Study Design and Structure
Subjects visited the laboratory at the Children’s Exercise and Nutrition Centre on two occasions. Visit 1 took place in room temperature (21–24°C) conditions. During this visit we determined, for each subject with CP, the treadmill belt speed and slope that would yield a moderate intensity exercise (HR = 140–150 beats·min−1) that the subject could sustain for three bouts of 10 min. We did not choose a lower-intensity exercise because our previous findings with lower-intensity exercise in the heat in this population (14) showed no physiologically significant differences (in relevant physiologic variables) between the subjects with CP and CON. Pilot work also showed that not all the subjects with CP could sustain (for the three 10-min bouts in the heat in visit 2) an exercise intensity in thermoneutral higher than that which we chose. We have previously reported a group mean maximum HR for these subjects (in thermoneutral conditions on the treadmill) of 189 beats·min−1 (12). A HR of 145 beats·min−1 is about 77% of maximal HR, which we define as moderate intensity exercise.
In visit 2 the climatically controlled chamber was set at 35 ± 1°C, 45–50% RH with air motion < 0.2 m·s−1. During this visit, four of the subjects with CP had their exercise intensity increased for the last two bouts to ensure they reached the desired intensity. Each CP-CON pair, however, always walked at the same speed and slope for each bout. One subject with CP, who walked without support over ground, was unable to do so on the treadmill, even after the treadmill (walking) teaching and habituation session. This subject held on to the treadmill handrail with one hand during the treadmill walks. One other subject, who likewise walked without support over ground, occasionally held on to the handrail with one hand during the treadmill walks. Because we could not control the amount of body weight supported by the upper limb, the CON matches for these two subjects did not hold on to the railing during their walks. The mean treadmill belt speed and slope were 0.9 ± 0.4 m·s−1 and 3.3 ± 0.6%, respectively. Each CP-CON pair was tested during the same season, and during the same time of day. Data collection took place within 1–2 wk for each subject with the exception of one subject with CP who, due to scheduling issues, completed the study within a 16-d period. The minimum time between visits 1 and 2 was 2 d. Because testing took place during the same season for each CP-CON pair and because the CP-CON subjects were similar in physical activity levels, it was assumed that they were similarly acclimatized to the testing environmental conditions.
Protocols and Measurements
Subjects completed questionnaires about physical activity (modified from Bar-Or (2)), health status and diet (time, content, and amount of the last meal and snack), with the assistance of a parent if needed. Pubertal stage (pubic hair for boys, breast development for girls) was self-determined, based on photographs (15) according to the criteria of Tanner (25). Total body length was estimated from arm span because not all the subjects with CP could stand erect. Body adiposity was estimated by summing the medians of three skinfold measurements taken at the biceps, triceps, subscapular, and suprailiac sites on the dominant side. Body mass (Mott Electronic Scale, UMC1000, accuracy ± 20 g; Ancaster Scale Co. Ltd., Brantford, ON, Canada) was measured after subjects emptied their bladder. To subsequently calculate nude body weight, clothes, including shoes, were also weighed (Accuba Scale, 1200, accuracy ± 0.20 g). Boys wore shorts, socks, and athletic shoes. Girls wore the same with the addition of a bikini top. The same shoes were worn for both visits. Topographic distribution of spasticity was based on the classification of Minear (17). One person (DM) determined the severity of gross motor involvement using the Gross Motor Function Classification System (21), a five-level grading system, where level I refers to those with the mildest involvement. The degree of lower limb spasticity was assessed using the modified Ashworth scale (4), a five-level scale (0 = no spasticity; 4 = rigidity) that is feasible and commonly used with the CP population (24). Lower-limb passive range of motion (to screen for contractures) was assessed by goniometry using standardized techniques modified from McDowell et al. (16). Gross motor function related to walking was measured using the Walking, Running, and Jumping component of the gross motor function measure (22). Walking proficiency was also determined by measuring the comfortable walking speed on level ground (30-m walkway) using the median of a triplicate measurement. Subjects rested in the sitting position between each trial until HR (Polar Vantage XL, Polar CIC, Port Washington, NY) was within 10% of its preexercise value. Borg’s 6–20 RPE scale (5) was then introduced and subjects were instructed in its use as previously described (3).
Participants were also familiarized with the equipment and taught to walk on the treadmill without using the handrails. They were then habituated to walking on the treadmill (13). After resting for 10 min, the subjects performed 3 × 10-min treadmill walking bouts while HR was continuously measured and stored as 5-s averages in the receiver. The exercise bouts were separated by 10-min rest periods. To accommodate the subjects to the mouthpiece, they were connected to a metabolic cart (Vmax 29 Pulmonary Exercise System, SensorMedics Corp., Yorba Linda, CA) that was calibrated just before data collection. Expired air was collected for 6 min (minutes 4–9) during each bout. Expired gas data were averaged over 20-s increments, and the information was stored in the Vmax system’s computer. There was a 1-min break in each walking bout (after minute 3) to allow proper insertion of the mouthpiece. Pilot work showed us that most subjects with CP could not tolerate the mouthpiece for the entire 10 min of the three exercise bouts and they could not insert it properly while walking. During the last 20 s of the third minute and of the final minute of each walk subjects were asked to rate their perceived exertion using Borg’s 6–20 RPE scale. These metabolic and RPE data were discarded.
The desired speed and slope was that which would yield (for the subjects with CP) a HR of 140–150 beats·min−1. The initial speed was each (CP) subject’s comfortable treadmill walking speed, determined at the end of the treadmill habituation period. They walked at this speed for 2 min and then the treadmill speed was adjusted accordingly. A slope was added for those subjects who could not maintain a walking speed that yielded the target HR. In general, it took 4–6 min (2–3, 2-min “steps”) to reach the target HR in the CP group. Each CON walked at the same treadmill belt speed and slope as their CP match.
Health status and diet were confirmed with a short questionnaire as in visit 1. Diet was standardized by giving all subjects two slices of toasted bread (Wonder Bread, no cholesterol) with jam (E. D. Smith, no sugar added). Subjects emptied their bladders and, with a parent’s assistance if necessary, inserted a rectal thermistor (YSI 400 series, Yellow Springs, OH) 8–10 cm beyond the anal sphincter to allow measurement of Tre. To measure Tsk, skin thermistors (Steri-Probe no. 499B, Cincinnati Sub-Zero Products, Inc., Cincinnati, OH) were affixed at the lateral mid-upper (dominant) arm, the distal one-third of the anterior thigh (dominant leg), and just posterior to the inferior angle of the scapula (dominant upper limb). Before entry to the climatic chamber, HR and body temperatures at rest (ante chamber, 21–24°C) were measured and recorded, and clothing and the HR monitor were weighed. Body mass was measured and recorded upon the subjects’ entry into the chamber and during the third and eighth minute of each rest period. Rectal and skin temperature were measured continuously during the subjects’ time in the chamber and stored as 1-min averages in a data logger (Mini Logger, Series 2000, Mini Miter Co., Inc., Bend OR), a light-weight box (25 g) that was attached to the small of the back of each subject with a narrow elastic belt. The temperature data were later downloaded to a computer for subsequent analysis. Rectal temperature was monitored during the first and eighth minutes of each rest period by connecting the rectal thermistor to a Doric bridge (model 450, ± 0.1°C). To maintain euhydration, subjects drank a predetermined amount of chilled (4 ± 1°C) water, 0.8% of their body mass, a modification (based of pilot data) of our previous work with subjects with CP arm cranking in the heat (14). The water was divided into three equal portions, with the first drink given upon entering the chamber, the second after the first exercise bout, and the third after the second exercise bout. If it was noted during the chamber session that the CP subject was gaining weight, to avoid hyperhydration, the final drink was not given. Each CP-CON pair drank the same amount of water relative to their body mass. The subjects were in the chamber for 68 min.
The exercise protocol in the chamber and the HR, expired gas, and RPE measurements were as in visit 1. The CP group worked at the speed and slope determined in visit 1. The CON subjects worked at the same speed and slope as their CP match. Immediately after leaving the chamber, subjects emptied their bladder and removed their clothes. Urine output and the clothes and equipment worn by the subject were weighed.
Calculations and Data Reduction
Oxygen uptake during each walk was determined from the steady-state V̇O2 (L·min−1) (the mean of minutes 5–9 of each exercise bout). This measure was used as an indirect estimate of metabolic heat production. Cardiovascular strain during treadmill walking in the heat (HRex) was determined as the average HR during the last minute of each walk. Body temperatures during the time in the chamber (with the exception of peak Tre, see below) were extracted from the minute-by-minute body temperature data at 13 time points (the last minute of the preexercise period and the 5th and 10th minute of each exercise bout and rest period). Mean Tsk was calculated as the sum of weighted local skin temperatures (0.4 trunk temperature, 0.4 thigh temperature, 0.2 upper-arm temperature), a modification of the weightings of Hardy and Dubois (11). Because it was not practical with the subjects with CP to record from a greater number of skin sites (the subjects had limited patience during set up and also found more skin temperature thermistors distracting), we decided to limit the measurement to three sites. To account for intersubject differences in Tre and Tsk before entering the chamber, the change from room temperature (21–24°C) in Tre (ΔTre) and in Tsk (ΔTsk) was also calculated. Peak Tre was defined as the highest minute-by-minute value for each subject during his or her time in the chamber. Sweating rate was calculated from the change in body mass (over the entire period in the chamber) corrected for water intake during the chamber session, urine output, respiratory water loss (18), and the change in the mass of the clothes and equipment. Sweating rate is reported relative to body surface area (7). The rating of perceived exertion was measured as the absolute rating the subject made on the Borg 6–20 RPE scale.
Intergroup differences (each CP-CON pair) and changes over time (for body temperatures) were assessed with a two-way, repeated measures ANOVA. The difference between any two means was assessed post hoc using Tukey’s HSD method. Differences between CP-CON pair members in the two groups for the sum of four skinfolds, body surface area, and sweating rate were assessed with a paired t-test. All analyses were performed with Statistica for Windows (Version 5.5, StatsSoft Inc, Tulsa, OK), with alpha = 0.01.
Within the CP-CON pairs, independent of exercise bout, V̇O2 was significantly (P = 0.0006) higher in the CP subjects (for bouts 1, 2, and 3, respectively, mean ± SEM, CP = 0.84 ± 0.08, 0.88 ± 0.11, 0.86 ± 0.12 L·min−1; CON = 0.57 ± 0.05, 0.62 ± 0.07, 0.62 ± 0.07 L·min−1). The mean difference between the groups was 0.26 L·min−1 (99% CI = 0.10–0.42 L·min−1). The higher V̇O2 in the CP group was a consistent finding for all CP-CON pairs (Fig. 1). From 32 min in the chamber onward, ΔTre was also significantly (P < 0.0002) greater for those subjects with CP compared with their CON match (Fig. 2). By the end of the last exercise bout (minute 58), the difference between the group means in ΔTre was 0.31°C (99% CI = 0.1–0.5°C). In addition, the subjects with CP started to show a significant (P < 0.0008) increase in ΔTre from 32 min in the chamber onward, whereas this did not occur in the CON subjects until minute 58 (Fig. 2). Peak Tre, was also significantly (P = 0.002) higher in those with CP (CP = 38.0 ± 0.07°C, CON = 37.6 ± 0.07°C; mean difference = 0.4°C, 99% CI = 0.1–0.6°C). Figure 3 shows that peak Tre was higher for the CP subjects in all but one of the CP-CON pairs. The ΔTsk was significantly (P < 0.0002) greater for the CP subjects compared with their CON matches from minute 11 in the chamber onward (Fig. 4). By the end of the last exercise bout (minute 58) the difference in ΔTsk between the group means was 1.1°C (99% CI = 0.4–1.9°C). Within the group of subjects with CP, by minute 11 the ΔTsk was significantly (P < 0.001) greater than during the preexercise period in the chamber (Fig. 4). The values for the CON group, however, did not change from their initial level (Fig. 4). Within the CP-CON pairs, independent of exercise bout, HRex was significantly (P = 0.0001) higher in the CP subjects (for bouts 1, 2, and 3, respectively, CP = 143 ± 3.8, 151 ± 2.7, 155 ± 3.4 beats·min−1; CON = 108 ± 4.3, 114 ± 5.1, 115 ± 5.3 beats·min−1). The mean difference between the groups was 37 beats·min−1 (99% CI 19–56 beats·min−1). The higher HRex in the CP group was a consistent finding for all but one of the CP-CON pairs (Fig. 5). There were no significant between-pair differences in sweating rate (CP = 181.7 ± 14.1 g·m−2·h−1, CON = 187.2 ± 22.9 g·m−2·h−1). Figure 6 shows that individual CP-CON pair differences in sweating rates were, however, variable. There were no significant differences in RPE between the CP and CON subjects (for the end of minutes 3 and 10 of bouts 1, 2, and 3, respectively, mean ± SEM, CP = 11.3 ± 0.88, 12.6 ± 0.76, 12.5 ± 0.90, 13.0 ± 0.93, 12.6 ± 0.92, 12.8 ± 0.92. CON = 10.4 ± 0.90, 10.4 ± 0.79, 10.8 ± 0.80, 11.2 ± 0.90, 10.9 ± 0.80, 11.2 ± 0.90).
This is the first reported study to investigate thermal strain in children and adolescents with spastic CP during treadmill walking in the heat. As expected, during short-duration walking exercise at the same speed and slope in a warm, moderately humid climate, the children and adolescents with mild, spastic CP, compared with individually matched (age, body size, biological maturity, gender, race) healthy CON, demonstrated: i) higher metabolic rates, ii) greater ΔTre, iii) greater ΔTsk, iv) higher HRex, and v) similar sweating rates. Contrary to our hypothesis, there were no differences in RPE between the CP and CON subjects.
For practical reasons, mechanical work or power was not measured in this study. Although the methods (kinematic-based estimates of mechanical power) have theoretical limitations (28), intersubject differences in mechanical power have been shown to explain 87% of the intersubject differences in V̇O2 for subjects with CP walking on the treadmill (0.83 m·s−1) (26). This would suggest that much of the increased metabolic rate seen in subjects with CP during treadmill walking may be due to their working harder than CON. Other research (27) has also shown that that the low walking economy in those with CP is related to increased lower limb antagonist muscle coactivation. Independent of why those with CP have a lower walking economy, when they are working at a higher absolute metabolic rate than CON subjects, they need to dissipate a greater absolute heat load. In this present study, the greater ΔTre and ΔTsk in the CP group relative to CON are indirect indicators of the increased heat gain in the CP group. The CP group is unable to completely dissipate the metabolic heat load they produce while treadmill walking at a moderate intensity in the heat. Previous research with subjects with mild CP showed that those with CP required 60% more metabolic energy as a group than healthy CON walking on the treadmill at the same speed (0.83 m·s−1) (27). In our study, those with CP had a 40% higher V̇O2 on average than did the CON. Because little information is available on the gross motor function of this previous group of subjects, it is difficult to determine why they were less economical relative to controls than the present group of subjects with CP. The comfortable ground walking speed of the previous group (1.3 m·s−1) reported elsewhere (12) was similar to that reported for the present subjects (Table 2).
Because HR is linearly related to V̇O2 at submaximal exercise intensities (1), the increased HRex in the CP group reflects their higher V̇O2 compared with the CON group. The higher HRex in the CP group may also reflect their increased thermal strain compared with CON. Because there were no differences in sweating rates between the CP-CON pairs, the subjects with CP may have been relying more on dry heat loss (conduction and convection) than their able-bodied counterparts, i.e., the increased HRex in those with CP may therefore have been due (in part) to an attempt to maintain cardiac output when an increased proportion of the blood was diverted to the skin for thermoregulation. It has been suggested that skin blood flow is determined more by core temperature than by sweating (30), and in this study the subjects with CP had the higher ΔTre and peak Tre. Further research is needed to determine whether the skin blood flow of those with CP differs from that of CON during moderate-intensity treadmill walking exercise in the heat. Our findings also support the hypothesis of Falk et al. (8), who suggest that the higher Tre, Tsk, and HR values of the younger compared with older able-bodied boys during treadmill walking (29), but not during cycling (9), may be due to age-related differences in walking economy (10), that is, younger boys are less economical than older boys and thus produce more metabolic heat.
Although this study, which used a repeated measures design (where each subject with CP was compared to their CON match), was not designed to investigate intersubject (CP group) differences in thermoregulatory responses to treadmill exercise in the heat, such differences among the subjects with CP may also exist. Figure 5 shows that by the end of the third exercise bout, six of the CP subjects had exceeded the target HRex range of 140–150 beats·min−1. Further research with a larger group of subjects with CP, grouped perhaps by severity of CP, would help to clarify the findings in Figure 5.
Although changes (due to climatic and metabolic heat stress) in Tre lag behind changes in esophageal and tympanic temperature (20), Figure 2 shows that, especially in the CP group, the increases in Tre are occurring during the exercise bouts. That this relationship is less obvious in the CON group is likely due to their lower metabolic rate, because in a previous study (14) using short-duration exercise in climatic conditions as in the present study, where metabolic rate was about 16% lower than in the present study, Tre did not change significantly from baseline throughout the chamber session for either the CP or the CON groups. With lower metabolic rates, Tre may respond too slowly to show increases in core temperature related to short-duration exercise. However, for ethical and comfort reasons, measurement of body core temperature at the esophagus, the preferred method (23), was not feasible. We also chose not to measure tympanic temperature because it is related to both skin and environmental temperature (19) and would have been at least somewhat influenced by the warm environmental conditions in this study.
As expected, the CP and CON subjects showed similar sweating rates. This finding is consistent with our previous work with this population with short-duration, lower-intensity arm cranking exercise in the heat (14).
Previous research has shown that for cycling exercise at a given power output, children and adolescents with CP perceive themselves to be working harder than healthy CON (3). When RPE was expressed relative to percent of peak power, however, these intergroup differences disappeared (3). Bar-Or and Reed (3) suggest that the intergroup differences in RPE at the same intensity are related to the lower fitness levels in the CP subjects compared with CON. Although we found the same pattern for RPE as in the previous study, these differences were not significant. Post hoc power calculations suggest that with 10 subjects in each group, we had adequate power (0.80) to detect differences in RPE of at least 2.9 units. The mean difference between the CP and CON groups in this study was 1.7 units. Thus, the subjects with CP may have perceived themselves as working harder although the results are inconclusive. Because the previous authors (3) did not report on the severity of the CP of their subjects, and the testing modalities are different (cycling in the previous study, treadmill walking in the present study), it is difficult to determine the reason for the difference in the findings between the two studies. It is of clinical relevance, however, that these subjects with CP whose metabolic rates were on average 40% higher than in CON do not strongly perceive themselves as working harder. From a clinical perspective, those with mild CP may not be aware of their work rate. Further research is needed to determine in free living situations in the heat, if these children and adolescents with CP self-regulate their physical activity levels.
Although neither group reached a Tre that is harmful to health, the pattern of those with CP (Fig. 2) shows that they were continuing to gain heat (because skin temperature was stable through most of the chamber session, see Fig. 4) as the chamber session went on. By midway through the second exercise bout, their ΔTre was significantly higher than during the preexercise phase. Thus, had they continued to exercise they would likely have continued to gain heat. This is in contrast to the pattern seen in Figure 2 for the healthy children and adolescents. For most of the chamber session, they were in thermal balance, neither gaining nor losing heat. It was only by the end of the third exercise bout that they started to become hotter than during the preexercise phase. From a clinical standpoint, if children and adolescents with CP who are engaging in short-duration exercise at moderate intensities in the heat do not self-regulate their activities, or are in situations where they are with able-bodied children (such as a school sports team) and thus are not able to self-regulate, they may be at risk for discomfort, which could affect enjoyment of the activity and possibly athletic performance.
It is unlikely that any intergroup differences in thermal strain were masked by differences between the groups in anthropometric variables or biological maturity. We successfully matched these characteristics (Table 1). In addition, although we did not a priori match for the sum of four skinfolds or body surface area, these characteristics were also not significantly different between the groups (Table 1). Moreover, during visit 2, the subjects were similarly hydrated (loss of body fluid over the time in the chamber was 0.04 ± 0.05% and 0.01 0.10% body mass, for the CP and CON groups, respectively) and acclimated to the testing environmental conditions (see Methods, above).
In conclusion, those with CP, compared with individually matched CON, demonstrated a higher V̇O2 during short-duration treadmill walking in the heat. Consistent with a higher metabolic heat load, they also demonstrated greater increases in body temperatures and HR. Because sweating rates were not different between the CP and CON groups, further research is needed to determine if those with CP rely more on dry heat loss. Finally, the failure to find a clear intergroup difference in RPE and the pattern of increasing rectal and skin temperature gain over time within the CP group suggest that further research is also required to determine if these subjects with mild, spastic CP self-regulate their physical activity during free living under climatic conditions as in this study.
1.Astrand, P.-O. Experimental Studies of Physical Work Capacity in Relation to Sex and Age
. Copenhagen: Munksgaard, 1952, pp. 37.
2.Bar-Or, O. Pediatric Sports Medicine for the Practitioner: From Physiologic Principals to Clinic Applications
. New York: Springer Verlag, 1983, pp. 343–348.
3.Bar-Or, O., and S. L. Reed. Rating of perceived exertion in adolescents
with neuromuscular disease. In: Perception of Exertion in Physical Work
, G. A. V. Borg (Ed.). Stockholm: Wenner-Gren, 1987, pp. 137–148.
4.Bohannon, R. W., and M. B. Smith. Interrater reliability of a modified Ashworth scale of muscle spasticity. Phys. Ther
. 67:206–207, 1987.
5.Borg, G. The perception of physical performance. In: Frontiers in Fitness
. R. J. Shepard (Ed.). Springfield, IL: Charles C Thomas, 1971, pp. 280–294.
6.Campbell, J., and J. Ball. Energetics of walking in cerebral palsy. Orthop. Clin. North Am
. 9:374–377, 1978.
7.Dubois, D., and E. F. Dubois. Clinical calorimetry: a formula to estimate the approximate surface area if height and weight be known. Arch. Intern. Med
. 17:863–871, 1916.
8.Falk, B. Effects of thermal stress during rest and exercise in the paediatric population. Sports Med
. 25:221–240, 1998.
9.Falk, B., O. Bar-Or, and J. D. MacDougall. Thermoregulatory responses of pre-, mid-, and late-pubertal boys to exercise in dry heat. Med. Sci. Sports Exerc
. 24:688–694, 1992.
10.Frost, G., O. Bar-Or, J. Dowling, and K. Dyson. Explaining differences in the metabolic cost and efficiency of treadmill locomotion in children. J. Sports Sci
. 20:451–461, 2002.
11.Hardy, J. D., and E. F. Dubois. The technique of measuring radiation and convection. J. Nutr
. 15:461–475, 1938.
12.Hoofwijk, M., V. Unnithan, and O. Bar-Or. Maximal treadmill performance of children with cerebral palsy. Pediatr. Exerc. Sci
. 7:305–313, 1995.
13.Maltais, D., O. Bar-Or, M. Pierrynowski, and V. Galea. Repeated treadmill walks affect physiologic responses in children with cerebral palsy. Med. Sci. Sports Exerc
. 35:1653–1661, 2003.
14.Maltais, D., V. Unnithan, B. Wilk, and O. Bar-Or. Responses of children with cerebral palsy to arm-crank exercise in the heat. Med. Sci. Sports Exerc
. 36:191–197, 2004.
15.Matsudo, S. M. M., and V. K. R. Matsudo. Self-assessment and physician assessment of sexual maturation in Brazilian boys and girls: concordance and reproducibility. Am. J. Hum. Biol
. 6:451–455, 1994.
16.McDowell, B. C., V. Hewitt, A. Nurse, T. Weston, and R. Baker. The variability of goniometric measurements in ambulatory children with spastic cerebral palsy. Gait Posture
17.Minear, W. L. A classification of cerebral palsy. Pediatrics
18.Mitchell, J. W., E. R. Nadel, and J. A. Stolwijk. Respiratory weight losses during exercise. J. Appl. Physiol
. 32:474–476, 1972.
19.Nadel, E. R., and S. M. Horvath. Comparison of tympanic membrane and deep body temperatures in man. Life Sci. I
. 9:869–875, 1970.
20.Nielsen, B., and M. Nielsen. On the regulation of sweat secretion in exercise. Acta Physiol. Scand
. 64:314–322, 1965.
21.Palisano, R., P. Rosenbaum, S. Walter, D. Russell, E. Wood, and B. Galuppi. Development and reliability of a system to classify gross motor function in children with cerebral palsy. Dev. Med. Child Neurol
. 39:214–223, 1997.
22.Russell, D., P. Rosenbaum, C. Gowland, et al. Gross Motor Function Measure Manual
. Hamilton, Canada: Neurodevelopmental Clinical Research Unit, McMaster University, 1993, pp. 1–112.
23.Sawka, M. N., and C. B. Wenger. Physiologic responses to acute exercise stress. In: Human Performance Physiology and Environmental Medicine at Terrestrial Extremes
, K. B. Pandolf, M. N. Sawka, and R. R. Gonzalez (Eds.). Indianapolis: Benchmark Press, 1998, pp. 97–151.
24.Suputtitada, A. Managing spasticity in pediatric cerebral palsy using a very low dose of botulinum toxin type A: preliminary report. Am. J. Phys. Med. Rehabil
. 79:320–326, 2000.
25.Tanner, J. M. Growth in Adolescence
. Oxford: Blackwell Scientific, 1962, pp. 32–37.
26.Unnithan, V., J. Dowling, G. Frost, and O. Bar-Or. Role of mechanical power estimates in the O2
cost of walking in children with cerebral palsy. Med. Sci. Sports Exerc
. 31:1703–1706, 1999.
27.Unnithan, V. B., J. J. Dowling, G. Frost, and O. Bar-Or. Role of cocontraction in the O2
cost of walking in children with cerebral palsy. Med. Sci. Sports Exerc
. 28:1498–1504, 1996.
28.van Ingen Schenau, G. J. Positive work and its efficiency are at their dead-end: comments on a recent discussion. J. Biomech
. 31:195–197, 1998.
29.Wagner, J. A., S. Robinson, S. P. Tzankoff, and R. P. Marino. Heat tolerance and acclimatization to work in the heat in relation to age. J. Appl. Physiol
. 33:616–622, 1972.
30.Yoshida, T. K. Nagashima, H. Nose, et al. Relationship between aerobic power, blood volume, and thermoregulatory responses to exercise-heat stress. Med. Sci. Sports Exerc
. 29:867–873, 1997.
Keywords:©2004The American College of Sports Medicine
HEAT PRODUCTION; RECTAL TEMPERATURE; SKIN TEMPERATURE; OXYGEN UPTAKE; HEART RATE; ADOLESCENTS