Dizziness during training: why it happens and what to do

Your vision goes dark on the third set of squats, the room tilts and you grab the rack. This happens to almost everyone who trains seriously, and most of the time the cause is boring and fixable: blood pressure, blood sugar, fluids or breathing. But the same sensation occasionally means something that needs checking, so it is worth knowing the difference.

Why your head spins

Your brain takes about 15 percent of total blood flow and tolerates zero interruption. When you stand up fast out of a squat or off a bench, a large volume of blood stays pooled in your legs for a moment, pressure at head level drops, and you get the familiar tunnel vision and buzzing. Your body usually fixes it within two to three seconds by raising heart rate and squeezing the vessels. The sensation itself is not the danger. Falling with a loaded bar on your back is.

Breath holding

On heavy sets almost everyone does a Valsalva: brace, hold, push. Chest pressure spikes, less blood returns to the heart, and the second you exhale your blood pressure crashes. If you hold your breath through all five reps of a deadlift set, dizziness at the end of the set is expected, not strange.

Low blood sugar

If your last meal was seven or eight hours ago and you then train for an hour, liver stores are near empty. This is less common in strength work than in long cardio, but it happens, most often in fasted morning sessions.

Dehydration and salt loss

Losing two percent of body mass in sweat, which is about 1.6 kg for an 80 kg person, measurably reduces blood volume and pushes heart rate up by 5 to 10 beats. In a warm gym that is one to two hours of work without drinking.

Overheating and over-breathing

Above 26 to 28 degrees Celsius in the gym, blood is diverted to the skin for cooling and less is left for muscle and brain. The opposite problem is hyperventilation: fifteen fast deep breaths before a set blow off too much carbon dioxide, brain vessels narrow, and you get dizzy before you have even touched the bar.

Causes that have nothing to do with training

Anemia, blood pressure medication and diuretics, heart rhythm problems, inner ear issues. With the inner ear, dizziness comes on when you turn your head or lie down rather than when you exert yourself, and lasts 10 to 60 seconds. Training does not cause these; it just finds them first.

What to do in the moment

1. Stop the set. Rack the weight or step off the treadmill, do not finish the reps.
2. Sit down immediately, better yet lie down and raise your legs 30 to 40 cm above heart level. Stay there 60 to 90 seconds.
3. Breathe calmly through your nose, around 12 breaths per minute. Do not breathe fast and deep, that makes it worse.
4. If you have not eaten, take 20 to 30 g of fast carbohydrate such as a banana or a spoon of honey, plus 300 to 500 ml of water in small sips.
5. Get up in two stages: sit for 30 seconds first, then stand.
6. Drop the rest of the session to 50 percent load and switch to supported work, lying or machine based. Skip anything overhead with free weights that day.

How to stop it repeating

Fluids and salt

Drink 400 to 600 ml of water two to three hours before training, then 150 to 250 ml every 15 to 20 minutes during the session. Weigh yourself before and after once, just to see your real losses; replace every kilogram lost with 1.2 to 1.5 litres over the next three to four hours. If your shirt dries with white salt marks and you train longer than an hour, add 500 to 1000 mg of sodium per litre.

Food

Eat 60 to 90 minutes before: 40 to 60 g of carbohydrate and 20 to 30 g of protein. If you train within half an hour of waking, take at least 20 to 30 g of fast carbohydrate. If you are dieting below 1500 kcal per day, dizziness is close to a rule rather than an exception.

Breathing and rest

Inhale before you lower the weight, brace through the hardest part of the lift, exhale as soon as you pass the sticking point. Do not hold your breath longer than three to five seconds per rep. On sets of eight reps or more, breathe every rep. Rest 2 to 3 minutes between heavy sets, and 3 to 5 minutes on sets of one to three reps.

Order and pacing

After a squat set, walk 20 to 30 steps instead of standing frozen or sitting down straight away. Do not spring up off the bench press. Leave the hot shower and the sauna for at least 15 minutes after your last set.

When to see a doctor

Seek urgent care if dizziness comes with chest pain or pressure, breathlessness out of proportion to the effort, an irregular or skipping pulse, any loss of consciousness even for a second, weakness on one side of the body, trouble with speech or vision, or a severe headache that started suddenly.

Book an appointment within a week if it happens on every third session or more often, if it also happens away from the gym, if you also have persistent fatigue and get winded climbing two flights of stairs, if you take blood pressure medication or diuretics or changed a dose in the last six weeks, or if you get dizzy when rolling over in bed.

Reasonable things to ask for: full blood count with haemoglobin and ferritin, blood glucose, electrolytes, blood pressure measured lying down and again after standing (a drop in the top number of more than 20 mmHg is a finding, not a coincidence), and an ECG.

The short version

• The usual causes are a pressure drop on standing, breath holding, low blood sugar, and losing two percent of body mass in sweat.
• When it hits: stop the set, lie down with legs raised for 60 to 90 seconds, then stand up in two stages.
• Prevention: 400 to 600 ml of water before, 150 to 250 ml every 15 to 20 minutes, and 40 to 60 g of carbohydrate 90 minutes out.
• Hold your brace no longer than three to five seconds, and rest 2 to 3 minutes between heavy sets.
• Chest pain, fainting, or dizziness that keeps happening outside the gym means a medical check, not a training tweak.