J Appl Physiol
91: 821–831, 2001.
Activation of the arousal response can impair
performance on a simple motor task
J. TIMOTHY NOTEBOOM, MONIKA FLESHNER, AND ROGER M. ENOKA
Department of Kinesiology and Applied Physiology,
University of Colorado, Boulder, Colorado 80309-0354
Received 2 November 2000; accepted in final form 23 March 2001
stressor; steadiness; pinch task; force
of several emotional responses,
including anxiety and fear, and is characterized by
feelings of apprehension, nervousness, and tension.
The physiological manifestations of arousal include
increased blood pressure, heart rate, sweating, dryness
of the mouth, hyperventilation, and musculoskeletal
disturbances, such as restlessness, tremors, and feelings of weakness (2, 3, 18, 30, 44). Although emotions
can be perceived in the cerebral cortex, the predominant outcome is the automatic effects mediated by the
autonomic, endocrine, and neuromuscular systems.
The automatic responses involve subcortical parts of
the nervous system, especially connections between
the nuclei of the amygdala, hypothalamus, and brain
stem (19). The neurotransmitters and hormones that
elicit these responses, however, can potentially modulate the function of the spinal circuits underlying motor
AROUSAL IS A COMPONENT
Address for reprint requests and other correspondence: R. M.
Enoka, Dept. of Kinesiology and Applied Physiology, Univ. of Colorado, Boulder, CO 80309-0354 (E-mail: [email protected]).
http://www.jap.org
performance (10, 21, 27). Because of this interaction,
elevated neuroendocrine activity during heightened
arousal has been implicated as a factor that can alter
motor output (22, 23).
One theory, known as the inverted-U hypothesis
(46), suggests that performance is maximized at intermediate levels of arousal (28, 30, 38, 45). For example,
scores in rifle shooting (40) and performance on a
throwing task (45) were found to vary with the level of
anxiety. Such studies, however, have not examined the
variation in arousal and performance during the execution of a task and usually did not consider possible
sex differences in arousal. For example, female rats
exposed to various stressors, including electric shock,
alcohol, and immobilization, responded with elevated
levels of several neuroendocrine substrates compared
with male rats (20, 34, 35). Similarly, psychologically
demanding tasks evoked elevated cardiovascular adjustments, immune system substrates, and neuroendocrine responses in women compared with men (25, 29).
These differences in the arousal response are likely
associated with sex-specific variations in the level of
neuromodulatory agents in the central nervous system.
To investigate the association between arousal and
motor output, we examined the ability of men and
women to perform a precision task in the presence
and absence of imposed stressors. Subjects were exposed
to one of two laboratory stressors, mental math or electric
shock. The purpose was to determine the effect of
arousal in men and women on the moment-to-moment
performance of a simple motor task. We expected to
find that the steadiness of a submaximal pinch task
would be reduced during the stressor conditions and
that the effect would be greater in women. Preliminary
results have been presented in abstract form (33).
METHODS
Twenty-nine subjects (14 men, 15 women; 18–44 yr) were
tested in this study. The subjects were recruited from the
general population. The subjects had no history of mental
pathology or neuromuscular disease, including any diagnosis
of an anxiety disorder or upper extremity injury for at least 6
The costs of publication of this article were defrayed in part by the
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8750-7587/01 $5.00 Copyright © 2001 the American Physiological Society
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Noteboom, J. Timothy, Monika Fleshner, and Roger
M. Enoka. Activation of the arousal response can impair
performance on a simple motor task. J Appl Physiol 91:
821–831, 2001.—The purpose of this study was to determine
the effect of arousal in men and women on the moment-tomoment performance of a simple motor task. We examined
the control of a precision task in the presence and absence of
imposed stressors. Twenty-nine subjects (14 men, 15 women;
18–44 yr) were randomly assigned to either a control group
or one of two stressor groups, Mental Math or Electric Shock.
Subjects presented with Math and Shock stressors, which
lasted 10 min, experienced significant increases in cognitive
and physiological arousal compared with baseline and control subjects. Heart rate, systolic blood pressure, and electrodermal activity were elevated 5–80% with presentation of
the stressors, whereas diastolic blood pressure and salivary
cortisol were unchanged. The greater levels of cognitive and
physiological arousal were associated with reductions in
steadiness of a pinch grip for the Shock subjects (⬃130%
reduction from baseline) but not for the subjects in the Math
group, who experienced heightened arousal but no change in
steadiness (10% reduction from baseline). Although women
exhibited more of a reduction in steadiness than men, the
effect was largely unrelated to the magnitude of the change
in arousal.
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AROUSAL AND MOTOR PERFORMANCE
mo. Subjects were randomly assigned to one of three groups:
a control group (5 women, 4 men; mean ⫾ SE age: 28.2 ⫾ 2.7
yr; range: 18–45 yr), a Mental Math group (5 women, 5 men;
25.1 ⫾ 1.2 yr; 19–30 yr) or an Electric Shock group (5 women,
5 men; 24.2 ⫾ 2.7 yr; 18–45 yr). Each subject in the Mental
Math and Electric Shock groups participated in one testing
session that comprised a 10-min baseline and a 10-min stressor condition. The subjects in the control group performed
two 10-min baseline conditions. The Institutional Review
Board at the University of Colorado approved all experimental procedures, and all subjects gave their informed consent
before participating in the study.
Cognitive Assessment of Anxiety
Physiological Assessment of Arousal
Several variables were assessed during the experiment to
quantify the level of physiological arousal. Moment-to-moment changes in heart rate, blood pressure, and electrodermal activity were recorded by use of electrodes placed on the
left hand. Heart rate and blood pressure were measured with
an inflatable cuff that was placed over the proximal portion of
the middle finger and connected to a Finapres device (Ohmeda, Louisville, CO). Electrodermal activity was measured
with electrodes (Biopac, Santa Barbara, CA) that were placed
on the distal pads of the fourth and fifth fingers. Electrodermal activity measures the bioelectrical characteristics of the
skin by applying a direct current to the skin and recording
the output as skin conductance (4). The flow of current along
the skin is influenced by the activity of the eccrine sweat
glands, which are located primarily in plantar and palmar
surfaces of the feet and hands. Because these sweat glands
are innervated by the sympathetic branch of the autonomic
nervous system, the change in skin conductance is often used
as an index of sympathetic activity. A Biopac data-acquisition system was used to collect the electrodermal activity,
heart rate, and blood pressure data. The data were sampled
at 200 Hz and stored on computer disks for later analysis.
In addition to these moment-to-moment measures, salivary cortisol samples, which are a measure of adrenal output
of free cortisol (24, 36), were collected at the beginning and
end of the session, similar to procedures used by Kirschbaum
et al. (24). Each subject chewed a cotton swab for 20 s, which
was then placed in a salivette for later analysis. Cortisol
levels were assessed using an enzymatic immunosolvent assay (Diagnostic Systems Laboratories, Webster, TX) to determine levels of free cortisol. Previous studies have established
the reliability of this technique (13, 37).
Motor Performance Task
The effect of heightened arousal on motor performance was
examined with a submaximal isometric pinch task, which
J Appl Physiol • VOL
Experimental Protocol
The session lasted ⬃25 min and was divided into two
phases: a nonarousal baseline phase and an arousal-induction phase. For the baseline phase, the subject sat quietly for
10 min and was instructed to relax. At the end of 10 min, the
pinch task was performed for 10 s. The VAS was assessed
three times during the baseline session: at the beginning,
middle, and end. Subsequently, subjects were either exposed
to one of the stressors (Mental Math group or Electric Shock
group) or performed a second baseline period (control group).
Mental math stressor. Subjects in the Math group performed serial subtraction of a four-digit number. In the first
5 min of the stressor, the subjects counted backward by 13,
starting from 1,022. Subjects were instructed to count as fast
and as accurately as possible. When a subject made a mistake, the investigator would say, “Stop. Begin again. 1,022,”
and the subject would repeat the task. To increase the difficulty of the task, subjects were asked to keep pace with a
metronome that produced an auditory signal once every 3 s.
After 5 min, the subject was told to stop counting and to
perform the pinch task and complete a VAS assessment.
Subsequently, the math task was continued for another 5
min. The subject was told, “This task is obviously too difficult
for you. Instead, please count backward by 7, again starting
from 1,022. Begin.” Immediately after the second bout of the
math stressor, the 10-s pinch task was repeated, and the VAS
was assessed. The subject was then instructed to sit quietly
for a 2-min recovery period, after which the VAS, state
anxiety (STAI-S), and salivary cortisol assessments were
performed.
Electric shock stressor. The Shock group followed a similar
protocol to the Math group, except that a variable-intensity
electric shock was used as the stressor. After the 10-min
baseline (nonarousal) condition, two 1 ⫻ 1-cm carbon electrodes were attached to the dorsal surface (back) of the left
hand. The electrode leads were attached to an electric stimulation device (Grass Instruments, Quincy, MA) that was
used to deliver a strong shock to the hand. The shock was
delivered as a twin-pulse rectangular waveform with a 0.2-s
duration and intensity ranging from 60 to 120 V. Two indicator lights were used to cue the subject regarding the possibility of an electric shock. When a red light was on, it was
not possible for the subject to receive the electric shock.
Alternatively, when a yellow light was on it was possible to
receive an electric shock. These no-threat and threat periods
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To determine the general level of trait anxiety, each subject completed the trait portion of the State-Trait Anxiety
Index (STAI) of the Spielberger Index, which consists of 20
questions that are answered by using a four-point Likerttype scale. The level of state anxiety was assessed at the
beginning and end of the experiment with the STAI-State
(STAI-S) test and at multiple intervals throughout the experiment with the visual analog mood scale (VAS). The VAS
is a 100-mm line anchored at either end with descriptive
polar phrases, such as “Not at all anxious” on the left side of
the 100-mm line and “Very anxious” on the right. The subjects were asked to place a vertical line bisecting the 100-mm
line to indicate the perceived level of anxiety at the moment.
was assessed at multiple intervals during the experimental
session. The experiments were conducted with the subjects
seated in a quiet room. The right arm rested on the arm of the
chair with the elbow at a right angle and the wrist midway
between maximum supination and maximum pronation.
The apparatus used for the pinch task was 4 cm wide and
weighed 1.2 N. It comprised a force transducer (ATI Mini-40)
mounted on a wooden platform. The sensitivity of the force
transducer was 0.06 N/V. The apparatus was held between
the distal pads of the thumb and index finger of the right
hand. Contact surfaces of the apparatus had a rough texture
(sandpaper) to ensure a secure grip.
Data from the force transducer were displayed on an
oscilloscope that was positioned 1 m in front of the subject at
eye level. The target force of 4 N was presented as a line on
the oscilloscope. The subject was instructed to match the
exerted force with the target force as accurately as possible.
Subjects were given up to 1 min of practice with this task.
Force was sampled at 200 Hz with the Biopac data-acquisition system and stored on computer disks for later analysis.
AROUSAL AND MOTOR PERFORMANCE
alternated in 20-s durations. During the threat condition
(yellow light), the subject was told that it was possible to
receive up to eight electric shocks. The pattern of electric
shocks was variable across the alternating 20-s cycles; however, this pattern was consistent across subjects. To further
heighten the arousal response, the subject was told that the
magnitude of the electric shock would vary across repetitions. Similar to the math stressor, there were two 5-min
bouts. Immediately after each bout, the 10-s pinch task was
performed, along with the VAS. After the 2-min recovery
period, a salivary cortisol sample was obtained, and the
posttest state anxiety was assessed.
Control condition. Similar to the two experimental groups,
the control group participated in the 10-min baseline period.
However, this group experienced no stressors during the
second 10-min period, and, as with the stressor groups, pinch
tasks were performed at the beginning, middle, and end of
each 5-min interval. At the end of the 20-min session, state
anxiety (STAI-S), VAS, and salivary cortisol were assessed.
Data Analysis
Statistical Analysis
A two-factor ANOVA (SPSS for Windows, SPSS) was used
to compare the dependent variables of trait and state anxiety
for the three groups. A three-factor ANOVA with one repeated-measure design (two factors between and one within)
was used to compare the dependent variables for the heart
rate, blood pressure, electrodermal activity, and salivary
cortisol between the sexes and the three groups, across time
points, and the interactions. A three-factor ANOVA with
repeated measures was applied to the cognitive assessment
data of the VAS scores between the sexes and the three
groups, across time points, and the interactions. A similar
three-factor ANOVA with repeated measures was applied to
the coefficient of variation for force between the sexes and the
three groups, across time points, and the interactions. An
alpha level of 0.05 was chosen for all initial statistical comJ Appl Physiol • VOL
parisons. Significant F statistics were followed by post hoc
tests to determine pairwise differences, using 95% confidence
interval methods. Data are reported as means ⫾ SE in Figs.
1–6 and means ⫾ SD in Tables 1 and 2.
RESULTS
The effects of a stressor condition on physiological
and cognitive measures of arousal and pinch task performance were determined for two types of stressors
and were compared with baseline conditions and with
a control group. The Math stressor consisted of paced,
serial subtraction from a four-digit number, whereas
the Shock stressor involved random-intensity, noxiouslevel stimulation to the left hand. The physiological
and motor performance data are presented as 10-s
epochs at three time points during the 25-min experimental session: near the end of the 8-min baseline and
at the midpoint and the end of an 8-min stressor.
Figure 1 displays representative data across each epoch for one subject in the Shock group.
Cognitive Component of Arousal
Trait anxiety scores did not differ significantly for
the three groups (Fig. 2A). The scores ranged from 21
to 62, which are considered low-to-moderate levels of
trait anxiety. All subjects also completed a before and
after state anxiety survey. The scores for the control,
Shock, and Math groups at the beginning of the protocol were 27.0, 28.6, and 30.8, respectively. Subjects in
the control group had end scores that were lower than
the initial scores (⫺5.6%), whereas the after values for
the Shock and Math stressor groups were elevated
significantly to 27.2% and 30.0%, respectively, above
the initial values (Fig. 2B).
The cognitive component of arousal was also assessed with the VAS. Each subject completed the VAS
at eight time points during the experiment: four times
(time points 1 to 4) during the baseline period, three
times (time points 5 to 7) during the stressor, and one
time (time point 8) at the completion of the stressor.
There were no between-group (P ⫽ 0.22) or withingroup (P ⫽ 0.55) differences during the baseline period,
nor were the tests significant for simple main effects on
sex (P ⬍ 0.41) or group (P ⬍ 0.06). In contrast, the
main effect of time was significant (P ⬍ 0.001), as was
the time-by-group interaction when comparing the
stressor conditions (P ⬍ 0.007). The VAS scores during
the stressor (time points 5, 6, and 7) for the Shock
(31.1 ⫾ 5.8, 35.6 ⫾ 7.0, and 39.7 ⫾ 7.4 mm, respectively) and Math groups (33.2 ⫾ 5.8, 45.4 ⫾ 7.0, and
36.1 ⫾ 7.4 mm, respectively) were significantly greater
than those for the control group (7.1 ⫾ 6.2, 8.6 ⫾ 7.5,
and 6.7 ⫾ 7.9 mm, respectively). The VAS score at time
point 5 represents anticipatory anxiety as this was
elevated after the subjects were informed about the
stressor conditions but before the actual presentation
of the stressor. One minute after completion of the
stressor (time point 8), subjects in the Shock group
(25.3 ⫾ 5.0 mm) had significantly elevated VAS scores
compared with the control subjects (5.1 ⫾ 5.3 mm) (P ⬍
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The dependent variables for the cognitive assessment of
anxiety were trait anxiety, before and after state anxiety,
and multiple VAS scores. The trait and state variables were
quantified by using standardized scoring techniques (43).
The VAS data were quantified by measuring the distance, in
millimeters, from the left end of the 100-mm line to the point
on the line where the subject marked the perceived level of
anxiety. The VAS was administered eight times during the
experimental session: two before baseline (time points 1 and
2); at the middle and end of the baseline (time points 3 and 4);
after giving instructions for the stressor condition, but before
stressor initiation (time point 5); at the middle and end of the
stressor condition (time points 6 and 7); and at the end of
recovery (time point 8).
The dependent variables for the physiological variables
were heart rate, blood pressure, and electrodermal activity,
which were assessed during three 10-s epochs. These 10-s
intervals were after the baseline period (time point 4) and at
the middle (time point 6) and the end (time point 7) of the
stressor. The three 10-s epochs were also analyzed for the
control subjects, except that time points 6 and 7 occurred
during a second baseline period. In addition, an assessment
of salivary cortisol was performed at the beginning and end of
the protocol in all subjects.
The dependent variable for the pinch task was the coefficient of variation (SD/mean force ⫻ 100) of the force during
the 10-s intervals at time points 4, 6, and 7. Increases in the
coefficient of variation indicate a reduction in steadiness.
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AROUSAL AND MOTOR PERFORMANCE
0.001) (Fig. 3A). However, the time-by-sex interaction
was not significant (P ⫽ 0.54). The women and men in
the two stressor groups combined (Fig. 3B) and for the
Shock group (Fig. 3C) and Math groups alone had
similar VAS scores. Taken together, these data indicate that subjects in the two stressor conditions experienced greater levels of cognitive arousal.
Physiological Arousal
Heart rate, systolic blood pressure, diastolic blood
pressure, and electrodermal activity were measured at
three time points during the study: baseline (time point
4), midstress (time point 6), and end-stress (time point
7) (Fig. 4). For heart rate, the simple main-effect test
for groups was not significant (P ⫽ 0.32), although the
main-effects test for time (P ⬍ 0.02) and sex (P ⬍
0.001) were significant. Heart rate at the end-stress
time point (70.9 ⫾ 1.7 beats/min) was significantly
elevated over baseline (67.4 ⫾ 2.0 beats/min) and midstress (68.3 ⫾ 1.8 beats/min) time points, whereas
average values for women (76.3 ⫾ 2.4 beats/min) were
elevated compared with average values for the men
(61.4 ⫾ 2.5 beats/min) (Table 1).
Simple main effects for sex (P ⫽ 0.27) and group (P ⫽
0.38) were not significant for electrodermal activity. In
contrast, the simple main effect for time (P ⬍ 0.001)
was significant, with the midstress value (113.7 ⫾ 42.0
S) being significantly greater than baseline (83.8 ⫾
37.6 S) (Table 1); however, the end-stress value
(113.0 ⫾ 47.7 S) was not significantly different from
baseline (P ⫽ 0.06). Similarly, when the data are presented as percent change from baseline (Fig. 4B), the
J Appl Physiol • VOL
simple main-effects test for group was significant (P ⬍
0.04), with electrodermal activity for the Shock group
(75.3 ⫾ 15.9%) significantly different from the control
group (12.7 ⫾ 16.9%), whereas the values for men and
women were similar (P ⫽ 0.28).
The results were similar for systolic blood pressure,
with a significant main effect for time (P ⬍ 0.01) and
sex (P ⬍ 0.02), whereas the main effect for group was
not significant (P ⫽ 0.08) (Table 1). In addition, there
was a significant time-by-group interaction, with the
end-stress value for the Shock group significantly different compared with both the baseline value for the
Shock group and the end-stress time point for the
control group (Table 2). When expressed as percent
change (Fig. 4C), the main effects test for group was
significant (P ⬍ 0.04), with the Shock group (11.8 ⫾
3.1%) exhibiting elevated values compared with the
control group (⫺0.3 ⫾ 3.3%), whereas values for men
and women were similar (P ⫽ 0.06). There were no
significant changes in diastolic blood pressure (Fig.
4D).
In addition, salivary cortisol was assessed immediately before and after the session. No group, sex, or
time differences were noted (Tables 1 and 2).
Pinch Task Performance
The submaximal pinch task was performed at multiple times during the baseline and stressor conditions. Steadiness during the task was quantified as
the coefficient of variation for force. Accordingly,
increases in the coefficient of variation indicate a
reduction in steadiness. Fluctuations in the force
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Fig. 1. Representative records of heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP),
electrodermal activity (EDA), and pinch-grip force for 1 subject in the Shock group. Target force for the pinch grip
was 4 N. Records represent 10-s epochs during the baseline period (10 min) and at the middle and end of the
stressor presentation. Total duration of the experiment was 25 min. bpm, Beats/min.
AROUSAL AND MOTOR PERFORMANCE
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Fig. 2. Trait and state anxiety of the subjects in the 3 groups. A: trait
anxiety scores based on the Spielberger State-Trait Anxiety Index. B:
percent change in state anxiety score from beginning to end of the
experiment. Values are means ⫾ SE. *Subjects in the 2 stressor
groups experienced a significant increase in state anxiety compared
with the control group (P ⬍ 0.03). %⌬, percent change.
during the pinch task (Fig. 1) varied across groups,
sex, and time. There were no significant differences
in coefficient of variation during the baseline period
across groups: 1.65 ⫾ 0.60, 1.65 ⫾ 0.51, and 2.15 ⫾
0.52% for the control, Shock, and Math groups, respectively. Although the main effects for time (P ⬍
0.01) and group (P ⬍ 0.02) were significant, the main
effect for sex was not significant (P ⫽ 0.10). The
coefficients of variation for mid- and end-stress time
points (2.3 ⫾ 0.2 and 2.8 ⫾ 0.3%, respectively) were
significantly different from baseline values (1.8 ⫾
0.1%), whereas the coefficient of variation for the
Shock group (3.01 ⫾ 0.33%) was significantly greater
than that for the control group (1.58 ⫾ 0.35%) (Fig.
5A). Similarly, there were significant differences between groups at the mid- and end-stress time points.
The coefficients of variation at these times for the
Shock group (3.25 ⫾ 0.38 and 4.33 ⫾ 0.57%, respectively) were elevated compared with baseline (1.64 ⫾
J Appl Physiol • VOL
Fig. 3. Scores on the visual analog scale (VAS) for the 3 groups of
subjects at 8 time points during the 25-min experiment. Data are
means ⫾ SE. Time points 1 to 4 were taken during the 8-min
baseline period. Time points 6 and 7 correspond to the middle and
end of the stressor presentation, respectively. A: VAS scores for
the Shock and Math groups were significantly greater than those
for the control group at time points 5, 6, and 7 (*P ⬍ 0.01), and the
score for the Shock group remained elevated at time point 8 (*P ⬍
0.01). B: men and women in the Math and Shock groups (n ⫽ 10
in each group). C: men and women in the Shock group (n ⫽ 5 in
each group).
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Fig. 4. Percent change from baseline
at the middle and end of stressor presentation for the 3 groups. Data are
means ⫾ SE. A: heart rate. B: electrodermal activity. C: systolic blood pressure. D: diastolic blood pressure.
ence between the Math and the control or Shock
groups. These data indicate that subjects exposed to
the electric shock stressor experienced a reduction in
steadiness during the pinch task.
There were several statistical interactions involving
differences between the men and women, including a
significant time-by-sex interaction (P ⬍ 0.04) (Fig. 5C).
Post hoc analysis indicated that the coefficient of variation values for the women at the end-stress interval
(3.45 ⫾ 0.47%) were significantly greater than baseline
(1.81 ⫾ 0.14%) but were not different from the men at the
end-stress interval (2.16 ⫾ 0.49%). In contrast, the coefficient of variation did not vary across time for the men.
The other significant sex effect involved the sex-by-group
interaction (P ⬍ 0.04) (Fig. 5D). The coefficient of varia-
Table 1. Comparison of physiological data for women and men and across all time points
Sex
Men
Women
Time
Baseline
Midstress
End-stress
Group
Control
Shock
Math
Heart Rate,
beats/min
Systolic Blood
Pressure, mmHg
61.4 ⫾ 10.6
76.3 ⫾ 9.2*
136.5 ⫾ 18.5
120.4 ⫾ 18.7*
67.4 ⫾ 12.9
68.6 ⫾ 12.1
71.3 ⫾ 12.0
65.5 ⫾ 8.9
72.3 ⫾ 14.0
68.9 ⫾ 12.1
Diastolic Blood
Pressure, mmHg
Electrodermal
Activity, S
Salivary
Cortisol, ␮g/dl
77.2 ⫾ 9.9
70.5 ⫾ 9.2
94.9 ⫾ 42.6
111.9 ⫾ 41.7
1.27 ⫾ 0.78
1.95 ⫾ 1.60
123.1 ⫾ 20.2
131.7 ⫾ 19.9†
130.4 ⫾ 20.8
72.0 ⫾ 10.1
75.2 ⫾ 9.9
74.7 ⫾ 10.2
83.8 ⫾ 37.6
113.7 ⫾ 42.0†
113.0 ⫾ 47.7
1.62 ⫾ 1.31
121.8 ⫾ 15.6
136.7 ⫾ 18.6
127.0 ⫾ 21.8
72.8 ⫾ 10.6
76.2 ⫾ 11.8
72.7 ⫾ 8.3
96.0 ⫾ 35.7
118.6 ⫾ 45.2
95.7 ⫾ 47.7
1.6 ⫾ 1.3
1.42 ⫾ 0.5
1.81 ⫾ 1.9
Data are means ⫾ SD. * P ⬍ 0.05, vs. men; † P ⬍ 0.05, vs. baseline.
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0.17%), along with a significant increase over each
corresponding time point compared with the control
group (1.65 ⫾ 0.18, 1.55 ⫾ 0.41, 1.52 ⫾ 0.61%,
respectively) (P ⬍ 0.001) (Fig. 5B). The sex-by-time
interaction was not significant (P ⫽ 0.05) (Fig. 5C),
whereas the sex-by-group interaction was significant
(P ⬍ 0.01) (Fig. 5D). In addition to a significant
elevation from baseline (1.64 ⫾ 0.17%), the mid- and
end-stress values (3.25 ⫾ 0.38 and 4.33 ⫾ 0.57%,
respectively) for the Shock group were significantly
elevated over the corresponding time points for the
control group (1.55 ⫾ 0.41 and 1.52 ⫾ 0.61%, respectively) (Fig. 5D). The change in coefficient of variation for the Math group did not differ statistically
across the three time points, nor was there a differ-
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Table 2. Comparison of physiological data by group and time
Heart Rate,
beats/min
Control
Baseline
Midstress
End-Stress
Shock
Baseline
Midstress
End-Stress
Math
Baseline
Midstress
End-Stress
Systolic Blood
Pressure, mmHg
Diastolic Blood
Pressure, mmHg
Electrodermal
Activity, S
Salivary
Cortisol, ␮g/dl
65.7 ⫾ 9.6
66.2 ⫾ 7.2
66.4 ⫾ 8.9
121.6 ⫾ 17.0
123.5 ⫾ 16.5
117.2 ⫾ 15.7
72.8 ⫾ 7.3
73.9 ⫾ 11.3
71.9 ⫾ 10.6
87.7 ⫾ 31.2
106.3 ⫾ 38.4
92.0 ⫾ 35.7
1.47 ⫾ 1.05
72.3 ⫾ 14.9
70.0 ⫾ 13.4
74.4 ⫾ 14.0
128.5 ⫾ 23.3
140.6 ⫾ 19.9
141.1 ⫾ 18.6*
73.8 ⫾ 11.9
77.3 ⫾ 10.3
77.4 ⫾ 11.8
85.2 ⫾ 31.9
132.3 ⫾ 37.2
138.2 ⫾ 45.2*
1.61 ⫾ 1.24
64.8 ⫾ 13.3
69.3 ⫾ 15.0
72.5 ⫾ 12.1
119.1 ⫾ 20.4
130.2 ⫾ 20.9
131.8 ⫾ 21.8
69.5 ⫾ 10.9
74.1 ⫾ 8.8
74.4 ⫾ 8.3
78.8 ⫾ 49.7
101.7 ⫾ 46.8
106.7 ⫾ 52.0
1.79 ⫾ 1.70
1.86 ⫾ 1.46
1.14 ⫾ 0.46
1.70 ⫾ 1.91
Data are means ⫾ SD. * P ⬍ 0.05 vs. baseline.
0.47%) in the Math group (Fig. 5D). In contrast, the
three-way interaction between sex, group, and time was
not significant (P ⬍ 0.06).
When the coefficient of variation was expressed as a
percent change from baseline for the two stressor time
points, the main effects tests were significant for
Fig. 5. Coefficient of variation for force
during the pinch-grip task. A: main
effect for group, showing the data
summed across the baseline, midstress, and end-stress time points.
*Significant difference between Shock
and control groups (P ⬍ 0.02). B:
group ⫻ time interaction, showing the
data at the baseline (time point 4), midstress (time point 6), and end-stress
(time point 7) intervals. *End-stress
and baseline intervals for the Shock
group are significantly different (P ⬍
0.01); #significant difference between
the end-stress interval and all intervals for the control group (P ⬍ 0.02). C:
sex ⫻ time interaction, showing the
data at baseline, midstress, and endstress intervals. D: sex ⫻ group interaction. *Significant difference for
women in the Shock group compared
with women in the control and Math
groups (P ⬍ 0.01); #significant difference between women in the Shock
group and men in the Shock and control groups (P ⬍ 0.02).
J Appl Physiol • VOL
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tion values for women (4.2 ⫾ 0.47%) in the Shock group
were significantly greater than those for the women
(1.67 ⫾ 0.47%) and men (1.49 ⫾ 0.52%) in the control
group, the women in the Math group (2.09 ⫾ 0.47%), and
the men (2.03 ⫾ 0.47%) in the Shock group (P ⬍ 0.04) but
did not differ significantly from values in men (2.47 ⫾
828
AROUSAL AND MOTOR PERFORMANCE
group, sex, and time. The Shock group (121.3 ⫾ 18.1%)
differed significantly from the control (⫺2.5 ⫾ 19.2%)
and Math (8.8 ⫾ 18.1%) groups (P ⬍ 0.001) (Fig. 6A).
Similarly, women increased by 67.3 ⫾ 14.8% compared
with 17.8 ⫾ 15.4% for the men (P ⬍ 0.03) (Fig. 6B), and
the end-stress time point (56.9 ⫾ 14.6%) was elevated
from the midstress time point (28.2 ⫾ 8.7%) (P ⬍ 0.02)
(Fig. 6C).
DISCUSSION
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Fig. 6. Percent change in the coefficient of variation for force during
the pinch-grip task, with main effects for group, sex, and time. A:
normalized fluctuations for the 3 groups of subjects, collapsed across
sex and the mid- and end-stress intervals, with values for the Shock
group significantly greater than those for the Math and control
groups (*P ⬍ 0.001). B: normalized fluctuations for sex, collapsed
across the 3 groups and the mid- and end-stress intervals, with
values for the women significantly greater than the values for the
men (*P ⬍ 0.03). C: normalized fluctuations at the mid- and endstress intervals, collapsed across sex and groups, with values at the
end-stress interval significantly greater than those at midstress
(*P ⬍ 0.02). Values are means ⫾ SE.
The purpose of this study was to determine the effect
of arousal in men and women on the moment-to-moment performance of a simple motor task. Subjects
performed a series of submaximal pinch tasks during a
baseline period and during a stressor condition. We
expected to find that the stressor conditions would
elevate arousal and result in a reduction in the accuracy of the pinch task. The main finding was that
subjects in the stressor groups, especially the Shock
group, displayed significantly reduced steadiness at
the midstress and end-stress time points. Furthermore, women in the Shock group exhibited more of an
impairment than men. This selective effect on performance was in contrast to the common effects of the
interventions on the arousal of the men and women in
the two stressor groups.
Previous studies have used the mental math and
shock stressors to heighten arousal. For example, Kirschbaum et al. (24) combined mental arithmetic and simulated public speaking to induce moderate psychological stress, as indicated by elevated heart rate and
salivary cortisol levels. Similarly, Al’Absi and colleagues (1) demonstrated elevated systolic and diastolic blood pressure, heart rate, and salivary cortisol
with mental arithmetic and simulated public speaking.
However, all physiological measures were attenuated
with repeated bouts of the same stressor. In addition to
measuring neuroendocrine and cardiovascular responses, Breznitz et al. (5) asked subjects to rate their
level of tension at multiple intervals during shock
stressors. Tension, as rated with a seven-point scale,
was significantly elevated during the shock stressor
compared with baseline, as were heart rate and plasma
epinephrine levels.
We used two assessments of the cognitive component
of arousal, the Spielberger state anxiety index and
VAS. The anxiety scores at the end of the test were
significantly elevated compared with those before the
test for the two stressor groups, whereas scores for the
control group actually decreased. Similarly, the VAS
scores for the Math and Shock groups were elevated
significantly compared with the control group scores
during the three stressor intervals. Although the state
anxiety index has frequently been used to assess temporal changes in state anxiety (14, 40, 42), the time
required to complete the 20-item questionnaire makes
it an impractical tool for the assessment of moment-tomoment changes in anxiety. In contrast, the VAS can
be used to assess emotional states rapidly. In a reliability study of the Spielberger state anxiety test and
AROUSAL AND MOTOR PERFORMANCE
J Appl Physiol • VOL
of either the Shock or control groups. The coefficient of
variation for force has been used in other studies as an
index of fine motor control (11, 26). In the present
study, the coefficient of variation ranged from 1.4% for
men in the control group during baseline to 6.1% for
women in the Shock group at the end-stress time point,
which is similar to the range reported previously (11).
Electric shock has been used to examine the startle
response. Grillon and colleagues (14–16) used a lighting system to provide threat and nonthreat conditions
while delivering noxious levels of shock. Electric shock
potentiated the acoustic startle response, elevated perceived tension, and enhanced reflex responses. Similarly, inescapable tail shock has been used to induce
acute and chronic stress in rats, resulting in long-term
neural, behavioral, and immune changes (9, 32). Several neural mechanisms may contribute to the association between electric shock and altered motor output.
Chua et al. (8), for example, identified a number of
paralimbic structures that were active during and immediately after unpredictable electric shock, perhaps
mediating changes in arousal associated with anticipatory states. This likely includes the amygdala, which is
involved in the initiation and maintenance of integrated stress responses that include projections to areas affecting stress hormones via anterior pituitary/
adrenal cortex, sympathetic activity, and descending
motor activity to the ventromedial horn of the spinal
cord. By influencing the prefrontal-striatal system at
both the cortical and striatal levels, the amygdala is
profoundly involved in motor, cognitive, and complex
behavioral functions (17).
Although men and women had similar arousal responses to the shock stressor, the reduction in steadiness during the pinch task was greater for the women.
The steadiness exhibited by women, as indicated by the
coefficient of variation for force, was reduced significantly at the end-stress time point compared with
baseline, whereas there was no change for men. In
addition, the coefficient of variation for the women in
the Shock group was significantly different from
women and men in the control group and for the men in
the Shock group. Although no sex effect was found for
the Math stressor, these findings indicate that the
accuracy of the pinch task was reduced in women who
experienced the electric shock stressor compared with
men.
There may be several explanations for the dissociation between arousal and performance for the women.
First, the measures of arousal used in this study may
not have been sensitive enough to identify sex differences. Levels of cognitive, cardiovascular, and electrodermal activity were elevated from baseline for the
stressors using noninvasive techniques, whereas cortisol levels were unchanged from baseline. However,
more invasive techniques may be needed to detect
changes in other components of arousal that differ for
men and women. The effects of electric shock in animals indicate that females respond with a greater level
of neuroendocrine activation, including ACTH, corticosterone, oxytocin, norepinephrine, and serotonin re-
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VAS, Cella and Perry (7) reported that the VAS measure of anxiety was significantly correlated (r ⫽ 0.53)
with the state anxiety scores and concluded that the
VAS is capable of measuring emotional states in a
quick, reliable, and relatively sensitive manner. We
found that state anxiety immediately after the stressor
increased by ⬃30% for the two stressor groups,
whereas the VAS scores at the three time points during
the stressor conditions increased by 200% from baseline values.
In addition to cognitive assessment, physiological
markers were used to measure the arousal response.
Generally, the two stressor conditions produced similar changes in heart rate, systolic and diastolic blood
pressure, electrodermal activity, and salivary cortisol.
However, diastolic blood pressure and cortisol measures were not different compared with the control
group, as found previously (1, 12). Although salivary
cortisol is frequently used as a marker of physiological
arousal, the delayed time course may explain the absence of group or time differences in this study. For
example, Kirschbaum et al. (24) noted peak cortisol
levels to occur at ⬃40 min after a laboratory stressor,
compared with the 25-min duration between our initial
and final measurements. The brevity of our testing
session likely explains the minimal changes in salivary
cortisol values we observed. Other authors using similar testing procedures have demonstrated good reliability for within- and between-day assessments (13,
37).
Increased neuroendocrine activity, especially enhanced activation of the sympathetic nervous system,
can result in changes in heart rate, blood pressure, and
electrodermal activity (6, 24). Stressor exposure also
activates the hypothalamus-pituitary-adrenal axis, resulting in elevated cortisol. In laboratory settings,
changes in these variables due to a stressor are usually
small, with substantial variability between subjects.
Consequently, the moment-to-moment assessment of
multiple variables has been recommended for a more
accurate interpretation of the arousal response (31).
Al’Absi et al. (1) assessed psychological and physiological variables, including heart rate, blood pressure, and
cortisol, at multiple intervals during both mental math
and public speaking stressors. Correlations between
the endocrine, cardiovascular, and psychological variables were significant for the speaking stressor, but not
the math stressor, although all values were significantly elevated over baseline. The ⬃19% increases
from baseline for heart rate and blood pressure found
by Al’Absi et al. (1) for the math stressor are similar to
the 14–18% increases that we found for the math and
electric shock stressors.
Of the two stressors used to elevate arousal, electric
shock had the greater impact on the steadiness of the
pinch task. The coefficients of variation for force at the
midstress and end-stress time points were significantly
elevated for the Shock group compared with baseline
values and for the control group. In contrast, the coefficient of variation for the Math group did not change
across the time points and was not different from that
829
830
AROUSAL AND MOTOR PERFORMANCE
We thank Dr. Robert Gotshall for the use of the Finapres device,
and Drs. Sandra K. Hunter, Douglas R. Seals, and Douglas L. Weeks
for comments on a draft of the manuscript.
This study was funded by National Institute on Aging Grant
AG-13929 (to R. M. Enoka) and the Foundation for Physical Therapy
(to J. T. Noteboom).
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