The influence of electrode shift over the innervation zone and normalization on the electromyographic amplitude and mean power frequency versus isometric torque relationships for the vastus medialis muscle

O2 uptake (V˙o 2) kinetics and electromyographic (EMG) activity from the vastus medialis, rectus femoris, biceps femoris, and medial gastrocnemius muscles were studied during constant-load concentric and eccentric cycling. Six healthy men performed transitions from baseline to high-intensity eccentric (HE) exercise and to high-intensity (HC), moderate-intensity (MC), and low-intensity (LC) concentric exercise. For HE and HC exercise, absolute work rate was equivalent. For HE and LC exercise,V˙o 2 was equivalent.V˙o 2 data were fit by a two- or three-component exponential model. Surface EMG was recorded during the last 12 s of each minute of exercise to obtain integrated EMG and mean power frequency. Only in the HC exercise didV˙o 2 increase progressively with evidence of a slow component ( phase 3), and only in HC exercise was there evidence of a coincident increase with time in integrated EMG of the vastus medialis and rectus femoris muscles ( P < 0.05) with no change in mean power frequency. The phase 2time constant was slower in HC [24.0 ± 1.7 (SE) s] than in HE (14.7 ± 2.8 s) and LC (16.7 ± 2.2 s) exercise, while it was not different from MC exercise (20.6 ± 2.1 s). These results show that the rate of increase inV˙o 2 at the onset of exercise was not different between HE and LC exercise, where the metabolic demand was similar, but both had significantly faster kinetics forV˙o 2 than HC exercise. TheV˙o 2 slow component might be related to increased muscle activation, which is a function of metabolic demand and not absolute work rate.

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Gender Comparisons of Mechanomyographic Amplitude and Mean Power Frequency versus Isometric Torque Relationships

Journal of Applied Biomechanics ◽

10.1123/jab.21.1.96 ◽

2005 ◽

Vol 21 (1) ◽

pp. 96-109 ◽

Cited By ~ 15

Author(s):

Travis W. Beck ◽

Terry J. Housh ◽

Glen O. Johnson ◽

Joseph P. Weir ◽

Joel T. Cramer ◽

...

Keyword(s):

Biceps Brachii ◽

Maximum Voluntary Contraction ◽

Fluid Pressure ◽

Mean Power ◽

Mean Power Frequency ◽

Power Frequency ◽

Isometric Torque ◽

Muscle Actions ◽

Best Fit ◽

Isometric Muscle

This study compared the patterns of mechanomyographic (MMG) amplitude and mean power frequency vs. torque relationships in men and women during isometric muscle actions of the biceps brachii. Seven men (mean age 23.9 ± 3.5 yrs) and 8 women (mean 21.0 ± 1.3 yrs) performed submaximal to maximal isometric muscle actions of the dominant forearm flexors. Following determination of the isometric maximum voluntary contraction (MVC), they randomly performed submaximal step muscle actions in 10% increments from 10% to 90% MVC. Polynomial regression analyses indicated that the MMG amplitude vs. isometric torque relationship for the men was best fit with a cubic model (R2= 0.983), where MMG amplitude increased slightly from 10% to 20% MVC, increased rapidly from 20% to 80% MVC, and plateaued from 80% to 100% MVC. For the women, MMG amplitude increased linearly (r2= 0.949) from 10% to 100% MVC. Linear models also provided the best fit for the MMG mean power frequency vs. isometric torque relationship in both the men (r2= 0.813) and women (r2= 0.578). The results demonstrated gender differences in the MMG amplitude vs. isometric torque relationship, but similar torque-related patterns for MMG mean power frequency. These findings suggested that the plateau in MMG amplitude at high levels of isometric torque production for the biceps brachii in the men, but not the women, may have been due to greater isometric torque, muscle stiffness, and/or intramuscular fluid pressure in the men, rather than to differences in motor unit activation strategies for modulating isometric torque production.

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