Motor unit firing rate patterns during voluntary muscle force generation: a simulation study.

Area of Science:

• Neuromuscular physiology
• Motor control

Background:

• Muscle force generation relies on motor unit (MU) recruitment and firing rates.
• Two primary paradigms exist: reverse 'onion skin' (higher threshold MUs fire faster) and 'onion skin' (lower threshold MUs fire faster).

Purpose of the Study:

• To compare the force generation capacity and variability of two MU control paradigms using a hand muscle simulation.
• To determine which MU recruitment and firing rate scheme is more efficient and results in lower force variability.

Main Methods:

• Simulated MU activity in a hand muscle.
• Analyzed force generation and variability under two distinct MU control paradigms (reverse 'onion skin' and 'onion skin').
• Evaluated performance across different muscle excitation levels.

Main Results:

• Both paradigms produced graded force at low excitation.
• Force generation capacity diverged around 50% excitation.
• 'Onion skin' yielded higher force output (54% max) at 100% excitation compared to reverse 'onion skin' (88% max).
• Force variability was lower with 'onion skin' at low-moderate forces, but higher at high forces.

Conclusions:

• MU recruitment and firing rate organization critically influence muscle force properties.
• Different firing patterns offer advantages at distinct levels of voluntary muscle force generation.
• The choice of MU control strategy may depend on task demands and desired force output.