BJMB
Brazilian Journal of Motor Behavior
Current Opinion
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2021
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Cross-education: Is it a viable method for rehabilitation?
JONATHAN P. FARTHING
1
| E. PAUL ZEHR
2
| ASHLEE M. HENDY
3
| JUSTIN W. ANDRUSHKO
1
| ANDREA MANCA
4
|
FRANCA DERIU
4
| JEREMY LOENNEKE
5
| MARCO A. MINETTO
6
| TIBOR HORTOBÁGYI
7
1
College of Kinesiology, University of Saskatchewan, Saskatoon, Canada.
2
Division of Medical Sciences; Exercise Science, Physical & Health Education; Centre for Biomedical Research, University of Victoria, Victoria, Canada.
3
Institute for Physical Activity and Nutrition (IPAN), School of Exercise and Nutrition Sciences, Deakin University, Victoria, Australia.
4
Department of Biomedical Sciences, University of Sassari, Sassari, Italy.
5
Department of Health, Exercise Science, and Recreation Management, University of Mississippi, Oxford, USA.
6
Division of Physical Medicine and Rehabilitation, Department of Surgical Sciences, University of Turin, Torino, Italy.
7
Center for Human Movement Sciences, University Medical Center Groningen, The University of Groningen, Groningen, The Netherlands.
Correspondence to: Jonathan P. Farthing, College of Kinesiology, University of Saskatchewan, Saskatoon, Canada.
email: jon.farthing@usask.ca
https://doi.org/10.20338/bjmb.v15i1.215
ABBREVIATIONS
MS Multiple sclerosis
RCT Randomized controlled trial
PUBLICATION DATA
Received 03 12 2020
Accepted 02 01 2021
Published 01 03 2021
In 1894, psychologists Edward W. Scripture, Theodate L. Smith, and Emily M.
Brown reported for the first time the curious observation that practicing a motor skill with
one hand also dramatically improved the non-practiced hand, giving rise to the
phenomenon now coined as cross-education. Cross-education is the increase in motor
output (i.e., force generation, skill) of the opposite, untrained limb following a period of
unilateral motor training.
1
The potential to exploit such inter-limb adaptations for the
purposes of rehabilitation of unilateral neurological or orthopedic injuries has captured the
attention of scientists and therapists for years.
The magnitude of cross-education varies greatly between muscles and
participants. In healthy adults, resistance training improves maximal voluntary force of the
untrained limb by up to ~20%, usually half of the trained limb’s improvement, but mirror
training,
2
non-invasive brain stimulation
3
and neuromuscular electrical stimulation
4
can
augment the transfer effects. Although not completely unraveled, researchers agree that
the effects are likely driven by neuroplasticity in the primary and supplementary motor
brain regions.
1
Until recently, it has remained unclear if cross-education could aid rehabilitation of
patients after a (unilateral) fracture, surgical intervention, a stroke, or multiple sclerosis
(MS). During experimental arm immobilization of healthy adults, cross-education offset
declines in strength and muscle cross-sectional area.
5
Cross-education appears to be
amplified in clinical settings, with evidence for improved grip strength and range of motion
after wrist fracture,
6
wrist and ankle strength in chronic post-stroke hemiparesis,
7
and ankle
strength and mobility in persons with MS.
8
Cross-education effects in MS were similar to
direct training of the more affected side;
8
efficacious for scenarios where the more affected
limb is unable to train or becomes fatigued.!
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Still, caution is needed in interpreting these data because the promising clinical
studies have small samples,
6,7,8
or lack a control or ‘standard of care’ comparison in a
randomized controlled trial (RCT) design,
7
do not show persistent effects at six months
follow-up,
5,8
or do not consistently show benefits beyond standard care for clinical-oriented
outcomes.
6,8
The largest RCT involving cross-education as an adjuvant post knee surgery
rehabilitation intervention reported no effects beyond standard care for neuromuscular or
functional assessments.
9
!
One hypothesis is that contraction history of the muscle influences inter-limb
outcomes after unilateral training, where improvements in the untrained muscles following
high-intensity strength training of the contralateral limb exceed gains from low-load direct
training of a limb. Cross-education may be lessened when both limbs are trained because
the local contraction history of the muscle inhibits potential signaling from the opposite limb
motor pathway.
10
Cross-education could be best applied clinically in isolation, and not in
combination with affected limb therapy - especially if it involves low load functional
movement.!
Amidst the limited evidence from large RCTs, can we say that cross-education is a
viable method of rehabilitation? Indeed, most clinical studies are positive, and critically,
none report negative outcomes. The risks of cross-education were based on the premise
that it can worsen inter-limb asymmetry and exacerbate neglect of an impaired limb. But
clinical studies so far suggest upper limb asymmetry was in fact reduced by cross-
education
6,7
and lower limb asymmetry was not worsened.
7,9
Clinical emphasis on avoiding
asymmetry may be short-sighted because it diverts focus from the absolute functional
capacity of the impaired limb. If clinical function of the impaired limb is improved, and
neuromuscular activation yields movements that before were not possible,
7
the risk of
enhancing asymmetry should be a secondary concern
1
that can be addressed by direct
exercise once functional ability is restored. Caution is important where we lack clinical data
on cross-education effects (e.g., acute and sub-acute stroke). Training the unaffected limb
is somewhat incompatible with the widely used constraint-induced movement therapy, and
the techniques are yet to be studied in conjunction. Perhaps the two are antithetical and
target different patients. The evidence suggests cross-education is most usefully applied
when the impaired or injured limb is very weak, immobilized, or unable to function unaided,
whereas ideal candidates to constraint-induced movement therapy must have a minimum
functional reservoir in order to benefit. Future studies need to assess whether adding
cross-education prior to direct training is functionally and clinically relevant.!
We suggest that contralateral training stimulates neuroplasticity in motor pathways
of the injured or impaired side, serving to offset weakness and wasting and stimulate
recovery after orthopedic injury or neurological impairment, or diminish effects of
neurological disease. The possible implications of cross-education for management of
contralateral musculoskeletal pain seem promising but require further investigation.
Importantly, we lack evidence from large RCTs that explore the combination of cross-
education with mirror training, electrical stimulation, and non-invasive brain stimulation. We
endorse collaborative efforts for clinical studies to explore these novel avenues as we
deepen our understanding of benefits and limitations of cross-education as a rehabilitation
method.
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REFERENCES
1. Manca A, Hortobágyi T, Carroll TJ et al. Contralateral Effects of Unilateral Strength and
Skill Training: Modified Delphi Consensus to Establish Key Aspects of Cross-Education.
Sports Med. 2021;51:11–20. 10.1007/s40279-020-01377-7.
2. Zult T, Goodall S, Thomas K, Solnik S, Hortobágyi T, Howatson G. Mirror Training
Augments the Cross-education of Strength and Affects Inhibitory Paths. Med Sci Sports
Exerc. 2016;48(6):1001-13. 10.1249/MSS.0000000000000871.
3. Hendy AM, Teo WP, Kidgell DJ. Anodal Transcranial Direct Current Stimulation Prolongs
the Cross-education of Strength and Corticomotor Plasticity. Med Sci Sports Exerc.
2015;47(9):1788-97. 10.1249/MSS.0000000000000600..
4. Minetto MA, Botter A, Gamerro G et al. Contralateral effect of short-duration unilateral
neuromuscular electrical stimulation and focal vibration in healthy subjects. Eur J Phys
Rehabil Med. 2018;54(6):911-920. 10.23736/S1973-9087.18.05004-9.
5. Andrushko JW, Lanovaz JL, Björkman KM, Kontulainen SA, Farthing JP. Unilateral
strength training leads to muscle-specific sparing effects during opposite homologous limb
immobilization. J Appl Physiol. 2018;124(4):866-876. 10.1152/japplphysiol.00971.2017.
6. Magnus CR, Arnold CM, Johnston G et al. Cross-education for improving strength and
mobility after distal radius fractures: a randomized controlled trial. Arch Phys Med Rehabil.
2013;94(7):1247-55. 10.1016/j.apmr.2013.03.005.
7. Sun Y, Zehr EP. Training-Induced Neural Plasticity and Strength Are Amplified After
Stroke. Exerc Sport Sci Rev. 2019;47(4):223-229. 10.1249/JES.0000000000000199.
8. Manca A, Cabboi MP, Dragone D et al. Resistance Training for Muscle Weakness in
Multiple Sclerosis: Direct Versus Contralateral Approach in Individuals With Ankle
Dorsiflexors' Disparity in Strength. Arch Phys Med Rehabil. 2017;98(7):1348-1356.e1.
10.1016/j.apmr.2017.02.019.
9. Zult T, Gokeler A, van Raay JJAM et al. Cross-education does not accelerate the
rehabilitation of neuromuscular functions after ACL reconstruction: a randomized
controlled clinical trial. Eur J Appl Physiol. 2018;118(8):1609-1623.
10.1007/s00421-018-3892-1.
10. Bell ZW, Wong V, Spitz RW et al. The contraction history of the muscle and strength
change: lessons learned from unilateral training models. Physiol Meas.
2020;41(1):01TR01. 10.1088/1361-6579/ab516c.
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Citation: Farthing JP, Zehr EP, Hendy AM, Andrushko JW, Manca A, Deriu F, Loenneke J, Minetto MA, Hortobágyi T.
Cross-education: Is it a viable method for rehabilitation?. BJMB. 2021:15(1):1-4.
Editors: Dr Fabio Augusto Barbieri - São Paulo State University (UNESP), Bauru, SP, Brazil; Dr José Angelo Barela -
São Paulo State University (UNESP), Rio Claro, SP, Brazil; Dr Natalia Madalena Rinaldi - Federal University of
Espírito Santo (UFES), Vitória, ES, Brazil.
Section Editors (Current Opinion): Dr Luis Augusto Teixeira - University of São Paulo (USP), São Paulo, SP, Brazil;
Dr Tibor Hortobágyi - University of Groningen, The Netherlands; Dr Renato de Moraes - University of São Paulo
(USP), Ribeirão Preto, SP, Brazil.
Copyright:© 2021 Farthing, Zehr, Hendy, Andrushko, Manca, Deriu, Loenneke, Minetto and Hortobágyi and BJMB.
This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No
Derivatives 4.0 International License which permits unrestricted use, distribution, and reproduction in any medium,
provided the original author and source are credited.
Funding: There was no funding for this study.
Competing interests: The authors have declared that no competing interests exist.
DOI:!https://doi.org/10.20338/bjmb.v15i1.215