Hello Ville! It does seem challenging to measure EMG activity during mountain biking. Which muscles are you including in the study and what are you measuring? Does your equipment allow for wireless communication between the sensors and the monitor? If not, I would suggest to stick some tape in the sensors and along the course of the wires to prevent them from moving. Even with such a solution, it would probably be worthwile to do some trial measurements during the biking to compare them with a "cleaner" signal obtained in more controlled activities. Although I have never dealt with EMG measurements in such an unstable activity, I would say that the vibrations will inevitably induce some contamination to the EMG signal.

Well we are planning at this point to measure some of these mm. oliquus internus abdominis, obliquus externus abdominis, multifidus, , erector spinaen lumbaric part and quadratus lumborum, not sure yet which muscles are the ones we should measure during mountain biking ( still writing theory for our thesis). We are planning to use some kind of tape.

 Hello Ville! I agree with the suggestion of Jose to stick some tape on the sensors to prevent them from moving. But another suggestion is to use a velcro strap around the sensors. This would help further anchor the electrodes to their proper positions since sweat could reduce the adhesiveness of the tape and might cause the sensors to move while pedaling and consequently affect your EMG measurements. 

Have you got any idea about what kind of EMG processing will be used, namely whether you will use data collected during a whole biking trail or only from specific points? I think it would be positive to take a few trial runs to see the best way of limiting signal interference, not necessarily with the study participants.

Hello Ville, I am sure Jose and Angelita suggestions are very useful, but I trouble you can not reduce vibration during the cycling, especially during real mountain biking. I think you need some simulations at the laboratory conditions. However, I am interesting in yours wireless work.

Dear Ville Hei,

we use the EMGs for temporal or spectral investigations of neuromuscular activation.

Two of my articles are useable for the chapter "material and methods" and an other article will be published soon. Our methodology is very easy for the treatment.

attached the abstracts. We are open for collaboration if you need a little help.

ABSTRACT: The purpose of this study was to compare O(2) uptake VO(2) and muscle electromyography activity kinetics during moderate and severe exercise to test the hypothesis of progressive recruitment of fast-twitch fibers in the explanation of the VO(2) slow component. After an incremental test to exhaustion, 7 trained cyclists (mean +/- SD, 61.4 +/- 4.2 ml x min(-1) x kg(- 1)) performed several square-wave transitions for 6 min at moderate and severe intensities on a bicycle ergometer. The (.)VO(2) response and the electrical activity (i.e., median power frequency, MDF) of the quadriceps vastus lateralis and vastus medialis of both lower limbs were measured continuously during exercise. After 2 to 3 min of exercise onset, MDF values increased similarly during moderate and severe exercise for almost all muscles whereas a (.)VO(2) slow component occurred during severe exercise. There was no relationship between the increase of MDF values and the magnitude of the (.)VO(2) slow component during the severe exercise. These results suggest that the origin of the slow component may not be due to the progressive recruitment of fast-twitch fibers.

Canadian journal of applied physiology = Revue canadienne de physiologie appliquée 01/2005; 29(6):758-72. DOI:10.1139/h04-049 • 1.30 Impact Factor

ABSTRACT:

Introduction

In one hand, during a fatiguing exercise the analysis of the myoelectric signal support the hypothesis of an increase of proportional number of active slow motor units. In the other hand, the slow component of oxygen consumption during a constant-rate-high-intensity exercise, seems to dependent on a progressive recruitment of fast-twitch fibers.

Methods and results

In front of this contradiction, the purpose of this study is to investigate the EMG activity of quadriceps femoris

muscle during a 90% of PMA cycling exercise.

Two main results were observed: 1) Integrated EMG decreased all exercise long (from 0,99 to 0,86 v); 2) MPF and MDF decreased in the

first part of the exercise (respectively from 82,5 to 81,25 Hz and from 108,75 to 107 Hz), followed by a progressive increase (respectively from 81,25 to 84,5 Hz and from 107 to 109,25 Hz).

Conclusion

Our results suggest a progression in the average frequency of the motor unit discharge towards the high frequencies, which

coheres with the hypothesis of the progressive recruitment of fast-twitch fibers during the VO2 slow component.

© 2003 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.

Keywords:

Intensive exercise; ElectroMyoGraphy; Oxygen conscemption

Constant-rate-high-intensity exercise and EMG. Available from: https://www.researchgate.net/publication/263533791_Constant-rate-high-intensity_exercise_and_EMG [accessed Oct 20, 2015].

ABSTRACT:: Mean Power Frequency (MPF) and Median Frequency (MDF) are usually used to investigate neuromuscular activation. Unfortunately, sometimes, contraction time duration of exercise are too short for spectral parameters calculation. It’s likely that our experiment investigate possibilities to calculate MPF and MDF through a whole intermittent isometric exercise including activity and rest.

We investigated maximal and sub-maximal activation of biceps brachii by surface electromyography. Several intermittent isometric contractions were performed with different combinations of muscle action time and rest period between contractions and we compared average of successive MPF and MDF computed without rest period (A processing) to MPF and MDF of the whole activation is computed with rest period (B processing).

For maximal activation, at first MPF values calculated with A processing compared to MPF values calculated with B processing did not appear significantly different with no incidences of muscle action time duration or rest time duration or the ratio of this parameter; second, MDF values are dependent of processing and at least sensibility of MPF versus MDF parameters appeared different.

For sub-maximal activation the lonely difference between frequencies, induced by processing, appeared at 75% of MVC.

These results support part of our hypothesis and present, an alternative possibility for MPF (and to a lesser degree for MDF) calculation, if activation time during intermittent contraction is not long enough.

Sincerey yours

Philippe

Article Constant-rate-high-intensity exercise and EMG

Hello Ville,

Firstly, I think you need some simulations at the laboratory conditions; but in wich domain you will analyze your dates of EMG signals? Frequency or time? There is a solution, if you should treat your data using a digital software (i.e, mathematical software, Matlab, Mathworks).

So we are now in the point we are waiting for summer since here in north lapland the MTB starts near summertime (not including fatbikes). We are planning to measure atleast TrA and Multifidus, does any of you suggest which muscles we should add for the measurement? The bikers we are going to measure will have nonspecific lowback pain and we are measuring the muscle fatigue and the muscle activation. We are still not sure if we are going to measure it during the MTB on trail or should we do the warmup run and measure before the MTB run and after. If we measure it before and after, is there something we are going to miss while measuring and can the muscle fatigue be optained during 2 different measures? 

I suggest you use 2 amplifiers one for upper trunk and secound for lower extrimity then sink this 2 data. Thoght technology devices may be good.