Painful, paralysing and PB-unfriendly, cramps can strike at any time. "There's no one definitive cause," says Dr Steve Ingham, head of physiology at the English Institute of Sport (eis2win.co.uk). Research in the Muscle & Nerve Journal shows that genetics might be one factor, yet there are several other possible reasons for cramping up.
Cramping your style: Fatigue
"All muscular contractions are controlled by electrical impulses in the brain, communicated via nerves," explains Dr Ingham. One theory says that very long runs overload and fatigue the nervous system. "Muscles get over-stimulated, so cramps are common after marathons," says physiotherapist Alex Floyd, of BUPA's Sports Medicine Centre of Excellence.Cut it out: Build long runs gradually, never extending mileage by more than 10 per cent weekly. Massages relax fatigued muscles: opt for deep-tissue work after a race.
Cramping your style: The wrong warm-up
"The membranes of muscle cells rupture under stress," says Ingham. These tears stimulate the growth of new, stronger muscle fibres. Yet too much stress, too soon, leads to an uncontrollable situation in which cell contents – including vital electrolytes – leak out, upping the likelihood of cramps.
Cut it out: Prime your system with a warm-up of dynamic, or moving, stretches, like leg swings to loosen up muscles and increase blood flow. Jog for a few minutes, followed by short bursts of running at target pace for that session.
Cramping your style: Sweet treats
"When you eat sugar or refined carbs, rising blood sugar puts muscles into a state of high-fuelled activity," says Floyd. Do this just before bedtime, and you might find yourself waking in agony with cramped legs. You still need sugar to fuel speedwork and long runs, but on rest days try to avoid sugar after midday, and eat more complex wholegrain products to avoid blood-sugar spikes.
Cut it out: Medicine & Science in Sports & Exercise reports that you can quell blood-sugar levels by up to 20 per cent by exercising before, rather than after, meals, possibly because exercise primes the body to process fuel more efficiently.
Cramping your style: Climate Change
"Muscles seem more inclined to cramp in very cold or hot weather – or in transition between different temperatures," says Floyd. You can minimise the effects of cold weather with compression kit, which dilates blood vessels, improves blood flow and helps keep muscles warm.
Cut it out: On cold days, do dynamic stretches before leaving the house, so you are semi-warmed up before stepping outdoors.
Cramping your style: Salt Imbalance
Hydration is a delicate balance: too little water and muscles will cramp; too much dilutes levels of the electrolytes your muscles need to process signals from the nerves, resulting in yet more cramps. This is where sugary isotonic drinks come in – they are specially formulated to keep electrolyte levels up during intense or long runs.
Cut it out: Physiotherapist Eric Clarke (ecsportsphysio.com) says, "Plain water is fine for short runs, but in hot weather or on longer runs, you sweat more, and need electrolytes." Stick to cool – not cold – water to avoid stomach cramps.