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From Fellrnr.com, Running tips
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It seems intuitive that excess body fat makes a runner slower. Body fat does not help you run, and adds weight that must be carried. The science seems to support this, as aerobic performance is based on how much oxygen you can use, and it is primarily [[Muscle|muscle ]] that is using that oxygen, not fat. But how much difference does body fat make?=[[VO2max|V̇O<sub>2</sub>max]] Changes=== Wild, optimistic Simplistic assumptions ==First wild assumption is that [[Jack Daniels Running Formula]] [[VDOT ]] is close enough to [[VO2max |V̇O<sub>2</sub>max]] to be useful. [[VO2max |V̇O<sub>2</sub>max]] is how much oxygen you can use per minute per Kg of body weight. The second wild assumption is that you can lose body fat without losing any muscle.
== Using VDOT for weight/performance changes ==
If [[VDOT/VO2max ]] is how much oxygen you use per Kg body weight, then you can multiply [[VDOT/VO2max ]] by body weight to work out the total max oxygen use. If you lose body fat only, then the total max oxygen should stay the same. You can then divide the total max oxygen use by the new body weight to get a new [[VDOT/VO2max]].
== A worked example ==
Let's work an example with a hypothetical runner who completes a marathon in 3:10 and weighs 220 Lb. A marathon time of 3:10 is a [[VDOT ]] value of 50, which we will assume is also a [[VO2max |V̇O<sub>2</sub>max]] of 50. A [[VO2max |V̇O<sub>2</sub>max]] of 50 means you consume 50 ml of oxygen per Kg of body weight per minute. If you weigh 220 Lb, which is 100 Kg, and your [[VO2max |V̇O<sub>2</sub>max]] is 50, that equates a total Oxygen consumption of 5000 (ml/min). Reversing the equation above, 200 Lb is 91 Kg and 5000 / 91 is a [[VO2max ]] of 55. A [[VDOT ]] of 55 equates to a marathon time of 2:56. That's a reduction of 14 minutes in marathon time. The [[VDOT Calculator]] will work out this for you. =Body fat and heat dissipation=Unless the temperature is quite cold, our maximum running speed is defined by our ability to shed heat. In turn, our ability to shed heat is defined by height and weight and because we cannot change our height, our weight becomes the main determinant.therefore, losing body fat can improve our ability to run at speed in mild or warm conditions.
If you have 30% body fat, reducing it to 20% body fat, you will get a performance improvement. But if your body fat is already low, reducing it will just impair your health. Reducing your body fat too low is dangerous, as some body fat is essential to life. Concerns with body fat and body image can lead to eating disorders. These problems can come from reducing calorie intake to the point where the diet lacks essential nutrients. However, this can involve pathological dieting - laxative abuse, vomiting, skipping meals, etc. This is very serious. Be mindful of the possibility of eating problems in yourself and those you care about, and seek qualified help if needed.
