Ask most people how to get fitter and “increase my lung capacity” sits somewhere near the top of the list. It feels intuitive: bigger lungs, more air, more performance. The evidence tells a more interesting — and more useful — story. For the vast majority of healthy people, your lungs are not the part of you holding your fitness back, and you cannot meaningfully enlarge them anyway. Understanding why points you towards what genuinely works, and towards a marker that matters for how long, and how well, you live.
What lung capacity actually is
“Lung capacity” usually means total lung capacity — the total volume your lungs hold when fully inflated — or vital capacity, the amount of air you can move in one big breath. These volumes are set mostly by body size, height, age and genetics. After your late teens and early twenties they are essentially fixed, and they decline slowly as you age. Your lungs are not a muscle you can grow with the right programme; they are more like the size of the room than the strength of the people working in it. It is worth knowing that even at maximal effort, most healthy people finish with a breathing reserve — they could still move more air if they had to. That spare capacity is a clue in itself: if the lungs are not running out, they are unlikely to be the first thing that gives way when you push hard.
Are your lungs the thing holding your fitness back?
The ceiling on your aerobic fitness is set by how much oxygen your body can deliver to, and use in, working muscle — your VO₂max, or maximal oxygen uptake. Decades of physiology point to oxygen delivery, chiefly how much blood your heart can pump, as the primary limit — not the lungs (Bassett & Howley, 2000). When oxygen delivery is altered by altitude, blood doping or beta-blockers, VO₂max moves with it. The healthy respiratory system, by contrast, is close to ideally built for the task: even during hard exercise it keeps your arterial blood almost fully oxygen-saturated, with capacity to spare (Dempsey et al., 2020). In most people, the bottleneck is the heart and circulation, not the lungs.
Can you actually make your lungs bigger?
Because those static lung volumes are largely structural, endurance training does not meaningfully increase them in healthy adults. What training does change is everything on the delivery-and-use side: your heart pumps more blood with each beat, your total blood and plasma volume rises, and you build more capillaries and mitochondria in muscle (Lundby et al., 2017). Endurance athletes who have large lungs mostly started that way — it is more a matter of genetics and selection than training carving out extra volume. Chasing “bigger lungs” means training for an adaptation that largely does not happen.
So do breathing exercises and lung trainers work?
Handheld respiratory-muscle trainers and structured breathing work are not useless — but they act on the muscles that move air, not on the size of your lungs. A systematic review and meta-analysis in healthy people found that respiratory-muscle training produced modest improvements in endurance performance, most likely by making the breathing muscles stronger and more resistant to fatigue (Illi et al., 2012). That can help at the margins, particularly for committed endurance athletes. It is not a route to a larger set of lungs, and for most people it is not where the meaningful gains lie.
When the lungs really do limit you
There are exceptions, and it is worth being honest about them. In a subset of highly trained athletes, the demand at maximal intensity can outstrip what even a healthy respiratory system supplies, and arterial oxygen levels fall — a phenomenon called exercise-induced arterial hypoxaemia (Dempsey & Wagner, 1999). If you have a lung condition such as COPD, the picture is different again: here the lungs genuinely constrain you, yet supervised exercise through pulmonary rehabilitation reliably improves exercise capacity and quality of life, even when measured lung function barely changes (Lamberton et al., 2024). If you become breathless at rest or on mild exertion, that is a reason to see a doctor — not to buy a breathing gadget.
What to train instead: the oxygen you can actually use
The number worth improving is not lung size but VO₂max: the most oxygen your body can take in and use during hard exercise. It is also one of the strongest markers of long-term health. Higher cardiorespiratory fitness is a powerful, independent predictor of lower all-cause mortality — so robustly that it has been argued VO₂max should be treated as a clinical vital sign (Harber et al., 2017), and it has been described as a key predictor of longevity (Strasser & Burtscher, 2018).
The encouraging part is that VO₂max responds quickly to the right stimulus, and the lever is intensity, not hours. Short, hard efforts do the work. Sprint interval training — repeated brief all-out sprints — reliably raises VO₂max in previously sedentary and recreationally active adults (Sloth et al., 2013). A stripped-back version, reduced-exertion high-intensity interval training (REHIT), raised VO₂max by 15% in men and 12% in women over six weeks, using 10-minute sessions built around one or two very short all-out sprints (Metcalfe et al., 2012).
This is the principle CAROL is built on. Its signature workout is about five minutes, structured around two 20-second all-out sprints, and designed to trigger those same adaptations without long, grinding cardio. You are not trying to grow your lungs — you are training your heart, blood and muscle to move and use more oxygen. Consistency matters more than any single session: a couple of genuinely hard, brief efforts each week, sustained over months, is what shifts the number. And because the sessions are short, that consistency is realistic to hold on to — which, in the end, is what turns a training effect into a longevity benefit.
The bottom line
You cannot meaningfully increase the capacity of healthy lungs, and you almost certainly do not need to. For nearly everyone, fitness is limited by oxygen delivery and use, not lung size — so the productive question is not “how do I increase my lung capacity?” but “how do I raise my VO₂max?”. Favour intensity over duration, protect the marker that tracks with a longer life, and let your lungs do the job they are already well built for. If breathlessness is new, persistent, or happens at rest, speak to a healthcare professional first.
