Running Physiology: A Cascade of Changes

Posted by Filed Under: Science and Research, Training

See the related article: “Turn Down That Stereo!”
Why does it take a period of time before you feel warmed up and comfortable after starting a run?

The answer begins with how your body responds to the increased demands of exercise. When you start exercising, your body must do the following:

  1. Increase the rate of oxygenation of blood and removal of carbon dioxide waste products (respiration);
  2. Increase the amount of blood flow to the muscles of the body (cardiac output); and
  3. Increase the energy supply to the muscles to meet the demands of exercise.

These events do not happen immediately. Let’s look at each one of the above elements.

Increased Respiration

  • Controlled by the nervous system;
  • Is the process of ridding the body of carbon dioxide and getting more oxygen into the bloodstream for aerobic energy production.

Increased Cardiac Output

  • Controlled by sympathetic nervous system (the fight-or-flight response);
  • Most limiting factor in performance;
  • Cardiac stroke volume, which is how much blood your heart can pump with each beat, is what improves the most with training; and
  • Cardiac output is defined as stroke volume multiplied by heart rate, which gives you blood flow in liters per minute.

Energy Supply

  • Aerobic training primarily relies on fat burning and oxygen to produce energy;
  • Aerobic energy production has greater capacity than anaerobic systems, but is produced at a slower rate; and
  • The trigger to start aerobic energy production is not fully understood. It appears to involve neurological stimulation that triggers the release of signaling proteins, neurotransmitters and hormones.

It takes time for all these systems to come “online” to meet the increased demands of exercise. So begin slowly until the body reaches its peak energy efficiency. As your body ramps up its energy production, you can ramp up your pace accordingly.

In summary, running initiates a neurological cascade of events leading to increased respiration, heart rate and a release of signaling proteins, neurotransmitters and hormones. This latter process leads to increased aerobic metabolism. The exact series of events is still unclear, but it is the metabolic changes that take the most time.

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  1. Aaron Engelsrud on August 21st at 5:11 am

    I don’t typically do much of a warm up – it’s not that I don’t realize the importance of warming up, rather it’s a time constraint issue. I don’t always have the time to devote to a warm-up, I run at lunch or early in the morning, and I need to squeeze things in. The warm-up is the first to go.

    I have found that my body reacts OK to this lack of warm up (not to say I couldn’t do better with a solid warm-up). I seem to have a heart rate set point that I hit within the first minute of running (right now this is around 145 – 155 bmp) and it is typcially very close to what my average HR ends up being at the end of the run. I can be standing at the end of my driveway pre run and my HR is at 55 bpm and by the end of the block I’m at 145. So, I guess what I’m saying is my ‘ramp-up’ period is very short.

    Is this good, bad, or otherwise? Is this a conditioning issue? Should I be concerned about this sudden jump? (Just FYI, this happens reguardless of how slowly I start out)

    Nice article and thanks for the info!


  2. Dr. Lee Miller D.C. on August 21st at 12:21 pm

    This response is to Aaron E’s question.

    What you have happening may be completely normal for you. There is a tremendous amount of variation from person to person regarding heart rate and warm-up time. This is why using the old 220 minus age formula to determine max heart rate is unreliable for some people.

    If in doubt, I recommend a VO2 max test that can determine what your heart rate should be during a training run.

    If you are concerned about a possible heart abnormality, your physician can do a number of tests to rule this in or out.

    Most likely, if this is a comfortable heart rate for you to train at regardless of warm up, it is just the way your body responds to exercise.

  3. Turn Down That Stereo! : Complete Running Network on January 7th at 11:37 pm

    […] When I taught running clinics I would use this analogy when someone would ask “why does it take me 15 to 30 minutes before I feel comfortable when I run?” I would tell her that her speed (volume) is too high at the beginning of her run and thus her body is not physically or mentally prepared for it. It is best to begin your run at a nice comfortable slow pace (turn down the radio). As you get used to the pavement, increase your speed (volume) gradually. Then after an adequate period of running in which you are nicely warmed up (your body will know), you can “get the lead out” with relatively little discomfort when your favorite straight-away or hill presents itself. —————- Looking for the physiological explanation? Read “Running Physiology: A Cascade of Changes.” […]