title: The Influence of Load and Speed on Individuals' Movement Behavior.
abstract: Because individuals' movement patterns have been linked to their risk of future injury, movement evaluations have become a topic of interest. However, if individuals adapt their movement behavior in response to the demands of a task, the utility of evaluations comprising only low-demand activities could have limited application with regard to the prediction of future injury. This investigation examined the impact of load and speed on individuals' movement behavior. Fifty-two firefighters performed 5 low-demand (i.e., light load, low movement speed) whole-body tasks (i.e., lift, squat, lunge, push, and pull). Each task was then modified by increasing the speed, external load, or speed and load. Select measures of motion were used to characterize the performance of each task, and comparisons were made between conditions. The participants adapted their movement behavior in response to the external demands of a task (64 and 70% of all the variables were influenced [p ≤ 0.05] by changing the load and speed, respectively), but in a manner unique to the task and type of demand. The participants exhibited greater spine and frontal plane knee motion in response to an increase in speed when compared with increasing loads. However, there were a large number of movement strategies exhibited by individual firefighters that differed from the group's response. The data obtained here imply that individuals may not be physically prepared to perform safely or effectively when a task's demands are elevated simply because they exhibit the ability to perform a low-demand activity with competence. Therefore, movement screens comprising only low-demand activities may not adequately reflect an individual's capacity, or their risk of injury, and could adversely affect any recommendations that are made for training or job performance.
authors.affiliation: 1Faculty of Kinesiology and Physical Education, University of Toronto, Toronto, Ontario, Canada; and 2Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada.
authors.forename: David M
authors.initials: DM
authors.lastname: Frost
authors.forename: Tyson A C
authors.initials: TA
authors.lastname: Beach
authors.forename: Jack P
authors.initials: JP
authors.lastname: Callaghan
authors.forename: Stuart M
authors.initials: SM
authors.lastname: McGill
mesh_terms: D000328:Adult; D061388:Firefighters; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D060051:Occupational Injuries / Q000209:etiology / Q000517:prevention & control; D011897:Random Allocation; D013131:Spine / Q000502:physiology*; D016474:Weight-Bearing