HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Rennie, M. J. Search for Related Content PubMed PubMed Citation Articles by Rennie, M. J. Related Collections Perspectives

How to avoid running on empty

Michael J. Rennie

Energy production by skeletal muscle shows a range of output which is unmatched by any other tissue. At rest, muscle oxygen consumption trickles along at about 2 ml kg^-1 min^-1 using mainly fatty acids and a little bit of carbohydrate, processed to lactate only. However, when the system is activated (for example in a 5000 m runner), working muscle oxygen consumption may be nearly 200-fold more. If ATP were not resynthesized after its use by myosin ATPase a marathon runner would need over 20 kg to finish! Even this power output is not maximal: the ultimate rate of ATP utilization occurs during jumping and throwing events and it may be many times higher than during maximal aerobic work. In mechanical engines a single type of fuel (gas, diesel oil, petrol, electricity) is used at all power outputs but in muscle a number of different types of fuel are used (e.g. creatine phosphate, glucose, glycogen, lactate, ketone bodies, free fatty acids and triglycerides) as appropriate to the task. Some fuels are stored in muscle and some are imported via the blood. Some are catabolized to produce ATP without the involvement of oxygen and some are fully oxidized to CO₂ and water. By and large the processes which have the highest power output rely on fuels stored in very small amounts (e.g. creatine phosphate) and those which have the highest capacity (e.g. ATP production from fatty acid oxidation) can sustain only moderate power outputs.