J Appl Physiol
91: 2487–2492, 2001.
Influence of isometric exercise on blood flow and
sweating in glabrous and nonglabrous human skin
ADHAM R. SAAD, DAN P. STEPHENS, LEE ANN T. BENNETT,
NISHA CHARKOUDIAN, WOJCIECH A. KOSIBA, AND JOHN M. JOHNSON
Department of Physiology, University of Texas Health Science Center
at San Antonio San Antonio, Texas 78229-3900
Received 2 March 2001; accepted in final form 19 July 2001
arteriovenous anastomoses; muscle mass
in skin blood flow
(SkBF) are controlled by two arms of the sympathetic
nervous system: an active vasodilator system and a
noradrenergic vasoconstrictor system (7, 11, 13, 23). It
is generally agreed that glabrous skin lacks influence
from active vasodilator nerves (12); therefore, reflex
control of SkBF in those regions is thought to be controlled entirely by the noradrenergic vasoconstrictor
system. Glabrous skin is characterized by an absence
of hair and includes the palms, soles, and lips. SkBF in
glabrous skin is also characterized by large spontaneous fluctuations, which are a manifestation of changes
in blood flow through arteriovenous anastomoses
(AVAs) (2, 3, 5, 16). Neither these fluctuations in blood
flow through the AVAs nor the AVA architecture is
present to any significant degree in nonglabrous skin
(11).
REFLEX THERMOREGULATORY CHANGES
Address for reprint requests and other correspondence: J. M.
Johnson, Dept. of Physiology, 7756, Univ. of Texas Health Science
Center at San Antonio, 7703 Floyd Curl Dr., San Antonio, TX
78229-3900 (E-mail: [email protected]).
http://www.jap.org
It is well documented that isometric exercise elicits
physiological responses such as increases in heart rate
(HR), mean arterial pressure (MAP), cardiac output
(CO), and sympathetic nerve activity directed to skeletal muscle (9, 14, 17–22, 30). It has also been reported
that isometric exercise leads to an increase in skin
sympathetic nerve activity (SSNA) (4, 19, 21, 29–30).
However, in normothermia, forearm SkBF does not
appear to be influenced by isometric exercise (7, 14, 19,
26). Although most measurements of SkBF during isometric exercise have concentrated on the forearm, the
vasomotor control in glabrous skin, rich in AVAs, may
differ from that in the forearm skin. Indeed, glabrous
skin is considered to be much more responsive to environmental stimuli than nonglabrous skin (5, 6, 23).
Therefore, we sought to test whether the site of measurement was an important consideration in the cutaneous vasomotor responses to isometric exercise. Specifically, we tested the hypothesis that glabrous skin would
show a more marked reflex response than nonglabrous
skin to isometric exercise. We made measurements of
SkBF from both glabrous and nonglabrous skin of the
upper and lower extremities to establish whether there
may be regional differences in the responses to isometric
exercise. Included in the analysis were measures of the
variation in SkBF in glabrous skin as an index of AVA
function. We also measured sweat rate (SR) to include
another potential site of reflex effects (15). Because other
reflex responses to isometric exercise are dependent on
the active muscle mass (10, 20, 22, 24), we hypothesized
that any cutaneous vasomotor or sudomotor responses
would show a similar dependence. Hence, we used both
isometric handgrip (IHG) and isometric leg extension
(ILE) to involve different muscle masses as another possible factor in the cutaneous vasomotor and sudomotor
responses.
METHODS
Eight healthy, moderately active men (aged 20–31 yr,
24.8 ⫾ 0.6 yr) participated in this institutionally approved
study. Each subject provided voluntary written informed
consent before his participation. Subjects refrained from the
The costs of publication of this article were defrayed in part by the
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marked ‘‘advertisement’’ in accordance with 18 U.S.C. Section 1734
solely to indicate this fact.
8750-7587/01 $5.00 Copyright © 2001 the American Physiological Society
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Saad, Adham R., Dan P. Stephens, Lee Ann T. Bennett, Nisha Charkoudian, Wojciech A. Kosiba, and
John M. Johnson. Influence of isometric exercise on blood
flow and sweating in glabrous and nonglabrous human skin.
J Appl Physiol 91: 2487–2492, 2001.—The distribution of the
reflex effects of isometric exercise on cutaneous vasomotor
and sudomotor function is not clear. We examined the effects
of isometric exercise by different muscle masses on skin blood
flow (SkBF) and sweat rate (SR) in nonglabrous skin and in
glabrous skin. The latter contains arteriovenous anastomoses (AVAs), which cause large fluctuations in SkBF. SkBF
was measured by laser-Doppler flowmetry (LDF) and reported as cutaneous vascular conductance (CVC; LDF/mean
arterial pressure). SR was measured by capacitance hygrometry. LDF and SR were measured at the sole, palm, forearm,
and ventral leg during separate bouts of isometric handgrip
(IHG) and isometric leg extension (ILE). CVC and its standard deviation decreased significantly during IHG and ILE
in the palm and sole (P ⬍ 0.05) but not in the forearm or leg
(P ⬎ 0.05). Only palmar SR increased significantly during
IHG and ILE (P ⬍ 0.05). We conclude that the major reflex
influences of isometric exercise on the skin include AVAs and
palmar sweat glands and that this is true for both arm and
leg exercise.
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VASOMOTOR AND SUDOMOTOR RESPONSES TO ISOMETRIC EXERCISE
J Appl Physiol • VOL
CVC data for each 20-s period were calculated. Standard
deviations of the 20-s summaries of CVC data were then
averaged over three 2-min periods: preceding, during, and
after exercise. These values were then compared for the
group by one-way ANOVA with repeated measures followed
by a Student-Newman-Keuls multiple-comparison test. The
level of significance was set at P ⬍ 0.05 for all analyses.
RESULTS
Figure 1 represents a typical response to the protocol
from a single subject. On the average, MAP increased
from 93.1 ⫾ 1.3 to 107.7 ⫾ 1.2 mmHg during IHG and
from 94.0 ⫾ 1.7 to 116.8 ⫾ 1.0 mmHg during ILE. HR
increased from 67.1 ⫾ 2.6 to 78.3 ⫾ 2.6 beats/min during
IHG and from 68.6 ⫾ 2.7 to 87.5 ⫾ 2.3 beats/min during
ILE. In each case, the response was greater during ILE
than during IHG (P ⬍ 0.05). With each bout of exercise,
there was a consistent, significant reduction in the average level of CVC at the palm. Note also that the temporal
variation in CVC at that site was also markedly reduced
during each of the exercise bouts. In contrast, CVC levels
in the nonglabrous skin (forearm) showed no consistent
response to isometric exercise.
Figure 2 depicts the average responses in CVC from
all four skin sites to both IHG and ILE. During both
ILE and IHG, there were significant decreases in CVC
to both glabrous regions (palm and sole) (P ⬍ 0.05). In
contrast, the nonglabrous regions (leg and forearm)
showed no significant changes in CVC during either
exercise type (P ⬎ 0.05). Therefore, regardless of the
active muscle group, the only significant changes in
blood flow occurred at the glabrous regions. There were
no significant differences in responses in CVC between
the palm and sole during the same type of exercise (P ⬎
0.05). This was also true for the leg compared with the
arm. There was a significant difference in the responses in CVC at the palm between IHG and ILE,
with a greater vasoconstriction during ILE (P ⬍ 0.05)
(Fig. 2). There was no significant difference in the
responses in CVC between the two exercise types at the
other three sites (P ⬎ 0.05).
A striking feature of the responses in CVC at the palm
(Fig. 1) and sole was a sudden marked reduction in the
spontaneous temporal variations. To analyze this objectively, we compared the average standard deviations in
CVC before, during, and after exercise (Fig. 3) and found
that, for both the palm and the sole, the mean standard
deviation during exercise was significantly less than that
before or after exercise (P ⬍ 0.05). In contrast, in the
forearm and leg, changes in variability were not consistent, increasing to a small but significant degree in the
forearm during exercise (P ⬍ 0.05) but not changing
significantly in the leg (P ⬎ 0.05).
Figure 4 shows the average responses in SR to IHG
and ILE from the four skin sites. There was a significant increase in SR only at the palm, and this was true
for both types of isometric exercise (both P ⬍0.05).
There was a trend for SR to increase at the sole, but
this tendency did not achieve statistical significance
(P ⫽ 0.15 during ILE and P ⫽ 0.20 during IHG). Palm
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consumption of alcohol, tobacco, or caffeine for at least 12 h
before the experiment. No subject was taking medication at
the time of the study. Measurements of maximal voluntary
contractions (MVCs) for both IHG and ILE were taken at
least 1 h preceding experimentation. All experiments were
performed at the same time of day to avoid any diurnal
effects (1).
SkBF was measured as laser-Doppler flow (LDF) (model
MBF3D, Moor Instruments). Cutaneous vascular conductance (CVC) was calculated as the ratio of LDF to MAP. Each
site was instrumented with an aluminum fitting that housed
a LDF flow probe. The housing also served as a heating unit
used to control local temperature at the site of blood flow
measurement and allowed for the measurement of SR at that
site. SR was measured by capacitance hygrometry. MAP and
HR were measured noninvasively at the finger by photoplethysmography (Finapres, Ohmeda, Englewood, CO). Both
SkBF and SR were always measured on the left extremity at
each of four sites: palm at the thenar eminence, ventral
forearm, arch of the sole, and ventral leg over the tibia.
Whole body skin temperature (Tsk) was controlled at 34°C
through the use of a water-perfused suit, with Tsk recorded as
a weighted average of thermocouple measurements from six
sites (26). A Tsk of 34°C was used because it is considered to
be a thermoneutral skin temperature. The water-perfused
suit covered the entire body with the exceptions of the head,
feet, hands, and arm and leg areas of LDF measurement.
Local skin temperatures at the sites of LDF and SR measurement were also controlled at 34°C throughout each study. All
measurements were sampled once per second.
The subject was outfitted in the water-perfused suit 1 h
after MVC measurement. Subjects were seated throughout
all studies. Laboratory light level was dimmed and the sound
level reduced during the study to minimize environmental
influences, which can markedly change blood flow to glabrous
skin (16). After an initial baseline period of at least 10 min,
the subject performed a 2-min isometric exercise bout at 30%
MVC. Every isometric exercise bout was preceded by at least
5 min of baseline and followed by at least 5 min of recovery.
Each subject performed four bouts: two of IHG and two of
ILE. ILE and IHG were always performed by the right
extremity. The order of exercise type was randomized. The
study was performed as a series of two experiments, which
were identical except for the site of measurement of SkBF
and SR. In one experiment, SkBF and SR on the sole and
ventral leg were measured and, in the other, measurements
were made from the palm and forearm. These experiments
were performed on separate days at the same time of day. It
is important to note that all measurements were recorded
from the nonexercising limbs.
Data analysis. CVC data are expressed as means ⫾ SE.
CVC was expressed as a percentage of the 5-min baseline
period before each exercise bout. Both normalized CVC data
and SR data were then summarized into 20-s averages.
These 20-s averages were analyzed by repeated-measures
ANOVA with a Dunnett’s multiple-comparison test. Two-way
ANOVA compared responses in CVC at the palm, forearm,
sole, and ventral leg during the same type of exercise. Furthermore, responses in CVC to IHG and ILE were compared
by two-way ANOVA at all four sites.
Changes in MAP during IHG and ILE were compared to
determine whether there was an effect of muscle mass. This
was achieved by a paired t-test analysis comparing the increases from the last 20 s before exercise to the last 20 s of
exercise. The same comparison was made for HR.
To examine whether fluctuations in CVC were affected by
exercise, for each subject the standard deviations of the 1-s
VASOMOTOR AND SUDOMOTOR RESPONSES TO ISOMETRIC EXERCISE
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SR was significantly greater during ILE than during
IHG (P ⬍ 0.05).
DISCUSSION
We sought to characterize the vasomotor and sudomotor responses to isometric exercise in both gla-
brous and nonglabrous human skin. Our primary
finding was that there were significant vasoconstrictor responses in the glabrous skin of the palm and
the sole to both ILE and IHG (Fig. 2). These reductions in the average level of CVC in glabrous skin
were accompanied by decreases in the second-to-
Fig. 2. Average responses (⫾SE) in CVC at the 4 sites [palm and forearm (A) and leg and sole (B)] during both
isometric leg extension (ILE) and isometric handgrip exercise (IHG). F and E, Responses in nonglabrous skin (leg,
forearm); ■ and 䊐, responses in glabrous skin (palm, sole); F and ■, responses to IHG; E and 䊐, responses to ILE.
Pre, preexercise; post, postexercise. *Significantly different from the 1-min control (preexercise) value, P ⬍ 0.05.
#
Significantly different from the palm IHG values, P ⬍ 0.05.
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Fig. 1. Responses in cutaneous vascular conductance (CVC; in arbitrary units/mmHg) at the palm and forearm, mean
arterial pressure (MAP), and heart rate (HR) to 2 periods each of isometric handgrip (bouts 1 and 3) and isometric leg
extension (bouts 2 and 4). Exercise periods are denoted by the shaded areas. Note that palmar CVC is sharply reduced
throughout each period of exercise and that the spontaneous variability in palmar CVC is also reduced. CVC from
forearm skin did not show a consistent response to isometric exercise, falling slightly in some cases and rising or not
changing in others.
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VASOMOTOR AND SUDOMOTOR RESPONSES TO ISOMETRIC EXERCISE
Fig. 3. Standard deviations (⫾SE) in CVC normalized to baseline from the 4 sites before, during, and after IHG and ILE. A: palm. B: sole. C:
arm. D: leg. Ex, exercise. *Significantly different
from pre- and postexercise (P ⬍ 0.05). # Significantly different from exercise and postexercise,
P ⬍ 0.05. † Significantly different from exercise,
P ⬍ 0.05. This index of variability showed significant reductions at both glabrous skin sites with
both IHG and ILE.
One consideration for the difference in response between the two skin types is the difference in the microvascular anatomy between glabrous and nonglabrous skin. It is well known that AVAs are found
Fig. 4. Average sweat rate (SR) data (⫾ SE) for all 4 sites during both IHG and ILE. A: palm and forearm IHG. B: sole
and leg IHG. C: palm and forearm ILE. D: sole and leg ILE. Only palmar sweating was consistently and significantly
elevated during isometric exercise. *Significantly different from the 1-min control (preexercise) value, P ⬍ 0.05.
J Appl Physiol • VOL
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second variation of blood flow (Fig. 3). As in earlier
studies, we found no consistent changes in CVC in
nonglabrous skin to isometric exercise in normothermia (7, 8, 14, 19, 25, 26).
VASOMOTOR AND SUDOMOTOR RESPONSES TO ISOMETRIC EXERCISE
J Appl Physiol • VOL
SR to increase significantly, whereas cutaneous vascular resistance was not significantly changed. Differences in methods, protocols, and thermal environments
preclude a conclusive explanation for these differences.
In our view, the likely case is that both AVAs and
sweat glands in that region are targets for the reflex
effects of isometric exercise. Environmental factors can
influence the response of AVAs to nerve activity. For
example, in preliminary work, we noted mild skin
cooling abolished both the spontaneous fluctuations in
blood flow to glabrous skin and the reduction in CVC
with isometric exercise (A. R. Saad, D. P. Stephens,
and J. M. Johnson, unpublished observation). We cannot say whether this explains the difference between
our findings and those of Saito et al. (19) but consider
the possibility worth further study.
An important role for the thermal background also
applies to nonglabrous skin. Crandall et al. (7, 8) noted
that there was no consistent or significant reduction in
CVC in the forearm to IHG in normothermia. However,
during hyperthermia, IHG provoked a significant reduction in forearm CVC. In that study, selective blockade of the adrenergic vasoconstrictor system led to the
conclusion that the reduced CVC in response to IHG in
hyperthermia was due to inhibition of the cutaneous
active vasodilator system (7, 8). Of note is that the
reflex origin of this inhibition is most likely the muscle
metaboreceptor reflex because it was slow to develop
and it was sustained by postexercise ischemia (8).
Kondo et al. (15) made similar observations for sweating in both glabrous and nonglabrous skin when subjects were moderately warm. The vasoconstriction
noted in glabrous skin in the present study probably
has its origin in central command (18). The response is
rapid in onset and followed the same time course as
previously described for the SSNA response to central
command (28–30).
We observed an increase in SR on the palm during
IHG and ILE (Fig. 4). Although SR did not increase
significantly on the sole, there was a trend for SR to
increase (P ⫽ 0.15 during ILE and P ⫽ 0.20 during
IHG). Saito et al. (19) found a significant increase in SR
at the sole during IHG. In an earlier study, Crandall et
al. (7) found no response in SR of the forearm to IHG in
normothermic conditions, but they did note an increase
in SR when IHG was performed during heat stress.
These results and observations by Bini et al. (4) and
Kondo et al. (15) indicate that our observation of a
sudomotor response in the palm might extend to other
areas, depending on thermal conditions. Another possibility is that the lack of consistency in the response of
SR at the foot may reflect the amount of water that
reaches the skin surface as opposed to the stimulation
of the sweat glands. It is unlikely that the lack of
sweating at the foot represents a difference in the
neural control of sweating between the sole and the
palm because some of our subjects did sweat at the sole
during exercise, as in the study by Saito et al. (19).
Others did not, however, which indicates that the sole
has lower sensitivity for sweating than the palm. This
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predominantly in glabrous skin regions (11–13). Additionally, it is assumed that the large variations in CVC
observed in glabrous skin represent AVA function (2, 3,
5, 16, 27). These fluctuations are evident in measurements of CVC at the palm and sole (see Figs. 1 and 3).
It is likely, therefore, that the differences in response
in CVC between those regions relate directly to the
presence or absence of AVAs.
In support of this conclusion, we examined the
changes in the pattern of blood flow at the glabrous
sites. The large blood flow fluctuations in glabrous skin
were first characterized by Burton in 1939 (5), who
described the parallel fluctuations in blood flow between the contralateral finger and toe. Thoreson and
Walløe (27) characterized the fluctuations in more detail through ultrasonic Doppler methods. They also
concluded that the fluctuations were caused by the
opening and closing of the anastomotic vessels. In the
present study, these fluctuations in CVC in glabrous
skin decreased greatly during exercise (Figs. 1 and 3).
In nonglabrous skin, the observed effects were not as
consistent. In the leg, there were no significant
changes in the variability of CVC during isometric
exercise, whereas, in the arm, it increased slightly. The
reduction in variability as well as in the mean levels of
CVC in the palm and sole indicates that the AVAs have
more sustained vasoconstrictor tone during isometric
exercise than at rest. The absence of consistent
changes in CVC at the nonglabrous sites is generally
consistent with other studies in which blood flow was
measured (7, 14, 25, 26). This supports the notion that
decreased AVA blood flow caused the observed changes
in CVC in glabrous skin and that there is little or no
effect on blood flow through nutritional vessels.
In addition to comparisons of regional responses to
exercise, we also compared the blood flow and SR
responses between the two exercise types. During ILE,
a much larger muscle mass is exercised than in IHG.
Therefore, we examined whether active muscle mass
would influence the degree of response. We found a
significant difference in the response of CVC and SR in
the palm between IHG and ILE (Fig. 2). CVC was more
reduced and SR was greater during ILE than IHG,
suggesting that the degree of response is dependent on
the muscle mass exercised, which is consistent with
past studies (10, 20, 22, 24). However, we did not see
significant differences in blood flow responses between
ILE and IHG at the remaining three sites. In fact,
blood flow responses at the leg, sole, and forearm appear almost identical between the two exercise types
(see Fig. 2). We also found that the increases in MAP
and HR from rest to the peak of exercise were significantly greater during ILE than during IHG, which
further supports a muscle mass effect (10, 20, 22, 24).
At this point, it is not clear why such a role for muscle
mass would exist in palmar skin but not in other
regions.
Our results appear to differ from those of Saito et al.
(19), who measured SkBF and SR on the sole, as well
as SSNA in the tibial nerve, which innervates the sole.
Of particular interest is that those investigators found
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We thank P. G. Taylor for contributions to the study. We also
thank all the subjects for their willing participation.
This work was supported by National Heart, Lung, and Blood
Institute Grant HL-59166.
Present address of N. Charkoudian: Anesthesia Research, Mayo
Clinic, 200 First St. SW, Rochester, MN 55905.
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possibility might be tested in future studies by varying
the exercise intensity or the length of the exercise bout.
Several investigators noted an increase in SSNA
during isometric exercise (4, 19, 28–30). Saito et al.
(19) reported increases in SSNA from the tibial nerve,
which innervates the sole. Taking those findings and
ours together, it is likely that these increases in SSNA
to glabrous skin are targeting both AVAs and sweat
glands. In other studies (4, 28–30), recordings taken
from the nerves targeting nonglabrous regions also
showed increases in SSNA in response to isometric
exercise. However, we saw no changes in SkBF or SR
in nonglabrous skin. At this point, it is not possible to
make any firm conclusions about the targets of these
increases in SSNA. A future direction would be a comparative study between tibial and peroneal nerve recordings during isometric exercise. In such a study,
measurements of SkBF and SR on the sole and lower
leg would be made along with nerve recordings from
the tibial and peroneal nerves during isometric exercise.
Taken together, the findings show the primary cutaneous responses to isometric exercise in normothermia
to be in the AVAs and sweat glands of glabrous skin. In
the palm especially, these responses are graded with
the active muscle mass.