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Mind Over Matter: Mental Training Increases
Physical Strength
Erin M. Shackell and Lionel G. Standing
Bishop's University
This study tested whether mental training alone can produce a gain in
muscular strength. Thirty male university athletes, including football,
basketball and rugby players, were randomly assigned to perform mental
training of their hip flexor muscles, to use weight machines to physically
exercise their hip flexors, or to form a control group which received
neither mental nor physical training. The hip strength of
each
group was
measured before and after training. Physical strength was increased by
24%
through mental practice (p = .008). Strength was also increased
through physical training, by
28%,
but did not change significantly in the
control condition. The strength gain was greatest among the football
players given mental training. Mental and physical training produced
similar decreases in heart rate, and both yielded a marginal reduction in
systolic blood pressure. The results support the related findings of
Ranganathan, Siemionow, Liu, Sahgal, and Yue (2004).
The idea of using mental practice to enhance performance has
recently become common. In this procedure, participants are asked to
rehearse a motor or cognitive skill by using mental imagery of
themselves performing it successfully, without any overt behavior or
muscular activity on their part. In the field of
sports
psychology, websites
and books now proliferate which promote mental training to enhance
athletic performance (e.g., Cohn, 2006; Ungerleider, 1996). Professional
teams today often utilize mental training programs for their athletes, and
some have suggested that mental strength training should receive as
much emphasis as physical training.
There are now several hundred papers in the literature which support
the idea that prior mental practice produces measurable gains in skilled
performance, for both cognitive and physical tasks, as summarized in
meta-analyses by Feltz and Landers (1983) and Driskell, Copper, and
Moran (1994). Concurrent mental set or mood may also of course
influence motivation and skilled performance either positively, as shown
by improved scores for speed and accuracy in subjects who adopt a
positive mental attitude (e.g., Ainscoe & Hardy, 1997; Spencer &
Norem, 1996), or negatively, as shown by reduced scores when the test
Author
info:
Correspondence should be sent
to:
Erin
M.
Shackell & Lionel G.
Standing, Department of
Psychology,
Bishop's University, Sherbrooke QC,
Canada JIM 0C8.
North American Journal of Psychology, 2007, Vol. 9, No. 1 189-200
©NAJP
190 NORTH AMERICAN JOURNAL OF PSYCHOLOGY
instructions include anxiety-inducing cues (e.g., Steele & Aronson
1995).
However, the more controversial claim has also been made that prior
mental training alone can also substantially increase performance in a
task which requires simple muscular strength, as opposed to skill or fine
motor control in space and time (Cupal & Brewer, 2001; Reiser, 2005;
Smith, Collins, & Hoknes,
2003;
Smith & Collins, 2004). This claim has
yet to be validated conclusively, partly because methodological issues
abound. The claimed effect is, however, conceptually similar to
experimental demonstrations that hypnosis can produce various
physiological changes, such as wart-removal or breast enlargement
(Barber, 1984; Ewin, 1992; Willard, 1977), and is also parallel to the
many findings in the field of medicine that mental changes can create
measurable physical benefits, such as recovery of ovulation produced by
psychotherapy (Berga, Marcus, Loucks, Hlastala, Ringham, & Krohn,
2003),
or reduction in blood pressure induced by classical music (Chafm,
Roy, Gerin, & Christenfeld, 2004). Mental practice is now recommended
during treatment in some medical cases (e.g., stroke recovery; Bell &
Murray, 2004). The influential bio-informational theory of Lang (1979),
which suggests that in mental training the prepositional content of mental
imagery can directly modify the efferent activity of the brain, provides a
possible conceptual basis for this claim.
Ranganathan, Siemionow, Liu, Sahgal, and Yue (2004) have recently
tested in detail whether strength gains in the little finger abductor and
elbow flexor muscles may be produced by mental training. They also
examined the cortical functions that control contractions of these muscle
groups, as well as EMGs, blood pressure, and heart rate. After mental
training it was found that the finger abductor group muscles had
significantly increased their abduction strength by 35% above baseline,
or 40% when measured four weeks after the training had ended. (The
physical training group increased in finger abduction strength by 53%).
The elbow flexion group increased their strength by
13.5%;
however, this
value was not statistically significant. The authors conclude that mental
training enhances the cortical output signal, causing a higher activation
level and an increase in strength, although the EMG signal is not
measurably affected by training.
The present experiment tests the same general hypothesis by using a
different muscle group, the hip flexors, to determine whether a
measurable gain in strength may be induced through mental training.
Representing a modified version of the study by Ranganathan et al.
(2004),
this experiment attempted to replicate their central finding in a
shorter time fi-ame of two weeks, as opposed to 12 weeks. Hip flexion
uses primarily the iliacus and psoas muscles (Andersson, Nilsson, Maa,
Shackell & Standing STRENGTH VIA IMAGERY 191
6 Thorstensson, 1997), and was selected because these muscles cannot
readily be exercised in other contexts or with free weights.
METHOD
Participants
Thirty male undergraduate students, who were football, basketball
and rugby players at Bishop's University, were used as participants (18,
7 and 5 subjects, respectively). Of these 30 participants, 10 were
randomly assigned to a mental training group which mentally practiced
hip flexions. Ten more participants were assigned to a physical training
group, which exercised using a hip flexor weight machine. A further 10
participants formed a control group, which was given no mental or
physical training. The subjects' ages, heights, and body weights are
summarized in Table 1, while Table 2 indicates that their pre-test scores
fall into the healthy-normal range for blood pressure and pulse.
TABLE
1
Subject Characteristics in the Mental Training, Physical
Training, and Control Groups
Age in years
Height (cm)
Body weight (Ib)
Mental
M SD
19.8
190.0
218.7
n = 10 for each group
1.40
4.22
36.39
Physical
M SD
19.2
185.7
213.2
1.23
7.63
36.07
Control
M
21.3
85.1
216.9
SD
2.45
9.68
51.08
As an incentive to take part in the study, the participants were
rewarded with one Blast protein bar for each 15 minute session.
Materials
Subjects were measured pre-training and post-training in each
condition to determine whether strength gain occurred. A hip flexor
weight machine (Atlanta Precision), measuring pounds of force in
increments of 5 lb from a baseline of 30 lb, was employed to assess
initial and flnal strength, as well as being used in the training process for
the physical training group. An electronic sphygmomanometer (Physio
Logic Automatic Inflation) was utilized to measure systolic and diastolic
blood pressure together with heart rate, and a balance beam scale was
used to weigh each participant.
192 NORTH AMERICAN JOURNAL OF PSYCHOLOGY
Procedure
Each participant was tested for strength at the beginning and the end
of the study, using a hip flexor task. In this task, the subject stands next
to a padded bar and attempts to raise his left leg sideways while the
weight of
the
bar is varied by the experimenter, the fmal weight achieved
being the measure of strength.
TABLE 2 Scores Obtained Pre- and Post- Mental Training, Physical
Training, and Control Treatment, for Weight Lifted in Hip Flexions
(Ib),
Blood Pressure (mmHg), and Heart Rate (beats per min)
Mental Physical Control
M SD M_ SD M_ SD
Weight lifted (pre) 135.0" 25.5 127.5" 30.2 171.5"" 47.3
Weight lifted (post) 167.0^376.0 163.5'' 37.7 177.5 43.7
Blood pressure, systolic (pre) 131.4 13.2 135.9 12.7 128.8 7.0
Blood pressure, systolic (post) 128.1 9.7 133.8 8.9 129.3 8.1
Blood pressure, diastolic (pre) 79.6 9.8 89.7 9.0 85.7 5.3
Blood pressure, diastolic (post) 78.1 6.5 86.0 8.3 84.4 6.0
Heart rate (pre) 59.2° 5.8 61.8^ 6.6 63.1 4.8
Heart rate (post) 58.3"= 5.5 60.0^ 6.6 63.2 5.5
n = 10for each group: ""V < 01;
"'''p
< .05
All testing was performed on an individual basis by a female
experimenter (EMS). Participants were recruited at random in a
university sports center, during personal workouts, or before/after team
practices. After each participant had given informed consent, he was
randomly assigned to the mental training, physical training or control
group. During the first session, the experimenter recorded the
participant's height, body weight, age, blood pressure, heart rate, and
initial weight lifted. Subjects in the mental or physical training condition
were instructed as specified below, and asked to return every working
day for the following two weeks at 10:00 a.m., 2:00 p.m., or 4:00 p.m., to
receive further instruction. Participants in the control condition were
tested for strength initially, as for the other two groups; however, they
were told not to return until the end of
the
two week study period. At the
end of two weeks, all participants were again tested for blood pressure
and heart rate, and then repeated the weight-lifting task. Participants were
thanked and debriefed following the last testing session. There were no
drop-outs.
Shackell & Standing STRENGTH VIA IMAGERY 193
Mental Training
The mental training was carried out for two weeks, with five training
sessions of 15 min each per week. During each training session the
participant was instructed to mentally envision himself using the hip
flexor machine for four sets of eight repetitions, each set being followed
by a 60 second period of rest. During each session, he was instructed to
imagine himself using the hip flexor machine and increasing the lifted
weight by five pounds each day. It was emphasized to the participant that
this mental exercise was not simply a visualization of himself performing
the task, but that he was required mentally to imagine an increase in
weight lifted with each five pounds added. This mental process is
referred to by Ranganathan et al. (2004) as "visualization-guided brain
activation training." Five pound increments were used in order to provide
a change for each session that could be readily imagined. In this process,
the mental training subjects were asked to first visualize themselves
standing on the platform attached to the hip fiexor machine. The subjects
were then requested to imagine themselves extending their left leg
sideways as far as they could within their range of motion.
Physical Training
Physical training was the same as the mental training, except that
each step was physically carded out by the subject instead of being
mentally visualized. An additional weight was added only every three
sessions, as the available weights on the hip flexor machine increased by
15 Ib steps. As in the other two conditions, pre-training and post-training
tests were administered to evaluate muscular strength.
A third group of subjects did not mentally or physically exercise their
hip flexors, but were given the same pre-training and post-training
muscular strength test as the other groups.
Because physiological responses such as heart rate and blood pressure
commonly decrease with training, these variables were also recorded at
the start and the conclusion of
the
study to indicate possible changes.
RESULTS
Effect of Mental and Physical Training on Hip Strength
Descriptive statistics for weight lifted, blood pressure, and heart rate,
before and after training, are given in Table 2. To examine the effect of
training type on strength, a 3 x 2 mixed ANOVA (training type x
practice) was perfonned on the scores for weight lifted, showing that hip
strength overall was higher for the post-test than the pre-test, F(l, 27) =
33.1,
p = .001. Strength overall did not differ significantly between the
three types of training, F(2, 27) = 1.85, p = .\%. h Training Type x
Practice interaction was found, F(2, 27) =
4.81,
;>
= .016. This occurred
194 NORTH AMERICAN JOURNAL OF PSYCHOLOGY
because mental and physical training both produced substantial increases
in strength, of
32
Ib and 36 Ib respectively, whereas the control treatment
yielded a nonsignificant increase of only 6 Ib, t{9) =
1.50,
p
=
.168. These
means are shown in Figure 1.
When tested individually, the increases in strength produced by
mental training and by physical training were both statistically reliable,
t{9) = 3.40,p = .008; t{9) = 4.61,p =
.001.
These two increments did not
differ significantly, /(18) =
.327,
p = .75.
200 n
175-
150
75 ^
50
25-1
0
i Pre-test
d Post-test
Mental Physical
Training TrainingControl
FIGURE
1
Mean weight (Ib) lifted in hip flexion task, before and after
mental training, physical training control, and control treatment. Error
bars represent the standard error of the mean.
It should be noted that due to sampling variation, the control group
was stronger in the pre-test than both the mental training group, r(18) =
2.15,
p = .046, and the physical training group, /(18) = 2.48,^3 = .023. By
Shackell & Standing STRENGTH VIA IMAGERY 195
the end of
training,
however, it was no stronger than these groups, /(18) =
.56,
p = .57 and r(18) =
.77,
p = .45, respectively.
The subjects' pre- and post- training scores in the control group were
highly correlated, r(8) = .964, /? = .001. Within the mental and physical
training groups, this correlation was .60 and .76, p = .066 and .011,
respectively.
Strength Changes in Players of Different Sports
The eighteen subjects who played football were compared against the
others, who played basketball or rugby; these latter were pooled, due to
the small number of subjects in these categories: 7 and 5, respectively. A
3x2x2 mixed ANOVA (training type x practice x sport category)
indicated that there was a significant Practice x Sport interaction, F{\,
24) =
5.23,/J
=
.031.
This interaction represented the larger improvement
that training produced in the footballers compared to the other athletes. In
the mental training group, this gain in strength was 44.17 and of 13.75 Ib,
respectively, whereas in the physical training group, the strength of the
footballers and the other athletes increased by 42.5 and 26.25 Ib,
respectively. At the pre-test before training, the hip strength of the
football players at 146.1 Ib was intermediate between that of the
basketballers and the rugby players (130 and 170 Ib, respectively). Their
body weight at 221.4 Ib was also intermediate among the three groups
(198.4 and 222.8 Ib, respectively). The positive effects of mental training
are not due to the number of football players being greater for this group,
since there were 6 football players in each of the three training groups.
There was no Training type x Practice x Sport interaction, F(4, 21) = .27,
Effect of Mental and Physical Training on Blood Pressure and Heart
Rate
In two 3
X
(2) mixed ANOVAs, no significant changes in systolic or
diastolic blood pressure (mmHg) were observed from the pre-test to the
post-test, F(l, 27) = .86, p = .36, and F(l, 27) = 1.37, p = .25
respectively. However, systolic pressure dropped by 3.3 and 2.1 mmHg
respectively during the mental and physical training conditions, whereas
it increased trivially by 0.5 mmHg for the control condition. This
reduction in systolic pressure, while non-significant for each group alone
(p > .05), is reliable for the two training groups pooled, x^(l) = 5 0, p =
.025.
No reliable trend was found for diastolic changes.
A 3
X
2 mixed ANOVA indicated a significant effect of training in
reducing heart rate, shown as a Heart rate x Training type interaction,
F(2,
27) =
5.15,;?
= .013. This interaction represents a significant pulse
decrease in the mental and physical groups during training, of 0.9 and 1.8
196 NORTH AMERICAN JOURNAL OF PSYCHOLOGY
beats per minute respectively, as compared to an increase in the control
group of
0.1
bpm. The mental and physical training groups did not differ
significantly regarding this decrease in heart rate, according to the
Scheffe test, p = .71. No difference between football players and other
athletes was found in blood pressure or heart rate as a function of
training, all/j > .10. An association was noted between the subjects' pre-
test heart rate and their weight, pooled over all conditions, r(28) = .67, p
=
.001.
However, no significant correlations were found between strength
changes and heart rate, weight, age, or height, allp > .05.
DISCUSSION
The present data indicate that while only a trivial and non-significant
gain in strength occurred for the control subjects, who performed no
physical or mental exercises during the study, both the mental and the
physical training treatments caused a significant increase in the weight
that subjects could lift in hip flexions. This increase in strength was
similar between the two training groups, and was substantial (23.7% and
28.3%,
respectively). It also resembles the magnitude of the effect
reported by Ranganathan et al. (2004), and supports the central
conclusions of that study. Since the present experiment differs from the
study of Ranganathan et al. in employing a novel and larger muscle
group, with short-term isotonic rather than long-term isometric training
and some changes in methodology, these positive results support the
extemal validity of Ranganathan's findings. The results also correspond
to the conclusions of Reiser (2005), although this latter study obtained an
increase in bench press strength of only 5.7% from mental training, and
14%
from physical training.
The data presented by Ranganathan et al. (2004) suggest that the
basis of the mental training effect is central rather than peripheral:
substantial changes in EEG occur in mental training and correlate well
with the observed strength increase. The same conclusion applies to the
recent observation of changes in brain function as a result of mental
practice in a fmger-tapping task (Nyberg, Eriksson, Larsson, &
Marklund, 2006). However, muscular action potentials during imagery
also have often been reported (e.g., Shaw, 1940). Many past studies have
found reductions in blood pressure and heart rate after either physical
exercise or mental relaxation training (e.g., Amigo, Gonzalez, & Herrera,
1997;
Pawlow & Jones, 2002), but the effect of mental exercise on these
measures has not been reported previously. Although the reductions
found here for heart rate and systolic pressure both reached statistical
significance, as they were not large these findings call for replication.
Also,
the measurement of blood pressure may be problematic, as it is
intrinsically labile and varies with many extraneous variables including
Shackell & Standing STRENGTH VIA IMAGERY 197
stress,
nervousness, fatigue, etc. (McAlister & Straus, 2001); therefore it
is necessary to assume that these intruding factors function similarly
across training conditions.
Although the present data clearly support the experimental
hypothesis, assuming that the participants followed the specified
protocol, possible demand characteristics of the task and experimenter
effects should be considered (Ome & Evans, 1965; Rosenthal, 1976).
While a conscious effort was made by the test administrator to keep from
suggesting any expected trends to the participants, the increase in final
strength scores conceivably could be due to the participant's desire to
produce positive results, or from criterion shifts influencing the point at
which he decides that he cannot increase his effort due to discomfort
(Rollman, 1979). Such unwitting experimenter effects and demand
characteristics of the task are emphasized, for example, by the effects of
expectancy upon relaxation-induced blood pressure lowering (Agras,
Home, & Tayor, 1982). However, the persistence ofthe mental training
effect in the study by Ranganathan et al. (2004) several weeks after the
training period had ended, and the strong effects of mental training
observed upon cortical motor potentials, argue against any simple
dismissal of the phenomenon as an artifact, although further analysis of
altemative hypotheses is still called for. There is also the empirical
problem that some studies report positive results for the effects of mental
training on strength (Yue & Cole, 1992; Yue, Wilson, Cole, & Darling,
1996),
while others do not (Herbert, Dean & Gandevia, 1998), a
discrepancy which possibly may be attributed to uncontrolled incidental
factors such as the superiority of intemal over extemal imagery
(Ranganathan et al, p. 954; Hinshaw, 1991/1992; Wang & Morgan,
1992).
While not part of the experimental hypothesis, the strength gain of
each subject in relation to his chosen sport was also examined. Greater
benefits were found among the football players than the other athletes,
for both physical and mental training. This effect is of some interest, as
the football players were no stronger at the pre-test than the other
subjects, nor heavier. Therefore the greater absolute increase in strength
observed for football players also represents a greater percentage
increase.
This study used only male participants, to control subject gender as a
variable which might interact with the gender of the experimenter
(always female in this case), but presumably to the same extent in each
training condition. Future research in this area ideally would use both
male and female participants, as well as male and female experimenters.
The hip fiexor exercise was chosen as a means of measuring strength
gain based on the fact that this muscle group is one that none of the
198 NORTH AMERICAN JOURNAL OF PSYCHOLOGY
athletes had previously and consciously made any effort to exercise. It
seemed logical to predict that greater strength gain could be
demonstrated in a muscle group that rarely is used rather than one that is
already well exercised before the study. The high correlation between the
hip flexion scores obtained before and after the control treatment
indicates that this measure shows statistical reliability here, although this
is not always the case (Emery, Maitland, & Meeuwisse, 1999). The much
lower correlations found after training may be attributed to the marked
variations that occur between different individuals in response to the
same training program (Bouchard, An, Rice, Skinner, Wilmore, Gagnon,
Pemsse, Leon, & Rao, 1999).
It would be valuable to conduct simultaneous mental and physical
practice, to examine their combined effect on strength gain, as is
sometimes recommended in the literature on mental practice (Jackson,
Doyon, Richards, & Malouin, 2004). It is hoped that subsequent studies
with prolonged mental training will explore the limits of the effect, and
provide more evidence as to the ultimate powers of mental imagery.
However, stating the issue as one of mind over matter sets up an
unnecessary dichotomy since all mental states are intrinsically embodied
as physical events in the nervous system, if we reject the existence of
disembodied mind and accept central state theory (Armstrong, 1968).
Therefore, rather than referring to the conventional 'mind over matter',
we may summarize the present results as showing the power of CNS
activity over long-term muscular strength.
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Author Note. The authors are grateful to the participants for conscientious
participation, and to the reviewers for their helpful suggestions. Communications
may be sent to eshackell03@ubishops.ca or lstandin@ubishops.ca.