Relationship between intensity of quadriceps muscle neuromuscular electrical stimulation and strength recovery after total knee arthroplasty

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 (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.

Trial registration: ClinicalTrials.gov NCT00800254.

Figure 1.

Participant setup for assessment of neuromuscular electrical stimulation (NMES) training intensity at the 3.5- and 6.5-week testing sessions (left) and sample torque data from a representative participant at the 3.5-week testing session (right). Average (Avg) torque was the average peak quadriceps muscle torque across 10 electrically elicited contractions during the NMES training intensity assessment. MVIC=maximal voluntary isometric contraction, Pre-op=preoperative.

Figure 2.

Relationship between neuromuscular electrical stimulation (NMES) training intensity and percent change in quadriceps (Quad) muscle strength and activation at 3.5 and 6.5 weeks after total knee arthroplasty (TKA). Neuromuscular electrical stimulation (NMES) training intensity is represented as a percentage of the maximal voluntary isometric contraction (MVIC) at the preoperative (Pre-op) session. Percent changes in quadriceps muscle strength and activation at 3.5 and 6.5 weeks after TKA were calculated as [(value after NMES − value before NMES)/value before NMES] × 100. Solid lines represent data at 3.5 and 6.5 weeks after TKA, and dashed lines represent data without a potential outlier's data point at 3.5 weeks after TKA. Adjusted R² values are shown on each graph, and asterisks indicate significance (P<.05).

Figure 3.

Immediate changes in normalized quadriceps (Quad) muscle torque and activation after an NMES session. Asterisks indicate significant differences between values before NMES application (Pre NMES) and values after NMES application (Post NMES) (P<.05, paired t test).