title: Acute changes in knee-extensors torque, fiber pennation, and tendon characteristics.
abstract: The aim of the current study was to examine the relationships between quadriceps torque, vastus lateralis pennation angle (theta), and patella tendon stiffness (K) at 07:45 and 17:45 h. Using short-duration static contractions, simultaneous recordings were made of vastus lateralis (VL) electromyograph (EMG), theta and patella tendon K. Peak isometric extension torque (Peak torque Ext(corr)) increased by 29.4+/-6.5% at a knee angle of 70 degrees (p=0.03) in the evening compared to the morning. In the contracted muscle, a 35.0+/-11.0% (p=0.02) time-of-day (TOD)-related change in theta (to a greater evening compared to morning theta) was observed. Morning and evening measures of theta were also made, both at rest and at a standardized force level (250 N), to separate architecture change effects from increased torque capacity effects. Significant increments in theta in both the resting muscle (13.0+/-5.1%, p=0.046) and during the standardized exertions (8.0+/-3.1%, p=0.04) were observed in the evening versus the morning. Increases in theta with TOD were significantly correlated with the 40% (p=0.018) decrease in K both during the standardized contractions (r=0.788, p<0.001) and at rest (r=0.77, p=0.026). These data show that TOD affects K and theta and that these two important factors involved in in-vivo muscle torque generation capacity are associated. The data also show that despite the potentially deleterious effects of the direction of the changes in both K and theta with TOD, peak torque Ext(corr) still shows a significant upward shift in the evening relative to the morning.
authors.affiliation: Centre for Rehabilitation and Human Performance Research, Directorate of Sport, University of Salford Manchester, Manchester, England. s.pearson@salford.ac.uk
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Pearson
authors.forename: Gladys N L
authors.initials: GN
authors.lastname: Onambele
mesh_terms: D000328:Adult; D002940:Circadian Rhythm; D004576:Electromyography; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000502:physiology; D010329:Patella / Q000033:anatomy & histology / Q000502:physiology; D013710:Tendons / Q000502:physiology*; D019415:Torque