## 2 Materials and Methods
### Study Protocol and Measurements  
First, the subjects' basic demographic data and other important physical activity data were collected, and possible exclusion factors were checked. This was followed by a standardised ten-minute warm-up consisting of five minutes of low-intensity stepping exercise and thigh muscle stretching. After the warm-up, the mechanical properties of the involuntary contractions of the anterior and posterior thigh muscles were recorded using the TMG system (TMG-S1, Ljubljana, Slovenia). Five thigh muscles were examined, namely the rectus femoris, the vastus medialis and the vastus lateralis on the front of the thigh and the biceps femoris and semitendinosus on the back of the thigh. The measurements of the quadriceps heads were performed at a knee flexion of 30\({}^{\circ}\), and those of the hamstrings at a knee flexion of 5\({}^{\circ}\). A mechanical sensor was positioned perpendicularly to the skin over the belly of each muscle. For the rectus femoris, the sensor was placed at the midpoint of the line connecting the anterior inferior iliac spine and the base of the patella. For the vastus medialis, it was positioned at the midpoint of the line between the base of the patella and the muscle's innervation point. For the vastus lateralis, the sensor was placed at two-thirds of the distance from the anterior superior iliac spine to the lateral border of the patella. For the biceps femoris, placement was at the midpoint of the line connecting the ischial tuberosity and the lateral epicondyle of the tibia. For the semitendinosus, the sensor was positioned midway between the medial tibial condyle and the ischial tuberosity. Two self-adhesive surface electrodes (5 \(\times\) 5 cm, UltraStim X, Axelgaard Manufacturing Co. Ltd., Lystrup, Denmark) were affixed 2.5 cm distal and proximal to the measurement site. A rectangular monopolar electrical pulse of 1 ms duration was then applied to induce a muscle twitch. The output current was between 25 and 100 mA. We gradually increased the current upwards from 25 mA in 15 mA increments until the maximum Dm of each muscle was reached. The displacement-time curve of the maximal mechanical muscle response to the electrical twitch was decomposed to obtain Dm, Td, Tc and Ts, which were used for further analysis. Dm was defined as the peak amplitude in the curve. Td was defined as the time between the electrical stimulus and the displacement of the sensor to 10% of Dm. Tc was the time from 10% to 90% of Dm was reached. All electrode and sensor placements were performed by the same trained investigator to minimise inter-rater variability. The muscle strength of the test subjects was then tested using an isokinetic dynamometer (Humac NORM, CSMI, Stoughton, MA, USA). A gravity correction was used for all measurements. The subjects were tested in a seated position, with the chest and pelvis fixed to the chair of the isokinetic dynamometer with safety belts to prevent involuntary synergistic movements of other body parts. The concentric muscle torques of the knee extensors and flexors were measured from 0\({}^{\circ}\) to 90\({}^{\circ}\) knee flexion. To avoid mechanical overloading of the patellofemoral joint during the eccentric torque test, the range of motion was reduced to 10-90\({}^{\circ}\) knee flexion. Before starting the measurements, subjects were familiarised with the protocol by performing either 8 concentric or 5 eccentric contractions at a submaximal intensity at each of the measured joint velocities. Due to the faster fatigue of the muscle, we opted for a lower number of test contractions before the eccentric tests. The maximum concentric torque of the extensor and flexor muscles of the knee of the dominant leg was measured at all three angular velocities (60\({}^{\circ}\)/s, 180\({}^{\circ}\)/s and 240\({}^{\circ}\)/s), followed by the measurements of the maximum eccentric torques.