Modern Interpretation.

A modern reading frames recovery as the period during which adaptation actually happens. Training is the stimulus; recovery is the response. Without sufficient recovery, the stimulus produces drift instead of progress — and eventually, breakdown.

• Autonomic balance — sympathetic activation enables output; parasympathetic activation enables restoration. Chronic imbalance toward sympathetic drive is one of the more reliable markers of under-recovery.
• Sleep architecture — deep sleep and REM serve different restorative roles. Quality and timing matter alongside total duration.
• Allostatic load — the cumulative cost of repeated adaptation to stressors. Recovery is what keeps that cost from compounding.
• Oscillation — living systems alternate effort and rest, arousal and ease. Loss of oscillation tends to precede loss of function.

A systems framing is useful for thinking about recovery. It is not a guarantee that any particular practice works for any particular person on any particular day. The science remains lively and the modalities remain contested — see Open Questions for the unresolved parts.