Mike O'Hearn

No major exercise guideline (WHO, ACSM) prescribes an ideal session length; recommendations are built around cumulative weekly volume, not the duration of a single session. A 45-minute and a 90-minute workout can deliver an equivalent training stimulus if the effective volume (sets close to failure, load, intensity) is comparable — raw duration is only a rough proxy. O'Hearn's framing correctly redirects attention toward effort rather than an arbitrary clock, and corrects a real myth ('you need X minutes'). Its blind spot: it says nothing about the minimum volume actually needed to progress — a short session with too few quality sets still won't cut it. The point holds as a corrective to a duration myth, but it's a general principle rather than an actionable protocol on its own.