Caffeine Decreases Neuromuscular Fatigue in the Lumbar Muscles: A Randomized Blind Study

Background. The purpose was to evaluate a possible ergogenic effect on postural muscles, still unknown through Biering-Sorensen's lumbar extension test.Methods. A double-blind, controlled placebo, crossover study. 51 healthy, physically inactive male subjects (18-25 years) with average body mass (BMI 18.5-24.9 kg/m2) were recruited. The subjects received oral caffeine (6 mg/kg) and saline (0.3%) in two cross-evaluations separated by one week.Results. The primary outcome was the time in the Biering-Sorensen test after 1 hour of treatment. The secondary results were peak lumbar extension force, rating of perceived exertion, electromyography (EMG's) median frequency and muscle recruitment of multifidus spinae and transversalis/interne oblique muscles, and cardiovascular vari-ables (heart rate and blood pressure). 27 subjects were blindly treated with caffeine and saline. Caffeine was ergogenic during the Biering-Sorensen test. It increased lumbar extension time (F = 0.34, p < 0.05), but not peak force. The perception of effort decreased with caffeine (F = 0.37, p < 0.05). Caffeine increased muscle stimu-lation frequency (p < 0.05) and recruitment (t23 = 0.49, p < 0.05) of multifidus spinae. In the transversalis/interne oblique muscles, caffeine increased the median frequency (t23 = 0.13, P<0.05) and the distribution of higher frequencies (p < 0.05). Caffeine also increased muscle recruitment in the transversalis/interne oblique muscles (t23 = 0.94, p < 0.05). Tachycardia and increased blood pressure at the lumbar test were higher in the caffeine condition (p < 0.05).Conclusions. Caffeine is ergogenic for postural muscles. Decreased rated perceived effort (RPE) and improved muscle activity suggest central mechanisms of caffeine.Study registration. The trial was prospectively registered (trial RBR-blinded) in the Brazilian Clinical Trials Register (http://www.ensaiosclinicos.gov.br/).