title: Repetitive eccentric muscle contractions increase torque unsteadiness in the human triceps brachii.
abstract: Torque steadiness and low-frequency fatigue (LFF) were examined in the human triceps brachii after concentric or eccentric fatigue protocols. Healthy young males (n=17) performed either concentric or eccentric elbow extensor contractions until the eccentric maximal voluntary torque decreased to 75% of pre-fatigue for both (concentric and eccentric) protocols. The number of concentric contractions was greater than the number of eccentric contractions needed to induce the same 25% decrease in eccentric MVC torque (52.2+/-2.9 vs. 41.5+/-2.1 for the concentric and eccentric protocols, respectively, p<.01). The extent of peripheral fatigue was approximately 12% greater after the concentric compared to the eccentric protocol (twitch amplitude), whereas LFF (increase in double pulse torque/single pulse torque), was similar across protocols. Steadiness, or the ability for a subject to hold a submaximal isometric contraction, was approximately 20 % more impaired during the Ecc protocol (p=.052). Similarly, the EMG activity required to hold the torque steady was nearly 20% greater after the eccentric compared to concentric protocol. These findings support that task dependent eccentric contractions preferentially alter CNS control during a precision based steadiness task.
authors.affiliation: Neuroscience Department, College of Medicine, University of Toledo, Toledo, OH, USA.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Meszaros
authors.forename: Masaki
authors.initials: M
authors.lastname: Iguchi
authors.forename: Shuo-Hsiu
authors.initials: SH
authors.lastname: Chang
authors.forename: Richard K
authors.initials: RK
authors.lastname: Shields
mesh_terms: D000328:Adult; D001132:Arm; D004551:Elbow Joint; D004576:Electromyography; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D019415:Torque; D004561:Transcutaneous Electric Nerve Stimulation