Why don't I have the energy I had 10 years ago?
Losing stamina compared to a decade ago is often a measurable drop in VO2 max, not just getting older. What VO2 max is, how it's tested, and how it can be improved.
- Preventive screening
- Fitness
- Longevity
Medically reviewed by Dr. William Aung, DocDocDash’s partner doctor network.
Last reviewed: October 2026.
Quick answer: A noticeable drop in energy and stamina compared to 10 years ago is often linked to a decline in VO2 max, a measure of how efficiently your body uses oxygen during physical activity. VO2 max naturally decreases with age, but the rate of decline varies widely and is heavily influenced by fitness level, muscle mass, and cardiovascular health, all of which can be measured and, to a meaningful extent, improved.
You used to climb stairs without thinking about it. Now you notice you’re a little more out of breath, a little more tired by mid-afternoon, even though your routine hasn’t changed much. It’s tempting to write this off as simply “getting older,” but there’s often a more specific, measurable explanation behind that gradual shift in energy and endurance.
The feeling of reduced stamina usually isn’t random. It typically reflects a real physiological change, most commonly a gradual decline in cardiovascular efficiency and muscle mass, both of which affect how well your body delivers and uses oxygen during activity.
Several factors contribute to this over time:
Natural aging. Cardiovascular fitness and lung efficiency tend to decline gradually from your 30s onward, even in people who stay reasonably active, simply due to age-related changes in the heart, lungs, and blood vessels.
Gradual muscle loss. Without targeted strength maintenance, muscle mass declines starting in your 30s, which reduces your body’s oxygen demand efficiency and makes the same activity level feel more taxing than it used to.
Reduced activity consistency. Busy schedules, especially for women balancing work and family responsibilities, often mean activity levels quietly decrease over years without a single dramatic change, making the decline easy to miss until it’s noticeable.
Underlying health factors. Sometimes reduced stamina reflects something more specific, like anemia, thyroid changes, or early cardiovascular changes, which is why persistent, unexplained fatigue with exertion is worth discussing with a doctor rather than assuming it’s purely about age.
What Your VO2 Max Says About Your Fitness, and How Testing It Can Help
VO2 max measures the maximum amount of oxygen your body can use during intense exercise, essentially, a direct measure of your cardiovascular and muscular efficiency. It’s considered one of the most reliable indicators of overall fitness and, notably, is also linked to longevity and long-term cardiovascular health in research.
How it’s tested. VO2 max testing typically involves a supervised treadmill or cycling test with a mask measuring your oxygen use as intensity gradually increases. It’s a controlled, medically supervised assessment, not a strenuous ordeal, and provides a precise number rather than a vague impression of fitness.
Why the number matters. Your result places you within a fitness range for your age and sex, giving you a concrete baseline. Unlike a general sense of “I feel less fit,” a VO2 max score shows you specifically where you stand and, when retested over time, whether changes you’re making are actually working.
What you can do with the result. VO2 max can be improved with consistent, targeted cardiovascular training, often more than people expect, even later in life. Having a baseline number turns a vague goal (“get fitter”) into something measurable and trackable.
This kind of testing is particularly useful if fatigue or reduced stamina has been bothering you but basic bloodwork hasn’t shown an obvious cause, since it can help clarify whether the issue is cardiovascular fitness or something else entirely.
If fatigue is accompanied by other symptoms like breathlessness at rest or chest discomfort, it’s also worth exploring DocDocDash to rule out underlying heart-related causes first.
Frequently Asked Questions
Is it normal for VO2 max to decline with age?
Yes, some decline is a normal part of aging, typically starting in the 30s. However, the rate of decline varies significantly and can be slowed considerably with consistent cardiovascular training.
Can VO2 max actually be improved, or is the decline permanent?
It can be improved. Regular, moderately intense cardiovascular exercise has been shown to meaningfully increase VO2 max at virtually any age, though the extent of improvement varies by individual.
Do I need a VO2 max test, or is a regular fitness check enough?
A VO2 max test gives a more precise, objective measurement than a general fitness assessment, which is particularly useful if you want to track specific progress or better understand unexplained fatigue.
A Simple Rule to Carry Forward
Reduced stamina compared to a decade ago isn’t just “getting older”, it’s often a measurable, specific change in how efficiently your body uses oxygen. A VO2 max test turns that vague feeling into a clear number you can track and improve.
Ready to take the next step? DocDocDash can help you find hospitals and clinics offering VO2 max and fitness assessments, compare what’s included, and book a consultation, all in one place.
Sources: General sports medicine and exercise physiology literature on VO2 max and age-related decline.