Rohmert's law
Encyclopedia
Widely used in the human factors
Human factors
Human factors science or human factors technologies is a multidisciplinary field incorporating contributions from psychology, engineering, industrial design, statistics, operations research and anthropometry...

 and ergonomics
Ergonomics
Ergonomics is the study of designing equipment and devices that fit the human body, its movements, and its cognitive abilities.The International Ergonomics Association defines ergonomics as follows:...

 field, Rohmert's law states that the maximum force one's muscles can exert decreases exponentially from the time one begins continuously exerting the said force. It is commonly used to calculate "maximum holding time" for any particular task.

Maximum force decays exponentially due to the amount of energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

 (in the form of oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 and ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...

) the body is able to supply to the muscles. The circulatory system
Circulatory system
The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...

s keeps muscles flooded in nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...

s at all times, so that muscles have a supply of fuel ready to burn at any given moment. A task requiring maximum force burns a large amount of those nutrients at the onset of the task; the circulatory system is then unable to replenish the nutrients at a rate fast enough to maintain maximum force for long. As a result, the maximum force the muscle is capable of producing is limited by the bottleneck
Bottleneck
A bottleneck is a phenomenon where the performance or capacity of an entire system is limited by a single or limited number of components or resources. The term bottleneck is taken from the 'assets are water' metaphor. As water is poured out of a bottle, the rate of outflow is limited by the width...

 in nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...

 availability, and decreases exponentially.

Imagine a theoretical arm wrestling
Arm wrestling
Arm wrestling is a sport with two participants. Each participant places one arm on a surface with their elbows bent and touching the surface, and they grip each other's hand...

match with two perfectly matched opponents, each exactly as strong as each other. They both begin the match by exerting maximum force on each other's hands, but very soon, their arms get fatigued and the actual force being exerted on each others' hands drops off quickly. They are still exerting as much force as they can, but their muscles are burning energy faster than can be replenished, and their maximum force is decreasing exponentially. Eventually their arms are completely fatigued; they are basically just holding hands and applying what little force their muscles can muster, wondering when the other will give up.

While Rohmert's law applies to maximum force, the inverse is true as well; the less force one is asked to exert, the longer one will be able to exert that force before their muscles become fatigued. If one is asked to exert zero force, they can theoretically hold the position indefinitely.

Rohmert's law has been found to be true across all humans. While everyone has a different initial maximum force they can apply, their maximum force will decrease according to the same exponential curve as everyone else.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK