Effects of Hip and Knee Positions on EMG Activity and Torque Production of Hamstrings and Quadriceps Muscles in Normal Healthy Adults.
Michael Hauber, SPT; Brackon Lundy, SPT; Logan Pettz, SPT; Brian Sanderson, SPT; John Seipel, SPT; John Williams, SPT
Faculty Mentor: Mohamed Kohia, PT, PhD
Purpose/Hypothesis: The objective of this study was to find out if changing hip and knee positions would have any effect on quadriceps and hamstrings electromyography (EMG) activity and torque production. It was hypothesized that changing the position of hip and knee joints would affect the torque production and EMG activity of quadriceps and hamstring muscles. Subjects: 19 subjects aged 24±3 years without history of injuries participated in this study. Materials/ Methods: Maximal isometric torque of the quadriceps and hamstring muscles was measured using the Biodex Isokinetic Dynamometer at hip angles (0°, 45°, 90°) and knee angles (15°, 60°, 90°). Surface electrodes were secured to the vastus medialis (VM), vastus lateralis (VL), rectus femoris (RF), biceps femoris (LH), and semitendinosus / semimembranosus (MH) to record the EMG activity of those muscles during maximal isometric contraction. Rest periods were allotted between trials and the order of angle selection was randomized to avoid the effect of fatigue. Results: Quadriceps torque, there was a sig diff between hip angles with peak torque at 90°, and a sig diff between knee angles with peak torque at 90°. Hamstrings torque, there was a significant interaction between hip and knee angles. Peak torque occurred with the hip at 90° and the knee at 15°, lowest torque occurred with the hip at 0° and the knee at 90°. EMG activity of the VM, there was no sig effect of hip or knee angles. For the VL, there was a sig effect between knee angles. Peak EMG activity occurred at 90° and lowest EMG activity was at 15°. EMG activity of the RF, there was no sig diff between hip or knee angles. For the LH, there was a sig interaction between hip and knee angles. Peak EMG activity occurred with the hip at 0° and the knee at 15°. Lowest EMG activity occurred with the hip at 90° and the knee at 15°. For the MH, there was a sig interaction between hip and knee angles. Peak EMG activity occurred with the hip at 45° and the knee at 90°. Lowest EMG activity occurred with the hip at 45° and the knee at 15°. Conclusions: The results of this study suggest that changing the hip and knee joint angles produces a significant effect on quadriceps and hamstring torque production and EMG activity. Clinical relevance: It is our recommendation to consider positioning the hip and knee at 90° for optimal quadriceps torque, and positioning the hip at 90° and the knee at 15° for optimal hamstrings torque. Hamstrings activation is dependent on hip and knee position whereas quadriceps activation is dependent on knee position only. These findings should be considered by physical therapists during rehabilitation of those muscles.
Faculty Mentor: Mohamed Kohia, PT, PhD
Purpose/Hypothesis: The objective of this study was to find out if changing hip and knee positions would have any effect on quadriceps and hamstrings electromyography (EMG) activity and torque production. It was hypothesized that changing the position of hip and knee joints would affect the torque production and EMG activity of quadriceps and hamstring muscles. Subjects: 19 subjects aged 24±3 years without history of injuries participated in this study. Materials/ Methods: Maximal isometric torque of the quadriceps and hamstring muscles was measured using the Biodex Isokinetic Dynamometer at hip angles (0°, 45°, 90°) and knee angles (15°, 60°, 90°). Surface electrodes were secured to the vastus medialis (VM), vastus lateralis (VL), rectus femoris (RF), biceps femoris (LH), and semitendinosus / semimembranosus (MH) to record the EMG activity of those muscles during maximal isometric contraction. Rest periods were allotted between trials and the order of angle selection was randomized to avoid the effect of fatigue. Results: Quadriceps torque, there was a sig diff between hip angles with peak torque at 90°, and a sig diff between knee angles with peak torque at 90°. Hamstrings torque, there was a significant interaction between hip and knee angles. Peak torque occurred with the hip at 90° and the knee at 15°, lowest torque occurred with the hip at 0° and the knee at 90°. EMG activity of the VM, there was no sig effect of hip or knee angles. For the VL, there was a sig effect between knee angles. Peak EMG activity occurred at 90° and lowest EMG activity was at 15°. EMG activity of the RF, there was no sig diff between hip or knee angles. For the LH, there was a sig interaction between hip and knee angles. Peak EMG activity occurred with the hip at 0° and the knee at 15°. Lowest EMG activity occurred with the hip at 90° and the knee at 15°. For the MH, there was a sig interaction between hip and knee angles. Peak EMG activity occurred with the hip at 45° and the knee at 90°. Lowest EMG activity occurred with the hip at 45° and the knee at 15°. Conclusions: The results of this study suggest that changing the hip and knee joint angles produces a significant effect on quadriceps and hamstring torque production and EMG activity. Clinical relevance: It is our recommendation to consider positioning the hip and knee at 90° for optimal quadriceps torque, and positioning the hip at 90° and the knee at 15° for optimal hamstrings torque. Hamstrings activation is dependent on hip and knee position whereas quadriceps activation is dependent on knee position only. These findings should be considered by physical therapists during rehabilitation of those muscles.