You feel like someone is stabbing a knife into your ribs

Experts don’t know exactly what causes those sharp, fleeting pains called side stitches, but many believe they’re due to diaphragm spasms triggered by rapid breathing, says Tom Holland, exercise physiologist and author of Beat the Gym. Eating too close to your workout may play a role. And side stitches occur more frequently in novice exercisers.
What to try: To stop a stitch, slow your pace and take deep breaths while contracting your abdominal muscles. Stretch your arms overhead or to the side. To prevent a stitch: Eat light pre-exercise meals, and wait at least 30 minutes after eating before you work out. Always warm up for five to ten minutes; gradually increase workout intensity.
Need to clear your head? These 12 breathing exercises should help.
Your nose is suddenly a dripping tap

Exercise, especially in cold, dry air, can trigger a runny, congested nose, a condition known as exercise-induced rhinitis. “Increased nasal breathing during exercise dries out the nose’s mucous membranes, which makes the nose secrete more mucus to protect the nasal airway,” says Dr William Silvers, an asthma, allergy and immunology specialist .
What to try: If your nose is really interfering with your workout, ask your doctor to prescribe a nasal spray, and use it at least 30 minutes before you exercise. Pack plenty of tissues in your pockets.
Check out these 7 exercise mistakes that make you look older.
You have to go the bathroom

Badly. It’s called runner’s trots, but don’t be fooled by the name: Even walkers can experience loose bowels, especially when logging long distances. During exercise, your body directs blood flow away from your gut to working muscles, which can trigger diarrhoea, Holland says. Dehydration and pre-race anxiety may exacerbate the problem.
What to try: Don’t eat anything for two hours before exercising. Skip high-fibre and high-fat foods, caffeine and artificial sweeteners, all of which can make things worse. Drink plenty of fluids before, during, and after exercise. Begin your workouts after bowel movements, and make sure you have access to a restroom.
Here are 9 medical reasons why you need to wee all the time.