title: Caffeine-induced increase in voluntary activation and strength of the quadriceps muscle during isometric, concentric and eccentric contractions.
abstract: This study investigated effects of caffeine ingestion (8 mg/kg) on maximum voluntary torque (MVT) and voluntary activation of the quadriceps during isometric, concentric and eccentric contractions. Fourteen subjects ingested caffeine and placebo in a randomized, controlled, counterbalanced, double-blind crossover design. Neuromuscular tests were performed before and 1 h after oral caffeine and placebo intake. MVTs were measured and the interpolated twitch technique was applied during isometric, concentric and eccentric contractions to assess voluntary activation. Furthermore, normalized root mean square of the EMG signal was calculated and evoked spinal reflex responses (H-reflex evoked at rest and during weak isometric voluntary contraction) as well as twitch torques were analyzed. Caffeine increased MVT by 26.4 N m (95%CI: 9.3-43.5 N m, P = 0.004), 22.5 N m (95%CI: 3.1-42.0 N m, P = 0.025) and 22.5 N m (95%CI: 2.2-42.7 N m, P = 0.032) for isometric, concentric and eccentric contractions. Strength enhancements were associated with increases in voluntary activation. Explosive voluntary strength and voluntary activation at the onset of contraction were significantly increased following caffeine ingestion. Changes in spinal reflex responses and at the muscle level were not observed. Data suggest that caffeine ingestion induced an acute increase in voluntary activation that was responsible for the increased strength regardless of the contraction mode.
authors.affiliation: Department of Exercise Science, University of Rostock, Ulmenstrasse 69, 18057 Rostock, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Behrens
authors.affiliation: Department of Orthopaedics, University Medicine Rostock, Doberaner Strasse 142, 18057 Rostock, Germany.
authors.forename: Anett
authors.initials: A
authors.lastname: Mau-Moeller
authors.affiliation: 1] Department of Exercise Science, University of Rostock, Ulmenstrasse 69, 18057 Rostock, Germany [2] Institute of Exercise Physiology and Public Health, Trotzenburger Weg 15, 18057 Rostock, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Weippert
authors.affiliation: Department of Exercise Science, University of Rostock, Ulmenstrasse 69, 18057 Rostock, Germany.
authors.forename: Josefin
authors.initials: J
authors.lastname: Fuhrmann
authors.affiliation: Department of Orthopaedics, University Medicine Rostock, Doberaner Strasse 142, 18057 Rostock, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Wegner
authors.affiliation: Department of Orthopaedics, University Medicine Rostock, Doberaner Strasse 142, 18057 Rostock, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Skripitz
authors.affiliation: Department of Orthopaedics, University Medicine Rostock, Doberaner Strasse 142, 18057 Rostock, Germany.
authors.forename: Rainer
authors.initials: R
authors.lastname: Bader
authors.affiliation: Department of Exercise Science, University of Rostock, Ulmenstrasse 69, 18057 Rostock, Germany.
authors.forename: Sven
authors.initials: S
authors.lastname: Bruhn
mesh_terms: D000328:Adult; D002110:Caffeine / Q000494:pharmacology*; D004576:Electromyography; D005071:Evoked Potentials / Q000187:drug effects; D005260:Female; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D053580:Muscle Strength / Q000187:drug effects*; D052097:Quadriceps Muscle / Q000187:drug effects* / Q000502:physiology*; D055815:Young Adult
chemical_list: D002110:Caffeine