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Posted: October 22, 2005

Science of Sport: Running Thresholds And Transitions

By Owen Anderson, Ph. D. (Copyright © 2004-2005)

Running and life are filled with thresholds and transitions.

During my travels to Nairobi, I often stayed at the Windsor Hotel on the outskirts of the city. Rising early, I would walk down Thika Road, past the sprawling coffee estates and the lavish mansions, through the apartment blocks on the outskirts of town, and finally into the shantytowns which ringed the downtown area. As I plunged into the teeming throng of humanity, I was always reminded of Ama Ata Aidoo's famous poem, Issues, which begins:

We met
them
daily in the
streets:
the mothers and the children
for whom they'd got
the best recipes for
cooking
stones.

I would turn down Moi street and make a final transition into the New Stanley Hotel, where, in the dark lounge, I could enjoy a moment's respite from the tempest outside before beginning my business for the day. On my stroll back to the Windsor, I passed through each threshold - from desperate poverty to barely making it to modest hopefulness to lavish richness - once again.

Mimicking life, exercise also has many abrupt transition points. For humans, the movement speed of 2 meters per second represents one such precipitous passage. At all velocities of 2 meters per second or less (e. g., at all tempos of 13:24 per mile or slower), walking requires less energy than running, and so we almost always walk at such speeds.

If we want to move faster than 2 meters per second, we invariably jog or run, because running is more economical than walking at such tempos. We automatically adjust gait to minimize the energy cost of locomotion, and so we rarely see individuals jogging at 15-minute per mile pace - or walking at 10 minutes per mile.

Another important transition occurs at a walking speed of about 5 kilometers per hour (a tempo of around 19 minutes per mile). Exercise scientists have known for years that if one plucks an average person "off the street" and asks him/her to walk "normally", he/she will usually settle in at a pace of about 4.8 to 5 kilometers per hour. This is nothing new: Human footprints left in Kenyan/Tanzanian mud two million years ago suggest that these first imprint-leavers were strolling through East Africa with an alacrity of 5 kilometers per hour, too!

Not surprisingly, the velocity of 5 kilometers per hour is an important threshold point. Above 5 kilometers per hour, the oxidation of carbohydrate by leg muscles increases dramatically, and as a result perceived effort rises significantly. Below 5 kilometers per hour, carb-burning falls off, fat breakdown ascends, and perceived effort moderates considerably. The human brain monitors carbohydrate oxidation during exercise quite carefully - and rather perversely cranks up perceived effort when carb-burning is on the upswing. In effect, the brain tries to keep exercisers from burning up their carbohydrate (glycogen) stores by making the process of doing so feel too difficult. This is a key reason why sustained runs at a high intensity such as vVO2max feel so incredibly hard. Nothing bad is really happening to your muscles at vVO2max - it's just that the brain doesn't like such red-hot exertions, given its constant worries over the glycogen depots in the muscles. The brain is content at a pace of ~5 kilometers per hour because carb-burning is minimal, and thus 5 km/hour is a universal walking speed.

An extremely important transition point during running is called the lactate threshold, or lactate-threshold speed, which happens to be an excellent predictor of running peformance. Lactate-threshold speed is simply the running velocity above which lactate begins to accumulate rapidly in the blood.

Historically, the lactate threshold was thought to be caused by a lack of oxygen in the muscles, which thus forced the sinews to do more anaerobic work, subsequently leading to a release of lactate into the blood. The remedy for a lackadaisical lactate threshold was usually thought to be high-mileage training, which was supposed to enhance the functioning of the cardiovascular system and improve the delivery of oxygen to the muscles (and the utilization of oxygen once it got there). In theory, this expansion of aerobic capacity would cure a languid lactate threshold.

However, such conceptions ignored the simple and unavoidable facts that lactate threshold occurs at just 50 percent of max aerobic capacity in many untrained individuals and at 85 percent of max aerobic capacity in many elite runners - in other words in situations in which oxygen is quite plentiful and the oxygen-delivery-and-utilization system has not been taxed to its limit.

Recent research suggests that the real "problem" which produces the lactate threshold actually is unrelated to oxygen delivery and in fact resides in the "shuttle systems" which exist in the walls of muscle-cells' mitochondria. To understand how this works, it is important to know that within muscle cells molecules of an important chemical called NAD work as "carriers". NAD's job is to pick up high-energy hydrogens (which have been stripped off carbohydrate molecules, for example) and then carry them to the "shuttle mechanisms" in the walls of the mitochondria. The hydrogens can then leave NAD, shuttle through the mitochondrial walls, and move inside the mitochondria; in the presence of oxygen, the energy contained in the hydrogens is then transformed into ATP, the actual energy muscles need to perform the work of running. If the shuttle mechanisms are operating too slowly during exercise, NAD takes some of its hydrogens which should have been dropped off at the mitochondrial walls and shuttled inward and instead donates them to a chemical called pyruvate, thus forming lactic acid. As lactic acid accumulates, it can begin pouring out of the muscles into the blood, thus creating a lactate threshold.

As you can see, the formation of lactic acid can occur independently of whether a muscle cell has adequate supplies of oxygen, and lactate-threshold velocity is probably much more a reflection of mitochondrial shuttling ability, rather than oxygen supply. If the shuttles are working slowly and a runner is attempting to move swiftly, lots of lactic acid will be formed (and the runner's lactate threshold will be lousy).

To improve lactate threshold, then, your task as a runner is to upgrade your mitochondrial shuttles. Running lots of miles at a moderate pace just won't do the trick, because your shuttles can handle such exertion quite easily (inward hydrogen movement through the shuttles is moderate during moderate running, and so there is no stimulus for the shuttles to undergo a make-over). What you need instead is training which really taxes your shuttles.

One such workout involves going to your favorite place for a workout, warming up thoroughly, and then alternating one-minute intervals at close-to-max speed with two-minute, easy-jog recoveries. You don't have to worry about your actual speed during the one-minute bursts (just shoot for a pace which feels faster than your vVO2max), and you shouldn't kill yourself with the session - the idea is to just keep working until you feel satisfactorily tired. Your shuttles will be extremely stressed by the repeated one-minute fly-outs - and the resulting shuttle make-over will have you flying along in your races as your high-energy hydrogens pour into your mitochondria.

It's good news that super-charging your shuttles is so easy, and I have some additional great news for you: My advanced marathon training program is now available. This program is designed for experienced runners who can begin the plan with a volume of 40 miles per week and progress to 60-plus weekly miles over a 26-week period. It contains my most-sophisticated training techniques.

Many marathon schedules available to the public consist of little more than filling in a training log with miles. My program is quite different. It has the exact training you need to optimize your vVO2max, lactate threshold, running economy, strength, and power. It has the strengthening sessions you need to minimize your risk of injury and recover quickly. It also has the specific, goal-pace long runs which are so essential for marathon success.

The cost? Just $299 - a bargain when you consider that you are getting more than six months of extremely productive marathon training. This price works out to be about $11 per week - not bad for scientifically validated information which has been tested on runners with a wide range of abilities. Please act soon, though, as the price must increase to $399 on November 1, 2005.

To obtain my advanced program, which is now available to the running community for the very first time, please click here. I personally promise that you will not regret your decision. An intermediate marathon program for runners capable of running 26 to 45 miles per week is also available (please use the same link).

Very kindest regards,

Owen Anderson, Ph. D.

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