Dear Alexandre,

Thank you for your suggestion. Since the lifting task involved lifting a box from the floor to the shoulder height, do you mean that we need to measure the isometric MVC EMG for each 10 degrees of flexion or extension of trunk, hip, knee and ankle? Even if we measure all those EMG values, which one should be used for normalization?

I wonder whether we can use the resting EMG during quiet standing as the reference EMG value and then use it to normalize the muscle EMG signals during the repetitive lifting task. Will this work? However, one may argue that the resting EMG of the subjects may not be the same.

What do you think?   

Dear Arnold,

I agree with Alexandre. Perhaps you need to provide sufficient warm-up before taking the EMG output of an MVC, to avoid the pheomenon of post-activation potentiation which can be quite apparent http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3164001/ . If you are looking at many muscles together, there is probably the phenomenon of load-sharing taking place, which does not allow for a simultaneous max contraction of all muscles involved within the sunergistic contraction https://www.researchgate.net/publication/282721665_A_comparative_study_of_load_sharing_among_back_and_leg_muscles_during_squat_and_half-kneeling_lifts .

Hope these explain your results so far.

George

Article A comparative study of load sharing among back and leg muscl...

Hey Arnold,

This is an interesting problem that many researchers experience. In my opinion your problems come partially by the fact that your subjects perform isometric MVC and perform isotonic tasks with some loading involved. Changes in muscle length plus loading can definitely increase the registered EMG.

I agree with Alexandre, you may have a more appropriate MVC if you test joints at the optimal length, and the use of some stabilization device is required for maximizing the consistency of the method across subjects. Also, pay attention to the fact that MVCs may be underestimated if no habituation to the task is provided (check this paper: http://link.springer.com/article/10.1007%2Fs00421-010-1599-z). Moreover, verbal encouragement, time of the day the test is conducted, room temperature and other factors can influence your MVC measurement.

Let us know if this helps.

Hey Arnold, as Anderson George and Alexandre said, each muscle should be tested for MVC reference values in different positions, I think, you can use as a hint the SENIAM webpage, where within Recommendations/Sensor locations you will find sites for al lthe muscles listed with you - you will also find there something called 'Clinical Test', which the testing position (isometric contraction is SENIAM recommendation). You might like to review other methods then MVC, there is a comparison available online - see the link. 

https://repositorio-aberto.up.pt/bitstream/10216/64430/2/67854.pdf

Hi Arnold,

While the best pre-study set up may require a number of MVICs at a number of joint angles, you are likely facing an issue in which you have data that has been collected and processed and interpreting that data in which the value is greater than a "maximal" contraction results in some problems.  There are alternative methods by which you can  normalize EMG data given the differences in activation of a dynamic versus isometric contraction.  Below is a study in which the EMG activity was normalized to the maximum voltage across all trials during a dynamic movement (walking in different conditions).  While not normalized to an MVIC, we had the same issues with our EMG being greater than maximum.

I hope this helps.

Article Alterations in neuromuscular activation patterns in short-le...

Dear Alexamdre, George, Anderson, Krzysztof and Doug,

Thank you so much for your suggestions. I will study each of your suggestions.

Thanks again.

Arnold

Hi Arnold,

Passing the 100% value can tell that subjects did not got maximum muscle activity in the isometric position. For some exercise and position it is hard to get MVC if you are not trained enough. In patients with pain and other symptoms, it is very hard to have them fully contract their muscles since they are using a protection mechanics by avoiding from joint motion.

If you are collecting data on healthy subjects, you need to change your exercise, add more load to the MVC trail or choose a different joint position for maximum results.

In case you are dealing with subject with pain, I would recommend to use the subMVC. In this case you will get results higher than 100%, but those are expected.

I hope if helps.

Thanks,

Dr. Haddas

Hey Arnold,

I have encounted the same problem once, but I consider it is ok and it may not influence your results.

As we all konw, there is a specific method for each muscle to measure MVIV, and we use this acquired MVIC to normalize the EMG measured during exercise. however, how can we know whether the acquired MVIC is the most largest activity for the target muscle? because it is greater than the figure measured during exercise? or because we acquired it by the way recommended from articles and books or that the target muscle can recruit most motor units?

I do not think we can measure the true MVIC of a target muscle using instrument, and of course, I do not mean the acquired MVIC is useless. It is still useful in our research, but we need to recognize the natural meaning of the acquired MVIC. It is a figure measured by instrument using a specific method, and the figure reflects the target muscle activity at a specific condition. Then we use the figure to nirmalize the same muscle activity in another condition.

Therefore, if the EMG is over 100% MVC value, do not worry, the only thing you need to notice is to use the same way to measure other data of target muscle, and make sure all data were normaloizd by the "MVIC" acquired in the same position.

I hope this helps.

Thanks.

Shutang HE