Lab 4 - contractility and fatigue of skeletal muscle Flashcards
what is the objective of lab 4
to observe and measure muscle contraction and understand the effect of fatigue on muscle strength in dominant and non-dominant hands
How will EMG activity be related to grip strength?
EMG will plot the the maximum grip strength as a function of the area under the absolute integral of the EMG activity during muscle contraction
true or false: the strength of the straited muscle contraction is directly proportional to the amount of electrical activity in the muscle, therefore the raw data is sufficient to quantify the amount of electrical activity in the muscle
FALSE
although it is true that strength of contraction is directly proportional to electrical activity, the raw data is not sufficient to interpret the amount of electricity generated.
need to calculate the absolute values of the EMG contraction amplitude s
L4 Equipment
-regular IWorx stuff
- laptop
- disposable electrodes
- FT-220 hand Dynamometer (squeezy thing)
- bathroom scale and large pail (5-10L) to calibrate dynamometer
-string
-ruler
L4 what is the correct placement of the EMG electrodes
FOREARM
red (+1 input) : just below inner elbow
black (-1 input) : mid forearm slightly medial
green (ground):wrist lightly medial
L4 E1&E3 procedure, results, analysis:
- procedure: subject sits with forearm resting on bench and dynamometer in hand. subject squeezes hand 4 times with increasing strength/intensity. repeat for opposite hand (mark which recording is dominant vs non-dominant)
-results:
EMG: top panel, erratic up and down lines for as long as the contraction lasts. increasing amplitude with increasing grip strength.
dynamometer: bottom panel. square curves for as long as the squeeze lasted. increasing amplitude with increased grip strength.
-analysis:
place cursors just before a contraction and just after.in the analysis window, record the “abs area” for the EMG absolute integral and record “V2-V1” for the force curve absolute integral.
repeat for all 4 strengths for both D and ND hand trials.
measure the circumference of the dominant and non-dominant forearms in cm (3 cm below the elbow)
L4 E2 & 4 procedure, results, analysis:
E2: EMG intensity and fatigue in D and ND hands.
-procedure: subject sits with arm resting on table and dynamometer in hand. subject squeezes as long as possible (until fatigue). when the muscle strength drops to below half the initial strength, stop the recording. repeat for ND hand
-results:
EMG (top): large initial spike that evens out relatively quickly and remains constant.
muscle force (bottom): large initial spike that decreases to below half gradually.
-data analysis: place cursors at the relaxation periods just before the contraction and just after half max amplitude.
record the maximum muscle force (V2-V1) for both D and ND arms
in the plot of the absolute integral (AI) of EMG activity and AI under force curve have a linear relationship
yes. The relationship increases linearly.
I.e. the relative amount of electricity causing the contraction is linearly proportional to the relative strength of the muscle.
why does the amplitude of the EMG and force curve increase with increased grip strength?
- spindle fibers fire more often with increased contraction strength
- more spindle fibers are recruited during a stronger contraction due to increased intensity of signals in the motor neuron
Is one of the forearms stronger than the other? how do you know?
yes. the dominant arm is stronger than the other. this is known because the maximum force of the D hand was 50% higher than the max force for ND hand
is there a relationship between forearm circumference and relative strength? if so, what is it
YES
increased circumference = more muscle fibers to recruit which results in increased strength.
the D arm is usually larger
how does the time to fatigue to half-strength in the D forearm compare to the ND forearm?
D more resistant to fatigue because more daily endurance tasks improve fatigue resistance
