Effectiveness of Surface Electromyographic Biofeedback-triggered Neuromuscular Electrical Stimulation on Quadriceps Femoris Torque and Recruitment

Context: Injury and pathology often result in physiological impairments including decreased strength, muscular performance, and arthrogenic muscle inhibition. Neuromuscular electrical stimulation initiated by a surface electromyographic biofeedback threshold (sEMG-triggered NMES) is effective in neurological populations but has been minimally applied to orthopedic populations. Objective: The purpose of the study was to investigate the effectiveness of sEMG-triggered NMES on maximal isometric knee extensor torque and neuromuscular recruitment.Design: Counterbalanced crossover study design.Setting: University research laboratory. Participants: Twenty-two healthy persons (14 men, 8 women; age = 22.9 ± 4.7 years; height = 171.7 ± 6.1 cm; mass 76.6 ± 19.4 kg) participated.Intervention: Maximal isometric knee extensor torque @ 60° knee flexion was assessed with sEMG-triggered NMES applied to the quadriceps femoris compared to voluntary contraction alone on two separate testing sessions 2 to 7 days apart.Main outcome measures: Peak torque, peak torque to body weight ratio, and time to peak torque were assessed. Results: Analysis of variance (ANOVA) showed peak torque produced with sEMG-triggered NMES (191.6 ± 59.8 Nm) was significantly greater than without (167.4 ± 54.7 Nm). Average Peak torque to body weight ratio with sEMG-triggered NMES (224.8 ± 66.9 Nm) produced significantly greater torque than without (196.4 ± 51.1 Nm). Time to peak torque with the sEMG-triggered NMES (3.3 ± 1.6 sec) was significantly faster than volitional contractions (4.2 ± 2.1 sec) during the sEMG-triggered NMES testing session and significantly quicker than all volitional contractions (3.9 ± 2.7 sec) for both testing sessions. Conclusions: sEMG-triggered NMES is more effective in producing greater quadriceps femoris torque while producing quicker neuromuscular recruitment than voluntary contractions alone. Results support the use of sEMG-triggered NMES applications to improve knee extensor torque and recruitment of the QF to influence arthrogenic muscle inhibition, facilitate QF recruitment, and improve strength. Key Words: sEMG-triggered NMES; Torque; Recruitment; Quadriceps