From fibre to function: are we accurately representing muscle architecture and performance?

Area of Science:

• Biomechanics
• Comparative Anatomy
• Musculoskeletal Physiology

Background:

• Muscle fiber architecture is crucial for kinetic and energetic performance, underpinning muscle function and adaptation across species.
• The 'fiber to function' paradigm is widely applied but relies on limited fiber measurements, a limitation rarely tested.
• Previous studies quantifying muscle architecture often use a small sample size of fiber measurements.

Purpose of the Study:

• To quantitatively assess the impact of small sample sizes on muscle architectural property characterization.
• To investigate the implications of these potential errors on predicting in-vivo muscle dynamics and interspecies adaptations.
• To validate the accuracy of current methods for quantifying muscle architecture.

Main Methods:

• Utilized diffusion tensor imaging (DTI) and deterministic fiber tractography to rapidly acquire over 3000 fiber measurements per muscle.
• Employed statistical subsampling simulations to evaluate the effect of small sample sizes (n < 25) on architectural property accuracy.
• Conducted dynamic musculoskeletal simulations of human locomotion and comparative analyses between humans and chimpanzees.

Main Results:

• Analyzing a small number of fibers (typically < 25) can lead to substantial errors in estimating muscle architectural properties like mean fiber length and physiological cross-sectional area.
• Inaccuracies in fiber architecture characterization significantly affect predictions of in-vivo dynamics and muscle function within a species.
• Error magnitudes impact assessments of muscle specialization, potentially leading to erroneous conclusions about evolutionary adaptations between species.

Conclusions:

• The common practice of using minimal fiber measurements to represent entire muscles is statistically unsound and can generate significant errors.
• These findings necessitate a re-evaluation of how muscle architecture is quantified across diverse biological research fields.
• Accurate muscle architecture quantification is critical for reliable predictions of muscle function, performance, and evolutionary adaptation.