National Sleep Foundation

Chapter 7: Sleep-Related Movement Disorders

Sleep-Related Leg Cramps

Sleep-Related Leg Cramps (also known as “nocturnal leg cramps”) are painful sensations caused by sudden and intense muscle contractions, usually in the calf or the foot’s small muscles. They may arise during either sleep or wakefulness. The contractions range in duration, with an average length of nine minutes per episode (many patients also have residual pain after the cramping passes).56  Frequency of episodes ranges from less than once a year to several times a night.

References 

56 Allen RE, Kirby KA, “Nocturnal Leg Cramps,” Am Fam Physician. 2012 Aug 15;86(4):350-355.