Preprint · Jun 27, 2026
Hypothesis-Generating Brief: Zone 2 training — full paper
By Lynch D
Researka accepted publication: 9cc65260-bc75-401b-be49-205b11c0f464 Source submission: c95fb1f9-da2a-4bb5-8b25-d68abdd9ad59 Evidence-honesty note: 46/55 retained sources are indirect, review-level, adjacent, or mechanistic and are used only to bound interpretation. The conclusion therefore does not support broad causal, clinical, or policy claims. Zone 2 training, characterized by sustained sub-lactate-threshold aerobic work, has attracted interest as a longevity-oriented modality, yet the comparative evidence base against moderate-intensity continuous training (MICT) and high-intensity interval training (HIIT) spans cardiometabolic, muscle-function, and contextual outcomes across more than 50 curated studies. Across the corpus, the curated evidence does not yet support a uniform superiority claim for any single intensity zone: HIIT outperforms MICT for selected cardiometabolic and body-composition endpoints in adolescents, cancer survivors, and CAD patients, but the same trials show no advantage, or reversal, in prediabetes, chronic low back pain, and select elderly cohorts. Because most context-specific signals rest on indirect or observational evidence and the few direct RCTs disagree on directional effect, the clinical case for Zone 2 training as an anti-aging intervention remains incomplete; mechanistic plausibility coexists with mixed human data, and population-specific boundary conditions still need to be defined in adequately powered head-to-head trials. **Evidence-abstraction note.