Angular ranges as a reliable isokinetic method to assess shoulder rotator muscles

Area of Science:

• Biomechanics
• Kinesiology
• Sports Medicine

Background:

• Shoulder joint muscle balance is crucial for function and assessed using internal and external rotator ratios.
• Traditional methods rely on peak torque (PT), neglecting the angular positions where peak torque occurs.
• This limitation impacts the accuracy of muscle balance assessments.

Purpose of the Study:

• To introduce and validate a novel sectorial analysis method for isokinetic assessment of shoulder muscle balance.
• To compare the reliability of this new method against the conventional peak torque approach.
• To determine if sectorial analysis provides a more accurate reflection of functional muscle capacity.

Main Methods:

• 22 healthy men underwent isokinetic testing of shoulder rotators at 60°/s in concentric and eccentric modes.
• Peak torque (PT) and average torque over 10° ranges (T) were recorded for internal and external rotators.
• Physiological and functional ratios were calculated using both the classic PT approach (PT-ratios) and the new sectorial approach (T-ratios).

Main Results:

• Significant differences were found between PT-ratios and T-ratios (P < 0.05).
• T-ratios varied significantly across different angular ranges (P < 0.05).
• Sectorial analysis (T-ratios) demonstrated higher reliability, particularly over non-extreme angular ranges, compared to PT-ratios (ICC=0.14-0.75).

Conclusions:

• The sectorial analysis method offers superior reliability for assessing shoulder muscle balance compared to the peak torque method.
• This angular range-based approach provides a more functionally relevant evaluation by considering the complete range of muscle exertion.
• The findings suggest a more comprehensive understanding of shoulder joint muscle dynamics is achievable with sectorial analysis.