Caffeine can increase muscular endurance through its effects on the central nervous system as a stimulant.[1][2]. Effects may be more consistent when consumed 60 minutes prior to exercise.[3] Though individual variation is high for caffeine side effects and tolerance, doses of 3–6 mg/kg of body mass are typically recommended for improving muscular endurance.[1]
Creatine monohydrate increases muscular endurance by increasing stores of creatine phosphate, which rapidly produces energy in the form of adenosine triphosphate (ATP) when it is burned. Faster ATP replenishment means an athlete is able to accomplish more repetitions or exert more effort.[4][5] As a normal diet contains 1–2 g per day of creatine, it typically takes 5 g per day for 5–7 days to saturate muscle creatine stores. A maintenance dose is typically 3–5 g per day.[4]
Additionally, beta-alanine can benefit muscular endurance during bouts of exercise lasting 1–10 minutes. Four weeks of 4–6 grams per day of beta-alanine can increase muscle carnosine concentrations, thereby helping to balance acidity in the cell, and may also attenuate neuromuscular fatigue. It should be known before consuming that beta-alanine may produce a strong tingling sensation on the skin that is harmless.[6][7]
Other supplements with some promise but less overall consistency for improving muscle endurance include nitrates, sodium bicarbonate, and citrulline.[8][9][10]