Effects of Caffeine on Muscle Glycogen Utilization and the Neuroendocrine Axis during Exercise

Abstract

To examine the effect of caffeine ingestion on muscle glycogen utilization and the neuroendocrine axis during exercise, we studied 20 muscle glycogen-loaded subjects who were given placebo or caffeine (6 mg/kg) in a double blinded fashion 90 min before cycling for 2 h at 65% of their maximal oxygen consumption. Exercise-induced glycogen depletion in the thigh muscle was noninvasively measured by means of 13C nuclear magnetic resonance spectroscopy (NMR) spectroscopy, and plasma concentrations of substrates and neuroendocrine hormones, including beta-endorphins, were also assessed. Muscle glycogen content was increased 140% above normal values on the caffeine trial day (P < 0.001). After cycling for 2 h, caffeine ingestion was associated with a greater increase in plasma lactate (caffeine: +1.0 +/- 0.2 mmol/L; placebo, +0.1 +/- 0.2 mmol/L; P < 0.005), epinephrine (caffeine, +223 +/- 82 pg/mL; placebo, +56 +/- 26 pg/mL; P < 0.05), and cortisol (caffeine, +12 +/- 3 mg/mL; placebo, +2 +/- 2 mg/mL; P < 0.001) levels. However, plasma free fatty acid concentrations increased (caffeine, +814 +/- 133 mmol/L; placebo, +785 +/- 85 mmol/L; P = NS), and muscle glycogen content decreased (caffeine, -57 +/- 6 mmol/L muscle; placebo, -53 +/- 5 mmol/L muscle; P = NS) to the same extent in both groups. At the same time, plasma beta-endorphin levels almost doubled (from 30 +/- 5 to 53 +/- 13 pg/mL; P < 0.05) in the caffeine-treated group, whereas no change occurred in the placebo group. We conclude that caffeine ingestion 90 min before prolonged exercise does not exert a muscle glycogen-sparing effect in athletes with high muscle glycogen content. However, these data suggest that caffeine lowers the threshold for exercise-induced beta-endorphin and cortisol release, which may contribute to the reported benefits of caffeine on exercise endurance.

Cortisol responses to mental stress, exercise, and meals following caffeine intake in men and women

“…1 shows declining cortisol levels on the placebo day from the preexercise (C+60) time period through 40 min postexercise (Post+40). Exercise that is of short duration and moderate intensity may not activate a cortisol response if glucose levels remain normal (Sung et al, 1990), although long duration and intense exercise will increase cortisol output to high levels as a function of metabolic demands on fuel homeostasis (Laurent et al, 2000;Luger et al, 1987;Scavo et al, 1991). Despite the moderate intensity of the exercise protocol we used, the much larger HPA response to the mental stressors is striking.…”

“…Caffeine increases cortisol levels during periods of stress (Lovallo et al, 1989(Lovallo et al, , 1996Lane et al, 1990;Sung et al, 1990) both in the lab and in daily life (Lane, 1994), during naturalistic stressors such as medical school examinations (Shepard et al, 2000), and in relation to exercise (Laurent et al, 2000;Sung et al, 1990). Caffeine's effect on cortisol may be greater in persons with higher levels of central nervous system activation, such as those at high risk for hypertension (al'Absi et al, 1998).…”

Cafeína não altera os níveis de Imunoglobulina A Salivar (IgA-s) em jogadores de voleibol

“…Sabe-se que as concentrações de IgA-s são reduzidas tanto durante (gleeson et al, 1999) quanto após (nieMan et al, 2002) períodos de exercício extenuantes tanto pela intensidade como pela duração. Essa redução parece estar associada ao aumento nos níveis de cortisol, que também é elevado em exercícios agudos vigorosos seguidos da ingestão de cafeína (huCkleBridge, CloW;evans, 1998;laurent et al, 2000). Lovallo et al (2006) afirmam que a cafeína eleva a secreção de cortisol, assim como o exercício, e ressalta que, quando combinamos os dois fatores, há um efeito substancial e prolongado em homens.…”

Metabolic effects of a caffeinated sports drink consumed during a soccer match

“…However, researchers who studied the effect of caffeine intake on the use of MG during aerobic exercise found no differences between caffeine intake and the placebo (Laurent, Schneider, Prusaczyk, Franklin, Vogel et al, 2000). Other authors also observed that post-exercise caffeine intake results in an increase in the rate of resynthesis of muscle glycogen in the recovery period after strenuous exercise (Pedersen, Lessard, Coffey, Churchley, Wootton, et al, 2008).…”