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, η_p² =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.

CME/CNE Information: Activity Available Online: To access the article, post-test, and evaluation online, go to http://www.cmscscholar.org Target Audience: The target audience for this activity is physicians, physician assistants, nursing professionals, and other health-care providers involved in the management of patients with multiple sclerosis (MS). Learning Objectives: Accreditation Statement: In support of improving patient care, this activity has been planned and implemented by the Consortium of Multiple Sclerosis Centers (CMSC) and Delaware Media Group. CMSC is jointly accredited by the Accreditation Council for Continuing Medical Education (ACCME), the Accreditation Council for Pharmacy Education (ACPE), and the American Nurses Credentialing Center (ANCC), to provide continuing education for the healthcare team. Physician Credit The CMSC designates this journal-based activity for a maximum of 0.5 AMA PRA Category 1 Credit(s)™. Physicians should claim only the credit commensurate with the extent of their participation in the activity. Nurse Credit The CMSC designates this enduring material for 0.5 contact hours (none in the area of pharmacology). Disclosures: Editor in Chief of the International Journal of MS Care (IJMSC), has served as Physician Planner for this activity. He has received royalties from Springer Publishing, intellectual property rights/patent holder from Biogen, and consulting fees from Ipsen Pharma, and has performed contracted research for Biogen, Adamas Pharmaceuticals, and Acorda Therapeutics.Francois Bethoux, MD, has served as reviewer for this activity. She has disclosed no relevant financial relationships.Laurie Scudder, DNP, NP, has disclosed no relevant financial relationships.Whitney R.D. Duff, PhD, has disclosed no relevant financial relationships.Justin W. Andrushko, MSc, has disclosed no relevant financial relationships.Doug W. Renshaw, MEd, has disclosed no relevant financial relationships.Philip D. Chilibeck, PhD, has disclosed no relevant financial relationships.Jonathan P. Farthing, PhD, is the co-owner of Lead Pilates and Integrated Health Therapies, where the study interventions occurred.Jana Danielson, MBA, has disclosed no relevant financial relationships.Charity D. Evans, PhD, The peer reviewers for the IJMSC have disclosed no relevant financial relationships. The staff at the IJMSC, CMSC, and Delaware Media Group who are in a position to influence content have disclosed no relevant financial relationships. Note: Disclosures listed for authors are those applicable at the time of their work on this project and within the previous 12 months. Method of Participation: Release Date: April 1, 2018 Valid for Credit Through: April 1, 2019 In order to receive CME/CNE credit, participants must: Statements of Credit are awarded upon successful completion of the post-test with a passing score of >70% and the evaluation. There is no fee to participate in this activity. Disclosure of Unlabeled Use: This educational activity may contain discussion of published and/or investigational uses of agents that are not approved by the FDA. CMSC and Delaware Media Group do not recommend the use of any agent outside of the labeled indications. The opinions expressed in the educational activity are those of the faculty and do not necessarily represent the views of CMSC or Delaware Media Group. Disclaimer: Participants have an implied responsibility to use the newly acquired information to enhance patient outcomes and their own professional development. The information presented in this activity is not meant to serve as a guideline for patient management. Any medications, diagnostic procedures, or treatments discussed in this publication should not be used by clinicians or other health-care professionals without first evaluating their patients' conditions, considering possible contraindications or risks, reviewing any applicable manufacturer's product information, and comparing any therapeutic approach with the recommendations of other authorities.

The contralateral effects of unilateral strength training, known as cross-education of strength, date back well over a century. In the last decade, a limited number of studies have emerged demonstrating the preservation or “sparing” effects of cross-education during immobilization. Recently published evidence reveals that the sparing effects of cross-education show muscle site specificity and involve preservation of muscle cross-sectional area. The new research also demonstrates utility of training with eccentric contractions as a potent stimulus to preserve immobilized limb strength across multiple modes of contraction. The cumulative data in nonclinical settings suggest that cross-education can completely abolish expected declines in strength and muscle size in the range of ∼13% and ∼4%, respectively, after 3–4 weeks of immobilization of a healthy arm. The evidence hints towards the possibility that unique mechanisms may be involved in preservation effects of cross-education, as compared with those that lead to functional improvements under normal conditions. Cross-education effects after strength training appear to be larger in clinical settings, but there is still only 1 randomized clinical trial demonstrating the potential utility of cross-education in addition to standard treatment. More work is necessary in both controlled and clinical settings to understand the potential interaction of neural and muscle adaptations involved in the observed sparing effects, but there is growing evidence to advocate for the clinical utility of cross-education.

BACKGROUND: Integrity of the corticospinal tract (CST) is an important biomarker for upper limb motor function following stroke. However, when structurally compromised, other tracts may become relevant for compensation or recovery of function. METHODS: We used the ENIGMA Stroke Recovery data set, a multicenter, retrospective, and cross-sectional collection of patients with upper limb impairment during the chronic phase of stroke to test the relevance of tracts in individuals with less and more severe (laterality index of CST fractional anisotropy ≥0.25) CST damage in an observational study design. White matter integrity was quantified using fractional anisotropy for the CST, the superior longitudinal fascicle, and the callosal fibers interconnecting the primary motor cortices between hemispheres. Optic radiations served as a control tract as they have no a priori relevance for the motor system. Pearson correlation was used for testing correlation with upper limb motor function (Fugl-Meyer upper extremity). RESULTS: From 1235 available data sets, 166 were selected (by imaging, Fugl-Meyer upper extremity, covariates, stroke location, and stage) for analyses. Only individuals with severe CST damage showed a positive association of fractional anisotropy in both callosal fibers interconnecting the primary motor cortices ( r [21]=0.49; P= 0.025) and superior longitudinal fascicle ( r [21]=0.51; P=0 .018) with Fugl-Meyer upper extremity. CONCLUSIONS: Our data support the notion that individuals with more severe damage of the CST depend on residual pathways for achieving better upper limb outcome than those with less affected CST.

This review examines the experimental evidence regarding unilateral resistance training frequency, intensity, the type of training, training volume, and adjuvant therapies on the cross-education of strength. CINAHL, MEDLINE, APA PsycInfo, SPORTDiscus, and Web of Science were systematically searched with gray literature searches and pearling of references thereafter. Experiments were included in the review if they performed a unilateral resistance training intervention that directly compared the dose of a training variable on the cross-education response in healthy or clinical populations following a minimum of two weeks of training. Experiments must have reported maximal strength outcomes for the untrained limb. For each experiment, the study population, intervention methods, the dosage of the training variable being studied, and the outcomes for the untrained, contralateral limb were identified and collectively synthesized. The search returned a total of 912 articles, 57 of which qualified for inclusion. The results show that experimental trials have been conducted on resistance training frequency ( n = 4), intensity ( n = 7), the type of training ( n = 26), training volume ( n = 3), and adjuvant therapies ( n = 17) on the cross-education of strength. This review maps the available evidence regarding exercise design and prescription strategies to promote the cross-education of strength. It appears that traditional resistance training frequencies (i.e., 2–3×/week) at high intensities are effective at promoting cross-education with eccentric muscle actions showing additive benefits. There is experimental evidence that neuromodulatory techniques can augment cross-education when layered with unilateral resistance training versus training alone. Registration identifier (osf.io/9sh5b). The cross-education of strength is moderated by exercise design and prescription in clinical and non-clinical populations. This review synthesizes the available evidence regarding exercise design strategies for unilateral resistance training and provides evidence-based recommendations for the prescription of unilateral training to maximize the cross-education of strength. Greater insights regarding the timing and effectiveness of cross-education interventions in clinical scenarios will strengthen the use of unilateral resistance training for individuals who may benefit from its use.

Introduction: The neural pathways that contribute to force production in humans are currently poorly understood, as the relative roles of the corticospinal tract and brainstem pathways, such as the reticulospinal tract (RST), vary substantially across species. Using functional magnetic resonance imaging (fMRI) we aimed to measure activation in the pontine reticular nuclei (PRN) during different submaximal handgrip contractions to determine the potential role of the PRN in force modulation. Methods: Thirteen neurologically intact participants (age: 28 ± 6 years) performed unilateral handgrip contractions at 25%, 50%, 75% of maximum voluntary contraction during brain scans. We quantified the magnitude of PRN activation from the contralateral and ipsilateral sides during each of the three contraction intensities. Results: A repeated measures ANOVA demonstrated a significant main effect of force (p = 0.012, η_p² = 0.307) for PRN activation, independent of side (i.e., activation increased with force for both contralateral and ipsilateral nuclei). Further analyses of these data involved calculating the linear slope between the magnitude of activation and handgrip force for each region of interest (ROI) at the individual-level. One-sample t-tests on the slopes revealed significant group-level scaling for the PRN bilaterally, but only the ipsilateral PRN remained significant after correcting for multiple comparisons. Conclusions: We show evidence of task dependent activation in the PRN that was positively related to handgrip force. These data build on a growing body of literature that highlights the RST as a functionally relevant motor pathway for force modulation in humans.