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 were 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 (R2=.68) and activation (R2=.22). At 6.5 weeks, NMES training intensity was related to a change in strength (R2=.25) but not to a change in activation (R2=.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.
Footnotes
Dr Stevens-Lapsley, Ms Balter, Dr Eckhoff, Dr Schwartz, Dr Schenkman, and Dr Kohrt provided concept/idea/research design. Dr Stevens-Lapsley, Ms Balter, Dr Schwartz, Dr Schenkman, and Dr Kohrt provided writing. Dr Stevens-Lapsley and Ms Balter provided data collection, data analysis, and project management. Dr Stevens-Lapsley, Dr Schenkman, Dr Schwartz, and Dr Kohrt provided fund procurement. Dr Eckhoff provided study participants. Dr Stevens-Lapsley, Dr Eckhoff, Dr Schwartz, Dr Schenkman, and Dr Kohrt provided facilities/equipment. Dr Schwartz provided institutional liaisons. Ms Balter, Ms Wolfe, Dr Eckhoff, Dr Schwartz, Dr Schenkman, and Dr Kohrt provided consultation (including review of manuscript before submission). The authors acknowledge Dana Judd, PT, DPT, for assistance with participant testing and treatment; Roger Enoka, PhD, and John Kittelson, PhD, for consultation and guidance on research design and implementation; and Tami Struessel, PT, DPT, for consultation and guidance on physical therapy interventions. They also thank the physical therapists at the University of Colorado Hospital.
This study was approved by the Colorado Multiple Institutional Review Board.
This study was supported by the National Institute on Aging (K23AG029978), an American College of Rheumatology New Investigator Award, a Foundation for Physical Therapy Marquette Challenge Grant, and a Clinical and Translational Science Award Grant (UL1 RR025780). A peer-reviewed research grant from Empi Inc, a DJO Global company, was used to support the purchase of Empi 300PV electrical stimulators and recruitment and transportation costs for participant visits.
This work was part of a clinical trial with ClinicalTrials.gov registry number NCT00800254.
- Received December 20, 2011.
- Accepted May 23, 2012.
