Understanding Neurophysiological Factors in Effective Stretching Techniques

Neurophysiological Properties of Skeletal Muscle

A muscle's reaction to stretch and the success of stretching therapies are also influenced by the neurophysiological characteristics of the muscle tendon unit. Specifically, the Golgi tendon organ (GTO) and the muscle spindle are two sensory organs of muscle-tendon units that are mechanoreceptors that provide the central nervous system with information about the physical environment within the muscle-tendon unit. This knowledge frequently causes muscular reactions that could affect how beneficial a stretch is.

Spindle of Muscle

The primary sensory organ of muscle, the muscle spindle, is responsive to rapid, continuous (tonic) stretch. Muscle spindles are primarily responsible for detecting and transmitting information on changes in muscle length and their rate of change. Afferent sensory fiber terminals, efferent motor fiber endings, and specialized muscle fibers known as intrafusal fibers make up muscle spindles, which are tiny, enclosed sensors. The extrafusal muscle fibers that make up a skeletal muscle's major body are separated from and parallel to the bundles of intrafusal muscle fibers. When a muscle is stretched, intrafusal fibers are also strained since they are connected to extrafusal muscle fibers at their ends. Even intrafusal muscle fibers, contraction is limited to the ends (polar regions) and not the middle (equatorial region). As a result, when an intranasal muscle fiber contracts, its central lengthening and activation of the nuclear bag and chain's sensory receptors occur.

Neuromuscular Control: Alpha and Gamma Mechanisms

Gamma motor neurons, which have small diameters, are responsible for adjusting the sensitivity of muscle spindles to detect changes in length by innervating the contractile polar areas of intrafusal muscle fibers. Extrafusal fibers are innervated by alpha motor neurons with large diameters. Based on the placement of their nuclei in the equatorial region, nuclear bag fibers and nuclear chain fibers are the two general types of intrafusal muscle fibers. Nuclear bag fibers give birth to primary (type l) afferent terminals, which detect and initiate muscle contraction in response to both brief and prolonged stretching. On the other hand, the nuclear chain fibers' secondary (type II) afferents are only responsive to prolonged stretching. The alpha or gamma motoneurons on which the primary and secondary afferents synapse are responsible for stimulating the extrafusal or intrafusal muscle fibers that correspond to them. Stretching the muscle generally is one method of stimulating these sensory afferents; another method involves contracting the intrafusal muscle fibers through the gamma efferent neural pathways.

Organ of Golgi Tendon

Situated close to the musculotendinous connections of extrafusal muscle fibers, the GTO is a sensory organ. A GTO's job is to keep an eye on variations in the muscle-tendon units' tension. These enclosed nerve terminals send sensory data through fibers that are weaved amid a tendon's collagen strands. These sensory organs are sensitive to even minute variations in tension on a muscle-tendon unit caused by active contractions during normal movement or passive stretching. Alpha motoneuron activity is inhibited and tension in the muscle-tendon unit is reduced when GTO activation signals to the spinal cord are sent when muscle tension increases. In the context of the neuromuscular system, inhibition is characterized by a reduction in neuronal activity and a change in synaptic potential, which lessens a muscle's ability to contract. The GTO was formerly believed to be a muscle protection mechanism that only reacted to extremely high levels of tension in the muscles. Since then, nevertheless, it has been demonstrated that the GTO has a low threshold for firing and that it regulates the tension in the muscle during passive stretching or the force of active muscular contractions during movement.

Stretch-Related Neurophysiological Response of Muscle

Extend reflex

The primary and secondary afferents of intrafusal muscle fibers detect changes in length when a strong or brief stretch force is applied to a muscle tendon unit. Extrafusal muscle fibers are activated by these afferent signals when they synapses with alpha motor neurons in the spinal cord. Stretch reflex is the name given to this motor reaction, which is characterized as an increase in or facilitation of active tension in the stretched muscle. The efficiency of the stretching process is believed to be compromised by this increased tension, which opposes lengthening. The opposing side of the joint's muscle(s) may experience decreased activity, or inhibition, when the stretch reflex is triggered in the muscle that is being stretched. This phenomenon, known as reciprocal inhibition, has only been observed in research with animal models thus far. A moderate, low-intensity, protracted stretch is thought to be better than a rapid, short-duration stretch in order to reduce the activation of the stretch reflex and the ensuing rise in muscular tension.

Inhibition of Autogenesis

On the other hand, if the stretch force is extended, the GTO has an inhibitory influence on the degree of muscle tension in the muscle-tendon unit in which it lies. We refer to this phenomenon as autogenic inhibition. It is believed that GTO's inhibition of a muscle's contractile components helps trigger reflexive muscle relaxation during a stretching exercise, allowing a muscle to elongate against less force. Because the GTO fires and suppresses tension in muscle, the stretch reflex is less likely to be elicited when a low-intensity, slow stretch force is applied to muscle. This is because the parallel elastic component of the muscle, the sarcomeres, can remain relaxed and lengthen. In conclusion, current research indicates that tensile stresses applied to the viscoelastic, noncontractile connective tissue within and surrounding muscle are more likely to cause improvements in muscle extensibility than to inhibit (reflexively relax) the contractile components of muscle.

Factors and Forms of Stretching Activities

The success and results of stretching therapies are determined by several crucial factors. The alignment and stabilization of the body or a body segment during stretching, the intensity, duration, speed, frequency, and mode of the stretch, and the incorporation of neuromuscular factors and functional activities into stretching programs are the determinants (parameters) of stretching, all of which are interrelated. A therapist has a wide range of alternatives for creating stretching programs that are safe, effective, and match the needs, functional goals, and abilities of several patients by adjusting the determinants of stretching interventions. The majority of studies comparing the kind, degree, length, and frequency of efficient stretching have used young, healthy individuals as their subjects.

Stretching Methods and Therapeutic Considerations

A balance of scientific evidence and sound clinical judgment by the therapist must continue to guide many decisions, especially those concerning the type, intensity, duration, and frequency of stretching, as the findings and recommendations of these studies are difficult to generalize and apply to patients with long-standing contractures or other forms of tissue restriction. Stretching exercises fall into four main categories: ballistic stretching, cyclic (intermittent) stretching, static stretching, and stretching methods based on PNF principles. Stretching in any of these ways works well to lengthen tissue and improve range of motion. The many ways that Bach can be performed manually or mechanically, passively or actively, by a therapist or on their own by a patient have led to the creation of numerous terminology that are used in the literature to characterize stretching therapies.

Stabilization and Alignment

Just as proper alignment and efficient stability are necessary for all therapeutic exercises, goniometry, and muscle testing, they are also critical components of efficient stretching.

Alignment

For the patient's comfort and stability during stretching, the right alignment or positioning of the patient in relation to the particular muscles and joints to be stretched is essential. Alignment impacts the soft tissue's baseline tension, which in turn affects the range of motion that is accessible for the joint. In addition to the alignment of the muscles and joint to be stretched, the alignment of the trunk and adjacent joints must also be considered. For instance, while the knee is flexed and the hip is extended, the rectus femoris, a muscle that connects the lumbar spine and pelvis, should be stretched efficiently by keeping the body in a neutral position. Avoid alignments that impair the necessary distance between the origin and the insertion, such as the pelvis anterior tilt, hip flexion, or abduction in our example, as efficient stretching necessitates maximizing this space. Similarly, the trunk should be upright rather than hunched when a patient self-stretches to increase shoulder flexion.

NOTE:

The following stretching exercises include specific recommendations for alignment and placement. In cases where a patient is unable to assume recommended postures due to discomfort, limited range of motion in adjacent joints, or inadequate neuromuscular control, or if their cardiopulmonary capacity is inadequate, the therapist must assess the situation critically and choose a different position.

Consistency

Stabilize (fixate) the proximal or distal attachment site of the muscle-tendon unit being extended in order to accomplish an effective stretch of a particular muscle or muscle group and related periarticular structures. The capacity to efficiently optimize the origin-insertion distance is diminished in the absence of stability, as the attachment sites are allowed to move with the tissue. While either location can be stabilized, therapists typically stabilize the proximal connection and move the distal section while performing manual stretching. During self-stretching exercises, one section may be stabilized while the other moves by the patient actively contracting their muscles or by a stationary object like a chair or doorframe. When the proximal segment moves during self-stretching, the distal connection frequently stabilizes the movement. Multiple body segment stabilization aids in preserving the ideal alignment required for a successful stretch. For instance, to prevent strain on the low back, the pelvis and lumbar spine must remain in a neutral position when the hip is extended during iliopsoas stretching. Manual contacts, belts or straps, body weight, and a solid surface like a table, wall, or floor are examples of sources of stabilization.

Stretch Intensity

The tensile force applied to soft tissue in order to elongate it determines the intensity of a stretch. It is generally accepted by academics and doctors that low load, low intensity stretching is the best approach. Compared to high-intensity stretching, low-intensity stretching is more comfortable for the patient and reduces muscular guarding, both voluntary and involuntary, allowing the patient to stay relaxed or participate in the stretching exercise. Stretching at low intensity produces the best rates of range of motion improvement without subjecting tissues which may have been weakened by immobilization to undue strain or risk of damage. It has also been demonstrated that low-intensity stretching is superior to high-intensity stretching in terms of elongating thick connective tissue, which is a major cause of chronic contractures, while causing less soft tissue injury and pain after the exercise.

Stretch Time

The length of stretch that is anticipated to be safe, effective, practical, and efficient for each scenario is one of the most crucial choices a therapist takes when choosing and executing a stretching intervention. The amount of time tissues are held in a stretched state while a stretch force is applied is referred to as the duration. The term "duration" usually refers to the length of time that a single stretch cycle is applied. If a treatment session involves multiple repetitions of a stretch cycle, the total duration of the stretch cycle, also known as the total elongation time, is represented by the cumulative time of all the stretch cycles. The number of repetitions required during a stretching session often increases with the length of a single stretch cycle.

Optimizing Stretching Parameters for Improved Flexibility

To find the most efficient combination of cycle and duration, numerous combinations have been researched. The optimal combination of single stretch time and number of stretch repetitions that results in the largest and most sustained gains in range of motion (ROM) or reduction of muscle stiffness remains unclear despite several studies conducted over several decades. In the end, the stretch time needs to be considered in relation to the intensity, frequency, and mode of the stretch. To distinguish between a stretch that is long-duration and one that is short-duration, many descriptors are employed. A long-duration stretch is characterized by terms like static, sustained, maintained, and protracted, whereas a short-duration stretch is characterized by terms like cyclic, intermittent, or ballistic. None of these descriptions have a set time period associated with them, nor is there a time frame that separates long-duration from short duration stretches.

Static Extension

A popular stretching technique is called "static stretching," in which soft tissues are stretched just over the point of tissue resistance and then maintained there for a while using a constant stretch force. The length of the static stretch might be chosen in advance or it can depend on the patient's response and tolerance during the stretch. There is a great deal of variation in defining how long a static stretch is. When either a manual stretch or a self-stretch is utilized, the phrase has been used to describe a single stretch cycle that can last anywhere from five seconds to five minutes every repetition. The duration of the static stretch might be anywhere from almost an hour to several days or weeks if a mechanical device is used.