I've ridden 90 KM (and at reasonable speeds - 30+ KM/h) without issues, but rode my first Gran Fondo (140 KM) and experienced various spasms while riding. There were aid stations with food so I ate bananas - seemed to help, but the distance between stations was ~40 KM so I'd still get spasms... The spasms were mostly quad/back of the leg - I only got a calf one once and it was much more brief than the others.

Can anyone shed light on why I experienced these, and what I can do to prevent it in the future? My hamstrings have always been short/tight, takes a while in Yoga/etc for them to loosen up. The seat angle was tipped a little more back than I usually ride, didn't seem like a seat height issue...

3 Answers 3


There are several reasons for muscle spasms/cramps, but they basically boil down to one of two causes:

  • Some sort of bogus nerve activation
  • The inability of the muscles to "reset" themselves

The bogus nerve activation situation can occur because of some sort of nerve irritation, or due to one of several somewhat rare and rather serious medical conditions. Given that the latter are unlikely, nerve irritation -- either in the spine or where the nerves pass through the piriformis muscle in the butt -- would be the possibility to be concerned with. But if you had this you'd likely be complaining of "electric" sensations running down the leg.

So most likely the problem is with the muscles being unable to "reset".

It's important to understand how muscle cells work. They do not need (new) energy to contract. Rather, a muscle cell is like a stretched spring that's been propped into the stretched position -- it's ready to contract as soon as the "prop" is removed. To remove the "prop" and allow the muscle to contract, the associated neuron causes calcium to be released into the muscle cells. This triggers a cascade of chemical reactions and the muscle contracts.

To "reset" the muscle the calcium must be "pumped" out of the cells and energy (glucose converted to ATP) must be used to mechanically re-extend the muscle fiber.

A cramp occurs when something prevents this "reset".

The two likely causes of this inability to reset are a failure of the calcium "pump" and the simple absence of sufficient energy to do the reset. This can be more than a simply unpleasant situation, since if a muscle cell is fully "depolarized" for long enough (more than a minute or so) it dies. (Thankfully, this full depolarization occurs fairly rarely in healthy individuals, though it's not uncommon in football "boot camps" when run by clueless coaches.)

Several factors are involved in the calcium pump mechanism, but, in addition to glucose/ATP, the "electrolytes" sodium, potassium, and magnesium play important roles.

(There are also several genetic disorders such as myoadenylate deaminase deficiency and McArdle's Disease that can cause "reset" cramps in susceptible individuals. And MADD is actually fairly common, affecting about one individual in 50.)

So basically a shortage of glucose, sodium, or potassium can lead to failure to reset and associated cramping. A shortage of glucose will generally affect a small portion of the muscle being most strenuously exercised, vs causing a cramp of an entire muscle group. So if your cramp is widespread and not isolated to a small portion of muscle then it's probably due to electrolyte imbalance.

In particular, when major muscles are being exercised to the max and the body is running low on electrolytes, it will "borrow" them from muscles that are not being so vigorously exercised. So you may experience, eg, cramps of the muscles along the inside of the legs, even though you're not exercising those muscles to any significant degree. (But you might also experience cramps of the muscles you ARE exercising vigorously, depending on a number of factors.)

A widespread cramp is thus generally a sign of a electrolyte imbalance, and ingesting more sodium, potassium, and/or magnesium is probably called for. (The body has substantial stores of calcium in the bones, so a short-term deficiency of calcium is unlikely. Plus, a localized shortage of calcium causes a sort of paralysis vs cramping.)

Note that what you experience a day or two after the cramp gives some clue as to what happened. With a simple cramp the affected muscles are apt to be sore the next day (and for maybe a day or two thereafter), just as if you had overworked them in the gym. But if the pain takes 36-48 hours to appear (and the pain remains for weeks) it's likely some degree of rhabdomyolysis -- actual muscle injury due to depolarized muscle cells. This would be a clue that you're doing something seriously wrong.

  • Wow. It never felt electric, nor was it widespread -- it felt to me like individual muscles along the back of the quad would "activate" - it was never a show stopper, just kept me from getting to usual speed/throwing off rhythm. It's been little more than 24 hours since the ride, no strain in the legs at all. Took a yoga class this evening, hamstrings seemed a little more flexible than before the ride.
    – OMG Ponies
    Jun 26, 2012 at 3:31
  • There are also several causes for "fasciculations", where individual muscles twitch randomly and uncomfortably. Anxiety, oddly, is one major cause. Jun 26, 2012 at 3:43

Usually, this has to do with a combination of food intake, water intake, and sweating. From those, the one that varies the most between rides is sweating, due to climatic changes and clothing changes.

Anytime you sweat a lot, the body loses electrolytes, and the hydroelectrolytic balance of the body is stressed. Then, depending on what you have eaten/drunk before the ride, and on what you eat and drink during the ride, you might experience these cramps even for normal distances and efforts. From my experience, eating/drinking LESS than you should is usually worse than eating/drinking more (provided that "drinking" excludes alcohol...).

Prevention of these might be normal hidration (pure water) if sweat volume is not excessive, and some isotonic fluid or fruit/fruit-juice if sweating is significant.

Hope this helps

  • I've been getting into the habit of taking water with me -- didn't generally need it when doing 90 KM but it was nice to get a couple of mouth fulls. I sweat a lot, and tend to have salt/white on my face/etc at the end of a strenuous ride.
    – OMG Ponies
    Jun 26, 2012 at 3:34
  • @OMGPonies -- I can't conceive of NOT taking water on a 90 KM ride. You should be downing a quart (liter) or so in that distance, if the weather is warm. Jun 26, 2012 at 11:37
  • @OMGPonies That's what I'm talking about: too much salty sweat, too little water. I know some bikers are a bit like camels, but under-hydration seems to be, by far, the cause of your cramps, IMO. Jun 26, 2012 at 13:10
  • I'm working on better hydration, but even when I completely exerted myself on a 90 KM ride -- the worst I had was muscle strain, never spasms. The Fondo was very hilly, and I think the spasms started around the 40 K mark
    – OMG Ponies
    Jun 26, 2012 at 14:04
  • As far as I know there is no scientific evidence pointing towards dehydration and/or electrolyte imbalance as causes of sweat. Note that as you sweat your blood actually becomes saltier because sweat has a lower salt content than blood. You should keep on drinking to your thirst, but it wont help prevent cramps, and too much is dangerous! Jun 27, 2012 at 8:37

Your ride was 1.5 times longer than your regular trainings -maybe even in a race context- and you (however so slightly) changed your setup. This is a recipe for spasms or cramps in the active muscles. The muscles you use are not used to that kind of activity, so some protest is to be expected.

To prevent in the future:

  • build up to the longer distance in smaller increments
  • don't change your setup.
  • If you are doing races, try to train with rides longer than the race you are training for.

There is no scientific evidence that food/water/electrolyte intake beyond what your body requests (through hunger/thirst/fatigue) helps, but it is important to keep eating and drinking during rides to replenish the resources you use. Finally, there is some evidence that stretching the muscles you expect to spasm/cramp during the race but before they actually start to do so helps.

  • The Fondo is billed as "not a race", but most treat it as such -- trying to "get a good time". I've been riding ~170 KM every weekend, but over two days (90 on Sat, 80 on Sun).
    – OMG Ponies
    Jun 26, 2012 at 14:06

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