APK teardown reveals what Garmin’s muscle sensor could measure

Our Garmin Connect teardown has uncovered detailed fields for muscle oxygen saturation and total haemoglobin concentration. The code offers a clearer picture of what Garmin’s expected Muscle Battery hardware could measure during an activity.

More than a single oxygen reading

The APK includes fields for average, minimum and maximum saturated haemoglobin percentage. It also contains average, minimum and maximum total haemoglobin concentration.

Garmin tracks both because they measure different things. Saturated haemoglobin measures the amount of oxygen-carrying haemoglobin in the muscle, while total haemoglobin measures the total amount of haemoglobin present, whether it is carrying oxygen or not. Together, they give Garmin a more complete picture of what is happening inside the muscle during exercise.

MUSCLE_OXYGEN
Muscle Oxygen
sensor_name_type_muscle_oxygen

avg_saturated_hemoglobin_percent
min_saturated_hemoglobin_percent
max_saturated_hemoglobin_percent

avg_total_hemoglobin_conc
min_total_hemoglobin_conc
max_total_hemoglobin_conc

That is more detailed than simply recording one muscle oxygen number at the end of a workout. It suggests Garmin Connect can follow how muscle oxygen changes throughout an activity, then identify typical levels, the lowest point reached and the highest recovery point.

Average saturated haemoglobin percentage would provide a broad view of muscle oxygen availability across the session. The minimum value could show when the working muscle became most depleted, while the maximum may reflect recovery during easier sections, rest intervals or the period immediately after an effort.

Total haemoglobin concentration adds another layer. This measurement reflects changes in blood volume within the monitored tissue, which can help distinguish between a drop in oxygen saturation and a wider change in local blood flow.

Taken together, the fields point to a device that would collect continuous tissue-level data rather than occasional spot checks. That would make sense for running, cycling, strength training and interval sessions, where the pattern of depletion and recovery may be more useful than a single final score.

The device would need specialised optics

Current Garmin watches cannot produce these readings from the wrist. Muscle oxygen monitoring normally relies on near-infrared spectroscopy, using several light wavelengths to estimate oxygenated and deoxygenated haemoglobin inside a specific muscle.

That also explains why the likely device would need to sit directly over the muscle being measured. A cyclist may place it on the thigh, while a runner could use the calf or quadriceps. An upper-arm position might work for strength training or general conditioning.

The fields in Garmin Connect suggest the sensor would need to record continuously and send more than a basic SmO2 percentage. It would also need enough optical information to calculate total haemoglobin concentration and track changes over time.

This points towards a dedicated optical pod. Garmin watches could act as the display and recording device, while the sensor itself handles the specialised measurements.

That matches our reporting in April on the Garmin Muscle Battery patent filing. This described software for analysing muscle oxygen saturation and related performance data.

Muscle oxygen sensors are not new

Muscle oxygen sensors have been around for years, although they remain few and far between. Muscle oxygen sensors have been around for years, although they remain few and far between. They have never really caught on outside serious endurance athletes. We reviewed the Humon Hex back in 2019, while Moxy remains one of the better-known options.

The difference is that these have always been third-party products sitting on the edge of the Garmin ecosystem. They can send muscle oxygen data to compatible watches, but Garmin has zero control over the hardware and the algorithms.

A Garmin-made sensor would allow the company to integrate muscle oxygen data tightly with its existing metrics. Muscle Battery could potentially sit alongside Body Battery, Training Readiness, and other Garmin metrics. The same Garmin Connect 5.27 teardown also revealed the likely Enduro 4 and possible Fenix 9.