title: Predicting Endurance Time in a Repetitive Lift and Carry Task Using Linear Mixed Models.
abstract: OBJECTIVE
  Repetitive manual handling tasks account for a substantial portion of work-related injuries. However, few studies report endurance time in repetitive manual handling tasks. Consequently, there is little guidance to inform expected work time for repetitive manual handling tasks. We aimed to investigate endurance time and oxygen consumption of a repetitive lift and carry task using linear mixed models.
  
  
  METHODS
  Fourteen male soldiers (age 22.4 ± 4.5 yrs, height 1.78 ± 0.04 m, body mass 76.3 ± 10.1 kg) conducted four assessment sessions that consisted of one maximal box lifting session and three lift and carry sessions. The relationships between carry mass (range 17.5-37.5 kg) and the duration of carry, and carry mass and oxygen consumption, were assessed using linear mixed models with random effects to account for between-subject variation.
  
  
  RESULTS
  Results demonstrated that endurance time was inversely associated with carry mass (R2 = 0.24), with significant individual-level variation (R2 = 0.85). Normalising carry mass to performance in a maximal box lifting test improved the prediction of endurance time (R2 = 0.40). Oxygen consumption presented relative to total mass (body mass, external load and carried mass) was not significantly related to lift and carry mass (β1 = 0.16, SE = 0.10, 95%CI: -0.04, 0.36, p = 0.12), indicating that there was no change in oxygen consumption relative to total mass with increasing lift and carry mass.
  
  
  CONCLUSIONS
  Practically, these data can be used to guide work-rest schedules and provide insight into methods assessing the physical capacity of workers conducting repetitive manual handling tasks.
authors.affiliation: Land Division, Defence Science and Technology Group, Fishermans Bend, Australia.|Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Australia.
authors.forename: Ben
authors.identifier: http://orcid.org/0000-0003-3262-5956
authors.initials: B
authors.lastname: Beck
authors.affiliation: Land Division, Defence Science and Technology Group, Fishermans Bend, Australia.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Ham
authors.affiliation: Land Division, Defence Science and Technology Group, Fishermans Bend, Australia.
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Best
authors.affiliation: Land Division, Defence Science and Technology Group, Fishermans Bend, Australia.
authors.forename: Greg L
authors.initials: GL
authors.lastname: Carstairs
authors.affiliation: Land Division, Defence Science and Technology Group, Fishermans Bend, Australia.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Savage
authors.affiliation: Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Australia.
authors.forename: Lahn
authors.initials: L
authors.lastname: Straney
authors.affiliation: Centre for Human and Applied Physiology, Faculty of Health and Behavioural Sciences, University of Wollongong, Wollongong, Australia.
authors.forename: Joanne N
authors.initials: JN
authors.lastname: Caldwell
mesh_terms: D000328:Adult; D000465:Algorithms; D001696:Biomechanical Phenomena; D006801:Humans; D017770:Lifting; D016014:Linear Models; D008297:Male; D008889:Military Personnel; D008962:Models, Theoretical; D010101:Oxygen Consumption / Q000502:physiology*; D010807:Physical Endurance / Q000502:physiology*; D013997:Time Factors; D016474:Weight-Bearing / Q000502:physiology; D055815:Young Adult