By the end of this blog, you should have a start point for reading, a new perspective on flexibility and a few techniques to go away and use.
You should know that as a Personal Trainer, I used to have an excellent reputation for my assisted stretching skills. These skills helped me convert members to clients and bring clients in for extra training sessions.
However, when I pushed myself to read more research and focus on goals, I changed my thoughts on flexibility. Now I rarely use flexibility training in the form of stretching.
In the UK, the Level 2 Gym Instructor course and the Level 3 Diploma in Personal Training both advocate a mobilisation in the warm-up and then flexibility training in the cool down.
Flexibility is an essential part of the cooldown for level 3, where the reasons given are as follows –
Stretch appropriate muscles
Appropriate muscles are associated with the range of motion assessments and postural assessments. So vague, but they do link back to the ACSM, so what do they say?
More active people are more flexible.
There is nothing else and no reason to do flexibility training, even though they then give flexibility guidelines. I must mention that they do hint at posture, but they rule out DOMS. Posture is a whole new blog post.
So even before looking into the research, the primary source of reasoning for stretching to improve flexibility fails unless the client personally requests specific stretches for their own reasons.
How does a stretch work?
The visual of a specific muscle stretching comes from a
joint showing more range of motion after a technique than before it, so you see
the bones move further around a joint. So to understand why this happens, it's essential
to understand what blocks the muscle from lengthening.
Due to the wording used, it would be easy to think that the joints show more range of motion because the muscle physically gets longer. If this were accurate, then the range of motion would not change if the client was conscious or unconscious. In the research, the ability for a muscle to stretch is restricted on a neurological level (unless it is a bone block from the joint), certainly in the short term. There is little evidence the conscious level does change the available range of motion, although this evidence is only anecdotal. I am not saying you should take this as a reason. The feeling of stretch is usually just the sensation of stretch resistance, which is neurological. PNF stretching relies on this neurological process.
When measured, the stretch of the muscle seems to happen in two parts. The slack in the belly of the muscle is used up first. Then the range is found through the tendon.
The long-term effects of stretching can be an increase in muscle length. A loaded end range stretch can result in hypertrophy too (just an aside), but interestingly and in line with the ACSM research, full-range resistance training also brings on an increase in flexibility.
The only concern with stretching is that the technique could reduce muscle stiffness, which is vital during some tasks (such as low-intensity cardiovascular training).
What should you stretch?
As I mentioned earlier, posture is a topic to go into later. However, I will share with you that when we get to that blog post, it seems that posture is a better clue to mood than predicting pain or an upcoming injury!
So I have my conclusion, but please reach your own by looking at the research I have provided as a jumping-off point to help you find other papers to read.
My conclusion is that improving flexibility will happen if you focus on improving motor skills with your client. These exercises will be beneficial if you use loaded and full-range movements. Stretching techniques do not seem to be necessary. However, at the end of a training session, the pleasant feeling of a reduced sense of stretch resistance may be precisely what your client wants. Since it is difficult to see where stretching has negatives after a workout, I do not see the problem with stretching to make your client feel nice. I would do this in the same way as I would put in exercises a client liked, even if they didn't full link into the fitness outcomes of the client. The reason for this is that I think the main goal and measure of any training session should be that the client comes back again.
A Reading List to Jump off of
ACSM's Complete Guide to Fitness & Health Second Edition Barbara A. Bushman, PhD
Gleim GW, McHugh MP. Flexibility and its effects on sports injury and performance. Sports Med. 1997 Nov;24(5):289-99. doi: 10.2165/00007256-199724050-00001. PMID: 9368275.
Simão R, Lemos A, Salles B, Leite T, Oliveira É, Rhea M, Reis VM. The influence of strength, flexibility, and simultaneous training on flexibility and strength gains. J Strength Cond Res. 2011 May;25(5):1333-8. doi: 10.1519/JSC.0b013e3181da85bf. PMID: 21386731.
Seymore KD, Domire ZJ, DeVita P, Rider PM, Kulas AS. The effect of Nordic hamstring strength training on muscle architecture, stiffness, and strength. Eur J Appl Physiol. 2017 May;117(5):943-953. doi: 10.1007/s00421-017-3583-3. Epub 2017 Mar 9. PMID: 28280975.
Herbert RD, Héroux ME, Diong J, Bilston LE, Gandevia SC, Lichtwark GA. Changes in the length and three-dimensional orientation of muscle fascicles and aponeuroses with passive length changes in human gastrocnemius muscles. J Physiol. 2015 Jan 15;593(2):441-55. doi: 10.1113/jphysiol.2014.279166. Epub 2014 Dec 15. PMID: 25630264; PMCID: PMC4303388.
Krabak BJ, Laskowski ER, Smith J, Stuart MJ, Wong GY. Neurophysiologic influences on hamstring flexibility: a pilot study. Clin J Sport Med. 2001 Oct;11(4):241-6. doi: 10.1097/00042752-200110000-00006. PMID: 11753061.
Nordez A, Gross R, Andrade R, Le Sant G, Freitas S, Ellis R, McNair PJ, Hug F. Non-Muscular Structures Can Limit the Maximal Joint Range of Motion during Stretching. Sports Med. 2017 Oct;47(10):1925-1929. doi: 10.1007/s40279-017-0703-5. PMID: 28255938.
Magnusson SP. Passive properties of human skeletal muscle during stretch maneuvers. A review. Scand J Med Sci Sports. 1998 Apr;8(2):65-77. doi: 10.1111/j.1600-0838.1998.tb00171.x. PMID: 9564710.
Konrad A, Stafilidis S, Tilp M. Effects of acute static, ballistic, and PNF stretching exercise on the muscle and tendon tissue properties. Scand J Med Sci Sports. 2017 Oct;27(10):1070-1080. doi: 10.1111/sms.12725. Epub 2016 Jul 1. PMID: 27367916; PMCID: PMC5479471.
Feldman AG. The Relationship Between Postural and Movement Stability. Adv Exp Med Biol. 2016;957:105-120. doi: 10.1007/978-3-319-47313-0_6. PMID: 28035562.
Steffen K, Nilstad A, Krosshaug T, Pasanen K, Killingmo A, Bahr R. No association between static and dynamic postural control and ACL injury risk among female elite handball and football players: a prospective study of 838 players. Br J Sports Med. 2017 Feb;51(4):253-259. doi: 10.1136/bjsports-2016-097068. PMID: 28148513.