Muscle force and muscle torque in humans require different methods when adjusting for differences in body size

Area of Science:

• Biomechanics
• Human Physiology
• Exercise Science

Background:

• Muscle strength (S) normalization for body size (m) uses various methods in medical, ergonomic, and sports studies.
• Existing methods often overlook differing S-m relationships for muscle torque versus muscle force.
• This discrepancy impacts the accuracy of strength assessments across different measurement types.

Purpose of the Study:

• To investigate the distinct relationships between muscle strength and body size for muscle force and muscle torque.
• To determine appropriate normalization methods for each type of muscle strength measurement.
• To refine biomechanical models for accurate strength assessment.

Main Methods:

• Isometric testing of six muscle groups for both muscle force and muscle torque.
• Analysis of the strength-to-body mass relationship using the allometric model S=k.m(b).
• Comparison of experimentally derived exponent (b) values with theoretical predictions (b=0.67 for force, b=1.00 for torque).

Main Results:

• Experimentally determined exponent (b) values were higher for muscle torque than muscle force in most groups.
• Mean (SD) values for b were 0.67 (0.19) for muscle force and 1.02 (0.34) for muscle torque.
• These findings align with theoretical predictions based on geometrical similarity.

Conclusions:

• Allometric scaling (b≈0.67) is recommended for normalizing muscle force data.
• Ratio standards (b≈1.00) are recommended for normalizing muscle torque data.
• Employing distinct methods enhances the accuracy of body size adjustments in strength testing.