Cardio: how much do you really need?

Cardiorespiratory fitness (CRF) — the capacity of the heart, lungs, and circulatory system to deliver oxygen to working muscles — is one of the strongest independent predictors of all-cause mortality in the epidemiological literature. A 2018 JAMA Network Open study found that low aerobic fitness was a stronger predictor of mortality than smoking, hypertension, diabetes, or obesity — and that improvements in aerobic fitness at any age produced significant mortality risk reduction. The good news: you don’t need elite fitness levels to capture most of the health benefit. The dose-response curve is steep at the low end — going from completely sedentary to moderately active produces the largest proportional risk reduction, with diminishing returns at very high fitness levels.

The guidelines and what they mean

The WHO and most national health guidelines recommend 150-300 minutes of moderate-intensity aerobic activity per week, or 75-150 minutes of vigorous-intensity aerobic activity (or an equivalent combination). Moderate intensity means you can hold a conversation but are breathing noticeably harder than at rest — brisk walking, light cycling, gentle swimming, dancing. Heart rate typically 50-70% of maximum. Vigorous intensity means you can speak in short phrases only — running, fast cycling, vigorous swimming, HIIT. Heart rate typically 70-85% of maximum. The «10,000 steps per day» recommendation is a useful rough proxy for moderate physical activity but is not directly derived from cardiovascular research — the actual evidence supports duration and intensity targets rather than step counts specifically.

LISS vs. HIIT — what the evidence says

LISS (Low-Intensity Steady State) — sustained moderate-intensity exercise for 30-60+ minutes (running, cycling, walking) — has the broadest evidence base for cardiovascular health, is easier to recover from, can be done daily, and is highly sustainable long-term. It is the primary mode recommended for general cardiovascular health. HIIT (High-Intensity Interval Training) — alternating short bursts of very high intensity (85-95% max HR) with recovery periods — produces comparable cardiovascular adaptations in significantly less time and has strong evidence for improving VO2max, insulin sensitivity, and metabolic markers. A typical HIIT session (10-20 minutes) can produce cardiovascular training effects equivalent to 30-40 minutes of LISS. The tradeoff: HIIT requires more recovery time, carries higher injury risk, is harder to sustain as daily activity, and is psychologically demanding. The most effective approach for most people: primarily LISS (most sessions) with 1-2 HIIT sessions per week for time efficiency and fitness plateau-breaking.

Fitting cardio into a complete fitness program

The cardio-strength balance

For people who want to do both cardio and strength training (the evidence-optimal combination for longevity and body composition), the sequencing and balance matters. General recommendations: perform strength training before cardio in the same session when both are done together (strength performance degrades more after prior cardio than vice versa); allow at least 6 hours between strength and intense cardio sessions if training twice daily; and don’t sacrifice strength training for excessive cardio if body composition and longevity are the goals — the combination of both is superior to maximizing either alone. The interference effect (high cardio volumes blunting strength adaptations) is real but modest at typical recreational exercise volumes.

Incidental movement matters

An important insight from recent research: incidental physical activity (non-exercise movement throughout the day — walking between locations, taking stairs, standing rather than sitting) contributes meaningfully to cardiovascular health and metabolic outcomes. People who exercise for 30 minutes but sit motionless for the other 16 waking hours have worse metabolic profiles than people who don’t formally exercise but move consistently throughout the day. Breaking up prolonged sitting (standing or walking for 5 minutes every hour) produces measurable improvements in blood glucose regulation, regardless of formal exercise habits. Structured exercise and incidental movement complement rather than substitute for each other.