## 4 Discussion
In summary, the data indicate that P4, followed by P1, P2, and P3, imposes greater demands on the LG muscle than the custom-fitted P5, particularly during the early and late phases of the pedal stroke. These findings highlight that handlebar and saddle adjustments can significantly affect calf muscle engagement. As in P5, custom fitting may reduce the need for heightened RLG activation, potentially minimising fatigue and enhancing pedalling efficiency. Consequently, for commuter cyclists, optimising bike configuration improves comfort. It may decrease calf muscle strain, underlining the importance of a tailored approach in bike fitting to optimise both comfort and performance. Correspondingly, the EMG analysis of the biceps femoris (BF) muscle highlights a distinct pattern, with position P5 consistently eliciting the highest BF activity, particularly during the initial 40% of the pedalling cycle and into the later phases. These findings indicate that P5 requires greater BF activation, likely due to increased hip extension and a more pronounced hamstring engagement for propulsion and stabilisation throughout the cycle. The significant differences observed in the early and late phases across comparisonsunderscore how positional adjustments influence BF recruitment patterns. In comparing P1 and P5, position P5 displayed higher BF muscle activity during the initial phase of the cycle than P1, suggesting that the custom-fitted configuration (P5) increases the demand for hamstring involvement early in the pedal stroke. This likely reflects a more optimised hip extension mechanic, enhancing engagement of the BF as part of the posterior chain. For P2 vs. P5, P5 similarly exhibited a pronounced early peak in BF activity (10-35%) and higher activity in the late phase of the cycle. These results suggest that the individualised adjustments in P5 may increase BF recruitment at the onset of the cycle and during the final phase, which may be due to enhanced hip extension requirements and stabilisation needs for effective pedal stroke execution. The increased late-phase BF engagement in P5 could reflect ongoing muscle involvement for stabilisation and propulsion as the rider completes each cycle. The P3 vs. P5 comparison further reinforces this pattern, with P5 eliciting significantly higher early-phase BF activity. The notable early peak suggests a more demanding hip extension role, while the elevated late-phase activation may indicate continuous BF engagement for balance and propulsion. This increased activity highlights that the custom adjustments in P5 foster a more robust hamstring involvement than the standard LeMond saddle height with low handlebars in P3. Finally, in the P4 vs. P5 comparison, position P5 showed slightly higher (though not significantly different) BF activity during the early phase than P4. This again suggests that P5's adjustments require enhanced initial hamstring engagement, likely due to the optimised alignment for hip extension mechanics. The late-phase BF activation in P5 suggests a sustained stabilising role, which may aid in efficient force application and rider stability. To conclude, position P5, with its custom-fitted configuration, places greater demands on the BF muscle than other tested positions. This increased activity, particularly in the early and late phases, suggests that an individualised setup can enhance hamstring recruitment, potentially benefiting propulsion and pedal stroke stability. In P1, the forward-leaning posture promotes aerodynamics but demands increased BF activation for propulsion and knee stability due to the closed hip angle. Similarly, in the customised P5 position, greater BF activation in the initial and final phases of the pedal stroke complements reduced VLO activity, facilitating a balanced and economical distribution of force. This interaction suggests stabilising the knee by counteracting anterior tibial translation caused by VLO, as evidenced by previous research [40; 41].