Accuracy of Two Methods in Estimating Target Muscle Force During Shoulder Submaximal Isometric Contractions.

Area of Science:

• Rehabilitation Science
• Exercise Physiology
• Biomechanics

Background:

• Submaximal isometric exercises are crucial for pain management and neuromuscular facilitation.
• Traditionally, ipsilateral maximal voluntary isometric contraction (MVIC) serves as the reference for these exercises.
• When ipsilateral MVIC is not clinically feasible, alternative methods like no reference (NR) or reciprocal reference (RR) are considered, though their accuracy at the shoulder is unproven.

Purpose of the Study:

• To evaluate the accuracy of the NR and RR methods in estimating target muscle force.
• To assess these methods during shoulder external rotation (ER) and internal rotation (IR) submaximal isometric contractions in healthy adults.

Main Methods:

• An observational, cross-sectional study was conducted on 48 healthy participants.
• Isometric shoulder force was measured using a hand-held dynamometer.
• Participants performed randomized NR and RR submaximal contractions, with RR involving a contralateral MVIC reference.

Main Results:

• Both NR and RR methods demonstrated significant moderate to good correlations with actual submaximal efforts (r = 0.620–0.691).
• Correlations remained significant regardless of the test side or shoulder motion (ER/IR).
• No significant differences in accuracy were observed between the NR and RR methods for either ER or IR.

Conclusions:

• Both the NR and RR methods exhibit moderate to good accuracy for estimating shoulder isometric forces.
• The accuracy of these methods is not affected by the side of the test or the direction of the force.
• Either the NR or RR method can be reliably used for prescribing shoulder isometric exercises when an ipsilateral reference contraction is not possible.