Concepts of Exercise Physiology for Runners

Capillaries. Myoglobin. Slow-twitch fibers. Glycogen. These are the stuff of long-distance running. The Kenyans have lots of them. President Bush (#1 and #2) has them. And you have them too. This is also the stuff of exercise physiology.

Exercise physiology is the science behind what you do on the roads and trails every day. And while you may run to improve your racing times, to relieve stress, or to lose weight, your body is constantly adapting and improving. Running does many wonderful things to make your body a more efficient running machine. Here are 6 concepts from exercise physiology for runners:

I. Your muscles adapt very specifically to training

This means is that if you run on flat terrain, you will not have trained your muscles to run uphill. And if you run slowly, you will not have trained the additional fast-twitch muscle fibers needed to race at a faster pace.

Your muscles are composed of several types of muscle fibers. You have probably heard the terms "slow-twitch" and "fast-twitch" fibers. The fast-twitch fibers actually come in 3 varieties, fast-twitch A, B and C. When you run slowly you use your slow-twitch fibers almost exclusively, but as you increase speed, you also use your fast-twitch A fibers, and at peak speed you use all types of fibers.

What does this mean for your running?

When you train slowly, you only activate your slow-twitch fibers, so the fast-twitch fibers stay untrained. You need to train those fast-twitch fibers in order to improve your racing performances!

Sounds like lots of speedwork, right?

Not necessarily. Dr. Phillip Gollnick, an exercise physiologist and biochemist at Washington State University has shown that the recruitment of additional muscle fibers is determined by the amount of force required by the muscle, not the speed. What this suggests is that you can increase your speed by increasing the force your leg muscles can exert.

The best way to increase the force your legs can produce while running is to run uphill. Uphill running will increase the power of your leg muscles, and you can translate this into increased speed. And while you won't be able to completely replace speedwork, you should be able to reduce the frequency of interval sessions. Hill training can also provide a welcome alternative to going to the track on a cold, windy day.

There is one additional point that needs to be made. There is also a neural component to increasing speed. This means that your nervous system has to allow you to run fast.

Sounds like lots of speedwork again, doesn't it? Well, you can teach your legs to run fast relatively painlessly by running strideouts (short accelerations of about 100 meters), or running down gentle downhills, preferably on grass. Teach your legs to turnover quickly and rhythmically, and let the strength you developed running uphill increase your speed.


II. Why you "die" when you go out too hard in a 5K, 5 miler or 10K

In races of these distances, you are running at close to your VO2 max, and at or slightly above your anaerobic threshold. What this means is that you have very little room for error. If you go out too hard, your muscles will quickly build-up lactic acid. Your muscles then become more acidic. This shuts down the enzymes that drive energy production, and you find out all about rigormortis, "the bear", and how it feels to run carrying a refrigerator.

VO2 max is the maximum amount of oxygen that your cardiovascular system can transport to your muscles (oxygen is a very good thing) and that your muscles can then use to produce energy. Your anaerobic threshold is the percentage of your VO2 max at which your body starts to build-up lactic acid rapidly. Since with even pacing you are already running at or slightly above your anaerobic threshold in races of 5K to 10K, going out too fast puts you into "oxygen debt", and the only way to repay that debt is to slow down!

To run your best times at these distances, therefore, you should run an even pace. You can afford to run 5-10 seconds faster for the first mile, but even this small gain will probably be given back by the end of the race. If you have a tendency to go out hard in races and then slow down, try running a more even pace next time. Exercise physiology says your times should improve.

III. Delay fatigue in races lasting longer than 1 hour by taking in carbohydrates during the race

If you consume carbohydrates during races lasting more than one hour (10 miles or longer), you will supply extra carbohydrate fuel to the muscles, and delay or prevent depletion of your muscles' glycogen stores.

Glycogen is stored in your muscles and liver, and is your primary fuel source in races from the mile up to the marathon. Your body can only store a limited amount of glycogen. How much depends on your level of fitness, how much you rested for the race, and the quantity of carbohydrates you ate in the last 3-4 days before the race.

When you start to run low on glycogen, your body uses more fat, and fat is 15% less efficient than carbohydrate as an energy source. The easiest way to consume carbohydrates during a race is with a sports drink. Sports drinks have the added benefit of providing needed fluid too.

How much is enough?

If you drink 7 oz. every 15 minutes (that's about the maximum amount that will empty from your stomach) of a drink containing 6% glucose, you will take in about 48 grams of carbohydrate per hour. Each gram of carbohydrate contains 4.1 calories, so you will be taking in 200 calories per hour. If you run the marathon in 3 hours, therefore, you will take in about 600 calories during the race. And since the average runner uses about 100 calories per mile, you will potentially delay "hitting the wall" by 6 miles!

What makes a good sports drink?

Make sure that the drink is no more than 8% glucose (or other sugars) because high concentration drinks stay in your stomach and slosh around longer. In addition, make sure the drink contains sodium to increase absorption. Although you will lose other electrolytes in your sweat, it is a relatively small percentage of your body's stores, and won't hurt your performance.

Finally, make sure that you can tolerate the drink while running. Practice drinking during training to ensure that your drink tastes good after 10 or 20 miles and doesn't upset your stomach.

IV. Why do you get so sore after races with big downhills? (Why do you walk downstairs backwards for a week after the Boston Marathon?)

The soreness that you feel a day or two after a hard effort is called delayed-onset muscle soreness or DOMS. DOMS is particularly painful after races with a lot of downhills. I was reminded of this several years ago when I was given the predominantly downhill leg of the Lake Winnepesaukee relay in New Hampshire and was unable to walk downstairs frontwards for 4 days.

Running downhills feels easier, uses less oxygen, and builds up less lactic acid than running uphills. So, why does it make us so sore afterwards?

When you run downhill your muscles contract eccentrically. You have probably known for some time that you are eccentric (if not ask your non-running friends), but this is something completely different. Normally when your muscles contract they shorten, but when your muscles contract eccentrically they lengthen. Eccentric contractions use fewer muscle fibers than normal (concentric) contractions, but appear to make those muscle fibers contract more vigorously and make the surrounding connective tissue take more shock.

Dr. Priscilla Clarkson and colleagues at the University of Massachusetts, has shown that this increased concentration of force causes microscopic damage to the muscle fibers and connective tissue, which leads to swelling, which stimulates nerve endings, which causes pain. This is why you have to walk downstairs backwards.

The good news is that DOMS can be reduced with training. Say you want to prepare for the Boston Marathon, there are 3 approaches you can take. The first is to run some downhills in training and each week to progressively increase the steepness and length of the downhills and the speed at which you run them.

The second approach is to dive right into a tough downhill workout, get sore as hell, and get it over with. Your subsequent workouts will hurt less, but you may be in a lot of pain for several days.

The final approach is the one that Bill Rodgers used to prepare for Boston. Bill would run 10 to 15 miles over the famed Newton hills a couple of times per week in the months leading up to "the marathon". He no doubt developed some muscle soreness each time, but by marathon day, his legs were used to both uphill and downhill running. Although he may not have realized it at the time, Bill prepared his muscles to run eccentrically. He won the Boston Marathon 4 times.

V. The role of protein for runners

Carbohydrates and fats provide over 90% of the fuel you use while running. Protein, therefore, supplies less than 10% of your energy needs, and then only if you are already low on glycogen. So, eating more protein to provide energy is a waste of money.

Protein is important, however, in other ways. It rebuilds body tissues, and enzymes, hormones, immune system cells and hemoglobin are produced from it. So, how much protein does a runner need?

The average person needs approximately 0.8 grams of protein per kilogram bodyweight per day. Studies have shown that a distance runner in heavy training needs, 1.2 to 1.6 grams per kilogram bodyweight per day.

This means that Olympic Marathoner Cathy O'Brien, who weighs about 105 pounds (48 kilograms), needed about 76 grams of protein when she was in heavy training. A 180 pound man (82 kg.) in heavy training, on the other hand, would need, at most, 131 grams of protein.

How much is that in ounces? There are 28.4 grams in one ounce, so Cathy's 76 grams equals 2.7 ounces of protein, and the 180 pound man's 131 grams equals 4.6 ounces. What all these numbers mean is that you don't need much protein. Unless you are a vegetarian, you probably eat much more protein than necessary to rebuild body tissues, and build enzymes, hormones, etc. And vegetarians, if they balance their meals properly can also easily meet their protein requirements.

VI. To recover more quickly, eat carbohydrates as soon as possible after a race or long run

When you run long distances, you deplete your body's glycogen stores, which are your body's stockpiles of carbohydrates for energy. Part of the recovery process before you can run hard again is the replenishment of those glycogen stores.

Studies have shown that your muscles will replace their glycogen stores at the fastest rate during the first 1-2 hours after running. Glycogen resynthesis continues at a higher than average rate for 10-12 hours after a glycogen-depleting run. After 10-12 hours, the rate of glycogen replenishment decreases to the normal level.

What this means is that you will recover more quickly if you eat and drink carbohydrates soon after your long runs and races. Don't wait several hours to eat. If your stomach doesn't feel up to a meal within an hour or so after running, eat a bagel or a banana, or drink some carbohydrates to get the replenishment process started, then eat more when your stomach can handle it.

By re-building your glycogen stores as quickly as possible, you will recover more quickly, and be able to train hard again sooner.


Related article:
Should runners lift weights?

Text copyright by Pete Pfitzinger
Pete Pfitzinger is an exercise physiologist with over 20 years of coaching experience, Pete adheres to the principle that every runner is unique and that training programs must be tailored to the athlete's individual strengths and weaknesses. 

Pete Pfitzinger is co-author of two successful books:

Road Racing for Serious Runners
Road Racing for Serious Runners
Buy it here

Advanced Marathoning
Advanced Marathoning
Buy it here

This article has informational purpose and  isn't a substitute for professional advice.

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