Aside from streaming on an iPad, one of the few entertainments on offer when riding a stationary bike is tracking your heart rate. Breaking 150 beats per minute provides a fleeting (and doubtless misplaced) sense of achievement. Yet the wearable heart monitor that came with my exercise bicycle proved unreliable; one’s BPM never truly drops from 137 to 69 in one second. This is to explain why I bought the fitness freak’s fetish: an Apple watch.

Its heart-rate monitors are accurate. I opted for a reconditioned older model, not only half the price of the new ones but inclusive of the blood oximeter function, which a medical technology suit has forced Apple to eliminate in current American models until the litigant’s patent runs out in 2028. I’d never much cared about tracking my blood oxygen

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