Hydration: The Free Performance Boost Most Athletes Ignore

Nutrition • Published December 8, 2014 • Updated October 1, 2026 • By PJ Newton

If I told you there was a legal, free, universally available way to help protect your training output, you would want to know what it is.

It is water. Easy to overlook when you are busy researching supplements.

Let fluid losses build up during a long session — particularly in the heat — and performance can suffer. How much depends on the workout, the conditions, and the athlete.

Here is a practical system for staying on top of it.

Why dehydration hits harder than most people expect

A fluid deficit adds cardiovascular strain and makes it harder to regulate body temperature. A familiar pace can feel harder. The ACSM guidance emphasizes starting exercise hydrated and matching your plan to your own losses.

Hydration helps reduce heat-illness risk. In military training, acclimatization, work-rest breaks, equipment, workload, and illness also matter. Drinking enough does not guarantee that you will avoid heat exhaustion or heat stroke. Cramps can have other causes too. The NATA heat-illness statement covers the wider prevention plan.

Drinking more fluid than you lose can cause hyponatremia — dangerously low blood sodium — even with sports drinks. Adding electrolytes does not make over-drinking safe.

Step 1: Start every day hydrated

A planning starting point: half your bodyweight in ounces of drinks per day — 100 ounces for a 200-pound athlete. This is a rough coaching estimate, not a minimum everyone has to hit.

Adjust up or down for thirst, training, and conditions. Heat and high sweat losses usually call for more. Cold can blunt thirst cues; keep water accessible. Food and other drinks contribute to your total water intake too.

Whole fruits and vegetables contribute meaningful water intake and should be the foundation of your diet regardless.

Step 2: Manage hydration during training

Simple starting estimate for longer sessions: divide your bodyweight by 30 to get ounces per 15 minutes.

Example: 200 lb ÷ 30 = ~6.5 oz every 15 minutes.

Do not force that amount down. A cool session and a hot, loaded ruck have different demands. If you do not know your sweat rate, start by drinking to thirst. Refine the plan with a sweat test, and avoid drinking enough to gain bodyweight during exercise.

More precise method: run a sweat rate test.

Weigh yourself before training, after emptying your bladder, naked or in minimal dry clothing. Record kilograms.
Train for a measured amount of time. Record how much you drink in liters and, if you urinate during the test, how much.
Towel off and weigh yourself afterward under the same conditions.
Estimate sweat loss: kilograms lost + liters drunk − liters of urine.
Divide by the session length in hours to get liters of sweat per hour.

Example: you start at 90 kg and finish at 89 kg after one hour. You drank 0.5 L and did not urinate. Estimated sweat loss is 1 + 0.5 = 1.5 L, so your sweat rate is about 1.5 L/hour. Your remaining fluid deficit is about 1 L, because you already drank the other 0.5 L.

For conversions, 1 kg is about 2.2 lb and 1 L is about 34 fluid ounces. Repeat in your actual training conditions. The NATA calculation gives an estimate to guide drinking, not a requirement to replace every drop immediately.

Sweat also contains electrolytes, particularly sodium. The amount varies substantially between athletes. During long, sweaty training days, use food and an electrolyte drink as needed alongside water rather than assuming everyone loses the same amount of salt.

Step 3: Rehydrate after training

If you need to recover quickly for another session, aim to replace roughly 125–150% of your remaining fluid deficit over the next few hours, with food or electrolytes. If you finish one pound lighter — about 16 fluid ounces of water — that is roughly 20–24 ounces afterward. Do not use total sweat loss here if you already replaced part of it during training.

With a normal meal and plenty of time before the next session, you can usually restore fluid balance through regular eating and drinking. You do not need to chug the full amount at once.

On electrolyte supplements

This is one of the few places a supplement is worth considering — not because electrolytes are magic, but because flavor can make drinking easier for some people.

Options worth trying: LMNT (unflavored is excellent for high-volume sessions), Osmo Active Hydration, Salt Stick, NUUN tablets. Test individually — some people have GI sensitivity to certain formulations.

The bottom line

Before you research supplements, optimize sleep, or dial in your macros — make sure you are drinking enough water.

Follow the three steps above for one week and note your energy, recovery, and training output. If fluid losses have been getting ahead of you, this is a useful place to make an adjustment.

For a complete recovery picture, the importance of sleep post is the natural complement to this one — hydration and sleep together are the two most underinvested free performance tools available.