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Physical Therapy Reviews
ISSN: 1083-3196 (Print) 1743-288X (Online) Journal homepage: http://www.tandfonline.com/loi/yptr20
The effect of unilateral training on contralateral
limb strength in young, older, and patient
populations: a meta-analysis of cross education
Lara A. Green & David A. Gabriel
To cite this article: Lara A. Green & David A. Gabriel (2018): The effect of unilateral training
on contralateral limb strength in young, older, and patient populations: a meta-analysis of cross
education, Physical Therapy Reviews, DOI: 10.1080/10833196.2018.1499272
To link to this article: https://doi.org/10.1080/10833196.2018.1499272
© 2018 The Author(s). Published by Informa
UK Limited, trading as Taylor & Francis
Group
Published online: 29 Oct 2018.
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The effect of unilateral training on contralateral limb strength in young,
older, and patient populations: a meta-analysis of cross education
Lara A. Green and David A. Gabriel
Department of Kinesiology, Brock University, St. Catharines, ON, Canada
ABSTRACT
Background: Cross education is the contralateral strength gain following unilateral training
of the ipsilateral limb. This phenomenon provides an ideal rehabilitation model for acute or
chronic rehabilitation; however, previous cross education meta-analyses have been limited
to a handful of studies.
Objectives: The present meta-analysis aimed to (1) be as inclusive as possible, (2) compare
cross education in young able-bodied, older able-bodied, and patient populations, (3) com-
pare cross education between training modalities, and (4) detail the impact of methodo-
logical controls on the quantification of cross education.
Methodology: A review of English literature identified studies that employed unilateral
resistance training and reported contralateral strength results. Studies were separated to
examine the effect of population, training modality, limb, sex, and familiarization on the
magnitude of cross education. The percent strength gain and effect size were calculated for
ipsilateral and contralateral limbs.
Results: A total of 96 studies fit the predetermined inclusion criteria and were included in
the analysis. The included studies were further divided into 141 units employing separate
unilateral training paradigms. These were separated into young, able-bodied (n¼126), older,
able-bodied (n¼9), and neuromuscular patients (n¼6). Cross education was an average of
18% (standardized mean difference (SMD)¼0.71) in young, able-bodied participants, 17%
(SMD ¼0.58) in healthy able-bodied participants, and 29% (SMD ¼0.76) in neuromuscu-
lar patients.
Conclusion: Cross education was present in young, older, and patient populations and simi-
lar between upper and lower limbs and between males and females. Electromyostimulation
training was superior to voluntary training paradigms.
KEYWORDS
Cross education;
cross-transfer; unilateral
strength training;
electromyostimulation;
contralateral strength
transfer; stroke; elderly
Background
Cross education is the strength gain that is found in
the contralateral limb following a unilateral training
program on the homologous limb. Cross education
was first reported in 1894 by Scripture et al. [1]
who determined that task steadiness and muscular
strength could be improved in the contralateral limb
following unilateral training. This phenomenon is of
great importance for clinical applications and
rehabilitation, and requires further mechanistic
investigation. Cross education provides a beneficial
rehabilitation model for unilateral injuries or disor-
ders; including, acute injuries or immobilization
(casting) of a single limb, and neurologic disorders,
such as stroke, affecting the body unilaterally.
Previous research has proposed that cross
education can be explained by two distinct, but not
necessarily mutually exclusive, hypotheses: ‘cross-
activation’and ‘bilateral access’[2,3]. The
‘cross-activation’hypothesis proposes that unilateral
activity excites both ipsilateral and contralateral
cortical motor areas. With this hypothesis, the uni-
lateral training causes adaptations in both hemi-
spheres, though to a lesser extent in the untrained
hemisphere. Alternatively, the ‘bilateral access’
hypothesis suggests that the homologous untrained
muscle can access the unilateral adaptations of train-
ing through interhemispheric communication from
the associated motor areas [2,3].
Previous meta-analyses and systematic reviews
have determined that the average contralateral
strength gain from cross education is approximately
8–12% [4–7]. This amount corresponds to approxi-
mately 35–60% of the strength increase that is found
in the ipsilateral (trained) limb [4,6,8]. Manca
et al. [7] further separated their estimate of cross
education into lower limb (16.4%) and upper limb
(9.4%). However, these previous reviews of cross
education were limited to 2 [9], 8 [8], 10 [10], 13
[6], 16 [4], and 31 [7] articles. There are several fac-
tors that make the review of cross education compli-
cated and limited, including the name discrepancies
CONTACT Lara A. Green lara.green@brocku.ca Department of Kinesiology, Brock University, St. Catharines, ON L2S 3A1, Canada.
ß2018 Informa UK Limited, trading as Taylor & Francis Group
PHYSICAL THERAPY REVIEWS
https://doi.org/10.1080/10833196.2018.1499272
confounding the search for studies, and the variety
of training paradigms. However, the primary reason
for the small ‘sample sizes’of cross education
reviews is the stringency of inclusion criteria. The
reviews by Munn et al. [6], Carroll et al. [4], Cirer-
Sastre et al. [10], and Manca et al. [7], were limited
to the analysis of randomized controlled studies. In
addition, only studies with full data (means and
standard deviations) for each of the ipsilateral
experimental, contralateral experimental, and con-
trol limbs were included.
The inconsistent terminology and the uninten-
tional examination of cross education using the
contralateral limb as a ‘control limb’for unilateral
training has confounded the analysis of the field.
Cross education of strength has been referred to by
many names including cross-transfer, cross-over, or
contralateral training. Similarly, the cross education
of skill following unilateral practice is typically
referred to as interlateral transfer of learning, bilat-
eral transfer, or intermanual transfer. These studies
generally focus on single session practice, rather
than training, and the transfer of a skill, rather than
strength. Although widely studied, the practice para-
digms and the outcome measurements of the cross
education of skill vary drastically across studies
making them extremely difficult to quantitatively
compare. Therefore, this meta-analysis focuses solely
on the cross education of strength.
Lastly, variability in training paradigms makes it
difficult to compare cross education between studies.
There is a considerable variation in the duration
(number of sessions), volume (contractions per ses-
sion), intensity (load), and modality (type of con-
traction or stimuli) of unilateral training. The
reviews by Carroll et al. [4], Munn et al. [6], and
Manca et al. [7] limited their analyses to studies
employing training intensities greater than 50%
maximal strength for a minimum of 2 weeks. Most
notably, the previous meta-analyses included only
isometric, isokinetic, and dynamic training [4,6,7,
10], specifically excluding ‘alternative’training via
electromyostimulation (EMS), transcranial magnetic
stimulation, vibration, or acupuncture.
The present analysis prioritized inclusivity over
selectivity to capture the greatest overview of the
field. A review of literature was undertaken to
include as many ‘contralateral strength transfer’
studies as possible, including studies that uninten-
tionally examined cross education by using an
untrained contralateral limb as a control for unilat-
eral training. The present analysis included studies
using ‘alternative’training, specifically EMS training
(or neuromuscular electrical stimulation (NMES)),
since previous meta-analysis have not previously
included ‘non-traditional’forms of strength training.
In order to advance the use of cross education for
rehabilitation purposes, the analysis was not limited
to healthy populations as long as strength was
assessed pre and post intervention.
Methods
Definitions
For the purpose of this analysis the term study will
refer to an article as referenced. The term unit will
refer to a training paradigm within a study, while
the term limb will be the designated trained,
untrained, or control limb of a participant. For
example, one study may have two units within it
where one unit was assigned to one type of training
(e.g. eccentric training, elbow flexion training, low
frequency training, etc.) and another unit was
assigned to a separate training paradigm (e.g. con-
centric training, knee flexion training, high fre-
quency training, etc.).
Literature search
The included studies were collected from an
ongoing review of cross education and unilateral
training literature. Studies were identified using
Google Scholar, PubMed, and Research Gate using
the search terms: cross education, cross-transfer,
interlimb transfer, and contralateral strength gain.
The reference list of each identified study was exam-
ined to include previously noted cross education
studies not identified in the database search. In add-
ition, studies using unilateral training were identi-
fied using search terms including: unilateral strength
training, dominant AND non-dominant control
limb and were examined for the unintentional
observation of cross education where the contralat-
eral limb was designated as a control limb.
Inclusion criteria
The selection of inclusion criteria was designed to
be as inclusive as possible for the broadest
review possible.
Population. All ages, sexes, and abilities were
included in the present review. Units were separated
into three groups: (1) young able-bodied (young)
participants (<50 years of age), (2) older able-bod-
ied (older) participants (>50 years of age), and (3)
neuromuscular disorder (patient) populations.
Training paradigm. All training types aimed at
improving strength were included in the present
study, including EMS training which has been previ-
ously excluded from cross education meta-analyses.
Training modalities (contraction types) were sepa-
rated into the following categories: isometric,
2 L. A. GREEN AND D. A. GABRIEL
isokinetic, dynamic (including isotonic), EMS, or
‘other’. If two types of voluntary contractions were
performed for training, then the unit was placed in
the ‘other’category. The EMS category consists of
stimulation alone or superimposed on a voluntary
contraction. Any training intensity (load) was
included as long as it was greater than 0% maximal
strength (i.e. the intention was strength gain, rather
than endurance gain). The criteria for number of
sessions was >5 sessions to include training stimuli
rather than mechanistic examinations.
Outcomes. Studies were included if strength was
measured and reported in any manner including: pre-
training and posttraining means, mean gain, or per-
cent gain. Studies were further separated into units
only where separate training paradigms were
employed, rather than separate outcomes. Where one
training unit had multiple outcomes, the single out-
come that was homologous to the training modality
(i.e. closest in contraction type, joint angle, speed of
contraction, etc.) was selected, with the exception of
EMS, vibration, or electroacupuncture training, where
avoluntarycontractionwasselected.Whenmultiple
contraction types were used for training, as well as
testing, the contraction type used most in training was
selected as the outcome measure.
Sample size. The inclusion criterion for unit sample
size was 3 to get an appropriate mean and standard
deviation for effect size calculation. No control group
was required for inclusion in the analysis.
Analysis
Effect size. Where means and standard deviations
were reported effect size was calculated for each
limb within a unit using The Cochrane
Collaboration Review Manager (RevMan V.5.3) [11].
The standardized mean difference (SMD) and 95%
confidence intervals were calculated using inverse
variance as the statistical method, and random
effects as the analysis model. Statistical significance
(Z-score) was calculated in RevMan to determine if
the effect size is greater than null. Where standard
error (SE) was reported it was converted to standard
deviation (SD) using the following formula includ-
ing group sample size (n):
SD ¼SE
ffiffiffi
n
p
The effect size was calculated where possible for
the experimental limbs (trained and untrained) and
the control limb(s). If both limbs of the control
group were measured (dominant and non-domin-
ant) then each limb was separately used as a control
for the experimental limb. If only one control limb
was tested then it was included as the control for
both the trained and untrained experimental limbs.
Percent gain. Where means were reported the
percent gain of the trained and/or untrained limb
was calculated according to the following formula:
%Gain ¼PostPre
Pre 100
If only percent gain was reported but not pre-
training or posttraining mean values then the per-
cent gain was included as reported.
Cross-body transfer. The magnitude of cross-body
transfer was calculated to determine how much of
the training effect was transferred to the untrained
limb. The calculation was conducted for each unit
as follows:
Cross-body Transfer ¼Untrained %Gain
Trained %Gain 100
Comparisons. Independent sample t-tests were
performed using SAS 9.4 (SAS Institute Inc., Cary,
NC, USA) with a 0.05 significance level. The magni-
tude of percent gain in the untrained (cross educa-
tion) limb and the trained limb was examined
between (1) upper versus lower limb, (2) males ver-
sus females, and (3) familiarized versus non-fami-
liarized units. The upper limb training consisted of
elbow flexion, wrist flexion and extension, and
handgrip exercises amongst others. The lower limb
training consisted primarily of knee extension and
flexion, and secondarily plantar flexion and dorsi-
flexion exercises. The effect of sex was examined
from units that were composed of only males or
only females. Finally, familiarization was taken as
reported and included anything from a familiariza-
tion contraction or testing procedures familiariza-
tion to an entire familiarization session.
Results
Study and unit characteristics
A total of 113 studies were identified and 96 studies
were included in the analysis (Figure 1). The 17
excluded studies did not fit the following criteria:
no strength measure (4 studies), no strength data
113 S tudi es
Identified
17 Studies Excluded:
No strength measure (4)
No strength data (4)
No pre-test data (4)
< 5 training sessions (2)
< 3 participants (3)
96 Studies
Included
(141 units)
87 Studies
Young Able-Bodied
(126 units)
8 Studies
Older Able-Bodied
(9 units)
6 Studies
Patient Population
(6 units)
Figure 1. Flow diagram of the identification and
review process.
PHYSICAL THERAPY REVIEWS 3
reported for untrained limb (4 studies), no pretest
data (4 studies), less than 5 training sessions (2
studies), and less than 3 participants (3 studies).
The remaining 96 studies included a total of 141
units. Of those, 126 units (from 87 studies [12–97])
included young, able-bodied participants with a
median age of 23 years and a median sample size of
11 (range 3–342) participants. Nine units (from 8
studies [13,27,72,92,93,98–100]) included older,
able-bodied participants with a median age of 69
years and a median sample size of 11 (range 6–14).
The remaining 6 units (from 6 studies [101–106])
were conducted using neuromuscular patient popu-
lations with a median sample size of 10 (range
5–21) participants. The neuromuscular disorder
breakdown is as follows: stroke patients (three stud-
ies), patients with various neuromuscular disorders
(one study), multiple sclerosis (one study), and
osteoarthritis patients (one study).
Outcome measures
The training characteristics are presented in Table 1
for each of the groups. The results of effect size and
percent gain for the number of units that fit each
criterion are reported for the untrained (cross edu-
cation) limb in Table 2 and for the trained limb in
Table 3. Forest plots are presented for the untrained
limb in Figure 2 for the young group and Figure 3
for the older (A) and patient (B) groups.
The average percent gain (above baseline
strength) in the untrained contralateral limb of
young participants following unilateral training in
the ipsilateral limb was 18%, as calculated from 126
units. A review of 86 units with adequate cross edu-
cation data (means and standard deviations of the
untrained limb) resulted in an effect size of 0.71
(95% CI: 0.60–0.83, p<0.001). The amount of cross
education was similar amongst different training
modalities with the exception of EMS training. EMS
training was employed in 10 units, which demon-
strated an average strength gain of 27%. Six units
reported enough data to calculate effect size which
was large [107] at 1.57 (95% CI: 0.81–2.33,
p<0.001). This is greater than the small effect size
of 0.10 (95% CI: –0.04–0.23, p¼0.16) in the control
limb, which corresponded to a mean 2.2% gain.
The average percent gain in the untrained limb
of older participants following unilateral training
was 15%, as calculated from 9 units. A review of 6
units with adequate cross education data resulted in
an effect size of 0.58 (95% CI: 0.22–0.94, p<0.01).
The modes of training included: dynamic (5), iso-
kinetic (2), isometric (1), and resistance tubing (1).
The amount of cross education in the Patients sub-
group was a 29% strength gain (calculated from 6
units), which corresponded to a large effect size of
0.76 (95% CI: 0.21–1.31, p<0.01, calculated from 4
Table 1. Median and range of training characteristics.
Training characteristic
Young Older Patients
Median (range)
Number of
training sessions
21 (6–84) 27 (6–36) 18 (16–27)
Training volume
(sets x reps)
30 (3–250) 34 (20–40) 33 (24–42)
Training intensity
(% maximum)
100 (10–100) 100 (70–100) 100 (80–100)
Table 2. Effect size (standardized mean difference), percent gain, and controlled percent gain for the untrained (contralat-
eral) limb.
N(units) Effect size (95% CI) N(units) % gain Cross-body transfer
Young 86 0.71 (0.60, 0.83) 126 18 70%
Isometric 24 0.73 (0.56, 0.89) 37 15 65%
Isokinetic 23 0.61 (0.41, 0.80) 31 20 70%
Dynamic 27 0.65 (0.43, 0.86) 41 18 71%
EMS 6 1.57 (0.81, 2.33) 10 27 77%
Other 6 0.46 (0.18, 0.74) 7 12 80%
Older 6 0.58 (0.22, 0.94) 9 15 48%
Patients 4 0.76 (0.21, 1.31) 6 29 77%
Control limb 38 0.10 (–0.04, 0.23) 48 2.2 –
CI: confidence interval; EMS: electromyostimulation. , p<0.001, for effect size only. Cross-body transfer is the amount of strength gain transferred
from the ipsilateral limb to the contralateral limb.
Table 3. Effect size (standardized mean difference), percent gain, and controlled percent gain for the trained (ipsilat-
eral) limb.
N(units) Effect size (95% CI) N(units) % gain
Young 81 1.11 (0.96, 1.25) 123 29
Isometric 25 1.11 (0.90, 1.32) 37 25
Isokinetic 20 0.95 (0.79, 1.11) 30 31
Dynamic 23 1.18 (0.89, 1.47) 39 31
EMS 7 1.87 (0.93, 2.82) 10 35
Other 6 0.53 (0.24, 0.81) 715
Elderly 6 1.44 (1.00, 1.87) 931
Patients 2 0.56 (0.11, 1.01)429
Control limb 32 0.13 (–0.02. 0.27) 39 3.0
CI: confidence interval; EMS: electromyostimulation. p<0.05, p<0.001, for effect size only.
4 L. A. GREEN AND D. A. GABRIEL
units). Five of the studies employed strength training
(resistive exercises) of the less-affected limb, one study
[102] employed kicking and tracking movements of
the less-affected limb while secured to a tilt-table.
The influence of limb, sex, and task familiariza-
tion had no influence on the percent gain of the
untrained or trained limb, or the cross-body trans-
fer, as presented in Table 4.
Figure 2. Forest plot of standardized mean difference (SMD) for each young unit included in the analysis for the untrained
(cross education) limb. Light grey lines indicate cutoff values for small (0.2), moderate (0.5), and large (0.8) effect sizes.
PHYSICAL THERAPY REVIEWS 5
Discussion
The primary aim of the current meta-analysis was
to prioritize inclusivity for the largest systematic
analysis of cross education. Secondarily, this meta-
analysis aimed to further cross education within the
rehabilitation field by quantifying the presence of
cross education in young and older able-bodied par-
ticipants, as well as in patient populations. By care-
fully identifying the crucial inclusion criteria and
reducing inclusion selectivity this meta-analysis was
able to include data from 96 studies with 141 units
of training groups.
The cross education gain was an 18% increase
from baseline strength in young, able-bodied adults;
a 15% increase in older, able-bodied participants,
and a 29% increase in a patient population consist-
ing of poststroke, neuromuscular disorders, and
osteoarthritis patients. The values of cross education
are higher than the previous and most widely cited
estimates of 8% by Carroll et al. [4], and Munn
et al. [6], and higher than the recent estimate of
12% reported by Manca et al. [7] The cross-body
transfer to the untrained limb ranged from 52% to
80% of the ipsilateral training effect.
The separation of training modalities allowed for
the analysis of cross education and training adapta-
tion from different contraction types with sufficient
sample sizes and statistical power. This identified
the advanced capabilities of EMS training producing
a cross education effect of 27%, of which previous
meta-analyses excluded [4,6,7,10]. Compared to
cross education produced by isokinetic (20%),
dynamic (18%), and isometric (15%) voluntary con-
tractions, it is evident that EMS training produces a
superior transfer of strength. The logistical ease of
EMS training for varying populations and the asso-
ciated voluntary strength gains, make it an ideal
modality for cross education in rehabilitation set-
tings. Additionally, EMS training provides a viable
alternative for patients (e.g. osteoarthritis) where
pain or joint stiffness are limiting factors in conven-
tional strength training protocols [108].
The rehabilitative benefits of cross education are
present, both as a strength gain and a prevention of
strength loss. Andrushko et al. [109] detailed the
preventative effects (sparing of muscle atrophy) of
unilateral limb training during a period of contralat-
eral limb immobilization. Alternatively, the present
meta-analysis has demonstrated the presence of a
strength gain in the contralateral (more-affected)
limb of patient populations, following unilateral
training of the less-affected limb. Dragert and Zehr
[101] reported significant improvements in the
timed-up-and-go (TUG) test following unilateral
dorsiflexion training poststroke, and small but non-
significant improvements in the modified Ashworth
and Berg balance tests. Similarly, Kim et al. [102]
Figure 3. Forest plot of standardized mean difference (SMD) for each older (A) and patient (B) unit included in the analysis for
the untrained (cross education) limb. Light grey lines indicate cutoff values for small (0.2), moderate (0.5), and large (0.8)
effect sizes. DF: dorsiflexion; KE: knee extension; MS: multiple sclerosis; OA: osteoarthritis.
6 L. A. GREEN AND D. A. GABRIEL
demonstrated significant increases in gait velocity,
cadence, stride length, symmetry, and double sup-
port periods following unilateral kicking movements
of the less-affected limb, poststroke. Manca et al.
[103] compared functional gains following direct
versus contralateral training of the more-affected
versus less-affected limb, respectively. Significant
improvements in timed walking tests were seen in
both groups. However, the direct training group had
larger effects as well as significant improvements on
the TUG test, for which contralateral training group
did not. Taken together, the contralateral strength
gains of cross education are promising for the
rehabilitation of functional movements, specifically
when the more-affected limb is unable to perform
strength training.
There were numerous methodological deficiencies
that were identified by previous meta-analyses
including the need for control group data [6] and
the lack of familiarization [4]. Both of these meth-
odological controls are instituted for the purpose of
minimizing ‘quick jumps in strength’that would
over-estimate the magnitude of cross education. The
present meta-analysis included 48 control units for
the cross education limb reporting an average
strength gain of 2.2% (median: 2.1%, range:
–6%–11%). Therefore, the inclusion of a control
group is important to account for the over-estima-
tion of cross education due to extraneous factors
such as task familiarization.
It has been shown that task familiarity and famil-
iarization contractions can increase force approxi-
mately 3–11% within a single session [110–113].
Carroll et al. [4] estimated that the effect of famil-
iarization on the overestimation of cross education
was approximately 4%. Therefore, it is surprising
that there was no significant difference in the
strength gain between groups that were familiarized
and those that were not. It was hypothesized that a
lack of familiarization would overestimate the mag-
nitude of the cross education and training strength
gain. The likely reason for the absence of difference
in the strength gain is the lack of reporting in the
majority of studies as to what was considered to be
‘familiarization’. Since most studies neglected to
detail the method of familiarization, any study
which noted that its participants were ‘familiarized’,
be it a demonstration, a single test contraction, or
an entire session, was included in the
‘familiarized’group.
The large number of units included in the pre-
sent meta-analysis allowed for the comparison of
cross education between upper and lower limbs and
between sexes in 135 units of able-bodied partici-
pants. Manca et al. [7], separated 31 studies into
upper and lower limb training finding a larger mag-
nitude of cross education in the lower limb (16.4%)
compared to the upper limb (9.4%). However, the
present meta-analysis found no significant difference
between cross education in the lower (18%) and
upper (17%) limbs. Similarly, there was no signifi-
cant difference (p¼0.60) in the magnitude of cross
education between males (16%) and females (17%),
However, comparison between sexes in the trained
limb revealed slightly larger (p¼0.06) training adap-
tations in females (33%) compared to males (26%).
This resulted in a slightly larger (p¼0.17) cross-
body transfer of strength in males (65% transfer)
compared to females (54% transfer).
To date, many studies have assumed an equality
between sexes in the magnitude of cross education,
often citing the review by Zhou [8], which does not
compare sexes. In the literature, only two studies
[43,100] included sex comparisons following unilat-
eral training. Both studies also found significant dif-
ferences between sexes in the magnitude of the
training adaptation, but no difference in the magni-
tude of cross education. This indicates that there is
a difference in the amount of transfer (or ratio
between trained and untrained limbs) between the
sexes, however previous literature is conflicting.
Hubal et al. [43] found a significantly higher
strength cross-body transfer ratio in females (21%)
compared to males (16%). Alternatively, Tracy et al.
Table 4. The number of units that fall within each category: sex of the unit, the usage of familiarization, the limb involved,
and the presence of a control group from the able-bodied participants.
Number of units Number of participants % gain (untrained) % gain (trained) Cross-body transfer
Overall: able-bodied 135 2362 29 18 68%
Limb trained
Lower 68 791 18 28 68%
Upper 67 1571 17 30 69%
Sex of unit
Males only 65 997 16 26 65%
Females only 27 747 17 33 54%
Both sexes 34 506
Unknown sex 9 112
Familiarized
Yes 67 1387 18 29
No 68 975 17 29
Control group (Y/N) 79/56
Note: the presence of a control group (‘Y’) does not indicate the reporting of control results. significant difference in % gain or cross-body transfer
between unit categories (lower vs upper; males vs females; yes vs no familiarization), p<0.05.
PHYSICAL THERAPY REVIEWS 7
[100] found a significantly lower strength transfer
ratio in females (32% transfer) compared to males
(36% transfer).
Conclusion
A review of 141 unilateral training units resulted in
a cross education strength gain of 18% in young
adults, 15% in older adults, and 29% in a patient
population, which is higher than previous estimates
[4,6,7] of 8% to 12%. The cross education effect
was accompanied by a significant moderate to large
effect size in each population. The average cross-
body transfer ranged from 48% to 77% slightly
higher that previous estimates of 35–60% [4,6]. The
present analysis identified: the presence of cross
education in young and older able-bodied partici-
pants as well as patient populations; the efficacy of
EMS training over voluntary modalities; and the
equivalence in cross education between upper and
lower limbs as well as in males and females. The
15–29% magnitude of cross education is promising
for the use of unilateral training in rehabilitation.
Disclosure Statement
No potential conflict of interest was reported by
the authors.
Notes on contributors
Lara A. Green recently completed her Ph.D. in health
biosciences at Brock University examining the phenom-
enon of cross education. David A. Gabriel completed his
Ph.D. in biomechanics at McGill University in 1995. He
worked as a post-doctoral fellow in orthopedic biomech-
anics at the Mayo Clinic until 1997. He is currently a
professor at Brock University.
ORCID
Lara A. Green http://orcid.org/0000-0001-6648-8107
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