P < 0.05) with an inconstant value during ROM. ER/IRT was significantly lower than ER/IRPT in more than 80% of ROM.

Discussion/Conclusion

ER/IRPT and ER-ECC/IR-CONPT are classically determined according the peak torque value of RE and RI, regardless of the difference between angle for which each value is reached. However, we showed a variation of ER/IRTorque and ER-EC/IR-COTorque during the ROM. Coombs (2002) has already reported the effect of angular knee position on the hamstring/quadriceps torque ratio value. ER/IRTorque and ER-EC/IR-COTorque appears an additional indicator on the dynamic glenohumeral strength balance.

In addition to PT ratio, ER/IRTorque and ER-EC/IR-COTorque ratios during the range of motion could assess to risk factors for shoulder injuries, specific adaptations to exercise training and rehabilitation.