The brain controls behaviour and has to manage the body’s resources (including energy) at the same time. How the brain coordinates and combines computations for controlling behaviour in response to metabolic state is little understood.
I examined internal metabolic state and its role in motor coordination. I found that internal metabolic state modulates human motor coordination, with a lower energy expenditure associated with performing a velocity-controlled centre-out reaching task when in a low metabolic state.
One approach to understanding human motor coordination is to consider motor cost functions. Many cost functions have been proposed yet the form and implementation of the cost function in the human motor system remains largely unknown. I have shown how an approximately quadratic metabolic energy cost function can be derived from the physiological properties of muscles and muscle fibres, producing a biophysically plausible cost of motor control. I then used this cost function to predict the manner in which coordination would change during an isometric force production task. I showed my predictions were correct, with motor effort shifting from muscles with higher metabolic energy costs towards muscles with lower metabolic energy costs.
I examined the effect of internal metabolic state on muscle fibre recruitment regimes. I found no significant effect here, suggesting that fibre recruitment is computed in an independent manner to muscle coordination and supporting hierarchical control of human motor coordination.
To directly uncover the composite cost function of reaching movements, I used model based inverse optimal control to show how differences in hand reaching trajectories between metabolic states can be described by a single parameter representing a trade-off between motor variability and energy expenditure.