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Ann. psychophysiol. 
ISSN 2412-3188 (Online)|2410-1354 (Print) 

APP| Published By AEIRC| https://doi.org/10.29052/2412-3188.v10.i1.2023.XX-XX 

Original Article 

Changes in muscle tension patterns 
predicting the start of nocturnal leg cramps: 
A pilot study 
Jacqueline L. Chaney & Richard A. Sherman 

Saybrook University, Pasadena, California, USA 

Abstract 
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. 

Keywords 
Nocturnal Leg Cramps, NLC, SEMG, Muscle Tension, Cramps, Leg Pain. 

Citation: Chaney JL, Sherman RA. Changes 
in muscle tension patterns predicting the 
start of nocturnal leg cramps: A pilot study. 
APP. 2023; 10(1): 08-11 

Corresponding Author Email: 
drrichsherman@gmail.com 

DOI: 10.29052/2412-3188.v10.i1.2022.08-11 

Received 16/03/2023 

Accepted 26/05/2023 

Published 01/06/2023 

Copyright © The Author(s). 2023. This is an 
open-access article distributed under the 
terms of the Creative Commons Attribution 
4.0 International License, which permits 
unrestricted use, distribution, and 
reproduction in any medium, provided the 
original author and source are credited.  

Funding: The Behavioral Medicine 
Research and Training Foundation (Port 
Angeles, Washington, USA) purchased 
the recording devices and computer and 
then loaned to the investigators to use in 
the study. 

Conflicts of Interests: The authors have 
declared that no competing interests exist. 

https://doi.org/10.29052/2412-3188.v10.i1.2023.
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ISSN 2412-3188 (Online)| 2410-1354 (Print) 

APP| Published By AEIRC| Volume 10 Issue 1 

Introduction 
An estimated 50%–60% of adult patients 
presenting to primary care frequently report 
nocturnal leg cramps1. Nocturnal leg cramps 
(NLCs) affect the lower limbs, typically 
impacting the calf, hamstring, or foot 
muscles at night2,3 and often interrupt sleep1. 
The etiology of leg cramps is unclear1,4. 
While some cases are associated with 
myopathic, neurologic, and metabolic 
causes, most cases are idiopathic with no 
known cause1.  

While the description of nocturnal leg 
cramps always includes sudden, abrupt leg 
pain occurring during nighttime sleep1,5, 
none of the literature shows that an actual 
muscle cramp is taking place6. No treatments 
of idiopathic nocturnal leg cramps are 
successful1,7. Quinine is the most studied 
pharmacological intervention but is unsafe 
due to dangerous risk factors3.  

Methodology 
This pilot study measured raw surface 
electromyograms (SEMG) during nighttime 
sleep from one calf of six subjects 
experiencing NLCs. The project was 
approved by Saybrook University's 
Institutional Review Board (Pasadena, 
California, USA), and all subjects signed an 
explanatory consent form before 
participating in the study. Subjects were 
recruited by word of mouth from people 
living near the first author. The study 
gathered data for up to 3 consecutive nights 
to capture a night in which participants 
reported a painful awakening and a night to 
obtain baseline tension in which participants 
did not report a painful awakening. The 
recordings captured muscle activity 30 
minutes prior to and up to 30 minutes after 
the subject reported a painful awakening. All 
six participants were Black women living in 
the United States of America between the 
ages of 23 and 56 (mean of 48 with SD of 13) 

who met the criteria for5,6 and had histories 
of nocturnal leg cramps for between 4 and 15 
years (mean of 10 with SD = 4) occurring at 
least 3 times per month. The criteria 
excluded individuals receiving 
pharmaceutical treatment for cramps or 
those diagnosed with restless leg syndrome 
(RLS), a different problem than NLCs5. 

Participants’ patterns of relative calf muscle 
activity during nighttime sleep were 
recorded using a wireless ambulatory 
Cricket device (Somaxis, INC., California, 
USA) which had the advantage of not having 
wires running from sensors on the calf to a 
recording device. The investigators feared 
wires would interfere with the subjects' 
normal movements. The device was not 
calibrated sufficiently, so only the percent 
change in the signal could be used when 
subjects' recordings were compared. The 
device's motion sensor was not sensitive 
enough to detect movement artifacts 
indicative of a spam starting so changes in 
the raw signal typical of movements8 were 
used to estimate when movement artifacts 
were recorded. When subjects 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. 

Result 
For the four subjects recorded on nights 

without leg cramps, the 60-minute segments 

showed typical, movement artifact-free 

baseline instabilities8 ranging from 15 to 

100% with few spikes in the recording (Table 

1). During the night when the subjects were 

awakened by pain in their calves, all six 

showed similarly stable, 30-minute, pre-

awakening baselines free of movement 

artifacts with few spikes. In the average of 41 



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ISSN 2412-3188 (Online)| 2410-1354 (Print) 

APP| Published By AEIRC| Volume 10 Issue 1 

seconds (SD = 11, range of 25 – 50 seconds) 

just before awakening with pain, all six had 

large increases in patterns of relative muscle 

tension not associated with patterns of 

movement (mean increase of 217%, SD 157, 

range 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. See 

Table 1 for details of the individual results.  

Table 1: Summary of Recordings 

Discussion 
Even given the device limitations, the data 
demonstrated increased muscle tension 
significantly above baseline for all six 
subjects who reported awakening with 
painful cramping.  

Although it is assumed that the pain from 
nocturnal leg “cramps” (NLC) are a result of 
muscle activity preceded by changes in 
surface electromyograms (SEMG) as is 
found for typical cramps8, the authors were 
unsuccessful in finding any studies 
demonstrating this predictive relationship. 

Theories about complex underlying 
mechanisms abound, but facts are few and 
far between. The lack of published studies is 
very odd as NLCs are one of the most 
common pain syndromes, and muscle 
tension recordings from major muscles have 
been made by rehabilitation physicians 
evaluating pain syndromes since the late 
1940s9. The lack of such published studies 
indicates that there must have been attempts 
to perform them but that the results were 
never published or are buried in older books. 
This study is the first to indicate that such a 
predictive relationship. 



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ISSN 2412-3188 (Online)| 2410-1354 (Print) 

APP| Published By AEIRC| Volume 10 Issue 1 

A seventh subject who had leg pain due to 
tumors in her feet was recorded. She showed 
no significant changes in muscle tension 
during the night's recording. 

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 objectively record 
microvolts is in progress to confirm these 
initial findings.  

Acknowledgment 
Drs. Jerry R Devore and Sam Kohlenberg 
assisted with different aspects of the 
methodology.  

References 
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American Family Physician. 2012; 86(4): 350–
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2. Katzberg H. D, Khan AH, So YT. Assessment:
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Neurology. Neurology. 2010; 74(8): 691–696.  

3. Monderer RS, Wu WP, Thorpy MJ. Nocturnal
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4. Rana AQ, Khan F, Mosabbir A, Ondo W.
Differentiating nocturnal leg cramps and
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5. Hallegraeff JM, de Greef M, Krifren W, van
der Schans C. Criteria in diagnosing nocturnal
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6. Weiner IH, Weiner HL. Nocturnal Leg Muscle
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7. Tipton PW, Wszolek Z K. Restless legs
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865–872.

8. Sherman RA. Pain: Assessment &
intervention from a psychophysiological
perspective (2nd ed.). 2011; Association for
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9. Basmajian, J. Muscles Alive: Their functions
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Williams & Wilkins.

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