NOTE: This article first appeared February 12, 2015, in the Vallarta Daily online newspaper (vallartadaily.com), as the fourth of a series of monthly columns I am writing on Intelligent Movement Forever. From now on my column will appear bi-monthly, so the next column will be published in early April.
Dear Daily Vallarta Readers and Movers,
In this February 2015 column, I am going discuss and describe a hot topic that is trending in yoga/fitness/movement circles: the topic of STRETCHING. This column will: (1) look at commonly accepted definitions of stretching (2) introduce a new definition of stretching that is based on exercise science research, (3) describe what happens when we stretch a muscle, (4) introduce Resistance Stretching, and (5) give readers enough evidence-based information to choose a stretching practice that will create flexibility, without damaging the muscles and tissue.
To begin, let me introduce you to Jules Mitchell, one of my Yoga colleagues and intelligent movement heroes. Jules, a well-known Yoga Therapist in the South Bay of Los Angeles, CA, recently earned her Master’s Degree in Exercise Science, emphasizing biomechanics. Her Master’s Thesis and soon-to-be published book is a comprehensive literature review on the science of stretching. In the meantime, she is blogging and talking about her findings, and their application to yoga, in particular, and movement, in general, at julesmitchell.com.
Jules’ blog entries are the primary source for what I present, although I myself am entirely responsible for my interpretation of the research information that Jules has blogged. And I am also responsible for the necessary oversimplification of the ideas presented here. Such is the nature of scientific research and newspaper columns based on scientific research. I promise to do my best.
As Jules reviewed the current research on the science of stretching, she came to believe, and I tend to agree, that the emphasis on (passive, long-held) stretching in (most) yoga communities (and some, although fewer, fitness communities), is “often misunderstood (I would say misplaced), resulting in anecdotal information unsupported by the vast body of evidence published by Exercise Scientists.” Jules points out that there is no interest in extreme stretching in the Research and Exercise Science community.
When Jules and I met as Yoga Teachers at South Bay Spectrum in Manhattan Beach, CA, five or so years ago, I was teaching a very popular Yin Yoga class (long-held stretches) there. I no longer teach Yin Yoga. I have found better ways to stretch, I think. This is not to disparage Yin Yoga or any yoga practice. It is just a recognition, for me, that scientific research can increase our awareness of how our bodies move and help all of us evolve as teachers, and as students of yoga and other forms of intelligent movement. Only a few of us are ready to study movement as a science, but a lot of us do want our movement practice and training to be based on scientific evidence. Thank you, Jules! Note: The propensity for breakdown in tensile strength due to overstretching in yoga is also being chronicled in Matthew Remski’s book/project, What Are We Actually Doing in Asana?
Jules started to re-examine what she had learned in yoga about stretching (more is better) the day she heard a “popping” sound somewhere near her primal hamstring tendon while trying to deepen into standing forward fold. More stretching did not and could not relieve the pain. I myself have experienced a chronic right hamstring injury from long-held seated forward folds in my (earlier) yoga practice. It is almost gone now, but I have been avoiding seated forward folds and long-held stretches.
This is why it is so important to me that I get this new information on safe stretching out to you, dear readers. I hope you understand what I am saying. But I know it is complicated. If you have some questions, please let me know in the comments section after this column.
What is STRETCHING, a common definition:
Most of us, until now, have defined the term “stretching” by what we think stretching does for us, not what it is. We define stretching something like this: to create length in a particular muscle and, thereby, increase flexibility or range of motion (ROM) in the joint associated with that muscle. This common definition of STRETCHING defines stretching by what we want to have happen when we stretch (flexibility). I am going to invite you to set that definition aside, for now, consider a new definition, and look at what actually happens when we stretch a muscle.
What is STRETCHING, a new definition:
Jules defines stretching as “TENSILE LOAD”. She does not define tensile load. But, “tensile” is the “ability to be stretched” and tensile load is a load place on a tensile material. In the situation we are presenting, tensile load, is a load or stress that pulls on a muscle. Within the very term tensile is the maximum ability or capacity to stretch. The science of stretching looks at the ability of a muscle to withstand tensile load, expressed as the greatest stress that the material (or muscle) can stand without breaking.
I hope you will agree that this new definition of stretching is a better place to start our discussion about stretching, because it defines what stretching is rather than its result (or desired or imagined result). Using this definition, we will look at what happens when a muscle is stretched, or loaded, in the discussion below. We will use the terms muscle and muscle-tendon unit interchangeably, because a muscle has a tendon on either end. The tendon connects a muscle to bone at the joints, and the tendon is always affected by the load. Sometimes we will use the term, connective tissue, to refer to the tendon, which is made up of connective tissue.
Tensile loading of muscles is not the same a tensile loading of a construction material because of the biomechanical complexities of muscle that do not apply to tensile building material. When a muscle is loaded (stretched), a complex cellular process is triggered that results in an adaptation. The cells are signaled to produce more collagen to increase the capacity to withstand the load. However, when a muscle is overloaded (overstretched), there is a reduced capacity to withstand the load. See discussion below.
What happens when a muscle-tendon unit is stretched?
Scientific research tells us that the force of a tensile load (stretch) can change the length of the muscle-tendon unit, just like we want it do or think it can, BUT the stretch is never permanent and, if we stretch too far, injury or failure can occur.
The early stage of a stretch is called creep. Most creep occurs in the first 4% of the duration of the stretch or the first 15-20 seconds of a stretch. This is a very short period! During the rest of the stretch, the muscle-tendon unit continues to stretch (creep), but at a much slower pace. When the load is removed, the original shape (or length) returns (recovers). In summary, most elongation of a muscle tendon occurs at the very beginning of a stretch. It is measurable, but it is only temporary.
The muscle will slowly but surely return to its pre-stretch length, once the load is removed (stretching stops). This is called recovery. Like anything that cannot be stretched, there is a mechanical limit to the ability of a muscle to stretch. Creep and recovery happens you stretch a muscle within that limit.
What happens when a muscle-tendon unit is overstretched?
If you stretch a muscle beyond its mechanical limit, it will be permanently deformed. If you continue to stretch a muscle even further, it will break (injury). Science of Stretching research says that the range (how far something can stretch) for human connective tissue is somewhere around 4% before the tissue starts to break and 8% for total tissue failure. Dear Readers, this is a very small stretch! When you stretch beyond this safe zone, the collagen fibers (the fibers that stretch) will tear and this weakens the structural integrity of the tissues. This tissue damage can also result in inflammation and scar tissue formation. Repairing these fibers may take up to 2-3 years. Bottom line: if you are trying to improve your flexibility, you do not want to stretch your muscle-tendon unit past the safe zone.
Alert! Alert! Flexible people have a much stronger tendency to overstretch joints. They keep stretching beyond the muscle, into the joint, until they feel pain and then it’s too late. However, flexible students do not benefit from becoming even more flexible. And overstretching can also wear down the cartilage that protects our joints and keeps them articulately smoothly.
Safe Stretching by Re-educating the Nervous System
There is good news…. If you are willing to abandon everything you thought you knew about stretching and flexibility.
Safe stretching IS available in the form of shorter-holds. Safe stretching can improve flexibility if you stretch frequently with the right amount of force (shorter holds vs longer holds). Jules recommends holding stretches no more than 30 – 60 seconds, which is beyond the initial creep, but before total tissue failure.
I think it is helpful to recognize that the improved flexibility (range of motion) that results with regular, safe (within mechanical limit) stretching is not a matter of body mechanics or muscle length. Rather, it is controlled by the nervous system. Our nervous system is designed to allow us to perform joint positions that are safe (will not result in injury). When your body moves in an extreme and unfamiliar way, e.g., extreme stretching, your nervous system slams on the brakes, usually long before a muscle can fully lengthen. On the other hand, when a muscle is stretched frequently within the mechanical limit, the nervous system will ultimately allow the extra range of motion, because of what is called increased stretch tolerance.
Summing it up, when flexibility is an issue, Jules and Science of Stretching research say that extreme stretching is not going to help. Moving frequently in the end ROM and increasing the load is the answer.
Another Approach: Resistance Stretching
The stretching we have discussed so far has been passive stretching, where the stretcher relaxes into (holds) the stretch. We believed, until now, that passive stretching would increase flexibility and range of motion. However, now we know that that is not always the case. As discussed above, extreme stretching is more like than not to create tissue injuries.
So and instead, many movement and personal trainers, including myself, are adding another type of stretching to the stretching toolbox. It is called resistance or eccentric stretching. The resistance stretching practice that I know (there are several) is called Ki-Hara, and my description of resistance stretching, its characteristics and benefits, come from what I know about Ki-Hara Resistance Stretching. Ki-Hara and other resistance stretching methods, combine flexibility, strength, and core development. The stretching phase of Ki-Hara is also called eccentric training.
During Ki-Hara Resistance Stretching, the muscles are being contracted and lengthened at the same time, so the muscles are only taken as far as they resist, which keeps stretching safe and effective. Resistance stretching begins with a shortened muscle, maintains the contraction, and stretches the muscle through the entire range, not just the end of the range. As a result, tension is removed along the entire range, the range of motion is increased, and the muscles are strong throughout their ranges of motion.
By keeping a muscle contracted while lengthening, Ki-Hara creates a balance of strength and flexibility within the muscle. In fact, a muscle can only be as flexible as it is strong. And vice versa. In Ki-Hara stretching, the stretch movement and the return movement work in tandem to create that balance of strength and flexibility in a muscle. Furthermore, recent exercise science research shows that eccentric contractions actually increase the number of sarcomeres in the muscle, over time, especially at the end ranges, which creates longer muscles and, in turn, greater range of motion. Sacomeres are the basic functional unit within muscle cells. The process of growing more sacomeres is called sacomeregenesis. Look for more research in the future on eccentric stretching and sacomeregenesis.
Ki-Stretching can be practiced with the assistance a certified trainer providing the resistance. There are also self-stretches that can be the basis for an individual home practice. www.ki-hara.com. Ki-Hara is very popular with Olympic and other elite athletes, because it is safe, effective stretching, and because it requires low VO2 max, that is, it is less taxing than other forms of strength training. (But that is a topic for another day and another column, isn’t it?)
Below are links to videos of Olympic Athletic Dara Torres demonstrating 3 Ki-Hara hamstring self-stretches. I hope you will try them out to see what Ki-Hara is all about!
Video 1: medial hamstring
Video 2: central hamstring
Video 3: lateral hamstring
I hope the information I shared in this column will help you understand what happens when you stretch and inspire you to avoid overstretching, create a stretching practice that is safe and effective, and, explore Ki-Hara Resistance Stretching as a safe and effective alternative to more familiar forms of stretching.
I am also looking forward to seeing you at my Mobility Class on Thursday nights at 7 pm at Crossfit Vallarta (free to Crossfit members, 50 pesos for drop-ins). I am also available by appointment for private or semi-private sessions at my home Pilates/Fitness Studio in Versalles. Or invite me to come to your hotel, villa, condo, or apartment. Contact me at firstname.lastname@example.org for more information.
Wishing Each and Everyone Intelligent Movement Forever,