The science behind
The GRASPOR device and textile sleeve combine two technologies that monitor muscle activation (by surface Electromyography, sEMG) and blood oxygenation (by Near InfraRed Spectroscopy, NIRS). For comfort, textile electrodes that enable detection of electrical impulses when muscles are activated, are integrated into a close-fitting sleeve. The GRASPOR device, that clicks into the sleeve, is equipped with LED’s which near infrared light penetrates the tissue to a depth of approx. 1.7cm to detect oxygen levels within the muscle.
What do we measure?
GRASPOR’s Muscle Oxygen is measured using the known principles of Near Infrared Spectroscopy where light in the near-infrared spectrum is shone into the tissue and differences detected in returned light. Since human tissue absorbs relatively little light in the near-infrared range, it is possible to exploit differences in absorption of light in oxygenated and deoxygenated hemoglobin to detect the relative concentration of oxygenated blood in the muscle.
Muscle Oxygen, is automatically calibrated at the start of each recording and you should either sit or stand still until a value is shown for Muscle Oxygen.
When a muscle is activated, it produces an electrical signal, leading to changes in the tension of the muscle resulting in movement or force. sEMG detects these signals which provide information about the timing and strength of contraction, of a muscle. The Muscle Activation metric records how strongly your quadriceps and hamstrings are activated, expressed as a percentage of the maximal contraction performed during calibration. The calculated percentage value is averaged over 20 seconds to show a stable trend for the individual muscle group.
View the “Introduction to GRASPOR” video-guide to see how to perform maximal contraction on your bike, alternately activating your hamstrings and quadriceps, as a reference for subsequent muscle work.
The Activation Ratio is based on the Muscle Activation measures and shows the balance between activation of your quadriceps and hamstrings. It is a measure of how much the individual muscle groups contribute to total activation.
For example, when Quadriceps are activated at 30% of their maximal activation (based on the calibration) and Hamstrings are activated 20%, Activation Ratio is calculated at 30/(20+30)=60%. It is especially important to keep an eye on changes in Activation Ratio that are not related to e.g. position changes, as this may be an indicator of fatigue development earlier in one muscle group than the other as described in detail in the “Minimize injury” video-guide.
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