Activity of a muscle with multiple fibres


I’m seeking for a way to estimate the activity of a muscle that has multiple fibres. Do I have to make an average of the activity in each fibre, or I must use a ratio of the distinct sums of muscles forces on muscle strength (e.g. sum(F1, F2, F3) / sum(Strength1, Strength2, Strength3)) ?

Thank you.


Hi Pierre,

I would usualy take the max of the fiber’s actvity for the muscle. If you prefer the average method I think taking the average of the activity of each fiber is ok. As i recall lots of muscles modelled with multiple fibers have the same strength for all the fibers anyway.

The choice of the method also depends on what you want to do with the data. If for example you want to compare it to an other data set it is good to have it defined in a similar way.

Best regards, Sylvain.

Hi Sylvain,

If you take the max of the fiber’s activity, you do not take into account the whole muscle, but rather one part of the muscle, right ?


I think that really depends of the goal of your study. Taking the max of all the fibers will be good for comparing to EMG. It can also be good for ergonomic studies where high activity is linked to fatige and discomfort (in that case even if only one part of the muscle is highly activated it still brings discomfort).

But that’s maybe not what you want… taking the average is also fine if that fits you purpose. It will indeed take all the fibers into account, but there may be an important gap between the lowest and highest activated fibers. Again depending on your study it could be relevant or not.

Hi Sylvain,

Thank you for your answer. I think that my interpretation of EMG signals was wrong. I should first study the EMG theory more deeply.



There are many exercises in building of muscles. It will indeed take all the fibres into account, but there may be an important gap between the lowest and highest activated fibres. That’s all great to know about.

Hi Sylvain,
if I want activation for caculating of muscle synergies, what’s your suggestion for converting of fibers activation to one muscle activation?

Hi Mehrdad,

I think this question relates to this post

Please see answers here.

Best regards