In a study of 18 adults, an hour-long mentally demanding task before cycling led participants to stop about 11% sooner than after a neutral documentary; they rated the fixed-intensity ride harder, while measured leg-muscle activation did not meaningfully differ.
All 18 adults took the same challenging, fixed-intensity cycling test twice, once after sustained-attention work and once after watching a neutral documentary. Researchers suggested mental fatigue may change how the brain interprets effort; the article says the small study and single cycling test cannot establish whether the result applies to other forms of exercise.
The article suggests scheduling a harder workout before a mentally demanding day when possible, warming up before deciding to skip exercise, and switching to an easier session or rest if genuinely exhausted.
