Physical Therapy and EMS after Total Knee Arthoplasty: More Current = More Muscle

Relationship between intensity of quadriceps muscle neuromuscular electrical stimulation and strength recovery after total knee arthroplasty. Physical Therapy. 2012 Sep;92(9):1187-96.

Abstract
BACKGROUND:
Neuromuscular electrical stimulation (NMES) can facilitate the recovery of quadriceps muscle strength after total knee arthroplasty (TKA), yet the optimal intensity (dosage) of NMES and its effect on strength after TKA have yet to be determined.

 

OBJECTIVE:
The primary objective of this study was to determine whether the intensity of NMES application was related to the recovery of quadriceps muscle strength early after TKA. A secondary objective was to quantify quadriceps muscle fatigue and activation immediately after NMES to guide decisions about the timing of NMES during rehabilitation sessions.

 

DESIGN:
This study was an observational experimental investigation.

 

METHODS:
Data was collected from 30 people who were 50 to 85 years of age and who received NMES after TKA. These people participated in a randomized controlled trial in which they received either standard rehabilitation or standard rehabilitation plus NMES to the quadriceps muscle to mitigate strength loss. For the NMES intervention group, NMES was applied 2 times per day at the maximal tolerable intensity for 15 contractions beginning 48 hours after surgery over the first 6 weeks after TKA. Neuromuscular electrical stimulation training intensity and quadriceps muscle strength and activation were assessed before surgery and 3.5 and 6.5 weeks after TKA.

 

RESULTS:
At 3.5 weeks, there was a significant association between NMES training intensity and a change in quadriceps muscle strength (R(2)=.68) and activation (R(2)=.22). At 6.5 weeks, NMES training intensity was related to a change in strength (R(2)=.25) but not to a change in activation (R(2)=.00). Furthermore, quadriceps muscle fatigue occurred during NMES sessions at 3.5 and 6.5 weeks, whereas quadriceps muscle activation did not change.

 

LIMITATIONS:
Some participants reached the maximal stimulator output during at least 1 treatment session and might have tolerated more stimulation.

 

CONCLUSIONS:
Higher NMES training intensities were associated with greater quadriceps muscle strength and activation after TKA.

Chad’s comments:

This one is simple. More current equals more muscle.

Researchers used the following parameters:

  • Biphasic symmetrical wave form
  • 50 Hz
  • 15 seconds on (including 3 second ramp up), 45 seconds off
  • 15 contractions per session
  • 250 uS
  • mA as tolerated

Also the subjects in this study were able to reach higher intensities of current with means of 83.7 mA with some reaching 100 mA, which is approximately double that of the last blog I posted. In part because they were using square wave currents (my favorite) and electrodes used were 96 cm (what I think is about right) vs 20 cm in the last study. Current intensity is difficult to compare however, because pulse durations were different making direct comparisons difficult. With several of their subjects maxing out their machines with at 100 mA with a pulse duration of 250 uS, they could have raised the pulse duration to 300-400 as the EMPI 300PV used in the study has the ability to do.

As always, if you have any further questions or need for clarifications, please don’t hesitate to ask. Being aware that some of my blog ideas are contentious and occasionally a bit out of the field of my expertise, I encourage my readers to come forth with any questions/comments that are of interest or concern. Your comments are valued and welcomed.

Chad Reilly is a licensed physical therapist, located in North Phoenix, practicing science based medicine with treatment protocols unique and effective enough to proudly serve patients from Phoenix, Scottsdale, Mesa, Chandler, Tempe, Peoria, and Glendale.

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