Associations Between Practice-Related Changes in Motor Performance and Muscle Activity in Healthy Individuals: A Systematic Review
Brueckner et al. Sports Medicine - Open
Associations Between Practice-Related Changes in Motor Performance and Muscle Activity in Healthy Individuals: A Systematic Review
Dennis Brueckner 0 2
Rainer Kiss 1
Thomas Muehlbauer 0
0 Division of Movement and Training Sciences/Biomechanics of Sport, University of Duisburg-Essen , Gladbecker Str. 182, 45141 Essen , Germany
1 Department of Health and Social Affairs, FHM Bielefeld-University of Applied Science , Bielefeld , Germany
2 Division of Sports Medicine and Engineering, Hochschule Koblenz-University of Applied Sciences , Remagen , Germany
Background: A well-learned motor skill is characterized by the efficient activation of muscles that are involved in movement execution. However, it is unclear if practice-related changes in motor performance correlate with those in quantitative markers of muscle activity and if so, whether the association is different with respect to the investigated muscle (i.e., agonist and antagonist) and quantitative myoelectric parameter. Thus, we conducted a systematic review and characterized associations between practice-related changes in motor performance and muscle activity in healthy individuals. Methods: A computerized systematic literature search was performed in the electronic databases PubMed, Web of Science, and SPORTDiscus up to September 2017 to capture all relevant articles. A systematic approach was applied to evaluate the 1670 articles identified for initial review. Studies were included only if they investigated healthy subjects aged 6 years and older and tested at least one measure of motor performance (e.g., error score, movement time) and quantitative muscle activity (i.e., amplitude domain: iEMG [integrated electromyography], RMS [root mean square]; time domain: duration of muscle activity, time to peak muscle activation). In total, 24 studies met the inclusionary criteria for review. The included studies were coded for the following criteria: age, learning task, practice modality, and investigated muscles (i.e., agonist and antagonist). Correlation coefficients for the relationship of motor performance changes with changes in electromyography (EMG) amplitude, and duration were extracted, transformed (i.e., Fisher's z-transformed rz value), aggregated (i.e., weighted mean rz value), and back-transformed to r values. To increase sample size, we additionally extracted pre and post practice data for motor performance and myoelectric variables and calculated percent change values as well as associations between both. Correlations were classified according to their magnitude (i.e., small r ≤ 0.69, medium r ≤ 0.89, large r ≥ 0.90). Results: Five studies reported correlation coefficients for the association between practice-related alterations in motor performance and EMG activity. We found small associations (range r = 0.015-0.50) of practice-related changes in motor performance with measures of agonist and antagonist EMG amplitude and duration. A secondary analysis (17 studies) that was based on the calculation of percent change values also revealed small correlations for changes in motor performance with agonist (r = − 0.25, 11 studies) and antagonist (r = − 0.24, 7 studies) EMG amplitude as well as agonist (r = 0.46, 8 studies) and antagonist (r = 0.29, 5 studies) EMG duration. (Continued on next page)
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Conclusions: Our systematic review showed small-sized correlations between practice-related changes in
motor performance and agonist and antagonist EMG amplitude and duration in healthy individuals. These
findings indicate that practice-related changes can only partly be explained by quantitative myoelectric
measures. Thus, future studies investigating biomechanical mechanisms of practice-related changes in motor
performance should additionally include qualitative measures of muscle activity (e.g., timing of muscle activity, level of
coactivation) and other biomechanical variables (i.e., kinetics, kinematics).
The present systematic review characterized
associations between practice-related changes
in motor performance and muscle activity in
Irrespective of the investigated myoelectric
parameter (i.e., amplitude and duration) and
muscle (i.e., agonist and antagonist), our
analyses revealed small-sized correlations between
changes in motor performance and muscle activity
following motor practice.
The observed small associations imply that
practicerelated changes in motor performance can only
partly be explained by quantitative myoelectric
measures, and thus, we recommend to additionally
include qualitative measures of muscle activity (e.g.,
timing of muscle activity, level of coactivation) and
other biomechanical variables (i.e., kinetics, kinematics)
in future investigations.
Motor learning is defined as the changes, associated with
practice or experience, in internal processes that
determine a person’s capability for producing a motor skill
]. For example, as learning a motor skill progresses,
movement error and duration are reduced. These
performance improvements are related to changes in the
gradation and timing of force produced by the muscles
involved in the skilled performance. The level and
duration of muscle involvement during execution of a
learned movement task is reflected in their myoelectric
activity that can be recorded and displayed by the use of
The effects of motor practice on myoelectric activity
have been investigated for more than six decades. One
of the first studies [
], conducted in the late 1950s,
investigated relatively simple movements, i.e., participants
practiced filing and chiseling for 2 to 6 weeks. For both
tasks, practice resulted in an increased movement
fluidity and a change in the EMG pattern from
agonistantagonist coactivation early in practice to reciprocal
activation of both muscles late in practice. Ten years
later, Kamon and Gormley [
] confirmed this result
using a more complex movement task. In their
experiment, subjects practiced the single knee circle mount on
the horizontal bar. Over the 3-month practice period,
they found a fluent execution of the exercise that was
accompanied by a shift from continuous and overlapped
muscle activity to phasic muscle activation. Thus,
reciprocal, phasic, or sequential muscle activation seems to
be qualitative indicators of resulting changes in the
muscle activation pattern due to motor practice.
Further research tried to extend these findings with
the aim to establish quantitative parameters of
practicerelated myoelectric changes. While some authors
reported decreases [
] in muscle activity following
practice, others found increases [
] or no changes [
Therefore, the current evidence is conflicting, with a
lack of studies systematically reviewing practice-related
myoelectric changes associated with those in motor
performance in healthy subjects. Moreover, previous studies
primarily examined the effects of practice on measures
of motor performance and muscle activity, separately,
but did not report the relationship between the two.
Consequently, there is still a gap in our knowledge
regarding potential associations between practice-induced
adaptations in motor performance and muscle activity.
Further, if there is such an association, information on
the direction (i.e., positive or negative) and size (i.e.,
small, medium, or large) of the correlations need to be
examined. A review of this topic will provide a better
understanding of motor control processes and is suitable
to provide information on how these processes change
with skill acquisition. From a more practical point of
view, the presented line of research is needed to
determine the influence of motor practice on
myoelectric activity in order to get insights that can be used for
the design and evaluation of practice programs. Thus,
the aim of this systematic literature review was to
characterize associations between practice-related changes
in motor performance and muscle activity in healthy
individuals considering different well-established EMG
variables (i.e., amplitude domain: integrated EMG [iEMG],
root mean square [RMS]; time domain: duration of
muscle activity, time to peak muscle activation). Since
motor learning is characterized by a reduction in the force
level and the time required to execute the practiced task,
EMG amplitude and duration should also decrease,
especially for the agonist muscle.
A computerized systematic literature search was
conducted in PubMed, Web of Science, and SPORTDiscus
from January 1950 up to September 2017. The following
Boolean search strategy was applied using the operators
AND, OR, NOT: (((motor learning OR motor practice
OR skill acquisition) AND (muscle activity OR muscle
activation OR EMG analysis OR electromyographic
activity OR neuromuscular activity) NOT (patients OR
disease))). The search was limited to full-text original
articles, human species, and English language. Further,
we checked the reference lists of each included article in
an effort to identify additional suitable studies for
inclusion in the database.
To be eligible for inclusion, studies had to meet the
following criteria: (a) participants of the experimental
groups had to be healthy subjects and (b) at least one
measure of motor performance and muscle activity had
to be assessed in the study. Studies were excluded if (a)
they investigated children (6–12 years), adolescents (13–
18 years), seniors (≥ 65 years), patients, or people with
diseases; (b) it was not possible to extract pre and post
practice values from the results section; or (c) authors
did not reply to our inquiries sent by email. Based on
the predefined inclusion and exclusion criteria, two
independent reviewers (DB, TM) screened potentially
relevant papers by analyzing the titles, abstracts, and full
texts of the respective articles to elucidate their
eligibility. If no consensus was achieved between the two
reviewers, a third reviewer (RK) was contacted.
Coding of Studies
Each study was coded for the following variables:
number of participants, age, learning task, practice modality,
investigated muscle, motor performance, and muscle
activity outcomes. For the latter one, we divided in
measures of EMG amplitude (e.g., iEMG, RMS) and duration
(e.g., duration of muscle activity, time to peak
activation). For studies that reported multiple parameters
within these outcome categories, the most representative
parameter was included for further analysis. With regard
to EMG amplitude, iEMG was defined as the most
important variable. In terms of EMG duration, duration of
muscle activity was used. As a function of the respective
motor performance measure (i.e., error score or number
of successful hits), the pre to post practice change can
be negative or positive. Thus, a negative percent change
value would indicate practice-related performance
improvements (i.e., decrease in error score), and a positive
percent change value would indicate a performance
decrement (i.e., increase in error score) following practice.
Statistical Analyses In a first approach, associations
between practice-related changes in motor performance
and muscle activity were assessed using the reported
Pearson product-moment correlation coefficient (r
value). To pool r values derived from different studies,
“Fisher’s z′ transformation” was used, i.e., Pearson
product-moment correlation coefficients were
converted to the normally distributed variable z′ (i.e.,
ztransformed rz value). The formula for the
transformation is (Eq. 1):
z0 ¼ 0:5½ ln ð1 þ rÞ− ln ð1−rÞ
where ln is the natural logarithm [
]. In addition, the
included studies were weighted according to the
magnitude of the respective standard error (SE). The formula
for the calculation of the SE is (Eq. 2):
SE ¼ 1=√ðN −3Þ
where N stands for the respective sample size [
Afterwards, weighted mean rz values were computed. To
classify and interpret the correlation sizes, rz values were
back-transformed to r values. Based on the
recommendations of Vincent [
], values of 0 ≤ r ≤ 0.69
indicate small, 0.70 ≤ r ≤ 0.89 medium, and r ≥ 0.90 large
sizes of correlation. In a second approach, pre and post
practice data for motor performance and myoelectric
variables were extracted from other studies to calculate
percent change values. Afterwards, associations between
practice-related changes in motor performance and
muscle activity were computed.
Figure 1 displays a flow chart that illustrates the different
stages of the systematic literature search and the selection
of articles over the course of the search. The initial search
identified 1670 studies that were potentially eligible for
inclusion. After removal of duplicates and exclusion of
ineligible articles, 21 studies remained. We identified another
three articles from the reference lists of the included
articles. Therefore, 24 studies were included in the final
analysis with 17 and 11 studies that investigated parameters
of EMG amplitude and duration, respectively.
Table 1 illustrates the main characteristics of the
included studies (n = 17) examining practice-induced
adaptations on motor performance and measures of
EMG amplitude. Fourteen studies (n = 232 subjects)
were performed with young adults only [
one study (n = 12) with young and middle-aged adults
, one study (n = 28) with young and old adults [
and one study (n = 22 subjects) did not report subjects’
]. Maximal effort tasks (i.e., fast/ballistic accurate
movements) were investigated in five studies [
6, 16, 19,
] and submaximal effort tasks (i.e., target oriented
or time/velocity constrained) were examined in 12
4, 5, 7–9, 12–15, 17, 18, 21
]. The literature search
revealed a number of practice sessions ranging from one
to ten. The number of trials per session ranged from ten
to 200. One study reported a duration of 16 min per
session . The number of investigated agonist and
antagonist muscles ranged from one to two.
Table 2 shows the main characteristics of the included
studies (n = 11) that examined practice-related changes
on motor performance and measures of EMG duration.
Nine studies (n = 159 subjects) were conducted in young
adults only [
6, 9, 13, 16, 23–27
], one study (n = 12) with
young and middle-aged adults [
], and one study (n = 28)
with young and old adults [
]. Due to the possible
influence of biological aging, data for the old adults were
excluded from our data analyses. Maximal and submaximal
effort tasks were used in four [
6, 16, 20, 23
] and seven
9, 13, 21, 24–27
], respectively. One to ten practice
sessions were performed that included ten to 120 trials
per session. The number of studied agonist and antagonist
muscles ranged from one to two.
Associations Between Practice-related Changes in Motor
Performance and Muscle Activity
Five studies [
] reported correlation coefficients
for the association between practice-related changes in
motor performance and myoelectric activity. Figure 2a, b
illustrates the relationships of motor performance with
agonist and antagonist EMG amplitude, respectively.
Weighted mean rz values amounted to 0.55 for measures
of agonist EMG amplitude (I2 = 40%, chi-square = 6.63,
df = 4, p = 0.16, five studies: [
]) and 0.33 for
outcomes of antagonist EMG amplitude (I2 = 0%,
chisquare = 0.64, df = 3, p = 0.002, four studies: [
8, 19, 21,
]). Back-transformed r values of 0.50 (R2 = 25%) and
0.32 (R2 = 10%) indicated small correlations.
Additionally, one study  reported a small correlation of motor
performance with measures of agonist (rz = 0.36, r = 0.347,
R2 = 12%) and antagonist (rz = 0.02, r = 0.015, R2 = 0%)
In addition, pre and post practice data for motor
performance and myoelectric activity were extracted from
17 studies to calculate percent change values and
associations between both. Figure 3 displays scatterplots for
changes in motor performance with agonist (Fig. 3a) and
antagonist EMG amplitude (Fig. 3b). Our analysis
revealed negative, small associations of motor performance
with agonist (r = − 0.25, R2 = 6%, p = 0.283, 11 studies, 20
data points; Fig. 3a) and antagonist (r = − 0.24, R2 = 6%,
p = 0.043, 7 studies, 10 data points; Fig. 3b) EMG
amplitude (Additional file 1: Table S1). Figure 4 shows
scatterplots for alterations in motor performance with
EMG electromyography, NR not reported, SD standard deviation
Submaximal effort task: manual spelling of
words; 1 session including 7 blocks, 42
Submaximal effort task: target-oriented force
production while maintaining a constant
pedaling speed; 1 session, 18 trials/session
Agonist and antagonist muscles: tibialis anterior,
soleus, vastus lateralis, medial gastrocnemius,
rectus femoris, semitendinosus
Maximal effort task: ballistic (maintain
maximum velocity) wrist flexion; 10 sessions,
EMG duration for agonist (Fig. 4a) and antagonist
muscles (Fig. 4b). Our analysis yielded positive, small
associations of motor performance with agonist (r =
0.46, R2 = 21%, p = 0.095, 8 studies, 14 data points;
Fig. 4a) and antagonist (r = 0.29, R2 = 8%, p = 0.634, 5
studies, 5 data points; Fig. 4b) EMG duration
(Additional file 2: Table S2).
The present systematic literature review characterized
associations between practice-related changes in motor
performance and muscle activity in healthy individuals
considering different myoelectric variables (i.e., agonist
and antagonist EMG amplitude and duration). This
research is important for a better understanding of
myoelectric adaptation processes initiated by motor practice.
Especially, we focused our analyses on well-established
EMG measures in the amplitude (e.g., iEMG, RMS) and
time (e.g., time to peak muscle activation) domain
because these are particularly related to modifications in
the spatial and temporal characteristics of muscle force
production following practice. We hypothesized that
improvements in motor performance following practice are
accompanied by reductions in EMG amplitude and
duration, especially observed in the agonist muscle. We
found only small-sized associations between
practicerelated alterations in motor performance and agonist
and antagonist muscle activity. This finding was
independent from the used data source, that is, associations
reported in the literature and correlation coefficients
additionally calculated from extracted pre and post
practice data for measures of motor performance and
myoelectric activity. In general, our findings indicate that
practice-related changes in motor performance might
only partly be explained by changes in quantitative
myoelectric parameters (i.e., agonist and antagonist EMG
amplitude and duration). A possible reason for the
small-sized associations between practice-related
alterations in motor performance and agonist and antagonist
muscle activity could be the concurrent effect of skill
acquisition on qualitative EMG parameters, such as the
timing of muscle activity or the amount of coactivation.
In this regard, previous research [
] showed that
during motor practice, the EMG pattern alters from
continuous and overlapped muscle activity (i.e., early in
practice) to phasic and reciprocal activation (i.e., late in
practice). As a consequence, further research is needed
to determine the relationship between changes in motor
performance and qualitative EMG variables due to motor
practice. Additionally, besides the mentioned changes in
qualitative myoelectric parameters, adaptations in kinetic
(e.g., joint torques, forces) and kinematic (e.g., joint
positions, angles, angular velocity, acceleration) variables
might have influenced our findings of small-sized
correlations between changes in motor performance and muscle
activity following practice. For example, Corcos et al. [
reported significant improvements in movement
kinematics (e.g., increased peak moment velocity and acceleration)
as a function of practice in young adults aged 20 to
25 years. Further, Christou et al. [
] showed that
practicing an endpoint accuracy task resulted in a significantly
reduced variability of the force trajectory, peak force, and
time-to-peak force in healthy adults and was significantly
related (range r = 0.394–0.585) to the improvement in
time endpoint error. Thus, we recommend that future
studies should add kinetic and kinematic analyses to the
investigation of modifications due to motor practice.
The observed correlations differed in terms of their
direction. More specifically, in four out of five studies
that previously reported correlation coefficients between
practice-related changes in motor performance and
agonist EMG amplitude, the r value was positive.
Contrary, a negative r value was obtained from the extracted
pre and post practice data between motor performance
and agonist EMG amplitude. However, the reason for
this findings cannot unambiguously be explained using
our data set because only three of the included 20 data
points indicated an increase in myoelectric activity
although motor performance improved as a result of
practice. Additionally, positive associations were
detected for practice-related changes in motor
performance with agonist and antagonist EMG duration but
negative relationships were found for motor
performance with agonist and antagonist EMG amplitude. In
other words, as motor performance improved agonist
and antagonist EMG duration decreased, yet agonist and
antagonist EMG amplitude increased. What are likely
explanations for the observed difference in correlation
direction? A decrease in agonist and antagonist EMG
duration corresponds with reports [
6, 16, 25
reductions in movement time required to execute a practiced
task. With regard to agonist EMG amplitude, an
increase could be caused by the specific demands of the
utilized practice task. More specifically, when the goal is
to increase the speed of limb movement during practice
(e.g., to perform fast accurate movements [
would lead to an increase in the magnitude of muscle
activity (e.g., agonist EMG amplitude) as proposed by
the “speed-sensitive strategy” . In terms of antagonist
EMG amplitude, an increment might be elicited by the
specific role of antagonist muscles when performing the
practice task. Contrary to agonist muscles that are
responsible for efficient movement execution, antagonist
muscles mainly have assistive or stabilizing function
necessary to decelerate the limb movement that leads to
extended myoelectric activation [
A limitation of this systematic review is that only five
studies were found that reported correlation coefficients
for alterations in motor performance associated with
those in muscle activity. To increase sample size, we
additionally extracted pre and post practice data for
measures of motor performance and muscle activity
from another 17 studies. From this, percent change
values were calculated followed by correlational analyses.
As a consequence, an indirect comparison of
practicerelated changes in motor performance with muscle
activity was performed that requires substantiation by
further studies that directly compare practice-related
alterations in motor performance associated with
changes in muscle activity via correlational analysis.
Further, practice-related alterations in motor performance
were assessed along with associated changes in
quantitative (i.e., EMG amplitude, duration) but not in
qualitative (i.e., timing of muscle activity, amount of
coactivation) myoelectric variables or other
biomechanical variables (i.e., kinetics and kinematics). Thus,
we recommend that future studies should conduct
comprehensive electromyographic examinations
together with kinetic and kinematic analyses of pre and
post practice data. In addition, the observed
practicerelated changes in muscle activity could be influenced
by differences in the used practice task (i.e., maximal
versus submaximal effort tasks). Maximal effort tasks
such as fast/ballistic accurate movements were
investigated in six studies and require an increase in limb
speed, and thus, an increase in EMG amplitude would
be an appropriate change. Submaximal effort tasks
were examined in 18 studies and include
targetoriented and time-/velocity-constrained movements
where the goal is to reduce movement error, time, or
velocity. In this case, a decrease in EMG amplitude
and duration would be an adequate adaptation. As a
consequence, further research is needed to determine
whether practice task category (i.e., maximal versus
submaximal effort task) influences the relationship between
practice-related changes in motor performance and
muscle activity in healthy individuals. Finally,
correlations do not show cause and effect. Hence, the
investigated associations could be affected by other not
yet examined variables such as alterations in
qualitative (i.e., timing of muscle activity, amount of
coactivation) myoelectric parameters or other
biomechanical variables (i.e., kinetics, kinematics).
The present systematic review revealed small-sized
correlations between practice-related changes in
motor performance and agonist and antagonist EMG
amplitude and duration in healthy individuals. Our
findings indicate that practice-related adaptations in
motor performance of healthy persons can only partly
be explained by changes in quantitative myoelectric
measures. Consequently, future studies investigating
practice-induced adaptations are advised to integrate
qualitative myoelectric as well as other biomechanical
variables (i.e., kinetics, kinematics).
Additional file 1: Table S1. Pre and post practice data for motor
performance and EMG amplitude. (XLSX 37 kb)
Additional file 2: Table S2. Pre and post practice data for motor
performance and EMG duration. (XLSX 31 kb)
We acknowledge support by the Open Access Publication Fund of the
University of Duisburg-Essen.
Availability of Data and Materials
All data and materials are available in this manuscript.
The last author (TM) designed the research question and conducted the initial
review and first manuscript draft. The first author (DB) conducted the entire
literature search using the selection criteria and coding of studies and
performed the statistical analyses. The second author (RK) contributed
substantially to all sections of the manuscript. All authors read and approved
the final manuscript.
Ethics Approval and Consent to Participate
Consent for Publication
Dennis Brueckner, Rainer Kiss, and Thomas Muehlbauer declare that they have
no competing interests.
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