Stamina enhancement can be described as an increased ability to engage in physically and mentally taxing activities without the development of fatigue. Although this effect is commonly mistaken for stimulation, it differs as it is not a direct increase in one's energy levels. Instead, it is an increase in one's resilience in performing an activity combined with a mitigation of general fatigue. Psychoactive substances that directly increase a person's endurance without stimulation are known as actoprotectors. These are defined as "substances that enhance body stability against physical or mental loads without increasing oxygen consumption or heat production."  Although actoprotetors are extremely uncommon, there are many compounds are capable of inducing endurance enhancement alongside other effects such as stimulation, focus enhancement, and motivation enhancement. These commonly include most stimulants such as amphetamine  and specific psychedelics  such as LSD.
- The Pharmacology of Actoprotectors: Practical Application for Improvement of Mental and Physical Performance (PubMed.gov / NCBI) | http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3762282/?report=classic
- Morozova, E., Yoo, Y., Behrouzvaziri, A., Zaretskaia, M., Rusyniak, D., Zaretsky, D., & Molkov, Y. (2016). Amphetamine enhances endurance by increasing heat dissipation. Physiological reports, 4(17). | https://dx.doi.org/10.14814%2Fphy2.12955
- Psychedelics and extreme sports | https://www.maps.org/news-letters/v21n1/v21n1-25to29.pdf