THE INFLUENCE OF RESISTANCE AND AEROBIC TRAINING ON MOTOR UNIT CONTROL PROPERTIES DURING AN ISOMETRIC TRAPEZOID MUSCLE ACTION AT 70% OF MAXIMAL VOLUNTARY CONTRACTION
Elizabeth C. Lewis1, Jeremy M. Harmening2, Emily E. Teefey2, & Trent J. Herda2; 1Augustana College, Sioux Falls, SD; 2University of Kansas, Lawrence, KS
PURPOSE: The purpose of this study was to examine motor unit (MU) control strategies of the vastus lateralis (VL) between resistance trained (RT) versus aerobically trained (AT) individuals. METHODS: Five RT (5 males; age = 25 ± 4 yrs, body mass = 96 ± 20 kg) and 5 AT (2 males and 3 females; age = 19 ± 1 yrs, body mass = 56 ± 10 kg) volunteered for this study. The RT individuals performed 4 - 8 h∙wk-1 of resistance training and could back squat ≥ twice their body weight (207.5 ± 27.5 kg). The AT individuals performed 7 - 10 h∙wk-1 of running with an average distanced run of 61 ± 15 miles h∙wk-1. Electromyography (EMG) sensor (Delsys, Boston, MA) was placed over the VL. Each participant completed 3 isometric maximal voluntary contractions (MVC). The isometric trapezoid muscle action at 70% MVC was calculated from the highest MVC. For the isometric trapezoid muscle action, the force was increased at a rate of 10% MVC/s to the deserved force level for 12 s followed by a decrease of 10% MVC/s back to baseline. Decomposition techniques were applied to the surface EMG signals to extract action potentials and the firing events of single MUs. For each MU, the recruitment (REC) and derecruitment (DEREC) thresholds and firing rates at recruitment (IFR) and peak firing rates (PFR) were calculated. Linear regressions were performed on the IFR and PFR versus REC and the REC versus the DEREC. Statistical procedures were performed on the linear regression coefficients to examine possible differences between the RT and AT. RESULTS: All relationships were significant with the R2 ranging from 0.40 to 0.75. For IFR and PFR versus REC relationships, there were no significant differences (P > 0.05) between slopes for the RT (mean ± SE, -0.113 ± 0.010, -0.298 ± 0.024) and AT (-0.114 ± 0.008, -0.311 ± 0.017). In contrast, the Y intercept for the PFR versus REC for the AT (32.4 ± 0.791) was greater (P < 0.05) than the RT (29.8 ± 0.978). For the DEREC versus REC, the RT (1.13 ± 0.051) had a significantly greater slope (P < 0.05) than the AT (0.77 ± 0.034). CONCLUSION: The data from the present study indicated within muscle differences between individuals as a function of training status. The AT had greater peak firing rates across the force spectrum (i.e., greater Y intercept value) than the RT individuals. In addition, the RT individuals tended to derecruit MUs at higher force levels (i.e., greater slope value) than initial recruit force levels in comparison to the AT individuals and, thus, suggesting there was greater MU potentiation in the RT individuals.
Lewis, EC; Harmening, JM; Teefey, EE; and Herda, TJ
"THE INFLUENCE OF RESISTANCE AND AEROBIC TRAINING ON MOTOR UNIT CONTROL PROPERTIES DURING AN ISOMETRIC TRAPEZOID MUSCLE ACTION AT 70% OF MAXIMAL VOLUNTARY CONTRACTION,"
International Journal of Exercise Science: Conference Proceedings: Vol. 11
, Article 13.
Available at: http://digitalcommons.wku.edu/ijesab/vol11/iss1/13
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