The effect of a physiological concentration of caffeine on the endurance of maximally and submaximally stimulated mouse soleus muscle

Abstract

The use of caffeine as an ergogenic aid to promote endurance has been widely studied, with human literature showing the greatest benefit during submaximal muscle activities. Recent evidence suggests that the acute treatment of skeletal muscle with physiological concentrations of caffeine (70 μM maximum) will directly potentiate force production. The aims of the present study are: firstly, to assess the effects of a physiological concentration (70 μM) of caffeine on endurance in maximally activated mouse soleus (relatively slow) muscle; and secondly, to examine whether endurance changes when muscle is activated submaximally during caffeine treatment. Maximally stimulated soleus muscle treated with 70 μM caffeine resulted in a significant (17.6 %) decrease in endurance. In contrast, at a submaximal stimulation frequency, caffeine treatment significantly prolonged endurance (by 19.2 %). Findings are activation-dependent such that, during high frequency stimulation, caffeine accelerates fatigue, whereas, during low frequency stimulation, caffeine delays fatigue.

Fig. 1

The effects of 70 μM caffeine treatment and stimulation frequency on soleus muscle power output following continues work loop stimulation. Values are displayed as a percentage of maximal work loop power output [data represented as mean and SE; n = 8 in each case; significant differences (*p < 0.05) in power output at each individual time point between 140 Hz control and 140 Hz caffeine treated]

Fig. 2

Typical effects of fatigue on work loop shape for control soleus stimulated at 140 and 40 Hz (a and c, respectively) compared with those treated with 70 μM caffeine (b 140 Hz caffeine, d 40 Hz caffeine) (arrows indicate where stimulation typically started, towards the end of lengthening, and finished, during shortening; 0.4s, 2.4s, 4.8s and 7.2s represent time since the start of the fatigue protocol)

Fig. 3

Effect of 70 μM caffeine treatment and stimulation frequency on recovery of soleus muscle following fatigue (data represented as mean and SE; n = 8 in each case; asterisks represent significant differences in power output at each individual time point between 140 Hz control and 140 Hz caffeine treated)