## 2 Materials and Methods
### Procedures
The MVIC involved the subject performing knee extension against resistance. * Right Lateral Gastrocnemius (RLG): involved in plantar flexion (dropping) of the foot during the lower phase of pedalling. The sensor was positioned on the central belly of the muscle, approximately one-third the length from the knee to the heel, on the right side. The MVIC involved the subject performing plantar flexion against resistance. * Right Biceps Femoris (RBF): which contributes to knee flexion and hip rotation, aiding in the pedal pulling motion. The sensor was placed in the middle of the muscle, halfway between the ischial tuberosity and the lateral insertion of the tibia on the right side. The MVIC involved the subject performing knee flexion against resistance. * Right and Left Erector Spinae (RES/LES): maintains spinal stability and proper posture for efficient power transmission and reduced fatigue. Sensors were positioned 2 cm on either side of the spinous process of the T12 vertebra, on both the right and left sides. The MVIC involved the subject performing a back extension against resistance. The placement of sensors and data processing followed the standardised procedures recommended by SENIAM to minimise cross-talk and ensure reliable signal acquisition. Calibration involved testing each muscle at trace and maximum activity levels to ensure the sensors accurately detected muscle activity. Each participant performed a series of 3 repetitions for each of five movement tasks for a cycling test on a trainer, based on positions P1-P5:  
* P1 (aft saddle with low handlebars): the rider performs at a forward-leaning angle, which promotes aerodynamics but can increase muscle activation in the lower back and core to maintain balance. * P2 (aft saddle with high handlebars): this position encourages a more upright stance, allowing the rider to engage the glutes and hamstrings more effectively due to a slightly more open hip angle. * P3 (LeMond saddle height with low handlebars): with saddle height proportionate to the inseam, this setup aims for an optimal balance in pedal stroke efficiency and lower body engagement. The low handlebars challenge the rider's core stability and quadriceps activation, potentially maximising force in the downstroke. * P4 (LeMond saddle height with high handlebars): raising the handlebars in this configuration allows for a more open hip angle while maintaining optimal saddle height for efficient pedalling. This setup typically promotes sustained power output with reduced lower back strain, allowing riders to maintain high cadence and stable force application. * P5 (customised position for optimal comfort and performance): this position is tailored to support comfort and performance, allowing the rider to achieve consistent output at a constant speed with minimal musculoskeletal strain. The pedalling frequency was fixed at 85 revolutions per minute (RPM), corresponding to an approximate speed of 20 km/h (easily achievable for users of urban bicycles), and was consistent for all participants. All experimental trials were conducted on the same day, with positions tested randomly to minimise potential order effects. The interval between trials within the same position was 30 s, while the interval between different positions ranged from 1 to 2 min, depending on the time required to adjust the bicycle settings. Participants were informed about the testing process but were blinded to the specific position being evaluated. The same laboratory technician responsible for data collection ensured consistent recording across all trials.