EXAMINING MOTOR UNIT POTENTIATION OF THE VASTUS LATERALIS DURING AN ISOMETRIC TRAPEZOID MUSLCE ACTION AT 50% OF MAXIMAL VOLUNTARY CONTRACTION
Jonathan D. Miller1, Omar M. Rehman1, Lauren M. Marquess1,Michael A. Trevino1, Eric M. Mosier1, and Trent J. Herda1. 1University of Kansas, Lawrence, KS; e-mail: email@example.com
Analysis of motor unit action potential trains (MUAPT) during submaximal isometric trapezoid muscle actions in the first dorsal interosseous (FDI) and tibialis anterior (TA) muscles have indicated that motor unit (MU) firing rates are typically lower at derecruitment (DEREC) than at recruitment (REC). In addition, the MUs of these muscles tended to DEREC at higher forces than REC. This phenomenon is a result of increased MU twitch forces (potentiation). PURPOSE: The purpose of this study was to investigate potentiation in the VL. METHODS: Twenty-three healthy subjects (mean ± SD: age = 21±3 yrs; height = 174±10 cm; mass = 75±20 kg) participated in this study. Each subject completed a 22-s isometric trapezoid contraction of the leg extensors at 50% maximal voluntary contraction with electromyographic (EMG) signals recorded from the VL. The EMG signals were decomposed into individual MUAPTs. For each MU, 4 parameters were extracted from the firing rate data: (1) the REC threshold (expressed as a percentage of MVC [%MVC]), (2) the DEREC threshold (%MVC), (3) firing rate at REC (FRREC, pulses per second [pps]), and (4) firing rate at DEREC (FRDEREC, pps). Linear regressions were performed on the DEREC vs. REC relationships and the difference between FRREC and FRDEREC (FRDEREC – FRREC, [ΔFR]) vs. FRREC relationships for each subject. Slope, y-intercept, and r values were calculated for both relationships and each subject. RESULTS: For the DEREC vs. REC relationships, all relationships were significant (P < 0.05, r = 0.57 – 0.99) and the mean (± SD) slope and y-intercept were 1.18 ± 0.43 DEREC/REC and -3.11 ± 10.9 DEREC, respectively. Thus, the lower threshold MUs were DEREC at lower forces than REC with the inverse being true for the highest threshold MUs. For the ΔFR vs. FRREC relationships, 15 of the 23 relationships were significant (R = 0.00 – -0.94) and the mean (± SD) slope and y-intercept were -0.80 ± 0.59 ΔFR/ FRREC and 7.67 ± 6.11 ΔFR, respectively. The majority of MUs decomposed in the present study had a positive ΔFR with this effect being more pronounced in higher threshold MUs. CONCLUSIONS: In the present study, MUs were reported to have lower forces at DEREC than at REC and have slightly higher firing rates at DEREC than REC. Thus, potentiation was limited at DEREC for the VL unlike for the FDI and TA muscles.
Miller, JD; Rehman, OM; Marquess, LM; Trevino, MA; Mosier, EM; and Herda, TJ
"EXAMINING MOTOR UNIT POTENTIATION OF THE VASTUS LATERALIS DURING AN ISOMETRIC TRAPEZOID MUSLCE ACTION AT 50% OF MAXIMAL VOLUNTARY CONTRACTION,"
International Journal of Exercise Science: Conference Proceedings:
3, Article 12.
Available at: http://digitalcommons.wku.edu/ijesab/vol11/iss3/12
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