The 400m Sprint Myth, Fat Loss & the Cori Cycle

The 400m Sprint Myth, Fat Loss & the Cori Cycle

A 400m sprint is often called one of the best ways to loose fat.

400m sprinters are athletes with a very low body fat percentage which confirms this statement from a purely observational point of view.

The high lactic acid production of a 400m sprint is often mentioned here as the reason for the effectiveness of the 400m sprint for fatloss. Lactic acid is a by-product during vigorous exercise. Especially with maximal demands in the range of 20 seconds to 70 seconds. A decisive point here is the focus on „maximal demands“. 60 seconds jogging is a load of 60 seconds but not as intense and therefore not as close to the maximum and performance and energy-demanding as 60 seconds sprint. A 60 second sprint is about 400m for most trained athletes. 

Why 400m Sprints don’t work in real life

The statement on the 400m sprint and this excellent effect on fatloss is basically true. In a theoretical world. In real life, its not. Its true for for less than 1% of the population who can actually sprint 400m. For over 99% of the population it is 400m with a mixture of walking, jogging or running. This is due to the low load in relation to the maximum and considering the work done basically not effective. It made feel demanding from a subjective standpoint, yet the output and there energy-demand is too low paired with a higher risk for energy which eliminates 400m Sprint as a valid option to speed up fatloss.

Still, one question has to be answered: Why does short exercise with high intensity and high lactic acid production have such an effective effect on fat loss? 

The most overlooked answer is: The Cori cycle.

What is the Cori cycle?

The Cori cycle – named after its discoverers and Nobel laureates Gerty Cori and Carl Cori – describes the cycle of glucose and its degradation products between skeletal muscle and liver. This process takes place in the liver because the skeletal muscles themselves cannot produce new glucose from lactic acid. The muscle lacks the enzymes for gluconeogenesis. As we have already seen, lactic acid is produced under anaerobic conditions when glucose is broken down. On the one hand the conversion from one molecule glucose to lactic acid costs 2 molecules ATP – the cellular energy substrate – on the other hand 6 molecules ATP are necessary to convert one molecule lactic acid in the liver back to glucose via the Cori cycle. Lactic acid is therefore a very energy-demanding process from several directions.

Why Sprinters are lazy and lean 

This is an important reason why sprinters, especially 400m sprinters, have such a low body fat content, although they only cover 1 to 5 km, depending on the sprint distance, even in high volume training weeks. With 100m sprinters it is 1km to 2km in the most training high volume weeks of the year. For 400m sprinters up to 5km per week, depending on the training approach. In comparison, a marathon runner runs over 100km in training intensive weeks. 

So a marathon runner completes about 100 times the amount of work measured in kilometers. Still, the marathon runner is not even close to as lean as the sprinter. Why? Because the sprinter puts much greater demand on the Cori cycle.

So, the practical question at this point is: How can one use this fact to program and periodize intervaltraining that maximize fatloss with personal training clients based the energy demand created by lactic acid and the Cori cycle considering that 400m Sprints are not an real option?

And Tabatas are definitely not the answer.

All the Best by programming your Interval training to maximize the effectiveness of the Cori cycle in maximizing fat loss!

More about optimizing the training based on the Cori Cycle during the YPSI Interval Training Program Design & Periodization Seminar, which will be held for the first time in english in February this year in Hasselt, Belgium

Picture: Preparing for sprints.

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