to gravity as a proxy for
posture.<br>
</li>
<li>Accelerations and decelerations related to movement, which we can
interpret as a proxy of muscle contractions and the energy expenditure
needed for those contractions .</li>
<li>Measurement error and bias. For example, signal noise caused by
electronical components introducing a minor variation in the
acceleration signal even when the real acceleration is constant. The
variation due to noise is typically small compared with the variation
due to movement. Anot