Measuring forearm oxygen yourself: wearable sensors
Yes, there are small wireless sensors that strap onto the forearm and track muscle oxygen while you climb. They're the same kind of device used in many of the studies on this site. They're good for watching your own trends, and poor for comparing yourself with other people or with lab numbers.
In plain words
A wearable muscle-oxygen sensor shines near-infrared light into the skin and measures how much comes back. Blood rich in oxygen and blood low in oxygen absorb the light differently, so the sensor can estimate how much oxygen is in the muscle underneath, many times a second. Tape one over your finger flexors and you can watch the line drop on hard moves and rise on rests, see your own refill half-time, and compare shaking low with shaking high. But the light only reaches about 2 cm deep, fat and skin get in the way, and where you put the sensor changes the numbers. So compare yourself with yourself, using the same spot and the same routine.
Memory hookSame spot, same routine, compare yourself with yourself.
What's available
The technology is called near-infrared spectroscopy (NIRS). Wearable, wireless versions have been sold since 2006. A 2024 systematic review of sports studies found that 130 studies used wearable devices to measure muscle oxygen during exercise. Of those, 40 % used the PortaMon (Artinis Medical Systems, the Netherlands) and 24 % used the Moxy (Fortiori Design, USA). The same manufacturer behind the PortaMon also makes the newer PortaLite and the smartphone-based Train.Red sensors. This list isn't a recommendation; check current models, prices and support yourself.
Muscle oxygen saturation (often called SmO₂ or StO₂) and changes in oxygenated and total haemoglobin, a few centimetres under the sensor.
Your own trends: the dip during hard sections, the rise during rests, your refill half-time on a rest, the effect of arm position or shaking.
Comparing people, comparing devices, comparing with lab numbers, and seeing the deepest finger muscle.
Getting useful data
Placement
The main finger-bending muscle used in crimping, the deep finger flexor (FDP), lies deep in the forearm, beneath the more superficial finger flexor (FDS). In climbers the border between the two was about 18 mm deep, and most sensors read only about 20 mm deep, so the reading mostly reflects the superficial flexor. The recommended site is on the inside of the forearm, a third of the way from the bony bump on the inside of the elbow to the wrist.
(a skin pen or a photo with a ruler) and use the same spot every time.
, parallel to the muscle fibres, as the researchers recommend. Turned across the forearm, some readings changed.
the studies covered the sensor with a bandage or sleeve so daylight doesn't leak in.
so it doesn't shift when the forearm tenses; movement creates false readings.
A simple routine on the wall
- Rest seated for two minutes with the sensor on to get a starting level.
- Climb a route you know well. Tap a marker in the app (or note the time) at the crux and at each rest.
- At a rest, find the lowest value and the time it takes to recover half of the drop back to your starting level. That's your own half-time for that rest, in that position.
- Repeat another day on the same route: shake low for one rest and with the hand by the hold for another, and compare.
Reading the line
means the forearm is using oxygen faster than the blood brings it, typically on hard holds.
means delivery is winning, as on rests or easy holds.
on a rest is the "levels off" moment: a good time to go (see go-or-stay).
WarningSome lab tests stop the blood flow with an inflated cuff on the upper arm to measure recovery. Don't do cuff tests on yourself or others outside a lab with trained staff.
The evidence
- Measured Of 130 studies using wearable muscle-oxygen devices during exercise, 40 % used the PortaMon and 24 % the Moxy. The review lists limited penetration depth, low spatial resolution and fat-tissue interference as the main limitations, and notes that 128 of 191 studies didn't measure fat thickness. Perrey et al. 2024, a systematic review. Sports Med 54(4):975–996.
- Measured The border between the superficial and deep finger flexors was 17.6 mm (SD 4.0) deep, so the superficial flexor dominated the signal; most NIRS devices reach about 20 mm. With the sensor across the fibres instead of along them, mean oxygenation read 5.5 % higher and re-oxygenation between late contractions 2.7 % lower; recovery half-time after a cuff test didn't change. The authors recommend the reference site with the sensor parallel to the fibres. Vandenhaute et al. 2026: forearm ultrasound in 28 climbers and a sensor test in 22. Front Sports Act Living 8:1845130.
- Measured Responses to arm position varied a lot between individuals, so your own numbers may differ from group averages. Štěpánová et al. 2026: 51 adult men. BMC Sports Sci Med Rehabil, 2026.
- Measured Climbing studies cover the sensor to block light and use a reference site on the inside of the forearm. Fryer et al. 2015, J Strength Cond Res 29(6):1633–1639; Vandenhaute et al. 2026.
- Coaching practice The on-the-wall routine above is a practical suggestion, not a validated test.
Try it
your own half-time with the half-time chart. Use the slider to match your curve.
arm low vs arm up from Arm position on a rest.
the research library for how the studies used these sensors.
Common mistakes
skin, fat thickness and placement make absolute numbers personal.
a few centimetres can change the reading.
look for patterns across several climbs.
most sensors mainly see the muscle tissue closer to the skin.