How to Increase Stamina: What the Evidence Says

If climbing stairs leaves you breathless, or your energy fades before your day does, the instinct is usually to plan longer workouts: more miles, more minutes, more sessions. The evidence points in a different direction. Stamina has a physiological definition, a measurable ceiling, and — as it turns out — a remarkably efficient way to raise it.

What stamina actually is

Strip away the gym vocabulary and stamina is cardiorespiratory fitness: the capacity of your heart, lungs, blood and muscles to supply and use oxygen over time. Its standard measure is VO₂max — maximal oxygen uptake, the maximum amount of oxygen your body can use during intense exercise, expressed in ml/kg/min.

Everything you experience as endurance sits downstream of this number. A higher VO₂max means any given task — a hill, a deadline sprint for the bus, a long day on your feet — occupies a smaller fraction of your capacity, so it simply feels easier.

Why your stamina deserves attention beyond the gym

The case for raising cardiorespiratory fitness is one of the strongest in preventive medicine. An overview of meta-analyses covering more than 20.9 million observations from 199 cohort studies found that adults with high fitness had less than half the all-cause mortality risk of those with low fitness (HR 0.47), and that each 1-MET increase — roughly 3.5 ml/kg/min of VO₂max — was associated with an 11–17% reduction in mortality risk (Lang et al., 2024). Stamina, in other words, is not just a performance attribute. It is one of the best-documented predictors of how long you live.

What actually builds it: intensity or duration?

Both work — but not equally per minute invested. The physiology explains why. A detailed review in The Journal of Physiology concluded that interval training produces the classic endurance adaptations — a stronger cardiac stroke volume, more mitochondria, better oxygen delivery — and that exercise intensity is a key driver of those adaptations, with brief intense intervals matching much larger volumes of continuous exercise (MacInnis & Gibala, 2017).

The trial data agree. A meta-analysis of sprint interval training found an average VO₂max improvement of 7.8% from programs of repeated all-out cycle sprints — and, strikingly, that reducing the number of sprints per session did not reduce the gains (Vollaard et al., 2017). More recent pooled data reach the same conclusion at larger scale: an average 8.3% VO₂max increase across 78 studies, with extra sprint repetitions adding no meaningful benefit (Hutchinson et al., 2026).

The minimum effective dose

This is the logic behind REHIT — Reduced Exertion High-Intensity Interval Training — the protocol CAROL Bike is built around: two 20-second all-out sprints inside a roughly five-minute ride. In the original six-week trial, three short sessions a week (10-minute lab sessions in which the sprints were built up from 10 to 20 seconds over the program) raised VO₂max by 15% in men and 12% in women, alongside a 28% improvement in insulin sensitivity in men — despite the participants rating the effort as only "somewhat hard" (Metcalfe et al., 2012).

Even the frequency requirement is lighter than you'd expect. A randomised trial comparing two, three and four REHIT sessions per week over six weeks found improvements of roughly 8–10% in every group, with no significant advantage to training more often (Thomas et al., 2020).

Honest caveats

Three points of nuance the headlines usually skip. First, individual responses vary: in any training study some people improve dramatically and a minority improve little, which is why we recommend REHIT is individualised and progress is tracked over weeks rather than judged on any single session. Second, very short protocols beat doing nothing decisively, but against a well-executed program of longer moderate exercise the outcome is closer to a draw — achieved in a fraction of the time. The advantage of minimal protocols is efficiency and adherence, not magic. Third, there is a floor: the sprints must be genuinely all-out. Effort you can comfortably hold is not the stimulus the studies describe.

The bottom line

To increase stamina, raise your VO₂max — and the evidence says intensity, not accumulated hours, is the most efficient lever. Two all-out 20-second sprints, two to three times a week, improved fitness by 10–15% within six weeks in controlled trials (Metcalfe et al., 2012; Thomas et al., 2020), and each increment of fitness you gain is associated with a measurably lower long-term mortality risk (Lang et al., 2024). Stamina is not built by suffering longer. It is built by asking your body, briefly and regularly, for everything it has.