Physical force is the measure of the effort exerted by an animal on physical objects. Increasing physical strength is the goal of strength training.
The physical strength of an individual is determined by two factors; the cross-section of muscle fibers recruited to generate strength and intensity of recruitment. Individuals with a high proportion of Type I slow-twitch muscle fibers will be relatively weaker than a similar individual with a high proportion of Type II fast-twitch fibers, but will have a greater inherent capacity for physical endurance. The genetic inheritance of the type of muscle fibers defines the extreme limits of physical strength (with the exception of the use of stimulating agents such as testosterone), although the unique position in this envelope is determined by the ‘training. The individual muscle fiber ratios can be determined by a muscle biopsy. Other considerations are the ability to recruit muscle fibers for a particular activity, the angles of the joints and the length of each limb. For a given cross section, shorter limbs are able to lift more weight. The ability to gain muscle also varies from person to person, depending primarily on the genes that dictate secreted hormone levels, but also on gender, age, health, and nutrients adequate. A maximum repeat test is the most accurate way to determine maximum muscle strength.
There are different ways to measure the physical strength of a person or a population. Resistance analysis is usually performed in the area of ergonomics where a particular task (eg lifting a load, pushing a trolley, etc.) and / or posture is evaluated and compared to the capabilities of the section. Population. intended for. External reactive moments and forces on the joints are usually used in such cases. The strength capacity of the joint is indicated by the amount of moment that the muscular force can create at the joint to counter the external moment. Skeletal muscles produce reactive forces and moments in the joints. To avoid injury or fatigue, when the person performs a task, such as pushing or lifting a load, the external moments created at the joints due to the load of the hand and the weight of the body segments must ideally be less than the moment muscular forces at the joint. One of the first sagittal plane models to predict force was developed by Chaffin in 1969. On the basis of this model, the moments external to each joint must not exceed the moments of muscular strength at this articulation. M j / L <S j Where, S j is the moment of muscle strength at the joint, j, and M j / L is the moment external to the joint, j, due to the load, L and the body segments preceding the joint in the top-down analysis. Downward analysis is the method of calculating reactive moments and forces at each joint, from hand to ankle and foot. In a 6-segment model, the joints considered are the elbow, the shoulder, the L5 / S1 disc of the spine, hip, knee and ankle. It is common to ignore the wrist joint in manual calculations. Software for such a calculation also uses the wrist, dividing the lower arm into hand and forearm segments.
Static force prediction is the method of predicting a person’s or population’s (anthropometry-based) force capabilities for a particular task and / or posture (isometric contraction). Manual calculations are usually performed using top-down analysis on a six- or seven-link model, based on available case information, and then compared to standard guidelines, such as those provided by the National Institute of Safety and Security. Health at work. predict capacity.