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Local cold acclimation of the hand impairs thermal

responses of the finger without improving hand

neuromuscular function

C. L. M. Geurts,1 G. G. Sleivert2 and S. S. Cheung3

1 Human Performance Laboratory, Faculty of Kinesiology, University of New Brunswick, Fredericton, NB, Canada

2 PacificSport Canadian Sport Centre Victoria, Victoria, BC, Canada

3 Environmental Ergonomics Laboratory, School of Health and Human Performance, Dalhousie University, Halifax, NS, Canada

Received 25 February 2004,

accepted 2 September 2004

Correspondence: G. G. Sleivert

PhD, Director of Sport Science

and Medicine, PacificSport

Canadian Sport Centre Victoria,

100-4636 Elk Lake Dr Victoria, BC

V8Z 5M1, Canada.

Abstract

Aim: To investigate the effects of cold acclimation on the thermal response

and neuromuscular function of the hand.

Methods: Ten healthy subjects [three female, seven male, age (mean SD):

27.9 7.9 years] immersed their right hand in 8 C water for 30 min,5 days a week for 3 weeks. On the first and the last day, neuromuscular

function of the first dorsal interosseus (FDI) muscle was tested.

Results: There was no significant change in maximal voluntary contraction

strength or evoked contractile characteristics of the FDI after cold acclima-

tion. Minimum finger temperature decreased significantly from 10.6 1.2 to

9.3 0.8 C after 3 weeks (P < 0.01), with most of the decrease occurring

after a single exposure. Mean finger temperature dropped significantly from

14.2 1.9 to 11.7 1.4 C following cold acclimation (P < 0.05), with

90% of this adaptation occurring after 5 days. Onset time of cold-induced

vasodilatation increased from 446 171 to 736 384 s (P < 0.05) and the

amplitude decreased from 5.3

3.2 to 2.5

2.1

C (P < 0.05). This wassignificantly different from the control group, who immersed their right hand

on the first and last days only.

Conclusion: These data suggest that cold acclimation does not enhance hand

temperature or function but may put the hands at a greater risk of cold injury

when exposed to the cold.

Keywords cold acclimation, cold-induced vasodilatation, contractile prop-

erties, evoked force, hand, skin temperature.

There are occupations in which manual work has to be

performed in a cold environment. Examples include

fisherman (LeBlanc et al. 1960, 1964), power-line work-

ers that must work outside in winter, and frozen-food

processing industry workers (Chiang et al. 1990). While

performing these manualtasks, it is notalways possibleto

protect the hands sufficiently against the cold because

bulky gloves impair manual dexterity (Geng et al. 1997).

When exposed to acute cold stress, the body responds

with a vasoconstriction of the extremities to maintain

the temperature in the core. After a prolonged period of

vasoconstriction, a paradoxical vasodilatation usually

occurs. This cold-induced vasodilatation (CIVD) was

first reported by Lewis (1930) and has long been

considered a protective mechanism for cold injury of the

fingers (Wilson & Goldman 1970). During a CIVD,

there is an increase in blood flow to the hand that

warms up the fingers. Ducharme et al. (1991) also

showed increased blood circulation in the large vessels

of the forearm during CIVD, which increased the

temperature of the forearm muscles. It is well known

that neuromuscular function is dependent on the

temperature of the muscle (Ranatunga et al. 1987),

therefore if CIVD increases muscle temperature of the

Acta Physiol Scand 2005, 183, 117124

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hand muscles due to an increased blood flow to the

extremities, this may have a beneficial effect on the

neuromuscular function in this region and could con-

ceivably improve manual dexterity (Heus et al. 1995).

Repeated exposure to cold stress results in a cold

acclimation, described by some as cold adaptation. The

literature on cold acclimation is ambiguous regarding

the effect of chronic or repeated cold stress on the humanbody. Studies on people living and working in the cold

have shown an increased skin temperature and enhanced

blood flow to the extremities while in cold conditions

(Miller & Irving 1962, Eagan 1963, LeBlanc et al. 1964,

Savourey et al. 1996). Other researchers have shown an

enhanced vasoconstriction after cold adaptation, result-

ing in a decreased skin temperature upon cold exposure

(Livingstone 1976, Leftheriotis et al. 1990, Bridgman

1991). There are numerous reasons for this diversity of

cold adaptation. The type of cold adaptation is probably

dependent upon the various experimental conditions

used to develop and test cold adaptation, such as

continuous vs. discontinuous exposures, moderate vs.

severe cold stress, variations in total exposure time

during both adaptation and testing, whole body vs.

extremity-only exposure, and air vs. water immersion.

The purpose of this study was to investigate the effects

of repeated cold-water immersion of the hand on

thermoregulation of the hand and on the neuromuscular

function of the first dorsal interosseus (FDI) muscle. In

this study, the hand was tested and acclimated in cold

water for 30 min to get a complete view on the CIVD

response that typically occurs after 10 min of cold stress.

Although contact cooling through handling material or

tools may impose a greater risk in daily life due to itsmore intense and rapid cooling effect (Jay & Havenith

2004), acclimation will most likely result from whole

hand cooling over a longer period of time. Cold water is

the safest and fastest way to cool the periphery without

putting the subjects at risk of cold injury. The whole

hand was cooled instead of only the finger because in

daily life people typically expose their whole hand when

working in a cold environment. Because the whole hand

was immersed, the cold stress would be larger than with

finger-only immersion; therefore, a water temperature of

8 C was chosen to minimize the extreme discomfort and

nausea often experienced by subjects. It was hypothes-

ized that repeated cold-water immersion of the hand

would enhance the CIVD response and that this would

improve neuromuscular function of the FDI muscle.

Materials and methods

Subjects

Twenty volunteers (12 male and eight female) partici-

pated in this study. The Ethics Committee of the

University of New Brunswick approved the study

protocol in advance. Each subject completed and

answered no to all questions on the Physical Activity

Readiness Questionnaire (PAR-Q) (CSEP 1998) and

provided written informed consent before participating.

Seventeen subjects (10 male, seven female, 26.9

6.6 years) were used for the analysis. One female

subject withdrew because of intolerance of the coldwater. The data of two male subjects were discarded

because they did not show a CIVD response during the

initial test, defined as an increase in finger temperature

of 0.5 C.

Experimental design

All subjects underwent in total four neuromuscular

function tests. The first two were conducted in thermo-

neutral condition and after 30 min hand cooling and

this was repeated 3 weeks later. The subjects were

assigned to two groups a priori to avoid time gaps

between the initial test and the acclimation trials. The

experimental group (EXP; three female, seven male; age

27.9 7.9 years; height 1.76 0.07 m; weight

74.3 10.4 kg) came into the laboratory five times a

week for 3 weeks to immerse their right hand up to the

styloid process into 8 C water for 30 min. On the first

and the last day of this cold acclimation period, they

underwent a neuromuscular function test. A control

group (CON; four female, three male; age of

25.6 4.1 years; height 1.74 0.08 m; weight

70.2 11.4 kg) arrived at the laboratory on the first

and last day only to undergo the neuromuscular

function test. The testing took place in September andOctober 2002 in eastern Canada (average ambient

outdoor temperature: 11.8 5.7 C).

Neuromuscular function test

Upon arrival on the first and the last day of the cold

acclimation period, a plastic mould was made for the

index finger and forearm. Two insulated ceramic chip

thermistors (MA-100; Thermometrics, New York, NY,

USA) were placed next to the nail bed of the right index

finger (Tif) and on the skin over the FDI muscle (Tfdi).

Skin temperature of the index finger was measured and

logged every 8 s on a data logger (Smartreader 8 Plus;

ACR, Vancouver, BC, Canada) interfaced with a

computer to prevent cold injury. Two stimulating

electrodes were placed on the ulnar nerve, 4 and 7 cm

proximal to the pisiform bone, respectively. The subject

was seated with the shoulder abducted and the forearm

resting on a stable base. Forearm and hand were

immobilized using a plastic mould and straps. The

subject was accustomed to the electric current and

familiarized to the feeling of tetanic stimulation. The

118 2005 Scandinavian Physiological Society

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current was delivered through supramaximal square

wave pulses of 200 ls duration by a constant current

stimulator (Digitimer; DS7A, Hertfordshire, UK).

The protocol used was similar to that of Geurts et al.

(2004) and was conducted as follows: first, the subject

performed an isometric maximal voluntary contraction

(MVC) with the index finger. The resulting abduction

force was amplified (100) and collected at 1 kHz forlater processing (WinDaq Pro+; Dataq1 , Akron, OH,

USA). Thereafter, one evoked twitch, evoked tetanic

contractions at 10 and 20 Hz stimulating frequencies,

and two voluntary force control trials at 25 and 50% of

the MVC, 40 s in duration, were performed. Two

minutes of rest separated each neuromuscular test. The

plastic mould and stimulating electrodes were removed

and the subject was then transferred to the hand cooling

station. The right hand was immersed up to the styloid

processes for 30 min in circulating 8 C water main-

tained with a chiller (Polyscience, Niles, IL, USA). After

30 min, the hand was removed from the water, dried

off, and the subject was transferred back to the

myograph and the neuromuscular testing, with excep-

tion of the MVC, was repeated. This process took about

35 min; in this time, the index finger warmed up on

average 6.2 2.6 C and the skin above the FDI by

6.1 2.4 C.

Data analysis

The onset time of the CIVD was defined as the time

from hand entry until the skin temperature of the index

finger first started to rise for more than 0.5 C and the

amplitude of the CIVD was defined as the apex of theCIVD minus the nadir of the CIVD. The minimum skin

temperature of the index finger (Tif min) and the average

temperature of the index finger (Tif mean) during the

30 min water immersion were averaged over the 10

experimental subjects and plotted vs. acclimation day

and then fitted with a simple exponential function [y

a + b exp()x/c)] (Gill & Sleivert 2001).

The following characteristics were calculated from

the evoked force measurements. Peak twitch force (PTF)

was defined as the peak amplitude of the force signal.

Time to peak force (TTP) was defined as the delay

between the stimulus and the peak amplitude. The half

relaxation time (1/2RT) was defined as the time

between the PTF and the point at which the peak force

was reduced to half its size. To determine the degree of

fusion in the tetanic forces at 10 and 20 Hz, an epoch of

200 ms was taken at peak force and the coefficient

of variation (CV) was calculated by dividing the

standard deviation by the mean force of this epoch.

The CV of the submaximal voluntary forces were

calculated in a similar manner by using an epoch of 1 s

after 20 s. High CV represent poorer force control.

For the temperature data, a two-sample t-test was

used to compare the difference between pre- and post-

test values across the experimental and control group.

The subjects were assigned to the experimental and

control group a priori, which resulted in a difference in

the pre-test temperature. Therefore, the different scores

of the pre- and post-tests were used for analysis.

Additional analysis was performed on the acclimationdata. A one-way analysis of variance (anova) with

repeated measurements (time, four levels) was per-

formed on day 1, 6, 11 and 15. When a main effect was

detected, Bonferroni post-hoc tests were applied to

determine significant differences between the days. For

the neuromuscular data, a two-way anova (group

time) with repeated measures on one factor (time,

consisting of four levels: pre-cold, pre-warm, post-cold

and post-warm) was used to test for differences in

responses between groups and across time. For all

statistics, type 1 error was protected at the 5% level. All

data are reported as mean SD.

Results

Thermoregulatory data

For the EXP group, minimum finger temperature

decreased from 10.6 1.2 to 9.3 0.8 C after

3 weeks of cold acclimation. The difference between

the pre- and post-test was significantly different

(P < 0.01) from that of the control group (9.2

0.5 C before, 9.3 0.8 C after). The time-course

of the minimum temperature response is shown in

Figure 1. Time-course analysis showed that the mod-elled minimum finger temperature was completely

adapted after a single exposure. Analysis of variance

confirmed a significant time effect and post-hoc com-

parisons revealed that the cold acclimation response

occurred between days 1 and 6 (P 0.02).

Figure 1 Minimum index finger temperature [mean (SD)]

during cold water immersion of the EXP group (open circles)

over the course of 15 days, and pre and post values of the CON

group (filled circles). *Significantly different from day 1:

P < 0.05 (repeated measures on day 1, 6, 11 and 15).


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The mean finger temperature over the 30-min immer-

sion significantly dropped from 14.2 1.9 C before to

11.7 1.4 C after cold acclimation (P < 0.05), com-

pared with that of the control group (12.1 1.5 C

before, 11.5 1.3 C after). The time-course analysis

shown in Figure 2 reveals that after a single exposure,

67% of the acclimation in mean finger temperature had

occurred, and 99% of cold acclimation was reached byday 5. Analysis of variance confirmed a significant time

effect and post-hoc comparisons revealed that the cold

acclimation response occurred between days 1 and 6

(P < 0.01).

The onset time for CIVD increased from 446 172 s

before to 736 385 s after acclimation in the EXP

group and the difference between pre- and post-test was

significantly different (P < 0.05) from that of the CON

group (534 263 s before, 573 247 s after). Time-

course analysis shown in Figure 3 reveals that 92% of

the acclimation had occurred by day 5.

The amplitude of CIVD decreased from 5.3 3.2 C

before to 2.5 2.1 C after acclimation, which was

significantly different (P < 0.05) from the control group

(3.0 3.0 C before, 3.0 2.9 C after). The time-

course of the amplitude change is displayed in Figure 4.

In addition, the skin temperature of the index finger

after 10 min of cold water immersion was significantly

decreased from 12.3 2.2 C before to 10.6 2.0 C

after acclimation in the EXP group (P < 0.04) com-

pared with the control group (10.5 1.3 before,

11.6

2.2 C after). An overview of all the tempera-ture data is shown in Table 1.

Comparison of the temperature data of EXP and

CON group combined for the pre-acclimation test

revealed no significant difference between the male

subjects and females subjects for the index finger

temperature. Only the onset time of the CIVD was

significantly later in the group of male subjects

(P < 0.04).

After 30 min of cold water immersion, the hand was

quickly placed in the hand myograph and strapped in.

As soon as the hand was out of the water, the hand

warmed up. Although finger and FDI temperature

increased on average 6.2 2.6 and 6.0 2.4 C,

respectively, both Tif and Tfdi were significantly colder

during the cold condition compared with the warm

condition (P < 0.01). During the neuromuscular testing,

the Tfdi in the warm condition was 32.6 2.8 C

before and 30.7 2.4 C after cold acclimation. In the

cold condition, the Tfdi was 18.8 2.8 C before and

17.6 3.4 C after cold acclimation. The Tif was

30.4 3.9 C before and 27.0 3.7 C after cold

acclimation in the warm condition and 19.2 3.2

and 15.7 2.7 C after cold acclimation in the cold

condition. These differences were not significantly

different between groups.

Neuromuscular data

Maximal voluntary contraction was not significantly

different between groups after acclimation and averaged

54.5 21.8 n before and 59.5 22.0 n after cold for

Figure 2 Average index finger temperature over 30 min cold

water immersion [mean (SD)] of the EXP group (open circles)

over the course of 15 days and pre and post values of the CON

group (filled circles). *Significantly different from day 1:

P < 0.05 (repeated measures on day 1, 6, 11 and 15).

Figure 3 Onset time for the CIVD [mean (SD)] of the EXP

group (open circles) over the course of 15 days of cold accli-

mation and the pre and post values of the CON group (filled

circles). *Significantly different from day 1: P < 0.05.

Figure 4 Amplitude of the CIVD [mean (SD)] of the EXP

group (filled circles) over the course of 15 days, and the

pre and post values of the CON group (filled circles).

*Significantly different from day 1: P < 0.05.



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the groups combined. An overview of the neuromuscu-

lar data is shown in Table 2. There was a significant

difference between the muscle characteristics in the

warm and cold conditions, but there were no significant

changes in neuromuscular function of the FDI as a

result of cold acclimation. The degree of fusion was

higher (as observed by the smaller CV) in the voluntary

force control trials than in the evoked tetanic contrac-

tions, but there was no effect of either thermal conditionor cold acclimation. There was no significant effect of

cold acclimation on any neuromuscular parameters

measured in this study.

Discussion

The unique aspect of this study was the time-course

data of local acclimation of the hand, coupled with the

prolonged immersion time and the neuromuscular tests

performed before and after local cold acclimation. We

found that immersing one hand repeatedly in cold water

resulted in an enhanced vasoconstriction and a blunted

CIVD response, with the majority of the acclimation

occurring within the first week of cold water immersion.

Most researchers who have reported a decrease in skin

temperature after cold acclimatization tested their

subjects during whole body cooling in air (Young et al.

1986, Savourey et al. 1996, OBrien et al. 2000) or

their subjects underwent a whole body cold exposure

during the acclimatization period (Paik et al. 1972,

Livingstone 1976, Bridgman 1991, Savourey et al.

1992). However, a lower core body temperature can

directly impair the CIVD response (Daanen et al. 1997).

In this study, the subjects were only subjected to local

hand cooling while sitting in a thermoneutral room

(ambient temperature 23.0 1.6 C). This is similar to

the exposures used in other studies using imposed

repeated local cooling of the periphery, but other

studies using this exposure regime on their subjects

found higher skin temperatures of the hand in the

adapted group (Adams & Smith 1962, Eagan 1963).The results in this study were therefore unexpected.

An enhanced vasoconstriction resulting in colder

hands may be expected to impair neuromuscular

function, as temperature is an important modulator of

the contractile function of skeletal muscle (Davies &

Young 1983, De Ruiter et al. 1999). In the present

study, a significant impairment in contractile character-

istics between the warm and cold condition was

observed and no beneficial adaptations in neuromuscu-

lar function were found after cold acclimation. Previous

research by Geurts et al. (2004) reported that a

decrease in Tfdi of 10.2 C resulted in an increase in

TTP and 1/2RT of 58 and 63 ms, respectively.

A larger change in temperature response in the hand

and finger may be needed to see significant changes in

neuromuscular function after acclimation. During cold

water immersion, the finger temperature was signifi-

cantly lower after cold acclimation. The skin tempera-

ture above the FDI was, however, less affected and this

decrease was not significantly different between groups.

The skin temperature directly above the FDI is closely

related to the muscle temperature of the FDI

Table 1 Temperature responses before

and after cold acclimation and the dif-

ference score for the experimental and

control group

Group Pre Post

Difference

(pre ) post)

Tif at entry (C) Exp 31.9 3.0 27.4 3.4 4.5 4.0

Con 28.3 3.2 27.3 3.0 0.9 4.5

Tif min (C) Exp 10.6 1.2 9.3 0.8 1.3 1.0

Con 9.2 0.5 9.3 0.8 )0.1 0.6*

Tif mean (C) Exp 14.2 1.9 11.7 1.4 2.5 1.8

Con 12.1 1.5 11.5 1.3 0.6 1.7*

Tif max (C) Exp 16.5 3.9 12.5 3.2 4.0 5.0

Con 13.4 2.9 12.8 2.4 0.6 2.2*

Onset time (s) Exp 446.4 171.7 736 384.9 )290 325

Con 533.7 263.2 573.7 247 )40 129*

Amplitude (C) Exp 5.3 3.2 2.5 2.1 2.8 3.6

Con 3.0 3.0 3.0 2.9 0.0 1.2*

Tif (after 10 min)

(C)

Exp 12.3 2.2 10.6 2.0 1.7 1.9

Con 10.5 1.2 11.6 2.2 )1.1 2.6*

Tif, skin temperature of index finger; Entry, finger temperature before water immer-

sion; Min, minimum temperature during 30-min immersion; Mean, average tem-

perature during 30-min immersion; Max, maximum temperature after the minimum

temperature; Onset time, onset time of CIVD. Amplitude isT

if max )

Tif min.

*Significant difference between experimental and control group on difference score

(P < 0.05).



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(Ranatunga et al. 1987). To our knowledge it is not

known if this relationship would change with repeated

cold water immersion of the hand. It is possible that

cold acclimation results in a more severe cutaneousvasoconstriction (Paik et al. 1972), causing the skin to

act more as an insulating layer over the FDI muscle. As

the skin above the FDI muscle is thin, we think this

effect, if present, will be negligible, and that the skin

temperature can be used as an indication of the muscle

temperature. Cold acclimation did not affect FDI

temperature and therefore it is not surprising that cold

acclimation did not affect neuromuscular function. This

also suggests that focusing on changes in finger thermal

responses may not be appropriate when investigating

manual dexterity or neuromuscular function of the

hand as a whole during cold exposure.

The longer cold exposure duration in the present

study than in typical studies on hand immersion, in

combination with whole-hand vs. single finger immer-

sion, may have had an effect on the study outcome. The

majority of studies on peripheral cold adaptation

immersed hands for a relatively brief period of

515 min (LeBlanc et al. 1960, Adams & Smith 1962,

Nelms & Soper 1962, Eagan 1963, Savourey et al.

1996), in contrast to the 30 min exposure utilized in the

present study. Upon closer examination of the values of

Tif min after 10 min and Tif min, it was found that there

was a significant decrease in skin temperature in the

final 20 min of exposure. It is possible that the extended

duration of cold exposure in the present protocolprecipitated the insulative adaptation that was

observed, and in the other studies the duration of

exposure was insufficient to fully maximize the vaso-

constrictive response.

Contact cooling can be expected to play a role in the

cooling of thehand when working in a cold environment.

Depending on the materials handled and contact force,

contact cooling is a more rapid and local cooling than

whole hand cooling (Jay & Havenith 2004). It may be

expected that in contact cooling only the local skin will

be cooled (Chen et al. 1996) and that the muscles, mostly

located on the dorsum of the hand will be less affected.

The local skin temperature in this case will determine the

contact time, and thus cooling, in such situations.

Another interesting finding of the present study was

that the time-course analysis showed that the modelled

minimal finger temperature during the 30 min immersion

decreased after only one single exposure. Cold acclima-

tion outside the laboratory was not expected as the

testing was conducted in September and October with

outside temperatures of 1018 C. Vasoconstriction

can be influenced by mental stress (Halperin et al.

Table 2 An overview of the neuromus-

cular data (mean SD) from the

warm (31.6 2.7 C) and cold test

(18.2 3.1 C) for the experimental

and control group

Group

Warm Cold

Pre Post Pre Post

MVC (n) Exp 55.1 20.5 61.2 16.4

Con 54.3 23.5 58.3 27.7

PTF (n) Exp 2.8 1.3 2.5 0.8 2.0 1.2 1.2 1.2

Con 2.3 1.2 1.8 0.8 1.6 1.5 0.8 0.3

TTP (ms) Exp 142 19 145 14 231 27 268 48Con 136 12 138 17 223 31 269 103

1/2RT (ms) Exp 78 18 72 20 173 46 174 55

Con 69 13 63 15 179 56 162 5.2

Fmax 10 Hz (n) Exp 10.9 5.3 11.7 10.0 20.5 7.6 15.5 8.6

Con 9.6 4.8 8.6 7.4 15.9 11.5 11.1 4.6

CV 10 Hz (%) Exp 2.6 1.0 2.5 1.0 1.4 0.6 1.6 0.7

Con 1.9 1.3 4.6 3.5 2.0 1.0 2.3 0.9

Fmax 20 Hz (n) Exp 32.3 9.4 30.8 10.8 33.7 10.1 24.8 7.2

Con 30.0 14.9 27.1 13.7 27.7 16.0 21.1 6.2

CV 20 Hz (%) Exp 1.6 0.9 1.2 0.6 1.1 0.7 1.0 0.6

Con 1.0 0.5 1.1 0.6 1.0 0.7 1.2 0.7

CV25%MVC

(10)2 %)

Exp 1.7 1.0 1.8 1.3 1.8 1.8 1.5 0.5

Con 2.2 0.9 3.5 2.4 2.6 2.5 2.2 1.5

CV50%MVC

(10)2 %)

Exp 1.8 1.2 4.2 7.7 2.7 1.7 2.2 1.1

Con 2.7 2.0 3.5 3.2 2.8 1.6 2.2 1.2

MVC, maximal voluntary contraction; PFT, peak twitch force; TTP, time to

peak force; 1/2RT, half relaxation time; Fmax 10 Hz, maximum force at 10 Hz

stimulating frequency; CV 10 Hz, SD/mean of 200 ms epoch of force response

at 10 Hz; Fmax 20 Hz, maximum force at 20 Hz stimulating frequency; CV 20 Hz,

SD/mean of 200 ms epoch of force response at 20 Hz.



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1983) as well as physical stress (Adams & Smith 1962).

Noradrenaline release is increased during psychological

stress and enhances vasoconstriction. It is possible that

the cold stress experienced in the first day caused an

additional mental stress on the second day resulting in an

enhanced vasoconstriction. Anticipation of the cold

water may have caused the small change in temperature

response observed in the control group, resulting in asmall decrease in mean Tif and amplitude as well as a

slight delay in onset of the CIVD. These changes were

substantially smaller than those observed in the experi-

mental group, and we would not expect the mental stress

of cold exposure to endure with the repeated cold

immersions experienced in the experimental group.

There was an uneven distribution of males and

females in the experimental and control group and this

may have caused differences between the two groups in

the pre-acclimation tests. Bartelink et al. (1993) found

lower index finger temperatures for females compared

with males and an enhanced vascular reactivity in

women, resulting in enhanced vasoconstriction and thus

lower temperatures. Female core temperature fluctuates

within the menstrual cycle with the highest core

temperatures during the luteal phase, with a difference

up to 0.59 C (Hessemer & Bru ck 1985) when tested at

03:00 h at the middle of the luteal phase. Jay &

Havenith (2004)2 found that hand/finger size had a

greater predictive power than sex. However, we did not

find a significant difference in index finger temperatures

in the initial test between the male and female subjects

in this study. Only the onset time of the CIVD was

significantly later in males compared with the females.

It has been previously reported that thermal sensationis rapidly habituated with cold exposure (Leppa luoto

et al. 2001). In addition, pain sensation is less in cold-

adapted individuals (Budd et al. 1993). This was also

reported in the older literature on Inuits (Brown & Page

1952), fishers (LeBlanc et al. 1960) and fish filleters

(Nelms & Soper 1962). Unfortunately, thermal sensa-

tion was not measured in this study; however, subjective

complaints indicated that the subjects did experience

less pain and cold at the end of the acclimation period.

Sawada et al. (2000) concluded that subjective judge-

ments may not be reliable indicators for monitoring the

risk of progressive tissue cooling and frostbite forma-

tion. If the fingers are getting colder after cold acclima-

tion but the subjects experience less pain or feel less

cold, cold acclimation could potentially put someone at

greater risk of cold injury.

In summary, unlike the majority of prior research,

repeated and prolonged cold water immersion of the

hand with the present protocol resulted in an attenuated

CIVD response of the fingers but no adaptive responses

in FDI temperature or neuromuscular function. The

rapid reduction in CIVD, after only a single cold

exposure of the hands, could potentiate the risk of cold

injury during subsequent cold exposure.

We would like to thank the subjects for their enthusiastic

participation. The study was supported by a Discovery Grant

(Cheung and Sleivert) from the Natural Sciences and Engin-

eering Research Council of Canada (NSERC). C. Geurts was

supported by a NSERC PGS-B Scholarship.

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