Surface electromyography (sEMG) is a well-established approach to monitor
muscular activity on wearable and resource-constrained devices. However, when
measuring deeper muscles, its low signal-to-noise ratio (SNR), high signal
attenuation, and crosstalk degrade sensing performance. Ultrasound (US)
complements sEMG effectively with its higher SNR at high penetration depths. In
fact, combining US and sEMG improves the accuracy of muscle dynamic assessment,
compared to using only one modality. However, the power envelope of US hardware
is considerably higher than that of sEMG, thus inflating energy consumption and
reducing the battery life. This work proposes a wearable solution that
integrates both modalities and utilizes an EMG-driven wake-up approach to
achieve ultra-low power consumption as needed for wearable long-term
monitoring. We integrate two wearable state-of-the-art (SoA) US and ExG
biosignal acquisition devices to acquire time-synchronized measurements of the
short head of the biceps. To minimize power consumption, the US probe is kept
in a sleep state when there is no muscle activity. sEMG data are processed on
the probe (filtering, envelope extraction and thresholding) to identify muscle
activity and generate a trigger to wake-up the US counterpart. The US
acquisition starts before muscle fascicles displacement thanks to a triggering
time faster than the electromechanical delay (30-100 ms) between the
neuromuscular junction stimulation and the muscle contraction. Assuming a
muscle contraction of 200 ms at a contraction rate of 1 Hz, the proposed
approach enables more than 59% energy saving (with a full-system average power
consumption of 12.2 mW) as compared to operating both sEMG and US continuously.Comment: 4 pages, 5 figures, 1 table, 2023 IEEE International Ultrasonics
Symposiu