Spasms that cause muscles to quiver are caused by involuntary contractions. Nerve fibers attached to a muscle group can cause the spasms. Quivering muscles are common and usually pass quickly when you relax. Uncontrollable twitching also may signal a more serious nervous system disorder, according to Medline Plus. You should see a doctor if the spasms don't respond to home care or are persistent.
Medical Causes
A deficiency in your diet from a lack of electrolytes, potassium or sufficient protein can lead to the spasms that start becoming apparent when you run, hike or do other exercises that require significant leg movements. Spasms and the associated quivering sensation can also occur as a result of a drug reaction, especially to corticosteroids, estrogen or diuretics. Other drugs such as caffeine or amphetamines can directly cause nerve endings to spark muscle spasms when they're triggered by movement. Nervous system disorders that cause muscle spasms include muscular dystrophy, myopathy and ALS, or Lou Gehrig's disease.
Exercise Induced
Exercise that strains your leg muscles can cause quivering and spasms. According to the American College of Sports Medicine, the involuntary, intense spasms typically occur at the end of a particularly long workout or training session. They are not always a result of dehydration. If you haven't exercised in a while and take on an intense workout, your muscles may not be prepared for the stress and react by quivering.
Prevention
Preparing for long workouts can help you prevent muscle spasms. Build up to intense workouts slowly to give your muscles time to adapt. According to the American College of Sports Medicine, you can't expect to get through a rigorous workout without consequences the very first time you undertake a long, intense exercise session. A well-balanced diet coupled with sufficient hydration from sports drinks with added electrolytes can help you stave off the cramps in your legs.
Treatment
There isn't a cure for muscle spasms when they're caused by exercise. When muscle spasms occur from over-exertion, you should stop the activity and place your leg in a fully stretched position. Don't bounce, but gently hold the stretch until you feel some relief. Lightly massage the cramping area until the spasms stop. Taking a hot shower or bath will also alleviate the quivering. Rest and wait to resume your running or other activity that caused the cramps to avoid another spasm.
