Why a sudden hard workout can set off an attack, what oxygen and VO2max have to do with it, and how steady training turns exercise from trigger into treatment.
Rarely. Blood oxygen stays near normal during exercise at sea level.
A sudden gap between energy demand and aerobic supply, plus surges in blood pressure, lactate and CGRP.
A long warm-up, steady aerobic work, and fitness built over weeks.
To see why exercise can set one off, it helps to know what an attack is. Migraine is not just a bad headache. It's a neurological disorder: the brain of someone with migraine is more sensitive to change and stimulation, and every so often it tips into an attack that follows a fairly predictable sequence. About 1 in 7 people worldwide have migraine, and women are affected around three times as often as men, partly because of swings in estrogen.
Yawning, food cravings, stiff neck, irritability or low mood, needing to pee more, trouble concentrating.
Zigzag flashing lights, a growing blind spot, pins and needles spreading up an arm, trouble finding words.
Usually one-sided and throbbing, worse with movement. Nausea, and sensitivity to light, sound and smells.
The "migraine hangover": tiredness, brain fog, tender scalp, feeling washed out.
This is a slice down the middle of the head, face on the left. Tap a number or a name to see what that part does in a migraine. The dashed line is the route a pain signal travels.
Aura comes from cortical spreading depression: a wave in which nerve cells fire in a burst and then fall silent, creeping forward over the cortex at about 3–5 mm per minute. When it crosses the visual cortex, the burst shows up as flickering zigzag lights and the silence behind it as a blind patch. Because the wave is slow, the aura grows and drifts across vision over 20–30 minutes. The wave can also irritate the trigeminal fibers in the meninges above it, one possible link between aura and headache.
Exercise is good for migraine in the long run, yet a sudden hard session is a well-known trigger. Both are true, and the physiology explains why.
In a Dutch headache-clinic study, 38% of 103 migraine patients had had attacks set off by exercise, most often running or cardio and racket sports. In over half of them the attack began during the workout itself; in the rest it came a few hours later. Neck pain as the very first symptom was more common in this group (33% vs 14%). Lab studies have also provoked attacks on purpose with intense indoor cycling.
In a healthy person exercising at sea level, blood oxygen saturation stays near normal, around 95% or higher, even during hard efforts. Very highly trained athletes can dip a few points. Low oxygen can trigger migraine: in a Danish study, breathing thin air until saturation fell to 70–75% for 3 hours set off attacks in 8 of 15 people with migraine with aura, against 1 of 15 on a sham day. That's far below what a workout produces, so it matters more at high altitude than at the gym.
What matters during exercise is less the oxygen in the blood and more how fast the muscles can turn oxygen into energy when demand suddenly jumps.
When you go from standing to running, your muscles need more energy within a second. Oxygen-based (aerobic) energy production can't switch on that fast: it climbs over the first one to a few minutes. The shortfall, called the oxygen deficit, is covered by fast emergency systems, stored phosphocreatine and anaerobic glycolysis. Glycolysis produces lactate. A sudden start makes this gap as big as it can be; a warm-up shrinks it because the aerobic system is already running.
Schematic curves to show the idea, not measured data.
Three separate things decide how well supply keeps up with demand. They usually improve together with training.
The most oxygen your body can use per minute at all-out effort, so the top speed of aerobic energy production. Limited mostly by how much blood the heart can pump.
How quickly aerobic production rises at the start of an effort. Slower in less fit people, which widens the energy gap.
How much of the ceiling you can hold before lactate piles up, roughly 50–85% of VO2max. Depends heavily on mitochondria and capillaries in the muscles.
All of this is about muscle energy. The brain uses a fairly steady share of oxygen whatever your fitness. It feels the workout indirectly: through lactate released into the blood, the jump in blood pressure, and messengers like CGRP.
VO2max sets the ceiling, so a given pace takes up a larger share of a smaller engine. A lower VO2max usually means you cross your lactate threshold at a lower speed, with a bigger jump in heart rate, blood pressure and lactate.
Schematic curves to show the idea, not measured data. Real thresholds vary widely from person to person.
The fitness link also shows up in large studies. People with migraine had lower peak oxygen uptake than headache-free people in a Norwegian study. Among more than 1.1 million Swedish men tested at military conscription, those with the lowest fitness were about 29% more likely to later need migraine medication than the fittest. These are associations: they don't show that low fitness causes migraine.
Each of these pushes on the trigeminal pain system from Plate 2, which in people with migraine already sits closer to its tipping point. The first three are the best-supported ideas, but the exact chain of events hasn't been proven.
The same body that gets triggered by sudden hard efforts usually benefits from steady ones. In a Swedish randomised trial of 91 patients, aerobic exercise three times a week worked about as well as topiramate, a standard preventive medication, for cutting attack frequency, and without its side effects. Training also raises VO2max, speeds up the ramp-up and pushes the lactate threshold higher, which shrinks the very gaps that make sudden efforts risky. The practical advice from that research:
Sources: Koppen & van Veldhoven 2013 · Amin et al. 2018 review · Arngrim et al. 2016, Brain · Swedish conscript study
Trigeminal fibers in structures 3, 4 and 5 are packed with CGRP. During an attack, CGRP levels rise in the blood draining the head, and giving CGRP by infusion triggers migraine-like attacks in people who have migraine (but not in people who don't). That made it a prime drug target: block CGRP or its receptor and the loop between nerve, vessel and brainstem gets interrupted. Rimegepant (Nurtec ODT, Vydura) is one of the drugs that does this.
During an attack, the trigeminal nerve dumps CGRP. It binds receptors on the muscle of meningeal blood vessels and on nearby nerve cells, so vessels widen, tissue gets inflamed, and pain signals get louder.
The CGRP receptor is built from two proteins sitting in the cell membrane: CLR, a seven-loop receptor, and RAMP1, a single-pass helper that shapes the binding pocket. Rimegepant is a small molecule that fits that pocket and doesn't turn anything on. It's a competitive antagonist: whichever molecule sits there first wins.
The brain is wrapped in the blood–brain barrier, which keeps most molecules out. Rimegepant crosses it poorly. That's fine, because the key CGRP sites (the trigeminal ganglion and the meningeal blood vessels) sit outside that barrier. Less drug in the brain itself is one reason drowsiness and dizziness are uncommon.
Triptans (sumatriptan and family) actively constrict blood vessels through serotonin receptors, including in the heart. Rimegepant only removes CGRP's push to widen. Vessels go back toward normal but aren't clamped, which is why it's an option for many people who can't take triptans.
The 75 mg tablet melts on the tongue, no water needed. Blood levels peak at about 1.5 hours and fall by half roughly every 11 hours. The liver clears it, mainly with the enzyme CYP3A4, so drugs that strongly block or speed up that enzyme change how much stays around. Maximum one dose per 24 hours.
Curve is an illustrative one-compartment model built from the published peak time and half-life, not patient data. Pain relief in trials often began within 1–2 hours and in many people lasted up to 48 hours.
Educational illustration only, not medical advice. Drawings are schematic and not to anatomical scale. If exercise reliably brings on attacks, or a headache during exertion is sudden and severe, see a doctor: exertional headaches occasionally have other causes that need checking.