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How much faster can I expect to run my 10 K races when I've lost 10 kg (18 lbs) per September 1 this year, compared to when I weighed 80 kg, in March of this year?

Some context.

I'm an experienced runner (16 years of more or less continuous training), male, 54 years old, who got injured in 2010 and gained a lot of weight, which I'm slowly trying to lose over the years (about 10 kg, 22 lbs, per year, started in 2013).

My current weight is 78 kg, 174 cm long, which gives me a BMI of 25.8. My current fastest recent 10 K race result is 46:02 minutes, half marathon 1:45 hours. That was when I still weighed 80 kg (176 lbs), BMI 26.4.

I'm training daily, around 60 km (37 mi) per week, one interval session, one intensive training run between 10 en 15 km, several easier sessions (for recovery), and a race or test run every week. I don't feel tired or over-trained.

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According to multiple sources a good estimate is about 2 seconds per pound per mile (This is something around 2.7 seconds per kg per km). Note that it is not a linear formula, there is a point where losing more weight will result in loss in muscle mass, which is likely going to hinder performance. Unfortunately I couldn't find any scholarly research on this topic.

Based on this number of 2.7 seconds per kg per km and that you have lost 10 kg and are running a 10k that evaluates to: 2.7 * 10 * 10 = 270 seconds! And that time is based on weight loss alone, so with additional training you could expect to do better!

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    +1. And agreed, 2ish secs/mile is around the right figure, and that time savings is generally on weight alone. Many people see even more than that because of increased training.
    – JohnP ♦
    Apr 20, 2014 at 16:38
  • Should I do some moderate strength exercise and eat relatively more protein to compensate for loss of muscle mass, or is my weekly mileage and training regime enough to maintain my strength? As I understand, the formula is not taking into account any factors like reduction of muscle mass, though my slow rate of weight loss should prevent that.
    – René Van Belzen
    Apr 21, 2014 at 7:55
  • Well, unless you are insanely muscular your BMI indicates that most of your weight loss will be fat instead of muscle. As for eating more protein I'm not sure how much you eat now, but maybe this will help.
    – Zack
    Apr 21, 2014 at 22:32

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