DPT-407- Exercise Prescription: Flexibility

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There are a number of definitions that can be used when referring to flexibility:

  • a measure of the range of motion (ROM) available at a joint or a group of joints (Cotton, 1997) 
  • the ability to move the joints in the needed range of motion demanded by the sport (Kreamer and Gomez, 2001)
  • the ability to readily adapt to changes in position or alignment; may be expressed as normal, limited, or excessive (Kendall et al, 1993)


  • increased range of motion
  • reduced muscle tension and increased physical and mental relaxation
  • reduced risk of joint sprains or muscle strains
  • reduced risk of back problems
  • decreased muscular soreness (DOMs) associated with other exercise activities
  • decreased muscle viscosity, causing contractions to be easier and smoother
  • improved co-ordination by allowing for greater ease of movement
  • improvement and development of body awareness
  • improved capability for circulation and air exchange
  • improvements in posture

Adapted from Alter, 1998, and Fredette, 1998

Perhaps, a further benefit that could be added to this list is the opportunity that flexibility work brings for interaction between the client and trainer. Those forms of passive stretching that rely on the personal trainer directing, and physically moving the client into stretch positions, demand a great deal of the trainers communication and general client care skills. This therefore, is an opportunity to win client confidence and to demonstrate skills.

Factors Affecting Flexibility


Young people are normally more flexible than older people (Wilmore et al, 1978). Babies and infants are very flexible and start to lose this natural flexibility as soon as they start to walk (when the joints become weight-bearing and need more stability). As we get older, muscle contractility remains, whilst elasticity is lost, resulting in tighter, stiffer muscles. There is also a reduction in activity levels as we age, which will cause a decrease in flexibility.


Studies have shown females to be more flexible than males in most joints and to remain so throughout adult life (Getchell, 1979). The reasons for this are uncertain, but may be attributed to the structural or anatomical differences or different activities and training experiences of boys and girls early in life. 

During pregnancy and in the post-natal period, women produce excess amounts of a hormone called relaxin to assist the birth process. The effects of relaxin are not restricted to solely the pelvic area, but act throughout the body, allowing greater flexibility than normal. Small levels are relaxin are constantly present, and will fluctuate slightly throughout a normal menstrual cycle.


An increase in temperature due to either direct heat or the weather can increase the range of motion and elasticity of muscle and tendons. Conversely, a decrease in temperature can result in a decrease in flexibility of as much as 20% (Wear, 1963).

Exercise and resistance training:

Active people tend to be more flexible than those with a sedentary lifestyle (Getchell, 1979). This is especially the case if the activity involves stretching exercises. Although a comprehensive resistance training programme may increase ROM (Leighton, 1964), resistance training exercises with a limited ROM and higher loads may actually decrease ROM (deVries, 1974).


Flexibility can be an inherited characteristic, as well as an acquired one. Some people are born with a naturally excessive ROM. This can create a greater potential for injury (i.e. joint dislocation) and it may be necessary to concentrate on strengthening the muscles acting over the joint in order to increase stability.


Female clients who constantly wear high heels may find that the muscles of the lower limb (gastrocnemius, soleus, peroneals) adaptively shorten over a period of time.

Physiology of Stretching

There are two proprioceptors (sensory nerves) that play an important role in protection of the muscle and connective tissue and thus in stretching. These are called muscle spindles and Golgi Tendon Organs (GTOs).

Muscle spindles are located within muscle fibres and their main function is to send messages back from the muscle to the central nervous system to inform about its state of stretch. If the muscle is stretched, distortion of the muscle spindle causes the myotatic reflex (automatic contraction) to come into play, thus avoiding damage through over-stretching. This muscle spindle activation (muscle contraction) is felt as the tension of the stretch. The amount and rate of contraction elicited from the stretch reflex are proportional to the amount and rate of stretching. Hence, the faster and more forceful the stretch, the faster and more forceful the reflex contraction of the stretched muscle; therefore, the greater the likelihood of the muscle tearing (particularly in an untrained muscle). 

GTOs are sensory nerves located near the musculotendinous junction. They are activated by a contraction in a muscle and are there to prevent an excessive tension occurring within the muscle, or the tendon of that muscle. In contrast to the muscle spindles, stimulation of the GTOs will cause a reflex relaxation of that muscle (the inverse stretch reflex). This resulting relaxation is important for certain stretches because the inhibition of the muscle in which they are located, will allow muscle fibres to lengthen and stretch further.

Relaxation that occurs in the same muscle because of GTO activation is called autogenic inhibition (Condon et al, 1987). This is achieved by contracting a muscle immediately before passively stretching it. The contraction will increase GTO activation, thus increasing the subsequent muscle relaxation during the stretch. Reciprocal inhibition is the relaxing effect that occurs in a muscle when the antagonist is contracting (Condon et al, 1987). This occurs to allow an easier contraction of the antagonist. Hence contracting the antagonistic muscle will allow for a greater stretch in the muscle being elongated.

The various forms of passive stretching to be discussed in detail in this section rely on the exploitation of both the autogenic and reciprocal inhibition mechanisms to enable the trainer to move and encourage the client into a greater range of motion. 

Methods of Stretching

There are several methods of stretching muscles:

Method of StretchingType of StretchingExample
Active stretchingStaticDynamicBallisticStanding chest stretchLeg swingsToe touches
Passive stretchingStaticPNFWall chest stretchSupine partner hamstring Stretch


Active stretching is accomplished using antagonist muscles and without assistance from an external force or object (Alter, 1998). It involves actively contracting one muscle or muscle group in order to stretch its opposing muscle group. For example, pectorals actively contract to stretch posterior deltoids and tibialis anterior actively contracts to stretch gastrocnemius. This type of stretching is very important for athletes, because it is an essential aspect of dynamic flexibility and thus has a greater correlation with sports performance than passive stretching (Iashvili, 1983).


This is where another body part or external factor, such as a wall or a partner, is used to facilitate the stretch. For example, a lying hamstring stretch where the hands are held behind the thigh or on the calf. This method is used by physiotherapists to increase joint range and muscle length. A trainer partner can assist by gently pressing parts of the subject’s body through full range. Great care and communication is required between partners using this method and so it is not recommended for beginners. Applying the external force incorrectly, excessively or too quickly may cause the stretch reflex to initiate, perhaps causing injury. However, it can be beneficial if the agonist is too weak and will provide a greater ROM than active stretching (Alter, 1998). 

Types of Stretch


This form of stretching involves quick, repetitive bouncing or bobbing actions. It is undertaken in order to increase the stretch beyond the muscle’s normal range using momentum and body weight. It is generally considered unacceptable for the average exerciser, due to the intra-muscular damage that may occur as a result of the stretch reflex. These stretching exercises can produce muscle soreness and even losses in resilience and elasticity. However, they are sometimes necessary as a more radical method of stretching adhesions and stubborn fibrous tissue in physiotherapy and rehabilitation.


This is similar to ballistic stretching, however, the limb movements do not end with bouncing or jerky movements, but instead, are performed under control (Alter, 1998). These stretches should mimic the movements of the following sport or activity and act as a kind of rehearsal. 

  • perform 10-15 repetitions of each stretch under control, gradually increasing the ROM

Static maintenance:

Static maintenance stretching is where the muscle is taken to the end of its normal range and held without bouncing. These are short stretches, held for 10-15 seconds (Moffat, 1988), and are used to maintain the normal length of the muscle. Following repeated contractions during exercise, the muscle becomes shorter and thicker and a maintenance stretch is used to return the muscle to its normal length.

  • take the stretch to the point of bind, maintaining good alignment and posture
  • hold for 10-15 seconds
  • repeat the stretch if desired

Static developmental:

These stretches are used in flexibility training to develop the length of the fibres themselves, thereby increasing range of movement at a joint. The following guidelines should be observed:

  • take the stretch to the point of bind, maintaining good alignment and posture
  • hold for 10 or more seconds, until the tension within the muscle has reduced 
  • relax and passively increase the ROM of the stretch until tension is felt again
  • again hold for 10 or more seconds, until the tension within the muscle has reduced
  • again increase the ROM of the stretch until tension is felt again
  • hold until the tension reduces, then slowly return the limb to its normal position
  • repeat the stretch if desired

Muscle energy techniques (METs):

MET is a form of passive stretching from the world of osteopathic technique. According to Chaitow (1996), MET, “…targets the soft tissues primarily, although it also makes a major contribution towards joint mobilisation…”. The technique itself evolved from the rehabilitative technique known as proprioceptive neuromuscular facilitation (PNF), developed by Herman Kabat in the late 1940s and early 1950s. Like PNF techniques, MET commonly uses an isometric contraction of the target muscle before the stretch is applied. MET, unlike PNF (which uses near maximal muscle contractions), uses only minimal force during the isometric phase. The stretching phase is generally, though not always, done passively.     

Perhaps the main form in which MET is applied is post isometric relaxation (PIR). 

The following is an example of a hamstring stretch, utilising PIR:

  • under the trainer’s instruction the client should adopt a comfortable and manageable position
  • the trainer explains to the client what is to be done and how the technique is to be carried out
  • the trainer lifts the leg into hip flexion and takes the passive stretch to the point of bind, maintaining good alignment and posture throughout
  • the trainer holds the limb at the point of bind for 10 or more seconds, until the tension within the muscle has reduced
  • the client performs an isometric contraction of 20-30% maximum force and holds this for 6-8 seconds. The trainer should direct the client to begin slowly and progressively build the level of contraction
  • the client relaxes (this can be aided by a deep inhalation followed by an exhalation as the stretch is administered) while the trainer passively increases the ROM of the stretch (increase hip flexion) until tension is felt again
  • this cycle is repeated 2-3 times, always finishing with a stretch and not a contraction
  • the trainer slowly returns the limb to its normal position

By isometrically contracting the target muscle (hamstrings in the above example) against the trainer, the client will activate the GTOs in that muscle and stimulate an autogenic inhibition response. This will create the necessary level of relaxation in that muscle to allow it to be stretched.  

Since, the technique is very hands on and necessitates the trainer and client communicating clearly to create a stretch, passive stretching using PIR provides an excellent medium for establishing a rapport with the client.   

When to apply:

PIR based techniques are best suited to the post-exercise period. This will allow the trainer to stretch out the muscles worked during the main session and provides a relaxing ‘wind down’ for the client after their exertions. A good passive stretching session, performed by a competent trainer really embodies the personal, one-to-one nature of personal training     

Safety issues:

Safety should always be a priority for both the client and the trainer. An awareness of body mechanics and posture are vital for the trainer throughout the PIR protocols, but particularly during the isometric contraction phase. Consequently, the trainer should plan carefully and communicate clearly and freely with the client.  

Trainer safety: the trainer may be at risk of injury if they do not take care of themselves during the application of PIR. However, by paying attention to their body mechanics and posture, the risk of injury can be virtually eliminated. Some useful tips for the trainer include:

  • if standing, pay close attention to the legs and feet. A wide stance should be used to maintain balance and stability, especially when resisting the isometric contraction of the client
  • be conscious of keeping the spine lengthened, rather than flexing and collapsing in on yourself. This will reduce the stress imposed on the spine
  • maintain a neutral lumbar spine. This will again reduce the stresses imposed on the back
  • brace the abdominals to prevent overarching of the spine
  • avoid unnecessary twisting or bending. Instead, the trainer should try and get the client to move to accommodate them
  • always try to use the trunk rather than the arms to resist the client’s isometric contractions. For instance, during the hamstring stretch the trainer should block the client’s contraction with their shoulder rather than the arm
  • always control the strength of the client’s contraction. The client should be instructed to “slowly build” the level of the contraction
  • remain in control at all times. For instance, the client should only contract the target muscles on the trainer’s instruction. In this way, the trainer will be able to prepare, and stabilise themselves effectively 

Client safety: the client should be encouraged to play an active role in the application of PIR techniques. They should be encouraged to develop an awareness of the muscles being targeted. Clients should also provide as much feedback as possible; this might include what they are feeling during PIR stretches or their levels of fatigue. To ensure safety clients must:

  • ask the trainer to stop if they experience pain at anytime. If the client does experience pain, the trainer should try repositioning the limb or ask the client to exert less force during the isometric contraction. If pain persists, do not continue until the cause of pain has been determined
  • follow the trainers instruction at all times
  • communicate freely with the trainer

When to Stretch

Although always advocated after a warm-up, stretching can be performed at any time of the day, appropriate to the client. Clients can be advised to stretch at home, watching TV, or at the office, in order to balance out periods of immobility in positions of poor posture. 

Stretching should form an integral part of the warm-up and cool-down. Static stretching in the warm-up has not been shown to decrease the incidence of injury, but may be selectively included in a ‘corrective’ form. An example of corrective static stretching would be to relax hypertonic pectorals when training the upper back (rhomboids and middle trapezius), for a more effective ROM during retraction. Corrective static stretching should only be used selectively on hypertonic muscles. 

Dynamic stretching can be more easily prescribed as part of the warm-up, using exercises that will mimic the general movement of the following session. Corrective static and dynamic stretches should be performed after some kind of pulse raising/temperature rising warm-up (Alter, 1998). In the post-training, cool-down part of the session, some kind of static stretching is advised. This may be static maintenance, static developmental, or a form of PNF stretch.

Warm UpCool Down
Static StretchingStatic Stretching
Dynamic StretchingDevelopmental
Non Ballistic End Range StretchingMuscle Energy Techniques (METs)

As well as setting specific and realistic flexibility goals, there are a number of guidelines an exercise specialist should follow for flexibility training (adapted and expanded from Alter, 1998, Fredette, 1998, and Holcomb, 2000):

Alter (1998) suggests some additional guidelines when undertaking a stretching programme:

  • wear loose, comfortable and appropriate clothing
  • remove all jewellery and discard any chewing gum
  • choose a clean, quiet place with a non-slip surface, preferably a firm mat

Following the guidelines above will be sufficient for most, but there are still a number of precautions when undertaking flexibility training (adapted and expanded from Fredette, 1998, and Holcomb, 2000).

For most individuals stretching will provide many of the benefits previously mentioned. However, there are certain individuals or groups for whom flexibility training may be likely to cause injury, or where the possible concerns outweigh the potential benefits. The table below lists the reasons why flexibility training (stretching) may be contraindicated (adapted from Alter, 1998, Fredette, 1998, and Minor and Kay, 1997).

Additional Videos:


Alter, M. J. (1998). Sport Stretch. 2nd Edition. Human Kinetics.

Chaitow. L. (2003). Muscle Energy Techniques. 2nd ed. Elsevier Science.

Condon, S. M. and Hutton, R. S. (1987). Soleus muscle electromyographic activity and ankle dorsiflexion range of motion during four stretching procedures. Phys. Ther., 60, 24-30.

Cotton, R. T. (1997). Testing and Evaluation. In ACE Personal Trainer Manual (R. T. Cotton, ed.) pp. 170-205, Ace Publishing.

deVries, H. A. (1974). Physiology of Exercise for Physical Education and Athletics. Brown.

Fredette, D. M. (1998) Exercise Recommendations for Flexibility and Range of Motion In ACSM’s Resource Manual for Guidelines for Testing and Prescription (J. L. Roitman ed.). pp. 456-465. 3rd Edition. Williams and Wilkins.

Getchell, B. (1979). Physical Fitness: A Way of Life. Wiley.

Kendall, F. P., McCreary, E. K. and Provance, P. G. (1993) Muscles testing and Function. 4th Edition, Lippinncott Williams & Wilkins.

Holcomb, W. R. (2000). Stretching and Warm-Up. In Essentials of strength training and conditioning (Baechle, T. R. and Earle, R. W. eds.). pp. 321-342. Human Kinetics.

Iashvili, A. V. (1983). Active and passive flexibility in athletes specializing in different sports. Soviet Sports Review18 (1), 30-32.

Kabat, H. (1958). Proprioceptive Facilitation in Therapeutic Exercises. In Therapeutic Exercises (Licht, M. ed.). pp. 150-164. Waverly Press.

Kreamer, W. J. and Gomez, A. L. (2001). Establishing a Solid Fitness Base In High-Performance Sports Conditioning(Foran, B. ed.). pp. 3-18, Human Kinetics.

Leighton, J. R. (1964). A Study of the Effect of Progresive Weight Training on Flexibility. J. Assoc. Phys. Ment. Rehab., 18, 101.

Minor, M. A. and Kay, D. R. (1997). Arthritis. In ACSM’s Exercise Management for Persons with Chronic Diseases and Disabilities (Durstine, J. L. ed.). pp. 149-152. Human Kinetics.

Moffat, R. J. (1988). Strength and Flexiblity Considerations for Exercise Prescription. In Resource Manual for ACSM Guidelines for Exercise Testing and Prescription (Blair, S.N., Painter, P. and Pate, R. eds.). pp. 456-465. Lea & Febriger.

Wear, C. (1963). Relationshipss of flexibility measurements to length of body segments. Research Quarterly34, 234-238.

Wilmore, J. H., Parr, R. B., Girandola, R. N., Ward, P., Vodak, P. A., Barstow, T. J., Pipes, T. V., Romero, G. T., and Leslie, P. (1978). Physiological Alterations Consequent to Circuit Weight Training. Med. Sci. Sports10, 79-84.

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