A 400m sprint is often called one of the best ways to lose 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 lactate production of a 400m sprint is often cited here as a reason for the effectiveness of the 400m sprint for fat loss. Lactate is a breakdown product during muscular exertion. Especially with maximum loads in the range of 20 seconds to 70 seconds. A crucial point here is the focus on “maximum loads”. 60 seconds of jogging is a load of 60 seconds but not as intense and therefore not as close to the maximum as well as performance and glucose-intensive as 60 seconds of sprinting. A 60 second sprint equates to about 400m for most trained athletes.
The statement about the 400m sprint and this excellent effect on fat loss is basically correct. However, only for less than 1% of the population who can actually sprint 400m. For over 99% of the population it's 400m with a mix of walking, jogging or running. This is basically not effective due to the low load in relation to the maximum and in view of the work done.
Basically, the question arises as to why short-term, high-intensity exertion and high lactate production have such an effective effect on fat loss. First of all, the answer is the Cori cycle.
The Cori cycle - named after its discoverers and Nobel Prize winners Gerty Cori and Carl Cori - describes the cycle of glucose and its breakdown products between skeletal muscle and liver. This process takes place in the liver because skeletal muscle cannot synthesize new glucose from lactate itself. It lacks the enzymes for gluconeogenesis that the liver has. As we have already seen, lactate is formed under anaerobic conditions when glucose is broken down. In anaerobic lactate metabolism, primarily exercise under 90 seconds, the conversion of one molecule of glucose yields only 2 molecules of ATP - the cellular energy substrate - on the other hand, 6 molecules of ATP are necessary to convert one molecule of lactate back to glucose in the liver via the Cori cycle . In comparison, 38 molecules of ATP are produced from one molecule of glucose in the aerobic area. The anaerobic lactate metabolism is therefore a very energy-intensive process.
This is an important reason why sprinters, especially 400m sprinters, have such a low body fat percentage, even though they only cover 1 to 5 kilometers, depending on the sprint distance, even in weeks of intensive training. For 100m sprinters, it's 1km to 2km during the most training-intensive weeks of the year. For 400m sprinters, depending on the training approach, up to 5km per week. In comparison, a marathon runner runs over 100km in weeks of intensive training.
Good Lactate and Cori Cycle Success in Maximizing Fat Loss!
More on optimizing training based on the Cori Cycle in the YPSI Interval Training Program Design & Periodization Seminar