unCoachJasonTM
VO2max
The monthly newsletter of RunCoachJason.com
Jason Karp, professional coach, consultant, freelance writer
July, 2007
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In
this issue:
Coach Jason to Speak at USATF Advanced Endurance & Sprints Summits
Stride Length and Stride Rate
Fat vs. Carbohydrates
VO2max and Altitude
In
Press
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Coach Jason to Speak at USA Track & Field Advanced Endurance & Sprints Summits
For those of you in the Chicago area this month, I will be speaking at the USA Track & Field Advanced Endurance and Advanced Sprints/Hurdles Summits on July 1-3, 2007 at Loyola University in Chicago. I will be giving two presentations at each summit—Lactic Acid: Fatigue’s Faulty Scapegoat and Chasing Mercury: Training to Combat Fatigue. The advanced coaching summits, multi-day seminars that focus on specific event groups with an emphasis on scientific concepts and training, are part of USATF’s level 3 coaching certification. For more information, go to http://www.usatf.org/groups/Coaches/education.
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In simple terms, your running speed equals stride length times stride rate. If you want to get faster, you have to increase either or both of these stride components. I often hear coaches tell their athletes to do specific workouts to increase their stride rates. However, research has shown that stride length increases preferentially over stride rate with increasing distance running speed. Stride rate changes only slightly, hovering between 80 to 90 steps per minute with each leg. The stability in stride rate has also been found as speed decreases due to fatigue. My own dissertation research, in which I’ve examined the coordination between breathing and stride rate, showed that average stride rate increased from 79 steps per minute at a very easy speed (70% of ventilatory threshold) to 87 steps per minute at near 5-K race pace. The faster runners didn’t necessarily take more steps than slower runners, as there was only a modest correlation (r = 0.62) between stride rate and 5-K speed, which explained only 38% of the variance in speed among runners. Stride length is thus explaining a much greater amount of variance in speed. Past research has suggested that the unconscious manipulation of stride length and stride rate at different speeds may be governed by what is most economical for the runner, such that there is a most economical stride length at a given speed and a most economical stride rate at all distance running speeds. So, if you want to get faster, focus on increasing your stride length (by increasing hip extension at push-off and by increasing the amount of force produced against the ground at push-off) rather than try to take quicker steps. *******************************************************************
Fat vs. Carbohydrates
There seems to be much confusion about which fuel—fat or carbohydrates—is being used at different running speeds. It has been known since the 1960s that carbohydrate is the body’s preferred fuel during exercise. To use mostly fat, you’d have to run at a very slow speed. Even at moderate speeds you’re using mostly carbohydrates. We see this all the time in the laboratory in an interesting variable called the respiratory exchange ratio (RER), which is the ratio of the volume of expired carbon dioxide to the volume of inspired oxygen. At rest, RER equals 0.7, when fat is used exclusively. As running speed increases, you rely more on carbohydrates and less on fat. At VO2max, when a lot of carbon dioxide is produced from carbohydrate metabolism, RER typically exceeds 1.1. As a matter of biochemistry, the breakdown of carbohydrates yields an RER of 1.0, which corresponds to your lactate threshold pace. When running faster than lactate threshold pace, you’re using exclusively carbohydrates. At an RER of 0.85 (halfway between 0.7 and 1.0), you’re using 50% fat and 50% carbohydrates. So once RER exceeds 0.85, which occurs at a moderate intensity, you’re relying more on carbohydrates than on fat. Exercise is largely a carbohydrate activity.
One
of the more elegant adaptations to endurance training is the greater reliance
on fat and less on carbohydrates at the same absolute speed. Say 8:00
pace corresponds to 75% VO2max and at that pace you use 40% fat and 60%
carbohydrates. With endurance training, that may change to 50% fat and
50% carbohydrates. But as your fitness improves, 8:00 pace will no
longer correspond to 75% VO2max (it may now correspond to 70% VO2max), so in
order to provide the same training stimulus, you’d have to run faster (maybe
7:45 pace) to keep the pace at 75% VO2max. Fuel use will then go back to
40% fat and 60% carbohydrates, albeit at a faster speed. Relative
intensity (% VO2max) dictates fuel selection.
Fuel
use is also a confusing issue in the marathon. Many coaches and runners
tend to think that the goal of marathon training is to teach your muscles to
rely more on fat and conserve carbohydrates. But this is incorrect, or
at least incomplete, since 1) how much of each fuel you rely on depends almost
exclusively on intensity and since running the marathon the best it can be run
means running 15 to 20 seconds per mile slower than your lactate threshold
pace, you will be relying mostly on carbohydrates the entire way, and 2) you
want to use carbohydrates in the marathon because you can regenerate ATP for
muscle contraction a lot faster by breaking down carbohydrates than you can by
breaking down fat. Using carbohydrates allows you to run faster than if
you were to use fat. The goal of marathon training, as it pertains to
fuel use, is to stimulate the molecular events that lead to synthesizing and
storing as much glycogen in your muscles as you can so you have the fuel that
you need to maintain the pace to the finish. Once you run out of
glycogen, you have no choice but to rely on fat, and the pace will slow
down.
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VO2max and Altitude
If
you’ve ever run at altitude, you know it’s a humbling experience.
Because the partial pressure of oxygen in the air is lower at altitude than at
sea-level, VO2max declines at altitude. A number of things dictate how
much of a decline you’ll see. Research has shown that runners with a
high sea-level VO2max, a low sea-level lactate threshold, who exhibit
hypoxemia (desaturation of oxygen from hemoglobin) at fast speeds at
sea-level, and who are male have a greater decline in VO2max at
altitude. Want to learn more? In my popular CD collection, The 3 Players of
Distance Running, you’ll get all the info you could ever want on VO2max,
lactate threshold, and running economy, including specific workouts to help
you reach your running goals! Purchase any CD for $9.95, any 2 CDs for $17.95, or the whole set for
just $23.95 (plus $2.95 shipping). Just
go to http://www.runcoachjason.com/merchandise
or e-mail jason@runcoachjason.com.
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In Press...
The
Three Players of Distance Running: An In-Depth Look at VO2max, Part 1 of
my series that explores the physiology of
distance running, appears in the Summer, 2007 issue of Track Coach, the
official technical publication of USA Track & Field.
Much has been written about strength training for the runner—everything from
lunges while holding dumbbells to calf raises on the edge of a stair to
endless repetitions of abdominal crunches while balancing on a big,
Have you ever walked through a gym and been intimidated by all the dumbbells,
barbells, and machines that put you in awkward positions that are best
reserved for the bedroom? You’re
not alone. Weight Training for Beginners, my article that
explains all the basics of weight training, including a sample program,
appears in the Summer, 2007 issue of Duke City Fit.
My
Fitness News contributions on training
smart, the best warm-ups for asthma, supplements, pre-exercise nutrition, and
training using multi-joint movements appear in the July, 2007 issue of Oxygen
magazine.
My
Fitness News contributions on burning
calories
during cardio, chocolate milk for recovery, weights for weight loss, exercise
and fatty livers, and ordering your exercises for optimal results appear in the
August, 2007 issue of Oxygen
magazine, on newsstands in July.
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To
view past newsletters, go to http://www.runcoachjason.com/newsletter.
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©2007
Jason Karp.
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