Acute Co-Ingestion of Caffeine and Sodium Bicarbonate on Muscular Endurance Performance

<b>Background:</b> Caffeine and sodium bicarbonate individually enhance muscular endurance by delaying fatigue, but their combined effects have scarcely been studied. <b>Objectives</b>: This study aimed to evaluate the acute effects of co-ingesting caffeine and sodium bicarbonate on muscular endurance at different loads in bench press and back squat exercises. <b>Methods</b>: Twenty-seven recreationally trained participants (female/male: 14/14; age: 23 ± 3.6 years) were randomized to four conditions in a double-blind, crossover design: (a) sodium bicarbonate and caffeine (NaHCO₃ + CAF); (b) sodium bicarbonate (NaHCO₃); (c) caffeine (CAF); (d) placebo (PLA); ingesting 0.3 g/kg NaHCO₃, 3 mg/kg caffeine or placebo (maltodextrin). Participants performed two muscle endurance tests on bench press and back squat exercises at 65% and 85% 1RM, performing as many repetitions as possible in one set until task failure. <b>Results</b>: CAF increased the number of repetitions (<i>p</i> < 0.001; η_p² = 0.111), mean velocity (V_mean, <i>p</i> = 0.043, η_p² = 0.16), and mean power output (W_mean, <i>p</i> = 0.034, η_p² = 0.15) compared to placebo. These effects were observed in back squat exercise at 65%1RM in V_mean (3.7%, <i>p</i> = 0.050, g = 1.144) and W_mean (5.2%, <i>p</i> = 0.047, g = 0.986) and at 85%1RM in V_mean (5.4%, <i>p</i> = 0.043, g = 0.22) and W_mean (5.5%, <i>p</i> = 0.050, g = 0.25). No ergogenic effects were found in NaHCO₃ + CAF) or NaHCO₃ conditions. <b>Conclusions</b>: CAF increased muscular endurance performance in male and female participants by increasing the number of repetitions, mean velocity, and power output; however, when NaHCO₃ was ingested, these effects were not detected.