Sitting is for bad. We know that but how about sitting when changing posture or fidgeting? What kind of sitting is really bad? How long we can sit, and what kind of movements are helping to avoid sedentary diseases like diabetes II and obesity?
The study published in Nature Scientific Reports dived deeper to answer in these questions. EMG inactivity duration and usual EMG inactivity bout duration measured with Mbody shorts proved to be important metrics in preventing or studying sedentary diseases.
Muscle inactivity has been hypothesized to be a key mechanism in metabolic risks of prolonged sitting. However, there is little longitudinal work considering changes in EMG inactivity duration and pattern of accumulation during normal daily life. The published results show that methodological factors have a significant impact on responsiveness of EMG inactivity duration and pattern of accumulation.
Even though sitting is considered a sedentary behaviour, some EMG activity was measured during sitting with all of the thresholds. This is consistent with previous research showing heterogeneity in how people activate their muscles during sitting and standing due to changing posture or fidgeting. On average, standing is more active than sitting due to postural muscle activation, and is expected to reduce thigh muscle inactivity
compared to sitting. However, many of the compared thresholds captured a high EMG
inactivity duration during both sitting and standing.
Total EMG inactivity duration has been shown to be adversely associated with HDL cholesterol and triglycerides in a sample of physically active adults. In addition, the pattern how this total volume of EMG inactivity is accumulated can be relevant for health. An analysis of the accumulation pattern showed that EMG inactivity duration was accumulated through shorter EMG inactivity bouts, the lower the EMG inactivity threshold was.
EMG inactivity bout can be interrupted by any muscle activity, like changing posture or fdgeting while seated. Fidgeting, like activities within prolonged sitting have been shown to improve limb blood fow and postprandial glycemic control in people with obesity. Already a very low level of voluntary muscle excitation, or involuntary excitation invoked by electrical stimulation, can increase insulin sensitivity in inactive patients or during bed rest.
Accuracy of data
Myontec Mbody "EMG shorts provide similar information than traditional bipolar EMG electrodes on the EMG signal amplitude but with smaller day-to-day coefficient of variation. EMG shorts have a relatively large electrode area and a longer inter-electrode distance, and they measure the electrical activity, or lack of thereof, several muscle fibres. Therefore, the present data cannot be directly compared to typical bipolar electrode measurements, which
captures signal from a smaller area. It was recently shown that ankle muscles do not activate homogeneously during standing. Some muscles, or some parts of individual muscles, may be “silent” during the excitation of others. Therefore, an electrode with a small pick-up area may not be representative of the whole muscle at a given timepoint. A longer inter-electrode distance increases the underlying pick-up volume, and thus improves how representative the signal is of the whole muscle excitation. The signal collected with EMG shorts is not intended to be selective of specific muscle fibres, yet is representative of several muscle fibres and covers some parts of the adjacent muscles (Fig. 1). This fact, combined with the larger interelectrode distance, may explain the better reproducibility of signal as compared to bipolar electrodes. On the other hand, the large textile electrodes reduce the high-frequency component in the signal, and while the high pass filter corner frequency of 50 Hz can effectively reduce movement artefact during rapid movements, it may also cut some of the signal originating from muscles."
The study was done in University of Jyväskylä, South-Eastern Finland University of Applied Sciences and Zhejiang University by A. J. Pesola, Y. Gao & T. Finni.
Read the whole article here.