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J. Pysical Fintness Japan (1979) 28, 239•`248

AGE DIFFERENCES IN SWEATING DURING MUSCULAR EXERCISE

TSUTOMU ARAKI*, YOsHIAKI TODA*, KENJI MATSUSHITA**

AND AKIRA TSUJINO***

Abstract

To study the age difference in sweating during muscular exercise, two series of

experiments were conducted under constant climatic conditions (29 •} 1•Ž DB, 60 •}

5 % RH, 0.45•}0.05 m/sec air flow). In series A, 7 to 20 years old male subjects

undertook 5-minute running or pedalling of a bicycle ergometer in various seasons. In

this series of experiments, pectoral sweat volume, sweat chloride concentration, rectal

and mean skin temperatures were in general determined every 5 minutes and, when

necessary, the total body sweat volume was calculated from the body weight loss. In

series B, the age difference in the sweating in relation to physical training was studied.

Subjects, 3 to 20 years old received experimental physical training of 5-minute or 500m-

running. Before and after the training, a work load of 3- or 5-minute outdoor running

was assigned to them. Furthermore, before and after the training, 10 and 11 years old

subjects were given a fixed mechanical work rate on a bicycle ergometer. In these

experiments, most of the parameters described above were measured. In series A, age

differences in sweating during exercise were noticed to be dependent on the intensity

of work load between pre- and post-adolescents. When the work load was heavy

enough to cause a rapid increase in rectal temperature, the sweat volume became

significantly less, the mean skin temperature was far higher, and the sweat chloride

concentration was remarkably smaller in the pre-adolescent subjects than in the post-

adolescent ones. In series B, an age difference in the effect of physical training was

also found on sweating during exercise. The effect of physical training on sweating in

the pre-adolescent individuals was generally less significant than in adults and sometimes

showed a different pattern from that of adults. From these results, it can be concluded

that sweating in the pre-adolescents is less adaptive, particularly to continuous severe

exercise and that physical training is less effective in them than in the post-adolescents.

(Received for publication March. 30, 1979)

Introduction

In our previous studies1,2)3) the important role of sweating for body temperature regu-

lation during exercise, especially to a prolong-ed one, was elucidated. However, this fact

was elaborated for adults and not for children

who were in the developing stage. It can

probably be assumed that even in children, sweating is very important as one of the factors for continuation of exercise. A fun-

damental approach to test this assumption is

to precisely determine sweating in children during exercise. There are many studies5)6)7)8)13) concerned with the sweating in children

exposed to a heat stress. It has been studied from clinical viewpoints also11)12). In com-

parison with adults, children showed the fol-lowing characteristics in sweating : (1) the sweating reflex is more rapid, (2) the sweat volume is larger, and (3) the sweat chloride concentration is lower. But, there is practi-cally no study available on the sweating of children during exercise. The sweating of post-adolescent people dur-ing exercise has been found to be improved by physical training1)2)3), but it is not known if children also respond similarly. This prob-lem also seems very important for the pre-scription of physical exercises for children.

* Department of Hygiene, Kobe University School of Medicine** Department of Physical Education, Osaka University of Prefecture

*** Department of Physical Education , Osaka Kyoiku University

240 Araki, Toda, Matsushita, Tsujino

The present study was designed to investi-

gate two problems (1) age difference in

sweating during exercise and (2) age differ-

ence on sweating response due to physical

training. Some of the results obtained will

be described in this paper.

Methods

For the present study, two series of ex-

periments were designed. The first (series

A) was to investigate the age differences in

sweating, and the second (series B) was to

study the age differences in sweating in rela-

tion to physical training. The subjects

employed in the present experiments were

chosen from healthy males and females who

grew well corresponding to their age and did

not regularly do any physical exercise except

those involved in physical education. The

subjects below 12 years did not manifest

either pubic hair or cracking of the voice,

whereas those over 13 years already did so.

Though all the experiments were not always

performed in the same season, they were

conducted in an almost constant climatic

conditions maintained at 29•‹ •}1•Ž DB, 60•}5

% RH and 0.45•}0.05m/sec of air flow. Be-

fore the experiment, all subjects were made

to rest on a chair for more than 40 minutes

under the aforementioned environmental con-

ditions. They also took neither food nor water

2 hours before the start and during the ex-

periment. Statistical analysis of the data was

done by the t-test. Other methods employed

for different experiments are outlined in their

respective sections.

A. Age differences in sweating

In this series, three experiments were con-

ducted.

Experiment (A) As shown in Table 1 (A),

in this experiment 4 subjects of each age

varying progressively from 7 to 16 years were

selected. In July and August, each subject

was made to work for 15-35 minutes at three

load levels on a bicycle ergometer designed

by us. The intensity of exercise to each

subject was determined depending on the

average pulse rate recorded every 5 minutes

during exercise with a pulse meter. That is

light, moderate and heavy loads mentioned in

this experiment corresponded to average pulse

rate of 110-120, 130-150 and 160-170beats/min

Table 1. Tabulated physical description of the subjects

respectively. Therefore, even at a same in-tensity of work load, resistance values on the ergometer differed depending on the indi-viduals and their ages. Irrespective of the intensity of load, the pedalling speed of the ergometer was set at 110 pedallings/min(timed with a metronome). During exercise, every 5 minutes capsule sweat samples were col-lected with a filter paper (12.6cm2) attached on the breast over the M. pectoralis major. The quantity of sweat produced was deter-

241Age Differences in Sweating During Muscular Exercise

mined by weighing the filter paper. The chloride content of this sweat was analysed

quantitatively by the method of Volhard-Harvey3). The total body sweat volume was estimated through body weight loss deter-mined by a precise balance with an accuracy of 10g.

To further confirm the age difference on sweating in many subjects, following two ex-

periments were performed in the aforemen-tioned climatic conditions.

Experiment (B) In November or December, each subject (Table 1 (B)) pedalled the er-

gometer at a 1.5kg load at the above-described speed for 40 minutes (7-15 years old) or 60 minutes (20 years old). In this experiment, together with the measurement of pectoral sweat rate and sweat CI concentration, the rectal temperature was recorded at a depth of 1Ocm every 5 minutes during exercise with a thermistor thermometer. Experiment (C) Seven subjects of each age, 9 and 20 years were selected (Table 1 (C)) for this experiment. Each subject received two levels of work load. The light load was small enough to induce an initial rise in the rectal temperature followed by the steady state, and the heavy load was strong enough to produce an almost linear increase in the rectal temperature within the experimental

period. The prerequisite condition for this experiment was that at both levels of work load the rectal temperature of all subjects behave similarly. In November, each subject was made to pedal the bicycle ergometer at a given load for 40 minutes (9 years old) or 60 minutes (20 years old) under the previously described conditions. In this experiment, in addition to pectoral and total body sweat rates, skin temperatures (forehead, forearm, breast, abdomen, thigh and lower leg) were measured every 5 minutes during the exercise with a thermistor thermometer. Mean skin temper-ature was calculated proportionately by meas-uring the six skin areas.

B. Age differences in the effect of physical training

In this series, to examine the age difference in sweating in relation to physical training, two experiments were performed. A heavy work load was applied for the experiment (A) and a relatively light load for the experiment

(B), to determine the effect of physical train-ing.

Experiment (A) As shown in Table 1 (D), the subjects consisted of the pre-adolescent children, 3 to 11 years old and post-adolescent adults 20 years old as controls. The subjects aged 9 years or over were given an experi-mental training of 5-minute outdoor running once a day, 3 or 4 times a week. They were asked to run without stopping as fast as they could. This training was continued for 5 to 7 consecutive weeks in April and May. The other subjects were requested to run 500m in the same way once a day, 2 to 5 times a week. This was continued for 8 to 16 weeks during November to February. Before and after the training, the following standard work loads were applied to determine the sweating : the subjects, 9 years or over per-formed a 5-minute outdoor running, whereas other subjects did a 3-minute indoor running simultaneous with a 10-and 2-minute walking respectively before and after the running, the speed of walking being maintained at 40 m/min. During exercise, the pectoral sweat volume was measured for 5 minutes in the subjects aged 9 years or over, and for 15 minutes in other subjects, with the aforemen-tioned methods. The C1 concentration of this sweat was also measured and the distances of the 5-or 3-minute running were recorded.

Experiment (B) All the subjects were pre-adolescents (three boys and two girls respec-tively 10 and 11 years old). Their physical data are given in Table 1 (E). The experi-mental training of 5-minute running was also

given to them once a day, 5 times a week for 7 consecutive weeks in January and Feb-ruary. Before and after the training, the following exercise was assigned to them ; each subject pedalled a handmade bicycle ergometer for 60 minutes at a lkg load at the above-described speed. This ergometer was different from the apparatus used in the series A. From 10 minutes before to the end of load application, the following items were measured every 5 minutes with the methods described above : the dorsal sweat volume, sweat Cl concentration, pulse rate, and rectal and mean skin temperatures. The total body sweat volume was also taken. In addition, the expired gas were sampled in a Douglas


Fig. 1 Mean and Standard deviation of pectoral

sweat volume at three levels of work load.

bag for 10 minutes just before the exercise and for 3 minutes at every 20 minutes in the exercise. They were analysed with a Roken-type gas analyser.

Fig. 3 Mean and standard deviation of the total

body sweat volume at three levels of work

load.

Results

A. Age differences in sweatingExperiment (A)In Figs. 1, 2, and 3, the average values of

the pectoral sweat volume, the sweat Cl concentration and the total body sweat vol-ume in 7-8, 9-10, 11-12, 13-14, and 15-16

years old subjects are shown at three levels of work load. In general, the pectoral sweat volume was proportional to the intensity of work load. This relationship was usually more apparent in older subjects than in

younger ones. In other words, when the work load was raised from a moderate to a

Fig. 2 Mean and standard deviation of the sweat chloride concentration at

three levels of work load.


Fig. 4 Pectoral sweat volume and the increase in the rectal temperature at

work from the resting value.

heavy level, subjects below 10 years old did not give an explicit increase in the sweat volume as compared with the other groups. At the light level of work load no age difference was observed in the total body sweat volume, while at the heavy level the total body sweat volume was significantly

(P<0.05) larger in subjects above 13 than in those below 12 years old. This fact cle-arly suggests that the age difference in sweat volume is found at above a certain level of work load. The sweat Cl concent-ration seemed to rise with the intensity of work load. This tendency was generaly more apparent in subjects above 13 years old. Therefore, the age difference became sig-nificant (P<0.05) when the work load in-creased to the heavy level.

Experiment (B)The amount of mechanical work in this

experiment was the same in all the subjects. The 7 years old subjects hardly completed the exercise when pulse rate was found to

be in a range of 180-210beats/min. Consid-ered from the results of Robinson10) and Katsuda et al4)., this value seemed to be a submaximum for children. Fig. 4 presents the individual values of the pectoral sweat volume and the increase from the resting value in the rectal temperature at work. In 7 and 9 years old individuals, the rectal temp-erature rose generally in an almost linear manner during exercise. The temperature remained constant after an initial rise in 15 and 20 years old individuals. The increase in rectal temperature exhibited a remarkable age difference (P<0.005), whereas there was no significant age difference in the

pectoral sweat volume, especially at the initial stage of exercise. These results supported the above-described fact that the total body sweat volume was smaller in subjects below 12 than in ones above 13 years old when the work load was of a heavy level. Though data are not graphically presented, the sweat C1 concentration was clearly lower at ages


Fig. 5 Pectoral sweat volume, rectal and mean skin temperature of the individual chosen from 9 and 20 years old subjects are shown in the left side of the figure . The right side of the figure represents mean and standard deviation of total body sweat volume of 9 and 20 years old subjects .

below 11 than at ages above 13 years .Experiment (C)Each of the 9 and 20 years old subject

pedalled the bicycle ergometer at two levels of work load. In Fig. 5, results of one subjecs each from 9 and 20 years old individuals are shown as an example , along with the average values of the total body sweat volume . At light level of work load which induced a small rise in rectal temperature , no significant age differences were found in the pectoral sweat volume at the initial stage of exercise , mean skin temperature, and the total body sweat volume. In contrast , at a heavy level which produced an almost linear increase in body temperature, the pectoral sweat volume of 20

years old individuals generally showed a rapid rise from an initial stage of load application , whereas that of 9 years old individuals increas-ed very slowly. Particularly the latent time of sweating was longer in the 9 years old subjects than in the 20 years old ones . Under heavy work load , the total sweat volume was significantly (P<0.005) more in older subjects than in younger ones . Another important fact found was in the mean skin

temperature in this experiment. At the light load, the mean skin temperature did not manifest any significant difference between the two ages. But, at the heavy level, as is described above, the 9 years old individuals exhibited a less increase in the sweat vol-ume, while the mean skin temperature rose more rapidly in the 9 years old subjects than in the 20 years old ones.

B. Age differences in the effect of physicaltraining

Experiment (A)Fig. 6 shows the mean values of the

pectoral sweat volume, the sweat C1 concent-ration and the running distance of subjects of different ages before and after the train-ing. For this experiment, 3 and 4 years old subjects were grouped together. The running distance of each individuals tended to be increased by physical training. That is , the physical training employed in this experiment can reasonably be concluded to improve the

physical performance of the subjects. The sweat volume in subjects of 11 years old and under was less affected by the training than that in the 20 years old subjects. The indi-


Fig. 6 The pectoral sweat volume, the sweat

chloride concentration and the running

distance before and after training.

viduals of 11 years old and under were less influenced by the training also in their sweat Cl concentration. It seems significant that the sweat Cl concentration in the 20 years old individuals was lowered by the training to the similar level to that of the younger

people. Experiment (B)

Also in this experiment, the mean distance of the 5-minute running was increased about 200m at the end of the training period. The values of the pulse rate and the energy expenditure during exercise on the bicycle ergometer became smaller in all the subjects after the training ; energy expenditure was diminished by the training from 98-140 to 77-109 kcal/m2.hr, and the pulse rate at the end of the exercise fell from 120-168 to 109-150 beats/min. There were, however, individ-ual variations in these decreases. These results may indicate that the physical train-ing of 5-minute running was useful for the improvement of physical performance.

In this experiment, the same amount of mechanical work was applied before and after the training. Fig. 7 shows the time course of dorsal sweat volume and the total body sweat volume before and after the training. The latent time of sweating seemed to be longer after the training than before. The total body sweat volume as well as the level of dorsal sweat volume during the

Fig. 7 The time course of dorsal sweat volume during exercise and the total body sweat

volume before and after training.


Fig. 8 The increases in the rectal and the mean skin teperature during

exercise before and after training from the resting values .

exercise tended to be lowered by the training , but these decreases were not as clear in

youngsters as it was in adults2)3). In other words, whereas the decrease in the energy expenditure due to training was similar in adults to those in the pre-adolescent subjects , the decrease in the total body sweat volume was generally more apparent in adults than in the pre-adolescents. Though data are not

graphically presented, the sweat Cl concent-ration barely exhibited any influence of

physical training. The rectal and mean skin temperatures during the exercise are shown in Fig. 8 as a difference of the resting values. The increase in the rectal tempera-ture generally became less by the training , whereas the mean skin temperature was barely affected by the training.

Discussion

A. Age differences in sweating The age difference in sweating during

exercise was significant between the younger and older subjects when separated at ages of

12-13 years. In other words, the age differ-ence was found between the pre- and the

post-adolescent ages. It also depended on the work load. In the younger groups, the follow-ing facts were observed : (1) At a heavy work load that causes a rapid rise in the rectal temperature, the sweat volume was significantly less in them than in the older subjects. (2) The sweat Cl concentration was generally smaller in the younger than in the older subjects. As the important role of sweating is ascribed to body temperature regulation by evaporative cooling, sweating in pre-adolescents seems to serve to a less extent for this purpose than in post-adoles-cents for the adaptation to exercise. As the difference in the sweating rate was

found between the pre- and the post-adoles-cence, it can be assumed that the age difference is dependent on sex hormones. For example, Tanaka13) indicated that male hor-mones promote sweating, whereas female sex hormone suppresses it. In addition to sex hormones, the behavior of the sweat volume


in the pre-adolescents observed in present experiment would suggest that the secretory capacity of the sweat gland and its sensi-tivity to the central nervous systems are inferior to those in the post-adolescent ones, and that the inter-play between the sweat

gland and the central nervous systems is not as efficient as in the post-adolescents. Though other influencing factors have to be consid-ered, the mechanism of sweating in the

pre-adolescents anyway can be concluded to be less adaptive for body temperature regu-lation than that of the post-adolescents. Wagner et al14), reported that, when pre- and

post-adolescent boys were forced to work at a high environmental temperature, the former were inferior to the latter in the secretory capacity and sensitivity of the sweat gland and that the mechanism of sweating proved to be deficient in the former. It is considered that the heavier the work load is, the greater the force is for adaptation on the less effiii-cient mechanism of sweating. This disad-vantage in the pre-adolescents is thought to be compensated by a higher increase in the mean skin temperature than that in the post-adolescent ones. The sweat Cl concentration depends on the net efficiency of filtration and reabsorption of chlorine in the sweat gland. In general, their efficiency is affected by the sweat volume. That is, as far as the same subject is con-cerned, generally the more sweat volume is, the higher is the sweat Cl concentration1) 3) Tanaka13) also reported that the amount of sweat secreted from a single sweat gland was less in younger people than in adults. Though this fact might support less sweat Cl concentration in the pre-adolescents, there might be other factors in the pre-adolescents that can storngly inhibit the salt loss.

B. Age differences in the effect of physical training

Age differences in sweating in relation to

physical training were also indicated in our experiments. In the pre-adolescents, sweating was normally less affected by physical train-ing : (1) When a heavy work load that was

physiologically close to a maximum was applied before and after training, the effect

of the training on the sweat volume and the sweat Cl concentration was not as high as

those of adults. (2) When the same mecha-nical work rate was applied before and after training, the;,effect of training on they sweat-ing did not show a similar pattern in the

pre- and post-adolescents. The less efficient sweating mechanism seems not to respond to physical training in the pre-adolescents. This assumption is supported by the fact that the mean skin temperature which plays an im-

portant role along with sweating for body temperature regulation was barely affected by physical training in the pre-adolescents, though it was lowered in adults2). These facts are very interesting for in adults, where a rapid rise of body temperature was offset by a remarkable increase in the sweat volume, in pre-adolescent subjects it was offset by a remarkable elevation of the skin temperature.

The sweat Cl concentration before and after training in the pre-adolescent subjects was very low and was close to the level of adults with low salt intake9). That is, the sweat Cl concentration in the pre-adolescents seems to be around the minimal level in man. For this reason, physical training will hardly have any influence on the sweat Cl concentration in the pre-adolescent subjects. There is a strong probability that in the pre-adolescents, irrespective of physical training, certain mechanisms work to prevent the loss of salt with great efficiency.

The sweating in the pre-adolescents can therefore be concluded to be less adaptive,

particulary continuous severe exercise and to respond less to physical training than in the post-adolescents.

*The research was supported, in part, by the grant for scientific researches from Ministry of Education.

AcknowledgementsThe authors express their deep thanks to

masters, chiefs, teachers, parents and subjects of primary schools and kindergartens which were involved in this study.

References

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3) Araki, T., Toda, Y, and Tsujino , A. (1974) Effect of physical training on the chloride

concentration in sweat. Jap. J. Physical Fitness and Sports Med. , 23, 12-24 (in Japanese)

4) Katsuda, S., Konno, M. and Konno, K.

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