How hydration affects VO₂ max
Written by Julie Stewart (opens in a new tab)
Medically reviewed by Ecler Ercole Jaqua, MD, MBA, DABOM (opens in a new tab)
Most athletes who want to improve VO₂ max focus on training: more intervals, more Zone 2, more volume, better recovery.
That’s the right move. Studies consistently show that high-intensity trainingOpens in a new tab, such as interval training, improves VO₂ max, even in elite athletesOpens in a new tab who are already fit. But if you’ve been consistently training hard and your VO₂ max isn’t improving, it’s worth looking at your hydration strategy.
VO₂ maxOpens in a new tab measures how much oxygen your body can take in, deliver, and use during hard exercise. Delivery is the key word here: To get oxygen to working muscles, you need enough blood volume for the heart to pump efficiently. When you’re dehydratedOpens in a new tab, blood volume drops. Your heart rate rises to compensateOpens in a new tab, making efforts feel harder than they should.
To be clear, hydration alone can’t improve VO₂ max. But it's an easily controllable lever to optimize when building up your training or pushing past a plateau
What Is VO₂ Max?
VO₂ maxOpens in a new tab measures the maximum amount of oxygen your body can use during hard exercise. It’s reported in milliliters of oxygen per kilogram of body mass per minute. That’s a mouthful.
Think of it as miles per gallon for your body. The higher your VO₂ maxOpens in a new tab, the more oxygen your body can use during hard efforts, which lets you sustain a faster pace, higher output, or longer effort before fatigue forces you to back off.
VO₂ maxOpens in a new tab reflects how effectively your body takes in oxygen, transports it to your muscles, and uses it to produce energy. Your lungs move oxygen into your blood, your heart pumps that oxygen-rich blood to your muscles, and your mitochondria use the oxygen to make adenosine triphosphate (ATP), the fuel that powers movement.
The more (or harder) you work out, the better every part of that process gets. Your heart pumps more blood with every beat, your muscles expand and recruit more blood vessels, and your cells grow new mitochondria — the cellular powerhouses that produce energy from oxygen.
That makes VO₂ max more than a fitness score. “It’s basically an indication of your overall cardiovascular efficiency — how your heart delivers nutrients and oxygen to all of your tissues," says cardiothoracic surgeon and LMNT partner Dr. Jeremy LondonOpens in a new tab.
That helps explain why VO₂ max is closely linked to long-term health and longevity. Landmark researchOpens in a new tab links every 3.5 mL/kg/min increase in VO₂ max with a 15% lower risk of serious cardiovascular events and a 13% lower risk of early death.
VO₂ maxOpens in a new tab declines with age — about 10% per decade, from around 48.0 and 37.6 for 20-something men and women, respectively, to 24.4 and 18.3 for men and women in their 70s. GeneticsOpens in a new tab influence your range, but training is what really moves the needle. In one study, athletes Opens in a new tabhad VO₂ max numbers about 10 to 19 points higher, on average, than non-athletes. That means everyday activities — from climbing stairs to chasing kids around — feel easier because their heart and muscles can deliver and use oxygen more efficiently.
How Do You Improve VO₂ Max?
Training drives VO₂ max improvement. Several protocols have research behind them, and each stresses your cardiovascular system differently. Some build a broad aerobic base. Others push your heart rate near its max. Here's a breakdown of the most well-supportedOpens in a new tab approaches:
| VO2 Max Training Strategies | Recommended Protocols |
|---|---|
| Zone 2 Training | Exercise continuously for 45–120 minutes at a pace where you can still hold a conversation (brisk walking, jogging, cycling, rowing, swimming). |
| VO₂ Max Intervals (4×4) | Alternate 4 minutes of very hard effort with 3 minutes of easy recovery. Repeat 4 times (about 28 minutes total). |
| Moderate-Interval HIIT | Perform 30 seconds to 2 minutes of hard effort followed by an equal or slightly longer recovery period. Repeat for 15–30 minutes. |
| Sprint Intervals | Go all-out for 20–30 seconds, then recover for 2–4 minutes. Repeat 4–8 times. |
| Tempo Training | Maintain a comfortably hard pace that you can sustain for 20–40 minutes without slowing down. |
| Hill Repeats | Run, hike, or cycle uphill for 1–3 minutes at a hard effort, then recover on the way down. Repeat 6–10 times. |
| Long Endurance Sessions | Spend 90 minutes or longer exercising continuously at an easy-to-moderate pace (running, cycling, hiking, swimming, etc.). |
| Cross-Training | Improve aerobic fitness by choosing activities like rowing, swimming, cycling, cross-country skiing, or elliptical training, especially to reduce repetitive stress from one sport. |
| Polarized Training | Structure your training so that most sessions (about 80%) are easy, while 20% are high intensity, rather than doing every workout at a moderate pace. |
How is VO₂ max measured?
There are a few ways you can measure or gauge your VO₂ max:
- Lab testsOpens in a new tab are the most accurate way to measure how much oxygen you use and carbon dioxide you produce during exercise. During a lab test, you’ll be asked to run on a treadmillOpens in a new tab or pedal a stationary bike at progressively higher intensities while wearing a mask. The mask will measure how much oxygen you inhale and how much carbon dioxide you exhale. The test continues until you reach your maximum effort.
- Wearables can also estimate VO₂ max using data such as your heart rate, pace, age, and body size, though they’re not as accurateOpens in a new tab as lab tests: One small 2025 study Opens in a new tabfound a popular wearable underestimated VO₂ max by about six points. Still, using the same device consistently can help you follow trends over time.
- The talk test won’t give you a VO₂ max number but it can help you monitor changes in your aerobic fitness. If you can carry a conversation or sing during exercise, you're in an easier zone; when talking gets difficultOpens in a new tab, note your pace and how hard it feels. The real question is: “How hard are you able to push yourself before you start breathing hard?” says Dr. London. As your VO₂ max improves, you’ll need to push your body harder to feel the same breathlessness.
How Hydration Affects VO₂ Max
DehydrationOpens in a new tab can temporarily lower VO₂ max during hard effort by reducing blood volume and making your heart work harder to deliver oxygen to your muscles.
Here’s how that works: The heart and blood vessels are a closed-loop system. Blood returns from your body to the heart, travels to the lungs to pick up oxygen, returns to the heart, and is then pumped to your working muscles. The more oxygen-rich blood your heart can pump each minute, the more oxygen your muscles have to use and produce ATP.
According to Dr. London, when you become even mildly dehydrated, there’s less blood circulating in that loop. Less blood returns to and fills the heart, so it pumps out Opens in a new tabless per beatOpens in a new tab. Your heart rate rises to compensate, but during intense exercise, it may not fully make up for that decline.
In a small study, recreational athletes saw an average 2% dip in Opens in a new tabVO₂ maxOpens in a new tab when they worked out mildly dehydrated versus well-hydrated. They also used less oxygen per heartbeat, a finding consistent with the heart filling with and pumping out less blood during intense exercise when dehydrated.
Staying hydrated helps preserve blood volume so your heart can eject Opens in a new tabmore bloodOpens in a new tab with fewer beats. “You can control a component of VO₂ max by controlling how efficiently the heart can work,” says Dr. London.
One underhydrated session won’t lower your underlying fitness but consistently showing up to workouts underhydrated could tank performance. Once you lose about 3% of your body weightOpens in a new tab in water, your workout can cross the line from the good type of difficult to the frustrating, I-want-to-quit kind. Repeatedly cutting workouts short or reducing their intensity could limit the training stimulus that helps improve VO₂ max over time.
How electrolytes support VO₂ max performance
ElectrolytesOpens in a new tab don’t directly increase VO₂ max. Fluid does most of the work of maintaining the blood volume your heart relies on to deliver oxygen to working muscles. “The main driver is the fluid itself, which helps maintain blood volume,” says Dr. London. “Sodium becomes a key player in extended-duration exercise.”
Sodium is the primary electrolyte lost in sweat. Getting enough sodium helps your body hold onto the fluid you drink instead of losing it, and — especially when paired with carbs — it can help water move from your gut into your bloodstream a little faster. More blood returning to the heart allows it to fill more completely and pump more oxygen-rich blood to your muscles with each beat.
ElectrolytesOpens in a new tab also support the electrical signals involved in nerve impulses and muscle contractions, including contractions of the heart.
“You're gonna spend all this time training — make certain that you're staying adequately hydrated and that your electrolyte balance is in play so that you get the maximum benefit from that,” says Dr. London. Pay attention to muscle cramps, fatigue, mood swings, brain fog, low energy, and just feeling “off.” They’re all potential signs of less-than-ideal electrolyte balanceOpens in a new tab.
How to Hydrate for Better VO₂ Max Performance
Hydration won’t increase your aerobic capacity on its own. Training is what produces the cardiovascular and muscular adaptations that raise VO₂ max. But hydration can help you express the fitness you already have and sustain the workout intensity needed to keep improving it.
When fluid and sodium are dialed in, your heart has a better shot at maintaining blood volume, stroke volume, and oxygen delivery during hard exercise. When they’re off, the same workout can demand a higher heart rate and feel harder than it should.
Electrolyte needs vary with your activity and sweat losses. Dr. London generally relies on his diet for electrolytes on rest and active-recovery days and typically doesn’t supplement for strength training alone. But if he’s doing a hard two hours of cycling, he replenishes with two water bottles mixed with electrolytes. On especially active days that include a long run, hours working in the sun, and a sauna session, he’ll mix a stick pack of LMNT with water before getting in the sauna, or drink a can of LMNT Sparkling to compensate for sweat losses. “It's not a switch; it's more of a dial based on my activity level for that given day,” he says.
Think of hydration as removing a limiter, not adding a booster. "Is it going to shift your VO₂ max in and of itself without doing the work?” says Dr. London. “No, but it is absolutely key to being able to maintain that level of activity and that level of stress on your body."
Frequently Asked Questions: Hydration and VO₂ Max
Q: Can dehydration lower my VO₂ max?
Dehydration can lower VO₂ max during a workout by reducing circulating blood volume. With less blood available to pump, your heart may deliver less oxygen-rich blood to working muscles, especially during hard efforts.
Q: How dehydrated do you have to be for VO₂ max to temporarily drop?
Even mild dehydration can affect VO₂ max. In a small studyOpens in a new tab, recreational athletes who didn’t drink for 12 hours had a 2% lower VO₂ max during eight to 10 minutes of hard stationary cycling than they did while hydrated. However, individual fluid needs can vary based on factors such as your underlying health, training habits, and climate.
Q: Can electrolytes increase VO₂ max?
No. Electrolytes don't increase your underlying VO₂ max. They help supportOpens in a new tab blood volume and oxygen delivery during exercise so you can better perform at the fitness level you've trained for.