Role of mechanical power estimates in the O-2 cost of walking in children with cerebral palsy

It has been established in able-bodied children that traditional biomechani cal descriptors of gait such as stride length or stride frequency do not fu lly account for the differences seen in the energy cost of locomotion noted with age. Hence, measures of total body mechanical power output have been adopted to explain these differences. Purpose: The aim of this study was to estimate the ability of this mechanical power calculation to explain the v ariability in the metabolic energy cost of treadmill walking in children wi th spastic cerebral palsy (CP). Methods: Thirteen subjects volunteered for the study. One group consisted of eight (6 male, 2 female) children with CP (age 12.2 +/- 2.7 yr) The second group consisted of five (4 male, 1 female ) able-bodied controls (age 13.4 +/- 2.8 yr). The treadmill walking protoco l consisted of one 4-min stage at 0% grade, 3 km.h(-1). Infrared markers we re placed on 12 anatomical landmarks and data were collected using the OPTO TRAK motion analysis system over a 5-s time period during the last 30 s of the 4-min stage. On-Line oxygen consumption (V) over dot O-2 measurements w ere obtained throughout using the Beekman Horizon Metabolic Cart. Results: Relative (V) over dot O-2 (mL.kg(-1)min(-1)) was significantly (P < 0.05) d ifferent between the two groups (CP: 16.6 +/- 6.5 vs control: 10.2 +/- 1.2) . Simple linear regression analysis demonstrated that mechanical power meas urements, incorporating transfers of energy between and within adjacent bod y segments, accounted for 87.2% of the total variability noted in (V) over dot O-2 for the children with CP, compared with only 2.4% in the able-bodie d subjects. Conclusions: The results indicate that mechanical power differe nces explain the majority of the variability noted in (V) over dot O-2 in c hildren with CP at a submaximal walking speed.