Upper Body Exercise Capacity in Youth With Spina Bifida

Transcription

1 ADAPTED PHYSICAL ACTIVITY QUARTERLY, O 1993 Human Kinetics Publishers, Inc. Upper Body Exercise Capacity in Youth With Spina Bifida Kenneth Coutts, Donald McKenzie, Christine Loock, Richard Beauchamp, and Robert Armstrong University of British Columbia The purpose of this study was to describe the upper body exercise capabilities of youth with spina bifida, which would permit comparison of their abilities to norms. Forty-two children with spina bifida age 7 to 18 years were tested for maximal handgrip strength, anaerobic arm-crank power output, and peak arm-crank oxygen uptake. Analysis of variance was used to compare age, gender, and level of disability differences within the total sample. This analysis indicated no significant effect of level of disability on any of the upper body exercise capacity measures. Significant gender and age effects were noted for grip strength and anaerobic and aerobic capabilities. The sample exhibited handgrip strength comparable to that of nondisabled youth but low anaerobic power and peak oxygen uptake values. Some individual subjects, however, had "normal" values for all tests suggesting that a lower level of participation in regular physical activity rather than spina bifida per se may be responsible for the generally lower physical capacity found in the total sample. The purpose of this study was to quantify the exercise capacities and responses of children with spina bifida and to compare their performance abilities with those of nondisabled children. Bar-Or (1983) and Rowland (1990) provide comprehensive reviews of the information available on the general exercise responses of children and the effects of numerous chronic clinical conditions and illnesses on the exercise capacities of children. Studies on the disease-specific benefits of regular exercise in children with chronic diseases have also recently been reviewed by Bar-Or (1990). Winnick and Short (1985), in a comprehensive fitness study of youth with various disabilities, provide data on the influence of these disabilities on a number of basic muscular performance tests. No specific studies, however, have been found that investigate the influence of spina bifida on the exercise responses and physical performance capacities in children. Al- -- Coutts and McKenzie are with the School of Physical Education, University of British Columbia, 6081 University Blvd., Vancouver, BC, Canada V6T 1Z1. Loock and Armstrong are with the Department of Paediatrics, and Beauchamp is with the Department of Orthopaedics.

2 Exercise Capacity and Spina Bifida 23 though the loss of muscle function below the effective level of the spinal lesion directly affects motor performance, it is reasonable to suspect that general activity levels and patterns are also affected in children with spina bifida. The exercise capacity of intact, functional muscle groups may, thus, be indirectly affected in this population. Methods A volunteer sample of 42 children with spina bifida age 7 to 18 years (19 males, 23 females) were recruited from a total population of 120 registered with a regional spina bifida clinic. Informed consent was obtained for each subject on a form approved by the institution's ethical review committee. The exercise response and physical performance measurements represented a portion of the total data collected on the sample during this project. The exercise response measurements were performed over a 2-hr period during a single visit to the laboratory due to practical limitations of subject availability. That is, the tests were carried out in conjunction with a subject's periodic visit to the clinic, and many of the subjects were only available for this format of data collection. Initially, the weight, age, and functional level of disability of the subject were determined. A functional level of ability was used and subjects were classified as normal ambulation (low spinal lesion), ambulation with assistive devices (midspinal lesion), or manual wheelchair (high spinal lesion) based on the subjects' normal means of locomotion. Three physical performance tests involving upper body musculature were then administered in the following order: maximal handgrip strength for both right and left hands, a Wingate 30-s anaerobic power test, and a continuous, progressive maximal oxygen uptake test. A minimum rest period of 5 min occurred between the handgrip and the anaerobic power test followed by a 30-min rest before the maximal oxygen uptake determination. A calibrated hand dynamometer with adjustable grip strength was used to measure the grip strength, and the higher value from two trials with each hand was recorded. A Monarch cycle ergometer was modified for arm cranking for the anaerobic power test. The modifications to the ergometer included replacing the pedals with handgrips, using a lighter pendulum weight so that full-scale resistance was 3.5 kg rather than 7 kg with a calibrated scale read to the nearest.25 kg, and mounting the ergometer on a table so that the crank shaft was at or slightly below the sitting shoulder height of the subject. Flywheel revolutions of the ergometer were recorded every 5 s through use of a computer data acquisition system, and power outputs were calculated from the recorded revolutions and resistance setting. Per the recommendations of Bar-Or (1987), the ergometer resistance was initially set at 0.05 kg per kilogram of body mass to the nearest.25 kg with adjustment to a lighter resistance for subjects unable to attain or maintain reasonable cranking speeds ( crank rpm). Following a warm-up period, the subject was instructed to achieve close to maximal speed against a light resistance, and then to give maximal effort for the 30-s test period once the test resistance was applied to the ergometer. Subjects were verbally encouraged and informed of the elapsed time throughout the test. The peak power (highest value over any 5-s interval) and the average power output over the entire 30 s were determined for each subject.

3 24 Coutts, McKenzie, Loock, Beauchamp, and Armstrong The maximal oxygen uptake test involved continuous, progressive exercise on an arm crank ergometer by the subject with power output increments of 16 W every 2 min. In an attempt to standardize the total exercise time and follow the general guidelines for maximal oxygen uptake determination in children (Bar- Or, 1987), we estimated the maximal aerobic power output as 60-70% of the subject's peak anaerobic power and set the initial power output two increments below this estimate so that subjects would attain their maximal aerobic power output and oxygen uptake during the third stage or between 4 to 6 min of exercise. Because the estimated maximal aerobic power for some of the younger subjects was below 48 W (i.e., three stages of 16, 32, and 48 W), the initial resistance and increments were scaled down proportionally. We used criteria of a peak heart rate of 160 beats per minute or higher, a respiratory exchange ratio greater than 1.0, and a plateau in oxygen uptake (increase of less than 3 ml/kg/ min) from the penultimate to the last minute of exercise to ascertain that a peak oxygen uptake was attained by each subject. Descriptive statistics were calculated for the sum of right and left handgrip strength, peak and average anaerobic power, peak oxygen uptake, and peak aerobic power in absolute values and relative to body mass. Heart rate, minute ventilation, ventilatory equivalent for oxygen (VEQ), respiratory exchange ratio (RER), oxygen pulse, and exercise time for the peak oxygen uptake test were also determined. Subjects were grouped by gender (male vs. female), age (7-12 vs years), and level of disability (ambulatory vs. assisted ambulatory vs. manual wheelchair user) for comparison purposes, and we used a three-way univariate analysis of variance to explore group differences using the.05 level of significance. Correlations of test result variables with body mass were also determined to assist in the interpretation of the data. Results In the initial three-way analysis of variance, no significant levels of disability effects were noted in any of the variables; the groups were collapsed across this factor, and a two-way analysis that used just the gender and age factors was carried out. Table 1 presents the data for the handgrip strength for these groupings. The analysis of variance for absolute handgrip strength (kg) indicated significant gender (F = 6.57, df = 1,38, p<.05), age (F = 32.89, df = 1,38, p<.05), and interaction (F = 12.54, df = 1,38,p<.05) effects. Analysis of the simple effects showed that the gender difference was present only in the older age group (F = 17.96, df = 1,17, p<.05) and the age difference was due to the male group (F = 72.37, df = 1,17, p<.05), reflecting the greater strength increase with age for the male subjects. Relative to body mass (kgkg), grip strength exhibited only a significant gender difference (F = 8.47, df = 1,38, p<.05) with the males having the higher values. The peak absolute anaerobic power (W) presented in Table 2 showed significant gender (F = 6.70, df = 1,38, p<.05), age (F = 16.86, df = 1,38, p<.05), and interaction (F = 7.70, df = 1,38, p<.05) effects, and the relative pe k power measure (Wkg) exhibited similar gender (F = 12.68, df = 1,38, p<.05?, age (F = 9.28, df = 1.38, p<.05), and interaction (F = 6.27, df = 1,38, p<.05) effects. The gender difference in absolute and relative peak power was due to a significant difference in the older age group (F = 7.35, df = 1,17, p<.05 and F = 7.65, df =

4 Exercise Capacity and Spina Bifida Table 1 Handgrip Strength (M*SEM) Age Mass Handgrip Sum of right and left (years) Gender n (kg) (kg) (kg/kg) Table 2 Anaerobic Power (MkSEM) Age Peak power Average power (years) Gender (W) (W/kg) (w) (WIkg) 1,17, p<.05, respectively), whereas the age effect was attributed to the male group (F = 13.32, df 1,17, p<.05 and F = 9.12, df = 1,17, p<.05, respectively). Thus the interaction effect reflects a larger increase with age in the male group. Average anaerobic power showed a pattern of between-group differences similar to peak power with significant gender (F = 6.7.7, df = 1,38, p<.05 and F = 12.44, df = 1,38, p<.05), age (F = 18.74, df = 1,38, p<.05 and F = 8.76, df = 1,38, p<.05) and interaction (F = 8.54, df = 1,38, p<.05 and F = 6.35, df = 1,38, p<.05) effects for the absolute (W) and relative (Wkg) values, respectively. The gender effects were accounted for by the older age group (F = 8.23, df = 1,17, p<.05 and F = 12.63, df = 1,17, p<.05) and the age effects by the male group (F = 16.02, df = 1,17, p<.05 and F = 10.09, df = 1,17, p<.05) indicating again that the interaction effects in average anaerobic power (absolute and relative values) were due to a significant increase with age in the male group. The results of the peak oxygen uptake test for subjects who met one or more of the criteria of the test are shown in Table 3, with Table 4 indicating values for a number of physiological variables during the attainment of peak oxygen uptake. The mean exercise times indicated that peak oxygen uptake was reached in the third stage of the progressive loading protocol ( s) for all groups with no significant differences between the groups. Individual subjects

5 Coutts, McKenzie, Loock, Beauchamp, and Armstrong Table 3 Peak Oxygen Uptake (M+SEM) Age Exercise Power output Oxygen uptake (years) Gender n time (s) (W) (Wlkg) (Umin) (mllkglmin) Table 4 Physiological Data at Peak Oxygen Uptake (MSEM) Age Heart rate V,BTPS VEQ 0,pulse (years) Gender (beatslmin) (Umin) RER (UL) (mllbeat) had exercise times ranging from 180 to 480 s (3-8 min). Absolute power output (W) at peak oxygen uptake showed significant age (F = 9.88, df = 1,25, p<.05) and interaction (F = 8.04, df = 1,25, p<.05) effects with the significant increase with age in the males (F = 16.03, df = 1,13, p<.05) accounting for these effects. The only significant effect for the relative power output (W/kg) was for gender (F = 6.57, df = 1,25, p<.05), reflecting the higher male values. Analyses of the differences between groups in the peak absolute and relative oxygen uptake values showed results similar to the aerobic power output results, with significant age (F = 9.69, df = 1,25, p<.05) and interaction (F = 8.93, df = 1,25, p<.05) effects noted in the absolute value (Llmin) and only a gender effect (F = 3.96, df = 1,25, p<.05) in the relative measure (ml/kg/min). The higher absolute peak oxygen uptake of the older male group (F = 14.95, df = 1,13, p<.05) was responsible for the noted age and interaction effects in this variable. Analysis of the physiological data in Table 4 indicated no group differences in peak heart rate, RER, or the ventilatory equivalent for oxygen. Minute ventilation and oxygen pulse values exhibited no overall gender difference, but both variables exhibited significant age (F = 13.51, df = 1,25, p<.05 and F = 6.00, df = 1,25, p<.05, respectively) and interaction (F = 8.65, df = 1,25, p<.05 and F = 8.00, df = 1,25, p<.05) effects. Both effects were attributable to the higher,

6 Exercise Capacity and Spina Biiida 27 older male group values for ventilation (F = , df = 1,13, p<.05) and oxygen pulse (F = 11.03, df = 1,13, p<.05). Discussion The use of upper body muscle performance and exercise tests provided a practical means of evaluating the functional abilities of intact muscle groups in subjects with spina bifida regardless of level of disability. The tests were generally well tolerated with good cooperation from the subjects. All subjects were able to complete the handgrip and Wingate anaerobic power tests, but only 29 of the 42 subjects successfully completed the peak oxygen uptake test. Four subjects were unable to tolerate the mouthpiece used in this test, which may reflect the heightened gag reflex associated with spina bifida and which suggests that use of a face mask breathing valve should be considered in future studies of this population. Nine additional subjects did not meet any of the criteria for reaching peak oxygen uptake. Eight of these nine subjects were in the younger age group (7-12 years), and the apparent reason for the early termination of the test in these subjects was local muscle fatigue. The necessity of using a single laboratory visit with only a 30-min recovery period following the 30-s anaerobic test may have contributed to early fatigue in the aerobic test in some subjects. Also, the guidelines for maximal oxygen uptake testing in children presented by Bar-Or (1983) are based on experience with lower limb (treadmill or cycle ergometer) testing, and their appropriateness for testing upper body aerobic function is open to question. Winnick and Short (1985) reported mean values for the sum of right and left handgrip strength for nondisabled boys ranging from 32 kg for 10- to 11- year-olds to 86 kg for 16- to 17-year-olds, whereas for the same age groups, the values for nondisabled girls went from 25 kg to 53 kg. The handgrip strength of the young subjects with spina bifida in this study appeared to be reasonably consistent with these normative values with a similar larger increase in strength with age for the male subjects. The analysis of the peak and average anaerobic power results indicated the large increase in anaerobic function generally found (Bar-Or, 1983; Inbar & Bar- Or, 1986) over the age range of the subjects. It was apparent that the male subjects showed much greater increases even in the power outputs relative to their greater increases in body mass. The anaerobic power values of the male subjects with spina bifida, however, were well below the means for a Wingate arm test reported by Inbar and Bar-Or (1986). They found peak power values of about 150 W for males under 10 years old, which increased with age up to 375 W for 16- to 18-year-olds, but it is not clear that their sample was representative of the nondisabled population, so this comparison should be viewed with caution. A few of the male subjects in the present study did achieve anaerobic power outputs similar to these previously reported values, indicating that spina bifida, per se, may not limit the development of anaerobic power in functional muscle groups, which is a reasonable expectation. The relatively low average values, therefore, may reflect a low level of the regular physical activity needed to develop the anaerobic capabilities in these subjects. The aerobic capacities of the subjects in the present study were also deemed to be below average in comparison to data that indicate treadmill maximal oxygen

7 28 Coutts, McKenzie, Loock, Beauchamp, and Armstrong uptakes of about 50 ml/kg/min for males aged 6 to 16 and a value moving from the high 40s to the low 40s in females aged 6 to 16 (Bar-Or, 1983). This difference from normative data did not appear to be as large as the anaerobic power differences, but Bar-Or (1983) cautioned that his norms should be interpreted "merely as guidelines" because they were not established on the basis of a normative study. This comparison is also tenuous due to the use of average correction factors to convert maximal treadmill oxygen uptake values into peak arm crank values (peak arm crank values representing about 65% of maximal treadmill values; Astrand & Rodahl, 1986). Thus, a normative maximal treadmill oxygen uptake of 50 ml/kg/min would be converted to a peak arm crank value of 32.5 ml/kg/min, which is about 30% higher than the 25 ml/kg/min found in the subjects with spina bifida. However, six of the male subjects attained peak oxygen uptakes greater than 30 ml/kg/ min, with 36.6 ml/kg/min being the highest value recorded. These higher male values occurred in subjects who were normally ambulatory without assistive devices (n = 3) or who used manual wheelchairs (n = 3), which suggests that their normal activities were more conducive to the development of their upper body aerobic capacities than the subjects who ambulated with the aid of assistive braces. Within the limits of the testing procedures and sample used in this study and the validity of the norms, the tests of upper body muscle function and exercise responses in a sample of young subjects with spina bifida indicated normal strength performance, extremely low anaerobic capabilities, and slightly low aerobic capacities. The performances of some subjects, however, were comparable to normative data, suggesting that increased activity and training could improve their muscular and cardiovascular functional abilities. References Astrand, P.O., & Rodahl, K. (1986). Textbook of workphysiology. New York: McGraw- Hill. Bar-Or, 0. (1983). Pediatric sports medicine for the practitioner: From physiologic principles to clinical applications. New York: Springer-Verlag. Bar-Or, 0. (1987). Importance of differences between children and adults for exercise testing and exercise prescription. In J.S. Skinner (Ed.), Exercise testing and exercise prescription for special cases: Theoretical basis and clinical application (pp ). Philadelphia: Lea & Febiger. Bar-Or, 0. (1990). Disease-specific benefits of training in the child with a chronic disease: What is the evidence? Pediatric Exercise Science, 2, Inbar, O., & Bar-Or, 0. (1986). Anaerobic characteristics in male children and adolescents. Medicine and Science in Sports & Exercise, 18, Rowland, T.P. (1990). Exercise and children's health. Champaign, IL: Human Kinetics. Winnick, J.P., & Short, F.X. (1985). Physical fitness testing of the disabled: Project unique. Champaign, IL: Human Kinetics.