Why These Weights?

Physical inactivity is one of the strongest modifiable risk factors for premature mortality. Dose-response curves plateau around 300–450 minutes/week of moderate activity, but even modest amounts yield large reductions.

• Effect of physical inactivity on major non-communicable diseases worldwide — Lee IM, Shiroma EJ, Lobelo F et al.. The Lancet, 2012.
• Dose-response associations between accelerometry measured physical activity and sedentary time and all cause mortality — Ekelund U et al.. BMJ, 2019.

Sleep gets the largest weight because deficient sleep degrades every other component: exercise recovery, insulin sensitivity, cognition, immunity. Meta-analyses consistently show a U-shaped relationship between sleep duration and all-cause mortality.

• Sleep duration and all-cause mortality: a systematic review and meta-analysis of prospective studies — Cappuccio FP, D’Elia L, Strazzullo P, Miller MA. Sleep, 2010.
• Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society on the Recommended Amount of Sleep for a Healthy Adult — Watson NF et al.. Sleep, 2015.

Time-restricted eating and periodic fasting improve markers of metabolic health, though clinical outcomes remain less certain than sleep or exercise. Effect sizes vary with adherence and baseline diet quality.

• Effects of Intermittent Fasting on Health, Aging, and Disease — de Cabo R, Mattson MP. New England Journal of Medicine, 2019.
• Fasting, Circadian Rhythms, and Time-Restricted Feeding in Healthy Lifespan — Longo VD, Panda S. Cell Metabolism, 2016.

Morning natural light anchors the circadian system — the primary driver of sleep quality, mood and hormonal rhythms. Larger cohort data also links avoidance of sun exposure to increased mortality, though causal pathways beyond vitamin D are still debated.

• Avoidance of sun exposure as a risk factor for major causes of death (Melanoma in Southern Sweden cohort) — Lindqvist PG, Epstein E, Nielsen K et al.. Journal of Internal Medicine, 2016.
• Entrainment of the human circadian clock to the natural light-dark cycle — Wright KP Jr, McHill AW, Birks BR et al.. Current Biology, 2013.

The Finnish KIHD cohort (2,315 men, 20+ years follow-up) showed a clear dose-response between sauna frequency and reduced cardiovascular and all-cause mortality. Mechanisms include heat-shock proteins, endothelial function and blood-pressure effects.

• Association Between Sauna Bathing and Fatal Cardiovascular and All-Cause Mortality Events — Laukkanen T, Khan H, Zaccardi F, Laukkanen JA. JAMA Internal Medicine, 2015.
• Cardiovascular and other health benefits of sauna bathing: a review of the evidence — Laukkanen JA, Laukkanen T, Kunutsor SK. Mayo Clinic Proceedings, 2018.

Human evidence for cold exposure is thinner than for sauna — most work is on acute physiological markers (norepinephrine, brown adipose tissue) rather than long-term outcomes. Included as a legitimate adjunct at a modest weight while the field matures.

• The Effect of Cold Showering on Health and Work: A Randomized Controlled Trial — Buijze GA et al.. PLoS ONE, 2016.
• Human physiological responses to immersion into water of different temperatures — Šrámek P, Šimečková M, Janský L et al.. European Journal of Applied Physiology, 2000.

Recovery captures the modulating factors — HRV-guided rest days, stress management, active recovery — that determine whether stimulus becomes adaptation or injury. Ignored in most trackers, but heavily emphasised in modern sports-science consensus.

• Recovery and Performance in Sport: Consensus Statement — Kellmann M, Bertollo M, Bosquet L, Brink M et al.. International Journal of Sports Physiology and Performance, 2018.
• Heart Rate Variability and Training Intensity Distribution in Elite Rowers — Plews DJ, Laursen PB, Kilding AE, Buchheit M. International Journal of Sports Physiology and Performance, 2014.