Patella tendon moment arm function considerations for human vastus lateralis force estimates.

Area of Science:

• Biomechanics
• Human Physiology
• Musculoskeletal Modeling

Background:

• In vivo muscle force estimation relies on moment arms (MAs), which are challenging to measure non-invasively.
• Subject-specific MAs can vary with contraction and are difficult to determine at high levels without radiation.
• Generic MA functions may impact force predictions and the muscle's force-length relationship accuracy.

Purpose of the Study:

• To investigate how different literature-based patella tendon moment arm (MA) functions influence the vastus lateralis (VL) muscle's force-angle relationship.
• To compare the feasibility of various MA functions for estimating in vivo VL muscle forces across different knee flexion angles.

Main Methods:

• Eleven participants performed maximal voluntary isometric knee extensions at six angles (40°-90°).
• In vivo VL muscle force was estimated using peak knee extension torque, quadriceps PCSA, and 19 different patella tendon MA functions.
• Statistical analyses were performed to assess differences in maximum VL force and force-angle relationships across MA functions.

Main Results:

• Significant differences in maximum VL force (p ≤ 0.039) and the shape of the force-angle relationship (p < 0.01) were observed across the tested MA functions.
• Maximum VL force occurred at different knee flexion angles depending on the MA function used.
• Only geometric imaging-based MA functions yielded feasible VL force-angle relationships across the studied knee angles.

Conclusions:

• The choice of patella tendon moment arm (MA) function significantly impacts the estimation of vastus lateralis (VL) muscle force and its force-angle relationship.
• Geometric imaging-based MA functions provide more feasible estimations of VL muscle forces compared to other literature-derived functions.
• Averaging geometric imaging-based MA functions is recommended for estimating quadriceps muscle forces when subject-specific MAs are not available.