title: Determination of friction and pulling forces during a weighted sled pull.
abstract: Pulling or pushing weighted sleds has been included in various exercise programs. Coaches and researchers may wish to calculate work performed or estimate forces during these exercises, which would involve calculating coefficients of friction: static friction coefficient (μs) and dynamic friction coefficient (μd). The purpose of this study was to establish a reliable method for determining μs, μd, and pulling forces while pulling a weighted sled with different loads to quantify horizontal forces and work performed for training, assessment, and/or research. A nylon tether was attached to a sled-mounted force transducer, and a winch was used to pull the tethered sled at a constant velocity for 20 seconds. Three different loads were pulled: 44.8 kg (the unloaded weight of the sled), 90.0 kg (44.8 kg sled with an additional load of 45.2 kg), and 136.2 kg (44.8 kg sled with an additional load of 91.4 kg). Each load was pulled 10 times using the winch for a total of 30 trials. The static friction coefficient (mean ± SD) was 0.47 ± 0.01 (coefficient of variation [CV] = 2.2%), 0.42 ± 0.01 (CV = 3.0%), and 0.39 ± 0.01 (CV = 2.7%), whereas dynamic friction coefficient (mean ± SD) was 0.35 ± 0.01 (CV = 1.6%), 0.33 ± 0.01 (CV = 3.7%), 0.31 ± 0.00 (CV = 1.0%) for 44.8, 90.0, and 136.2 kg, respectively (p < 0.01). When all trials and loads were combined, μs = 0.43 ± 0.04 and μd = 0.33 ± 0.02 with CV of 8.3 and 5.6%, respectively. The friction coefficients determined in this study were very repeatable, as indicated by the low CV. Coaches, athletes, and researchers who wish to determine μs and μd for their own specific equipment and surfaces can use the methods described here to do so.
authors.affiliation: Biomechanics Laboratory, Department of Health, Sport, and Exercise Sciences, University of Kansas, Lawrence, Kansas, USA. matthew.andre@ku.edu
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Andre
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Fry
authors.forename: Luke A
authors.initials: LA
authors.lastname: Bradford
authors.forename: Kevin W
authors.initials: KW
authors.lastname: Buhr
mesh_terms: D017276:Friction; D006801:Humans; D010806:Physical Education and Training / Q000379:methods*; D055070:Resistance Training / Q000295:instrumentation*; D019876:Sports Equipment