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

Abstract

Cross education (CE) occurs after unilateral training whereby performance of the untrained contralateral limb is enhanced. A few studies have shown that CE can preserve or "spare" strength and size of an opposite immobilized limb, but the 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 nondominant 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 4 weeks. Pre- and posttesting involved wrist flexors and extensors eccentric, concentric and isometric maximal voluntary contractions (via dynamometer), muscle thickness (via ultrasound), 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 nonimmobilized 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 nonimmobilized wrist flexors (training: 7.1% vs. control: -3.7%; P = 0.02). Strength preservation was nonspecific to contraction type ( P = 0.69, [Formula: see text] = 0.03) yet specific to the trained flexors muscle. These findings suggest that eccentric training of the nonimmobilized limb can preserve size of the immobilized contralateral homologous muscle and strength across multiple contraction types. NEW & NOTEWORTHY Unilateral strength training preserves strength, muscle thickness, and muscle cross-sectional area in an opposite immobilized limb. The preservation of size and strength was confined to the trained homologous muscle group. However, strength was preserved across multiple contraction types.

Keywords: bilateral transfer; cross education; cross transfer; eccentric strength; muscle lengthening.

Fig. 1.

Changes in wrist flexion (A) and wrist extension torque (Nm; B) averaged across contraction types [concentric (CON), isometric (ISO), and eccentric (ECC)] from pre- to posttesting for each group. The left arm was immobilized during training. Data represent means ± SD in Nm. *P = 0.049, significant group × time interaction for left wrist flexion torque. †P = 0.038, significant group × time interaction for right wrist flexion torque. ‡P < 0.001, significant time main effect for left wrist extension torque.

Fig. 2.

Muscle cross-sectional area (MCSA; cm²) changes for the left, immobilized and right arms of the training and control groups from pre- to posttesting. Data represent means ± SD in cm². *P = 0.019, significant arm × time interaction for control group only. †P = 0.012, significant group × time interaction for the left arm only.

Fig. 3.

Changes in muscle thickness for wrist flexors (A) and wrist extensors (B) between groups. Note the observed significant effects only for the wrist flexors. Data represent means ± SD in cm. *P = 0.011, significant group × time interaction for the left wrist flexors. †P = 0.026, significant group × time interaction for the right wrist flexors.