Effect of knee joint angle on side-to-side strength ratios

Area of Science:

• Biomechanics
• Exercise Physiology
• Musculoskeletal Research

Background:

• Knee extensor and flexor strength testing traditionally uses different joint angles due to muscle length-tension relationships.
• Optimizing strength testing efficiency requires identifying a single angle suitable for both muscle groups.

Purpose of the Study:

• To determine an optimal knee flexion angle for isometric strength testing of both knee extensors and flexors.
• To analyze the effect of knee flexion angle on side-to-side peak torque ratios and flexor-to-extensor torque ratios.

Main Methods:

• Eighteen active young adults (9 males, 9 females) participated.
• Isometric knee extensor and flexor strength were measured at 30°, 60°, and 90° of knee flexion.
• Analysis focused on side-to-side peak torque ratios, raw torque values, and flexor-to-extensor torque ratios.

Main Results:

• Side-to-side knee extensor peak torque ratios and flexor-to-extensor torque ratios varied significantly with knee flexion angle (p=0.024, p=0.011).
• Side-to-side knee flexor peak torque ratios did not show significant differences across angles (p=0.311).
• Symmetrical strength measurements (closer to 100%) for both muscle groups were observed primarily at 60° knee flexion.

Conclusions:

• 60° of knee flexion is recommended for simultaneous clinical testing of knee flexor and extensor strength.
• Hamstring strength can be assessed for side-to-side symmetry at any of the tested angles.
• Findings support more efficient and flexible clinical knee strength testing protocols.