Heart-rate training
ANT+ vs Bluetooth for swim heart rate: why broadcast wins on the pool deck
If you’ve ever tried to put heart-rate monitors on a whole training group, you’ve met the problem: it works fine for a few swimmers, then falls apart. The reason usually isn’t the sensors; it’s how the signal gets from the swimmer to your screen.
Two ways to send heart rate
Bluetooth is a connection. Your device pairs one-to-one with each sensor, and every pairing holds open a connection. That’s perfect for one athlete and a watch. But devices have a ceiling, practically somewhere around 7 to 15 simultaneous connections, and each one is a thing that can drop, need re-pairing, or refuse to reconnect mid-set.
ANT+ can broadcast. Instead of pairing, each sensor simply transmits, and a single receiver listens to everything in range at once. There’s no pairing step and no per-swimmer connection to lose. One receiver hears the whole squad.
Why that matters for a squad
On a pool deck, broadcast is the difference between “monitor a couple of lanes” and “monitor everyone.” With ANT+, adding the twenty-first swimmer costs nothing; they’re just another broadcast in the air. With Bluetooth, you’re fighting the connection ceiling and babysitting re-pairs. This is the core reason apxswim captures live heart rate over ANT+, and it’s a claim Bluetooth-based setups can’t easily make.
The honest part: neither goes through water
Worth being straight about, because a knowledgeable coach will ask: neither ANT+ nor Bluetooth transmits through water. Both sit in the 2.4 GHz band, which is absorbed within a few inches of submersion. Nobody is streaming heart rate from the bottom of the pool.
What happens is the sensor (a chest strap, or an optical armband worn on the temple or goggles) transmits when it’s at or near the surface: at the wall, on the turn, on recovery. The ANT+ advantage isn’t magic underwater range; it’s that, at every moment the signal is available, one receiver picks up the entire squad cleanly. The edge is scale, not water penetration.
What this looks like in apxswim
Pair an ANT+ receiver, and apxswim reads every broadcasting sensor in range, with no pairing, no per-swimmer setup, and maps each reading to the right swimmer and their zones. Combine that with threshold pace from the CSS calculator in apxswim and you can see, in real time, who’s training where you intended.