# Mallard hindlimbs locomotion system respond to changes in sandy ground hardness and slope

## TL;DR

Mallards adjust their hindlimb movements to adapt to different ground hardness and slopes, helping them move efficiently on soft terrain.

## Contribution

This study reveals how mallard hindlimb joints adapt to varying ground conditions during locomotion.

## Key findings

- Mallards increase speed with longer stride length and shorter stance phase duration on different ground conditions.
- Reduced ground hardness and increased slope delay joint adjustments in the TMTPJ, ITJ, and knee.
- Hip joint undergoes two brief extensions during uphill movement, aiding posture and propulsion.

## Abstract

Mallards inhabit soft grounds such as mudflats, marshes, and beaches, demonstrating remarkable proficiency in traversing these grounds. This adeptness is closely linked to the adjustments in the operation of their hindlimbs. This study employs high-speed videography to observe postural adjustments during locomotion across mudflats. Analysis of spatiotemporal parameters of the hindlimbs reveals transient and continuous changes in joints (tarsometatarso-phalangeal joint (TMTPJ), intertarsal joint (ITJ), knee, and hip) during movement on different ground hardness and slope (horizontal and uphill). The results indicate that as the stride length of the mallard increases, its speed also increases. Additionally, the stance phase duration decreases, leading to a decrease in the duty factor. Reduced ground hardness and increased slope lead to delayed adjustment of the TMTPJ, ITJ, and knee. Mallards adjust their stride length by augmenting ITJ flexion on steeper slopes, while reduced hardness prompts a decrease in TMTPJ flexion at touch-down. Additionally, the hip undergoes two brief extensions during the stance phase, indicating its crucial role in posture adjustment and propulsion on uphill grounds. Overall, the hindlimb joints of the mallard function as a whole musculoskeletal system, with each joint employing a distinct strategy for adjusting to adapt to various ground conditions.