THE ACTION CURVE Action Potential Length-Tension Relation Curve Muscle Force Curve Periodization Training Goldilocks Principle Stress -- General Adaptation Syndrome
"The harder the conflict, the more glorious the triumph. What we obtain too cheap, we esteem too lightly; it is dearness only that gives everything its value. I love the man that can smile in trouble, that can gather strength from distress and grow brave by reflection. 'Tis the business of little minds to shrink; but he whose heart is firm, and whose conscience approves his conduct, will pursue his principles unto death." -- Thomas Paine

THE ACTION CURVE is common in the Physiology of Physical Training and is a reminder of how the body responds to Physical Training. The curve turns up in many natural systems of the human body. The curve often represents the storing of potential energy and the release of energy. The highs and lows of potential and kinetic energy are present at many levels of physiology, and are considered in the design and programming of training sessions and long-range workout schedules. Here is a rundown of four important curves that describe the theory behind Physical Training.

Action Potential
An Action Potential is a wave of depolarization that occurs in nerves and muscles. Electrolytes or ions, such as sodium and potassium are in a state of potential energy when polarized across a nerve membrane. Depolarization is the reversal of that potential. A wave of depolarization travels down a nerve to conduct the impulse. The Action Potential of a nerve is transferred chemically by a Motor Endplate (motoneuron) that transmits the nervous Action Potential to a muscular Action Potential which causes muscle fibers to contract. A stimulus causes the potential to reverse or depolarize when a threshold is reached and a depolarization wave travels or propagates along a nerve or muscle. In maximal strength and power activities the ability to activate as many motoneurons as possible for a task brings top performance. The number of neurons fired and the frequency that the neurons are fired sum up the neural activity causing the magnitude of whole muscle contraction. The Action Potential curve is plotted as Voltage (Potential) versus Time. Action Potential graphs actually look narrower and are not as symmetrical as the graphic shown above.

Length-Tension Relation Curve
Muscles have an optimal length that produces stronger contractions. When muscles are placed in a shortened position they are weaker. When muscles are lengthened to a position of overstretching, they also produce weaker contractions. There are overlapping contractile filaments inside the muscle fibers that have an optimal overlap and greater contractile force output somewhere between the extremes of too-short and too-stretched. The Length-Tension Relationship combined with the efficiency of the line of pull of muscles near a joint are very important in understanding why strength varies at different joint angles and when teaching weight training techniques. Many machine settings are designed to optimize the length of working muscle. Care must be taken to determine that efforts to reach optimal muscle length do not occur at the expense of joint safety. The Length-Tension Relation Curve is plotted as Tension Developed versus Muscle Length.

Muscle Force Curve
There is a period of time when a muscle contraction is at its maximum following the nerve stimulus. This period of contraction is called the Maximum Intensity of the Active State. The window of opportunity for this state is small. The Maximum Intensity is not developed instantaneously, but it happens quickly and declines immediately. The Force-Time Relationship is important to athletes with maximum strength goals because athletes may have the best opportunity to move a weight in the fraction of seconds that the Active State reaches a maximum. The Muscle Force Curve is plotted as Force versus Time.

Periodization Training
An athlete cannot train heavy all the time because muscles need time to recover and adapt to gain greater strength and power. Athletic performance involves strength, power, speed, endurance and technique. Variety is an important part of training because specific components of athletic performance can be addressed while other components are allowed to rest. The Periodization Curve is actually a continuum of up and down curves that plot an overlap of Training Intensity and Training Volume versus Time (usually one year). The one year time period is considered a Macrocycle and is subdivided into Mesocycles (months) and Microcycles (weeks).

There's More Too
When you consider human interaction during sports, with a machine or with another human being there is almost always an optimal magnitude of effort applied to get the best results. During a basketball free throw, if too little force is applied to the ball, it falls short as an air ball. Too much force? ... it bounces off of the backboard. It takes a few tries to find optimal force for optimal performance; and the force applied is not necessarily in the middle as the graph below implies. Finding an optimal magnitude in the "middle" (of the x-axis) to optimize a result (y-axis) is known as "following the Goldilocks Principle," as in the Porridge is TOO COLD, TOO HOT or JUST RIGHT.

Stress and the General Adaptation Syndrome explained by Hans Selye¹ has a similar optimal magnitude in the middle. Too little stress causes a person to lack the ability to adapt and cope with stress. When a person is physically under-stressed, the body also deconditions into an unhealthy state. For example, people with casts for broken bones lose muscle mass while the cast is in place. The performance of muscles under a cast declines from lack of use and needs to be reconditioned when the cast is removed. Lack of exercise can also put women at higher risk of osteoporosis. People who are continuously over-stressed are more likely to develop illnesses and diseases (e.g., heart attack, ulcer, respiratory infection, carpal tunnel syndrome, etc.) and are more likely to be involved in accidents.

 

The Action Curve is a helpful reminder to keep your lifestyle tuned to optimal performance and health. APRIORIATHLETICS.COM is dedicated to helping you discover and rely on that optimum.

1. Hans Selye Biography from Selye-Toffler University

© Copyright 1988-2006 Mark D. Bostrom

Return to APRIORIATHLETICS.COM, Front Page.

Return to "What this site is about."