I once took apart a Fit Meter, and inside I found an IrDA transceiver module very similar (if not identical) to the TFBS4650 Infrared Transceiver. This means for communication, the Fit Meter very likely uses IrDA 9.6 kbit/s to 115.2 kbit/s SIR (but knowing Nintendo, they may have changed it a bit).
IrDA is NOT the same as what a TV remote uses. Unlike with a TV remote, there is no 38khz carrier frequency. Instead, the "frequency" of our signal depends on whether the how fast the data is being sent-- 9.6 kbit/s, 115.2 kbit/s, or somewhere in between.
If you want to know what the exact waveforms of this communication may look like, check out the IrDA Physical Layer guide (skip to pages 6 and 7 for a look at the waveforms).
Edit: I don't know the speed at which a Fit Meter communicates. But if it communicates at 115.2 kbit/s, then:
But the infrared transmitter is not turned on for the entire 8.7 microseconds. Here is an image of an IrDA waveform (from the guide I linked above) showing how 0's and 1's are sent.
- To send a "0" bit, the transmitter turns on its infrared light for 3/16th of our bit time. In our case that's 1.63 microseconds.
- To send a "1" bit, the infrared transmitter doesn't turn on at all. It stays dark during the entire bit time.
(I am myself interested in someday taking a look at Fit Meter IR communication.)