How much faster will you run if you lose weight? You'll be amazed!

I was wondering what the effect of carrying a few extra pounds was on running times. I found on the web that scientists have done treadmill time trials with runners who wore known amounts of excess weight. They found that on average runners lost 23 metres distance per 1% excess weight per 12 mins running time. See runnersconnect.net/running-...

This implies (I think) that if you know how much excess weight you are carrying and your current time for 5k you should be able to calculate roughly what your 5k time might be if you lost the excess weight. Its a bit complicated but here goes...

1. Divide your current weight by your target weight to find the excess weight %

2. Divide your current 5k time in minutes by 12 to find your time factor

3. Multiply your time factor by your excess weight % and then by 23 to find the number of metres you are losing over 5k

4. Divide that number by 5000 to find the % distance you are losing

5. Multiply your current time by 1 minus the % distance you are losing to get your potential time (multiply the decimal by 60 to get accurate seconds).

Example 1

Current weight = 160lbs (11 stone 6lbs)

Target weight = 140lbs (10 stone)

Current 5k time = 36 mins

1. Excess weight % = 160 / 140 = 1.12 ie 12% overweight

2. Time factor = 36 mins / 12 = 3

3. Metres lost = 3 x 12 x 23m = 828m

4. Proportion of 5k lost = 828m / 5000m = 0.17

5. Potential 5k time at target weight = 1 - 0.17 (0.83) x 36 mins = 29.88 = 29mins 53secs

Example 2

Current weight = 1901bs (13 stone 8lbs)

Target weight = 160lbs (11 stone 6lbs)

Current 5k time = 40 mins

1. Excess weight % = 190 / 160 = 1.188 ie 19% overweight

2. Time factor = 40 mins / 12 = 3.333

3. Metres lost = 3.333 x 19 x 23 = 1456m

4. Proportion of 5k lost = 1456 / 5000m = 0.29

5. Potential 5k time at target weight = 1 - 0.29 (0.71) x 40 mins = 28.4 = 28mins 24secs

I hope that this gives real encouragement to those amongst us who are doing C25K as part of a weight loss programme. Let me know how you get on running your own figures through the calculation. Or leave your own figures for current weight, target weight & current 5k time below and I will work it out for you...

ChrisL

PS: The above calculation is simply about the effect of carrying the excess weight. It makes no allowance for any improvement due to increased fitness as you lose weight nor to any improvement in movement or running technique over the time. So you should actually run faster than it predicts if you get fitter as well as lighter (I think).

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35 Replies

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  • Very interesting :) I currently run a 34min 5k, if I lost weight to my target weight I'd run it in 29mins 14secs and if I got enough weight off to be in the top end of a normal BMI range I'd do it in 24mins 17secs. My target weight is a lot more realistic than BMI measurement, nice to know I'd do sub 30mins, the holy grail! Keep posting these interesting bits, your last post was an interesting to read too. Happy running!

  • Hey LoveFood1984, that's great! Thanks for doing the maths. Those numbers seem to make sense don't they? And hopefully its encouraging to know that you can expect a double celebration when you get down to your target weight.

  • I'd love a double celebration, despite doing couch to 5k and now being able to run 5 miles my weight has stubbornly not changed (I'm at a loss, I must be eating more somewhere!) time to try speed work to get my time down, probably easier than losing weight ;)

  • Sheesh! My predicted 5K time is currently about 55 minutes. This calculation tells me that if I shed my excess weight, I would get it down to about 35 minutes! I'd be over the moon if I ever got that sort of time!

  • Hi Dewines. Remember that this calculation is simply about the effect of carrying the excess weight. It makes no allowance for any improvement due to increased fitness as you lose weight nor to any improvement in running technique over the time. So you should actually run faster than it predicts if you get fitter as well as lighter...

  • I'm a simple girl, I can't handle all those sums, but I did lose weight through myfutnesspal as I knew I would run better!!! I'd love to get faster though..

  • Hi Chris more stats to excite me . Like juicy ju I find it hard to work out but luckily example 1 is almost exactly my figures so am very pleased Weight loss really slow at 1/2 lb a week and not sure if will ever get to target but thought of improving 5k time might just spur me on . Thanks

  • Very interesting! I have found since losing a fair bit of weight, my times have started dropping much quicker then I thought they would. I held the same weight that I'd lost in my arms, and couldn't imagine running with it now! Off to calculate using this method. Thanks!

  • Hi NextJenn. It would be interesting to know if my calculation would have correctly predicted your current 5k time at your current weight based on your previous weight & time...?

  • I certainly run faster now than I did when I was three stone heavier. Thanks to 5:2 and C25K I'm slimmer and fitter than since I was a teenager!

  • Hi Gingernut49. Can you remember your old weight & 5k time? If you could let me have them and your current weight & 5k time I could do the maths to see how accurate this calculation really is. If you don't want to reveal your weights just divide your old weight in lbs by your current weight to give me a ratio (eg 1.25). Cheers

  • I don't measure my runs nowadays as (at my age!) I'm not bothered about running for more than 5k or calculating anything - I just know that nowadays I cover more ground in the time that Laura takes to do the three c25k+ podcasts. I was three stone heavier when I started.

  • Wow that is some recommendation for the programme. I see you did 5:2 as well. I am tempted to do 6:1 as I have been told to get my cholesterol down but don't really need to lose any weight. Any tips?

  • Your best first step is to watch the BBC Horizon programme that the diet stemmed from, "Eat, Fast and Live Longer" vimeo.com/54089463 which I can honestly say changed my life. I do 6:1 nowadays to keep my new weight maintained and, with running around 5k three times a week, the weight has stayed off since last April. I'm going to do at least 6:1 for the rest of my life for the health benefits. I weigh myself once a week to keep an eye on the scales, then I know whether to do 6:1 or 5:2 the following week.

  • I watched the video the other day. Interesting. Thanks

  • I got a headache before I was half way through that. For a moment I was transported back to the horror of triple maths on a Monday morning at school. I'm impressed by you and all those working through their calculations.

  • I got a headache half way through reading that. For a moment I was transported back to triple maths on a Monday morning at school. I'm impressed by you and all those working through their calculations. Great work !

  • Well, that explains it. I really actually am running backwards ! :-)

  • I think those numbers confirm my own suspicions, that if I want to get much quicker I need to lose a bit of fat. I am a bit into the over weight category so it's probably about a stone I could do with losing but have solid legs and I think the effort of lifting them up all of the time does impact on my speed! Thanks for posting.

  • Wow - according to this (and assuming my maths is tight!) I can lose ten mins off my time, by getting down to my current target weight - not even as far as my optimum weight! Thats a weight that get sme to halfway in the healthy BMI zone, rather than at the mid point of the obese bracket, so quite ambitious...

    But 10 mins off the time is yet another motivator so thanks for that!

  • Wow! My head is spinning from the maths but it makes sense, less weight - go faster! Thanks for the interesting post. My problem isn't just running faster but also continually running for longer as I seem to want to stop and walk :(

  • I've lost a lot of weight but I'm not running any faster. At 56 maybe I'm destined to be a tortoise.

  • But are you trying to run faster MissWobble? Or are you settled in a comfortable pace? 56 is the new 36 so there is plenty of time to get faster if you want to (I have to believe that as I am 53 myself and am still a few minutes off my target time).

  • Yes, I'm trying. I'm doing some Fartlek stuff but I just get too tired. I don't seem to have any ooomph and am soon puffing and panting, and struggling so am not covering enough distance towards my 10 k goal. I am running every other day, come what may. So I'm not a quitter. I eat healthily and thought I was fit but clearly not fit enough

  • I have read very contradictory advice about stepping up to 10k. Some people/websites say that if you can do a reasonable 5k you should be able to do 10k without too much bother. Others say it takes longer to get from 5-10k than it does from 0-5k. Everyone seems to agree that doing 10k should bring your 5k speed up though... Good luck.

  • ChristL I am trying the Bridge to 10k, but I am very very slow. I want to increase distance and hope a little speed will come with that, but I'm not so sure speed will. I've been recommended doing Farlek, but feel very tired after and even my fastest Farlek run is really only a little faster then my usual jog. I know I must try and do more Farlek. If weight is not really an issue and nor injury, than should people be running sub 30 minutes for their 5k's?

  • Gosh TinyRun that is a big question and I am no expert - just an enthusiastic beginner - but I will try to answer it...

    What I suspect from all that I have read about this is that most able-bodied MEN should with adequate training be able to achieve their age-graded equivalent time for 5k if they are are fit and not carrying any extra weight.

    30mins is 2.32 times as long as the elite 30 year old male athletes do 5k. So should a fit 30 year old man who is not overweight be able to manage that? I would have thought so. I am 53, reasonably fit and not overweight but I have only been running for 4 weeks and I can do it quite easily even though I am still walking for nearly 50% of the time.

    For women it is harder. Women are not as fast as men. 5k in 30 mins is only 2.02 times the time of an elite 30 year old woman. To be the same as the men's target of 2.32 times the elite time the women's time works out at 34:20 so arguably at 30 years of age that should be the target for women.

    As we get older than 30 we get slower. If you are over 30 I suggest you first look at my other post healthunlocked.com/couchto5... to find your age-graded time. but be aware that when I did that post I did not make the allowance for 2.02x versus 2.32x as discussed here. You have given me more work to do & I shall repost an amended table when I have time...

    Then on top of that if you are carrying extra weight the calculation in this post will give you an indication as to how much that weight is slowing you down.

    Long story short - If you are female, over 30 or carrying any extra weight at all, and particularly if you tick more than one of those boxes, you will find 5k in 30mins much more difficult - or even impossible. Unfortunately working out what your gender-elite adjusted, age-graded, weight adjusted target time should actually be is really quite complicated.

    Hope this helps...

    ChrisL

  • Thanks Chris.

  • Eek ChrisL it's made me all confused! I think not only do we need to increase speed and distance to improve our times, but to also add in other types of exercise. in any form, like stretches etc. I guess any extra exercise will make our bodies and minds fitter.

  • Very interesting, thanks for this :) I'll see how I get on with this!

  • Wow, if I've done that right then my target time would be 25 mins - currently about 42!

    That's inspiring. I've already lost 2.5st and want to lose at least the same again. Very motivating.

  • Aware the post is a little old now, but if you're still following it, thought you might find my results interesting. down from about 11st4 to 10st6. Time down from 25 minutes to 22.30, your calculation would work it out at just over 23 minutes, but I am aware I should be fitter from the body weight training stuff I've been doing... and also, I may be a itny bit lighter than that now, that was as of a few days ago. All in all the calculation seems to work to a good tolerance with me. Hadn't run for a while and then just was able to go so much faster having lost the weight.

  • Current weight: 130kg

    Target weight: 100kg

    30% overweight.

    Time factor: 34/12 = 2.833

    Metres lost: 2.833 * 30 * 23 = 1,955

    Proportion of 5k lost: 1,955 / 5,000 = 0.391

    Potential 5k time at target weight: (1 - 0.391) * 34 = 22 minutes

    That would be amazing, sounds a little optimistic to me :)

  • Im a bit skeptical of the math here. Let me know if I have errors.

    Current weight- 215 pounds (I currently have bmi over 30)

    Target weight- 150 pounds

    5k time- 38.5 minutes

    43% overweight

    Time factor- 3.21

    Meters lost 3.21x43x23=3175

    Prop. Of 5k lost 3175/5000=.635

    Potential 5k time at 150 pounds= (1-.635)x38.5=14.05 minutes.

    Don't think this 54 year old will get anywhere near this.

  • Went back to the article that you cited and came up with a formula that seems to match their results.

    CW-Current weight

    TW-Target weight

    Potential 5k time at TW = 1/(.0383x(CW/TW-1)+(1/(5k time))).

    Inserting the figures from my previous post, I came up with 23.56 minutes. Still seems optimistic, but within the range of possibility.

    This formula uses their 115 meter loss. For the 90 meter loss sub .03 for the .0383 in the formula.

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