Angle–torque relationship and muscular activity patterns during concentric contractions with a novel variable cam system

Introduction Understanding the angle -torque relationship requires recognizing that torque can differ across contraction modes. This study aimed to analyze the performance of the Variable Moment Arm Cam® (VMAC®) by examining torque production and muscle activation during concentric leg extension contractions across the full range of motion (ROM) (100°–0°) and comparing them with those obtained using an isokinetic dynamometer. Methods In total, 22 young men (20.55 ± 2.19 years; 175.41 ± 7.21 cm; 72.80 ± 9.90 kg; 18.00 ± 5.83% body fat; 23.63 ± 2.82 kg·m⁻ 2 ) participated in four randomized moments of torque and muscle activity assessments, two using the VMAC® and two using an isokinetic dynamometer. Torque and muscle activity data were synchronized and recorded across the entire ROM (100°–0°) and evaluated at 5° intervals. Results The VMAC® system produced strength curves that closely matched those observed when using the isokinetic dynamometer across the initial and mid-ROM joint angles (100°–35°), peaking around mid-ROM (70°–65°). Muscle activity differed across conditions while the torque production remained similar. Conclusion The VMAC® generated torque patterns comparable to isokinetic dynamometry, showing the strongest alignment at mid-ROM, supporting the use of this system to replicate natural human strength curves while highlighting the opportunity to refine cam geometry.