Influence of climate on heart rate in children: comparison between intermittent and continuous exercise

Heart rate (HR) monitoring is commonly used to assess 24-h energy expenditure (EE) in children but it has been found to overestimate the true values. One reason for this may be the effect of climatic heat stress on HR. An equation has been previously developed to adjust HR measured during continuous exercise for the influence of climate. Since play in children is rarely of a continuous pattern, one objective of this study was to compare the effects of climatic heat stress on the HR response to intermittent and to continuous exercise. A second objective was to determine whether the previously developed equation is suitable for intermittent exercise. A group of 12 boys and 8 girls (aged 8-11 years) cycled in a climatic chamber. The exercise consisted of continuous cycling for 5 min at 35%, 55%, and 75% of peak oxygen up take (random order) followed by alternating cycling at the same resistance and cadence (30 s) and rest (30 s) for 3 additional min. The oxygen uptake (VO2) and HR were determined for 2 min at the end of continuous cycling and for 2 min during intermittent cycling. Climatic conditions (randomly assigned) were dry bulb temperature T(db) 22 degrees C, 50% relative humidity (rh); T(db) 28 degrees C, 55% rh; T(db) 32 degrees C, 52% rh; or T(db) 35 degrees C, 58% rh. The difference between HR measured at a given T(db) (HR(meas)) and HR at 22 degrees C and at the same VO2 was then calculated (deltaHR). The deltaHR increased linearly with increasing temperature but was not related to VO2 or to exercise type. However, a small but significant difference was found if the published equation was used with data from intermittent exercise. The accuracy of the existing equation adjusting HR(meas) for the influence of T(db) (HR(corr)) could be improved to HR(corr) = HR(meas) x (1.18308-(0.0083218 x T(db))). In conclusion, the effects of climatic heat stress on HR were similar in continuous and intermittent exercise, and HR can be adjusted for the influence of climate in groups of pre- and early pubertal children during rest, intermittent and continuous exercise at ambient temperatures between 22 degrees C and 35 degrees C, thereby reducing the error in predicting EE from HR.