Hate to break it to you, but this schematic is terrible.
There is no need for current limiting in this circuit. You don't have any unknown loads on your supply line.
That TSOP17 IR receiver has an absolute maximum output current rating of 5mA, which is definitely exceeded when you are discharging a cap through it + shorting the supply rail through that PN junction of that PNP. The receiver could already be damaged.
The circuit reacts to pretty much any 38kHz IR signal. ANY. You threadmill could just be outputting an IR signal for some sort of isolated PC communication (kind of like the one you find on multimeters).
Use a small microcontroller (like a Tiny13) to decode the signal from the receiver and trigger the relay. A lot more reliable and you can also program the exact codes into it.