Well, it happens when your muscle just refuses to move.  If you are lifting weights and, all of a sudden, you can’t complete the set, your muscles have become temporarily stuck.  The easiest way to try to avoid momentary muscle failure is to warm up using smaller weights and then gradually work up to the largest weights you want to use.  Eventually, you want to really give your muscles a good workout and make them tired, but you need to work up to that point, if you don’t want to be unable to finish your weightlifting sets properly.

You see, muscles don’t work well if they aren’t warmed up.  You won’t reach your maximum potential that way.  In fact, just the opposite, you might injure your muscles and be unable to do a workout routine at all.  Your muscles have to be warmed up, in order to build muscle easily and safely.

Even though it is a great way to avoid momentary muscle failure, remember that a warm up is just that, a warm up.  You can’t use warm up exercises all the time.  If you do, you won’t be challenging your muscles at all and you won’t help them to get bigger and stronger.  So, you need to remember to use bigger weights and more intense workouts, after you have done a proper workout, if you want to build up your muscles.

Eventually, you do want your muscles to get exhausted.  It’s not something that you want early in your workout routine, though.  You need to prevent it from happening too early by doing a good warm up.  Only then can you achieve momentary muscle failure when you want, which is after your muscles have had time to exercise.