Sports Nutrition Glossary: Plain-English Definitions

Sports nutrition has a language problem. The science is sound, but the words used to describe it are borrowed from physiology labs and supplement marketing in roughly equal measure, and the result is a wall of jargon between an athlete and a decision they could make in thirty seconds if the terms were plain. Osmolality, multi-transporter, sensory-specific satiety. These describe simple things. They just sound like they do not.

This is a plain-English sports nutrition glossary, written for the athlete reading a label on a Saturday morning, not for a journal. Each term gets a short definition, what it means for you in practice, and where it shows up on the products you are comparing. Where a topic has a fuller explanation elsewhere on the Performance Lab, there is a link. Use it as a reference: bookmark it, jump to a term, get the answer, get back to training.

Jump to: Bonking · Calcium · Carbohydrate · Carbohydrate oxidation rate · Dual / multi-transporter · Electrolyte · Fructose · Gel · Glucose · Glycogen · GLUT5 transporter · Glycogen depletion · Gut training · High-carb fuelling · Hydration · Hyponatremia · Isotonic / hypotonic / hypertonic · Maltodextrin · Magnesium · Osmolality · Periodised nutrition · Potassium · Sodium · SGLT1 transporter · Sucrose · Sweat rate · 2:1 ratio · VO₂ max · Zone 2

Bonking

The sudden, severe drop in energy that hits when the body runs out of available carbohydrate during prolonged exercise. Also called hitting the wall.

In practice: Your legs feel hollow, your pace falls off a cliff, and your head goes foggy, often in the final third of a long effort. It is a fuelling problem far more often than a fitness problem. The fix is taking on carbohydrate earlier and more consistently, before the tank empties. We cover the mechanism in why you're still bonking.

Calcium (citrate vs. carbonate)

A mineral and minor electrolyte. The form matters for absorption: calcium citrate is absorbed more readily and is gentler on the stomach than calcium carbonate, which needs stomach acid to break down.

In practice: Calcium is a small player in exercise hydration compared with sodium, but when it appears in an electrolyte blend, the citrate form is the more bioavailable and stomach-friendly choice.

Carbohydrate

The body's primary fuel during moderate-to-high-intensity exercise. In sports nutrition it usually means glucose, fructose, maltodextrin, or sucrose, supplied to keep working muscles fed.

In practice: This is the number that matters most on a fuelling product. Grams of carbohydrate per serving tells you whether a product was built to fuel an effort or just to hydrate it. More on using it in using carbohydrates to fuel your performance.

Carbohydrate oxidation rate

The rate at which the body actually burns ingested carbohydrate for energy, measured in grams per hour. It is the real-world ceiling on how much fuel you can use, not just swallow.

In practice: Glucose alone tops out around 60 grams an hour because of transporter limits. Combining glucose and fructose raises the ceiling, which is the entire reason the 2:1 ratio exists (Jentjens & Jeukendrup, 2004).

Dual transporter / multi-transporter

A fuelling approach that uses more than one type of carbohydrate to recruit more than one absorption pathway in the gut, raising total carbohydrate uptake.

In practice: This is the science behind every 2:1 product. Glucose uses one doorway into the bloodstream, fructose uses another. Open both and you absorb more per hour. On a label, "maltodextrin and fructose" or "glucose and fructose" signals a multi-transporter formula.

Electrolyte

A mineral that carries an electrical charge in body fluids and governs hydration, nerve signalling, and muscle contraction. The main ones for athletes are sodium, potassium, magnesium, and calcium.

In practice: You lose electrolytes in sweat, sodium most of all. Replacing them supports fluid balance and muscle function. But electrolytes do not fuel the effort, which is a common and costly confusion, addressed in electrolytes alone won't fuel a long ride.

Fructose

A simple sugar found in fruit. In sports nutrition it is paired with glucose because it is absorbed by a different transporter, allowing higher total carbohydrate uptake.

In practice: Fructose is the second half of the 2:1 ratio. On its own at high doses it can cause GI distress, but balanced against glucose at roughly two parts glucose to one part fructose, it extends how much you can absorb without the gut rebelling.

Gel

A concentrated carbohydrate paste, usually 20 to 40 grams per packet, designed for fast intake during exercise.

In practice: Convenient and portable, but expensive per gram of carbohydrate and easy to over-rely on. Many athletes who fuel mostly on gels are paying a premium and stacking GI load. A drink mix often delivers the same carbohydrate for less, which is part of the cost discussion in what it actually costs to fuel a four-hour ride.

Glucose

The body's preferred simple sugar and the form carbohydrate is ultimately used as for energy. Absorbed via the SGLT1 transporter.

In practice: Glucose is fast and reliable but limited: the SGLT1 pathway saturates around 60 grams an hour. That ceiling is why glucose-only products struggle to fuel long, hard efforts on their own.

Glycogen

The stored form of carbohydrate, held in muscle and liver. It is the body's onboard fuel tank for exercise.

In practice: You start a session with a finite glycogen store. Fuelling during exercise spares it and extends how long you can hold an effort. When it runs low, you bonk.

GLUT5 transporter

The protein that carries fructose across the gut wall into the bloodstream. It works independently of the glucose transporter.

In practice: GLUT5 is the second doorway. Because it handles fructose and not glucose, recruiting it via a 2:1 formula adds absorption capacity on top of the glucose pathway rather than competing with it.

Glycogen depletion

The state of having drained your stored carbohydrate. It is the physiological event underneath bonking.

In practice: Depletion is gradual, then sudden. Consistent carbohydrate intake from early in a long effort delays it. Waiting until you feel empty to start fuelling is waiting too long, which is the point of the 90-minute mark.

Gut training

The practice of progressively training your digestive system to tolerate and absorb higher amounts of carbohydrate during exercise.

In practice: The gut adapts like any other system. Most GI problems at races come from trying a high intake the body has never practised. Build tolerance in training over weeks, as laid out in training your gut.

High-carb fuelling

An approach that targets the upper end of carbohydrate intake during exercise, broadly 80 grams an hour and above, enabled by multi-transporter formulas and a trained gut.

In practice: Useful for long, hard efforts and for athletes who have built the tolerance. It is not automatically better for everyone, and chasing very high numbers without gut training tends to backfire. The nuance is in 120g of carbohydrates per hour.

Hydration

Maintaining adequate body fluid during exercise, primarily by replacing water and electrolytes lost through sweat.

In practice: Hydration and fuelling are related but separate jobs. A hydration product manages fluid and electrolytes; it does not necessarily fuel the effort. Knowing which one is in your bottle is half of fuelling well.

Hyponatremia

A dangerously low blood sodium concentration, usually caused by drinking large volumes of plain water without replacing sodium during long exercise.

In practice: More common than most recreational athletes realise on long, hot efforts. The defence is taking sodium alongside fluid rather than over-drinking water. This is a genuine medical risk on ultra-distance events, not a marketing talking point.

Isotonic / hypotonic / hypertonic

Terms describing a drink's concentration relative to body fluid. Hypotonic is more dilute, isotonic is roughly equal, hypertonic is more concentrated.

In practice: Concentration affects how fast a drink empties from the stomach and delivers fluid. Hypotonic and isotonic mixes tend to hydrate faster; very concentrated mixes deliver more carbohydrate but can sit heavier. It comes down to osmolality, below.

Maltodextrin

A carbohydrate made of chains of glucose molecules, derived from corn or other starches. It is absorbed as glucose but has a lower osmolality than free sugar, so it is gentler on the stomach at higher concentrations.

In practice: Maltodextrin is the workhorse of most performance drink mixes, including the glucose side of a 2:1 formula. It lets a product carry a lot of carbohydrate without becoming syrupy. It is the first ingredient on the Olway® Performance Drink Mix label.

Magnesium (citrate, oxide, glycinate)

A mineral involved in muscle and nerve function. The form determines absorption: magnesium citrate and glycinate are well absorbed, while magnesium oxide is cheap but poorly absorbed.

In practice: When magnesium appears in an electrolyte product, the form tells you whether it is doing much. Oxide is largely there for the label; citrate or glycinate is the more usable choice.

Osmolality

A measure of how many dissolved particles are in a fluid. In drink mixes it determines how concentrated the solution is and how quickly it leaves the stomach.

In practice: This is why maltodextrin matters. A given amount of carbohydrate delivered as maltodextrin has fewer dissolved particles than the same amount as simple sugar, so it carries more fuel at a tolerable concentration. Lower osmolality at a given carb load generally means easier digestion.

Periodised nutrition

Adjusting carbohydrate intake to match the demands of specific sessions and training phases, rather than eating the same way every day (Burke et al., 2011).

In practice: High-intensity and long sessions get high carbohydrate; easy recovery sessions need less. Matching fuel to the session is more effective than a flat approach, and it is cheaper than over-fuelling everything.

Potassium (citrate)

An electrolyte that works alongside sodium in fluid balance and muscle contraction. Lost in sweat, though in smaller amounts than sodium.

In practice: A supporting electrolyte rather than the headline. Potassium citrate is the well-absorbed form. Useful in the mix, but sodium is the one that does the heavy lifting on a long, sweaty effort.

Sodium (citrate vs. chloride)

The primary electrolyte lost in sweat and the most important to replace during long exercise. Sodium citrate is gentler on the stomach and can help buffer acidity; sodium chloride is plain salt.

In practice: Sodium supports fluid balance and helps prevent hyponatremia and cramping on long efforts. Olway® Performance Drink Mix uses sodium citrate at 200mg per serving for that reason. For higher sweat or heat, you add an electrolyte product on top.

SGLT1 transporter

The protein that carries glucose (and sodium) across the gut wall. It is the main glucose absorption pathway and it saturates at roughly 60 grams of glucose per hour.

In practice: The SGLT1 ceiling is the reason glucose-only fuelling tops out around 60 grams an hour. To go higher, you recruit the separate fructose pathway, which is what the 2:1 ratio does.

Sucrose

Table sugar, a molecule of glucose bonded to fructose in a roughly 1:1 ratio. Used in some drink mixes as a combined carbohydrate source.

In practice: Sucrose does provide both glucose and fructose, but in a fixed 1:1 ratio rather than the 2:1 that research favours for oxidation efficiency. Products built on sucrose alone are partway to a multi-transporter approach, not all the way there.

Sweat rate

How much fluid you lose to sweat per hour, which varies widely by individual, intensity, and conditions.

In practice: Your sweat rate drives how much fluid and sodium you need to replace. You can estimate it by weighing yourself before and after a measured hour of exercise. It is the basis of any personalised hydration plan.

2:1 ratio

A carbohydrate blend of two parts glucose (or maltodextrin) to one part fructose, designed to recruit both gut transporters and raise carbohydrate oxidation on longer efforts.

In practice: The 2:1 ratio lets you absorb meaningfully more carbohydrate per hour than glucose alone, up to around 90 grams, which is where most everyday athletes train. It is the formula behind Olway® Performance Drink Mix, and the full science is in the 2:1 ratio breakdown.

VO₂ max

The maximum rate at which your body can use oxygen during exercise, a common measure of aerobic fitness.

In practice: A useful fitness benchmark, but not directly a nutrition term. It matters here because higher intensities, expressed as a percentage of VO₂ max, burn proportionally more carbohydrate, which raises your fuelling needs.

Z2 / Zone 2

A training intensity zone, roughly the upper end of easy aerobic effort, where you can still hold a conversation. Used to build aerobic base and fat-burning efficiency.

In practice: Zone 2 sessions burn a higher proportion of fat and a lower proportion of carbohydrate, so fuelling needs are lower than for hard sessions. It is a clear example of why periodised nutrition makes sense: not every ride needs 90 grams an hour.

Using this glossary

Most of sports nutrition reduces to a handful of these ideas working together. Carbohydrate fuels the effort, transporters set the ceiling on how much you can use, the 2:1 ratio raises that ceiling, electrolytes keep the system running, and periodisation matches the fuel to the session. Once those connect, the labels stop being a wall of jargon and start being a short list of numbers you can read.

Keep this page handy and come back to it whenever a term trips you up. When you are ready to put it to work, the best endurance drink mixes in Canada comparison applies these ideas to real products, and you can find Olway® at a retailer near you on the stockists page.

References

Jentjens RLPG, Jeukendrup AE. Oxidation of combined ingestion of glucose and fructose during exercise. Journal of Applied Physiology. 2004;96(4):1277–1284. doi:10.1152/japplphysiol.00974.2003
Burke LM, Hawley JA, Wong SHS, Jeukendrup AE. Carbohydrates for training and competition. Journal of Sports Sciences. 2011;29(sup1):S17–S27. doi:10.1080/02640414.2011.585473
Podlogar T, Wallis GA. New Horizons in Carbohydrate Research and Application for Endurance Athletes. Sports Medicine. 2022;52(Suppl 1):5–23. doi:10.1007/s40279-022-01757-1