A comparison of five methods to normalize joint moments during running

Area of Science:

• Biomechanics
• Human movement analysis
• Sports science

Background:

• Net joint moments (NJM) are commonly normalized using physical characteristics like mass and height to compare individuals.
• Ratio scaling of NJM requires adherence to four key assumptions for valid interpretation.
• These assumptions include linearity, origin-passing regression, minimal distributional changes, and removal of correlation.

Purpose of the Study:

• To assess the validity of different ratio scaling methods for normalizing NJM in runners.
• To determine which scaling variables best meet the statistical assumptions for NJM normalization.

Main Methods:

• Data from 59 individuals running at 10 km/h were analyzed.
• Standard inverse dynamics were used to calculate sagittal-plane hip, knee, and ankle NJM.
• Ratios were computed using participant mass, height, leg length, and combinations thereof.

Main Results:

• No single scaling variable satisfied all assumptions across all joints.
• Scaling by mass, mass*height, and mass*leg length met assumptions for the knee joint moment.
• These methods also satisfied assumptions for the log-transformed hip joint moment.

Conclusions:

• Scaling by mass, mass*height, and mass*leg length are recommended for normalizing running NJM.
• Researchers are urged to verify statistical assumptions before drawing conclusions.
• Supplementary tools are provided to aid in assumption checking and discuss scaling consequences.