Determining the potential sites of neural adaptation to cross-education: implications for the cross-education of muscle strength

Abstract

Cross-education describes the strength gain in the opposite, untrained limb following a unilateral strength training program. Since its discovery in 1894, several studies now confirm the existence of cross-education in contexts that involve voluntary dynamic contractions, eccentric contraction, electrical stimulation, whole-body vibration and, more recently, following mirror feedback training. Although many aspects of cross-education have been established, the mediating neural mechanisms remain unclear. Overall, the findings of this review show that the neural adaptations to cross-education of muscle strength most likely represent a continuum of change within the central nervous system that involves both structural and functional changes within cortical motor and non-motor regions. Such changes are likely to be the result of more subtle changes along the entire neuroaxis which include, increased corticospinal excitability, reduced cortical inhibition, reduced interhemispheric inhibition, changes in voluntary activation and new regions of cortical activation. However, there is a need to widen the breadth of research by employing several neurophysiological techniques (together) to better understand the potential mechanisms mediating cross-education. This fundamental step is required in order to better prescribe targeted and effective guidelines for the clinical practice of cross-education. There is a need to determine whether similar cortical responses also occur in clinical populations where, perhaps, the benefits of cross-education could be best observed.

Neuromuscular electrical stimulation in early rehabilitation of patients with postoperative complications after cardiovascular surgery

“…Nevertheless, there are well-known observations of strength gain in contralateral muscles that have not been exposed to stimulation [ 8 , 20 ] ; this phenomenon is called cross education and may be explained by changes in the nervous system. [ 21 ] The non-detection of this phenomenon in our study may be explained by the short duration of the NMES course (for example, changes in the contralateral limb appeared after 3 weeks of exposure [ 20 ] ).…”

Contralateral Effects of Unilateral Strength and Skill Training: Modified Delphi Consensus to Establish Key Aspects of Cross-Education

“…Questions for the first and second themes emerged from works that identified salient features of the phenomenon and its central and peripheral mechanisms [7,8]. Questions for the third theme were informed by both seminal works [29][30][31][32] and the most recent syntheses of the available evidence [12,15,20]. Questions on the practical aspects and on the clinical outreach (themes 4 and 5) were developed iteratively by the members of the research team (AM, FD, TH) and based on the few clinically oriented reviews that are available [10,13,14,33].…”

“…First reported more than one century ago in the psychomotor literature [4][5][6], this well-known phenomenon continues to attract the attention of both basic and applied scientists who investigate its physiological underpinnings and explore its potential to treat unilateral impairments. The findings of more than 100 individual studies on strength and skill transfer have been summarized in narrative [1,[7][8][9][10][11][12][13], systematic [14,15], and meta-analytic reviews [16][17][18][19][20]. Overall, the aggregate data confirm the robustness of the phenomenon and identifies contexts in which the transfer is particularly consistent among the studies, e.g., voluntary dynamic contractions, eccentric contractions, electrical stimulation, whole-body vibration, and…”

Training Based on Electrical Stimulation Superimposed Onto Voluntary Contraction Would be Relevant Only as Part of Submaximal Contractions in Healthy Subjects

“…Indeed, Bezerra et al ( 2009 ) observed that VOL + ES would cause additional training effects and greater cross-education compared with VOL training, because it would activate the same neural pathways that are used normally in voluntary exercise, with additional afferent inputs (centrally integrated) provoked by the electrostimulation. The review article by Frazer et al ( 2018 ) linked to neural adaptations as part of the cross-education would reinforce this assumption.…”