Inverse dynamics are quite complicate and time consuming. So I would prefer for a rough estimation a method using EMG and perhaps cross section determination using MRI. Any suggestions?
Hi,
Alhough the relationship is not linear, you can use Root Mean Square value of EMG obtained at 100% Maximal Voluntary Contraction to estimate muscle force (i.e. by scaling RMS signal value of sEMG signal to this value)
Is this directly indicative of the force in Newton or must I relate this somehow to the cross section of the muscle?
well, in general it is used to estimate relative force of the maximal voluntary contraction value. I think that, if you can measure the 100% Maximal voluntary contraction value in newtons, you can use RMS value of the surface EMG signal to estimate applied force in newtons.
So, I am interested in estimating e.g. thigh muscles. Using an isometric dynamometer I could measure the max. moment at maximal voluntary contraction. From that the total quadriceps force could be calculated. However, there still remains the question how this force distributes to the single components of the quad. Could this be estimated be sEMG of the vasti etc. values?
Yes, this would be tough.. Even if proportion of muscle components to the force do not change - which would depend on movement and force level- , there still remains the question of finding at least proportions at the 100% MVC level contraction. multiple sEMG recordings can not alone give force proportions if you measure total force of multiple muscles in action. Distribution problem goes to biomechanics -as you have mentioned at the start-.
Hi, I am not a biomechanic person. But I am also interested in estimating muscle forces or stress generated while walking, swinging arms and legs.
Amplitude of EMG signals is not proportional to the muscle force. In particular, if the muslce length is long and muscle is not agonist, we can easily observe the nonlinearity. Generally, if the linearity is satisfied, F = G * PCSA * NEMG. G(gain) and PCSA(N/m^2) are known values at several literatures. So we can predict the muscle force. However, I think validation is always needed case by case.
Never use absolute values of EMG measurements, since it depends on very much factors (Position, fatique, Distance ..) Relative to "maximal voluntary contraction" is a standard value for measurings, but maximum is very individual.
Lutz,
Your idea of using a dynomometer to measure total extension moment, and then use EMG to "distribute" the loading is, I believe, similar to the approach used by many biomechanical models (OpenSIM etc...). They calculate a moment from inverse dynamics and then distribute the load according to predictive equations based on EMG. If you are able to do something like this, it could be a useful approach, however, as mentioned already, individuals vary greatly in how they recruit their muscles to achieve a joint moment. If you are studying intra-subject difference, this isn't as much of an issue, but inter-subject difference might be difficult to detect.
Hi everyone.
Could you please suggest me an article who describes the methodological procedures to obtain the Root Mean Square Value? Thank you.
Although EMG could measure force production within a subject, Mechanmogram/vibromyogram (MMG/VMG) may be a better discriminator of absolute muscle force values. Matheson et al.
Matheson, G.O.; Maffey-Ward, L.; Mooney, M.; Ladly, K.; Fung, T.; Zhang, Y.T. 1997. Vibromyography as a quantitative measure of muscle force production, Scandinavian journal of rehabilitation medicine 29, 29-35.
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