Regular physical activity alters the postocclusive reactive hyperemia of the cutaneous microcirculation

Abstract

Regular physical activity leads to increased endothelium-dependent vasodilatation. Postocclusive reactive hyperemia (PRH) is a transient increase of blood flow after the release of an arterial occlusion and has been used as a clinical tool to estimate endothelial function. The aim of our study was to assess the potential effect of regular physical training on PRH of skin microcirculation. Skin blood flux was estimated by laser-Doppler fluxmetry (LDF) in two groups of subjects: 12 highly trained athletes and 12 age-matched sedentary controls. LDF was measured on two specific skin sites: volar aspect of the forearm (nonglabrous area) and finger pulp of the middle finger (glabrous area). After the release of a 3-min occlusion of the brachial artery, we determined the following indices of PRH: the time to peak (tpeak), the maximal LDF (LDFpeak), the recovery time (trec), the area under the PRH curve (AUC). Baseline LDF did not differ between the trained and sedentary subjects in either site. On the forearm, we found no significant differences in either PRH parameter. On the contrary, on the finger pulp, there were statistically significant differences in the tpeak and the AUC (p < or = 0.05). The results show an altered PRH response of skin microcirculation in the finger pulp in the trained subjects. We may speculate that this could be the result of an increased endothelial vasodilator capacity. Further, the potential adaptations of the endothelium differ between the glabrous and nonglabrous skin sites.

Full text

Clinical Hemorheology and Microcirculation 45 (2010) 365–374
DOI 10.3233/CH-2010-1320
IOS Press
365
Regular physical activity alters
the postocclusive reactive hyperemia
of the cutaneous microcirculation
Helena Lenasi∗and Martin ˇ
Strucl
Institute of Physiology, Medical Faculty, University of Ljubljana, Ljubljana, Slovenia
Abstract. Regular physical activity leads to increased endothelium-dependent vasodilatation. Postocclusive reactive hyperemia
(PRH) is a transient increase of blood flow after the release of an arterial occlusion and has been used as a clinical tool to
estimate endothelial function. The aim of our study was to assess the potential effect of regular physical training on PRH of
skin microcirculation. Skin blood flux was estimated by laser-Doppler fluxmetry (LDF) in two groups of subjects: 12 highly
trained athletes and 12 age-matched sedentary controls. LDF was measured on two specific skin sites: volar aspect of the forearm
(nonglabrous area) and finger pulp of the middle finger (glabrous area). After the release of a 3-min occlusion of the brachial
artery, we determined the following indices of PRH: the time to peak (tpeak), the maximal LDF (LDFpeak ), the recovery time (trec),
the area under the PRH curve (AUC). Baseline LDF did not differ between the trained and sedentary subjects in either site. On the
forearm, we found no significant differences in either PRH parameter. On the contrary, on the finger pulp, there were statistically
significant differences in the tpeak and the AUC (p≤0.05). The results show an altered PRH response of skin microcirculation
in the finger pulp in the trained subjects. We may speculate that this could be the result of an increased endothelial vasodilator
capacity. Further, the potential adaptations of the endothelium differ between the glabrous and nonglabrous skin sites.
Keywords: Skin microcirculation, laser–Doppler fluxmetry, postocclusive reactive hyperemia, endurance, endothelium
1. Introduction
Skin microcirculation has gained increasing interest over the last decades as it is easily accessible and
has been proposed to reflect generalized microvascular function [21, 27]. As skin is the main organ for
heat elimination from the body, its blood flow has been estimated to vary between 300 ml/min/kg up to
8 l/min/kg in the settings of strenous exercise in a hot environment [23, 25]. Moreover, it has been shown
that endurance-trained subjects have a higher skin blood flow at any given level of workload and core
temperature, when compared with matched sedentary controls [12, 20, 38, 41]. It is thus obvious that the
regulation of skin blood flow is a delicate and complex phenomenon that comprises a well coordinated
interplay of central as well as local mechanisms [24–26, 39]. One of the most important local mechanisms
is endothelium that in physiological conditions releases vasodilators and vasoconstrictors in a balanced
way. Furthermore, the control of skin blood flow is strongly site-dependent: acral parts (glabrous areas)
contain arteriovenous anastomoses (AVAs) that represent a functional entity for heat elimination and
are predominately under symphathetic neural influence [23, 45, 47]. On the other hand, nonglabrous
areas with no AVAs receive also vasodilatory symphathetic nerve fibres with no uniformely confirmed
∗Corresponding author: Helena Lenasi, MD, Institute of Physiology, Medical Faculty, Zaloˇ
ska 4, 1000 Ljubljana, Slovenia.
Tel.: +386 1 543 7513; Fax: +386 1 543 7501; E-mail: helena.lenasi.ml@mf.uni-lj.si.
1386-0291/10/$27.50 © 2010 – IOS Press and the authors. All rights reserved

366 H. Lenasi and M. ˇ
Strucl / Regular physical activity and the postocclusive reactive hyperemia
vasodilator that may well be nitric oxide (NO) [23, 26, 39]. To which extent endothelium contributes to
the regulation of vascular tone and vasodilatation in glabrous and nonglabrous skin areas has not been
extensively studied [23, 26, 33, 39].
Skin microcirculation and endothelial function in general have been shown to be impaired in many
cardiovascular diseases [6, 15, 17, 19, 30] and in hyperlipoproteinemia [30], in diabetes [5], some
neurological diseases [40], in smokers [37], as well as with aging [2, 22, 36, 43].
One of the measures to improve endothelial dysfunction due to reduced NO bioavailability seems to
be regular physical activity. Participation in regular aerobic training has confirmed an improvement of
endothelium-dependent vasodilatation in many diseases such as hypertension [19], coronary heart disease
[17] and diabetes [6] in the vascular beds of active tissues. It has also been shown in young [18, 28, 31,
42, 44] and older [2, 42] healthy trained subjects that endurance training is associated with an enhanced
responsiveness of the cutaneous microcirculation to endothelium-dependent stimuli. Nevertheless, the
results on the impact of endurance training on the endothelium-dependent vasodilatation, specially in
skin microcirculation of healthy, are controversial [3, 7, 18, 28, 38, 42]. Also, the mechanisms of an
enhanced cutaneous microvascular responsiveness induced by training remain unclear.
Thus, establishing measures to preserve or improve endothelial function are of great clinical importance.
One of the widely used clinical methods to evaluate endothelial function, that is easily applicable, is
assessment of postocclusive reactive hyperemia (PRH) [8, 30, 49]. PRH is a transient increase of blood
low after a temporal occlusion of the corresponding artery. Factors contributing to this phenomenon
include vasodilators released from endothelium in response to increased shear stress as well as locally
released metabolites accumulated in the ischemic tissue and myogenic component [9, 11, 32, 45, 49].
The aim of our study was therefore to assess the impact of training on the PRH of skin microcirculation in
two representative measuring sites. We hypothesised that the endothelial vasodilator capacity, estimated
by indices of PRH, might be increased in trained due to repetitively increased shear stress to which
endothelial cells are exposed during bouts of aerobic exercise. We measured cutaneous blood flux in
two groups of subjects with significantly different aerobic fitness by the use of laser Doppler fluxmetry
(LDF) in the middle finger pulp (representative of glabrous area) and on the volar aspect of the forearm
(nonglabrous area) before and after a 3-min occlusion of the brachial artery.
2. Methods
2.1. Subjects
We recruited two groups of men: 12 endurance-trained cyclists who performed regular training (at least
15 hours of intense aerobic exercise weekly for many years) and were competing at a national level and 12
age-matched sedentary men who performed no regular exercise. The anthropometric characteristics and
baseline blood pressure as well as the resting heart rate were assessed upon the arrival to our laboratory.
All subjects were healthy normotensive nonsmokers and had been taking no medications nor had a family
history of cardiovascular diseases. The study conformed to the Declaration of Helsinki and was approved
by the National ethics commitee. All subjects gave written informed consent.
2.2. Measurements
Subjects had abstained from food, caffeine-containing drinks and alcohol for at least eight hours prior
to their attendance and were asked to refrain from strenous exercise for at least 24 hours. All experiments

H. Lenasi and M. ˇ
Strucl / Regular physical activity and the postocclusive reactive hyperemia 367
were performed in a temperature-controlled room (24 ±1oC) in the forenoon with subjects laying in a
supine position; prior to any measurements subjects lied for 30 min to acclimatize.
Cutaneous microcirculation blood flux was measured by means of laser Doppler fluxmetry described
elsewhere [8, 16, 31, 48]. A two-channel laser Doppler fluxmeter (Periflux 4001 Master, Perimed, Sweden)
with a laser beam of 780 nm wavelength was used and the LDF data were expressed in arbitrary perfusion
units (PU). Before the measurement, the device was calibrated for zero calibration. The LD probes were
attached as follows: (1) to the finger pulp of the middle finger of the nondominant arm to assess the LDF
in glabrous area and (2) to the volar aspect of the nondominant forearm, avoiding superficial veins to
assess the LDF in the nonglabrous area. The sampling frequency was 500 Hz and the digitalized LDF
signal was simultaneously transmitted to a personal computer for further analysis.
At both measuring sites, skin temperature was continuously recorded locally by a digital thermometer
(Peritemp PF4005, Perimed, Sweden). Arterial pressure of the digital artery was measured on the fourth
finger (Finapress, Ohmeda 2300) and a standard ECG was continuously monitored.
2.2.1. Protocol 1
To assess the effect of acute exercise on LDF in glabrous and nonglabrous area.
Only sedentary males participated in this protocol that was held on a separate occasion. We carried out
this protocol to assess the extent of potential increase in skin perfusion in glabrous vs. nonglabrous site
following acute bout of exercise. After obtaining baseline recordings of the LDF and skin temperature for
5 min at the two measuring sites (finger pulp and volar forearm), the LD probe holders were left in place and
subject began cycling on a standard cycloergometer at a workload of 40 Watt that was gradually increased
to a submaximal level, predicted from the estimated submaximal heart rate according to the subject’s
age. The subject cycled at this workload for 20 min. Immediately after having stopped the exercise, the
subject again lied in a supine position, the LD probes were fixed to the very same measuring sites as
before exercise and LD fluxes and skin temperatures were traced as long as to reach the resting values.
2.2.2. Protocol 2
To assess the indices of postocclusive reactive hyperemia (PRH) in glabrous and nonglabrous area of
the trained and the sedentary.
After a 5-min baseline recordings of the LDF in the finger pulp and the volar forearm had been obtained,
brachial artery was occluded to suprasystolic pressure with an inflatable arm cuff for three minutes. LDF
was continuously monitored (biological zero). After three minutes, the cuff was released and the LDF
was recorded as long as 5 min after returning to the baseline level. The following indices of PRH were
determined: peak flow (LDFpeak), defined as the maximal LDF after release of the occlusion, time to peak
(tpeak), defined as the time to reach LDFpeak after cuff deflation, the recovery time (trec), defined as the
total duration of PRH, i.e. the time in which the LDF returns to its baseline value, the area under the
curve (AUC), defined as an integer of the PRH curve and reflecting perfusion debt repayment [30, 37,
49]. The representative LDF tracings of the two representative measuring sites following the release of
an occlusion are presented in Fig. 1.
2.3. Assessment of physical fitness
Physical fitness was evaluated on a separate occasion by measuring the resting heart rate and maximal
oxygen consumption (VO2max). VO2max was assessed by a maximal graded exercise test on a standard cycle
ergometer with the initial workload of 40 Watt that was incrementally increased by 30 W in sedentary

368 H. Lenasi and M. ˇ
Strucl / Regular physical activity and the postocclusive reactive hyperemia
012345678
LDF (PU)
0
50
100
150
200
250
300
AUC
t
rec
t
peak
LDF
peak
occlusion
012345678
0
50
100
150
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250
300
t
rec
Time (min)
LDF (PU)
0
10
20
30
40
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413 7652
AUC
tpeak
LDFpeak
trec
occlusion
AB
Fig. 1. Representative tracings of the postocclusive reactive hyperemia in the two sites: (A) middle finger pulp and (B) volar
forearm. PRH was induced by a transient 3-min occlusion of the brachial artery. LDF, laser Doppler flux; PU, perfusion units,
LDFpeak, maximal LDF after release of the occlusion; tpeak , time to peak; trecovery , recovery time (duration) of PRH; AUC, area
under the curve.
and by 40 W in athletes every three minutes until exhaustion. During the test, heart rate was continuously
recorded by electrocardiogram as well sphygmomanometric blood pressure of the brachial artery.
Oxygen consumption and the CO2content in the expired air were recorded via face mask by a gas
analyser and respiratory exchange ratio (RER) was calculated. VO2max was defined as the mean of the
two highest consecutive 30-s VO2 measurements that met the following criteria: attainment of the plateau
of VO2 with increasing exercise intensity and RER exceeding 1.1.
2.4. Data acquisition and statistical analysis
LDF data were analyzed off-line by the ‘Nevrocard LDDA’ acquisition system. The baseline LDF data
reported are averaged over a 3-min period. The maximal LDF responses to acute exercise (protocol 1) were
averaged over 10 s-intervals. As for the protocol 2, LDFpeak was expressed as a percentage increase over the
baseline. The trec was obtained as the interception point of the fitted PRH curve and the average LDFbaseline
line. AUC was calculated as an integer of the PRH response (sum of the averaged 1 sec-recordings of the
LDF).
The results are presented as group means ±SEM. The LDF increase over the baseline after the release
of arterial occlusion in each subject was evaluated by ANOVA for repeated measurements. The paired
or unpaired two-tailed Student’s t-test was used to compare the LDF data between rest and postexercise
for each group and the parameters of PRH between the two groups, respectively. A p-value of less than
0.05 was accepted as statistically significant.
2.5. Reproducibility assessment
To test the reproducibility of the method, baseline LDF and PRH-induced changes were recorded on
two separate occasions at the same time of the day, under the same conditions in six subjects. These
individual coefficients of variation were then averaged across subjects to provide overall estimates of
intraindividual variability.

H. Lenasi and M. ˇ
Strucl / Regular physical activity and the postocclusive reactive hyperemia 369
3. Results
Anthropometric characteristics and some baseline cardiovascular parameters of the subjects are shown
in Table 1. The only significant difference between the sedentary and trained group was observed in
the resting heart rate. Furthermore, the VO2max was significntly greater in the trained, as expected:
65 ±1 ml/min/kg in trained and 41 ±1 ml/min/kg in sedentary. Both latter parameters reflect an increased
aerobic fitness level in the trained group.
The baseline LDF as well as skin temperature did not differ in either measuring site between the trained
and sedentary (t-test, Table 2). LD fluxes were significantly greater in the finger pulp compared to the
volar forearm in both groups (Table 2).
3.1. The effect of acute exercise on LDF of glabrous and nonglabrous area
Acute 20-min cycling at submaximal aerobic workload caused a significant increase in LDF in the finger
pulp (glabrous area) as well as in the volar forearm (nonglabrous area) (p≤0.01). Skin temperature
increased by 1.5 ±0.9oC. The increases of LDF in six sedentary subjects in response to exercise are
Table 1
Anthropometric characteristics and some hemodynamic parameters of subjects
Sedentary Trained
Age (years) 24.9 ±1.1 22.6 ±0.9
Height (cm) 182.6 ±1.4 180.6 ±2.2
Body weight (kg) 76.9 ±2.6 79.5 ±2.6
psystol (mmHg) 120.4 ±2.0 117.3 ±2.5
pdiastol (mmHg) 80.9 ±2.1 77.3 ±1.7
Heart rate (beats/min) 69.3 ±3.6 50.0 ±2.5*
psystol-digital (mmHg) 102.2 ±4.6 99.3 ±4.3
pdiastol-digital (mmHg) 78.9 ±2.80 74.3 ±3.2
psystol, systolic blood pressure of the brachial artery; pdiastol , diastolic blood pres-
sure of the brachial artery; psystol-digital, systolic blood pressure of the digital artery;
pdiastol-digital, diastolic blood pressure of the digital artery; LDFbaseline , baseline
LDF, PU, perfusion units. Results are mean±SEM, n= 12.
*p≤0.05.
Table 2
Baseline laser Doppler flux (LDF) and skin temperature in the finger pulp and on
the volar forearm in trained and sedentary
Volar forearm Finger pulp
Sedentary Trained Sedentary Trained
LDFbaseline (PU) 14.2 ±2 15.6 ±1.7 176 ±20* 202 ±16*
Tskin (◦C) 32.2 ±0.7 32.6 ±0.3 32.9 ±0.3 33.4 ±0.2
LDFbaseline, baseline LDF; PU, perfusion units; Tskin , temperature of the skin over the
reperesenative measuring site. Results are mean ±SEM, n= 12.
*p≤0.01, finger pulp vs. volar forearm for the trained and for the sedentary group.

370 H. Lenasi and M. ˇ
Strucl / Regular physical activity and the postocclusive reactive hyperemia
presented in Fig. 2. Of note is a high variability of maximal LDF after exercise (the LDF increment
ranged from 150% up to 700%).
3.2. The effect of fitness status on postocclusive reactive hyperemia in glabrous
and nonglabrous area
The release of a 3-min occlusion of the brachial artery caused a significant increase of LDF in the
finger pulp and on the forearm in all subjects (Fig. 1). On the volar forearm none of the indices of PRH
reached statistical difference between the groups of trained and sedentary (Table 3, t-test) although there
was a trend toward statistical diference regarding the AUC (Table 3, p= 0.09, t-test). On the contrary, the
tpeak and the AUC of PRH in the finger pulp significantly differed between the two groups. The tpeak was
shorter in trained whereas the AUC significantly larger in the group of trained compared to the sedentary
(Table 3, p≤0.05, t-test). Other indices of PRH in the finger pulp did not reach a statistical difference.
*
*
0
50
100
150
200
250
300
350
400
450
after acute
excercise
LDF (PU)
volar forearm
finger pulp
resting
Fig. 2. LDF response to acute exercise in the glabrous and nonglabrous skin area. LDF was assessed on the finger pulp (glabrous
area) and on the volar forearm (nonglabrous area) before (resting) and after 20-min acute submaximal exercise on cycloergometer.
LDF, laser Doppler flux; PU, perfusion units; n=6,*p≤0.01, LDF in the volar forearm (empty bars) after vs. before exercise
and LDF in the finger pulp (filled bars) after vs. before exercise.
Table 3
Indices of postocclusive reactive hyperemia (PRH), as assessed on the volar forearm
and in the finger pulp in the trained and sedentary after a 3-min occlusion of the
brachial artery
Volar forearm Finger pulp
Sedentary Trained Sedentary Trained
LDFpeak (PU) 52 ±560±9 374 ±26 410 ±36
tpeak (sec) 7.3 ±0.6 8.1 ±1.6 36 ±529±5*
trec (sec) 62 ±669±5 143 ±20 164 ±12
AUC (PU*sec) 1260 ±181 1423 ±195 10527 ±662 14560 ±750*
LDF, laser Doppler flux; PU, perfusion units; LDFpeak, peak, maximal LDF; tpeak,
time to rich LDFpeak;t
rec, recovery time; AUC, area under the curve. Results are
mean ±SEM, n= 12, *p≤0.05, trained vs. sedentary.

H. Lenasi and M. ˇ
Strucl / Regular physical activity and the postocclusive reactive hyperemia 371
3.3. Reproducibility
The intraindividual coefficients of variation were ranged between 3.3% and 41.2% (mean 19.9 ±5%)
for the baseline LDF and between 5.1% and 44.2% (mean 23.5 ±6%) for the response to the release of
the arterial occlusion.
4. Discussion
The main finding of our study is that certain indices of the cutaneous PRH differ between sedentary
and highly-trained healthy men in the finger pulp but not in the forearm. We may imply an enhanced
vasodilator capacity of the finger pulp microcirculation induced by aerobic training. Further, the potential
adaptations to physical conditioning as assessed by indices of PRH are probably different in glabrous
and nonglabrous skin sites.
To our knowledge, no study that applied laser Doppler fluxmetry and performed PRH to assess the
microvascular reactivity simultaneously evaluated the impact of physical training on the reactivity of
cutaneous microcirculation in the two representative measuring sites: glabrous and nonglabrous one. The
indices of PRH in trained compared to sedentary in our study were different between the two distinct
sites. Different responses of glabrous and nonglabrous skin have been already shown in acute static [46]
and dynamic [47] exercise.
Most studies assessed the impact of chronic training in the forearm skin as a representative of
nonglabrous site and the results are not consistent. The study of Heylen showed an increased AUC
and the recovery time of PRH and no changes in the time to peak and half time of PRH in highly trained
windsurfers [18]. Nevertheless, they used a 5-min occlusion of the brachial artery in contrast to our 3-min
occlusion. Vassalle and coworkers also showed an enhanced endothelium-dependent vasodilatation in
trained that also correlated with the plasma levels of NO [42]. They attributed the higher post ischemic
peak LDF in trained to an increased release of NO in trained [15, 17, 42]. The discrepancy to our study
could hardly be attributed to any factor as the VO2max as well as the type of sports and the time of artery
occlusion were comparable. Actually we also hypothesised to get an enhanced PRH in trained as we
have shown that acute exercise in addition to the regions with AVAs, also significantly increases blood
flow in the forearm skin. Moreover, there are reports that blood flow in the forearm skin microcircula-
tion is increased in trained compared to sedentary exposed to the same level of exercise intensity [12,
20, 38, 41]. These observations may partly explain the fact that at the given internal temperature the
treshold for heat elimination is lower in trained [23] and may well be the consequence of an endothelial
adaptation.
Contrary to our expectations and to the aforementioned studies [12, 20, 38, 41] we have shown no
differences in either index of PRH in the forearm between the trained and the sedentary. Similar results
in healthy were observed in the study of Colberg et al. [6]. The results are also in agreement with
Boegli who also did not confirm differences in the peak LDF and AUC of PRH between trained and
sedentary [3]. If we rely on the assumption that PRH could be considered as a measure of endothelial
function [49], a possible explanation could be that the nonglabrous sites predominantly serving the nutri-
tive blood flow are not subject to variation of blood flow due to thermoregulation to that extent as to
induce changes in the responsiveness of endothelium. In the light of former observations [12, 20, 38,
41] and our results of acute exercise this seems less likely. Another explanation would be that mecha-
nisms other than endothelial vasodilators predominate in PRH. It could be that the sedentary subjects

372 H. Lenasi and M. ˇ
Strucl / Regular physical activity and the postocclusive reactive hyperemia
accumulate more ischemic metabolites during the occlusion that strongly contribute to an increase of
AUC; it is a well known phenomenon that the extraction of oxygen from blood due to adaptations of
oxidative metabolism enzymes is better in trained compared to sedentary [13]. Further, the potential
endothelial adaptation could be masked by an increase in oxidative stress induced by strenous exercise
in highly trained [1, 14]. This seems less probably as it would likely affect also the reactivity of the
finger pulp microcirculation. Last but not least athletes may exhibit an altered sensitivity of the vas-
cular smooth muscle cells to endothelial vasodilators that, contrary to the observation of Boegli [3],
we proposed in our previous study [31]. Nevertheless, these are only speculations that need further
clarifications.
As for the finger pulp we have shown that the time to peak was shorter and the AUC of the PRH
larger in trained. This is the first study that assessed the impact of strenous aerobic training on the LDF
response in the finger pulp to a 3-min occlusion of the brachial artery. We have already shown an increased
AUC in the finger pulp of trained men after an 8-min occlusion of the digital artery [31]. Since it has been
suggested that shorter times of occlusion more faithfully reflect the contribution of NO and thus endothelial
component of PRH [35] we induced a shorter occlusion (of the brachial artery). We may speculate that
an increased AUC of PRH in our study could be a consequence of an enhanced endothelium-dependent
vasodilatation of the finger pulp microcirculation in the trained. Also, the shorter tpeak may reflect more
rapid increase of LDF due to more vasodilators released from the endothelium as a consequence of
increased shear stress caused by flow increment after the release of arterial occlusion. This may be due to
NO, prostaglandins and endothelium-dependent hyperpolarizing factor. Namely, the exact contribution of
each of these mediators to the PRH remains to be uncovered since there are no uniform results regarding
this issue [7, 9, 11, 32, 45]. On the other hand, we can not exclude an adaptation of the central mechanisms,
i.e. sympathetic nervous system. Yet, the two potential adaptations should not be regarded as separate
phenomena: in fact there is an interplay between local and central mechanisms regulating vascular tone. It
is known that NO acts on presynaptic ␣2-adrenergic receptors on the sympathetic nerves [10]. NO is also
suggested to be a signalling molecule to bring about coordinated increases in cutaneous vasodilatation
and heat dissipation in skin [24–26]. Exercise training has been suggested to reduce sympathetic tone
and supress the pressor response to adrenergic agents by increasing NO release from the endothelium
[4]. The increased responsiveness of glabrous sites in trained can well be the consequence of an adjusted
interplay between local and central mechanisms regulating blood flow in these areas.
Our study has several limitations: it is cross-sectional and a prospective study may have been more
relevant. Another pitfall is the small number of subjects included. It is worth to note that there were
assumedly differences in the AUC in the forearm between trained and sedentary that did not reach
statistical difference. Finally, there is a need to standardize the measures to evaluate PRH [8, 48, 49] as
well as to reveal the strenght of each of the mechanisms contributing to PRH in human skin. Additional
studies using supplementary methods such as newly improved high resolution ultrasound combined with
fluorescence video angiography for the optimal assessment of perfusion in cutaneous, subcutaneous and
deeper tissue layers [29, 34] would strenghten our results and make them more reliable.
In conslusion, highly trained athletes exhibit a shorter tpeak and an increased AUC after a 3-min arterial
occlusion in the finger pulp. This might point to an increased vasodilator capacity of the glabrous skin
sites and may have clinical implications. The indices of PRH in the volar forearm are comparable between
the trained and sedentary. This reflects different mechanisms of adaptation to exercise in glabrous and
nonglabrous skin areas, at least with respect to PRH. Additional studies are needed to elucidate the control
of skin blood flow in glabrous and nonglabrous sites as well as the exact mechanisms contributing to the
cutaneous PRH.

H. Lenasi and M. ˇ
Strucl / Regular physical activity and the postocclusive reactive hyperemia 373
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