The
form of energy that is used by the body for exercise is adenosine triphosphate,
or ATP. The body generates ATP for exercise from a number of different sources,
with some processes requiring oxygen (aerobic) and some not requiring oxygen
(anaerobic). At any given time, the body is generating ATP from all pathways to
some degree, mainly depending on the intensity and duration of exercise being
performed. This information will be useful in understanding basic concepts in
sports nutrition, supplementation, recovery, and programming which will
optimize training and subsequently performance.
Anaerobic
pathways are capable of supporting short duration but high intensity exercise.
There are two major sources of anaerobic ATP: ATP generated from the phosphagen
system (involves creatine), and ATP generated through the breakdown of
carbohydrate in the muscles without oxygen (glycolysis). Generation of ATP by
these pathways dominates activities such as weightlifting, sprinting, jumping, and
throwing.
Aerobic
pathways are capable of supporting longer duration but relatively lower
intensity exercise. There are two major sources of aerobic ATP: the breakdown
of carbohydrate in the muscles with oxygen (carbohydrate oxidation) and the
breakdown of fat (lipid oxidation). Aerobic exercise of a higher intensity
preferentially utilizes carbohydrate oxidation, whereas lower intensity
exercise preferentially uses lipid oxidation (3). Activities dominated by
carbohydrate oxidation include racing from roughly 800m to marathon distances,
whereas activities dominated by lipid oxidation are leisure activities like
walking or jogging. Amino acids can also provide fuel for oxidation, but are
typically only used in negligible amounts unless there is an absence of
carbohydrate for fuel (1). This may occur during long lasting high intensity
exercise when the body’s carbohydrate reserves are depleted or when routinely
consuming low amounts of dietary carbohydrate.
Figure 1. Energy system relative
contribution to total work during maximal intensity exercise of short duration
(1)
High
intensity exercise of as short as 30 seconds relies predominantly on
carbohydrate sources of energy production, as shown in Figure 1. Even at 10
seconds of maximal exercise, carbohydrate sources are providing approximately
47% of ATP regeneration. This is assuming all of the aerobic contribution to
maximal intensity exercise is via carbohydrate oxidation. This trend continues
as duration increases, with the aerobic contribution raising to above 51% of
all ATP regeneration at about 75 seconds of maximal intensity exercise (2). The
prevalence of ATP generation from carbohydrate sources for high intensity
exercise has important implications for sports nutrition and recovery, and is
part of the reason why a high carbohydrate diet is recommended for Strength
Group workouts.
References
1.
Baker, J. S., McCormick, M. C., & Robergs, R. A. (2010). Interaction among
skeletal muscle metabolic energy systems during intense exercise. Journal of Nutrition and Metabolism, 2010,
1-13. Available from: http://downloads.hindawi.com/journals/jnume/2010/905612.pdf
2.
Gastin, P. B. (2001). Energy system interaction and relative contribution
during maximal exercise. Sports Medicine,
31(10), 725-741. Available from: http://xa.yimg.com/kq/groups/19520777/208685572/name/gastin+c%C3%B3pia.pdf
3.
Juekendrup, A. E. (2004). Carbohydrate intake during exercise and performance. Nutrition, 20, 669-677. Available from: http://www.finanzaonline.com/forum/attachments/arredamento-edilizia-impianti/1722042d1363511078-palestra-casa-un-consiglio-carboidrati.pdf_id-ials4lnexso8efgktkiusvs8w2rvlkgajfterggs9lauxvt0-act_view-1-r_folder-su5ct1g-.pdf
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