071: Can You Increase Flexibility Without Having to Stretch for Longer Periods of Time?Feb 13, 2023
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There are two primary factors when considering stretching time: 1) the time one spends in a single stretching exercise (stretch duration) and 2) the time it takes to achieve a specific flexibility goal (programme duration). The stretching literature reveals that most adults - male or female - can increase flexibility to high levels with regular training. Improvements in range of motion (ROM) are near-instantaneous, but these immediate changes in muscle length are a temporary biomechanical (viscoelastic) response of tissues to mechanical loading (Taylor et al., 2016). Semi-permanent enhancements are possible with chronic (6+ weeks) stretching, with different training methods offering varying results. They are semi-permanent because even long-lasting flexibility requires some amount of effort to maintain it. However, static forms of stretching (static passive, static active) tend to be more effective than dynamic ones (Medeiros & Martini, 2018). In addition to the stretching method utilised, other biology- (sex, age, health status) and training-related (intensity, duration, frequency) factors influence the total magnitude of change possible for each person.
A common question that trainees and researchers ask is, "How long?" As noted above, flexibility can be increased instantly with a single stretch, but the change in ROM does not last long. An oft-stated figure in discussions of optimal stretch duration is 15-30 seconds (Page, 2012). However, this comes with some caveats: 1) 15-30 seconds is usually the minimum effective dose for increasing flexibility; 2) Individuals with high levels of stiffness (tissues' intrinsic resistance to stretch) may need to hold stretches for longer; 3) Stiffness increases relative to increasing strain (changing length), so stretches have to be held for longer as one approaches a given flexibility goal (Guimaraes et al., 2020). Put differently, start by stretching for 15-30 seconds and gradually increase the duration over time as ROM increases. It is common for trainees to hold static passive stretches for up to two minutes by the time they achieve full splits.
Addressing the question of how much time it takes to achieve longer-lasting alterations in flexibility (programme duration) is a more challenging task. Knowing the time it will take to achieve a given level of flexibility would be particularly useful in managing orthopaedic conditions like osteoarthritis and injury. For example, providing a physiotherapy patient with a realistic timeline for restoring ROM (and, therefore, function) following an injury could motivate them to adhere to the treatment programme, thus leading to better treatment outcomes (Bassett, 2003). In addition, trainees looking to improve flexibility for general health or performance reasons want to know how long they should expect to spend working on their flexibility. Usually, the human desire for instant gratification will draw them to methods that promise quicker results; some authors even recommend utilising instant gratification in healthcare to incentivise patients to stick with physician guidelines (Deo et al., 2020).
Flexibility is unique among motor abilities because it improves quickly, usually daily. Progress in others, like strength, speed, and endurance, takes days and weeks to appear. Unfortunately, the actual rate or speed of increase is difficult to determine in research, mainly because of the poor methodological quality of many studies (Decoster et al., 2005). Findings vary, but a typical range reported in the literature is 3-20° over one to six weeks. Keep in mind that such results are based on isolated joint testing, whereas the majority of positions that people seek to improve challenge flexibility across multiple joints simultaneously. More joints involved in a movement or skill means more muscles offering resistance to stretch and, therefore, more time required to improve ROM.
The lack of ecological validity in many trials presents another barrier to answering the question of programme duration. Many trainees want to improve flexibility in positions not featured in clinical research, such as splits and backbends. While the results of a trial that tested hamstring stretches may be applied to positions like front splits (which require hamstring flexibility), differences in MTU structure between muscles prevent those findings from being applied to other muscle groups (like the adductors in side splits). However, practical experience tells us that timelines of 6-12 months are standard when adults with below-average starting flexibility achieve full front and side splits. It may be another 6-12 months until that flexibility becomes instantly available without a warm-up, also known as cold flexibility.
Although the literature frequently reports that static passive stretching is the most effective form of flexibility training, it will not always be the best choice for some people. Discomfort, boredom, and perceived notions of socially acceptable activities will affect how much effort a person puts into a given exercise. For example, middle-aged males - who have higher levels of tissue stiffness compared to females of the same age - from specific socioeconomic backgrounds may be hesitant to stretch due to its associations with traditionally "feminine" pursuits like yoga and dancing. But, of course, such beliefs are nonsensical because male full-contact karate athletes do the same stretching exercises to achieve the high kicks necessary for winning fights. However, it is possible to become flexible without doing any classical stretching. Reviews by Afonso et al. (2021) and Alizadeh et al. (2023) found that resistance training is as effective as stretching at increasing ROM, albeit light-intensity (gentle) stretching only. Therefore, if static passive stretching is not working, consider implementing strength training (barbells, dumbbells, resistance bands) through a full ROM, pushing the limit of range every set (or every other set if being conservative).
Static passive stretching may also prove less effective in individuals experiencing neurological guarding, which is common following injury or during sedentary lifestyles. Guarding is believed to be caused by nociceptive pathways transmitting painful stimuli that trigger allodynia - the sensation of unexpected pain in response to a stimulus that is not normally painful (Xu and Brennan, 2010). Moving into a ROM where a previous injury occurred or which has not been experienced in a long time can cause the central nervous system (CNS) to interpret the action as a threat, provoking a pain response to limit movement. PNF, which is a form of static active stretching that consists of isometrically contracting stretched muscles, has been used since the 1940s to regulate neural tension, relaxing chronically tight muscles and permitting greater flexibility. Incorporating isometric stretching, ideally after the main part of a workout and before the cool-down, can help move stubborn joints past their sticking points and open new ranges faster than static passive stretching alone.
Afonso, J., Ramirez-Campillo, R., Moscao, J., et al. (2021.) 'Strength Training Versus Stretching for Improving Range of Motion: A Systematic Review and Meta-Analysis.' Healthcare, volume 9, number 4, article 427.
Alizadeh, S., Daneshjoo, A., Zahiri, A., et al. (2023.) 'Resistance Training Induces Improvements in Range of Motion: A Systematic Review and Meta-Analysis.' Sports Medicine, epub ahead of print.
Bassett, S. F. (2003.) 'The Assessment of Patient Adherence to Physiotherapy Rehabilitation.' New Zealand Journal of Physiotherapy, volume 31, number 2, pages 60–66.
Decoster, L. C., Cleland, J., Altieri, C., et al. (2005.) 'The Effects of Hamstring Stretching on Range of Motion: A Systematic Literature Review.' Journal of Orthopaedic and Physical Therapy, volume 35, number 6, pages 377–387.
Deo, N., Johnson, E., Kancharla, K., et al. (2020.) 'Instant Gratification as a Method to Promote Physician Practice Guideline Adherence: A Systematic Review.' Cureus, volume 12, number 7, article e9381.
Guimaraes, C. F., Gasperini, L., Marques, A. P., et al. (2020.) 'The Stiffness of Living Tissues and Its Implications for Tissue Engineering.' Nature Reviews Materials, volume 5, pages 351-370.
Medeiros, D. M. & Martini, T. F. (2018.) 'Chronic Effect of Different Types of Stretching on Ankle Dorsiflexion Range of Motion: Systematic Review and Meta-Analysis.' The Foot, volume 34, pages 28–35.
Page, P. (2012.) 'Current Concepts in Muscle Stretching for Exercise and Rehabilitation.' International Journal of Sports Physical Therapy, volume 7, number 1, pages 109–119.
Taylor, D. C., Dalton, J. D., Seaber, A. V., et al. (2016.) 'Viscoelastic Properties of Muscle-Tendon Units: The Biomechanical Effects of Stretching.' American Journal of Sports Medicine, volume 18, number 3, pages 300–309.
Xu, J. & Brennan, T. J. (2010.) 'Guarding Pain and Spontaneous Activity of Nociceptors After Skin Versus Skin Plus Deep Tissue Incision.' Anesthesiology, volume 112, number 1, pages 153-164.