Posture, gait and the ecological relevance of locomotor costs and energy-saving mechanisms in tetrapods.

This research study explores the impact of limb posture on locomotion in tetrapods, including its effects on biomechanics, energy conservation, and locomotion cost. It finds that different postures and gaits have a significant effect on energy consumption and locomotion efficiency, with ecological relevance playing a more significant role than optimizing economy in locomotion.

Reanalysis of Locomotor Data

• The study reassesses locomotor data with respect to functionality, energetic efficiency, mechanical properties, and ecological perspectives. It mainly focuses on the effects of different limb postures (crouched vs. erect).
• Through regression analysis, it establishes non-linear associations between posture and many parameters including metabolic cost, muscle mass of the limb, effective mechanical advantage, and stride characteristics.

Crouched vs Erect Posture

• In smaller animals with a crouched posture, energy savings mechanisms such as spring and pendular movements are found to be insignificant. Thus, the metabolic costs of their locomotion are majorly determined by muscle activation costs.
• Stride frequency seems to be a significant functional parameter that influences decreasing locomotion costs in crouched animals.
• Contrarily, an erect posture in animals invokes a series of effects on the metabolic cost of locomotion. It increases the effective mechanical advantage, decreases relative muscle masses, and dramatically elongates metapodial limb segments (as limbs shift from digitigrade to unguligrade designs).
• Biological springs boost both in size and effectiveness in animals with an erect posture. All these factors contribute to reducing the metabolic cost of locomotion.

Cost and Ecological Relevance of Different Gaits

• Comparing the relative costs and ecological significance of different gaits, the study notes that running is less energy consuming than walking for smaller animals, up to the size of dogs.
• However, for larger animals like horses, walking is more economical than running.
• Regardless of energy costs, animals do not necessarily use their cheapest gaits for their predominant locomotion activity. This suggests that the choice of gait depends more on its ecological relevance than the need to optimize the economy of locomotion.