A Ab bs st tr ra ac ct t The objective of our study was to analyse the exer- cise intensity during uphill walking and to find out if there were any differences in heart rate (HR) between boys and girls. For the purpose of the study, a group of seven boys and twelve girls who were not equally physically fit made three mountain walking trips at different pace (directed pace, paces on the aerobic thresholds of the boys in the best and poorest physical condition). The walking trips took place over three weeks, always on the same day of the week, starting at the same hour. HR of the chil- dren was measured with Polar Coach measuring devices every fifteen seconds. Before and after the exercise, no differences in HR were found between boys and girls. The results expressed in percent- ages of individual aerobic threshold show that walk- ing was too hard for some of the children in the group. If the activity continued, it could be damaging or even dangerous for their cardiovascular system. On those children in the group who walked under their aerobic threshold walking didn’t have any physiological impact. Consequently, we would rec- ommend that groups of children taken to mountains should be homogeneous. Key words: mountaineering, heart rate, aerobic threshold, children F Fa ac cu ul lt ty y o of f S Sp po or rt t, , U Un ni iv ve er rs si it ty y o of f L Lj ju ub bl lj ja an na a, , S Sl lo ov ve en ni ia a * Corresponding author: Faculty of Sport, University of Ljubljana, Gortanova 22, SI-1000 Ljubljana, Slovenia T el.: +386 (0)1 5207756, fax: +386 (0)1 5207750 E-mail: blaz.jereb@sp.uni-lj.si I Iz zv vl le eč če ek k Namen raziskave je bil ugotoviti, kakšna je inten- zivnost hoje posameznika med pohodom v gore, pri katerem je skupina sestavljena iz hodcev, ki so različno kondicijsko sposobni, in če obstajajo raz- like v frekvenci srca (FS) med dečki in deklicami. V študiji je sodelovalo sedem zdravih, kondicijsko različno sposobnih dečkov in dvanajst deklic, ki so opravili tri pohode v različnih tempih (voden tempo, v aerobnem pragu kondicijsko najslabšega in v aer- obnem pragu kondicijsko najboljšega dečka). Pohode so opravili v treh tednih, vselej na isti dan v tednu, s pričetkom ob isti uri. FS je bila spremljana z merilci Polar Coach na vsakih petnajst sekund. Pred in med aktivnostjo med dečki in deklicami ni opaziti razlik v FS. Rezultati odstotkov odstopanja od indi- vidualnega aerobnega praga kažejo na to, da je bila za nekatere hoja prenaporna. Če bi takšna aktivnost trajala dalj časa, bi lahko škodljivo ali celo nevarno vplivala na njihov srčno žilni sistem. Na tiste udeležence pohoda, ki so hodili pod svojim aerobn- im pragom, hoja ni imela fizioloških učinkov. Na pod- lagi rezultatov sklepamo, da je smiselno voditi v gore otroke v homogenih skupinah. Ključne besede: gorništvo, frekvenca srca, aerobni prag, otroci Faculty of Sport, University of Ljubljana, ISSN 1318-2269 Kinesiologia Slovenica, 9, 1, 25-34 (2003) 2 25 5 H HE EA AR RT T R RA AT TE E R RE ES SP PO ON NS SE ES S T TO O U UP PH HI IL LL L W WA AL LK KI IN NG G I IN N 9 9 - -T TO O 1 10 0 - - Y YR R - - O OL LD D B BO OY YS S A AN ND D G GI IR RL LS S F FR RE EK KV VE EN NC CA A S SR RC CA A 9 9 I IN N 1 10 0 - - L LE ET TN NI IH H D DE EČ ČK KO OV V I IN N D DE EK KL LI IC C P PR RI I H HO OJ JI I N NA AV VK KR RE EB BE ER R B Bl la až ž J Je er re eb b* * D Da am mi ir r K Ka ar rp pl lj ju uk k S St to oj ja an n B Bu ur rn ni ik k I IN NT TR RO OD DU UC CT TI IO ON N The starting points for determination of the strain that an organism is put under involve biome- chanical, physiological and biochemical methods. Changes in an organism which appear as a consequence of training are usually monitored by measurement of HR, oxygen consumption and the concentration of lactate in blood (Fox, Bowers, & Foss, 1981). On the basis of the men- tioned parameters as well as others, such as cardiac output (Collier, 1956), stroke volume and some cardiovascular variables (Sahn, Demaria, Kisslo, & Weyman, 1978), it is possible to ade- quately describe the state of an organism before, during and after exercise. The majority of the parameters, however, can be obtained only with laboratory tests, which are too expensive or too complicated to be used in general practice. A simple parameter for assessment of exer- cise intensity is heart rate (HR) (Edwards, 1994). With the accuracy of an ECG, HR can be easi- ly measured with HR measuring devices (Hinson, 1994), during an exercise. Due to its simple use, direct monitoring, quick data transfer to a computer and data processing, the use of these devices in physical education increases (Hinson, 1994). Some authors (e.g. Anderson, & Godfrey, 1971; Bar-Or, Shephard, & Allen, 1971; Godfrey, Davies, Wozniak, & Barnes, 1971; Katsuura, 1986), who monitored HR during submaximal rate of work in boys and girls, conclude that boys have lower HR than girls. In most of these studies the physical characteristics of boys and girls were not significantly different; hence, the reason of lower HR in boys is most likely unrelated to body size. According to literature, these differences can be due to larger heart vol- ume in boys, which has been reported (Shephard at al., 1969; Wirth at al., 1978). Turley and Wilmore (1997) monitored the HR of 7- to 9-year-old boys and girls during four submaximal tests. There weren’t any differences in maximal oxygen consumption and physical character- istics between boys and girls, except for a significantly larger left ventricular mass in boys ver- sus girls (78.8 vs. 66.0 g). The trend was for HR to be lower in boys than in girls, but these differ- ences were only significant at 4 miles.h -1 (142.9 vs. 155.5 beats/min, respectively). Mountaineering is a part of physical education at school, requiring from teachers a lot of knowl- edge and responsibility. It is difficult for them to choose the adequate walking pace, since pupils are not equally pre-trained. The chosen pace could be too brisk (damaging) for someone and too gentle (ineffective) for another. The aerobic threshold calculated according to the Karvonen formula (Karvonen, Kentala, & Mustala, 1957) can serve as a criterion for the intensity of an exer- cise. Walking with the intensity within the boundaries of aerobic threshold improves general physical fitness: burns out fat, strengthens cardiovascular and respiratory system, builds up muscles, and improves endurance (Edwards, 1994). The aerobic threshold, calculated accord- ing to the Karvonen formula, could be taken as a basis for setting the suitable walking pace. The objective of our study was to monitor HR during uphill walking at different pace levels. We wanted to establish the differences in the response of an organism between boys and girls dur- ing uphill walking and to determine suitable walking intensity for each child. M ME ET TH HO OD D P Pa ar rt ti ic ci ip pa an nt ts s The sample group consisted of seven boys (height: M = 137 .3 cm; SD = 3.6 cm, weight: M = 35 kg, SD = 4. 1 kg, age: M = 9.5 yrs, SD = 0.6 yrs) and twelve girls (height: M = 141.7 cm, SD = 4.4 cm; Heart rate responses to uphill walking Kinesiologia Slovenica, 9, 1, 25-34 (2003) 2 26 6 weight: M = 35.8 kg, SD = 6.2 kg; age: M = 9.7 yrs, SD = 0.4 yrs). They were all members of the third class of the Raka Primary School. They were not equally physically fit. They were all healthy, when the measurements were taken. P Pr ro oc ce ed du ur re e The pupils from our sample group and their parents were acquainted beforehand with the pro- cedure and the purpose of the investigation as well as with the measurement technology. The parents signed their written consent allowing their children to take part in the investigation and the use of obtained data. In a three-week period, three walking tours at different walking pace were organised. The walk- ing path lead uphill, reaching a height difference of 144 m on a distance of 864 m. Walking was continuous, without any periods of rest. The members of the sample group sat quietly for 5 min- utes before they started walking. They all started walking at the same time. During the first walk- ing trip, the sample group was walking at the pace set by their teacher. During the second walk- ing trip, they were walking within the aerobic threshold of the weakest member of the group and, during the third walking trip, within the aerobic threshold of the strongest member of the group. Aerobic threshold was calculated according to the Karvonen formula: 70% * ( HR max – HR m ) + HR m L Le eg ge en nd d: : HR max maximal HR HR m morning HR Maximal HR was measured during a 600-m run one week before the first walking tour. Morning HR was measured by the parents of the sample group members at home before getting up in the morning. The results achieved during a 600-m run were used as a measure for determining the weakest and the strongest member of the group. HR after a 600-m run and during the walk- ing tours was measured with Polar Coach frequency meters. The level of aerobic physical strain was calculated according to the following formula: (HR av / HR aer. thresh. ) * 100 L Le eg ge en nd d: : HR av average HR HR aer. thresh aerobic threshold Percentage of walking intensity was calculated according to the following formula: (HR av / HR max. ) * 100 Legend: HR av average HR HR max maximal HR Basic statistical parameters were calculated for each of the walking tours. The results were later relativised. An independent sample t-test was used to compare the results of boys and girls. Heart rate responses to uphill walking Kinesiologia Slovenica, 9, 1, 25-34 (2003) 2 27 7 R RE ES SU UL LT TS S Physical characteristics of the members of our sample group (morning HR, max HR of a 600-m run, individual aerobic threshold and 600-m run time) are presented in Table 1. There were no significant differences between physical characteristics of boys and girls except for their height. The girls were significantly (p < 0.05) higher (141.7 vs. 137 .3 cm). T Ta ab bl le e 1 1: : B Ba as si ic c p ph hy ys si ic ca al l, , f fu un nc ct ti io on na al l a an nd d m mo ot to or ri ic c c ch ha ar ra ac ct te er ri is st ti ic c o of f p pa ar rt ti ic ci ip pa an nt ts s L Le eg ge en nd d: : n numerus HR max -600 m maximal HR at a 600-m run (beats/min) HR m morning HR (beats/min) AER. THRESH aerobic threshold (beats/min) TIME-600 m time at a 600-m run (min) * p < 0.05 The first walking tour was carried out at a set pace (Table 2). The most distinctive were the results of the weakest boy in the sample group (the poorest result in a 600-m run). He exceeded his aerobic threshold by 18%. The results of two of the boys were within their aerobic thresh- olds, while the results of four of the boys were below their aerobic thresholds by 7 to 9%. While walking at the set pace, six girls exceeded their aerobic thresholds, two of them by more than 10%. Three girls found the pace acceptable; they were walking within the aerobic threshold. For three girls the pace was too gentle, they walked with the intensity accounting for only 93 to 94% of their aerobic thresholds. Heart rate responses to uphill walking Kinesiologia Slovenica, 9, 1, 25-34 (2003) 2 28 8 T Ta ab bl le e 2 2 : : P Pa ar ra am me et te er rs s o of f u up ph hi il ll l w wa al lk ki in ng g a at t d di ir re ec ct te ed d p pa ac ce e. . L Le eg ge en nd d: : I directed pace HR max maximal HR at the pace (beats/min) HR avr average HR at the pace (beats/min) %int percentage of maximal HR (%) %at percentage of individual aerobic threshold (%) time walking time (min) When the boys from the sample group were walking within the aerobic threshold of the weak- est boy (Table 3), they were walking at 5 to 15% under their aerobic thresholds. Walking pace that would suit the weakest boy in the group was not intense enough for all the others to affect their aerobic capacities. One girl exceeded her aerobic threshold (105%). Two girls walked within their aerobic thresholds, while the others were walking below their aerobic threshold (6 to 17%). Heart rate responses to uphill walking Kinesiologia Slovenica, 9, 1, 25-34 (2003) 2 29 9 T Ta ab bl le e 3 3: : P Pa ar ra am me et te er rs s o of f u up ph hi il ll l w wa al lk ki in ng g a at t a a p pa ac ce e o on n t th he e a ae er ro ob bi ic c t th hr re es sh ho ol ld d o of f t th he e w we ea ak ke es st t b bo oy y a at t t th he e 6 60 00 0- -m m r ru un n. . L Le eg ge en nd d: : II pace on the aerobic threshold of the weakest boy at a 600-m run HR max maximal HR at the pace (beats/min) HR avr average HR at the pace (beats/min) %int percentage of maximal HR (%) %at % of individual aerobic threshold (%) time walking time (min) When the boys from the sample group were walking within the aerobic threshold of the strongest boy (Table 4), the weakest boy of the group exceeded his aerobic threshold by 16%; one boy exceeded his aerobic threshold by 3% and one by 6%. For those three boys in the sam- ple group the walking pace was too brisk. Other three boys were walking under their aerobic thresholds. Walking within the aerobic threshold of the strongest boy was too fast for five of the girls. They exceeded their aerobic threshold by 6 to 12%. Seven of the girls were walking close to their aerobic thresholds. Heart rate responses to uphill walking Kinesiologia Slovenica, 9, 1, 25-34 (2003) 3 30 0 T Ta ab bl le e 4 4: : P Pa ar ra am me et te er rs s o of f u up ph hi il ll l w wa al lk ki in ng g a at t a a p pa ac ce e o on n t th he e a ae er ro ob bi ic c t th hr re es sh ho ol ld d o of f t th he e s st tr ro on ng ge es st t b bo oy y a at t t th he e 6 60 00 0- -m m r ru un n. . L Le eg ge en nd d: : III pace on the aerobic threshold of the strongest boy at a 600-m run HR max maximal HR at the pace (beats/min) HR avr average HR at the pace (beats/min) %int percentage of maximal HR (%) %at % of individual aerobic threshold (%) time walking time (min) D DI IS SC CU US SS SI IO ON N Our study describes HR responses to uphill walking in 9- to 10-year-old boys and girls. It can be clearly seen that the HR of boys as well as girls changed with the change of walking pace. There were no significant differences in HR between boys and girls. The literature on similar topics states a few different results of HR for submaximal exercise. Katsuura (1986) studied a group of boys (mean age 1 1.2 yrs) and girls (mean age 1 1.0 yrs) whose physical characteristics and VO 2max values were not significantly different. They cycled at 300 and 450 kpm/min. They found that the HR of the boys was significantly lower (p < 0.05). In contrast, Bar-Or and col- leagues (1971) had 27 boys (mean age 11.6 yrs) and 29 girls (mean age 11.3 yrs) who per- Heart rate responses to uphill walking Kinesiologia Slovenica, 9, 1, 25-34 (2003) 3 31 1 formed a cycle exercise at different work rates. Physical characteristics of the children were not different, but the boys had significantly (p < 0.05) higher VO 2max (1.79 vs. 1.43 L/min) than the girls. In addition, they found that the HR of the boys was significantly (p < 0.05) lower at 250 and 525 kpm/min, but not at 450 kpm/min. Among 57 boys and 60 girls, aged 6 to 16 years, who cycled at one-third and two-thirds of their maximal working rate, Godfrey et al. (1971) found that the HR of the girls was higher than that of the boys at a given rate of steady-state work. Furthermore, they reported that the boys achieved higher maximal rates than girls. In one of the few studies that used the treadmill as the stimulus to investigate cardiovascular responses to exercise in children, Anderson and Godfrey (1971) exercised 20 boys and 21 girls, 5 to 15 years of age, at two different work rates. They held the treadmill speed constant and varied the slope, so that the lower work rate resulted in a HR of ~150 beats/min and the higher work rate a HR of ~180 beats/min. They reported that the girls had a higher HR. It is important to point out that these reported differences were not analysed statistically. The aim of the last study (Turley, & Wilmore, 1997) was to investigate whether differences exist between boys and girls in sub- maximal cardiovascular responses to exercises on both the treadmill and cycling ergometer. Twenty-four 7- to 9-year-old children (12 boys and 12 girls) participated in two maximal (one treadmill and one cycle) and four submaximal tests (two treadmills and two cycles). There were no significant differences between the boys and girls in maximal oxygen consumption (L/min or mL/kg min) or physical characteristics, except for a significantly larger left ventricular mass of the boys versus the girls (78.8 vs. 66.0 g). The trend of the HR was to be lower in boys than in girls, but this difference was only significant at 4 miles/h (142.9 vs. 155.5 beats/min, respec- tively). The mentioned study resembles our study most. In terms of age and other physical characteristics (see T able 1) boys and girls don’t differ much. As regards the characteristics of the HR (HR in the morning, HR at rest, HR max) and during a 600-m run (aerobic threshold, the results of the 600-m run; T able 1) no differences can be noticed. After studying the literature and processing the results of our investigation, it can be concluded that some investigators found differences in HR results of boys and girls, while others didn’t. It has to be noted that all investigations involved small sample groups, which can also be the cause of the differences in results. Another cause could be the age. Once they reach the age of 10, boys respond differently to intense exercise than girls (T urley, & Wilmore, 1997). In our study, as in that performed by Turley and Wilmore, no differences between boys and girls could be found. In both studies children were more than two years younger from those participating in the studies that showed that the HR of boys was lower than that of girls (Katsuura, 1986; Bar-Or et al., 1971; Godfrey et al., (1971). Another reason for the differences between boys and girls can be a larger left ventricle in boys (Shephard at al., 1969; Wirth at al., 1978). That causes an increase in SV and, consequently, a drop in HR. Lastly, the differences in HR can be due to the fact that the girls finished some of the difficult exercises prematurely (Bar-Or et al., 1971). In our study, the average HR before and during the exercise shows that there were no significant dif- ferences between boys and girls. If we considered only the average results, we could, in this age group, plan a mountain walking trip for boys and girls together. Individual results, which are an important part of the study, however, show a completely differ- ent picture. According to these results the walking trip was too hard for some of the children and might be even damaging for their cardiovascular systems, for they reached anaerobic intensity at some pace levels (Edwards, 1994). By the time they reach puberty, children are but poorly equipped with anaerobic abilities (Willmore, & Clostill, 1994). In cases in which children exercised with high intensity and consequently died, the major causes of death were head injuries, heart diseases and heat stroke (Anderson, 2001). That is a strong reason for avoiding Heart rate responses to uphill walking Kinesiologia Slovenica, 9, 1, 25-34 (2003) 3 32 2 over-exercising children. There weren’t any statistically significant differences between the results in boys and girls. However, as many as eight girls and only three boys exceeded their aerobic threshold while walking at a set pace (see Table 2). Individual differences became even more distinct when they were walking at the pace of the strongest boy (see Table 4). Seven girls and two boys exceeded their aerobic thresholds. On the other hand, many of the children who participated in our study didn’t even reach their aerobic thresholds during the walking trips at gentle walking pace (see Tables 3 and 4). The walking intensity that was reached at walking pace of the weakest child resulted in about 70% of the maximum HR. This intensity doesn’t have any considerable physiological impacts (Anderson, 2001). We have to keep in mind, however, that the differences between boys and girls appeared also at this pace. All the boys were walking under their aerobic threshold, while two of the girls almost reached their aerobic thresholds and one even exceeded it by 5% (see T able 3). The results of our inves- tigation are in this matter consistent with the results of those authors who also determined the differences in HR between boys and girls. Mountain walking is very popular among the Slovenians. Public opinion research has shown that it is at the top of the list of recreational activities. Many children, however, dislike endurance sports such as mountain walking. Given the unsuitable pace, we can even support their dislike. Too brisk a pace overburdens the cardiovascular and respiratory system and consequently causes fatigue, even exhaustion, and can as such be damaging for the organism. Walking at a gentle pace, on the other hand, doesn’t have the desired physiological effect and most chil- dren find such walks boring. In both cases the dislike of mountain walking increases. Consequently we would recommend that groups of people, particularly children, taken to mountain walking should be homogeneous. R RE EF FE ER RE EN NC CE ES S Anderson, O. (2001). Otroci lahko tečejo maraton, ne da bi škodili svojemu zdravju [Children can run marathon with- out causing damage to their health]. In Penca J. (Ed.), Vrhunski dosežek (pp. 10-14). Novo Mesto: Penca in drugi. Anderson, S.D., & Godfrey, S. (1971). Cardio-respiratory response to treadmill exercise in normal children. Clinical science, 40, 433-442. Bar-Or, O., Shephard, R.J., & Allen C.L. (1971). Cardiac output of 10- to 13-year-old boys and girls during submaximal exercise. Journal of applied physiology, 30, 219-223. Collier, C.R. (1956). Determination of mixed venous CO2 tensions by rebreathing. 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The Committee on M-mode standardization of the American Society of Echocardiography: Results of a survey of echocardiographic measurements. Circulation, 58, 1072-1083. Shephard, R.J., Allen, C., Bar-Or, O., Davies, C.T., Degre, S., Hedman, R., Ishii, K., Kaneko, M., LaCour, J.R., Di Pampero, P .E., & Seliger, V. (1969). The working capacity of T oronto schoolchildren. Canadian medical association journal, 100, 560-566. T urley, K.R., & Wilmore, J.H. (1997). Cardiovascular responses to submaximal exercise in 7- to 9-yr-old boys and girls. Medicine and Science in Sport Exercise, 29 (6), 824-832. Willmore, J.H., & Costill, D.L. (1994). Physiology of sport and exercise. Champaign: Human Kinetics. Wirth, A., Trager, E., Scheele, K., Mayer, D., Diehm, K., Reischle, K., & Weicker, H. (1978). Cardiopulmonary adjust- ment and metabolic response to maximal and submaximal physical exercise of boys and girls at different stages of maturity. European journal of applied physiology, 39, 229-240. A Ac ck kn no ow wl le ed dg ge em me en nt ts s: : The authors thank Slavka T omažin for technical assistance and the children for their co-opera- tion. Received: 28 October 2002 - Accepted: 2 June 2003 Heart rate responses to uphill walking Kinesiologia Slovenica, 9, 1, 25-34 (2003) 3 34 4