Nausea, Stitches and Cramp: What Your Gut Is Doing in the Middle of Class

Twenty minutes into a hard class, someone goes quiet. A teenager who was sharp in the warm-up is suddenly pale and asking to sit down. An adult finishes a round of kumite drills and stands at the wall, breathing carefully.

This happens in every club, every week, and is rarely discussed as anything more than you ate too close to class. Sometimes that is the whole story. Often it is not. The gut behaves differently under exercise than at rest, and knowing what changes turns guesswork into fixes.

Your gut loses the argument over blood

At rest, a large share of your circulation is dedicated to the digestive tract, which is doing real work: moving food along, absorbing it, secreting into it.

Start training hard and that arrangement is renegotiated within minutes. Working muscle needs blood, and so does skin, because you need to shed heat. The body meets that demand partly by pumping more and partly by supplying less elsewhere, and the digestive tract is first to be cut back. Gut blood flow falls, and falls further the harder you work.

The consequence is simple. Digestion slows, and whatever is in your stomach when the class gets hard sits there far longer than it would at rest. Almost everything else here follows from that one fact.

Four problems that feel like one

Students describe all of this as my stomach. It is actually four separate things with four separate answers.

Nausea and a stomach that sloshes

This is delayed gastric emptying. The stomach is holding a volume it cannot pass on at the usual rate, and a full stomach shaken by kicks, turns and impact produces nausea and that unmistakable sloshing feeling.

Emptying is slowed by large volumes, high fat, plenty of fibre, very concentrated drinks, and intensity itself. What leaves fastest is a small volume of dilute fluid, then simple carbohydrate, with fat and fibre slowest.

The stitch under the ribs

The sharp catching pain below the ribs on one side has a formal name in sports medicine: exercise-related transient abdominal pain. The mechanism is still debated rather than settled, and the better-supported explanations involve irritation of the membranes lining the abdominal cavity as the trunk moves.

What is consistent is what makes it more likely: training soon after eating, and drinking a large volume of a concentrated sugary drink shortly before.

Cramp

The arch of the foot that seizes in a long stance. The calf that locks during repeated kicks.

The familiar explanation is dehydration and salt loss, and in a long, hot session that is genuinely part of the picture. But cramp also turns up in cool rooms in well-hydrated people, and current understanding gives a large role to neuromuscular fatigue: a muscle worked hard in a shortened position, with the reflexes that regulate it tired too.

Treat both. Fluid and salt for long hot sessions, sensible load progression for everything else.

Reflux, and the belt

This one belongs to us specifically. An obi is tied firmly around the abdomen, and karate then asks you to brace the trunk repeatedly, exhale forcefully into a kiai, twist, and drop into stances. All of that raises pressure inside the abdomen.

Raise that pressure over a stomach still full and the contents get pushed upward. Hence the burning behind the breastbone, the sour taste at the back of the throat, and the dry cough late in class.

The karate-specific part

Generic advice about eating before sport misses several things that are true in our hall.

• The obi is an external pressure band a runner or swimmer does not wear
• Kiai and every sharp technique involve bracing and forced exhalation, which spikes abdominal pressure
• Hikite and tai sabaki twist the trunk repeatedly rather than moving it in one plane
• Kumite is intermittent and near-maximal, and intensity is the strongest single driver of reduced gut blood flow
• Kata brings static holds, deep positions and long exhalation, favouring reflux and stitch over nausea
• Seiza and kneeling work fold the abdomen over itself

So a kumite-heavy evening tends to produce nausea, and a kata-heavy one stitch and reflux. That difference is a useful clue for a student working out what to change.

What to change this week

• Finish a normal meal about three hours before class, and keep anything in the last hour small, low in fat and low in fibre
• If you need something close to class, make it a small portion of simple carbohydrate, not a proper meal
• Sip through the session rather than drinking one large volume at the door
• For a sixty to ninety minute class plain water is enough for almost everyone, and a concentrated sugary drink near the start makes stitch and nausea more likely, not less
• If a stitch arrives, slow down, make the out-breath longer than the in-breath, and press your palm into the area on a long exhale
• Loosen the obi a notch if reflux is your pattern, and do not lie flat straight after eating
• Change one variable at a time and give it two or three sessions before judging it
• Rehearse everything in ordinary training, never for the first time on a competition day

One more point worth knowing: tolerance is trainable. A gut repeatedly asked to handle a little food and fluid during exercise generally adapts. That is why a competitor should practise tournament-day eating in the weeks beforehand rather than improvising on the morning.

When it is not about food

Some of this is not nutrition at all, and it is important not to force it to be.

Watch for pain that continues long after class, pain that wakes a child at night, repeated vomiting, blood, unexplained weight loss, or symptoms that appear away from training. Those are not fuelling problems and belong with a doctor rather than a coach.

Every instructor also knows the child whose stomach hurts only before a grading, and who is fine ten minutes in. Take it seriously, but the answer is a conversation, not a change of breakfast.

Come and see a class for yourself

Most of this sorts itself out within a few weeks once someone is watching. A good instructor notices the student who goes quiet in the third round and asks what they ate, and when.

Kartal Karate Academy trains at Yakacık Spor Kulübü in Kartal, Monday to Saturday between 09:00 and 21:00, with Sensei Behzad Yaghoubian and Sensei Homa Yaghoubian, both International Karate Champions.

The first class is a free trial, so you can see how a session runs before committing to anything. Book at karatekartal.fit/en/register, or call +90 501 366 56 30.