The big idea

Why do details of animal mechanics deviate from mechanical work minimization? This question has led me to the following line of thinking:

The measured metabolic cost of steady, level locomotion does not relate closely to mechanical work

Instead, it relates closely to muscle activation, often related to a ‘cost of muscle force’.

However, muscle force should not impose an ‘ultimate’ demand if evolution and posture allows appropriate gearing between external and muscle forces.

What if muscle activation was ultimately demanded for the work and the power during the contraction?

With these thoughts, we see the importance of distinguishing between the mechanical work and the power during the contraction, and how the requirements for minimizing each of these may conflict.

Muscle mechanical compromise framework

So, the idea is that the Muscle-Mechanical Framework can account for observed deviation from work-minimizing gaits and behaviours, and can lead to quantitative predictions incorporating the interaction between muscle properties and mechanics.

IF muscle is activated fundamentally for work and power generation over the contraction, and

IF there is a cost to activating a mass of muscle, and

IF scaling of muscle work and power capacity is constrained

THEN any contraction briefer than about 0.1 seconds results in excess activation for power, and so deviation from work-minimization to reduce the power cost might be expected.

AND smaller/faster animals tend to have briefer contractions, leading to scaling predictions that are applicable to many aspects of gait and posture.