Sports Drinks Explained: Hypertonic, Hypotonic & Isotonic
Walk into any UK supermarket, and the sports drink aisle can feel like alphabet soup. Bottles, powders, “hydration tabs”… and all the things. Do you really need isotonic? What’s hypotonic? And when on earth would you drink something hypertonic?
In this blog, I’ll break it down in plain English. You’ll learn:
The difference between hypotonic, isotonic, and hypertonic drinks
When to use each type for training, recovery, or hot weather
UK examples you’ll actually find on the shelves
Signs your hydration is on track (and when it isn’t)
How to make your own budget-friendly sports drinks at home
By the end, you’ll know exactly which drink (or DIY mix) is right for you.
Why Sports Drinks Exist
At their core, sports drinks are just a mix of fluid + carbs + electrolytes. Depending on the concentration, they can:
Rehydrate you quickly
Top up your carbohydrate (energy) stores
Or do both at once
The trick is knowing which type to pick for your situation.
A quick word on osmolality
Osmolality is just a measure of how concentrated a liquid is. Your blood sits at around 275–295 mOsmol/kg. Sports drinks are categorised by how their concentration compares to that.
A drink that's more dilute than your blood gets absorbed faster. A more concentrated drink takes longer because your body has to dilute it first.
The Three Types of Sports Drinks
Hypotonic
What it means: Lower concentration of carbs (under 5%) and electrolytes than your blood. Therefore it’s absorbed quickly.
Purpose: Rapid hydration, not much energy.
Best for: Hot weather, short workouts, or when you don’t need extra carbs.
UK Examples:
High5 Zero electrolyte tabs
Nunn Sports tabs
Precision Hydration tabs
Lucozade Sport Hydro Active
Powerade Zero
DIY version: 1 litre water 50ml fruit juice + pinch of salt.
Worth keeping in mind: A large 2021 meta-analysis found hypotonic drinks were the most effective for maintaining hydration during continuous exercise. If pure hydration is your goal, hypotonic is actually the smarter choice.
Isotonic
What it means: Similar concentration to your blood (~6–8% carbs). Middle ground.
Purpose: Hydration and energy. The all-rounder.
Best for: Endurance training, team sports, or anything lasting longer than 60 minutes.
UK Examples:
Lucozade Sport
SIS GO Isotonic Gels
DIY version: 1 litre water + 200ml regular squash (not sugar-free) + pinch of salt.
Hypertonic
What it means: Higher concentration of carbs (over 8%) and electrolytes than your blood.
Purpose: Energy first, hydration second. Absorbs slowly.
Best for: Refuelling after training or ultra-endurance events (always pair with water).
UK Examples:
Coca-Cola (yes, really)
SIS GO Energy Powder (when made with less water for a stronger mix)
DIY version: 500ml fruit juice + pinch of salt (sip alongside water).
What About Hydration Tabs and Powders?
These have become one of the fastest-growing parts of the market, and they're worth a mention because they're genuinely practical. Electrolyte tablets (like High5 Zero or Nuun) dissolve in water to create a hypotonic drink. I like how easy they are to carry in a gym bag or pocket.
Powders like SiS GO Electrolyte sit more in the isotonic category depending on how you mix them. The beauty of powders is that you can adjust the concentration. Dilute it more for a hypotonic effect before or during exercise, or make it stronger for post-workout refuelling.
Signs Your Hydration Is On Track
Sports drinks only help if you actually need them. Here’s a simple check.
Signs You’re Hydrated
Pale yellow (straw-coloured) urine
You’re not overly thirsty
Steady energy levels
Normal sweating pattern for you
Signs You May Need to Pay More Attention
Dark yellow or strong-smelling urine
Feeling dizzy, lightheaded, or unusually fatigued
Headaches creeping in during or after exercise
Muscle cramps
Heart rate feels higher than usual for the same effort
What to Do
If it's mostly hydration you need, a hypotonic drink (or water with a pinch of salt) is usually enough. If you're flagging on energy as well as hydration, isotonic is your best bet. If you've finished training and need to replenish glycogen, a hypertonic option with water alongside can support recovery.
DIY Sports Drinks on a Student Budget
Here are three cheap and cheerful mixes you can make in your kitchen:
Hydration (hypotonic): 1 litre water + 50ml fruit juice + small pinch of salt
All-rounder (isotonic): 1 litre water + 200ml squash (not sugar-free) + pinch of salt
Fuel (hypertonic): 500ml fruit juice + pinch of salt + water on the side
Pro tip: A banana + water, a handful of raisins, or a slice of malt loaf can be just as effective as branded sports nutrition for most training sessions. Real food counts.
At a Glance
Hypotonic = fastest hydration (lower carbs, absorbed quickest)
Isotonic = hydration + energy (the everyday all-rounder)
Hypertonic = energy-focused (best post-training, always with water)
The research increasingly points to hypotonic drinks being the best option purely for hydration during exercise. But isotonic drinks remain the most practical choice for most people doing moderate-to-long sessions where energy and hydration both matter. And hypertonic? Think of it as recovery fuel, not a mid-workout drink.
Sources:
Rowlands, D. S., Kopetschny, B. H., & Badenhorst, C. E. (2022). The Hydrating Effects of Hypertonic, Isotonic and Hypotonic Sports Drinks and Waters on Central Hydration During Continuous Exercise: A Systematic Meta-Analysis and Perspective. Sports medicine (Auckland, N.Z.), 52(2), 349–375. https://doi.org/10.1007/s40279-021-01558-y
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