The Truth About Muscle Cramps.
Trail Notes | Female Athlete Racing
what actually happens when everything seizes up
The Truth About
Muscle Cramps.
You are running well. And then, without much warning, your calf or hamstring locks up so completely that you have to stop and stand there like a statue, waiting for something to release. You have been here before. Most trail runners have.
The questions that follow are almost always the same. Did I not drink enough electrolytes? Should I have taken more salt? Was it the heat? Was it not enough training? Was there something I should have done differently in the days before the race?
These are the wrong questions. Not because electrolytes do not matter at all, but because the electrolyte depletion model of muscle cramping is not well supported by evidence, and the athletes who keep chasing electrolyte solutions often keep cramping. The research has moved on. Understanding what is actually happening changes how you prepare, how you respond, and how much power you have over this in a race.
Cramps are a neuromuscular event. They are caused by fatigue, not by what you forgot to drink.
Cramps are not an electrolyte problem. They are a neuromuscular fatigue problem. And that distinction changes everything about how you address them.
The good news is that a neuromuscular problem has neuromuscular solutions — and one of them works in under a minute.
Trail Note · 01
Why the electrolyte model does not hold up
The electrolyte depletion theory of cramping was intuitive. Sweat contains sodium, potassium, and magnesium. Endurance exercise produces a lot of sweat. Therefore, running low on electrolytes must cause cramps. Drink more salt. Take magnesium tabs. Problem solved.
Except it does not solve the problem for most athletes, and the research does not support the model. When researchers measure blood sodium and electrolyte levels in cramping versus non-cramping athletes at the same race distance and conditions, the levels are not consistently different. Generalised electrolyte depletion would cause widespread muscle dysfunction throughout the body. But cramps are localised — they happen in the specific muscles under the highest load. Your calf cramps because it has been doing the most work for the longest time. Your hamstring cramps on the steepest hill because it is the muscle being most challenged in that moment.
That is not a salt deficiency. That is a fatigue signal from a specific, overworked neuromuscular system.
Trail Note · 02
What is actually happening in your muscle
In a healthy, well-functioning muscle, the nervous system operates a careful balance between excitatory signals (telling the muscle to contract) and inhibitory signals (telling the muscle to relax). This balance is what allows you to run smoothly — muscles firing when required, releasing when not.
Under fatigue, this balance shifts. The muscle spindles (sensory receptors that detect muscle stretch) become increasingly active and send strong excitatory signals to the motor neuron. At the same time, the Golgi tendon organs — the structures responsible for sending the inhibitory “relax now” signal — become less effective. The inhibitory signal weakens. The excitatory signal dominates.
When excitation overwhelms inhibition at the motor neuron, the muscle cannot turn off. It fires continuously and involuntarily. That is a cramp. The muscle has not run out of anything — the system controlling it has lost its balance under sustained demand.
The neuromuscular model in simple terms
Muscle fires when the “go” signal exceeds the “stop” signal.
Under fatigue, the “go” signal increases and the “stop” signal weakens.
When “go” dominates completely, the muscle cannot stop contracting.
The solution is to reset the balance, not to add electrolytes to the bloodstream.
Trail Note · 03
Why pickle juice works in 35 seconds
If you have ever heard trail runners swearing by pickle juice for cramps, the mechanism behind it is now understood — and it is not what most people assume.
Research by Miller et al. (2022) showed that pickle juice stopped electrically-induced muscle cramps in approximately 35 seconds. This is far too fast for any electrolyte to be absorbed and transported to the cramping muscle. When something works in 35 seconds after being swallowed, it is working on the nervous system, not on the blood chemistry.
Here is what is actually happening: the acidic, pungent compounds in pickle juice (primarily acetic acid) stimulate specialised receptors in the throat called TRP channels (transient receptor potential channels). These channels send a signal up the vagus nerve to the brainstem. The brainstem then modulates motor neuron activity, reducing the excessive excitatory signal that is causing the cramp. The system is reset. The muscle can relax.
This explains why other strong sensory stimuli (very salty, very sour, or pungent flavours) may also help. The mechanism is neural. You are treating the nervous system, not the muscle.
Pickle juice is not a salt replacement. It is a neural signal — a message sent from your throat to your brainstem to tell your cramping muscle that it is allowed to stop.
Trail Note · 04
Who is most likely to cramp
The neuromuscular fatigue model makes it very clear who is at highest risk: athletes who accumulate neuromuscular fatigue faster than their system can manage. This happens when:
Higher cramp risk when…
You start the race faster than your training-adapted pace. More effort earlier = faster fatigue accumulation.
The race is longer or harder than your long training runs. Your neuromuscular system hits unfamiliar fatigue territory.
You have undertaken less strength training than usual. Stronger muscles fatigue more slowly; less capacity = earlier neuromuscular threshold.
The terrain is significantly more technical, hilly, or steep than your training terrain.
It is hotter than training conditions. Heat accelerates cardiovascular and neuromuscular fatigue.
Notice that most of these risk factors are about load exceeding the system’s trained capacity. The solution is almost always: build capacity higher in training, or reduce load more conservatively on race day.
Trail Note · 05
How to train for cramp resistance
If cramps are a neuromuscular fatigue problem, the training solution is to raise the threshold at which neuromuscular fatigue reaches the cramping point. This is done through two primary mechanisms.
Train under fatigue
Long runs that actually accumulate fatigue. Running-specific fatigue in training raises the threshold at which the neuromuscular system loses its balance in races.
Strength training
Stronger muscles fatigue more slowly. Consistent calf, hip, and single-leg strength work increases the structural capacity that delays neuromuscular fatigue onset.
Race-specific terrain
Train on terrain similar to your race. Technical, steep, or long descents that your body has not encountered in training create neuromuscular demands your system is not prepared for.
Pacing discipline
Starting too fast is the most consistent trigger. A controlled first third extends the time before neuromuscular fatigue reaches the cramping threshold.
Trail Note · 06
What to do when you cramp in a race
Knowing the mechanism changes your race-day response. You are not trying to replace electrolytes that do not exist. You are trying to reset a neuromuscular system that has lost its balance under fatigue. Here is how to do that.
In the moment
Slow down or stop briefly — the cramp is a fatigue signal. Reducing load immediately is the first response.
Use your pickle juice or strong electrolyte shot — the TRP channel mechanism works fast. Carry a small bottle of pickle juice, or use a strong sour/salty shot. Take it at the first twinge, not after the full cramp has locked you up.
Gentle passive stretch — for a full calf or hamstring cramp, passive stretching (not aggressive forcing) allows the Golgi tendon organ to fire and restore some inhibitory signal. Do not force a locked muscle.
Walk before you run again — allow the muscle to re-engage at lower load before returning to running pace. Rushing back into full effort after a cramp increases recramp risk significantly.
Her Trails coaching cue
A cramp is not a failure. It is your body telling you that your neuromuscular system has hit its current limit. The response is reduce, reset, and restart — not push through it.
Trail Note · 07
What about salt tabs and electrolytes?
Electrolyte replacement still has a place in long endurance events, particularly in heat, and particularly for hydration, fluid balance, and gut function. The concern is not that electrolytes are useless — it is that chasing electrolytes as the primary cramp prevention strategy leads athletes to underinvest in the actual solutions.
Salt tabs may also have a small contribution to cramp management via the TRP channel mechanism — a strong salty flavour hitting the throat may provide some of the same sensory reset as pickle juice. But if you are taking salt tabs primarily to prevent cramps, and the cramps keep happening, the intervention is not working. The root cause is fatigue, not sodium deficiency.
Hydrate well, take electrolytes appropriately for heat and distance, and carry something strong and pungent for the moment your calf sends you the signal. But invest the real cramp prevention work in your training, your pacing, and your strength program.
Train the capacity. Pace the race. Carry the pickle juice. In that order.
Trail Note · 08
The reframe that changes the race
If cramps have derailed your races, the most important shift you can make is from blaming your electrolytes to understanding your fatigue. You are not a person who fails to drink the right things. You are an athlete whose neuromuscular system reached its current threshold earlier than you needed it to.
That threshold is trainable. It moves with your strength, your long-run consistency, your pacing discipline, and the specificity of your terrain preparation. The athletes who rarely cramp are not the ones who have found the right electrolyte tab. They are the ones whose neuromuscular systems have been trained to stay balanced under extended load.
You can build that. Carry the pickle juice for race day. Build the capacity for the next one.
Cramps are a fatigue signal. The answer is building capacity, pacing with patience, and resetting the system when it needs it.
Strength training. Consistent long runs. Patient starting effort. Pickle juice. In the bag, not just in the plan.
train the system. trust the process. carry the pickle juice.
Written by the Her Trails coaching team
Trail Notes are evidence-informed coaching journals written for women who train, race and run on trails. Made to be absorbed in ten minutes and remembered for a season.
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