Electric Muscle Stimulation Well Tolerated by Patients at Sufficient Intensities to Strengthen Muscle after Total Knee Replacement

Response of male and female subjects after total knee arthroplasty to repeated neuromuscular electrical stimulation of the quadriceps femoris muscle. Am J Phys Med Rehabil. 2010 Jun;89(6):464-72.

Abstract
OBJECTIVES:
To examine responses to repeated neuromuscular electrical stimulation of the quadriceps femoris muscle in male and female subjects after total knee arthroplasty.

DESIGN:
Sixty-four subjects who underwent total knee arthroplasty were treated with neuromuscular electrical stimulation two to three times a week for 6 wks in addition to an exercise program. Measures of the quadriceps femoris muscle’s maximal voluntary isometric contraction (MVIC), maximal electrically induced contractions, and current intensity, in response to ten electrically induced contractions per session over 15 treatment sessions, were monitored with an isokinetic dynamometer.

RESULTS:
Mean (SD) of maximal electrically induced contractions expressed as percentage of MVIC (%MVIC) was 44.5% (18.2%). Forces of MVIC and maximal electrically induced contractions were significantly stronger in the male subjects. However, there were no gender differences in %MVIC. All force measures increased significantly across time. Male subjects tolerated higher current intensities, with both sexes showing a similar pattern of habituation to current intensity.

CONCLUSIONS:
After total knee arthroplasty, most elderly subjects can tolerate neuromuscular electrical stimulation at current intensities sufficient to elicit quadriceps femoris muscle contractions within the therapeutic range recommended for muscle strengthening. Although male subjects can tolerate stronger current intensities, similar %MVIC is activated in female and male subjects with impaired muscle function, indicating a similar potential for treatment effectiveness.

Chad’s comments:

This was a study to see if the average post-op total knee arthroplasty patient could tolerate enough electric stimulation intensity to increase muscle strength. They found they could but current intensity reached in the study was less than what I regularly get with my patients and I think there are a number of reasons why.

Parameters used appear to be older style “Russian stimulation” currents with a 2500 Hz simusoidal alternating wave form, with 50 Hz burst modulation, 10 seconds on and 80 seconds off for 10 contractions. Males worked to an average of 54.8 mA current intensity and females 46.6 mA. They used two electrodes 7.6 cm x 2.7 cm on the quadriceps and trained 2-3 times per week for 6 weeks.

While they found positive effects I think they could have improved on their results by:

1. Using a biphasic square wave current with a wide pulse duration such that they could get a stronger muscle contraction with less current intensity.
2. Using larger area electrodes, so that there is less current density traveling through each part of the skin. Their electrodes were only 20.5 cm square, which is on the small side. The electrodes I use are almost round giving 81 cm square, decreasing current density and increasing comfort substantially.
3. Using more electrodes, EMS machines with multiple electrodes these days are inexpensive. Less than 4 channels and 8 electrodes seems like a waste. There is little reason to put 2 electrodes on a quadricep when you can fit 4 giving better muscle coverage, and while you are at it put 4 on the hamstrings which can’t be too strong following a knee replacement.
4. 80 seconds of rest sounds like it is on the long side and while it is still unknown what duty cycle is optimal for increasing muscle strength the 12.5% duty cycle is considerably less than what is being used in the majority of EMS and strength research, and taking such a long rest period between bursts might lessen the patients ability to get used to the stimulus and work up to higher intensity.

Improving EMS comfort is important because it makes rehabilitation enjoyable rather than drudgery and increasing the comfort of the current means you can get better muscle contractions with the stimulation and subsequently a greater recovery of muscle strength, return of function and less stress on other ailing lower extremity joints.

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Chad Reilly is a Physical Therapist, obtaining his Master’s in Physical Therapy from Northern Arizona University. He graduated Summa Cum Laude with a B.S. Exercise Science also from NAU. He is a Certified Strength and Conditioning Specialist, and holds a USA Weightlifting Club Coach Certification as well as a NASM Personal Training Certificate. Chad completed his Yoga Teacher Training at Sampoorna Yoga in Goa, India.