Rectus Abdominis Activation Study

7/29/2019 Rectus Abdominis Activation Study

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Known as abs or six-pack

Paired muscle running verticallyon each side of the anterior wall ofthe human abdomen

an important postural muscle. It isresponsible for flexing the lumbarspine when doing a crunch

assists with breathing and plays an

important role in respiration whenforcefully exhaling

helps in keeping the internalorgans intact and in creating intra-abdominal pressure, such as when

exercising or lifting heavy weights


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The maximum activation of the upperrectus abdominis during a sit-up ( from 0to 75) is when the trunk is flexed past 30with respect to the ground.


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Multiple papers have concluded that the exerciseswhich involve the greatest [rectus abdominis]

muscle activity are those which flex the trunk

forward against gravity from the supine position.Sternlicht, Rugg. The Electromyographic Analysis of Abdominal MuscleActivity Using Portable Abdominal Exercise Devicesand a TraditionalCrunch

For the exercises tested, there were no differences

between the upper and lower portions of the rectusabdominis muscle when EMG signals were

normalized and posture was controlled. Lehman, G. J. and McGill,S. M. (2001). Quantification of the Differences in Electromyographic Activity Magnitude between the Upper and Lower

Portions of the Rectus Abdominis Muscle During Selected Trunk Exercises. Physical Therapy, 81(5), 1096-110.


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Sit ups. Legs flexed 45 degrees. Legs supported. M. Flint. AnElectromyographic Comparison of the Function of the Iliacus and the Rectus

Abdominus Muscle

Flint study: Greatest activation of upper rectus is whentrunk angle ranges from 15 to 45 degrees and lower rectuswhen trunk angle is between 10 to 60 degrees


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Compare mean EMG values between the upperrectus abdominis and lower rectus abdominis todetermine if there is a difference between mean

activation of the two during the course of a sit-up(trunk angle 0 to 75 )

Pinpoint an angle (orrange of angles) of the

trunk during a sit-upwherein the upper rectusis maximally activated


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Recruited eight individuals with low abdominal fat

N=11 6 males, 2 females

B0dy fat percentage Mean (females): 24.85

Standard deviation: 0.353

Mean (males): 12.99

Standard deviation: 4.87

Our test subjectswere within theAthlete/Fitnessrange for body fatpercentage


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Wireless EMG Placement

Upper Rectus: 3 cmlateral tomidline/umbilicus and 2cm superior

Lower rectus:

3 cm lateral to theumbilicus and 2 cminferior to the umbilicus

Ground: HipBone


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All muscle activity will be reported as apercentage of Maximum Voluntary

Contraction (%MVC) 60 Hz notch filtering 600 Hz sampling rate with 16 bit resolution Rectify raw EMG signals then use a low pass

filter to remove artifacts and noise


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Perform sit-up with knees bent 45 degrees, feet supported

Hold the sit-up at each angle(15increments from 0 to 75) for a

maximum of 10 seconds,minimum of 2 seconds 2 minutes rest in between sit-ups

to avoid fatigue effects Repeat sit-up while holding 6.4lb

weight to upper chest to induce

maximal voluntary contractionduring the isometric sit-up.


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Legs bent, feet supported.Subject is doing a set to achieve maximumvoluntary contraction.

Actual electrodeplacement.


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Top: Raw data result of sampletest subject.

Bottom: Low-pass Filtered datafrom raw EMG (above) at 30

degrees

Used low-pass filtereddata for all calculations


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Mean activation of subjects during a sit up. Maximum activation ofupper rectus at 15 degrees. Maximum activation of lower rectus at 30

degrees.

Standarddeviations arehigh


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P values comparing the activation of the upper and the lower rectusabdominis at each angle is greater than =0.05, therefore we cannot rejectour null hypothesis that there is no difference between the activation of theupper and lower rectus abdominis.


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One way unstacked ANOVA (in Minitab) results for

lower and upper rectus activation at angles 0,15 ,30

,45, 60 ,75 shows p-value results of less than 0.05.

We CAN reject the null hypothesis and say that atleast 2 of the sample populations (ie: the muscleactivation means at the 6 different angles) comparedare different.

Next question: Which muscle activation mean at thedifferent angles for the upper and lower rectus areactually different? How are they different?


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Did a Tukeys Multiple Comparisons Test (5% error). Recap: Experimental data showed max activation at 15 for the upper rectus abdominis and 30 for the

lower rectus abdominisAfter theTukeys test: Upper rectus mean activation at 0 is different and less than the mean activation at 15 and 30 but the

same when compared to activation at 45 , 60 and 75 . We also CANNOT say that mean activation at15 of the upper rectus is different and higher than the mean activation at 30 , 45 , 60 and 75 .

Lower rectus mean activation at 0 is different and less than the mean activation at 15 and 30 but thesame when compared to activation at 45 , 60 and 75 . We also CANNOT say that mean activation at

30

of the lower rectus is different and higher than the mean activation at 15,30

, 45

,and 60

.The mean activation of the lower rectus at 30 was found to be different and greater than the mean

activation at 75. (from ANOVA/TukeyMultiple Comparisons test results)


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We cannot reject the possibility that the lower andrectus abdominis activation is the same.

Experimental data does not correspond with ourhypothesis that the max. upper rectus abdominis

activation is past 30. At first glance it seems tosomewhat follow the results of the Flint study. Even though it seems that our data shows that the

max. activation of upper and lower rectus is at 15 and30respectively, we cannot definitively say that mean

activations at these angles respectively are differentand higher than the other angles that it is comparedto (except 0 ).


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Clothing interfered with EMG reading Subjects anticipated next movement Extraneous movement of subjects

Artifacts from heavy breathing and/or heart rate (noteffectively filtered out by low pass filter) Subjects held weight incorrectly (not at upper chest) Subjects were not completely still during rest period EMG signal is hard to compare across subjects and is

not completely representative of what the actualmuscle is doing

Not enough test subjects for a robust study


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Subject stays completely still during restperiod

Subject holds weight to upper portion ofchest Recruit more test subjects for better test

results and more robust statistical data


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Break-up/re-write a hypothesis that will beeasier to test.

In our case:-Is the activation of the lower rectus

different from the upper rectus abdominis?-What is the angle where maximum

activation of the muscle occurs?-Is this maximum activation found at aparticular angle actually different and greaterthan the activation at other angles?


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Better understanding of abdominal muscle activation Data is useful for future development of abdominal

exercises and machines that can achieve the greatestmuscle activation with the least possibility of workand injury to the other muscles

Since we CAN conclude that we cant reject thepossibility that the lower and upper rectus abdominismuscle activations are the same, its possible thatthere is actually no need to develop preferentialexercise treatments for these 2 parts of the rectusabdominis during an abdominal exercise

EMG signal is mostly useful for studies that deal withmuscle activation timing

Rectus Abdominis Activation Study

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