An amphetamine experiment found longer treadmill endurance and a slower early core-temperature rise in rats. The paper’s higher muscle-temperature estimate came from a mathematical model, not direct muscle thermometry.
Morozova and colleagues measured core body temperature and oxygen consumption as rats ran with progressively increasing treadmill speed and incline at room temperature. Intraperitoneal amphetamine doses were compared with control conditions. A two-compartment model representing core and muscle temperatures was fitted to the experimental measurements to investigate possible mechanisms.
The 2-mg/kg dose prolonged running and slowed the early rise in core temperature without changing oxygen consumption. The 1-mg/kg dose did not produce the same measured effects. Modeling inferred greater core heat dissipation and predicted higher muscle temperature at the end of running. The inference is biologically interesting, but it should be identified as a model prediction rather than an additional directly observed temperature result.
Core temperature does not describe every tissue compartment, and longer endurance does not establish protection from injury. Model parameters depend on assumptions about heat production and transfer. Rats also dissipate heat differently from humans, so the dose, route and room-temperature exercise protocol cannot be transferred directly to an athlete or driver. The study offers a possible explanation for delayed fatigue while leaving human benefit and safety unresolved. It is especially important not to interpret a relatively cooler core as evidence that the whole organism is protected from overheating, or to combine it with findings under a different ambient temperature as though the conditions were identical.
See a separate rat endurance experiment involving running economy and heat.