The Physiology of Running 

The act of running is elegantly simple.  Running gives one a sense of being liberated, partly breaking the bonds of earth, freeing the mind, body, and spirit to soar. One has the opportunity to truly test one’s physical and mental stamina and to push to one’s limits.  Running was an act of survival for prehistoric man as he hunted or avoided being hunted.  Running became an honored event in the ancient Olympics as marathoners were considered heroes.  The simple goal of competitive running is to complete a course at the highest average speed without over-fatiguing and slowing down.  The specific physical traits that allow a runner to do this can be developed and improved through rigorous exercise.  This improvement can be maximized through a thoughtfully designed training program based on a working knowledge of running mechanics and physiology. The following information is a basic overview of the physiology of running to give you an understanding of what your body is doing and how our workouts will help you run longer and faster. 

Muscles in the human body cause movement by shortening in response to electrical neural impulses from the brain.  Millions of muscle fibers simultaneously shorten, and depending on where the muscle attaches, pulls bone in a motion called the power stroke.  The work done by a muscle obviously requires energy and this energy comes from the food we eat.  The chemical reactions in the body that release this energy from food is called metabolism.  The chemical used by muscles is called adenosine triphosphate (ATP).  In the presence of water and enzymes, ATP breaks down in the muscle as one phosphate molecule (P) comes off, and chemical bonding energy is released for muscles to use.  The other product of this reaction is adenosine diphosphate (ADP).  ADP can be recombined with the P to form ATP, but it takes more energy from more food.  This is the process of cellular respiration. 

ATP            ADP + P + ENERGY 

Some ATP is stored in muscles at all times for a quick burst of energy, but this amount is used up in seconds.  Therefore, the key to moderately fast sustained running is for the body to efficiently resupply the muscles with ATP.  This new metabolic energy to reform ATP comes from carbohydrates (CH), specifically glucose (C₆H₁₂O₆), delivered to the muscles through the circulatory system and then chemically broken down.  Oxygen (O₂) must also be delivered to complete this process. 

                        C₆H₁₂O₆ + 6O₂              6CO₂ + 6H₂O + ENERGY 

In order for muscles to continue to work efficiently for long periods of time without excessive fatigue, the circulatory and respiratory systems must deliver adequate amounts of CH and O₂ to the muscles and carry away the products of carbon dioxide and water.  At faster running speeds, all of the glucose cannot be broken down completely to CO₂ and H₂O, and the intermediate substance called lactate is produced.  This useable substance must either be broken down in the muscle cells (mitochondria) or be carried away.  If all of these reactants cannot be carried away fast enough then the blood system becomes overloaded and acidic.  The high acidity impairs the power stroke of muscles, painful muscle fatigue sets in, and running pace must slow down.  This overall process can be improved through training. 

There are 3 metabolic pathways that the body produces ATP, 2 with oxygen present in the muscles and 1 when oxygen is not.  

A.  Aerobic lipolysis produces ATP from fat and oxygen

            Fat + O₂            ATP     (130 ATP molecules per fat molecule) 

B.  Aerobic glycolysis produces ATP from carbohydrates and oxygen

            CH + O₂            ATP     (36 ATP molecules per glucose molecule) 

C.  Anaerobic glycolysis produces ATP without oxygen

                    CH            ATP     (2 ATP molecules per glucose molecule) 

The ATP-producing pathway that seems the best is A.  Unfortunately, fat is stored in the body and breaks down slowly, so it delivers ATP at a slow rate.  This slow rate is good for marathon runners, but not runners competing at 5000 meters that need ATP faster.  Of the remaining 2 pathways, aerobic glycolysis generates about 90% of the ATP at a 5000 meter pace.  At shorter race distances or during the sprinting portions of a longer race, anaerobic glycolysis becomes more important when oxygen cannot be delivered to the muscles fast enough.  In an 800 meter race, the anaerobic pathway may generate up to 50% of the required ATP. 

Physiologists have created an indicator of aerobic fitness called VO₂max.  This measurement is the maximum volume of oxygen that the body’s muscles can use per minute to continue to make ATP aerobically.  If running intensity increases past this point, oxygen consumption cannot, so the extra energy to run faster or up a steeper grade must come from the anaerobic pathway.  VO₂max is hard to measure, but since the heart rate increases with increasing training intensity, then heart rate can be used to indicate at what percentage of VO₂max one is training.  The maximum heart rate (HRmax) of an individual can be determined by subtracting one’s age from 220 beats per minute.  High school runners have a HRmax of about 200. 

The expression “practice makes perfect” comes from the fact that the human body’s response to repetitive training is to improve one’s ability to perform a desired action.  When the human body is physically stressed during running, the body’s response is to adapt in such a way as to improve the critical body systems.  If a runner trains at a slow speed for an adequate period of time, say 55-65% HRmax, then the metabolic pathway being stressed is aerobic lipolysis. If a runner trains at 65-75% HRmax for an adequate length of time, then the cardiovascular system and the aerobic glycolysis pathway is being improved.  If a runner trains at 75-95% HRmax, then a maximum benefit to the aerobic system and VO₂max can be achieved for racing purposes.  If a runner trains at 100% HRmax, then the anaerobic system can be developed.  Having a working knowledge of this physiology, a sequential season-long training program can be developed that will help a runner to progress from their individual starting point to an optimum performance at the end of the current season.  In addition, the same runner can then use progressively more challenging workouts in future years to continue their development through their high school career. 

The following chart shows nine areas of training focus for distance runners, the purpose of the training, and the general workout conditions required.  We will use this system as the basis for our workout program.  Credit for this running physiology-based training system goes to Dr. Larry Greene from the University of Colorado and Dr. Russ Pate from the University of South Carolina.  The season will generally progress from concentrations of strength endurance and cardiovascular fitness in the summer, increasing aerobic conditioning into the mid-season, and then anaerobic fitness and race training in the latter portion of the season, leading up to our final state competitions.

Bibliography 

Larry Greene and Russ Pate (2004), Training for Young Distance Runners, Human Kinetics. 

Joe Newton and Dr. John Durkin (1988), Running to the Top of the Mountain, J&J Winning Edge Press. 

Joe Newton and Joe Henderson (1998), Coaching Cross Country Successfully, Human Kinetics.