title: Analysis of the musculoskeletal loading of the thumb during pipetting--a pilot study.
abstract: Previous epidemiological studies indicate that the use of thumb-push mechanical pipettes is associated with musculoskeletal disorders (MSDs) in the hand. The goal of the current study was to analyze the loading in the muscle-tendon units in the thumb during pipetting. The hand is modeled as a multi-body linkage system and includes four fingers (index, long, ring, and little finger), a thumb, and a palm segment. Since the current study is focused on the thumb, the model includes only nine muscles attached to the thumb via tendons. The time-histories of joint angles and push force at the pipette plunger during pipetting were determined experimentally and used as model input; whereas forces in the muscle-tendon units in the thumb were calculated via an inverse dynamic approach combined with an optimization procedure. Results indicate that all nine muscles have force outputs during pipetting, and the maximal force was in the abductor pollicis brevis (APB). The ratio of the mean peak muscle force to the mean peak push force during the dispensing cycle was approximately 2.3, which is comparable to values observed in grasping tasks in the literature. The analysis method and results in the current study provide a mechanistic understanding of MSD risk factors associated with pipetting, and may be useful in guiding ergonomic designs for manual pipettes.
authors.affiliation: National Institute for Occupational Safety & Health, Morgantown, WV 26505, USA. Electronic address: jwu@cdc.gov.
authors.forename: John Z
authors.initials: JZ
authors.lastname: Wu
authors.affiliation: National Institute for Occupational Safety & Health, Morgantown, WV 26505, USA.
authors.forename: Erik W
authors.initials: EW
authors.lastname: Sinsel
authors.affiliation: National Institute for Occupational Safety & Health, Morgantown, WV 26505, USA.
authors.forename: Justin F
authors.initials: JF
authors.lastname: Shroyer
authors.affiliation: National Institute for Occupational Safety & Health, Morgantown, WV 26505, USA.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Warren
authors.affiliation: National Institute for Occupational Safety & Health, Morgantown, WV 26505, USA.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Welcome
authors.affiliation: Biomechanics Laboratory, Division of Orthopedic Research, Mayo Clinic, Rochester, MN 55905, USA.
authors.forename: Kristin D
authors.initials: KD
authors.lastname: Zhao
authors.affiliation: Biomechanics Laboratory, Division of Orthopedic Research, Mayo Clinic, Rochester, MN 55905, USA.
authors.forename: Kai-Nan
authors.initials: KN
authors.lastname: An
authors.affiliation: National Institute for Occupational Safety & Health, Morgantown, WV 26505, USA.
authors.forename: Frank L
authors.initials: FL
authors.lastname: Buczek
mesh_terms: D000328:Adult; D005260:Female; D005385:Fingers / Q000502:physiology; D018737:Hand Strength / Q000502:physiology; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D010865:Pilot Projects; D013647:Task Performance and Analysis; D013710:Tendons / Q000502:physiology*; D013933:Thumb / Q000502:physiology*; D016474:Weight-Bearing
keywords: Inverse dynamics; Modeling; Muscle–tendon force; Pipette; Thumb