title: Increased rate of force development and neural drive of human skeletal muscle following resistance training.
abstract: The maximal rate of rise in muscle force [rate of force development (RFD)] has important functional consequences as it determines the force that can be generated in the early phase of muscle contraction (0-200 ms). The present study examined the effect of resistance training on contractile RFD and efferent motor outflow ("neural drive") during maximal muscle contraction. Contractile RFD (slope of force-time curve), impulse (time-integrated force), electromyography (EMG) signal amplitude (mean average voltage), and rate of EMG rise (slope of EMG-time curve) were determined (1-kHz sampling rate) during maximal isometric muscle contraction (quadriceps femoris) in 15 male subjects before and after 14 wk of heavy-resistance strength training (38 sessions). Maximal isometric muscle strength [maximal voluntary contraction (MVC)] increased from 291.1 +/- 9.8 to 339.0 +/- 10.2 N. m after training. Contractile RFD determined within time intervals of 30, 50, 100, and 200 ms relative to onset of contraction increased from 1,601 +/- 117 to 2,020 +/- 119 (P < 0.05), 1,802 +/- 121 to 2,201 +/- 106 (P < 0.01), 1,543 +/- 83 to 1,806 +/- 69 (P < 0.01), and 1,141 +/- 45 to 1,363 +/- 44 N. m. s(-1) (P < 0.01), respectively. Corresponding increases were observed in contractile impulse (P < 0.01-0.05). When normalized relative to MVC, contractile RFD increased 15% after training (at zero to one-sixth MVC; P < 0.05). Furthermore, muscle EMG increased (P < 0.01-0.05) 22-143% (mean average voltage) and 41-106% (rate of EMG rise) in the early contraction phase (0-200 ms). In conclusion, increases in explosive muscle strength (contractile RFD and impulse) were observed after heavy-resistance strength training. These findings could be explained by an enhanced neural drive, as evidenced by marked increases in EMG signal amplitude and rate of EMG rise in the early phase of muscle contraction.
authors.affiliation: Department of Neurophysiology, Institute of Medical Physiology, Bispebjerg Hospital, University of Copenhagen, DK-2200 Copenhagen, Denmark. p.aagaard@mfi.ku.dk
authors.forename: Per
authors.initials: P
authors.lastname: Aagaard
authors.forename: Erik B
authors.initials: EB
authors.lastname: Simonsen
authors.forename: Jesper L
authors.initials: JL
authors.lastname: Andersen
authors.forename: Peter
authors.initials: P
authors.lastname: Magnusson
authors.forename: Poul
authors.initials: P
authors.lastname: Dyhre-Poulsen
mesh_terms: D000328:Adult; D004525:Efferent Pathways / Q000502:physiology; D004576:Electromyography; D006801:Humans; D007866:Leg; D008297:Male; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000294:innervation* / Q000502:physiology*; D009424:Nervous System Physiological Phenomena; D010806:Physical Education and Training; D014891:Weight Lifting