- Measuring mechanical efficiency (ME) is potentially useful to assess motor performance in individuals with physical disabilities. The purpose of this study was to determine the accuracy of predicting ME from heart rate (HR) during a self-paced stair-climbing test in children with a range of motor abilities. The participants were 12 normally developed children (ND) and 24 with cerebral palsy (CP), ranging in age from 5 to 15 years (mean: 8 years). Five were at level II, 11 at level III and 8 at level IVaccording to the gross motor function classification system. ME was calculated as the ratio of external work to O2 uptake (˙ VO2 ml/min) measured or predicted from HR. The absolute values of ˙ VO2 and HR during stair-climbing were not significantly correlated. However, the correlation between values above resting (d˙ VO2 and dHR) was significant (r = 0.61). Furthermore, when including body weight as a second variable the prediction of d˙ VO2 was significantly improved (r = 0.85). This resulted in a high correlation (r = 0.96) between measured and predicted net ME (MEnet). Predicted MEnet for 25 stairclimbing tests repeated after an average of 6 months resulted in an r-value of 0.92 with predicted MEnet of the first test. This study demonstrates that MEnet during stair-climbing can be predicted in children with a broad range of motor abilities from dHR and may be a simple tool to help define developmental stages or evaluating intervention efficacy. # 2007 Elsevier B.V. All rights reserved.