Clinical application of cross-education to unilateral limb immobilization

Abstract

Cross-education is a neural adaptation defined as the increase in strength or functional performance of the untrained contralateral limb after unilateral training of the opposite homologous limb. Since cross-education can improve strength in an untrained limb, there is therapeutic potential to apply cross-education to clinical rehabilitation settings; however, a large gap in the literature remains. The first objective of this thesis was to determine if cross-education could improve strength and functional performance (i.e. active range of motion (AROM), self-reported function) of an immobilized limb using a shoulder sling model in both healthy and injured participants. The second objective was to determine if cross-education could improve strength and functional performance (i.e. AROM, self-reported function) of wrist fracture rehabilitation after unilateral training of the non-fractured limb. Study 1 applied cross-education to non-injured participants who wore a shoulder sling and swathe and strength trained the non-immobilized limb. Strength (NORM dynamometer), muscle size (ultrasound), electromyography, and interpolated twitch were measured. Results showed cross-education increased strength and maintained muscle size in the immobilized limb after training the non-immobilized limb. Study 2 applied cross-education using a clinically relevant at-home resistance tubing shoulder strength training program to healthy participants. Results showed significant cross-education effects for untrained shoulder external and internal rotation strength (handheld dynamometer), and increased muscle size (ultrasound) in the trained supraspinatus and anterior deltoid. Study 3 applied cross-education using the clinically relevant strength training program (in Study 2) to post-shoulder surgery rehabilitation and measured strength (handheld dynamometer), muscle size (ultrasound), AROM (goniometer), and self-reported function (Western Ontario Rotator Cuff Questionnaire) (WORC). Results showed the training group had significantly greater supraspinatus muscle thickness at 6 months post-surgery compared to the control group; however, there were no cross-education effects for strength, AROM, or the WORC. Study 4 applied cross-education during rehabilitation from wrist fractures and measured strength (handgrip dynamometer), AROM (goniometer), and self-reported function (Patient Rated Wrist Evaluation) (PRWE). Results showed cross-education improved strength and AROM in the fractured limb 12 weeks post-fracture. In conclusion, there was evidence for cross-education to benefit a healthy immobilized limb and to use a clinically relevant shoulder strength training program to produce cross-education effects. When cross-education was applied to shoulder surgeries there were improvements in muscle size but no effect for strength, AROM or function. However, when applied to wrist fractures, strength and AROM were improved for the injured limb. These findings represent the first well-controlled evidence that cross-education may improve rehabilitation after unilateral injuries.