12-2 Factors affecting responsiveness of the quadriceps femoris
Factors affecting responsiveness of the quadriceps femoris muscle to neuromuscular electrical stimulation following total knee arthroplasty
Yocheved Laufer, PT, D.Sc, Lynn Snyder-Mackler, PT, ScD, FAPTA
Background: The effect of neuromuscular electrical stimulation (NMES) on muscle strength is dose-related and stronger electrically induced muscle forces during training result in greater strength gains.
Objectives: To determine the force of electrically induced contractions of the quadriceps femoris muscle in elderly subjects following total knee arthroplasty and to analyze the effects of various factors on the force of the elicited contractions.
Method: Fifty-six subjects, mean age of 66.0 (SD 12.2) following total knee replacement and receiving NMES as part of their rehabilitation program participated in the study. Regression analysis was used to determine the effects of gender, age, body mass index (BMI), muscle weakness, and central activation ratio on the force of electrically induced muscle contractions, expressed as the percentage of maximal voluntary isometric contractions (%MVIC). Significance was determined at p<0.05.
Results: The overall regression model was significant. Of the tested predictors, Body Mass Index and quadriceps femoris weakness correlated significantly with %MVIC. Age, gender, and central activation had no significant effect on %MVIC.
Conclusions: The force of electrically induced contractions in the majority of elderly subjects following total knee arthroplasty is within the therapeutic range for muscle strengthening. While increased BMI has a negative impact on the ability of NMES to elicit strong contractions, greater %MVIC is expected in weaker muscles.
Key Words: Neuromuscular electrical stimulation, total knee arthroplasty, quadiceps femoris, BMI, age, weakness, central activation