Engineering, 2012, 5, 99-102
doi:10.4236/eng.2012.410B025 Published Online October 2012 (http://www.SciRP.org/journal/eng)
Motor Imagery did not Improve Strength of Biceps Brachii*
Lanxiang H e , Zhijun Tian
College of Health S cience, Wu han Sports U niversity, Wuhan, China
Received 2012
ABSTRACT
Numerous studies have confirmed that motor imagery may result in plastic change in motor system as actual physical activity. How-
ever, whether motor imagery can improve muscle strength of the trained persons remains unclear. The aim of this study is to investi-
gate the effect o f motor imagery o n muscle stren gth. Total ly 12 healthy college stu dents were in volved in 4 weeks of mental rehear-
sal of right upper limb movements (flexion and extension of elbow) during 30 min supervision session three times a week. Electro-
myogram (EMG) and peak torque of biceps brachii, reaction time of subjects were analyzed. Results showed that no significant
change in EMG of biceps br achii was observed during motor imagery. After motor rehearsal for 4 weeks, statistically significant
difference i n E MG, p eak to rqu e and reacti vity were n o t ob ser ved (P > 0.05) when compared with the baseline data. Therefore, motor
imagery co ul d no t enhan ce muscl e st ren gth o f sub ject s. Whet her ment al p ractice i s a valid reh ab ili tatio n t echniqu e n eeds to be in ve s-
tigated further.
Keywords: Moto r Imager y; EMG; Peak Tor que; R eaction Time
1. Introduction
Motor imagery is a mental process of a movement without any
overt movement or without any muscle activation[1-2]. The
effects of motor imagery on motor learning and motor recovery
have been investigated extensively for many years. Numerous
studies have indicated that motor imagery may enhance motor
recovery and motor learning, which have many aspects in
common. One of possible mechanisms is that motor imagery
can result in the activation of motor cortex in brain, which is
the same as actual physical activity. However, it is still disputed
whether motor imagery can improve motor rehabilitation. Es-
pecially, whether motor imagery can enhance muscle strength
is still unclear.
In this study, 12 healthy college students were recruited for
participating motor imagery of upper limb movement (elbow
flexion and extension). The physiological parameters including
reaction time, EMG and peak torque of biceps brachii were
recorded and analyzed after 4 weeks of motor imagery. This
study aims to investigate whether motor imagery can increase
muscle strength of participants, which may be helpful for per-
sons with sport injury to improve their muscle strength or delay
their muscle atrophy.
2. Participants and Protocol
2.1. Participants
Totally 12 healthy college students (6 females and 6 males,
21-24 years old) volunteered to participate in this study. During
the study, all participants did not perform any physical exercise.
2.2. Protocol
At the 1st week of trial, baseline data of EMG, muscle strength,
and reaction time were collected. Then the participants were
instructed to perform motor imagery of right elbow flexion and
extension according to the protocol. At the 2nd week of trial,
the participants started to perform daily motor imagery for 30
min, three times per week for four consecuti ve weeks.
During motor imagery process, EMG of biceps brachii was
also recorded. At the 6th week of trial, their muscle strength,
EMG and r eaction time of right biceps were detected agai n.
3. Methods and Instruments
3.1. Messurement of Muscle Strength
Participants were seated in a chair. Their right arm was semi-
flexed and was mounted during all measurements. Strength of
biceps brachii was measured concentrically at 60° per second
on an isokinetic dynamometer (Biodex-4, USA). The peak tor-
que (Newton meters, N-m) was recorded and stored on a per-
sonal computer for offline analysis.
3.2. Messurement of Reaction Time
The reaction time was recorded by reaction time detector
(FYS-I, China). The red light signals were given from the front
of the subject. The subject pressed the button using his right
hand while responding to the red signal. The mean value of
three measurements was used fo r analysis.
3.3. Messurement of EMG
Electromyograph (ME6000T16, Finland）was used for col-
lecting EMG data. The surface electrodes attached to the skin
over biceps brachii. The skin was cleaned for the adherence of
the electrodes and detection of EMG. The raw EMG signals
were band-pass filtered (10-500 Hz) and recorded. The data
were collected at 1000 Hz and analyzed with Mega-Win soft-
*This research was supported by Wuhan Sports University.

L. X. HE, Z. J. TIAN
100
ware.
3.4. Data Analysis
The mean power frequency (MPF) and root mean square (RMS)
were calculated from the observed EMG. RMS was used as an
indicator of the total myoelectric activity. The MPF served to
indicate the firing rate of motor units as it is linearly related to
the action potential conduction velocity of the muscle fibre[3].
The Student t-test for paired samples ( measures before trial
and after trial) was applied using SPSS (version 13.0). The
significant difference was considered at the P value less than
5%.
4. Results
EMG signals of biceps brachii was detected motionless situa-
tion (Figure 1A), motor imagery (Figure 1B), isometric con-
traction (Figure 1C), and isotonic contraction (Figure 1D),
respectively. EMG activity in motionless situation and motor
imagery both were in baseline level. As shown in Table 1,
surface EMG activity of biceps br achii did not change signifi-
cantly after motor imagery for 4 weeks (P > 0.05). It suggested
that, EMG activity of biceps brachii did not exhibit a significant
change due to motor imagery of elbow flexion.
Strength of biceps brachii was also measured concentrically
at 60° per second on an isokinetic dynamometer. The peak
torque of biceps brachii after motor imagery was bigger than
that before motor imagery. The reaction time after motor im-
agery was shorter than that before motor imagery. As shown in
Table 1, no significant difference was achieved (P > 0.05).
5. Discussion
Learning a motion skill is just to establish a motion conditioned
reflex, which includes sensory input, signals integration by
brain cortex and signals output to effectors (muscle). The im-
provement o f th ese factors may b e in favor of learning a motion
skill.
(A.motionless B. motor imagery C. isometri c contracti on D. isotoni c contracti on)
Figure 1. Electromyogram of Bicipital Muscle of Right a rm.
Table 1. Reaction Time, Surfac e EMG and Peak Torque of Biceps Brachii (Mean±SD).
Surface EMG P eak Torque
（N.m） Reaction Time （s）
RMS (μV) MPF （ Hz ）
Before Trial 442.1±187.9 63.2±6.1 33.57±12.74 0.3567±0.0425
After Trial 429. 7±169.6 67.0±9.5 35.82±12.70 0.3299±0.0291
P >0.05 >0.05 >0.05 >0.05

L. X. HE, Z. J. TIAN
101
Brain functional representations and their connections have
plasticity [4]. Repeat motion training can stimulate or excite its
brain functional representations and strengthen their connec-
tions each other, which will be of benefit to sport performance.
Motor imagery is a mental activity. It is a dynamic state dur-
ing which the representation of a specific motor action is inter-
nally activated without any motor output. Increasing evidences
have confirmed that both motor imagery and actual physical
activity can activate cortical motor areas in the central nervou s
system. Therefore, the effect of motor imagery on learning
motion skill and motor recovery from sport injury has gained
tremendous attention.
Previous reports have demonstrated that mental practice can
increase i ts accu rac y thro ugh ping-pong ball tossing experiment,
which suggests that motor imagery may be a useful tool in
learning a new motor skill[5]. However, for learning the abduc-
tion of the big toe, only subjects who had some experience in
the task improved significantly after mental practice as well as
after ph ysical p ractic e[ 6] . For patien ts, mot or r ecover y is a kin d
of relearning of motor skill actually. Motor imagery has been
also proved to be helpful for motor recovery of patients with
stroke[ 7].
Mechanism of motor imagery is less well understood. Cur-
rently, two hypotheses are used for the explanation of motor
imagery[8-9]. The central mechanism has made an assumption
that motor imagery can stimulate the same cortical areas as
actual physical activity and strengthen the connections of rela-
tive functional representations, which is supported by function-
al magnetic r es onan ce imaging (fMRI).
The activation in dorsal premotor cortex, superior parietal
lobe and intraparietal sulcus is observed and the cortical repre-
sentati ons are over lapped partially during the motor imagery of
the participants [10]. Imagery of right-hand finger movements
can induce a cortical activation pattern including dorsal and
ventral portions of the premotor cortex, frontal medial wall
areas, and cortical areas lining the intraparietal sulcus in both
cerebral hemispheres[11]. Motor imagery not only has similar
functions of neural networks as real physical activity [12], but
also can modulate corticomotor excitability[13].
However, a novel continuous pointing method was used to
measure and precisely characterize self-motion perception dur-
ing actual movement and imagined movement through space.
The results have revealed that the spatial updating processes
that o ccur during actual self-motion were not evidenced during
imagined movement [14].
The peripheral mechanism has supposed that motor imagery
may result i n neural impulse o utput so th at myoelectrical acti v-
ity may increase and more fibers may contract synchronously,
thus improving muscle strength [15-17]
According to Fontani’s report, 30 male participants with
motor imagery (karate) have achieved same results in muscle
strength improvement as actual training group. However, no
obviou s change in reacti vity is n ot observed in mental imagery
group[16]. Similarly, 11 stroke patients subjected to motor
imagery training have greatly improved their limb functions
[16]. In contrast, 39 stroke patients involved in mental practice
for 4 weeks have revealed inconsistent results [18]. In our study,
healthy college students involved in mental practice for 4
weeks also d id not exhibit a significant ch ange in surface EMG
signal and peak torque when compared with the data before
trial, which suggested that 4 weeks of motor imagery training is
not enough to enhance muscle strength.
Muscle strength is highly correlated with neural system func-
tions such as modulating velocity and frequency of neural im-
pulse. Faster neural impulse from motor cortex to arm muscles
can lead to shorter reaction time. In the present study, motor
imagery did not result in the decrease of reaction time, thus
suggestin g that mental practice has no effect on th e modulation
of neural impulse velocity. This result is consistent with Fon-
tani’s report[16].
In a word, extensive investigations have demonstrated that
motor imagery can stimulate cortical functional areas, and the
rehabilitation of patients with dyskinesia may benefit from
motor imagery [19]. However, the improvement of muscle
strength through motor imagery is still lack of convincing evi-
dences. The motor imagery (elbow flexion) for 4 weeks can not
improve the strength of biceps in right arm. The optimal train-
ing protocol should be further explored in the future.
6. Acknowledgements
We are very grateful to Dr. Ning Chen for helpful comments
and revi s e.
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