Responses of children with cerebral palsy to arm-crank exercise in the heat

Purpose: In response to passive heating, adults with hemispheric brain infarction demonstrate lower skin temperatures (Tsk) and higher sweating rates (SR) on the affected side. It is unknown whether children with similar conditions demonstrate a similar response and whether this response is advantageous to defending body temperature during exercise in the heat. The purpose of this study was to determine whether children with spastic cerebral palsy (CP) demonstrate less thermal strain than healthy peers during short (10 min each) bouts of arm cranking, a mode of exercise where metabolic rate can be matched between the two groups.
Methods: Eleven young people (8.3–18.3 yr) with spastic CP and 11 individually matched (body size, age, and maturity) healthy controls (CON) performed 3 × 10-min arm-cranking bouts (40 rpm) in 35°C, 50% RH. Body mass, metabolic and heart rate (HR) responses, and body temperatures were periodically measured. Individuals within each CP-CON pair worked at the same intensity (0.55 ± 0.18 W·kg−1 body mass). Data were analyzed using a repeated measures ANOVA (alpha = 0.05).
Results: Subjects with CP showed no difference from CON in metabolic and HR responses, or SR (as inferred from body mass changes corrected for fluid intake and output). There were also no differences between the groups in the rectal temperature change from room temperature (21–23°C). The increase in Tsk from room temperature, however, was slightly (0.6°C) but significantly lower (P < 0.0001; 95% CI = 0.5–0.7°C) in the subjects with CP compared with CON.
Conclusion: Subjects with CP demonstrate thermal strain responses similar to CON during upper-body exercise at relatively low intensities for short duration in a warm climate.
When adults with hemispheric brain infarction are exposed to a heat stimulus at rest, the paretic side of the body compared with the nonparetic side shows increased sweating (5) and decreased skin temperature (6). Although it is unknown whether such atypical responses influence their ability to defend body temperature during exercise in a warm climate, any such responses could have a greater impact on children with such conditions compared with adults due to the children’s higher body surface area (BSA)-to-body mass ratio. One of the more common pediatric conditions similar to adults with hemispheric brain infarction is spastic cerebral palsy (CP) (13). When performing lower-body exercise children with CP, however, expend greater metabolic energy (and thus produce more metabolic heat) than do able-bodied children (2,21) due to increased lower-limb antagonist muscle co-contraction (21) and excessive mechanical power production (22). Use of upper-body exercise such as arm cranking could provide a means of matching their metabolic rate to that of able-bodied controls. Such a design would allow for investigation of the effect of CP on body temperature responses to exercise in a warm climate independent of between-group differences in metabolic heat production.
We therefore hypothesized that during short-duration arm-crank exercise of the same relative intensity in a warm, moderately humid climate, children and adolescents with CP compared with healthy controls individually matched for body size, age, and maturity would demonstrate: i) similar metabolic heat production, ii) lower increases in rectal temperature (ΔTre), iii) lower increases in mean skin temperature (ΔTsk), iv) similar heart rate (HR), and v) greater evaporative sweat loss. To test these hypotheses, children and adolescents with mild spastic CP and matched, healthy controls performed 3 × 10-min arm-cranking exercise bouts in 35°C, 50% relative humidity (RH), a climate that is similar to a very warm summer day in southern Ontario. We chose short-duration exercise as it reflects our clinical experience with the patterns of physical activity in subjects with CP. Pilot work with such patients has also revealed that they were not able to consistently exercise with the upper body at a moderate intensity for a longer duration.