A rat experiment found that amphetamine could increase running duration without improving running economy. In a warm environment, the lower tested dose prolonged running, while the higher dose did not, and both doses increased temperature at exhaustion.
Zaretsky and colleagues studied male Sprague-Dawley rats using treadmill protocols. Separate experiments examined maximal oxygen consumption, oxygen cost at selected workloads and time to exhaustion in a 32°C environment.
The drug conditions were 1 or 2 mg/kg amphetamine, with saline comparisons. These were controlled animal exposures, including intraperitoneal administration, rather than a study of human athletes taking oral medication.
The higher dose increased maximal oxygen consumption, while both doses increased the time required to reach that maximum. Neither dose improved running economy. Greater maximal oxygen use therefore did not establish a lower energy cost for the same work.
In the heat experiment, only the 1-mg/kg group ran significantly longer than controls. The 2-mg/kg group did not show that endurance advantage. Both amphetamine groups nevertheless reached higher core temperatures at exhaustion.
The authors interpreted the findings as consistent with fatigue masking, with heat production potentially offsetting benefit at the higher dose. The experiment did not identify every neural mechanism responsible for the endurance change.
Its exhaustion criterion was specific to the treadmill protocol. Rat core temperatures under that protocol are not validated human thresholds or a way to estimate the severity of a person’s intoxication.
The study shows why dose and environment matter when describing an ergogenic effect. “More endurance” cannot be assumed to mean greater efficiency or lower physiological strain.
Species, route and task differences prevent direct transfer to human performance or treatment. The findings support further mechanistic research, not a conclusion that amphetamine use is safe during exercise or that an individual’s functional state can be inferred from a drug result alone.
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