Where to wear your WHOOP: wrist, forearm, bicep
Why position matters
The sensor reads heart rate by lighting the skin and measuring the light bounced back by the blood moving underneath. Anything that lifts the sensor off the skin, or lets the device move, degrades the reading. Position is not a matter of taste.
The wrist
This is the default, and it suits the large majority of cases. The right spot is about two fingers above the wrist bone, towards the elbow — never on the joint, where the sensor loses contact with every flex.
Its limits show up in two situations: exercises that bend the wrist hard, and those where a bar or a handle presses on it.
The forearm
Sliding the band a few centimetres up, towards the middle of the forearm, changes a great deal. The skin there is more stable, less subject to flexing, and nothing presses on it during a movement.
It is the simplest fix for anyone whose training data looks erratic, and it needs no accessory: slide the band up and tighten slightly, the forearm being wider.
The bicep
WHOOP offers ways to wear the device on the upper arm. Readings there are often excellent, because the muscle moves little relative to the skin and no equipment rubs against it.
The trade-off is practical rather than technical: you can no longer glance at the device, and you have to pull back a sleeve to reach it. It is a training position, rarely an everyday one.
What does not work
Too far down the hand, on the protruding wrist bone, or over clothing. In all three cases the reading becomes unusable, and that is not a fault of the device.
In practice
Keep the wrist for daily life and for sleep. Move up to the forearm for sessions where you grip a bar, a handle or handlebars. It is the adjustment that solves the most data problems, before buying anything.
A woven band with a sliding clip lends itself to this better than a notched one: the fit adjusts continuously, so the same band works on the wrist and on the forearm. See also: getting the fit right.
For sessions where you move the band up the forearm, the lighter CoreKnit weave dries faster than a thick one.
Depending where
On the bicep, a firm weave prevents rotation: the CoreKnit mesh is made for it. On the wrist, Port adjusts more finely.