Limits...
Metabolic factors limiting performance in marathon runners.

Rapoport BI - PLoS Comput. Biol. (2010)

Bottom Line: Of those who attempt to race over the marathon distance of 26 miles and 385 yards (42.195 kilometers), more than two-fifths experience severe and performance-limiting depletion of physiologic carbohydrate reserves (a phenomenon known as 'hitting the wall'), and thousands drop out before reaching the finish lines (approximately 1-2% of those who start).The analytic approach presented here is used to estimate the distance at which runners will exhaust their glycogen stores as a function of running intensity.In so doing it also provides a basis for guidelines ensuring the safety and optimizing the performance of endurance runners, both by setting personally appropriate paces and by prescribing midrace fueling requirements for avoiding 'the wall.' The present analysis also sheds physiologically principled light on important standards in marathon running that until now have remained empirically defined: The qualifying times for the Boston Marathon.

View Article: PubMed Central - PubMed

Affiliation: Harvard Medical School, Boston, Massachusetts, USA. brapoport@post.harvard.edu

ABSTRACT
Each year in the past three decades has seen hundreds of thousands of runners register to run a major marathon. Of those who attempt to race over the marathon distance of 26 miles and 385 yards (42.195 kilometers), more than two-fifths experience severe and performance-limiting depletion of physiologic carbohydrate reserves (a phenomenon known as 'hitting the wall'), and thousands drop out before reaching the finish lines (approximately 1-2% of those who start). Analyses of endurance physiology have often either used coarse approximations to suggest that human glycogen reserves are insufficient to fuel a marathon (making 'hitting the wall' seem inevitable), or implied that maximal glycogen loading is required in order to complete a marathon without 'hitting the wall.' The present computational study demonstrates that the energetic constraints on endurance runners are more subtle, and depend on several physiologic variables including the muscle mass distribution, liver and muscle glycogen densities, and running speed (exercise intensity as a fraction of aerobic capacity) of individual runners, in personalized but nevertheless quantifiable and predictable ways. The analytic approach presented here is used to estimate the distance at which runners will exhaust their glycogen stores as a function of running intensity. In so doing it also provides a basis for guidelines ensuring the safety and optimizing the performance of endurance runners, both by setting personally appropriate paces and by prescribing midrace fueling requirements for avoiding 'the wall.' The present analysis also sheds physiologically principled light on important standards in marathon running that until now have remained empirically defined: The qualifying times for the Boston Marathon.

Show MeSH
Relative use of fat and carbohydrate as metabolic fuels depends on exercise intensity.Fractional usage of carbohydrate (plasma glucose plus muscle glycogen, blue filled curve, ) and fat (plasma free fatty acids plus muscle triglycerides, red filled curve, ) are shown as functions of relative exercise intensity, . (Based on the work of Romijn and colleagues: Points plotted correspond to data points from the 1993 study [24], and corresponding error bars are computed as described in the Methods section.)
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pcbi-1000960-g001: Relative use of fat and carbohydrate as metabolic fuels depends on exercise intensity.Fractional usage of carbohydrate (plasma glucose plus muscle glycogen, blue filled curve, ) and fat (plasma free fatty acids plus muscle triglycerides, red filled curve, ) are shown as functions of relative exercise intensity, . (Based on the work of Romijn and colleagues: Points plotted correspond to data points from the 1993 study [24], and corresponding error bars are computed as described in the Methods section.)

Mentions: The work of Romijn and colleagues [24] has made it possible to estimate the composition of the metabolic mixture consumed during exercise as a function of exercise intensity, as discussed in the Methods section: Figure 1 shows fractional usage of carbohydrate (plasma glucose plus muscle glycogen, ) and fat (plasma free fatty acids plus muscle triglycerides, ) as functions of relative exercise intensity, . These functions and the stoichiometry of muscle oxygen metabolism, reflected in the parameters and , permit the expression of in terms of power output as in Equation 1, derived in the Methods section.


Metabolic factors limiting performance in marathon runners.

Rapoport BI - PLoS Comput. Biol. (2010)

Relative use of fat and carbohydrate as metabolic fuels depends on exercise intensity.Fractional usage of carbohydrate (plasma glucose plus muscle glycogen, blue filled curve, ) and fat (plasma free fatty acids plus muscle triglycerides, red filled curve, ) are shown as functions of relative exercise intensity, . (Based on the work of Romijn and colleagues: Points plotted correspond to data points from the 1993 study [24], and corresponding error bars are computed as described in the Methods section.)
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2958805&req=5

pcbi-1000960-g001: Relative use of fat and carbohydrate as metabolic fuels depends on exercise intensity.Fractional usage of carbohydrate (plasma glucose plus muscle glycogen, blue filled curve, ) and fat (plasma free fatty acids plus muscle triglycerides, red filled curve, ) are shown as functions of relative exercise intensity, . (Based on the work of Romijn and colleagues: Points plotted correspond to data points from the 1993 study [24], and corresponding error bars are computed as described in the Methods section.)
Mentions: The work of Romijn and colleagues [24] has made it possible to estimate the composition of the metabolic mixture consumed during exercise as a function of exercise intensity, as discussed in the Methods section: Figure 1 shows fractional usage of carbohydrate (plasma glucose plus muscle glycogen, ) and fat (plasma free fatty acids plus muscle triglycerides, ) as functions of relative exercise intensity, . These functions and the stoichiometry of muscle oxygen metabolism, reflected in the parameters and , permit the expression of in terms of power output as in Equation 1, derived in the Methods section.

Bottom Line: Of those who attempt to race over the marathon distance of 26 miles and 385 yards (42.195 kilometers), more than two-fifths experience severe and performance-limiting depletion of physiologic carbohydrate reserves (a phenomenon known as 'hitting the wall'), and thousands drop out before reaching the finish lines (approximately 1-2% of those who start).The analytic approach presented here is used to estimate the distance at which runners will exhaust their glycogen stores as a function of running intensity.In so doing it also provides a basis for guidelines ensuring the safety and optimizing the performance of endurance runners, both by setting personally appropriate paces and by prescribing midrace fueling requirements for avoiding 'the wall.' The present analysis also sheds physiologically principled light on important standards in marathon running that until now have remained empirically defined: The qualifying times for the Boston Marathon.

View Article: PubMed Central - PubMed

Affiliation: Harvard Medical School, Boston, Massachusetts, USA. brapoport@post.harvard.edu

ABSTRACT
Each year in the past three decades has seen hundreds of thousands of runners register to run a major marathon. Of those who attempt to race over the marathon distance of 26 miles and 385 yards (42.195 kilometers), more than two-fifths experience severe and performance-limiting depletion of physiologic carbohydrate reserves (a phenomenon known as 'hitting the wall'), and thousands drop out before reaching the finish lines (approximately 1-2% of those who start). Analyses of endurance physiology have often either used coarse approximations to suggest that human glycogen reserves are insufficient to fuel a marathon (making 'hitting the wall' seem inevitable), or implied that maximal glycogen loading is required in order to complete a marathon without 'hitting the wall.' The present computational study demonstrates that the energetic constraints on endurance runners are more subtle, and depend on several physiologic variables including the muscle mass distribution, liver and muscle glycogen densities, and running speed (exercise intensity as a fraction of aerobic capacity) of individual runners, in personalized but nevertheless quantifiable and predictable ways. The analytic approach presented here is used to estimate the distance at which runners will exhaust their glycogen stores as a function of running intensity. In so doing it also provides a basis for guidelines ensuring the safety and optimizing the performance of endurance runners, both by setting personally appropriate paces and by prescribing midrace fueling requirements for avoiding 'the wall.' The present analysis also sheds physiologically principled light on important standards in marathon running that until now have remained empirically defined: The qualifying times for the Boston Marathon.

Show MeSH