Definition of organism for English Language Learners. : 1  an individual living thing. : 2  a system with many parts that depend on each other and work together.
Figuring out how many calories you burn when running is, on a simple level, a fairly straightforward calculation. Most experts (and lots of studies) suggest that a person of average weight burns about 100 calories in a mile of running.
When discussing race day nutrition it is important to understand the energy requirements. The average athlete expends approximately 100 calories per mile during a marathon. During a triathlon, the athlete expends approximately 500 to 1000 calories on the swim, 3,000 to 4,000 calories on the bike, and 2,500 to 3,000 calories on the run. Wow! That is some serious energy expenditure.