Zone 2 cardio
Conversational-pace cardio, 150+ minutes per week. Mitochondrial backbone of healthspan.
Why
Zone 2 is the intensity at which you can still hold a conversation but a song would be a stretch, roughly 60–70% of max heart rate. Sustained Zone 2 work increases mitochondrial density, improves fat oxidation, and is the single most consistently associated exercise input with all-cause mortality reduction in cohort studies.
Slot in your day
How to do it
How
Brisk walk, easy bike, slow jog. 30 minutes × 5 days, or 45–60 min × 3 days. The 'talk test' is the simplest gauge.
Ideal for
Anyone over 30; especially valuable as the foundation before adding higher-intensity work.
Sticking with it
Schedule it like a meeting. The session you 'fit in if there's time' is the session that doesn't happen.
Markers this may influence
Evidence
Lee 2012 Lancet Physical Activity Series (population-attributable risk analysis across >50 cohorts): physical inactivity caused ~9% of premature mortality worldwide, comparable to smoking and obesity. Kelly 2014 meta-analysis of walking and cycling (n=280,000 + n=187,000): each ~11 MET-h/week of either activity was associated with ~10–11% lower all-cause mortality.