Background: Quadriceps activation failure is a common phenomenon in patients with knee problems. The main purpose of this study was to examine the relationship between the voluntary muscle forces and the corresponding electrical stimulation elicited twitch forces, and to determine the level of quadriceps activation failure. Methods: Twenty adult subjects (16 male and 4 female) without knee pathology and seventeen patients (15 male and 2 female) who have undergone anterior cruciate ligament (ACL) reconstruction surgery participated in the study. The maximum voluntary contraction force and nine submaximum forces were measured using a KINCOM isokinetic dynamometer. The electrical stimulation was delivered at rest and during voluntary contraction. A Pearson's correlation coefficient and a regression equation were calculated for each subject, and for pooled data in the group of subjects without knee pathology. Results: The maximum voluntary contraction force with fully activated muscle fiber was reached for all subjects without knee pathology and for three of the patient subjects. The correlation coefficients between the twitch force and the voluntary force were -0.95 in the pooled data (p = 0.0001), -0.89±0.89(p<0.05) for the subjects without knee pathology, and -0.83±0.01(p<0.05) for the patients with ACL reconstruction. The measured maximum voluntary force in subjects after ACL reconstruction was 25% lower than the estimated value, which indicating insufficient quadriceps activation after knee surgery. Conclusions: The burst superimposition technique can be used to measure the level of quadriceps activation in healthy adults and in patients after ACL reconstruction and to guide the treatment goal setting in the physical therapy clinic.
Background: Quadriceps activation failure is a common phenomenon in patients with knee problems. The main purpose of this study was to examine the relationship between the voluntary muscle forces and the corresponding electrical stimulation elicited twitch forces, and to determine the level of quadriceps activation failure. Methods: Twenty adult subjects (16 male and 4 female) without knee pathology and seventeen patients (15 male and 2 female) who have undergone anterior cruciate ligament (ACL) reconstruction surgery participated in the study. The maximum voluntary contraction force and nine submaximum forces were measured using a KINCOM isokinetic dynamometer. The electrical stimulation was delivered at rest and during voluntary contraction. A Pearson's correlation coefficient and a regression equation were calculated for each subject, and for pooled data in the group of subjects without knee pathology. Results: The maximum voluntary contraction force with fully activated muscle fiber was reached for all subjects without knee pathology and for three of the patient subjects. The correlation coefficients between the twitch force and the voluntary force were -0.95 in the pooled data (p = 0.0001), -0.89±0.89(p<0.05) for the subjects without knee pathology, and -0.83±0.01(p<0.05) for the patients with ACL reconstruction. The measured maximum voluntary force in subjects after ACL reconstruction was 25% lower than the estimated value, which indicating insufficient quadriceps activation after knee surgery. Conclusions: The burst superimposition technique can be used to measure the level of quadriceps activation in healthy adults and in patients after ACL reconstruction and to guide the treatment goal setting in the physical therapy clinic.