Thursday, September 1, 2011

The Doc Answers Your Questions

Huge thanks to Dr. Inigo San Millan, Director of the Exercise Physiology and Human Performance Lab at the University of Colorado's Anschutz Health & Wellness Center, for answering your questions from this post. He’s been really busy working with the Pro Cycling Tour here in Denver, but managed to squeeze us in. 

There were so many questions, that I tried to pick the ones that seemed to address most concerns/inquiries.

Why can’t I lose weight?:

I have been exercising 5-6 days a week for a least an hour a day, alternating workouts, and 2x/week doing daily doubles, and my weight is the same as it was last November during my recovery season. I have been stuck at 148lbs forever it feels like. Most of my friends, who just started to run over the past month have been dropping weight like crazy, but I don't seem to be headed anywhere...I pay pretty close attention to my diet and not sure what to do about my weight plateau....

The doctor says…

What probably happens is that at the exercise intensity you run you are not using much fat as you probably use more glucose. This is a very common thing in recreational athletes who exercise several times a week, have a good diet and don't get to lose weight. It may or may not be a caloric intake problem but what I see for the most part is that you don't "burn" much fat when you exercise. Calories in and calories out may not be necessarily the same. Calories can be derived from fat and glucose (and a bit of protein) so calories are not always equal in terms of substrate utilization. When we see caloric expenditure (Kcals) on our heart rate monitor or gym bike screener we can never see whether those calories come from fat, carbohydrate or which % belongs to either one. As an example we can "burn" 700Kcals in a workout session but the majority (let's say 90%) can be derived from carbohydrates and therefore very little from fat. However we can also "burn" 700kcals by exercising at different intensities and levels and therefore can "burn" 70% of all Kcals derived from Fat and the rest from carbohydrates. So the same rate of caloric expenditure does not represent the same metabolic response to exercise and therefore substrate utilization. With the methodology I apply in the lab it is possible to determine fat and carbohydrate metabolism and responses to different exercise intensities and identify that individual training intensity that elicits the highest fat utilization and translate it in heart rate.

Why doesn’t running get easier?

I'd like know why running doesn't seem to ever get easier for me! I'm a race walker (4 full, 5 half marathons) but I've been running more and more over the past 12 months and it doesn't seem to get any easier! I always feel like my lungs are going to explode.

The doctor says…

This could be due to many different reasons but I would guess that your fitness level is not optimum and very possibly you are training at the wrong zones and therefore not improving. I would suggest doing a physiological test to know where you exactly are and to set your training zones.

Is physiological performance testing right for me?

I'd love to know if this testing is right for me. I'm a casual runner - 5ks and 10ks mostly - with weight and resistance training in between.

The doctor says…

This test is not just for the elite athlete but for anybody who wants to improve fitness levels and get to know how his/her body works during exercise and be able to improve and optimize time.

Why do we have to do long runs so slow?

I'd love to hear more about the theory of doing your long runs 1-2 minutes slower than anticipated marathon pace. I don't understand how I can possibly run marathon pace for 26.2 if I haven't at least trained a few long runs near that pace.

The doctor says…

The theory behind this is to improve your Type I muscle fibers (Slow Twitch). These are the fibers with the highest mitochondria density, highest fat utilization capacity, oxidative enzymes and lactate transporters. Training these fibers should be the base of any training and normally this intensity corresponds to a slightly lower than goal pace as goal pace is an intensity that recruits fast twitch muscle fibers (Type II's) and are more glycolytic (use more glucose) have less mitochondria density so also use less fat and produce more lactate. In a way, slow twitch muscle fibers are great assistants to fast twitch muscle fibers both during training and competition so slow twitch muscle fibers must be very robust. By training at specific heart zones we can elicit a higher efficiency in slow twitch muscle fibers.

How the heck can I become a faster runner?

I sure would like to know how to get faster. I have been running for 8 years, have done speed work and just don't get any faster. In fact this past half marathon I was 5 minutes slower than last year after doing more speed work. (2:40 half-marathon)I am over 50 so I know age probably has a lot to do with it.

The doctor says…

Age could be a factor, but believe me you should be able to improve your PR despite being over 50. It is possible that you are not training in the correct way and training zones and therefore not improving performance. It could be also possible that you are over trained and fatigued and therefore your body cannot recover properly and not improve as needed. We can easily monitor and check this through blood analysis and normally can identify the source of overtraining and/or fatigue and correct it.

Can VO2 Max be improved?

Can I improve my VO2? is it true that I can only improve my speed for 7 years (after initiating running) and after that, I will maintain for awhile and then decline in speed? is there a way to determine the minimum mileage I should be running every week in order to increase speed and endurance when NOT training for a marathon?

The doctor says…

Relative VO2max (ml/kg/min) can be increased as weight decreases. Absolute VO2 may increase depending on the fitness levels that you have. However, VO2 max, although it is a great indicator of cardiorespiratory fitness it is a poor predictor for performance. The last runner in a competitive marathon race can have the same or even higher VO2max than the winner. Whatever ultimately makes the difference are the local/metabolic adaptations and events happening at the muscle and cellular level. It is not just about how much O2 you can get into your muscles. It is about how well does muscles can deal with that O2 and how efficient they are at utilizing fats of carbohydrates as well as how efficient the cells and muscles are at dealing with byproducts of muscle metabolism like lactate or hydrogen anions. There are many of events going on at the muscle and cellular level and those are the ones that make the different. We can see your metabolic response and adaptations to exercise through the physiological test and set the right training zones to improve those metabolic and cellular responses and adaptations and therefore optimize your fitness level.

Regarding how many times you should be running per week in order to increase speed and endurance when not training for a marathon, it is quite individual and without physiological testing we cannot have real scientific parameters. But I would say that with 2-3 days of endurance you can maintain a good level of your mitochondria density and oxidative enzymes and with 1-2 days of intensity/interval training you should be able to maintain your glycolytic capacity (that of fast twitch muscles) which is very important during the competition.

How can I figure out my heart rate zones?

I'd like to know if there is a semi-effective way to determine heart rate zones WITHOUT getting this test done. The formulas online seem very standard, so I'm wondering if there's a way that I can tweak it to be more accurate, until I can afford the test.

The doctor says:

That is a good question but unfortunately the only way to know your heart rate zones is by performing a physiological test. As you point out, the formulas out there are very standard and for the most part quite inaccurate which can elicit the wrong training response and therefore jeopardize training and fitness level.

How many calories do I need?

How does one accurately find out their maintenance calorie intake?

The doctor says…

That is a good question. It is possible to do a basal calorimetry test to see your basal metabolic expenditure, although this can be tricky as probably not very accurate to represent the entire 24h caloric expenditure as it can really vary throughout the day and level of activity, stress, etc. I would say that if you are a healthy and fit individual a diet of about 1,500 to 2,000 Kcals depending on your body mass plus 45min to 1:30h of exercise 3-4 times a week should help you maintaining your caloric intake and balance.


If you are in the Denver area and would like to schedule a test, contact the Performance Lab at 720-848-8208. They may also be able to tell you how to find a testing option in your area.

I hope this was helpful. I know I learned a lot. Thanks Dr. San Millan!  Me and my slow twitch muscles are gonna grab a heart rate monitor and GO!

How about you? Did you learn anything?



  1. thank you so much for posting my question...makes me almost feel famous ah!
    with 2 days before my half marathon, it makes me feel better to know there is an scientific reason for my not losing weight...
    thanks for your blog, love your attitude toward life!

  2. Ok- I just have to get this done because I'm in the same boat as the person with question #1. I lost 40lbs just like *that* and now for the past year the scale has not budged even though I am swimming 2x/week, cycling on the weekends and running 2-3x a week. Maintenance is a great thing but its not where I want to be and I know I'm not overeating as I log my food. So frustrating!!


  3. THANK YOU DOC! Great information--just tell me how to get SUAR's body.

    Beth, be ready to be drawn! Stick figure style...but how do I incorporate sharting and TWSS????

  4. Great answers reiterating what I know, but can't make myself implement. I did have the metabolic assessment and heart rate zones. I know I need to keep my heart rate lower to burn more fat. How do you maintain cardio fitness while keeping your heart rate low? Such a frustrating conundrum as it seems I must choose between training for events or backing off the intensity and losing the remaining 25 pounds. I gave it a few weeks of light cardio and lost half a pound each week, but I felt like a slug! Ugh.

  5. Thanks for asking the doc! Great explanation of why long runs need to be slower. I was completely baffled by this when I trained for my first marathon. I thought it would be impossible to run :45 seconds per mile FASTER for 26.2 miles if I didn't train that way. When race day came, it all came together and worked perfectly. It's pretty amazing!

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  7. ooooh, GREAT reference post Beth. I will be passing this one on!!

  8. great Q&A and now I have something to look forward to when I am over 50! PR's! haha.

  9. Thanks for posting my question Dr Millan. I know I need to get this testing done so that I'll know what zones I need to train in to try and improve my speed, now I just need to find someone in my area!

  10. This is awesome. Definitely sharing with friends. Thanks!

  11. Thank you for this post! I DID learn something. And I am appreciative for the excellent info.

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