Muscle Contractile Properties in Patients with Repetitive Strain Injury

Abstract

Objectives

Repetitive strain injury [RSI] is a multi-factorial overuse syndrome that has been associated with local vascular and muscular impairments. Recently, we found vascular changes also in the non-affected site, which is suggestive for systemic changes in RSI. Whether RSI is associated with systemic changes in muscle function is unknown. The purpose of this study was to examine muscular function in the lower limb of patient with upper limb RSI.

Methods

Ten patients with RSI [including complaints in the forearm] and 10 healthy normal control subjects participated in the study. Local oxygen consumption of the forearm muscles was examined at baseline and after exercise using near-infrared spectroscopy. Quadriceps muscle contractile properties were examined using isometric contractions and electrical stimulations.

Results

Patients with RSI demonstrated a lower oxygen consumption in the forearm muscles after exercise [P  =  0.05], indicative for localized muscular changes, and a leftward shifted force–frequency relationship [analysis of variance, group-effect: P  =  0.02] in the quadriceps muscle. These contractile properties point in the direction of a larger amount of type II fibers in the quadriceps muscle of patients with RSI.

Conclusions

These findings suggest that the unaffected quadriceps muscles of patients with upper limb RSI probably demonstrate a predominance for type II fibers. Whether this reflects a systemic predisposition for subjects to be prone to develop RSI has to be elucidated.

Keywords:

• Repetitive strain injury
• cumulative trauma disorders
• contractile speed
• oxygen consumption
• near-infrared spectroscopy
• cumulative trauma disorders

ACKNOWLEDGEMENTS

We thank all participants that participated in the study. We are also grateful for Joris Koning who helped performing the measurements.

Declaration of Interest: The authors report no conflicts of interest.

Grant Support – None declared.