Is It Time Personal Trainers Stopped Stretching Clients?

I used to have a strong reputation for my assisted stretching. It converted members into clients and brought clients back for extra sessions. Then I pushed myself to read more research and focus on goals, and my thinking changed. Now I rarely use stretching for flexibility at all. Here's why, with a reading list at the end so you can reach your own conclusion.

Why flexibility in the first place?

It wasn't long ago that stretching was treated as an essential part of the warm-up. In the UK, the Level 2 Gym Instructor and Level 3 Diploma in Personal Training both advocate mobilisation in the warm-up and flexibility training in the cool down. For Level 3, the reason given is to "stretch appropriate muscles" — appropriate meaning those linked to range of motion and postural assessments. It's vague, but it links back to the ACSM.

So what does the ACSM actually say? That more active people are more flexible. That's essentially it. They then give flexibility guidelines and hint at posture (a topic for another day) while ruling out DOMS. So even before we open the research, the core justification for stretching to improve flexibility falls apart — unless a client specifically requests certain stretches for their own reasons.

How a stretch actually works

The visual of a muscle stretching comes from a joint showing more range after a technique than before, so you see the bones move further around the joint. It's tempting to assume this happens because the muscle physically gets longer. If that were true, range wouldn't change depending on whether the client is conscious or unconscious.

In the research, a muscle's ability to stretch is restricted neurologically in the short term (unless a bone block from the joint is the limit). There's little solid evidence that conscious level changes available range, though that's anecdotal. The feeling of a stretch is usually just the sensation of stretch resistance, which is neurological — and PNF stretching relies on exactly this process. When measured, the stretch seems to happen in two parts: first the slack in the belly of the muscle is used up, then range is found through the tendon.

Long-term, stretching can increase muscle length. A loaded end-range stretch can even bring on some hypertrophy. But in line with the ACSM research, full-range resistance training also increases flexibility. The one concern with stretching is that it may reduce muscle stiffness, which is actually useful during some tasks, such as low-intensity cardiovascular work.

What should you stretch?

Postural assessments, manual muscle testing, joint-by-joint range testing, and clients' own tests like sit-and-reach and toe touches are the usual ways trainers decide what to stretch. On posture, I'll save the detail for another post, but it seems to be a better clue to mood than a predictor of pain or injury.

My conclusion

Flexibility improves if you focus on improving your client's motor skills using loaded, full-range movements. Stretching techniques don't seem necessary. That said, at the end of a session the pleasant feeling of reduced stretch resistance may be exactly what your client wants, and it's hard to see a downside to stretching for comfort after a workout. I'd include it the same way I'd include any exercise a client enjoys, even if it doesn't map directly onto their fitness outcomes — because the main measure of any session is that the client comes back.

Reach your own conclusion by working through the research below.

A reading list to jump off from

Book: ACSM's Complete Guide to Fitness & Health, Second Edition, Barbara A. Bushman, PhD.

Papers:

• Gleim GW, McHugh MP. Flexibility and its effects on sports injury and performance. Sports Med. 1997;24(5):289-99.
• Simão R, et al. The influence of strength, flexibility, and simultaneous training on flexibility and strength gains. J Strength Cond Res. 2011;25(5):1333-8.
• Seymore KD, et al. The effect of Nordic hamstring strength training on muscle architecture, stiffness, and strength. Eur J Appl Physiol. 2017;117(5):943-953.
• Herbert RD, et al. Changes in the length and three-dimensional orientation of muscle fascicles and aponeuroses with passive length changes in human gastrocnemius muscles. J Physiol. 2015;593(2):441-55.
• Krabak BJ, et al. Neurophysiologic influences on hamstring flexibility: a pilot study. Clin J Sport Med. 2001;11(4):241-6.
• Nordez A, et al. Non-Muscular Structures Can Limit the Maximal Joint Range of Motion during Stretching. Sports Med. 2017;47(10):1925-1929.
• Magnusson SP. Passive properties of human skeletal muscle during stretch maneuvers. A review. Scand J Med Sci Sports. 1998;8(2):65-77.
• 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;27(10):1070-1080.
• Feldman AG. The Relationship Between Postural and Movement Stability. Adv Exp Med Biol. 2016;957:105-120.
• Steffen K, et al. 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;51(4):253-259.