title: Simulation of lower limb joint forces and muscle-activation during isokinetic and vibration leg press training
Creators: name: Schneider, Günter
Publisher: name: TU Wien
Year: 2015
Subjects: subject: OpenSim
subject: simulation
subject: muscle simulation
subject: leg press
subject: computer-controlled linear-motor powered leg press
subject: muscle activity
subject: quadriceps muscles
subject: EMG

description: The leg press presents an effective exercise device for the lower limb muscles where the individual works against resistance in both, concentric and eccentric way. Training on a legpress is often used in rehabilitation because it has a defined range of movement which reduces the impact on the joints. In recent years, a unique computer-controlled linear motor powered leg press was developed by the Comenius University (Bratislava, Slovakia) and the Ludwig Boltzmann Institute of Electrical Stimulation and Physical Rehabilitation (Vienna, Austria). The new device is able to operate in several working modes in a flexible way which enhances the efficacy of the training procedure. Next to classical isokinetic and isotonic loads, the computer- controlled linear-motor of this leg press can also generate vibrations with customized parameter setting. Former investigations estimate higher muscle activity during vibration training compared to isokinetic movement. The aim of this thesis is to examine these thoughts with the aid of simulation software. Various vibration and isokinetic training protocols were simulated and verified by EMG measurements. The simulation of the joint forces and muscle activation was conducted with the open-source software OpenSim 3.2 (Simbios, Stanford University, CA USA). In a subject input data to the simulation was acquired consisting of the foot movement and the leg press load. Simulation contained joint moments, muscle forces and muscle activities of lower limbs and was executed for isokinetic and vibration training at muscle force levels of 0%, 50%, and 100% of the maximum voluntary activation. The simulation results show most activity and force production in the vastus lateralis muscle. Isokinetic simulations featured higher muscle activity than vibration simulations as well as calculated muscle forces which behave the same way. In addition, EMG measurements were performed to verify the simulation results. Eleven muscles were record on the left lower limbs to monitor the muscle activities during the leg press training. Simulation results and EMG signals stated higher muscle activity during knee flexion phase. In contrary to simulation results, activation of knee extension antagonist muscles could be observed in EMG signals. In both cases, knee extension agonists became more dominant when voluntary muscle activation was raised. Most activity and force production was simulated for musculus vastus lateralis (VL) followed by other quadriceps heads. Simulation results featured higher muscle activities and forces while isokinetic training, unlike EMG data where that behavior could not be observed. Vibration training affects muscles on deep structural levels making simulations close to reality very complex. For analyzing e.g. knee force or similar parameters researchers are not able to measure in vivo, simulations are common.