Effects of caffeine on mouse skeletal muscle power output during recovery from fatigue

1 School of Science and the Environment, Coventry University, Coventry CV1 5FB; 3 School of Biology, University of Leeds, Leeds LS2 9JT, United Kingdom; and 2 Department of Biology, University of Antwerp, Antwerp B-2610, Belgium Submitted 7 July 2003 ; accepted in final form 17 September 2003 The effects of 10 mM (high) and 70 µM (physiologically relevant) caffeine on force, work output, and power output of isolated mouse extensor digitorum longus (EDL) and soleus muscles were investigated in vitro during recovery from fatigue at 35°C. To monitor muscle performance during recovery from fatigue, we regularly subjected the muscle to a series of cyclical work loops. Force, work, and power output during shortening were significantly higher after treatment with 10 mM caffeine, probably as a result of increased Ca 2+ release from the sarcoplasmic reticulum. However, the work required to relengthen the muscle also increased in the presence of 10 mM caffeine. This was due to a slowing of relaxation and an increase in muscle stiffness. The combination of increased work output during shortening and increased work input during lengthening had different effects on the two muscles. Net power output of mouse soleus muscle decreased as a result of 10 mM caffeine exposure, whereas net power output of the EDL muscle showed a transient, significant increase. Treatment with 70 µM caffeine had no significant effect on force, work, or power output of EDL or soleus muscles, suggesting that the plasma concentrations found when caffeine is used to enhance performance in human athletes might not directly affect the contractile performance of fatigued skeletal muscle. extensor digitorum longus; force; soleus; work Address for reprint requests and other correspondence: R. S. James, School of Science and the Environment, James Starley Bldg., Coventry Univ., Coventry CV1 5FB, UK (E-mail: r.james{at}coventry.ac.uk ).