Invited review: The speed-duration relationship across the animal kingdom.

The research aims to study the speed-duration relationship and its parameters in various animal species, including humans, horses, mice, rats, lizards, crabs, salamanders, and birds. It emphasizes the way in which environmental factors influence these parameters, particularly focusing on temperature changes in lizards and the endurance capabilities of lungless salamanders and painted ghost crabs.

The Speed-Duration Relationship

• In the context of this research, the speed-duration relationship refers to a hyperbolic relationship between an animal’s speed and the time duration during which it can maintain that speed.
• Two crucial parameters of this relationship are the asymptote critical speed (CS), which represents the maximum steady-state speed an animal can maintain and the curvature constant (D’), which corresponds to the maximum distance an animal can cover at speeds above CS before fatigue sets in.

Study Samples and Different Parameters

• The researchers performed direct assessments of the speed-duration relationship in humans, horses, mice, and rats.
• Endurance capabilities of lizards, crabs, and salamanders had been measured indirectly, from which the speed-duration relationship was derived.
• Due to technical hurdles with treadmill running and short greyhound race durations, dogs weren’t included in the study.

Findings from the Study

• The study found that for lizards, an increase in environmental temperature from 25°C to 40°C could double their CS without altering D’.
• It was observed that lungless salamanders had a very low critical speed, most likely due to the limitations of oxygen diffusion pertinent to cutaneous respiration.
• The painted ghost crab exhibited the highest endurance parameter ratio (D’/CS), allowing it to maintain high speeds for prolonged periods.

Birds, Fish, and Unassessed Species

• While the study did not specifically measure the speed-duration relationship in birds, it highlighted the high aerobic power of birds and the low metabolic cost of transport during flight that enables extreme feats of endurance during migrations.
• In fish too, the speed-duration relationship was not directly assessed. However, the sustainable swimming speed has been quantified in various species, which is conceptually analogues to the maximal steady state in humans.