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Adjusting Rx Factor
  • Posted: 02.04.2006, 21:50
       
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    "Herman wrote - I'm coming to the conclusion that the best potential use for adjusting the Rx is for an inexperienced marathoner or 1/2 marathoner to put some cushion in the calcs when projecting a race time from shorter races. I think I'm just going to stick with the standard 1.06 when using RunPro to compare race efforts of 1/2 marathon and lower."



    Herman,



    I shifted this over to the forum to share with everyone. I like using the adjustable Rx factor as an indicator of my level of fitness. I believe you mentioned that the standard 1.06 Rx factor correlated to record times at various distances. Chances are, there may not be too many people who could actually match the times predicted with a 1.06 as record holders are usually specialists. 5k US record holder Bob Kennedy proved he's not a marathoner.



    By having times for a 5k and a marathon to adjust the Rx to fit me, I'm insured of fairly accurate training paces. Not that a few seconds matters, but I always think it does. Also, the mentality of having the program taylored to me satisfies my geeky mind.

    Ray Green
  • Posted: 03.04.2006, 14:28
       
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    You are correct that an Rx of 1.06 reflects times posted by specialists at each distance, and that some variation of this value would probably better model the typical runner's abilities. The trick is determining what that variation should be.



    If one has a string of recent race times at various distances, then using them to come up with a personal Rx might not be a bad way to go. But keep in mind that as your 5k times improve, so to should your projected times for all other distances.



    If you have a string of gradually improving 5k's, and you keep trying to match the best time up with a marathon time you ran several months ago, you're going to get larger and larger Rx values. At some point, you have to accept the fact that your conditioning has improved and you may be able to post a better marathon, which shouldn't be too difficult a concession to make.....





    Herman
  • Posted: 04.04.2006, 01:39
       
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    This recent 5k took my Rx factor from 1.075 to 1.087 in order to match the 3:38 marathon with the 21:30 5k.



    I see how playing with the Rx factor and entering faster times alters the training paces. I feel like until I do run a better marathon, I need to let the spread stay as is. You and Eric have both stressed basing your training on what you have done and not what you hope to do. Another consideration is that I don't expect my marathon to improve much (if any) if I'm not doing marathon type training. Everytime I've entered a marathon off of a 5k base, I RLH for the first 15-18 miles and then drop like a bad habit.

    Ray Green
  • Posted: 08.04.2006, 09:01
       
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    Herm and Ray,



    Predicting results is a fine art and science. The Riegel formula and Herm's extension of this using RunPro are a great way making the process simple and allowing you to tailor the prediction process to your own individual characteristics.



    I like the way you can adjust the Rx factor to get an individual prediction curve.



    When I did the prediction engine in RunCoach I came up against similar problems. Also it has to apply to the general population so has less tailoring than the Rx adjustment approach but does address some of these issues. I will run a couple of the main ones and how RunCoach solves them.



    Riegel formula - This is based on world's best performance over a variety of distances. The issue here is that the world's best at 3k, 5k or even 10k is often not the same person who is world's best at the half or full marathon. Individual curves may be very different from the the sum of the world's best at each distance.



    RunCoach solves this by using data from actual people. There is a lot of data of individual PB's at various distances. Each person's individual curve should be used and this is how RunCoach does it. This solves two issues. Firstly slower runners may have a very different curve than faster runners. Secondly even runners who run the same times at certain distances will vary in how they individually handle other distances.



    The next biggest issue is that the further away the predicted distance is from the distance you are using as a base the more hazy the prediction gets. Sprint perfomance for somebody may be very different from how they handle distances like a marathon.



    RunCoach handles this by having three complete prediction systems that interlock and overlap. There is a sprint model, a middle distance model and a long distance model. The models are quite accurate around their distances but it drops off as they get further away.



    RunPro's Rx modification approach is another way of dealing with these issues and my suggestions based on what RunCoach does would be this.



    1) Find out your own particular Rx factor. This will almost certanily not be 1.07.

    2) You own Rx factor may vary depending on the distances you are predicting. I would suggest having a short distance Rx and a long distance Rx and using the appropriate factor.



    Predicting performance can be a very frustrating thing and often we get very good at it ourselves without using a computer. A computer prediction can often help however by giving us a goal or target to shoot for.



    Keep up the good work with RunPro Herm.



    All the best,



    Paul

  • Posted: 08.04.2006, 19:42
       
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    Excellent points, Paul. I hadn't really thought about defining separate Rx values for shorter and longer distances, but it's a great idea.



    As you say, race time prediction is tough to dial in when trying to deal with the population in general. A siingle scheme that adequately covers all distances and all abilities simply doesn't exist. Add other variations such as terrain, course accuracy, and weather (as I was so rudely reminded this morning), and things get really hairy.



    On the plus side, though, is the fact that we're not involved designing rockets, here. We just wanna know about how fast we might expect to go out in the next race, or see roughly how past races of different distances compare to one another. As programmers, a deviation of 30 seconds in the projection of a 10k may keep you and I awake at night. But it's not really that big a deal in the overall scheme of things. Most runners could plan a race strategy from either end of that 30 second spread and come out in good shape. It's blowing the *first mile* by 30 seconds that sinks the ship before it leaves the harbor.



    So, those runners who are obessed with dialing in the numbers can study the models, choose the one best suited to themselves, learn what adjustments need to be made, and fine tune their stratgies to the n'th degree (I'm in that boat). Those who are not quite so obsessed, but still want to better understand their potential and improve their times can use any of the prediction models with good results. Smiles all around!

    Herman
  • Posted: 21.02.2015, 12:15
     
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    I just want to be the first post on this classification. How are you coming with the updated version? I do not want to say anything about your program on my other forum until you give me the okay.



    ________________________
    sdji



    edited by: mrusman7, Feb 21, 2015 - 12:15 PM

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