skip to Main Content

Exercise Physiology

Training 101- Physiology

Why do we train? This is an introductory question I ask many athletes that I coach. Now there are many answers to that question, but to me the simplistic answer is that we train to get our bodies to produce enough energy (ATP) to meet the demand of moving our body for a certain amount of speed and time. That could mean racing a five minute mile, a three hour marathon or fifteen minute 5k. Whatever it is, your training should be designed to meet that energy demand for that goal.

I have been told many times that “There are many roads to Rome” during discussions about training.  As we know there are many routes to a destination, but the routes chosen should also be somewhat adaptable to you. Physiology has some principles such as individuality, specificity and progressive overload which should influence your training plan.

One of the most impactful factors in long-term running success is the amount of running you do; it’s not the intensity. Dr. Jason Karp, an instructor from my endurance class at the Olympic Training Center (OTC) sent this email to me which explaines it nicely:

If you do a lot of high-intensity interval training, especially at a young age, you will sacrifice your aerobic development and retard your progress as a runner.

The goal of endurance training is to increase the pace at which you can run aerobically, before oxygen-independent (anaerobic) metabolism begins to play a significant role. Because when the pace starts to become anaerobic, fatigue is imminent and you will slow down. So, the faster you can run before that happens, the faster you will run a race.  

You cannot keep getting faster by hammering more and more interval workouts. This is true for a variety of reasons, not the least of which is that the anaerobic side is limited (you can only increase speed by so much) and constantly pulling the pH of your muscles down with anaerobic workouts (a condition called acidosis) negatively affects muscle function. In contrast, the aerobic side is virtually unlimited, at least up to the point that your genetics will allow for further adaptation. 

If you have kids, or if you run yourself, the best way to train, especially in the developmental years, is to take a methodical approach, focusing on the aerobic training, increasing how much running you can handle each year, and sprinkling in just enough speed work to improve speed and create a peak in performance. You can improve speed from aerobic strength; doing it the other way around by trying to improve speed first doesn’t work. You’ll get faster more quickly that way, but your long-term development will get flushed in the toilet. It’s amazing to me how many coaches still don’t understand that.

For distance runners, the volume of training induces the biological signal for adaptation and dictates the performance capacity. And in order to accomplish a large training volume, the runner must perform most of the running at a relatively slow pace, and then by doing quality aerobic work.

Aerobic running develops many physiological and biochemical traits:

  1. It increases total blood volume.
  2. It increases the number of red blood cells and the amount of hemoglobin contained within them, giving your blood vessels a greater oxygen-carrying capability.
  3. It creates a larger spider web of capillaries around your muscle fibers, enhancing oxygen delivery to your muscles by shortening the diffusion distance from capillaries to mitochondria. Think of a highway system — you want lots of highways traversing your muscle fibers so that when oxygen takes an exit, it has only a short distance to travel to arrive at the mitochondria.
  4. It increases the volume of mitochondria in slow-twitch muscle fibers, where aerobic metabolism takes place.
  5. It increases aerobic enzyme activity, which enhances the speed at which the chemical reactions of metabolism occur.
  6. It enhances neuromuscular coordination, improving running economy, the oxygen cost of running at submaximal speeds.
  7. All of the above improves VO2max, the maximum volume of oxygen your muscles can consume per minute.

The more aerobically fit runners are, the more they will ultimately get from their subsequent speed work. Since recovery is an aerobic process, being more aerobically fit enables runners to recover faster during the rest intervals of interval workouts (which enables them to run more reps) and in the days following a workout (which enables them to do fast workouts more often when it is the right time to do them).

The best 800-meter runners and milers in the world run a lot of miles each week, because even a race that short requires a large aerobic engine (i.e., a high VO2max) and is more aerobic than anaerobic.

My last training session in 2014 at the OTC reported from new studies from the US and Europe that the 400 meter as being 46% aerobic.

To build our bodies to perform the way we would like to perform, training design is set up to work on our economy, increase threshold and Vo2.  You should be familiar with these as it is important to know why certain workouts are applied.

Coach Greg McMillan categorizes and explains the workouts perfectly:

Endurance Workouts

While Endurance is the overriding theme behind endurance training, there are actually three distinct purposes for endurance workouts.

  • The first is to recovery from a previous workout or race.
  • The second is to improve your endurance – the ability to run for longer and longer.
  • Third is to maintain your aerobic fitness level and maximize your aerobic capacity.

These goals are consequently represented by three distinct types of workouts: Recovery Jogs, Long Runs and Easy Runs. We’ll discuss each in detail so that as you venture out for a run, you’ll know how to train optimally for the particular workout you are doing.

Recovery Runs

You might find it helpful to think of a recovery run as a slow run. Your heart rate should stay below 65% of maximum (though it’s okay for it to reach around 70% by the end of the run). Believe me, you’ll find it difficult to run this slow at first, but you must. If you want to improve and get more from your training you must keep the effort very, very light.

Recovery runs should be used the day (or two) after a hard workout or race. Remember, the goal is simply to get the muscles warmed up and blood flowing to deliver essential rebuilding nutrients to the muscles. These runs work out the tightness that occurs from hard running. There is no other goal of a recovery jog. Therefore, these runs last only 15 to 45 minutes – the shorter the better.

Long Runs

Long runs need no introduction as most of us include one every seven to 21 days in our training programs. The purpose is simply time on your feet. Challenging your ability to keep running improves your endurance and is a cornerstone of distance training. While there are debates on just how long and fast your long run should be, the general recommendation is that you keep your heart rate around 70% of maximum with the runs lasting at least an hour and up to three and a half. They are slow runs with the challenge of simply running a steady pace for the entire duration of the run. Give the body time to really feel the stimulus of a long run. It will reward you with greater endurance adaptations that will serve you well in later workouts and races.

Easy Runs

The final true Endurance workout is the easy run. The majority of your training is likely to be comprised of easy runs and the purpose is to fully develop your aerobic fitness and then maintain it. Your heart rate is around 75% of maximum though it can reach 80 to 85% near the end of the run. Easy runs last anywhere between 15 minutes and an hour and a half. Again, one of the common mistakes we make is running our easy runs too fast. Keep them steady but don’t get into a pace where your breathing becomes noticeably faster.

Stamina Workouts

Stamina workouts introduce steady, medium-paced running into your program. The goal is to develop your ability to run a steady pace for long periods of time. Specifically, you increase your lactate threshold pace which leads to faster race times. The challenge with each of the four types of Stamina workouts is to keep from running too fast. These are moderate efforts and running faster does little but shorten the amount of time that you are in the correct zone. It’s much better with Stamina workouts to challenge yourself to go longer at a given pace than faster. I also find that it’s beneficial to do these workouts without a watch. Go by effort. Learn your body.

Steady-State Runs

The steady-state run is one of the most beneficial types of workouts especially as you complete your foundation training. Your heart rate will likely be between 83 and 87% of maximum and the runs should last at least 25 minutes and can go as long as an hour and 15 minutes.

These are pretty tough efforts not because of the pace but because of the duration of running so be prepared to increase your concentration to stay on pace and to take a good recovery day afterwards in order to reap the full benefits.

Unlike the three Endurance workouts discussed above, steady-state runs are the first workouts that require a warm-up. For all the remaining workouts, you should begin the run with 10 to 20 minutes at an easy pace. Following this warm-up (which may also include stretching and faster “strides”), you can proceed into the continuous steady-state run.

Tempo Runs

Tempo runs are slightly more intense than steady-state runs and are designed to increase your stamina. As the name suggests, you really improve your running tempo or rhythm with these workouts. They last between 15 and 30 minutes and are meant to be “comfortably hard” so don’t push the pace. Your heart rate will likely be between 85 and 90% of max.

Like the steady-state run, tempo runs are continuous efforts but you must preface them with a thorough warm-up.

Tempo Intervals

Tempo Intervals are like fast tempo runs broken into two to four repeats with relatively short recovery jogs. Workout should last between eight and fifteen minutes. Unlike the previous workouts, Tempo Intervals are the first workouts to allow for a recovery jog between hard efforts. In this case, you jog two to five minutes between each repeat then start the next one.

A tempo interval workout used can be two (or three) times two with three minute recovery jogs between repeats. Following a thorough warm-up, these provide a great training stimulus to prepare you for an upcoming 5K or 10K race. The effort required, the pace judgement and the mental discomfort all help immensely when race time comes.

Cruise Intervals

The Cruise Interval workout was popularized by the running coach, Jack Daniels. They, like the other Stamina workouts, are meant to increase your lactate threshold pace. Cruise Intervals are like shorter and slightly more intense tempo intervals. They last three to eight minutes. Like tempo intervals, they are followed by short recovery jogs (30 seconds to 2 minutes). You’ll probably find that it’s easy to run too fast on these. The tendency is to treat them like regular long intervals. However, keep it under control and work on a smooth, fast rhythm. Control in training is key to improvement.

Speed Workouts
Here’s where we get to the fast stuff. These workouts are what most of us think of as “speed work”. They last between 400m and 2000m.The goal here is to spend time at your maximum aerobic capacity (or VO2max). Because the pace is faster, you must take a recovery jog of about half the distance of the repeat (or jog for the same duration as the faster running). So if you run a 1200m repeat, you would jog for about 600m to recover. These workouts allow you to maintain your speed over a longer period of time.

Sprint Workouts

The final workouts are Sprint Workouts. These help your top-end speed and consolidate your stride and form.

Anaerobic Capacity Intervals

Anaerobic Capacity Intervals comprise the first workout. Like the Speed Workout described above they are repeated hard efforts with recovery jogs in between. They last only 100m to 400m with very long recovery intervals. It’s usually recommended that you take two to five times the duration of the fast running as a recovery jog before starting the next hard effort (or one to two times the distance of the repeat). For example, if you run repeat 200m, then you would jog for 200 to 400m before beginning the next one.

The goal is to flood the muscles with lactic acid and then let them recover. Your leg strength and ability to buffer lactic acid will improve, allowing you to sprint longer.


You’re probably familiar with “Strides” though you may call them wind sprints, pickups, striders or stride outs. They’re not unlike the fast accelerations that you do right before a race. Strides work to improve your sprinting technique by teaching the legs to turn over quickly. It’s really the neuromuscular system that we’re trying to develop here which is why they are shorter than anaerobic capacity intervals. They last only 50-200m because unlike the anaerobic capacity intervals, we don’t want lactic acid to build up during each stride. This inhibits the nervous system and interferes with the neuromuscular adaptations that we want. Accordingly, after each stride, you must jog easily for a minimum of 30 seconds and up to a minute and a half to make sure the muscles are ready for the next one. Not allowing for sufficient recovery after each stride is a common mistake. Take advantage of the longer recovery. It will allow you to put more effort into each stride which really helps develop your speed.

As you might imagine, the pace for strides is very fast – Note that this is not all-out sprinting. Run fast but always stay under control. These are quick efforts where you practice good form. You’ll be amazed at how much your finishing kick improves with these workouts.

You can incorporate some strides or “pick-ups” during the middle of your run or at the end. To perform, run fast for 15 to 25 seconds then jog easily for 30 seconds to a minute and a half before beginning the next one. Begin with four strides and build up to ten to 20.

Other Workouts

Hill Repeats

It’s rare that you find a great distance runner who didn’t get fast by training on hills. Kenyans and Ethiopians all train on hills. I find that hill training is one of the best workouts that you can do. It provides great stimulus to the cardiorespiratory system, develops your ability to buffer lactic acid, strengthens the legs, practices leg turnover that matches common race distances like the 5K and 10K yet avoids the pounding that is associated with traditional speed work. When hills are encountered during races, they pose no threat to you and you can run them better and more efficiently than other runners, both uphill and downhill.

To perform a hill workout, find a hill with a medium slope that takes between 45 and 80 to ascend. Run up at an effort equivalent to your race “effort”. Focus on good form with powerful push off and strong arm swing. Jog down the hill slowly to recover. You can also practice your downhill running technique by running down the hill occasionally at 5K race pace. Keep your body under control and add these descents in gradually as you will undoubtedly be sore afterwards.

While the above Hill Repeats outline the common type of hill workout, it is also recommend running on hilly courses often, especially during your foundation and stamina phases of training.

Coach Belo

Coach Belo is a USA Track & Field Level 3 and IAAF Level 5 Certified Coach for Endurance and Jump Events. Graduate work is in Exercise Science from Humboldt State University and currently is the Head Cross Country Coach at Mission Viejo High School and Director of GrassRoots Athletics.

Leave a Reply

Your email address will not be published. Required fields are marked *

Back To Top