Unilateral strength training leads to muscle-specific sparing effects during opposite homologous limb immobilization

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Abstract
Cross-education (CE) occurs after unilateral training whereby performance of the untrained contralateral limb is enhanced. A handful of studies have shown that CE can spare the strength and size of an opposite immobilized limb, but specificity (i.e., trained homologous muscle and contraction type) of these effects is unknown. The purpose was to investigate specificity of CE "sparing" effects with immobilization. The non-dominant forearm of 16 participants was immobilized with a cast and participants were randomly assigned to a resistance training (eccentric wrist flexion, 3 times/week) or control group for four weeks. Pre- and post-testing involved wrist flexors and extensors muscle thickness (via ultrasound), eccentric, concentric and isometric maximal voluntary contractions (via dynamometer), and forearm muscle cross-sectional area (MCSA, via peripheral quantitative computed tomography). Only the training group showed strength preservation across all contractions in the wrist flexors of the immobilized limb (Training: -2.4% vs. Control: -21.6%; P =0.04), and increased wrist flexors strength of the non-immobilized limb (Training: 30.8% vs. Control: -7.4%; P =0.04). Immobilized arm MCSA was preserved for the training group only (Training: 1.3% vs. Control: -2.3%; P =0.01). Muscle thickness differed between groups for the immobilized (Training: 2.8% vs. Control: -3.2%; P =0.01) and non-immobilized wrist flexors (Training: 7.1% vs. Control: -3.7%; P =0.02). Strength preservation was non-specific to contraction type (P =0.69, ηp2 =0.03), yet specific to the trained flexors muscle. These findings suggest that eccentric training of the non-immobilized limb can preserve size of the immobilized contralateral homologous muscle and strength across multiple contraction types.
Funding Information
  • Gouvernement du Canada | Natural Sciences and Engineering Research Council of Canada (Conseil de Recherches en Sciences Naturelles et en Génie du Canada) (RGPIN-2016-0529)

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