Concentric Muscle Contraction

Concentric muscle contractions (shortening contractions) are typically used to generate motion, whereas eccentric muscle contractions (lengthening contractions) are used for resisting or slowing motion, and isometric contractions are used for producing shock absorption and maintaining stability.

From: Atlas of Orthoses and Assistive Devices (Fifth Edition) , 2019

Gait Analysis

John A. Herring MD , in Tachdjian's Pediatric Orthopaedics , 2022

Concentric Contractions

Two large concentric contractions occur at terminal stance. The gastrocsoleus muscle contracts to lift the heel off the ground and push off. The iliopsoas muscle also contracts concentrically, flexing the hip and pulling the stance phase limb off the ground at terminal stance and early swing. The gastrocsoleus and iliopsoas muscles are believed to be the two primary accelerators of gait, although controversy exists as to which muscle contributes more toward forward propulsion of the body. 52 , 60 During swing phase, the anterior tibialismuscle undergoes a concentric contraction. This dorsiflexes the ankle and provides clearance for the swing foot.

Exercise in the Rehabilitation of the Athlete

Sheila A. Dugan , in Clinical Sports Medicine, 2007

Concentric

Concentric contraction involves shortening of the muscle with requisite movement of the origin or insertion and limb translation. 9 Athletes use concentric contractions to counter a load. They are used to accelerate the distal segment of the limb and attached equipment, such as a racquet or ball. With skill training, the ball can be released with kinetic energy at the appropriate time or toward the appropriate target. Initial concentric exercise training can be done using only the resistance of the limb mass against gravity or in a gravity-assisted or gravity-eliminated position. Progressive resistance can be advanced using a variety of equipment, including flexible cords, weighted balls, hand weights or resistance training equipment. Body positioning can be manipulated to provide for more functional alignment. In regard to rehabilitating athletes, one must remember that these concentric contractions are not performed in isolation and occur with a host of biomechanical challenges brought about by changes in trunk alignment or surface of play, just to name a few.

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Anatomy and biomechanics of the hand

James Chang MD , in Plastic Surgery: Volume 6: Hand and Upper Extremity , 2018

Biomechanical concept: muscle force production

Muscles can produce force in different ways. 59 Concentric contractions occur when muscle fibers can shorten to induce tendon stretch, tendon excursion, and/or joint motion. Eccentric contractions occur when tendon forces overpower the passive and active force the muscle can produce and the muscle fibers lengthen during muscle activation. Isometric contractions occur when the muscle is not allowed to shorten (calling this state of the muscle a "contraction", when in reality it remains the same length, is a historical artifact). The structural and biochemical properties of the sarcomere make the exact magnitude of muscle force for a given level of neural excitation a function of length of the fibers, velocity at which fibers shorten or lengthen, and its previous activation history. The force–length relationship of muscle (sometimes called the Blix curve) indicates that there is an optimal length of the fiber at which maximal force can be produced, and it drops at longer or shorter fiber lengths (Fig. 1.32). Thus, the length at which the muscle is placed in reconstructive surgeries or tendon transfers can greatly influence the force the muscle can produce postoperatively.The force–velocity relationship of muscle indicates that muscle force drops greatly from its isometric level when muscle fibers shorten rapidly during concentric contractions, and rises to a plateau almost double its isometric level when muscle fibers lengthen rapidly during eccentric contractions (Fig. 1.33).

Principles of Sports Rehabilitation

Jennifer Reed MD, FAAPMR , Jimmy D Bowen MD, FAAPMR, CSCS , in The Sports Medicine Resource Manual, 2008

Types of muscle action

Concentric contraction

Concentric contraction occurs when the total length of the muscle shortens as tension is produced. For example, the upward phase of a biceps curl is a concentric contraction.

Eccentric contraction

Eccentric contraction occurs when the total length of the muscle increases as tension is produced. For example, the lowering phase of a biceps curl constitutes an eccentric contraction. Muscles are capable of generating greater forces under eccentric conditions than under either isometric or concentric contractions. 17-19 Large tensile forces are generated during sudden eccentric contractions (e.g., a linebacker coming to a rapid stop at the line of scrimmage generates large eccentric quadriceps forces).

Traditional rehabilitation programs have often omitted eccentric training. Although there are no definitive studies to support eccentric training as an absolute prerequisite before returning to athletic play, 19 research is emerging to support its use, particularly for the rehabilitation of microtrauma/overuse injuries. For example, Roos and colleagues 20 designed a prospective randomized clinical trial to test the hypothesis that eccentric calf muscle exercises reduce pain and improve function in patients with Achilles tendinopathy. At 12 weeks, members of the group who performed eccentric exercises reported significantly less pain, and more patients in that group returned to sports participation after 12 weeks. 20

Isometric contraction

Isometric contraction occurs when muscle length remains relatively constant as tension is produced. For example, during a biceps curl, holding the dumbbell in a constant/static position rather than actively raising or lowering it is an example of isometric contraction. 21,22 Although the forces generated during isometric contractions are potentially greater than during concentric contractions, muscles are seldom injured during this type of contraction. Isometric exercises are often used during the early phases of rehabilitating a musculotendinous injury because the intensity of contraction and the muscle length at which it contracts can be controlled. 19

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Management of the Injured Athlete

Terri M. Skirven OTR/L, CHT , in Rehabilitation of the Hand and Upper Extremity , 2021

Advanced Functional Exercises

The more advanced functional and unconventional training techniques such as battle ropes, kettle bells, tires, sledgehammers, bodyweight suspension devices, and sleds have become more popular with the athletic population. 32 These different types of exercises require more in skill, technique, proper mechanics, and coordination than the conventional rehabilitation exercises. Unconventional exercises initiate the competitive drive in athletes and provide a positive mental boost.

A popular way to enhance muscle performance is through the use of plyometric training. Plyometric training is when the body goes through a quick stretching of the muscle from eccentric to concentric contraction. 32 The stretch shortening cycle requires the neuromuscular system to react quickly and efficiently after an eccentric muscle action to produce a concentric contraction for acceleration. 33,34 There are three phases to plyometrics: (1) prestretch (eccentric contraction), (2) amortization phase, and (3) shortening phase (concentric contraction). 33,34

The prestretch phase is also known as the loading phase. During this phase, there is an increase in muscle spindle activity. There are three important factors that need to be reinforced: rate, magnitude, and duration. The transition period between the eccentric contraction and concentric contraction of the muscles is called amortization. 32,33,34 This transition period is important because a prolonged rest period can decrease the potential energy produced during the exercise. The last phase in a plyometric exercise is the shortening phase. A quick concentric contraction that allows the movement to become explosive. 32,33,34

Plyometrics enhance excitability, sensitivity, and the reactivity of the neuromuscular system. 32,33,34 Additional benefits of using this type of exercises with athletes are increases in rate of force production, motor unit recruitment, firing frequency, and motor unit synchronization. 32,33,34 The ultimate goal is to increase the ability of the muscles to exert maximal force output in a minimal amount of time. 32,33,34 It is important to implement the appropriate types of plyometrics (upper extremity, lower extremity, core) into an athlete's rehabilitation depending on her or his sport.

Skeletal Muscle Mechanics

Joseph Feher , in Quantitative Human Physiology (Second Edition), 2017

Concentric, Isometric, and Eccentric Contractions Serve Different Functions

Because concentric contractions shorten, they are useful for the acceleration of one body part relative to another, including parts that are loaded with external objects. Isometric contractions are used to fix joints, usually to produce a platform on which other actions can be made. For example, delicate work by the fingers requires immobilization of the arm and shoulder to hold the hand still while the fingers do the work. Such immobilization is accomplished by simultaneously activating antagonistic muscles—those that move joints in opposite directions. Eccentric contractions are used to decelerate body parts, as in activation of the quadriceps muscles in the leg while going downstairs.

Table 3.4.1 shows the three types of contractions, their functions for movement, and the work performed.

Table 3.4.1. Types of Contractions and Their Uses

Types of Contractions Distance Change Function Work
Concentric Shortening (+D) Acceleration Positive W=F×(+D)
Isometric No change (0 D) Fixation Zero
Eccentric Lengthening (−D) Deceleration Negative W=F×(−D)

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Lower Limb Orthoses

Tze Yang Chung , in Braddom's Rehabilitation Care: A Clinical Handbook, 2018

Dorsiflexion Assist (Posterior Spring)

A posterior spring substitutes for concentric contraction of dorsiflexors to prevent flaccid foot drop after toe-off, and it also substitutes (albeit inadequately) for the eccentric activation of the dorsiflexors after heel strike. The posterior spring prevents rapid plantar flexion at heel strike during its compression in the posterior channel. The spring is again compressed during plantar flexion in the late stance before toe-off. It provides a downward thrust posterior to the ankle joint at toe-off, which results in dorsiflexion anterior to the ankle joint, helping in toe clearance during the swing phase.

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Skeletal Muscle, Function, and Muscle Fiber Types

Zsolt Radák , in The Physiology of Physical Training, 2018

2.1 Muscle Contraction

The axons of the neuromuscular junctions originate from the motor neurons located in the ventral horn of the spinal cord. The motor neuron and all the muscle fibers to which it connects is a motor unit. The neuromuscular synapse comprises of postsynaptic and presynaptic membranes. The presynaptic membrane is the axon terminal containing acetylcholine vesicles. Upon stimulation, the stored acetylcholine pool is released and binds its receptor on the postsynaptic membrane of the sarcolemma, causing ion channels to open, and allows sodium ions to flow across the membrane into the muscle cell. This generates an action potential which travels to the myofibril through the transverse tubule system, and the sarcoplasmic reticulum; consequently Ca-ions release, which results in muscle contraction. Ca-ions bind to troponin C, resulting in conformational changes, which allow myosin to bind to actin, producing muscle contraction. In a resting state, troponin-I of the troponin complex covers the actin-myosin contact area. Actin-myosin binding requires ATP, which binds to the myosin-heavy chains (head) (Fig. 2.6).

Fig. 2.6

Fig. 2.6. Molecular mechanism of muscle contraction. Action potential travels through the transverse tubule system and the sarcoplasmic reticulum, resulting in Ca-ions release. Ca-ions bind to troponin C resulting in conformational changes, which allow myosin to bind to actin, producing muscle contraction. During each actin-myosin binding, protein filaments slide on each other to produce a contraction, which requires ATP.

In the resting state of a muscle, myosin has ADP and Pi (inorganic phosphate) bound to its nucleotide binding pocket. In the first step of the actin-myosin binding process, inorganic phosphate is released, followed by a power stroke and the release of ADP. This will pull the Z-lines toward each other, thereby shortening the sarcomere, approximately 10–12   nm/stroke. In the next step, ATP binds to the myosin, which weakens the attachment between actin-myosin filaments, in turn allowing the release of actin and the break of the cross bridge. If the level of ATP is low, it may result in a contracture.

Myosin heads, which are involved in the formation of the cross bridges, have different characteristics in slow-twitch and fast-twitch muscle fibers. In fast-twitch muscle fibers, formation of the cross bridges between actin and myosin filaments occurs faster because of the higher ATPase activity of myosin, and also the binding capacity of their binding sites are significantly high. Following contraction, Ca-ions are transported back to the sarcoplasmic reticulum by active transport, and troponin C returns to its resting state, so the muscles are able to relax.

Fast strokes demand a great deal of ATP molecules, which challenges the metabolic capacity of the body. To create significant force, more cross bridges need to be formed, whereas fast movements require cyclic changes of cross bridges and high amounts of ATP. Thus, fast-twitch muscle fibers show high ATPase activity, which was described for the first time by a Hungarian scientist, Mihály Bárány. Slow muscle movements require fewer cross bridges to be formed in a given time frame, reducing the ATP demand. This explains why huge amounts of ATP are required by maximal velocity movements, and why lower amounts of ATP are necessary for maximal force movements and much less for endurance movements. This topic will be further discussed in the next chapters.

2.1.1 Types of Contractions

There are three types of muscle contraction: concentric, isometric, and eccentric. Labeling eccentric contraction as "contraction" may be a little misleading, since the length of the sarcomere increases during this type of contraction. Thus in this context contraction does not necessary imply shortening (Table 2.1).

Table 2.1. Types of contraction

−

In a concentric contraction, the force generated by the muscle is less than the muscle's maximum, and the muscle begins to shorten. This type of contraction is widely known as muscle contraction. It requires more energy compared to the other two types, but this contraction generates the least force.

−

An isometric contraction generates force without changing the length of the muscle, and no mechanical work is done since the muscle does not shorten. However, this type of contraction requires high amounts of energy because of the force generated by the muscle. This force is equal to the external load, thus the length of the muscle does not change.

−

In an eccentric contraction, the external force on the muscle is greater than the force that the muscle can generate, thus the muscle is forced to lengthen due to the high external load. The maximal force generated by the muscle is the highest; however, the energy consumption is the lowest.

Comparison of maximal force generation in concentric, isometric, and eccentric contractions show the following ranking: eccentric   >   isometric   >   concentric. This ranking can be explained by muscle-tendon characteristics.

Archibald V. Hill is the only scientist who received a Noble-prize for his work done on sport-related research: the mechanical work in muscles. Hill's three-element model is a representation of the muscle mechanical response. The model is constituted by a contractile element, a series element, and a parallel element (Fig. 2.7). The contractile element comes from the force generated by the actin and myosin myofibrils cross bridges. The series element represents the tendons, which are extensile but as much as muscles. The parallel element represents the passive force of the connective tissues such as fascia, membranes (epimysium, perimysium, endomysium), titin, and nebulin. In concentric muscle the force is generated collectively by the contractile element and at less extent the parallel element, while isometric muscle contraction involves the full contribution of the parallel element.

Fig. 2.7

Fig. 2.7. Hill's three-element model of muscle contraction. Force is generated by the contractile element, while the elastic elements store the energy.

In an eccentric contraction, the external force on the muscle is greater than the force that the muscle can generate, thus the series elastic elements are also forced to lengthen due to the high external load. This mechanical energy can be reclaimed during contraction, which provides a higher force. The model in Fig. 2.7 is a simplified explanation of why the different muscle contraction types produce different amounts of maximal force (Fig. 2.8).

Fig. 2.8

Fig. 2.8. Force-velocity relationship. A.V. Hill's force-velocity curve shows that the speed at which a muscle changes length also affects the force it can generate. The shortening velocity increases as the force declines, and so increasing force results in the decline of shortening velocity. If the force further increases the muscle is not able to shorten further; it contracts isometrically. If the external force on the muscle is greater than the force that the muscle can generate, the velocity turns to negative, in the case of eccentric muscle contraction.

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Fundamentals of Strength Training

Zsolt Radák , in The Physiology of Physical Training, 2018

Quick-Release Contractions

This method combines isometric and concentric contractions. At the beginning of exercises there is a 3–5   s isometric contraction to increase muscle tension; at a given joint angle contractile elements contract and lengthen elastic elements, thus during contraction the muscle contracts at a high speed. Several motor units are recruited in this way, thus this type of exercise improves neuromuscular coordination. Fast fibers are fatigable, thus this type of exercise prefers low repetitions and enough resting between sets. To carry out these exercises one needs a training partner or a special machine, since isometric contractions need to be executed with maximal intensity or close to it. Thus, it is recommended for professional athletes.

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The head, neck and trunk

NIGEL PALASTANGA BA, MA, MCSP, DMS, DipTP , ... ROGER SOAMES BSc, PhD , in Anatomy and Human Movement (Second Edition), 1994

Internal oblique (obliquus internus abdominis) (Fig. 6.25)

The internal oblique muscle lies deep to the external oblique, and is the middle of the three sheets of abdominal muscles. The muscle fibres arise from the lateral two-thirds of the inguinal ligament, the anterior two-thirds of the intermediate line of the iliac crest, and from the thoracolumbar fascia (see Fig. 6.00). From this attachment the fibres fan outwards with the most posterior fibres passing almost vertically to attach to the inferior borders of the lower four ribs. The more anterior and lower fibres pass upwards and medially, giving way to an aponeurosis along a line extending downwards and medially from the tenth costal cartilage to the body of the pubis. The aponeurosis has a complex involvement in the formation of the rectus sheath (see p. 644) before interlacing with that of the opposite side at the linea alba. That part of the muscle arising from the inguinal ligament passes medially and downwards, blending with the lower part of transversus abdominis to form the conjoint tendon which attaches to the pubic crest and pecten pubis. A few fibres from the inferomedial part of the muscle pass along the spermatic cord to form the cremaster muscle (see p. 653).

Nerve supply

The internal oblique is supplied by the anterior primary rami of the lower six thoracic nerves (T7 to T22) and also the first lumbar nerve (L1).

Action

Flexion of the trunk is produced by concentric contraction of the external oblique, internal oblique and the rectus abdominis of both sides. If the rib cage becomes the fixed point then these same muscles can lift the anterior part of the pelvis and alter the degree of pelvic tilt. This latter action has a significant effect in decreasing the lumbar lordosis, and as such is advocated by some in the management of low back pain. These muscles are also involved in rotation and lateral flexion of the trunk, as well as in general functional activities involving the abdomen which are discussed later (see p. 669).

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