Why does EMG increase with force?

As muscle fibers become fatigued and produce less force, additional motor units are recruited to maintain a constant muscle force and flexor joint torque to maintain the isometric position. As a result, the EMG magnitude increases as the muscle fatigues.

How does force relate to EMG activity?

The amount of force a muscle produces when electrically activated by EMG depends on the current (and previous) state of that muscle. The force a muscle produces depends on its length, velocity of movement, and frequency.

Why does EMG amplitude increase when load increases?

EMG amplitude increases because there are more muscle fibers firing action potentials simultaneously, and each fiber contributes some force, in order to generate a total force equal to the load. At the maximum load, the EMG amplitude will be at its maximum as well.

Is there a linear relationship between EMG and muscle force?

Some guidelines are given for the interpretation of the electromyogram (EMG). In static isometric contractions there is, usually a linear, relationship between muscle force and smoothed rectified EMG (SRE). It should be considered, however, that most of the time several muscles are active simultaneously around a joint.

What is the relation between the grip force and the EMG signal?

The EMG activity will be related to the grip strength by plotting the maximum grip strength as a function the area under the absolute integral of the EMG activity during the muscle contraction.

What is the relationship between surface EMG amplitude and muscle forces?

E.m.g. potentials and contractile responses may both sum non-linearly at moderate to high force levels, but in such a way that the rectified surface e.m.g. is still approximately linearly related to the force produced by the muscle.

What happens when grip strength increases?

When grip strength increases. Action potential frequency increases, the number of active motor units increases.

What affects EMG amplitude?

The difficulty in relating amplitude of EMG to amplitude of force lies in the fact that although EMG may give a reliable measure of the volume of active motor units, many factors, including muscle length, velocity, and activation/deactivation kinetics will influence the force an active motor unit produces (Hof 1984;

What would increase the force generated by a muscle?

The force generated by a muscle depends on the number of actin and myosin cross-bridges formed; a larger number of cross-bridges results in a larger amount of force.

How a smooth increase in muscle force is produced?

Wave summation. How a smooth increase in muscle force is produced. Multiple motor unit summation. The phenomenon in which the contraction strength of a muscle increases, due to increased Ca2+ availability and enzyme efficiency during the warm-up.

Is there a linear relationship between the muscle activity EMG and the grip strength force )? How does the muscle force relate to the EMG activity?

Terms in this set (19) Is there a linear relationship between the absolute area under EMG signals and the absolute area under the muscle contraction force? This should be a fairly linear graph with an up-slope curve. The EMG should be less when grip strength is low, and higher as the grip increases.

What does increased motor unit amplitude mean?

In general, amplitude indicates muscle fiber density and not the motor unit territory. High MUAP amplitude, when isolated, is considered a nonspecific abnormality except when it is significantly increased (more than twice the upper normal limit); then, it indicates a neurogenic process.

Why does summation result in an increased force of contraction?

At the molecular level, summation occurs because the second stimulus triggers the release of more Ca++ ions, which become available to activate additional sarcomeres while the muscle is still contracting from the first stimulus. Summation results in greater contraction of the motor unit.

How does EMG measure muscle activity?

During the test, one or more small needles (also called electrodes) are inserted through the skin into the muscle. The electrical activity picked up by the electrodes is then displayed on an oscilloscope (a monitor that displays electrical activity in the form of waves).

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