Exercise 3: Skeletal Muscle

What was exercise 3

skeletal muscle physiology

What was the objective

to determine the electrical activity of the forearm muscles and clench force under different conditions

Surface EMG was used to

hand dynamometer was used to

• measure the electrical activity of the forearm muscles

• To measure clench force

The flexor muscles of the forearm allow

allow for the development of tension during a clench, and for a decrease in the angle of wrist

Explain the two strategies used to increase force generated by whole muscle

1. action potential frequency in motor neurons are increased

2. additional motor units are activated (recruited)

What is the primary mechanism by which whole muscle regulates tension?

recruitment of motor units

-recruiting more motor units means more active skeletal muscle fibers and increased clench force

Action potentials in a motor neuron trigger

action potentials in all of the muscle fibers of a motor unit leading to contraction of he fibers

What were the different conditions in each objective

1. Relationship between EMG activity and clench force in the subjects dominant arm

   • the goal was to record EMG activity and clench force at a minimum of 4 intensity levels ranging from minimal to maximum (subject basiclly increased each force each time)

     2. Relationship between EMG and loss of tension during fatigue in the subjects dominant arm

        • examine the relationship between EMG signal and the abillity of the forearm muscles to produce tension for a period of time

     3. The effect of wrist position on maximum clench force and EMG activity in the subjects dominant arm

        • determine if wrist position of the wrists affect EMG acitivity and the maximum clench force achieved . The subject then changed wrist posotions to a 90 degree angle

is there a consistent relationship between EMG activity and clench force? What do you expect to happen to the EMG activity in the forearm muscles each time your subject is asked to clench harder

increase in motor neurons activated, increase in motor units recrited, leading to increase skeletal muscle activated , leading to increase EMG

Fatigue is defined as

a decrease abillity to generate force

Does the maximum force that ca be generated depend on position of the wrist?

Yes, muscles achieve maximum tension when they are at there optimal length (length tension relationship)

Where were the electrodes attached?

electrodes were placed on the subjects dominant forearm

-one electrode were placed on the ulnar side of the wrist

• another electrode was placed near the elbow to record EMG activity from the forearm muscles.

• this electrode placement will record EMG activity from several muscles of the forearm

In this experiment, what is EMG a measurement or “readout” of (be explicit about the physiological process EMG is representing and how it is different from clench force, below).

A surface EMG is used to measure the electrical activity of the forearm muscles by detecting the action potential train in muscle fibers. As the action potential propagates along the motor neurons to stimulate the muscle fibers, the resulting electrical activity is picked up by the electrodes. This allows EMG to measure the neural activation of the muscle fibers, while clench force quantifies the physical strength generated by the muscle contractions. EMG detects electrical signals from muscle activity , whereas clench force measures the mechanical output of these contractions.

In this experiment, what is clench force a measurement or “readout” of (again, be explicit about the physiological process clench force is representing, and how it is different from EMG above).

Clench force is a measure of the force produced by skeletal muscles during contraction, reflecting the strength that the forearm muscles generate when activated. The tension within a muscle is regulated by the recruitment of motor units, so recruiting more motor units leads to more active muscle fibers, leading to an increase in clench force. While EMG measures the neural activation and muscle fiber recruitment, it does not measure the force being generated. Clench force measures the tension the muscle creates during a contraction. EMG measures the electrical signals related to muscle activation, while clench force measures the physical strength generated by the muscle.

1. Describe the length-tension relationship in skeletal muscle in your own words. 

The length-tension relationship in skeletal muscle refers to the relationship between the length of a muscle and the amount of tension it can generate during contraction. Muscles produce maximum tension when they are at their optimal length. When the muscle is stretched beyond this optimal length or shortened too much the amount of tension it can generate decreases. Stretching or shortening the muscle from this optimal length results in a decrease in force generation due to reduced cross-bridge formation.

What does a students T-test allow you to determine

the probability of getting the difference in means you measured, in a samply of yur size, by chance (if null hypothesis were true)

if P=O what does this tell you

there is a 0% probability that the difference in means you observed was due to chance

If P=1 what does this tell you

there is a 100& probabillity that the difference in means you observed as due to chance

1.  Write a significance statement (full and thorough sentence) reporting the effect of wrist position on mean EMG (mV). Please refer to Scientific Writing Tutorial on Statistics.

If the p value was below 0.05

There is no significant difference between mean EMG in straight and flexed position