Ni pci 6229

A detailed description of the EMG recordings can be found in a previously published study from our group (Behrens et al., 2015 (link)). Briefly summarized, myoelectrical signals of the VM, RF, and VL were recorded using surface electrodes (EMG Ambu Blue Sensor N). EMG signals were amplified (2500×), band-pass filtered (10–450 Hz), and digitized with a sampling frequency of 3 kHz using an analog-to-digital converter (NI PCI-6229, National Instruments, Austin, United States). Data were saved on a hard drive for later analysis using a custom-built LABVIEW based program (Imago, Pfitec, Germany).

Electrically evoked and voluntary torques were measured using a CYBEX NORM dynamometer (Computer Sports Medicine^®, Inc., Stoughton, MA, United States). Participants were seated on an adjustable chair with the knee and hip fixed at 90° and 80° (0° = full extension), respectively. In order to avoid excessive movements of the participants during data recording, they were fixed with straps at the waist and chest. The subjects’ lower leg was affixed to the lever arm of the dynamometer and the dynamometer rotation axis was aligned with the knee joint rotation axis. During isometric strength testing, subjects were instructed to cross their arms in front of their chest and to push as hard as possible against the lever arm of the dynamometer. Strong verbal encouragement was given by the investigator and visual feedback of the torque-time curve was provided on a digital oscilloscope (HM1508, HAMEG Instruments, Mainhausen, Germany). Torque signals were digitized with a sampling frequency of 3 kHz using an analog-to-digital converter (NI PCI-6229; National Instruments, Austin). Data were saved on a hard drive for later analysis using a custom-built LABVIEW based program (Imago, Pfitec, Germany).

A detailed description of the EMG recordings can be found in a previously published study from our laboratory (Behrens et al., 2015 (link)). Briefly, myoelectrical signals of the vastus medialis (VM), rectus femoris (RF), and vastus lateralis (VL) muscles were recorded using surface electrodes in a bipolar configuration (EMG Ambu Blue Sensor N). EMG signals were amplified (2500×), band-pass filtered (10–450 Hz), and digitized with a sampling frequency of 3 kHz using an analog-to-digital converter (NI PCI-6229, National Instruments, Austin, TX, United States). Maximum compound muscle action potential amplitudes (M_max) elicited by electrical stimulation were measured peak-to-peak. Muscle activity during exercise was assessed by calculating the root mean square of the EMG signal (RMS-EMG) averaged for five contractions at the beginning, as well as at 25, 50, 75, and 100% of each trial, respectively. Only EMG data during the concentric phase of each repetition were considered for analysis. RMS-EMG of VM, RF, and VL was normalized to the corresponding M_max value (RMS ⋅ M^-1). To estimate the total muscle activity of the quadriceps during knee-extension exercise, RMS ⋅ M^-1 was averaged across VM, RF, and VL (Husmann et al., 2017 (link)).