Balancing on a tightrope or a slackline is an example of a neuromechanical task where the
whole body both drives and responds to the dynamics of the external environment, often
on multiple timescales. Motivated by a range of neurophysiological observations, here we formulate a minimal model for this system and use optimal control theory to design a strategy
for maintaining an upright position. Our analysis of the open and closed-loop dynamics shows
the existence of an optimal rope sag where balancing requires minimal effort, consistent with
qualitative observations and suggestive of strategies for optimizing balancing performance
while standing and walking. Our consideration of the effects of nonlinearities, potential parameter coupling and delays on the overall performance shows that although these factors
change the results quantitatively, the existence of an optimal strategy persists.