Hot yoga studios are offering it. Moksha studios too. Even some Bikram studios are offering Hot Yin classes. Does this make any sense? Isn’t “Hot Yin” an oxymoron? Often, it is recommended that students practice yin yoga when the muscles are cool, so that the stress of the posture can soak deeper into the connective tissues. The temperatures in studios offering Hot Yin are not the full on, 105°F (~40°C) maximum common in the hot yoga classes, but rather a “cooler” 95°F (~35°C). Still, at those temperatures, Hot Yin means that the muscles will take up the stress of the pose much more than the deeper tissues. So, why do so many studios and students love their Hot Yin classes?
Yin and yang are relative terms. Hot water, perhaps surprisingly, is yin – at least compared to boiling water. In the same vein, cold water can be yang compared to ice. There is nothing that is absolutely yin or absolutely yang: these terms are always relative to something. Hot Yin is yin compared to yoga practiced in even hotter temperatures or to more muscular, movement practices. Thus, Hot Yin is not an oxymoron.
But, is Hot Yin beneficial? Why do so many teachers believe Hot Yin doesn’t make sense? The overarching reason is physiological: when the muscles are warmed up, the muscle will take up most of the stress of a posture, leaving very little stress to be felt by the connective tissues. The interested reader can read about a simple experiment that illustrates this concept on my website, but I will repeat some of the highlights here. The experiment involves using a few elastic bands to represent our various tissues. A thick white elastic band shown in the accompanying images represents our ligaments and deeper, stiffer connective tissues. A thin blue elastic represents our muscles when they are warmed up, while a tan elastic band, which is the same length when it is unstressed as the blue one, represents our muscles when they are cool. Now, we join the “muscles” in series to the “ligaments” as shown in the top image.  Notice in the next two pictures what happens when we apply a stress.
The white elastic represents our ligaments, the blue band warm muscles, and the tan band cool muscles.
When the muscles are warm (the blue band), the muscles stretch more and take stress off the ligaments.
When the muscles are cool ( the tan band), more stress is experienced by the ligaments.
Notice how applying the same stress results in a different strain (which is the amount a material stretches) upon the white elastic. When the muscles are warm (using the blue band), the muscles stretch more and take stress off the ligaments: the white elastic stretches very little. When the muscles are cool (using the tan band), more stress is experienced by the ligaments: the white band stretches much more. There was a strain of 18% placed upon the “ligament” when the muscles are “warm”, compared to a 55% strain with the “cold” muscles. This experiment illustrates why we would like to have our muscles cooler than warmer when doing Yin Yoga – when the muscles are cool, more stress is applied to the ligaments, joint capsule and other fascia. For this reason, some teachers suggest that students should not do Yin Yoga when the body is hot. 
While it is certainly true that more stress will reach the ligaments and deeper connective tissues when the body is cooler, this does not mean that there is no benefit at all to stressing our tissues when the body is warm. Even with warm muscles, the ligaments received some stress. And, for many people, it is only when their body is warmed up that they can move deep enough into a posture to get a stress into their targeted tissues. In other words, some students need to be warm in order to get any sensation or stress.
We can generalize and say that the cooler the tissues, the more stress from a pose will be experienced by the deeper tissues, however this does not mean that no benefit is gained by stressing a warm body in a yin-way. Being warmed up may mean that most students won’t get the maximum physiological benefits, but they will still benefit. And, for some students, being warmer may be the only time they get those benefits.
Please realize that the benefits from Yin Yoga are not purely physical: students also benefit from the stillness the practice offers. The opportunity to come to an edge, become still and be with sensations is still available even in a hot room. Indeed, there may be more sensations in hot room to be aware of. The opportunity to practice mindfulness is enhanced by remaining still for 3, 5 or 10 minutes at a time. The temperature of the room does not diminish the quality of mindfulness practice. This is another reason many people are adding Hot Yin to their yoga practice: it is a chance to calm the mind and practice presence.
Another benefit is the energetic stimulation available in Yin Yoga. Whenever an edge is felt, whenever a posture gives us a challenge physically, tissues are being stretched or compressed. This tension creates mechanical, electrical and chemical signals that travel through the body and it can change the quality of the tissues that transmits these signals. In the East, this is called prana or chi, which flows through nadis and meridians. The Daoist call the mechanical stimulation acupressure. Even in a hot room, the body can experience acupressure, which stimulates energies to flow.
Hot Yin is not an oxymoron and can provide energetic, mental and physiological benefits. While it is true that more physiological benefits may be available to the student who practices in a cooler environment, it is not true to say that practicing Yin Yoga in a warm room is not healthy or beneficial. The fact that its popularity is growing so fast attests to the fact that people are getting benefits from the practice. Can it be too much? Is there a danger that, in a hot room, the tissues may be stretched too far? Of course, anything can be overdone. However, this is a risk for the normal yang hot yoga practice more than for the hot yin practice, because the hot yoga movements are deeper and more dynamic than those used in Yin Yoga.  Whether in a hot or cool room, students must always check in and see what their body is telling them, and respect those signals. Inherently, however, there is no reason to avoid Hot Yin … if you like being in a warm room, enjoy it! It is certainly better than doing no yin at all.
If you would like to comment on this article, we have created a thread on the Yin Yoga Forum. Feel free to let us know your questions or thoughts
- — Yes, we join these elastics in series because in our body, our muscles are actually in series with our ligaments! Despite what may have been described in older anatomy texts, the work of Jaap van der Wal has shown that the normal relationship between muscles and the tendons and ligments is serial, not parallel. See The Architecture of the Connective Tissue in the Musculoskeletal System – An often overlooked Functional Parameter as to Proprioception in the Locomotor Apparatus by Van der Wal J 2009 in Fascia Research II: Basic Science and Implications for Conventional and Complementary Health Care, Munich: Elsevier GmbH.
- — It is important to clarify one point here: we are not stating that our intention in Yin Yoga is to stretch our ligaments or joint capsules. We are trying to stress them, which is quite different. If a ligament is stretched beyond its elastic limit, which ranges from 4~10% depending upon which ligament is being targeted, it may plastically deform and stay stretched. That is not our intent. Our intention is to apply a healthy stress to the connective tissues so that the cells that create these tissues and live embedded within them are stimulated. Over time, these cells (fibroblasts) will secrete more collagen, which will make the connective tissues thicker, stronger and perhaps a little longer, thus increasing range of motion. (There are far more physiological reasons why this is beneficial, but they are beyond the scope of this article.) The fact that the elastic bands in our simulation do stretch is meant to show only the relative strength of the stresses being applied, not to imply that the ligaments actually stretch during our practice.
- — Hypermobile students are often warned about going too far and in a warmer environment, that possibility is greater than in a cooler room. However, Yin Yoga should not be more risky for hypermobile students than other forms of yoga. See my newsletter article on hypermobility and Yin Yoga. If a hypermobile student can do Hot Yoga with no danger, Hot Yin should not be a problem.