Flexibility Training / SMR / PNF
Flexibility
Flexibility can be simply described as the ability to move a joint through its complete range of motion (ROM). ROM of a joint is dictated by the normal extensibility of all soft tissues surrounding it.
Human Movement System
The HMS is composed of the skeletal, nervous, and muscular systems: If one segment of the kinetic chain is misaligned and not functioning properly, predictable patterns of dysfunction develop.
Kinetic Chain = linking of bony segments of the body via a series of joints. Misalignment’s can = dysfunctions/imbalances.
No consistent link between flexibility training and:
Reduction in musculotendinous injury.
Prevention of lower back pain.
Delayed onset muscle soreness (DOMS)
Muscle Imbalance Can Result In
1. Altered Reciprocal Inhibition
RI = Relaxation of a muscle when its opposing muscle (antagonist) is contracted.
Caused by a tight agonist, which inhibits its functional antagonist
E.G. Hip flexor muscle group AND glutes in running
2. Synergistic Dominance
Occurs when synergists (assister muscles) take over function for a weak or inhibited prime mover
E.G. Overhead squat
Mechanoreceptors
A mechanoreceptor is a sensory receptor that responds to mechanical pressure or distortion.
1. Muscle Spindles
Major sensory organ of the muscle located within muscle fibres
Sensitive to change in length and rate of length change
When a muscle is lengthened, the spindles are also stretched = this causes the muscle to contract in order to prevent damage.
This information is transmitted to the nervous system, exciting the alpha motor neuron and thus causing the muscle fibers to contract. This can
result in spasm in that area of the muscle or a feeling of tightness.
2. Golgi Tendon Organs
Located within the musculo-tendinous junction -> Where the muscle and the tendon meet
Sensitive to changes in muscular tension and rate of tension change: When muscle tension reaches a certain threshold (after a fatiguing contraction of the muscle) the GTO activity increases substantially and it’s response is to cause relaxation of the agonist muscle and excitement of the antagonist muscle. Also a defensive mechanism to protect muscle/tissue against sudden load.
Proper stimulation can cause relaxation in an overactive muscle -> Autogenic inhibition reflex is a sudden relaxation of muscle upon development of high tension.
PNF Stretching: Proprioceptive Neuromuscular Facilitation
Incorporates combinations of concentric, eccentric and isometric contractions, and passive stretching
Relaxation via muscle inhibition of the agonist muscle group to increase ROM – Autogenic inhibition – Reciprocal inhibition
Contraction should be at least 20% MVC (maximal voluntary contraction) for 6 secs, 10-30 sec assisted stretch, 1 – 2 days per week (ACSM)
Research suggests: Most effective method to increase ROM (particularly short term) + Safe and time efficient + Minimum of one rep twice per week to augment ROM (Sharman, Cresswell and Riek, 2006)
Theoretical mechanisms underpinning PNF (see review by Hindle et al. 2012, which is a required reading):
1. Autogenic Inhibition
This occurs in a contracted or stretched muscle and results in a decrease in the excitability of this muscle(s) because of inhibitory signals sent from the golgi tendon organs (GTOs) of the same muscle (Sharman et al., 2006). Autogenic inhibition relies on the body’s self-regulatory mechanisms of the GTOs in order to protect structures.
2. Reciprocal Inhibition
This occurs in the target muscle when the opposing muscle is contracted voluntarily in the form of decreased neural activity in the target muscle (Sharman, 2006). This inhibition of the target muscle, along with the concentric contraction of the opposing muscle, allows the muscle fibres of the target muscle to elongate even further, creating a greater stretching force a larger inhibitory influence on the target muscle (Etnyre and Abraham, 1986; Sharman et al., 2006).
3. Stress Relaxation
This occurs when the musculotendinous unit (MTU; i.e. the muscles and the connected tendons), is under a constant stress (Sharman et al., 2006). Subsequently, the force generated by the viscous material is decreased as it resists the elongation stimulus that stretching causes within the MTU. Since the viscous material loses its ability to resist the stretch over time, the MTU slowly increases in length; this is referred to as “creep” of the MTU (Sharman et al., 2006).
4. Gate Control Theory
This occurs when two kinds of stimuli, such as pain and pressure, activate their respective receptors at the same time (Mazzullo, 1978). When a muscle is stretched beyond its active ROM, a large force is sensed (and seen as potentially damaging), which invites the GTOs to activate in an effort to inhibit the force and prevent injury. In PNF stretching when the muscles and tendons are stretched and then contracted at this elongated length, this contraction decreases the nociception, or pain that is sensed, and therefore there is a reduced inhibition, produced by the GTOs. The GTOs adapt to the increase in length and force threshold, which allow for greater force production.
4 techniques that underpin PNF stretching:
1. Hold-Relax Technique: Autogenic Inhibition
Begin with a passive stretch of the target muscle (instructor lead) held at the point of mild discomfort for ~10 seconds;
The instructor then applies force to the target muscle(s) and instructs the client to hold the position (e.g. if the goal is to stretch the hamstrings, the instructor would aim to move the leg into hip flexion and knee extension);
The client isometrically contracts and resists the instructor’s force for ~6 seconds at an intensity of at least 20% MVC;
The client relaxes as the instructor passively stretches the client deeper in the ROM for ~20-30 seconds (do not go beyond mild discomfort);
Cycle may be repeated until desired ROM is achieved.
Which theoretical mechanism(s) is most likely responsible for increasing ROM with this technique? Autogenic Inhibition
2. Contract-Relax Technique: Autogenic Inhibition
Begin with a passive stretch of the target muscle (instructor lead) held at the point of mild discomfort for ~10 seconds;
The instructor then applies force to the target muscle(s) and instructs the client to hold the position (e.g. if the goal is to stretch the hamstrings, the instructor would aim to move the leg into hip flexion and knee extension);
The client then concentrically contracts the target muscle(s) through the joint ROM for ~6 seconds at an intensity of at least 20% MVC;
The client relaxes as the instructor passively stretches the client deeper in the ROM for ~20-30 seconds (do not go beyond mild discomfort);
Cycle may be repeated until desired ROM is achieved.
Which theoretical mechanism(s) is most likely responsible for increasing ROM with this technique? Autogenic inhibition
3. Hold-relax with (actually followed by) assisting antagonist contraction during stretch: Reciprocal Inhibation
Perform the hold-relax technique (as described for 1. above up until the isometric contraction is completed)
The instructor then asks the client to actively contract the opposing muscle group (e.g., hip flexors if stretching the hamstring group) to assist the instructor to take the stretch through a greater range of motion.
Which theoretical mechanism(s) is most likely responsible for increasing ROM with this technique? Reciprocal Inhibation
4. Contract-relax with (actually followed by) assisting antagonist contraction during stretch: Reciprocal Inhibation
Perform the contract-relax exercise (as described for 2. above), followed by the client actively contracting the opposing muscle group (e.g., hip flexors if stretching the hamstring group) to assist the instructor take the stretch through a greater range of motion.
Which theoretical mechanism(s) is most likely responsible for increasing ROM with this technique? Reciprocal Inhibation
Study: Effects of proprioceptive neuromuscular facilitation stretching and static stretching on maximal voluntary contraction.
This study was undertaken to investigate and compare the effects of proprioceptive neuromuscular facilitation (PNF) stretching and static stretching on maximal voluntary contraction (MVC). Thirteen male university students (age, 20 ± 1 years; height, 172.2 ± 4.6 cm; weight, 68.4 ± 6.7 kg; mean ± SD) completed 3 different conditions on 3 nonconsecutive days in randomized order: static stretching (SS), PNF stretching (PNF), and no stretching (control, CON). Each condition consisted of a 5-minute rest accompanied by one of the following activities: (a) control, (b) SS, or (c) PNF stretching. The hip flexion range of motion (ROM) was evaluated immediately before and after the activity. The MVC of knee flexion was then measured. Surface electromyography was recorded from the biceps femoris and vastus lateralis muscles during MVC tests and stretching. Although increases in ROM were significantly greater after PNF than after SS (p < 0.01), the decreases in MVC were similar between the 2 treatments. These results suggest that, although PNF stretching increases ROM more than SS, PNF stretching and SS is detrimental to isometric maximal strength. NOTE: Timing of MVC after stretching may have been imedietely after stretching which may have explained why isometric strength decreased.
SMR: Self-Myofascial Release
Fascia
Connective tissue fibers primarily made of a collagen that form sheets beneath the skin which attach, stabilize, enclose and separate muscles and other internal organs.
Assists in releasing knots by stimulating the Golgi tendon organ
Thought to decrease pain by increasing soft tissue extensibility, reducing muscle spasms and breaking up tissue adhesions
Creates autogenic inhibition: By applying a force to the muscle/fascia that is ‘tight or has knots’ a reflex-relaxation occurs via those GTO in response to the high tension that’s being applied.
Also suggested before static
Special Case – Myofascial Pain Syndrome
A musculoskeletal condition characterised by regional pain and muscle tenderness associated with myofascial trigger points (Desai et al. 2013);
Has the potential to result in a restricted ROM and an increased sensitivity to stretching (Lavelle et al. 2007);
Palpable taut band of muscle or fascia.
Treatment Options:
(Lavelle et al. 2007)
1. Spray (freeze) and stretch (“single most effective treatment”)
Passive stretching of the affected muscle after application of sprayed vapocoolant
Spray applied to entire muscle
Pressure applied resulting in passive stretch
Repeat multiple sprays over entire muscle whilst maintaining passive stretch
Repeat until full ROM is restored (max 3 reps).
2. Physical therapy (refer to physio)
3. Transcutaneous electrical stimulation (TENS) – Placing electrodes on trigger points or along areas of referred pain
4. Ultrasound: Vibration energy
5. Massage
6. Ischemic compression therapy (trigger release)
The application of a deep, sustained pressure to an active trigger point is believed to produce ischemia and release the taught band of muscle or fascia because its starving the muscle of O2 so it causes a release.
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