Cardiorespiratory Responses of Trained Boys to Treadmill and Arm Ergometry: Effect of Training Specificity

Transcription

1 Pediatric Exercise Science, 1998, 10, Human Kinetics Publishers, Inc. Cardiorespiratory Responses of Trained Boys to Treadmill and Arm Ergometry: Effect of Training Specificity Hazzaa M. Al-Hazzaa, Saeed A. Al-Refaee, Muhammed A. Sulaiman, Ma'ed Y. Dafterdar, Abdullah S. Al-Herbish, and Andrew C. Chukwuemeka The purpose of this study was to examine the maximal cardiorespiratory responses of trained adolescent male swimmers (SWM, N = 18), soccer players (SOC, N = 18), and moderately active reference subjects (CON, N = 16) to treadmill running () and arm ergometry (). Mean values (t SD) for skeletal age were similar among the three groups (12.5 f 1.9, 12.7 f 1.1, and _ 1.6 years, for the SWM, SOC, and CON, respectively). Allometric scaling procedures, relating V0,max and body mass, were used and mass exponents of.80 and.74 were identified for and data, respectively. During testing SOC attained significantly higher V0,max values when expressed in ml. kg-'. min-i, or ml. kgn.80. rnin-i than the other two groups. However, during testing, the SWM achieved significantly higher VO, peak values (ml.. rnin-' and scaled to arm-csa) than SOC. The ratio of -VAT to -VAT was significantly higher in SWM ( %) compared to SOC ( %), or CON (41.9 _+ 6%). In adult population, the cardiorespiratory responses of upper body exercise lave been extensively investigated (4,7,9, 14,21,31, 37) and reviewed (13,30). rhese findings indicated that, when compared with treadmill running or leg cycling, arm ergometry is associated with smaller muscle mass, lower maximal aerobic power (4, 7, 9, 21, 27, 31), lower peak heart rate (4, 7, 9, 21, 27, 31), higher heart rate at a given submaximal exercise load (4, 14,37), lower ventilatory anaerobic threshold (9), and higher arterial pressure (27). Furthermore, in untrained adults, peak oxygen uptake during arm cranking is shown to be around 70% of that during leg ergometry (30). These differences are believed to mainly be due to the fact that physiological responses to exercise are significantly affected by the quantity of H.M. Al-Hazzaa, S.A. Al-Refaee, M.A. Sulaiman, and M.Y. Dafterdar are with the Exercise Physiology Lab in the Department of Physical Education at the King Saud University, Riyadh, 11423, Saudi Arabia. A.S. Al-Herbish is with the Department of Pediatrics at the King Saud University. A.C. Chukwuemeka is with the Sports Medicine Hospital, General Presidency of Youth Welfare, Riyadh, Saudi Arabia.

2 Treadmill and Arm Ergometry active musculature. However, due to training specificity, well-trained upper body athletes have been shown to attain a substantially higher percentage of their leg V0,max during upper body exercise (32). Cardiorespiratory adaptations have been shown to be specific to the type of arm or leg training (6,15). In contrast to adults, the cardiorespiratory responses of children and adolescents to arm ergometry relative to leg work have not been previously addressed, though some comparisons of children's responses to treadmill running and cycling were reported in the literature (3, 8, 36). Moreover, children are thought to be metabolic nonspecialist (29) and have been shown to exhibit neither aerobic nor anaerobic specialization during prepubertal development (1 1). However, mode of testing could have been (partially) responsible for some of the previous findings, especially when swimmers were used as subjects (11). In contrast to the previous studies, Thorland et al. (35) have recently presented some data supporting metabolic specialization in young sprinters. Thus, issues related to the specificity of training adaptation and metabolic specialization in children and adolescent need further elucidation. Therefore, the aim of this study was to examine the cardiorespiratory responses of trained boys to two different modes of exercise testing, specifically treadmill running and arm ergometry. Two groups of young athletes participating in two different sports were included: swimming, which requires utilization of arm and shoulder muscles, and soccer, which involves running and mostly taxes the lower body musculature. Subjects Materials and Methods Fifty-two male adolescents, comprised of 18 swimmers, 18 soccer players, and 16 age-matched untrained boys, volunteered to participate in this study. Their ages ranged from 11 to 15 years. All the athletes were training for at least 1 year with an average of 7-8 hr per week. The untrained subjects were considered moderately active but not involved in any systematic training. Parental permission and adolescent consent were obtained prior to taking part in the study. In addition to chronological age, hand-wrist X-rays were taken for each participant, and skeletal age was blindly determined by a radiologist and confirmed by a pediatric endocrinologist, according to Greulich and Pyle methods (16). Anthropometery and Body Composition Body weight (kg) and height (cm) were measured using a Seca digital scale. Subscapular and triceps skinfolds were measured using Harpenden caliper. Body fat percent was then estimated through the use of Slaughter et al.'s equation (34). In addition, mid-arm circumference was measured using anthropometric tape. Muscle cross-sectional area (CSA) for the arm was then calculated using Gurney and Jelliffe's formula (17). Testing Procedures Each subject performed two maximal exercise tests, beginning with the treadmill running and followed, after about 3 to 7 days, with the arm ergometer test. Testing was conducted 2 hr after meals in a comfortable laboratory environment and as

3 close to the same time of the day as possible. All subjects were verbally encouraged to put forth maximal effort. Treadmill Running Testing. The treadmill test began with a familiarization and warm-up period lasting 10 to 15 min. During the warm-up period, the optimal running speed was also determined for each subject, which ranged from 8 to 12 kmlhr, depending on the subject's age and ability to run comfortably. Soccer players felt more comfortable with higher running speeds than did swimmers. The test protocol consisted of running at a constant speed with treadmill elevation increased 2% every 2 min until exhaustion. Arm Ergometry Testing. The arm ergometry test was performed on a Monarch Rehab Trainer that was secured to a table. The seat was hydraulically adjusted for each subject so that the acromion process was horizontal with the center of the axle connected to the hand grips. The pedal crank was positioned so that the arm would fully extend during each cranking cycle. Restraining straps were placed over the subjects shoulders to secure his trunk to the back of the seat in order to minimize shoulder and trunk movements. The arm ergometry test was a continuous progressive protocol starting with zero load for 2 min and increasing the work load by 10 W every 2 min until exhaustion. The cranking rate was set at 60 rpm. Test terminated when the subject was unable to maintain the cranking cadence. Cardiorespiratory Measurements. Expired air was collected and analyzed using an automated open-circuit system with 30-s sampling intervals (EOS-Sprint, Jaeger, Germany). Gas analyzers were calibrated before each test with a known mixture of gases. Oxygen uptake was considered maximal when the respiratory exchange ratio (RER) exceeded 1.O (during both treadmill and arm ergometry tests) and heart rate level exceeded 90% of the maximal predicted heart rate (during treadmill test only). However, during arm ergometry testing, four subjects in the untrained group could not reach or exceed RER of 1.0, despite the fact that their peak heart rate reached levels that were much higher than the average peak heart rate for their group. Heart rate was continuously monitored and recorded during the exercise test using a CM5 lead and a single-channel ECG monitor and recorder (Helligi, German~).., In addition. ventilatorv anaerobic threshold (VAT) was determined noninvasively through the gas exchange method. ~m~hasis wasplaced on the nonlinear increase in VE and a systematic increase in the ventilatory equivalent for 0, (VENO,) without an increase in ventilatory equivalent for CO, (VENCO,). However, VAT could not be determined for three swimmers and-one socce; players during treadmill and for three swimmers and two soccer players during arm ergometry. Statistical Analysis. Descriptive statistics using SPSS package were determined for all variables in each group of athletes. Pearson product-moment correlation was used to test the relationship between values of V0,max obtained during treadmill and arm ergometry in each group. Differences in the correlation coefficients were tested using the chi-square test for multiple comparisons. Analysis of variance (ANOVA) with a Scheffe post hoc test was performed to reveal differences in the subjects characteristics between the threegroups. Two-way analyses of variance (2 x 3) were also performed to test differences in cardiorespiratory variables across groups and testing modes. Statistical significance was set at.05. In addition, allometric scaling procedures relating V0,max to body mass were applied (25,40), and mass exponents of.80 and.74 were identified for treadmill

4 Treadmill and Arm Ergometry and arm ergometry data, respectively. V0,max values during arm ergometry were also scaled to the muscle cross-sectional area of the arm, where a scaling factor of 0.57 was identified and used. Results Physical characteristic of the subjects are presented in Table 1. There were no Aignificant differences between swimmers and soccer players in any of the physical characteristics. Furthermore, values of upper-arm circumference and arm crosssectional' area (CSA) were not significantly different between the three groups. However, the untrained group was significantly different from the soccer players in body mass and body fat percent. Maximal treadmill testing lasted between 9 and 15 min, while arm ergometer testing time ranged from nearly 7 to 12 min. Data of cardiorespiratory responses to treadmill running and arm ergometry are presented in Table 2 and Figures 1 and 2. The two-way analyses of variance revealed significant interactions in most of the variable. This means that the rank order of superiority is changed according to the mode of testing. The soccer players attained higher cardiorespiratory values than the swimmers when tested by treadmill, while the swimmers showed higher values compared to the soccer players when tested by arm ergometer. Values of treadmill V0,max calculated relative to body mass ( Wg. min) or relative to body mass raised to the power of.80 were significantly greater in the soccer players compared to both the swimmers and the untrained group. Indeed, V0,max values relative to body mass for the swimmers and the untrained subjects were not different from those values previously reported for untrained Saudi boys (1). As expected when using smaller muscle groups, the values of peak VO, obtained during arm ergometry were significantly lower than those obtained during treadmill running. When tested by arm ergometer the swimmers were able to at- Table 1 Physical Characteristic of the Subjects (Means and Standard Deviations) Variable Swimmers Soccer players Untrained Number of subjects Chronological age (year) Skeletal age (year) Body mass (kg) Body height (cm) Body surface area (m2) Body fat content (%) Lean body mass (kg) Arm circumference (cm) CSA-arm (cm2) Note. CSA-arm = mid-arm muscle cross-sectional area. ANOVA results: NS = no significant difference between the three groups; #: not equal; 1 = swimmers, 2 = soccer players, 3 = untrained group.

5 Table 2 Cardiorespiratory Response to lkeadmill Running () and Arm Ergometry ( [Means and Standard Deviations]) Ll m 2 Variable Mode Swimmers Soccer players Untrained p <.05 % B V0,max (mlkg. LBM. min)" Scaled to CSA V0,max ratio VEmax (Llmin)" ri'rd

6 Table 2 Continued Variable Mode Swimmers Soccer players Untrained p <.05 HRmax (bpm)' RERmax 0, pulse index* VAT (L/min)* VAT (mlkg. min)' VAT (% V0,max) Note. n = V0,max scaled to body mass for the whole groups (scaling factor for treadmill data was.80, and for arm ergometry data was -74). CSA = midarm muscle cross-sectional area (scaling factor for CSA was 0.57 and value is reported as mucm57. rnin). VAT = ventilatory anaerobic threshold. "Means that the interaction is <.01). $ '"ANOVA results: NS = no significant difference between the three groups; #: not equal; 1 = swimmers, 2 = soccer players, 3 = untrained group. 3 & 3 rn

7 601 ml. ~g" mi<' ml. Kg. mln. SWM SOC CON TREADMILL \j02 max Figure 1 -Treadmill maximal oxygen uptake (L. min-', ml kg1 min-i, and ml. kgo min-') in adolescent swimmers (SWM), soccer players (SOC), and untrained subjects (CON). Data are means + SEM (p <.05). tain significantly greater values of peak VO, expressed relative to lean body mass, relative to body mass, and scaled to mid-arm cross-sectional area compared to soccer players. In addition, the swimmers achieved during arm ergometry a substantially higher percentage of their treadmill V0,max than did the soccer players (66 vs. 51%). Result of ventilatory anaerobic threshold (VAT) during both treadmill and arm ergometry are also shown in Table 2. Absolute values of VAT (Vmin) obtained

8 Treadmill and Arm Ergometry SWM SOC CON ERGOMETRY \]On max Figure2 - Arm ergometry peak oxygen uptake (L. mind, ml. kg074 min-i, and scaled to arm muscle cross-sectional area) in adolescent swimmers (SWM), soccer players (SOC), and untrained subjects (CON). Data are means f SEM (p c.05). during treadmill or arm ergometsy did not differ among the three groups. During treadmill running, however, the soccer players attained significantly higher values of VAT expressed relative to body mass and as a percentage of V0,max compared to the other two groups. In each of the three groups, VAT as a percentage of V0,max occurred at a lower level during arm ergometry than during treadmill running. In addition, the ratio of VAT obtained during arm ergometry to that obtained during

9 Table 3 Correlation Coeffecients Between V0,max Values Obtained During Treadmill Running and Arm Ergometry Group (Llrnin) mvkg. min Scaled to body mass Swimmers r 33"".70"^ r' Soccer players r.68*".56* r' Untrained r.90"*.xi** treadmill was significantly higher in the swimmers ( %) compared to that of soccer players (41.2 f 5%) or the untrained boys (41.9 -t 6%). Furthermore, data on maximal heart rate and oxygen pulse index exhibited no significant differences among the three groups in any testing mode. However the rank order of mean distribution is different during treadmill running compared to arm ergometry. Soccer players ranked higher than the swimmers during treadmill, while during arm ergometry, the swimmers ranked higher than the soccer players. Result of zero order correlation coefficients of V0,max values obtained during treadmill and arm ergometry are presented in Table 3. The correlations are higher in the untrained subjects followed by the swimmers and then by the soccer players. However, their differences did not reach significance. The r values are diminishing as we go from absolute V0,max to that scaled to body mass. Discussion The findings of the present study indicated that during treadmill testing the adolescent soccer players attained higher V0,max values than the swimmers. During arm ergometry, however, the swimmers were able to achieve higher peak VO, values than the soccer players. These differences seen between the two groups of athletes in response to treadmill and arm ergometry testing could have been the results of training specificity, which were observed in adult studies (6, 15,41). In fact, when adults runners and cyclists were tested by means of treadmill and cycle ergometry, the runners achieved a higher VO, at VAT on the treadmill, whereas the cyclists' VO, at VAT was higher on the cycle ergometer (41). Peripheral (local) adaptations were likely to have been responsible for the differences seen between swimmers and soccer players, since previous study on adolescent boys had shown that skeletal muscle enzyme changes were specific to the mode of training (12). The present findings are also in agreement with previous work showing some evidences of metabolic specialization in young sprinters (35).

10 Treadmill and Ann Ergometry The mean value for V0,max (ml/kg - min) of the soccer players in treadmill testing is substantially above the average for the untrained subjects. Youth soccer involves a lot of running and is considered an energy-demanding sport (2). However, the swimmers, who were not different from the controls, cannot be classified as physically unfit. Besides the fact that running is not typical of swimmers' training, V0,max value of our swimmers is similar to the value reported for a group of adolescent swimmers training for 7 hr per week (23). Due to specificity of aerobic adaptation, our swimmers showed a greater peakv0, when tested by arm ergometry, something that could not be revealed by previous work (11). The differences in treadmill V0,max values between the swimmers and the soccer players are likely as a result of iest mode specificity, since Kilka and Thorland (19) reported a peak VO, value for a group of young swimmers tested during swimming that was similar to our soccer players' values. Furthermore, physical maturity has been shown to influence cardiorespiratory measures including absolute peak VO, (3) and anaerobic threshold (18). In the present study, the three groups of subjects have had similar means for skeletal age and thereby are biologically age-matched. Normalizing physiological data for body size has been suggested as an appropriate means of expressing growth data (25, 28,33,40). In the present study, reporting peak VO, values of arm ergometry relative to body mass resulted in similar means for the thee groups of subjects. However, scaling V0,max to body mass074 showed that the swimmers were significantly superior cornpired with the soccer players or the untrained boys. Enders et al. (10) who studied untrained adults, recommended the use of cross-sectional area of muscle plus bone of the upper arm to standardize V0,peak in arm cranking. In the present study, using peak VO, relative to muscle cross-sectional area of the upper arm resulted in the swimmers having higher values than the soccer players and the untrained group, but the difference did not reach a significant level. However, scaling V0,max values to crosssectional area of the upper arm muscle showed a significant-differences between the swimmers and the soccer players. Apparently, cardiorespiratory responses of children and adolescents to arm ergometry have not been investigated previously. Thus, no comparison can be made with our arm ergometry data. However, comparing treadmill cardiorespiratory responses to those of arm ergometry in the present study indicated that the former resulted in higher values for VO,max, HRrnax, VEmax, and VAT, irrespective of the subject groups. V0,max vaiues obtained during treadmill are roughly 40% higher than those obtained in arm ergometry. Such differences are higher than the 30% differences reported in adult studies (30). The differences in V0,max values across testing modes could be attributed mainly to greater active muscle mass required in treadmill running. Evidence also suggests that peripheral factors play a primary role in arm work, whereas central factors are considered more important in leg work (7). It has been reported recently that the blood flow itself, not the oxygen delivery, seems to limit performance during exercise with a small muscle mass (22). The present study showed that values of VAT as a percentage of V0,max during treadmill testing are similar to values occurred at the level of lactate threshold reported by Mocellin et al. (24), and slightly higher than those previously reported for comparable age groups (5,18,26,38,39). Differences in VAT reported in the present study and those reported previously may have been due to variations in testing protocols, methods of VAT detection, and aerobic fitness levels of the subjects. I

11 In our study, VAT occurred earlier during arm ergometry compared to treadmill running. Such findings have been observed previously in adults performing arm versus leg exercise (9). It is also believed that such factors as greater 0, transport are expected to delay the onset of exercise-induced metabolic acidosis in exercise involving large muscle mass (20). VAT expressed as a percentage of V0,max have been shown to be higher in children compared with adults (5, 18). At thipresent time, it appears that no data are available to compare with our VAT results on arm ergometry. Results for the correlation coefficients of V0,max values (mvkg - min) obtained during treadmill and arm ergometry ranged frbm.56 in the soccer players to.81 in the control group. Although the differences were not significant, the untrained group consistently had the highest correlation coefficient across all V0,max measures. ~ ookin~ at the coefficient of determination (mukg. min), it can beseen that there are higher variances associated between treadmill and arm ergometry in the untrained group (66%) than in swimmers (49%) or soccer players (31%). Central factors may have accounted for the common variance in the untrained group, since no peripheral adaptations could have occurred in this group of untrained subjects. In this regard, comparisons with our findings are only available from treadmill versus cycle ergometry testing in children. Boileau et al. (8) reported a correlation as high as.95 between treadmill and cycle V0,max values in year-old boys. However, in contrast to arm ergometry, boih treadmill and cycle ergometry predominantly stress the leg muscles. In summary, the findings of this study indicated that, during treadmill running, adolescent soccer players were able to attain higher V0,max values than skeletally age-matched swimmers. On the other hand, the swirnmek achieved higher peak VO, values during arm ergometry compared with soccer players. Such findings were consistent with the principle of training specificity observed in adult studies. Values of peak VO, during arm ergometry were roughly 60% of VO, obtained during treadmill tesiing, which is considerably lower than what was reported in adult studies. Furthermore, the ratio of ventilatory anaerobic threshold obtained during arm ergometry to that obtained during treadmill was significantly higher in the swimmers compared to soccer players or untrained boys. Thusj our findings support the concept of metabolic specialization in children and adolescents. References 1. Al-Hazzaa, H., and M. Sulaiman. Maximal oxygen uptake and daily physical activity in 7- to 12-year-old boys. Pediatl: Exerc. Sci. 5: , Al-Hazzaa, H., S. Al-Refaee, M. Sulaiman, K. Al-Muzaini, S. Alabood, K. Al-Jaloud, and M. Al-Dosery. Energy demands and fluids loss during youth soccer. Proceedings of the First Asian Congress on Science and Football. Tokyo, Japan, 1995, pp Armstrong, N., J. Williams, J. Balding, P. Gentle, and B. Kirby. The peak oxygen uptake of British children with reference to age, sex and sexual maturity. Eul: J. Appl. Physiol. 62: , Astrand, P., and B. Saltin. Maximal oxygen uptake and heart rate in various types of muscular activity. J. Appl. Physiol. 16: , Atomi, Y., K. Iwaoka, H. Hatta, M. Miyashita, and Y. Yamamoto. Daily physical activity levels in preadolescent boys related to V0,max and lactate threshold. Eul: J. Appl. Physiol , 1986.

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