Walking elicits muscle functional changes in the pectoral fin of Polypterus senegalus

Amphibious fishes are often used as models to help understand how early aquatic vertebrates overcame the mechanical and physical challenges posed by a terrestrial environment. The differences in posture and loading required on land affect fin function and, over longer durations, may elicit changes in muscle and tissue composition, altering performance. How the motor control patterns of fin muscles change in a walking gait is not known but may help explain the changes in bone remodelling and muscle fibre type that occur in Polypterus senegalus, when exercised or kept in a terrestrial environment. This study quantified instantaneous motor activation changes in all four fin muscle groups involved in the terrestrial walking gait in P. senegalus. We discovered that increases in the operating length of muscles and in the velocity of contraction (and subsequent expected rate of force production), prolonged muscle use, and changes in eccentric and antagonistic co-contraction occur in muscles when used for walking compared with swimming. It appears that subtle changes in motor patterns between swimming and walking can elicit large changes in functional performance, which helps explain muscle remodelling seen in fish that spend long periods of time in terrestrial environments.