The minimum effective dose of exercise for healthspan

Exercise is the only factor in the Helixspan model with a meaningfully positive range on both sides of zero — up to 3 years gained, not just years avoided. That reflects a genuine asymmetry in the evidence: physical activity doesn't just reduce disease risk, it actively improves cardiovascular efficiency, metabolic flexibility, muscular and bone strength, and — increasingly well documented — brain health and cognitive resilience with age.

The dose-response curve isn't a straight line

A large 2019 analysis in the BMJ, pooling accelerometer-measured activity data across multiple cohorts, found that the steepest drop in mortality risk happens at the lower end of the activity spectrum — moving from sedentary to lightly active produces a bigger relative risk reduction than moving from moderately active to highly active. In practical terms: the jump from zero exercise to roughly 30 minutes a week of moderate activity captures a large share of the available benefit.

This is the single most important — and most counterintuitive — finding behind the exercise factor in the model. It's not that more exercise doesn't help; it's that the marginal benefit per additional minute declines as total volume rises, following a curve that flattens out (though doesn't fully plateau) somewhere around 300 minutes of moderate-intensity activity per week.

What "moderate intensity" means in practice

• Moderate intensity: brisk walking, cycling on flat ground, swimming at an easy pace — activity that raises heart rate and breathing but still allows conversation.
• Vigorous intensity: running, fast cycling, most competitive sports — activity where sustained conversation becomes difficult. Vigorous minutes are generally treated as roughly double the value of moderate minutes.
• Non-exercise activity: walking to get somewhere, taking stairs, standing rather than sitting — smaller individually, but the accelerometer studies suggest this "incidental" activity matters more than commonly assumed, particularly for people who don't do structured exercise at all.

Why exercise also carries a negative range in the model

A model input that runs from −4 to +3 years might look asymmetric, but it reflects two different things being measured on the same scale: the −4 end represents a fully sedentary lifestyle — a known independent risk factor for cardiovascular disease, type 2 diabetes, and all-cause mortality, distinct from and additive to other risks like poor diet or excess weight. The +3 end represents the plateau benefit of consistent, moderate-to-vigorous activity most weeks. Sedentary behavior isn't simply "the absence of the +3 bonus" — a growing body of research treats prolonged sitting as its own risk factor even among people who exercise, though the calculator simplifies this into a single sliding input for usability.