Comparison Of Habitual Physical Activity Measured By Heart Rate And By Accelerometry In Cerebral Palsy

Abstract

Physical activity (PA) has physiologic, mechanical and behavioral components. We have previously shown that for children and adolescents with mild spastic cerebral palsy (CP), their habitual PA measured physiologically with monitored heart rate (HR) is related to their physiologic walking economy (oxygen cost of walking). We have also shown for this population that their habitual PA measured mechanically with tri-axial accelerometry is related to their biomechanical walking economy (vertical excursion of the center of mass relative to that expected in normal gait). In both instances, those with the higher levels of PA were the more economical walkers. The relationship between physiologic and mechanical measures of PA in this population, however, is unknown. PURPOSE To determine, in children and adolescents with cerebral palsy (CP), the relationship between; 1) habitual PA as measured by monitored HR and by tri-axial accelerometry and 2) habitual PA and gross motor function related to walking (GMF-W). METHODS Ten subjects (10.6–16.3 yr) with mild spastic CP, simultaneously wore a HR monitor and a tri-axial accelerometer for two weekdays and one weekend day. PAL, the ratio of total energy expenditure to resting energy expenditure, was determined from the monitored HR data, with individual HR-oxygen uptake calibrations and resting measures done in the lab. From the accelerometry data, total vector magnitude movement counts ± d−1 (TMC) and the number of minutes ± d−1 TMC were above the 90th percentile for the group (TMC90) were determined. GMF-W was measured in the lab using the Walking, Running and Jumping Dimension of the Gross Motor Function Measure. Relationships were analyzed using linear regression techniques. Alpha was set at .05. RESULTS PAL (1.33 ± .04) was significantly related (r=.75) to TMC (1.53 ± 105 ± 1.4 ± 104 counts) and (r=.78) to TMC90 (59.8 ± 8.1 minutes). PAL was also significantly related (r=.82) to GMF-W (82.1 ± 5.6%) as were TMC (r=.89) and TMC90 (r=.90). There was no significant relationship for PAL, TMC, TMC90 or GMF-W with age (r=.00001 to .21, P=.60 to 1.0). CONCLUSIONS For older children and adolescents with mild CP, those with higher levels of the physiologic component of PA, may also have higher levels of the mechanical component. Those with higher levels of either component of habitual PA, may also have the better gross motor function related to walking. Further research is needed to determine if, and to what extent, this gross motor function is related to metabolic and mechanical walking economy.