Hydration, Electrolytes & Muscle Cramps: Physio Tips for Ultra Races
Few things derail an ultra race faster than muscle cramps. One minute you’re moving well, the next your calves, quads, or hamstrings seize up and force you to slow — or stop entirely.
Hydration and electrolytes are often blamed, but at Thrive Physio, we know the story is more complex. While fluids and salts matter, muscle cramps during ultra races are usually a load and fatigue problem first, with hydration playing a supporting role.
Here’s what physiotherapists want ultra runners to understand about cramps — and how to reduce your risk on race day.
What Are Muscle Cramps, Really?
Exercise-associated muscle cramps are sudden, painful, involuntary muscle contractions that often occur:
Late in long races
During climbs or descents
When fatigue is high
In muscles that are already heavily loaded
They’re common in ultra running because of the duration, terrain, and cumulative fatigue involved.
Is Dehydration the Main Cause of Cramps?
Short answer: not usually on its own.
Research and clinical experience show that dehydration and electrolyte loss don’t fully explain why cramps happen. Many runners cramp despite drinking regularly, while others with similar hydration levels don’t cramp at all.
Hydration matters — but it’s rarely the sole culprit.
The Bigger Driver: Muscle Fatigue & Training Load
From a physiotherapy perspective, cramps are strongly linked to:
Muscle fatigue
Reduced neuromuscular control
Muscles working beyond their trained capacity
In ultra races, this often happens when:
Training hasn’t prepared muscles for race-specific demands
Elevation gain/loss exceeds training exposure
Pace is too aggressive early on
Strength endurance is lacking
Fatigue alters movement patterns
Cramps tend to occur in muscles doing the most work — not randomly.
Where Hydration & Electrolytes Fit In
While they’re not the sole cause, hydration and electrolytes still play an important role in supporting muscle function over long distances.
Hydration
Being significantly dehydrated can:
Increase perceived effort
Reduce blood flow to working muscles
Accelerate fatigue
Both under-drinking and over-drinking can cause problems, especially in long events.
Electrolytes
Electrolytes (particularly sodium) help with:
Fluid balance
Nerve signal transmission
Muscle contraction
Large sodium losses through sweat — especially in hot conditions or salty sweaters — can contribute to earlier fatigue and cramp risk.
Why “Just Take More Electrolytes” Isn’t the Fix
One of the most common mistakes we see is reacting to cramps by aggressively increasing electrolyte intake mid-race.
This often:
Doesn’t resolve cramps
Causes gut upset
Distracts from pacing and movement strategy
If cramps were purely an electrolyte issue, supplements would fix them instantly — but they rarely do.
Cramps usually reflect a mismatch between race demands and muscle capacity.
Practical Physio Tips to Reduce Cramp Risk
1. Train for the Specific Demands of Your Race
Muscles cramp when they’re asked to do more than they’re conditioned for.
That means:
Training on similar terrain
Preparing for both climbs and descents
Practising long periods of fatigue
Including back-to-back long runs appropriately
Specificity matters more than total mileage.
2. Build Strength Endurance
Strong muscles resist fatigue better.
Physio-guided strength training should focus on:
Calves, quads, hamstrings, and glutes
Eccentric control (especially for downhills)
Single-leg strength
Fatigue-resistant capacity, not just max strength
Strength training isn’t optional for ultra runners — it’s protective.
3. Pace Conservatively Early
Many cramps occur because the nervous system is overloaded early in the race.
Starting slightly easier than planned:
Preserves neuromuscular control
Delays fatigue
Reduces late-race cramp risk
Ultra racing rewards patience.
4. Hydrate to Thirst, Not Panic
Rather than rigid drinking rules:
Drink regularly
Use thirst as a guide
Adjust for heat and sweat rate
Practise your strategy in training
Consistency beats overcorrection.
5. Use Electrolytes Strategically
Electrolytes can be helpful when:
Races are long and hot
You’re a heavy or salty sweater
Intake is tested in training
More is not always better — tolerance matters.
6. Adjust Movement When Early Cramping Appears
Early warning signs include twitching or tightening.
Helpful strategies:
Shorten stride
Reduce pace briefly
Change cadence
Walk climbs earlier
Stretch lightly between contractions, not during severe cramping
Sometimes managing load in the moment is more effective than nutrition changes.
Why Some Runners Cramp and Others Don’t
Cramps aren’t a sign of weakness. They’re a sign that:
Muscle capacity
Nervous system tolerance
Training load
Race execution
…aren’t fully aligned yet.
The good news? These factors are modifiable.
Key Takeaways for Ultra Runners
Cramps are usually driven by fatigue and load, not just hydration
Electrolytes support performance but aren’t a magic fix
Strength endurance and race-specific training reduce cramp risk
Smart pacing matters more than last-minute supplements
Physiotherapy helps identify and address the root causes
How Thrive Physio Can Help
At Thrive Physio, we work with ultra runners to:
Identify why cramps occur
Build fatigue-resistant strength
Improve load tolerance
Optimise race preparation and recovery
Keep you moving forward when it matters most
If cramps have cost you a race — or you want to prevent them — a physio-led approach can make a real difference.
