Before revision:  Here, we examine and explain some non-straight-line walking phenomena from an energy minimization perspective. Using human subject experiments, we show that the metabolic rate while walking in circles increases with decreasing radius for fixed speed.
After revision:  Here, we examine and explain some non-straight-line walking phenomena are predicted by including an energy cost for turning. We quantified the cost of turning in humans, showing that the metabolic rate while walking in circles increases with decreasing radius for fixed speed.