title: Accuracy and repeatability of the Pedar Mobile system in long-term vertical force measurements.
abstract: Portable insole pressure systems can be used to measure the vertical force during long-term (hours) measurements to determine the patient's amount of weight bearing during daily activities in the hospital and at home. Especially for long-term measurements, the amount and duration of loading pressure insoles can have a large influence on the accuracy, as previous studies found a time-dependent behavior after a relatively short period (minutes) of constant loading. Therefore, this study assessed the accuracy and repeatability of a portable capacitive insole system (Pedar, Novel(GmbH)) to measure vertical force during long-term loading. Static loading experiments were performed during which the Pedar insoles were loaded with 5 and 10 N/cm2 for 7 h. Dynamic loading experiments were performed with one Pedar insole which was cyclically loaded with 300, 500 and 1000 N during two sessions of 1200 load cycles. The static and dynamic experiments were repeated 3 days later. Accuracy, due to offset drift, decreased in time during the start of the static experiments (percent error: -1.9% to 0.3% at hour 0; 26.3% to 34% at hour 7). The percent error for the dynamic experiments ranged from -16% to -19%, from -3% to -7% and from -8% to approximately 0% when the insole was loaded with 300, 500 and 1000 N, respectively. The amount of drift ranged from 12 to 62 N for the 500 and 1000 N loads, respectively. The mean day-to-day percentage difference for the static and dynamic experiments ranged from -2.3% to 0.5%, and from -2.9% to 3.0%, respectively. The results indicate that drift correction is necessary for accurate assessment of vertical force by the Pedar Mobile system to determine the amount of weight bearing during long-term measurements.
authors.affiliation: Department of Physical Therapy, Erasmus MC, University Medical Center, Dr. Molewaterplein 40, 3015 GD Rotterdam, The Netherlands. h.hurkmans@erasmusmc.nl
authors.forename: H L P
authors.initials: HL
authors.lastname: Hurkmans
authors.forename: J B J
authors.initials: JB
authors.lastname: Bussmann
authors.forename: E
authors.initials: E
authors.lastname: Benda
authors.forename: J A N
authors.initials: JA
authors.lastname: Verhaar
authors.forename: H J
authors.initials: HJ
authors.lastname: Stam
mesh_terms: D006801:Humans; D008991:Monitoring, Physiologic / Q000295:instrumentation*; D026741:Physical Therapy Modalities / Q000295:instrumentation*; D015203:Reproducibility of Results; D012775:Shoes; D016474:Weight-Bearing / Q000502:physiology*