Physical strength

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Natalia Zabolotnaya lifting 160 kilograms over her head Natalia Zabolotnaya 2012b.jpg
Natalia Zabolotnaya lifting 160 kilograms over her head

Physical strength is the measure of an animal's exertion of force on physical objects. Increasing physical strength is the goal of strength training.



An individual's physical strength is determined by two factors: the cross-sectional area of muscle fibers recruited to generate force and the intensity of the 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 would have a greater inherent capacity for physical endurance. The genetic inheritance of muscle fiber type sets the outermost boundaries of physical strength possible (barring the use of enhancing agents such as testosterone), though the unique position within this envelope is determined by training. Individual muscle fiber ratios can be determined through a muscle biopsy. Other considerations are the ability to recruit muscle fibers for a particular activity, joint angles, 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 person to person, based mainly upon genes dictating the amounts of hormones secreted, but also on sex, age, health of the person, and adequate nutrients in the diet. A one-repetition maximum test is the most accurate way to determine maximum muscular strength. [1] [2]

Strength capability

There are various ways to measure physical strength of a person or population. Strength capability analysis is usually done in the field of ergonomics where a particular task (e.g. lifting a load, pushing a cart, etc.) and/or a posture is evaluated and compared to the capabilities of the section of the population that the task is intended towards. The external reactive moments and forces on the joints are usually used in such cases. The strength capability of the joint is denoted by the amount of moment that the muscle force can create at the joint to counter the external moment.

Skeletal muscles produce reactive forces and moments at the joints. To avoid injury or fatigue, when person is performing a task, such as pushing or lifting a load, the external moments created at the joints due to the load at the hand and the weight of the body segments must be ideally less than the muscular moment strengths at the joint.

One of the first sagittal-plane models to predict strength was developed by Chaffin in 1969. [3] Based on this model, the external moments at each joint must not exceed the muscle strength moments at that joint.

Mj/L < Sj

Where, Sj is the muscle strength moment at joint, j, and Mj/L is the external moment at the joint, j, due to load, L and the body segments preceding the joint in the top-down analysis.

Top-down analysis is the method of calculating the reactive moments and forces at each joint starting at the hand, all the way till the ankle and foot. In a 6-segment model, the joints considered are elbow, shoulder, L5/S1 disc of the spine, hip, knee and ankle. It is common to ignore the wrist joint in manual calculations. Software intended for such calculation use the wrist joint also, dividing the lower arm into hand and forearm segments.

Prediction of static strength

Static strength prediction is the method of predicting the strength capabilities of a person or a population (based on anthropometry) for a particular task and/or posture (an isometric contraction). Manual calculations are usually performed using the top-down analysis on a six or seven-link model, based on available information about the case and then compared to standard guidelines, such as the one provided by the National Institute for Occupational Safety and Health, to predict capability.

See also

Related Research Articles

Weight training Common type of strength training and body building

Weight training is a common type of strength training for developing the strength and size of skeletal muscles. It utilizes the force of gravity in the form of weighted bars, dumbbells or weight stacks in order to oppose the force generated by muscle through concentric or eccentric contraction. Weight training uses a variety of specialized equipment to target specific muscle groups and types of movement.

Gluteus maximus Largest and most superficial of the three gluteal muscles

The gluteus maximus is the main extensor muscle of the hip. It is the largest and outermost of the three gluteal muscles and makes up a large part of the shape and appearance of each side of the hips. Its thick fleshy mass, in a quadrilateral shape, forms the prominence of the buttocks. The other gluteal muscles are the medius and minimus, and sometimes informally these are collectively referred to as the "glutes".

Muscle fatigue is the decline in ability of a muscle to generate force. It can be a result of vigorous exercise but abnormal fatigue may be caused by barriers to or interference with the different stages of muscle contraction. There are two main causes of muscle fatigue: the limitations of a nerve’s ability to generate a sustained signal ; and the reduced ability of the muscle fiber to contract.


Hypotonia is a state of low muscle tone, often involving reduced muscle strength. Hypotonia is not a specific medical disorder, but a potential manifestation of many different diseases and disorders that affect motor nerve control by the brain or muscle strength. Hypotonia is a lack of resistance to passive movement, whereas muscle weakness results in impaired active movement. Central hypotonia originates from the central nervous system, while peripheral hypotonia is related to problems within the spinal cord, peripheral nerves and/or skeletal muscles. Severe hypotonia in infancy commonly known as floppy baby syndrome. Recognizing hypotonia, even in early infancy, is usually relatively straightforward, but diagnosing the underlying cause can be difficult and often unsuccessful. The long-term effects of hypotonia on a child's development and later life depend primarily on the severity of the muscle weakness and the nature of the cause. Some disorders have a specific treatment but the principal treatment for most hypotonia of idiopathic or neurologic cause is physical therapy and/or occupational therapy for remediation.

Muscle contraction Activation of tension-generating sites in muscle

Muscle contraction is the activation of tension-generating sites within muscle fibers. In physiology, muscle contraction does not necessarily mean muscle shortening because muscle tension can be produced without changes in muscle length, such as when holding a heavy book or a dumbbell at the same position. The termination of muscle contraction is followed by muscle relaxation, which is a return of the muscle fibers to their low tension-generating state.

Strength training

Strength training or resistance training involves the performance of physical exercises which are designed to improve strength and endurance. It is often associated with the use of weights but can take a variety of different forms.

The term workload can refer to a number of different yet related entities.

Motor unit recruitment refers to the activation of additional motor units to accomplish an increase in contractile strength in a muscle. A motor unit consists of one motor neuron and all of the muscle fibers it stimulates. All muscles consist of a number of motor units and the fibers belonging to a motor unit are dispersed and intermingle amongst fibers of other units. The muscle fibers belonging to one motor unit can be spread throughout part, or most of the entire muscle, depending on the number of fibers and size of the muscle. When a motor neuron is activated, all of the muscle fibers innervated by the motor neuron are stimulated and contract. The activation of one motor neuron will result in a weak but distributed muscle contraction. The activation of more motor neurons will result in more muscle fibers being activated, and therefore a stronger muscle contraction. Motor unit recruitment is a measure of how many motor neurons are activated in a particular muscle, and therefore is a measure of how many muscle fibers of that muscle are activated. The higher the recruitment the stronger the muscle contraction will be. Motor units are generally recruited in order of smallest to largest as contraction increases. This is known as Henneman's size principle.

Motor control is the regulation of movement in organisms that possess a nervous system. Motor control includes reflexes as well as directed movement.

Complex training, also known as contrast training or post-activation potentiation training, involves the integration of strength training and plyometrics in a training system designed to improve explosive power. According to Jace Derwin:

Strength training and plyometric training are both effective measures for increasing athletic performance independent of each other, but a true program designed for power-based athletes needs to incorporate both disciplines. A study done in 2000 in the NSCA's Journal of Strength and Conditioning Research measured three different training protocols: strength training, plyometric training, and a combination of both. The group that used combined methods was the only group that showed significant increases in BOTH strength and power.

Musculoskeletal disorder

Musculoskeletal disorders (MSDs) are injuries or pain in the human musculoskeletal system, including the joints, ligaments, muscles, nerves, tendons, and structures that support limbs, neck and back. MSDs can arise from a sudden exertion, or they can arise from making the same motions repeatedly repetitive strain, or from repeated exposure to force, vibration, or awkward posture. Injuries and pain in the musculoskeletal system caused by acute traumatic events like a car accident or fall are not considered musculoskeletal disorders. MSDs can affect many different parts of the body including upper and lower back, neck, shoulders and extremities. Examples of MSDs include carpal tunnel syndrome, epicondylitis, tendinitis, back pain, tension neck syndrome, and hand-arm vibration syndrome.

Ballistic training

Ballistic training, also called power training, is a form of training which involves throwing weights, and jumping with weights, in order to increase explosive power. The intention in ballistic exercises is to maximise the acceleration phase of an object's movement and minimise the deceleration phase. For instance, throwing a medicine ball maximises the acceleration of the ball; this can be contrasted with a standard weight training exercise where there would be a pronounced deceleration phase at the end of the repetition i.e. at the end of a bench press exercise the barbell is decelerated and brought to a halt. Similarly, an athlete jumping whilst holding a trap bar maximises the acceleration of the weight through the process of holding it whilst they jump; where as they would decelerate it at the end of a standard trap bar deadlift.

Neutral spine "three natural curves [that] are present in a healthy spine."

Good posture refers to the "three natural curves [that] are present in a healthy spine.".It is also called neutral spine. Looking directly at the front or back of the body, the 33 vertebrae in the spinal column should appear completely vertical. From a side view, the cervical (neck) region of the spine (C1–C7) is bent inward, the thoracic region (T1–T12) bends outward, and the lumbar region (L1–L5) bends inward. The sacrum and coccyx rest between the pelvic bones. A neutral pelvis is in fact slightly anteriorly rotated which means the anterior superior iliac spines should be just in front of the pubic symphysis not in the same vertical line.

Muscle Contractile soft tissue of mammals

Muscle is a soft tissue found in most animals. Muscle cells contain protein filaments of actin and myosin that slide past one another, producing a contraction that changes both the length and the shape of the cell. Muscles function to produce force and motion. They are primarily responsible for maintaining and changing posture, locomotion, as well as movement of internal organs, such as the contraction of the heart and the movement of food through the digestive system via peristalsis.

A motor pool consists of all individual motor neurons that innervate a single muscle. Each individual muscle fiber is innervated by only one motor neuron, but one motor neuron may innervate several muscle fibers. This distinction is physiologically significant because the size of a given motor pool determines the activity of the muscle it innervates: for example, muscles responsible for finer movements are innervated by motor pools consisting of higher numbers of individual motor neurons. Motor pools are also distinguished by the different classes of motor neurons that they contain. The size, composition, and anatomical location of each motor pool is tightly controlled by complex developmental pathways.

The motor unit consists of a voluntary alpha motoneuron and all of the collective muscle fibers that it controls, known as the effector muscle. The alpha motoneuron communicates with acetylcholine receptors on the motor end plate of the effector muscle. Reception of acetylcholine neurotransmitters on the motor end plate causes contraction of that effector muscle.

Normal aging movement control in humans is about the changes in the muscles, motor neurons, nerves, sensory functions, gait, fatigue, visual and manual responses, in men and women as they get older but who do not have neurological, muscular or neuromuscular disorder. With aging, neuromuscular movements are impaired, though with training or practice, some aspects may be prevented.

Muscular evolution in humans is an overview of the muscular adaptations made by humans from their early ancestors to the modern man. Humans are believed to be predisposed to develop muscle density as early humans depended on muscle structures to hunt and survive. Modern man's need for muscle is not as dire, but muscle development is still just as rapid if not faster due to new muscle building techniques and knowledge of the human body. Humans are widely thought to be one of the fastest muscle growing organisms due to surplus of calories, specialized amino acids, and one of the lowest amounts of myostatin in the animal kingdom.

There is a growing research database which suggests that skeletal muscles, particularly postural muscles of the lower limb, undergo atrophy and structural and metabolic alterations during space flight. However, the relationships between in-flight exercise, muscle changes and performance are not well understood. Efforts should be made to try to understand the current status of in-flight and post-flight exercise performance capacity and what the goals/target areas for protection are with the current in flight exercise program.

The function of the lower limbs during walking is to support the whole-body against gravitational forces while generating movement patterns which progress the body forward. Walking is an activity that is primarily confined to the sagittal plane, which is also described as the plane of progression. During one gait cycle, there are two major phases: stance and swing. In a healthy individual walking at a normal walking speed, stance phase makes up approximately 60% of one gait cycle and swing makes up the remaining 40%. The lower limbs are only in contact with the ground during stance phase which is typically subdivided into 5 events: heel contact, foot flat, mid-stance, heel off, and toe off. The majority of stance phase (~40%) takes place in single-limb support where one limb is in contact with the ground and the contralateral limb is in swing phase. During this time interval, the lower limb must support constant changes in alignment of body weight while propelling forward. The hip, knee, and ankle joints move through cyclical kinematic patterns that are controlled by muscles which cross these joints. As postural changes occur, the body adapts by motor tuning an efficient muscular pattern that will accomplish the necessary kinematics required to walk.


  1. "Muscular Strength — Human Performance Resource Center".
  2. "Muscular Strength".(registration required)
  3. Chaffin DB, Andersson GB, Martin BJ (1999). Occupational Biomechanics, 3rd Edition. New York: John Wiley & Sons. ISBN   0-471-24697-2.