Effects of cross-education on the muscle after a period of unilateral limb immobilization using a shoulder sling and swathe

Magnus CR, Barss TS, Lanovaz JL, Farthing JP. Effects of cross-education on the muscle after a period of unilateral limb immobilization using a shoulder sling and swathe. J Appl Physiol 109: 1887-1894, 2010. First published October 21, 2010; doi: 10.1152/japplphysiol.00597.2010.-The purpose of this study was to apply cross-education during 4 wk of unilateral limb immobilization using a shoulder sling and swathe to investigate the effects on muscle strength, muscle size, and muscle activation. Twenty-five right-handed participants were assigned to one of three groups as follows: the Immob + Train group wore a sling and swathe and strength trained (n = 8), the Immob group wore a sling and swathe and did not strength train (n = 8), and the Control group received no treatment (n = 9). Immobilization was applied to the nondominant (left) arm. Strength training consisted of maximal isometric elbow flexion and extension of the dominant (right) arm 3 days/wk. Torque (dynamometer), muscle thickness (ultrasound), maximal voluntary activation (interpolated twitch), and electromyography (EMG) were measured. The change in right biceps and triceps brachii muscle thickness [7.0 +/- 1.9 and 7.1 +/- 2.2% (SE), respectively] was greater for Immob + Train than Immob (0.4 +/- 1.2 and -1.9 +/- 1.7%) and Control (0.8 +/- 0.5 and 0.0 +/- 1.1%, P < 0.05). Left biceps and triceps brachii muscle thickness for Immob + Train (2.2 +/- 0.7 and 3.4 +/- 2.1%, respectively) was significantly different from Immob (-2.8 +/- 1.1 and -5.2 +/- 2.7%, respectively, P < 0.05). Right elbow flexion strength for Immob + Train (18.9 +/- 5.5%) was significantly different from Immob (-1.6 +/- 4.0%, P < 0.05). Right and left elbow extension strength for Immob + Train (68.1 +/- 25.9 and 32.2 +/- 9.0%, respectively) was significantly different from the respective limb of Immob (1.3 +/- 7.7 and -6.1 +/- 7.8%) and Control (4.7 +/- 4.7 and -0.2 +/- 4.5%, P < 0.05). Immobilization in a sling and swathe decreased strength and muscle size but had no effect on maximal voluntary activation or EMG. The cross-education effect on the immobilized limb was greater after elbow extension training. This study suggests that strength training the nonimmobilized limb benefits the immobilized limb for muscle size and strength.