title: Sex differences in jaw muscle duty factors during exercise in two environments: A pilot study.
abstract: It is unknown if females and males use jaw muscles similarly during exercise. This pilot study assessed jaw elevator muscle duty factors (DFs=time of muscle activity/total recording time) at repeated sessions to test if DFs are reliable and different between sexes during exercises in two environments. Ten female and seven male subjects recruited from university soccer teams provided informed consent. Surface electromyography was recorded from masseter and temporalis muscles during biting and leg-extension laboratory exercises. Average activities to produce 20N bite-forces for each muscle and subject determined thresholds (5-80%·T20N) for subject-specific DF calculations during exercises performed in laboratory and natural environments. Subjects self-recorded via portable electromyography equipment during in-field leg-extension and weight-lifting exercises. Effects of variables on DFs were assessed via ANOVA (α=0.05) and simple effects testing (Bonferroni-adjusted p⩽0.012). All subjects used jaw muscles during exercises in both environments. DFs between laboratory sessions were reliable (R=0.84). During laboratory exercises, male temporalis DFs were significantly higher than female DFs from both muscles (p⩽0.001). During in-field exercises females had higher DFs during weight-lifting while males had higher DFs during leg-extensions. In-field sex differences were significant at most thresholds and showed larger effect sizes for leg-extension compared to weight-lifting exercises.
authors.affiliation: Private practice, Chesterfield, MO, United States.
authors.forename: Adam K
authors.initials: AK
authors.lastname: Reynolds
authors.affiliation: University of Missouri-Kansas City, School of Dentistry, Kansas City, MO, United States.
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Nickel
authors.affiliation: East Tennessee State University, College of Public Health, Johnson City, TN, United States.
authors.forename: Ying
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Texas A & M University, Baylor College of Dentistry, Dallas, TX, United States.
authors.forename: Danielle K
authors.initials: DK
authors.lastname: Leeper
authors.affiliation: University of Nebraska Medical Center, College of Dentistry, Lincoln, NE, United States.
authors.forename: Kelsey M
authors.initials: KM
authors.lastname: Riffel
authors.affiliation: University of Missouri-Kansas City, School of Dentistry, Kansas City, MO, United States.
authors.forename: Hongzeng
authors.initials: H
authors.lastname: Liu
authors.affiliation: University of Missouri-Kansas City, School of Dentistry, Kansas City, MO, United States. Electronic address: iwasakil@umkc.edu.
authors.forename: Laura R
authors.initials: LR
authors.lastname: Iwasaki
mesh_terms: D001732:Bite Force; D004576:Electromyography / Q000379:methods; D004777:Environment; D005260:Female; D006801:Humans; D007568:Jaw / Q000502:physiology*; D008297:Male; D008406:Masseter Muscle / Q000502:physiology*; D008410:Masticatory Muscles / Q000502:physiology; D010865:Pilot Projects; D012727:Sex Characteristics; D013703:Temporal Muscle / Q000502:physiology*; D055815:Young Adult
keywords: Duty time; Electromyography; Environmental sampling; Masticatory muscles; Sex differences