There are various challenges to operate autonomous robots for a long time in outdoor real-world environments. One of the most challenging tasks is to reduce the cost of transport when locomoting over hard ground or uneven complex terrain. This paper proposes using an artificial hormone system as a mechanism which responds to external environmental changes and alters robot behaviours to move with energy efficiency. Specifically, hormone systems are used to help the robot deals with terrain variations. The emergence of adaptive locomotion focuses especially on the cost of transport usage. The proposed system is tested in real sea turtle-inspired robot and environment. The results have shown that the robot can adapt its gait and demonstrate robust locomotion which associates with reducing the cost of transport while traveling in complex environments.