title: Standardization of measuring power output during wheelchair propulsion on a treadmill Pitfalls in a multi-center study.
abstract: OBJECTIVE
  In a multi-center study the power output of wheelchair propulsion, attained by a wheelchair drag test, differed among rehabilitation centers. The purpose of this study was to investigate what causes the differences in drag force among centers.
  
  
  METHODS
  A set of standardized drag tests was performed while systematically varying the calibration set of the force transducer, the tester and the wheelchair. In addition, the actual calibrated velocity and slope of the treadmill were measured.
  
  
  RESULTS
  Difference in drag force among centers was due to variation in wheelchair set-up and differences in the slopes between treadmills. The drag force was not significantly different when different testers performed the test. The belt velocity in almost all centers was lower than the manufacturer specified (assumed) velocity.
  
  
  CONCLUSIONS
  The drag test appeared a robust test as far as the tester is considered. Variation in wheelchairs and differences in the actual slopes of the treadmills affected the imposed drag force. The assumed velocity of the treadmill led to an overestimation of the power output. The power output in the multi-center study should be recalculated using the measured velocities and the wheelchair set-up should be more standardized.
authors.affiliation: Rehabilitation Center Amsterdam, The Netherlands. s.de.groot@fbw.vu.nl
authors.forename: S
authors.initials: S
authors.lastname: de Groot
authors.forename: M
authors.initials: M
authors.lastname: Zuidgeest
authors.forename: L H V
authors.initials: LH
authors.lastname: van der Woude
mesh_terms: D000054:Acceleration; D001696:Biomechanical Phenomena; D002138:Calibration; D004867:Equipment Design / Q000592:standards*; D016552:Ergometry; D005080:Exercise Test; D006801:Humans; D008328:Man-Machine Systems; D009038:Motion; D012015:Reference Standards; D012107:Research Design; D012399:Rotation; D013314:Stress, Mechanical; D014910:Wheelchairs