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

## TL;DR

Walking causes changes in muscle function in the pectoral fins of Polypterus senegalus, which may explain muscle adaptations in fish living on land.

## Contribution

The study reveals how motor control patterns change during walking in Polypterus senegalus, linking gait mechanics to muscle remodelling.

## Key findings

- Muscle operating length and contraction velocity increase during walking compared to swimming.
- Prolonged muscle use and changes in co-contraction patterns occur during terrestrial walking.
- Subtle changes in motor patterns lead to significant functional performance changes in fin muscles.

## Abstract

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.

Summary: In Polypterus senegalus, fin position, fin loading and muscle activation timing change during the stroke cycle when walking, possibly explaining muscle fibre-type changes seen in fish raised on land.