Abstract
Background: Hip flexion angle, manipulated through seat position during resistance exercise, alters quadriceps biomechanics. Its influence on muscle hypertrophy remains unclear.
Objective: To systematically evaluate the effect of hip flexion (seat angle) on quadriceps muscle activation, torque output, and hypertrophy.
Methods: A systematic review was conducted in accordance with PRISMA guidelines. PubMed, Scopus, and Web of Science were searched between January 2000 to December 2025. Studies involving adults performing resistance exercises with varying hip flexion angles and reporting outcomes related to quadriceps hypertrophy, electromyography (EMG), or torque were included. 10 studies (n = 157) met the inclusion criteria. Data were synthesized qualitatively across three domains: muscle activation, biomechanical outputs, and hypertrophy.
Results: After removal of duplicate & non-relevant studies, 37 full-text articles were assessed for eligibility, and 10 studies were included in the final qualitative synthesis. Higher hip flexion angles (≥70–90°) resulted in a significant reduction in rectus femoris activation (~15–35%; p < 0.05), while vastus muscle activation remained largely unchanged. Moderate hip flexion (45–60°) produced the highest overall activation. Torque output showed a similar pattern, peaking at moderate angles and decreasing by approximately 10–20% at higher flexion (p < 0.05). In contrast, total quadriceps hypertrophy increased across all conditions (~5–12%) with no significant differences between hip angles (p > 0.05). Regional adaptations were observed, with slightly reduced rectus femoris hypertrophy at higher hip flexion angles (non-significant).
Conclusion: Hip flexion angle influences quadriceps biomechanics by altering rectus femoris activation and torque production. However, it does not significantly affect overall quadriceps hypertrophy. Its primary effect appears to be regional rather than global.