Changes in muscle tension patterns predicting the start of nocturnal leg cramps: A pilot study

Background: Although it is assumed that nocturnal leg cramps (NLC) are based on actual muscle cramps, no articles show that nocturnal leg cramps are preceded by changes in surface electromyograms (SEMG), which might indicate that a natural muscle cramp is occurring. This exploratory pilot study was designed to identify patterns of calf muscle activity before the onset of subjects' awakenings with pain associated with nocturnal leg cramps (NLC) to establish a precursor relationship between changes in muscle tension and the start of NLCs. Methodology: Participants' relative calf muscle activity patterns during nighttime sleep were recorded for the entire night using a wireless ambulatory device on one night when subjects awakened with a leg cramp and one when there was no awakening. When the six issues awakened with pain from a leg cramp in the calf being recorded, relative muscle tension patterns were analyzed from 30 minutes before to 30 minutes after the awakening. These patterns were compared with 60-minute recordings on days when four subjects did not awaken with pain. Results: All six participants were women between the ages of 23 and 56 (mean of 48 with SD of 13) who met the criteria for and had histories of nocturnal leg cramps for between 4 and 15 years (mean of 10 with SD = 4). All six had significant increases in patterns of relative muscle tension not associated with patterns of movement for an average of 41 seconds (SD 11) before awakening with pain (mean increase of 217%, SD 157, rang 100% - 500% with spikes having a mean of 250% above baseline, mean 251, range 200 – 800%). Relative muscle tension remained nearly twice the original baseline for about 50 seconds after a painful awakening and did not return to pre-occurrence levels for up to 20 minutes. Conclusion: As Muscle tension changed before subjects were awakened by pain, the change in tension is not a reaction to the pain. The signal did not contain movement artifacts, so the change reflects a precursor to the pain, and nocturnal leg cramps are likely caused by muscle tension. Further research using a calibrated device to record microvolts objectively is in progress to confirm these initial findings.