Deload and rest
Evidence: limited
Rest days and lighter weeks are sound practice, but the scheduled in-training deload has thin trial support, unlike the well-evidenced race taper. Drive it by monitoring, not the calendar.
Rest days and periodic lighter weeks follow directly from the principle that adaptation happens during recovery. The principle is sound. The specific practice of a scheduled in-training deload week, however, has thinner evidence than its near-universal use suggests.
A supervised resistance-training trial found a one-week deload gave no advantage for size or power over training continuously, and endurance-specific deload trials are scarcer still (Coleman et al. 2024). The rationale rests largely on periodisation theory rather than direct evidence. This does not mean deloads are useless: they are a sensible hedge against accumulating fatigue and injury, and a reasonable default given how hard overtraining is to detect early. It means the precise schedule, the common “every fourth week” rule, is convention, not a finding, and is better driven by monitoring than by the calendar.
This contrasts sharply with the race taper, which is one of the best-quantified practices in the sport, with a 2 to 3% performance gain and well-defined parameters. The taper is evidence; the routine mid-block deload is reasonable practice.