title: In vivo vastus lateralis force-velocity relationship at the fascicle and muscle tendon unit level.
abstract: The force velocity relationship of in vivo human muscle fibers has often been derived from the torque-angular speed relationship during maximal voluntary isokinetic contractions. However, the assumption of a close association between joint performance and muscle mechanics is questionable. We aimed to determine the relationship between knee extension angular speeds, vastus lateralis fascicle and muscle tendon unit (MTU) shortening speeds, and maximal knee extensor force for the entire range of knee joint movement, for the isokinetic range, and for the ranges before, after and at peak torque occurrence, with different commonly used pre-loading conditions. Higher peak forces were observed when knee extensions were preceded by a pre-load, despite the similarity in fascicle shortening speeds. For the entire and the isokinetic range, MTU always shortened faster than fascicles, and this difference increased as joint speed increased. Interestingly, fascicle shortening velocities were greater before compared to after peak torque occurrence while the opposite happened at the MTU level. Assuming a close relationship between joint and fascicle dynamics results in an overestimation of muscle contractile component shortening velocity or force production at peak torque. The force velocity relationships obtained in vivo depend crucially on the test conditions, and the movement range used for analysis.
authors.affiliation: CAPES Foundation, Ministry of Education of Brazil, Brasília, DF 70040-020, Brazil; University of the State of Santa Catarina, Aquatic Biomechanics Research Laboratory, Brazil; University of Calgary, Human Performance Laboratory, Canada. Electronic address: heilianefontana@gmail.com.
authors.forename: Heiliane de Brito
authors.initials: Hde B
authors.lastname: Fontana
authors.affiliation: University of the State of Santa Catarina, Aquatic Biomechanics Research Laboratory, Brazil.
authors.forename: Helio
authors.initials: H
authors.lastname: Roesler
authors.affiliation: University of Calgary, Human Performance Laboratory, Canada.
authors.forename: Walter
authors.initials: W
authors.lastname: Herzog
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D052097:Quadriceps Muscle / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D013710:Tendons / Q000502:physiology*
keywords: Fascicle; Force–velocity relationship; Knee extension; Muscle mechanics; Muscle properties; Muscle tendon unit; Series elasticity; Vastus lateralis