Five Lessons I Have Learned From Physiology and How They Can Make Your Clients Better Runners

Lesson 1: Lactate threshold and running economy are more important than VO2max

While VO2max (the maximum volume of oxygen muscles can consume per minute) has received most of the attention among runners, a high VO2max alone is not enough to achieve good performance; it simply gains one access into the club, since a runner cannot attain an elevated level of performance without a high VO2max.  But, while your clients can improve their VO2max, it is largely genetically determined.  The other two major physiological players of distance running performance—lactate threshold (LT) and running economy (RE)—exert a greater influence on performances and are more responsive to training.  I have tested many runners in the laboratory with a high VO2max, but few of them were capable of running at the elite or even sub-elite level because they did not have a high LT or were not very economical.

Research has shown that the LT is the best physiological predictor of distance running performance.  It is an important physiological variable that demarcates the transition between running which is almost purely aerobic and running that includes significant oxygen-independent (anaerobic) metabolism.  It represents the fastest speed the runner can sustain aerobically.  (All running speeds have an anaerobic contribution, although at speeds slower than the LT, that contribution is negligible.)  Since the LT represents the fastest sustainable pace, the longer the race, the more important the LT.

For recreational runners, LT pace is approximately 10 to 15 seconds per mile slower than 5K race pace (about 80 to 85% maximum heart rate).  For those who are more trained, it’s about 25 to 30 seconds per mile slower than 5K race pace (about 90% maximum heart rate).  Subjectively, these workouts should feel “comfortably hard.”  Examples of workouts are:

• LT Run: 2 to 4 miles (or 10-20 minutes) at LT pace
• LT Cruise Intervals: 4 x 1 mile (or 5-7 minutes) at LT pace with 1 minute rest
• LT+ Cruise Intervals: 2 sets of 3 x 1,000 meters (or 3-4 minutes) at 5 to 10 seconds per mile faster than LT pace with 45 seconds rest and 2 minutes rest between sets
• LT/Long Slow Distance (LSD) Combo: 12 to 16 miles with last 2 to 4 miles at LT pace or 2 miles easy + 3 miles at LT pace + 6 miles easy + 3 miles at LT pace (for advanced marathoners).

Running Economy (RE) is the volume of oxygen consumed at sub-maximal speeds.  In 1930, David Dill and his colleagues were among the first physiologists to suggest that there are marked differences in the amount of oxygen various runners use when running at the same speeds, and that these differences in “economy” of oxygen use is a major factor explaining variances in running performance in athletes with similar VO2max values.  For example, research has shown that, while Kenyan runners have similar VO2max and LT values as their American/European counterparts, the Kenyans are more economical, possibly due to their light, non-muscular legs that interestingly resemble those of thoroughbred race horses.  The heavier your clients’ legs, the more oxygen it costs to move them.

RE is probably even more important than the LT in determining distance running performance because it indicates how hard your client is working in relation to his maximum abilities to use oxygen.  For example, if two runners, Jack and Martin, have a VO2max of 70 milliliters of oxygen per kilogram of body weight per minute and an LT pace of 6 minutes per mile, but Jack uses 50 and Martin uses 60 milliliters of oxygen while running at 6:30 pace, the pace feels easier for Jack because he is more economical.  Therefore, Jack can run faster before using the same amount of oxygen and feeling the same amount of fatigue as Martin.  I have yet to see a runner who has superior RE who does not also have a high VO2max and LT.

Despite its importance, RE seems to be the most difficult of the three physiological players to train.  While many runners and coaches think that RE is a reflection of running form, it is more influenced by those microscopic structures that affect oxygen delivery to and use by the muscles—capillaries and mitochondria, the densities of which are both enhanced with high mileage.  Research has shown that runners who run high mileage (more than 70 miles per week) tend to be more economical, which leads one to believe that running high mileage improves RE.  In addition to increasing mitochondrial and capillary density, the greater repetition of running movements may result in better biomechanics and muscle fiber recruitment patterns and a synchronization of breathing and stride rate, which may reduce the oxygen cost of breathing.  RE may also be improved by the weight loss that often accompanies high mileage, which lowers the oxygen cost.  Since VO2max plateaus with about 70 to 75 miles per week, improved RE may be the most significant attribute gained from running high mileage.  However, it’s hard to prove cause and effect, since it is not entirely clear whether high mileage runners become more economical by running more miles or are innately more economical and can therefore handle higher mileage.

Other forms of training, like intervals and tempo runs, can also improve RE since, as VO2max and LT improve, the oxygen cost of any sub-maximal speed is also likely to improve.  However, it is possible to become more economical without improving VO2max or LT, as research on power training with very heavy weights and plyometrics has shown.  Power training focuses on the neural, rather than metabolic, component of muscle force development to improve RE.

Lesson 2: There are different muscle fiber types

There are two types of runners—those who have superior speed, whose performance gets better as the race gets shorter, and those who have superior endurance, whose performance gets better as the race gets longer.  It’s important to acknowledge differences in runners’ muscle fiber types and their associated metabolic profiles.  The types of fibers that make up individual muscles greatly influence your clients’ performances.

Humans have three different types of muscle fibers, with gradations between them.  Slow-twitch (ST) fibers are recruited for all of your clients’ aerobic runs, while fast-twitch B (FT-B) fibers are only recruited for short anaerobic, high-force production activities, such as sprinting.  Fast-twitch A (FT-A) fibers, which represent a transition between the two extremes of ST and FT-B fibers, are recruited for prolonged anaerobic activities with a relatively high-force output, such as racing 400 meters.  It’s a given that your clients have more ST fibers than FT fibers, otherwise they would be sprinters rather than distance runners.  However, even within a group of distance runners, there is still a disparity in the amount of ST fibers.  Some runners may have 90 percent ST and 10 percent FT fibers (marathoners), while others may have 60 percent ST and 40 percent FT fibers (milers).  In lieu of a muscle biopsy to determine the exact muscle fiber type composition, ask your clients the following questions:

1. When you race, A) are you able to hang with competitors during the middle stages, but get out-kicked in the last quarter to half-mile or B) do you have a hard time maintaining the pace during the middle stages, but can finish fast and out-kick others?
   • If they answer a, they probably have more ST fibers.  If they answer b, they have more FT fibers.
2. Which type of workouts feel easier and more natural—A) long intervals (800-meter to mile repeats), long runs, and tempo runs, or B) short, fast intervals (200s and 400s)?
   • If they answer a, they have more ST fibers.  If they answer b, they have more FT fibers.
3. Which workouts do you look forward to more—A) long intervals and tempo runs or B) short, fast intervals?
   • If they answer a, they have more ST fibers.  If they answer b, they have more FT fibers.

Understanding your clients’ fiber types can help you train them more effectively.  While most runners do the same workouts to focus on a specific race, their training and racing should reflect their physiology.  For example, if a client has 90 percent ST and 10 percent FT fibers, his or her best race will likely be the marathon and his or her training should focus on mileage and tempo runs.  If a client has 60 percent ST and 40 percent FT fibers, his or her best race will likely be the 800 meters or mile, and his or her training should focus less on mileage and more on interval training.  If both runners want to race a 5K or 10K, the former runner should initially do longer intervals, trying to get faster with training, such as 1,200-meter repeats at 5K race pace, increasing speed to 3K race pace or decreasing the recovery as training progresses.  The latter runner should do shorter intervals, trying to hold the pace for longer with training, such as 800-meter repeats at 3K race pace, increasing distance to 1,200 meters or increasing the number of repeats as training progresses.  Thus, there can be two paths to meet at the same point.

Lesson 3: A larger, stronger heart can pump more blood and oxygen to runners’ muscles

The amount of blood the heart pumps with each contraction of its left ventricle is called the stroke volume.  Multiply the stroke volume by the heart rate, and you get the amount of blood pumped by the heart each minute, called the cardiac output.  The larger the left ventricle, the more blood it can hold; the more blood it can hold, the more blood it can pump.  A large heart is so characteristic of genetically gifted and highly trained runners that it is considered a physiological condition by the scientific and medical communities and identified as Athlete’s Heart.  Specific training can make hearts larger and increase both stroke volume and cardiac output.

Long intervals provide the heaviest load on the cardiovascular system because of the repeated attainment of the heart’s maximum stroke volume and cardiac output (and, by definition, VO2max).  Evolutionary biologists believe that the structure of an organism evolves to cope with the stresses to which it is subjected, which has led to the theory of symmorphosis—that an organism’s structural design is regulated by its functional demand.  As preeminent anatomist Ewald Weibel wrote, “…the quantity of structure incorporated into an animal’s functional system is matched to what is needed: enough but not too much.”  Remarkably, structural changes can also occur in the short term in response to training: bones increase their density, muscle fibers increase their metabolic machinery, and cardiac muscles grows larger.  In response to the imposed threat of running at the heart’s maximum ability to pump blood, the heart responds by increasing its contractility (pumping strength) and by enlarging its most important chamber so that more blood and oxygen can be sent to the working skeletal muscles.

In lieu of a laboratory test to tell you the velocity at which your clients’ VO2max is achieved (vVO2max), you can use their current race performances or heart rate.  vVO2max is close to 1.5-mile race pace for recreational runners and close to 3K or 2-mile race pace (10 to 15 seconds per mile faster than 5K race pace) for highly trained runners.  Your clients should be within a few beats of their maximum heart rates by the end of each work interval.  Examples of workouts are:

• 3 x 1,200 meters (or 4-5 minutes) @ vVO2max with 3 to 4 minutes recovery
• 4 x 1,000 meters (or 3-4 minutes) @ vVO2max with 2½ to 3 minutes recovery
• 6 x 800 meters (or 3 minutes) @ vVO2max with 2½ to 3 minutes recovery

Lesson 4: Metabolism is tightly regulated by enzymes and oxygen

Enzymes function as biological catalysts that speed up chemical reactions.  In the absence of enzymes, chemical reactions would not occur quickly enough to generate the energy needed to run.  The amount of an enzyme also controls which metabolic pathway is used.  For example, having more aerobic enzymes will steer metabolism toward a greater reliance on aerobic metabolism (Krebs cycle and electron transport chain) at a given sub-maximal speed.  Enzymes are also activated or inhibited (i.e., their effectiveness in speeding up chemical reactions can be either increased or decreased), determining which metabolic pathways are functional during certain cellular conditions.  Thus, enzymes essentially control metabolism and therefore control the pace at which your clients fatigue.

A number of studies have documented an increase in enzyme activity in response to training.  One of the first was published in 1967 in Journal of Biological Chemistry, in which aerobically trained rats increased mitochondrial enzyme activity, increasing the mitochondria’s capacity to consume oxygen.  More recently, a study published in Journal of Applied Physiology in 2006 found that citrate synthase (a key aerobic enzyme) activity significantly increased by 37 percent in novice runners after 13 weeks of training during which weekly mileage increased from 15 to 36.  Similarly, sprint training induces changes in the anaerobic enzyme profile of muscles and also increases aerobic enzyme activity, particularly when long sprints or short recovery between short sprints are used.  For example, a study published in Journal of Applied Physiology in 1998 found that sprint cycle training three times per week for seven weeks using 30-second maximum-effort intervals significantly increased both anaerobic and aerobic enzyme activity.  Research on changes in enzyme activity with sprint running is currently lacking.

Metabolism is also regulated by its patriarch—oxygen.  The availability of oxygen determines which metabolic pathway predominates.  For example, at the end of the metabolic pathway that breaks down carbohydrates (glycolysis), there is a fork in the road.  When there is adequate oxygen to meet the muscle’s needs, the final product of glycolysis—pyruvate—is converted into an important metabolic intermediate that enters the Krebs cycle for oxidation.  This irreversible conversion of pyruvate inside your clients’ muscles’ mitochondria is a decisive reaction in metabolism since it commits the carbohydrates broken down through glycolysis to be oxidized by the Krebs cycle.  However, when there is not adequate oxygen to meet the muscle’s needs, pyruvate is converted into lactate.  An associated consequence of this latter fate is the accumulation of metabolites and the development of acidosis, causing your clients’ muscles to fatigue and them to slow down.

The more aerobically developed your clients are, by focusing on increasing their mileage and doing LT runs, the more they’ll steer pyruvate toward the Krebs cycle and away from lactate production at a given pace.  That’s beneficial because the amount of energy your clients get from pyruvate entering the Krebs cycle is 19 times greater than what they get from pyruvate being converted into lactate.  While pyruvate will always be converted into lactate given a fast enough speed, the goal of training is to increase the speed at which that occurs.

Lesson 5: Carbohydrates are extremely important

The many proponents of diets like Atkins and South Beach would have the public believe that carbohydrates are some kind of poison.  Don’t listen to them.  Carbohydrates are a runner’s best friend.  Carbohydrates are stored in the skeletal muscles and liver as glycogen, and are also found as sugar (glucose) in blood.  When your clients run, their bodies use a combination of blood glucose and glycogen as fuel to regenerate the high-energy chemical compound ATP through a process called glycolysis.  Endurance performance is strongly influenced by the amount of pre-exercise muscle glycogen, with intense endurance exercise decreasing muscle glycogen content.  Carbohydrates are so important that ingesting them during prolonged exercise can even delay fatigue.  With the well-documented decrease in muscle glycogen content that accompanies endurance exercise, an empty-refill cycle becomes evident.  Since your clients’ muscles prefer carbohydrates as fuel, a metabolic priority of recovering muscle is to replenish muscle glycogen stores.  And the more their glycogen tank is emptied, the greater it’s refilled.  Empty a full glass, and you get a refilled larger glass in its place.  Much like university fraternity parties!

Glycogen synthesis is controlled by the hormone insulin and the availability and uptake of glucose from the circulation.  Insulin, which is secreted from the pancreas, is the primary signal for glycogen synthesis.  Through its effect on proteins that transport glucose, insulin draws glucose from the blood into muscle cells.  Glucose is then used to make new glycogen, which is simply a branched chain of glucose molecules.  The higher the blood insulin concentration and the greater the availability of glucose, the faster glycogen is synthesized and stored.  So, how do you increase your clients’ insulin concentrations and make glucose available?  Have them consume carbohydrates.

Research has shown that the synthesis of glycogen between training sessions occurs most rapidly if carbohydrates are consumed immediately after exercise.  Indeed, delaying carbohydrate ingestion for just two hours after a workout significantly reduces the rate at which muscle glycogen is resynthesized and stored.  To maximize the rate of glycogen synthesis, tell your clients to consume 0.7 gram of simple carbohydrates (preferably glucose) per pound of body weight within 30 minutes after they run and every two hours for four to six hours.  It would be even better if they can eat or drink more often, since research has shown that a more frequent ingestion of smaller amounts of carbohydrates has an even greater effect on glycogen synthesis, as it better maintains blood glucose and insulin levels.  Despite the many highly advertised commercial sports drinks, any drink that contains a large amount of carbohydrates is great for recovery.  My research published in International Journal of Sport Nutrition and Exercise Metabolism in 2006 showed that chocolate milk is a great post-workout recovery drink.

To help your clients get the most from their training and racing, learn these lessons.  Not only will they be rewarded with higher levels of fitness and new personal records, you’ll make a complex sport a little simpler.

References

1. Holloszy, J.O. (1967). Effects of exercise on mitochondrial oxygen uptake and expiratory enzyme activity in skeletal muscle. Journal of Biological Chemistry. 242:2278-2282.
2. Karp, J.R., Johnston, J.D., Tecklenburg, S., Mickleborough, T.D., Fly, A.D., and Stager, J.M. (2006). Chocolate Milk as a Post-Exercise Recovery Aid. International Journal of Sport Nutrition and Exercise Metabolism. 16(1):78-91.
3. MacDougall, J.D., Hicks, A.L., MacDonald, J.R., McKelvie, R.S., Green, H.J., and Smith, K.M. (1998). Muscle performance and enzymatic adaptations to sprint interval training. Journal of Applied Physiology. 84(6):2138-2142.
4. Trappe, S., Harber, M., Creer, A., Gallagher, P., Slivka, D., Minchev, K., and Whitsett, D. (2006). Single muscle fiber adaptations with marathon training. Journal of Applied Physiology. 101(3):721-727.