Fitness Training Expert aims to provide top quality fitness training advice, exercise information and educational resources for all fitness enthusiasts.  Expert fitness advice SEARCH THIS SITE FACEBOOK BRIDGEFIT ARTICLES   Stretching and Flexibility Training This article is an adaptation of research done as part of my dissertation in 2002 with the inclusion of more recent information and journal references relating to stretching and flexibility. Flexibility is defined as the range of motion (ROM) available at a joint or group of joints and stretching is the means of increasing this. There are three main methods of stretching which one may use. These are static, dynamic and proprioceptive neuromuscular facilitation (PNF). There are many researchers who have shown these to be effective methods of increasing flexibility, such as Moore and Hutton (1980), Osternig et al (1990), Sullivan et al (1992), Wallin et al (1985), Wyon et al (2009).     Anatomy and Physiological Function Muscles are connected to bones via tendons. This can be termed the musculo- tendinous unit. This has been represented as a model containing three components. These are the Parallel Elastic Component (PEC), Series Elastic Component (SEC) and Contractile Component (CC). The PEC is responsible for resting tension (passive) within a muscle. As the muscle is stretched the tension within the PEC increases (similar in concept to a bungee cord).  The SEC also contributes to this elasticity. The CC is thought to consist of the Actin and Myosin filaments of muscle and their cross bridges which serve to generate tension. This is an overly simplified synopsis of the musculo-tendinous unit, and I would encourage anyone interested in some challenging reading to have a look at Science of Flexibility by Michael J Alter. Muscles contain time dependant mechanical properties. When muscle is stretched and held at a constant length the tension decreases; known as stress relaxation (Taylor et al, 1990). The viscoelastic behaviour is dependant on force and duration of stretch (Kubo et al, 2001). Lower force and longer duration stretching favour more permanent deformation. Rosenbaum and Hennig (1995) suggest that the degree of stretch velocity a muscle receives is detected by the muscle spindle. This is a primary stretch receptor running parallel to the skeletal muscle fibres. The degree of muscle tension is also monitored by the Golgi Tendon organs, located at the musculo-tendinous junctions. They are thought to have an autogenic inhibitory response. This is where contracting muscle is stopped in response to too great a stretch of the opposing muscle. The opposing muscle also contracts to limit the stretch. For example if the Hamstrings were stretched too fast, the quadriceps would relax and the hamstrings would contract. Again this is a very simplified overview of the nervous systems responses to stretching and I would strongly recommend Stretching Scientifically: A Guide to Flexibility Training by Thomas J Kurz for more information. Stretching Methods Static Stretching Static stretching is when one takes their limb to its end range of motion, the point at where the muscle stretch is felt. The body is then held in this position for a designated time period. For example standing next to a table and placing one straight leg on this table, leaning forwards from the hip with an anterior pelvic tilt until the hamstring muscle stretch is felt. This stretch is entirely passive, using muscular relaxation to stretch the muscle. Static stretching can also involve an active component, for example lying in the supine position on the floor, raising one knee up to face the ceiling and from there contracting the quadriceps, extending the leg actively until a stretch is felt in the hamstring. Way back in 1976, Atha and Wheatley showed that most of the change in flexibility occurs during the first four repetitions of a stretch. This was also supported by Taylor et al (1990) who found four stretches of 30 seconds duration to be effective. More recently Ryan et al (2009) have found that two repetitions of a 30 second stretch significantly reduced stiffness of the musculo-tendinous unit, and did not decrease any further following a third and fourth stretch. One will find other studies indicating no additional benefit in stretching for longer than 30 seconds. Dynamic Stretching Dynamic stretching is a process where one would move their limb through a controlled range of motion repetitively. Kurz (1996) described up to 4 sets of 10 repetitions as being the most effective method, with specific emphasis on stopping repetitions when one reaches their maximum ROM for that set. The rationale was that continuing to take ones limb to the same end ROM for multiple repetitions was merely engraining this range within the body, and preventing further progress. Bandy et al (1998) on comparing dynamic stretching to static stretching found static stretching to give the greatest improvement in ROM. My own research showed static stretching to increase ROM by 11.29% compared to an 8.44% increase for dynamic stretching. PNF Stretching Proprioceptive neuromuscular facilitation! So termed due to the effect this method has on a variety of nervous system responses within the body. There are a variety of methods of PNF stretching which have all been shown to increase flexibility. One is the contract-relax method. This involves the muscle being taken to a passive stretch and held for 5-10 seconds, an isometric contraction of this muscle against resistance at this range for around 5-10 seconds, finally held at this new range  and stretched statically for up to 30 seconds. This process can be repeated a few times.   Another method is the contract-relax-antagonist-contract method. The main difference if the hamstring was being stretched (as per the contract-relax method) a contraction of the quadriceps (antagonist) would be initiated immediately after the isometric hamstring (agonist) contraction. Then the muscle is relaxed and stretched passively in its new range. The agonist contraction prior to the stretch is thought to initiate autogenic inhibition. The antagonist contraction is said to initiate reciprocal inhibition. It is these processes which are thought to contribute to PNF stretching providing the best results.  However a review of available literature by Sharman et al (2006) questioned this hypothesis, stating that it may be that PNF stretching influences the point at which the stretch is perceived or tolerated. This view supported that of Chalmers (2004) who stated that the greater ROM achieved with PNF over other methods must be explained by other mechanisms (tolerance for example) and not just the manner in which the proprioceptive signals are processed.   Please see the related article on the practical application of stretching methods.      Reference List   Alter, M.J. (1996) Science of Flexibility. Champaign; Human Kinetics.   Atha, J. and Wheatley, D.W. (1976b) Joint Mobility Changes due to Low Frequency Vibration and Stretching Exercise. British Journal of Sports Medicine. 10 (1): 26-34.   Bandy, W.D., Irion, J.M., Briggler, M. (1998) The Effect of Static Stretch and Dynamic Range of Motion Training on the Flexibility of the Hamstring Muscles. Journal of Orthopedic Sports Physical Therapy. 27 (4): 295-300.   Chalmers, G. (2004) Re-examination of the possible role of Golgi tendon organ and muscle spindle relfexes in proprioceptive neuromuscular facilitation muscle stretching. Sports Biomechanics. 3 (1): 159-83.   Kubo, K., Kanehisa, H. and Fukunaga, T. (2002) Effect of stretching training on the viscoelastic properties of human tendon structures in vivo. Journal of Applied Physiology. 92 (9): 595-601.   Kurz, T. (1994) Stretching Scientifically. Island Pond; Stadion Publishing Company, Inc.   Moore, M.A. and Hutton, R.S. (1980) Electromyographic investigation of muscle stretching techniques. Medicine and Science in Sports and Exercise. 12 (5): 322- 329.   Osternig, L.R., Robertson, R.N., Troxel, R.K. and Hansen, P. (1990) Differential responses to proprioceptive neuromuscular facilitation (PNF) stretch techniques. Medicine and Science in Sports and Exercise. 22 (1): 106-111.   Rosenbaum, D. and Hennig, E.M. (1995) The influence of stretching and warm-up exercises on achilles tendon reflex activity. Journal of Sports Sciences. 13 (6): 481-490.   Ryan, E.D., Herda, T.J., Costa, P.B., Defreitas, J.M., Beck, T.W., Stout, J. and Cramer J.T. (2009) Determining the minimum number of passive stretches necessary to alter musculotendinous stiffness. Journal of Sports Science. 27 (9):957-61.   Sharman, M.J., Cresswell, A.G. and Riek, S. (2006) Proprioceptive neuromuscular facilitation stretching: mechanisms and clinical implications. Sports Medicine. 36 (11):929-39.   Sullivan, M.K., Dejulia, J.J. and Worrell, T.W. (1992) Effect of pelvic position and stretching method on hamstring muscle flexibility. Medicine and Science in Sports and Exercise. 24 (2):1383-1389.   Taylor, D.C., Dalton, J.D., Seaber, A.V. and Garret, W.E. (1990) Viscoelastic properties of muscle-tendon units. The American Journal of Sports Medicine. 18 (3):300-309.   Wallin, D., Ekblom, B., Grahn, R. and Nordenborg, T. (1985) Improvement of muscle flexibility. The American Journal of Sports Medicine. 13 (4): 263-268.   Wyon, M., Felton, L. and Galloway, S. (2009) A comparison of two stretching modalities on lower-limb range of motion measurements in recreational dancers. Journal of Strength and Conditioning Research. 23 (7):2155-62 Related Stretching and Flexibility Articles Application of Stretching Methods