Intermittent swimming demonstrates energy-saving capabilities: experimental evidence from robotic fish

Abstract

• Duty cycle modulation drives intermittent swimming in live koi carp, with stable tail amplitude and minimal frequency adjustments. • Robotic fish enable precise power quantification, resolving limitations in isolating gait-specific energy costs in biological systems. • Reduced duty cycle decreases cruising power and cost of transport (COT) but imposes a speed-energy tradeoff, independent of frequency/amplitude variations. • Robotic validation confirms U-shaped energy-speed relationships predicted by vertebrate locomotor theory, overcoming empirical gaps in live fish studies. • Bioinspired engineering applications prioritize duty cycle optimization for autonomous underwater vehicles, bridging biomechanics and robotic design. Intermittent swimming, characterized by the combination of active propulsion and passive gliding, is a typical locomotion pattern in most aquatic creatures. While its potential for energy conservation has been widely hypothesized, the lack of direct quantitative evidence has led to ongoing debate and limited its practical implementation in underwater robotics. In this study, we first investigated the intermittent swimming behavior of koi carp under varying flow velocities. Our findings reveal that, rather than adjusting oscillation frequency or amplitude, koi carp primarily modify the coasting periods between consecutive oscillations to optimize their response to different hydrodynamic conditions. To directly understand this strategy through the view of swimming efficiency, we developed a biomimetic fish-like robot inspired by koi carp, which enabled precise measurement of energy consumption across a range of cyclic and intermittent swimming patterns. Experimental results show that fish-like intermittent swimming significantly reduces energy expenditure compared to cyclic swimming, with longer coasting periods correlating with greater energy savings. This provides direct evidence that energy savings primarily stem from the introduction of intermittency. Our study not only offers a novel quantitative framework for investigating intermittent swimming behaviors but also demonstrates the potential of bio-inspired strategies for advancing energy-efficient underwater robotics.