Moments, Arms, & Moment Arms

In a perspective article on scapular stabilization, the concepts of moments and moment arms came up. My fuzziest understanding is that they are related to rotation around a joint. And angles. And math. Usually, I ignore such words and cleave to the bigger picture. But scapulae are enticing black boxes to me and in the case of this article, moments and their arms seemed crucial to an understanding of the author’s theory of departure. This was the sentence that tossed me over the cliff: “Therefore, equal muscle forces are not mandatory – and could be clinically undesirable – because the muscles have different moment arms and thus different mechanical advantages for causing angular rotation in the joint.” I knew I needed help.

Historically, when I’ve tried to educate myself about biomechanical stuff (moments, arms, angles, etc.), my eyes glaze over and I hear this sound. Its hard to find someone writing about these biomechanical concepts in language that I can apply to my own understanding of yoga postures. So I reached out to my friend Christine McSween to help me understand. And that’s revisionist. Actually, Christine engaged with me in a Facebook group around this topic and we agreed to turn it into an educational interview for our group and the world.

Christine was drawn to the spiritual and mindfulness aspects of yoga in the beginning, but with further study she learned how amazing the physical body is along with a realization of the need for more education. With increased fervor, in 2015, she began pursuing a kinesiology degree at the University of Calgary with a focus in biomechanics. She teaches yin yoga, gentle yoga and Restorative Exercise.

Here is our conversation.

MM: I have a hazy understanding of a moment arm, but could not verbalize it well enough to get off the island. Can you give me the words?

CM: Can you let me know your definition first? I want to see what you’re working with!

MMI can’t! I don’t have my own words. My understanding is hazier than I thought. Sigh.

CM: I want to work through this a bit. Do you have a clearer understanding of a “moment” than the “moment arm”?

MM: Sadly, no. I clearly need a biomechanics lesson.

CM: Ok, I know where to start then!

CM: I’m going to draw a picture.

momentarm2

CM: As you can see in the picture, we have isolated the bicep as the force that will lift the forearm (of course we know this is super simplified).

The force in the bicep creates a moment – or rotation about the elbow joint (or axis of rotation). Because the bicep is only 5 cm down the forearm, it needs to create a LOT of force to lift the forearm. This is because the mass of the forearm is also creating a moment about the elbow joint due to gravity.

MM: (interrupting): Could you say a moment is any rotation about a joint? Does that mean there are an infinite number of moments for a given joint?

CM: YES!

CM: Often in biomechanics we talk about “resultant moments” which is the resultant effect of all the moments about a joint. If the resultant moment is not zero (can be negative or positive), then we have a rotation or movement. I will say though, that the center of mass (COM) is a resultant force, since we know gravity impacts the whole arm

MM: First things first. Can you give me an example of a resultant moment being negative or zero with no rotation/movement? And what is the significance of COM being a resultant force.

CM: When a resultant moment is zero, you have an isometric contraction. There are moment’s occurring, but because they cancel out, the resultant moment is zero. This is how we first learn to calculate forces from moments in physics and biomechanics classes. We assume static equilibrium (no movement) to simplify the calculations.

In our case the system of interest is the forearm. If the forearm rotates towards the upper arm (counterclockwise), this is a positive moment. If the forearm rotates clockwise (extending the elbow), this is a negative moment. Of course, if we flipped our picture around, it would be the opposite.

We use a resultant force for the COM because otherwise we would have to calculate every cell’s mass and every cell’s moment arm, which would have us calculating for days, or weeks, or years. Not ideal! Instead, we can actually measure the weight of the whole forearm, and measure one moment arm to the COM of the forearm. Yay! Only one calculation.

MM: Let’s move on to moment arms.

CM: Now a moment arm is the perpendicular distance from the line of force application to the axis of rotation. Or…the moment arm is the distance from the elbow joint, to the attachment of the bicep, as it relates to the angle of the bicep.

MM: I prefer the latter. And would another moment arm be the distance from the elbow to the hand to account for the mass of the forearm?

CM: No, usually the moment arm is to the center of mass. So probably somewhere in the middle of the forearm. If the hand is holding a weight, then there is another moment arm to the hand.

MM: Let me get this straight. Using the picture above, one moment arm is from the elbow joint to where the bicep attaches on the forearm. Another moment arm is from the elbow joint to the center of mass of the forearm, which is likely near the center of the forearm – but this is only if nothing is being held in hand, I assume. Yet another moment arm would be from the elbow joint to a dumbbell, if one were being held. Eh?

CM: You bet! Just remember the moment arm is in relation to the angle of the applied force. If the forearm is at 90 degrees (like in our picture), then the moment arm would be length from the elbow to the dumbbell. However; this will not be the case if the forearm is at an angle. The applied force is no longer perpendicular.

CM: An example of how awesome our body is with creating more efficiency is our beautiful patella!

MM: What is/are the moment arms in this animation?

CM: When there is no rock, there is a very tiny angle between the elastic and the stick, which leads to a very tiny moment arm. So more force is needed for rotation. When there is a rock, the angle is much larger, leading to a larger moment arm, so less force is needed for the same amount of rotation.

MM: We are looking at the angle between the “femur” and the “patella,” yes?

CM: No, the patella and the tibia. The femur isn’t within our “system of interest” in this case.

MM: Dammit.

MM: Ok, so we have the force of the muscle and an external force like gravity or a weight creating individual moment arms. Are these opposing forces? Are there others?

CM: They aren’t quite opposing forces, as they are opposing moments. The bicep is creating a positive moment, while the COM, and a weight in the hand would be producing negative moments. This concept might be more simple if you think about a balanced teeter totter. On either side of the fulcrum you have equal forces in the same direction. BUT the moment arms are opposing, creating opposite moments. Does that make sense? Because our bodies are so wonderfully complex, you could add as many forces as you like, or make it is complicated as you like. And this is why resultant moments are used so frequently. When you add everything together, all the moments and forces, what will happen?

MM: I’m hoping that is a rhetorical question! I suppose it would determine if and how movement happens around a given joint or all joints….

MM: I’m guessing that moment arms are more straightforward, when we are talking about hinge joints like elbows, right? But more complex if we are talking about, say, the scapula?

CM: It would still be the same process, but yes, more difficult to quantify merely because the moment arm would be so small, because of the angles involved.

MM: Wouldn’t there be multiple forces applied to a scapula since it has multiple muscular attachments, moves in multiple planes, and is involved in multiple joints? What is the relationship ship between multiple moment arms and movement in a joint as complex as the shoulder complex?

CM: Simply, this complex structure allows for almost infinite variability in movement. Which logically, makes sense. If our shoulders are “less stable” to allow for more movement, it would make sense to have a variety of options in order to make those movements happen.

MM: So what? Who cares? How is this useful information for a movement practitioner?

CM: Understanding moments and forces allows us to be creative with our cueing and provides a greater understanding of alignment. Plus, we can see how anatomy impacts our biomechanics. In my 21 Day Biomechanics Challenge , I will be using my friend and I as an example. 

MM: I thought it might be illuminating to bring in a yoga pose for you to identify forces and moment arms. I give a shout out to this Yoga Stick Figure from Justine Aldersey-Williams. I’ve been using her clever illustrations in my teaching materials for several years now. You can download over 200 images from her Etsy store for just $5.

moment_trik

Image: Justine Aldersey-Williams

MM: Let’s take one of these arrows that you’ve drawn on the figure and tell me what’s going on.

CM: Consider this a static triangle, so the sum of all the moments equals zero. And we want to know the effect of placing the hand on the ground/leg or block vs. having it hover. To remain static, how would the resultant forces of the back leg and obliques change? If the hand is hovering, the resultant forces in the leg and obliques would have to increase to prevent the torso from rotating clockwise towards the ground. When the hand is pressing against something, it provides an opposing force that will rotate the torso counterclockwise, and the resultant forces in the back leg will be smaller. You can try this yourself by practicing both situations. What takes more effort?

MM: That’s fantastic!

MM: I have one final question. If we are biotensegrity systems (and not lever systems) with fascia deeply and exquisitely  investing our connective tissues, how should this interconnectivity influence how we think about moments and moment arms in movement?

CM: This is a question I have been struggling with for a couple years now, trying to put my thoughts to words. I must emphasize that my answer to this question will probably evolve over time as I learn more.

Although yes, we are not built like traditional buildings, and are amazingly adaptable tension systems made for mobility, this does not negate the importance of traditional biomechanics. Neither system is wrong, they are just different models, or filters by which we can understand the physical world.

And I think you can combine these models. If you take a tensegrity structure, and expose it to an external force, a moment may still be created. That entire structure might rotate. Or deform. Or translate. There are a number of options.

I think people can assume that this model will destroy the old, but there is not much evidence for that at this time. Biomechanics researchers understand that the body is not a bunch of simple levers. Load is distributed throughout the structure – like tensegrity! But this doesn’t mean that classical biomechanics has no place. Especially when we are starting to learn these concepts. As you study further into biomechanics, you must take into account our biology – how biological tissues respond to forces.

Muscles DO produce force to cause rotation. So we need both models to understand what’s happening in the body as we move. Levers exist, and yet we are this system of tension and compression. As we lift the forearm, not only the muscles such as the bicep, and brachialis lift the forearm, but the triceps create tension and can also contribute eccentric forces, while muscles in the shoulder and chest create stability.

The biotensegrity model informs classical biomechanics, and helps us question our assumptions, but it does not negate the model. If I may quote Jules Mitchell, “Such theories provide a foundation for forward and radical thinking, but are prone to become “buzzwords” which dilute scientific understanding among the mainstream.”

So, why does this stuff matter? The article that started this conversation shows a fantastic combination of questioning classical biomechanics, and informing it with the biotensegrity model. But the basic elements of moments and forces don’t disappear. We still need to understand these concepts to help us move forward.

“The key point is that stability is context specific, depending on the system and the task being performed.” I think this statement could be applicable to many other areas of the body.


And there you have it. A big thank you to Christine for her generous time in taking complex biomechanical concepts and explaining them in the concept of yoga.

Yoga for Perimenopause

From time to time, I share postures included in published yoga research. I’ve used such lists to inform my own sequencing, both in group classes and when working privately with clients. Today’s share is a list of asanas that were included in a yoga protocol for a study of perimenopausal women. I’m not providing analysis or evaluation of the research, just the poses. In this study, 216 women were assigned to either a yoga group or an exercise group. The intervention was practiced for 45 minutes every day for 12 weeks.

Perimenopausal women have been shown to have increased blood sugar levels and may be at higher risk for diabetes and metabolic syndrome. It should go without saying that perimenopause is a stressful physiological state in women. Thus, the study measured blood sugar and stress hormone levels before the intervention period and again, after 12 weeks of intervention.

The study found yoga to be as beneficial or better than exercise at improving fasting blood sugar and stress hormone levels, with participants reporting calming effects of yoga practice and a general feeling of wellness.

And here, as promised, are the postures practiced in the yoga group. I’ve provided a visual of each asana using Yoga Stick Figures from Justine Aldersey-Williams. I’ve been using her clever illustrations in my teaching materials for several years now. You can download over 200 images from her Etsy store for just $5. Inconsistencies in naming & spelling of yogasana across yoga styles & teachers is to be expected, but these illustrations capture the basic shape of each pose. You’re welcome!

Asanas & approximate time held

Swastikasana (auspicious pose) 2 min

siddhasana

Vajrasana (thunderbolt pose) 2 min

virasana

Suptavajrasana (reclined Thunderbolt Pose) 2 min

supta-virasana

Tadasana (Mountain pose) 2 min

tadasana

Trikonasana (Triangle pose) 2 min

trikonasana

Parsvakonasana (extended side angle pose) 2 min

parsvakonasana

Paschimottasana (seated forward bend) 2 min

paschimottanasana

Purvatanasana (seated back arch) 2 min

purvottanasana

Janushirshana (head to the knee pose) 2 min

janusirsasana

Pavanamuktaasana (wind relieving pose) 2 min

apanasana

Bhujangasana (cobra pose) 2 min

bhujangasana

Shalabhasana (locust pose) 2 min

salabhasana

Dhanurasana (bow pose) 2 min

dhanurasana
Vakrasana (twisted pose) 2 min

marichyasana

Padottanasana (wide-legged forward bend) 2 min

pras_padottanasana
Shavasana (corpse pose) 5 min

savasana

Pranayama(breathing exercises)

Anuloma-viloma (alternative nostril) 5 min

Suryabhedana (right nostril) 5 min

Sheetali (through tongue) 2 min

Bhramari (honey bee sound during exhalation) 2 min

Namaste, Michele

More Exercises for Pronated or Flat Feet

I contend that barefooting is the best and most natural way to have strong, mobile, and healthy feet. But it takes time to transition to an unshod or minimally shod lifestyle and not everyone wants that. So, I make a point to keep up with and share biomechanics- and physical therapy-informed clinical research on foot health. In the past, I’ve suggested you add the short foot exercise for arch strengthening to your foot health protocol. I use it regularly with my clients and in my FootLove Workshops.

Here is another foot exercise to consider for pronated and flat feet and hallux valgus – the condition that leads to bunions. The Toe Spreading Exercise is easy to do. I suggest you do it standing, but you could also do it seated with your hips and knees flexed to 90 degrees. I use a yoga mat under my feet for comfort.

  1. Stand with your feet pelvis width distance apart and facing forward.
  2. Spread the toes on your right foot as far apart as you can. If you are unable to spread your toes on your own, reach down with your hand and help to spread them.
  3. Raise your heel
  4. Over a slow count to 5, lower your heel to the ground.
  5. Hold in that position for 5 seconds
  6. Relax the foot
  7. Some protocols have you repeating this up to 100 times! But you might just want to start with 5 or 10 reps. Repeat with your left foot.

A recent study suggests that along with the toe spreading exercises,  you also strengthen your gluteus maximus, commonly referred to as your butt. Your big butt muscle is responsible for externally rotating your hip joint, and a strong one is thought to alter alignment of the lower extremity, thus reducing foot pronation. The authors found that the exercise most effective for a strong butt is performed in a prone position (lying face down) by slightly lifting the knee while maintaining the hip joint in external rotation and the knee joint at 90° flexion.

I bring this exercise into the yoga world as a unique modification of salabhasana aka locust pose. Or, you could think of it as a hybrid between locust and bow poses. The study protocol called for 3 sets of 20 repetitions of single leg lifts. I think you could explore fewer reps of double legs and longer holds.

Namaste, Michele

Picking Strawberries Stacked the Best Yoga Practice of My Life

Internationally renowned biomechanist Katy Bowman coined the phrase “stack your life.” Instead of making errands, movement, family/friend time, studying, entertainment, etc. discreet events, each taking up precious amounts of time, you perform these experiences together, essentially stacking your life. For instance, today my partner and I walked (movement/exercise, family time). Partway through our walk, we listened to a podcast (edu-tainment). Our walk had a task associated with it – dropping off an item at a friend’s house (errand done!, friend time); and a destination -our local coffee shop, where we studied, chatted, and enjoyed seeing several regulars (community, family, coffee time). Infused in a stacked life are often values held dear – decreasing an environmental footprint by not driving, being an observing presence in our neighborhood, adding to its vibrancy by our street presence, and supporting a local business and the community it gathers. Stacking our lives in this way is rich and rewarding and does not carry the weight of feeling like there is not time to get done what we need.

I recently spent two hours picking strawberries and found it to be a another perfect way to stack my life. I stacked family time, support of a local farm, share in a harvest, participation in the agricultural bounty of our valley, securing food, and the best yoga practice of my life. Yoga? Yes, yoga.

For two hours, I organically cycled through countless variations of malasana (squat), uttanasana (forward fold), virasana/vajrasana (sitting back on heels), bharadvajasana, Yin’s deer pose, lunges, sukhasana (seated cross legged), ustrasana (camel), snippets of surya namaskar (sun salutations), and asanas for which there may be no name.

Obviously, I didn’t capture this on video, but here is a 15 second re-enactment in time lapse.

And listen to Katy’s podcast on stacking your life. It’s been one of the most inspiring podcasts that I’ve listened to this year.

strawberryyogastill

Namaste, Michele

Alphabet Feet

Our feet respond well to varied movements. I talked about this last year in my weird feet post. This is a spirited yogasana foot exercise mash-up that moves your foot and ankle through countless ranges of motion and is probably good for your neurobiology as well.

I taught this dynamic asana/exercise in my yoga class this morning. It’s kind of impossible for this not to devolve into silliness, so you might keep that in mind if you are a teacher using this in your class.

alphabet_feet

  1. Sit on the floor (could also be done in a chair) with your legs extended in front of you.
  2. Hand options: either place your hands alongside your hips to support you in sitting upright; or interlace your hands and press your palms away from you.
  3. Bend your knees and place the soles of your feet on the floor in a pre-boat pose position.
  4. Lift your right foot off the floor.
  5. Using your best “handwriting,” slowly trace the letter A (print, cursive, all caps or small – doesn’t matter) in the air with your right foot, using your big toe as a marker. Move mainly at the ankle joint and less so at the knee and hip. Take a breath.
  6. Trace the letter B. Breathe in, breath out.
  7. Trace the letter C. Full breath cycle.
  8. Trace the entire alphabet, pausing a breath cycle between letters.

In my class, we traced A-M with the right foot, took a forward fold and then N-Z with the left foot, which for most of the class was the non-dominant foot and quite a bit more challenging.

I like doing this in boat pose with hand stretches because it allows more of my muscles to participate. Come up with your own variation and share it with me.

Here is my video of A-G.

Learn more exercises for your feet from my teacher renowned biomechanist Katy Bowman with these brilliant exercise videos that you can stream or download to view as often as you like for just $5 each!

Toes-and-Calves-Screenshot-300x300

Schoolhouse Series: Toes & Calves

UnDuck-Your-Feet-Screenshot-300x300

Schoolhouse Series: Unduck Your Feet

Namaste, Michele

 

Yoga Protocol for Balance for Poststroke Pilot Study

I read the full text of a few yoga studies each week. As a former research librarian with the current salary of a yoga teacher & blogger, I rely on free full-text sources, and when those are not available, I lean on former colleagues to help a girl out. Shh. Don’t tell.

This morning, I read the study “Poststroke balance improves with yoga: a pilot study,” which found significantly improved scores for balance in the study group receiving a group yoga intervention, with those who completed yoga even crossing the threshold of balance impairment and fall risk. “Because of improved balance, participants increasingly attempted new activities in different and more challenging environments and were aware of potential fall risk but grew confident in maintaining their balance.” Incredibly life changing for these participants and potentially for our stroke clients.

Granted the sample size was small (47), there were methodological gems with this study:

  • Participants were randomly assigned to the study & control groups
  • Two yoga groups and a wait-listed control group were included
  • Attrition/retention was reported

I am always curious to see which asanas are included in these studies, so that I can make more evidence-based choices for when I work with clients, who are dealing with similar health related issues. It is frustrating that many studies do not provide details on the yoga interventions used. But, to my delight, this inspiring study included in its publication an outline of it’s yoga protocol!

I hope you find it helpful as you craft your next balance-themed class or private session – whether or not your client base includes those who have experienced stroke.

Namaste, Michele

Hot from the Inside: How Hot Yoga Heats Up 100% of Your Body Down to the Cellular Level and Puts You at Risk of Heat Stroke

The American Council on Exercise (ACE), self-identified as the largest non-profit health and fitness certification, education, and training organization in the world, just published a scorching report on the effects of Bikram yoga on core body temperatures.  Bikram-franchised studios teach trademarked Bikram Yoga, a 26 posture sequence with two breathing exercises in a room heated to 105° with 40-50% humidity for 90 min. Copycat studios teach this same sequence under the taglines of hot yoga, hot hatha, or hot 26 and under similar conditions of heat and humidity for a duration of 60-90 minutes. I have experience with one studio that regularly allowed its temperature to creep up towards 110° and 60% humidity.

Is hot yoga safe??

The obvious question has always been “is it safe to practice yoga in such extreme heat  and humidity?” Now we have an answer.  The study found that 60 minutes into a 90 min class, nearly half of the study’s participants had core temperatures over 103°. Core temperature is that of your insides including your blood, guts, and other organs. Outside of the context of a hot yoga experience, adults at 103° or 104° are heading to urgent care centers and emergency rooms.

According to Bikram Yoga’s founder, Bikram Choudhury: [Parenthetical use is Choudhury’s not mine. MM]:

“The room is kept at this temperature or more for the following:

  • Keeping the body from overheating (contrary to popular misconception) 
  • Protecting the muscles to allow for deeper stretching
  • Detoxing the body (open pores to let toxins out)
  • Thinning the blood to clear the circulatory system
  • Increasing heart rate for better cardiovascular workout
  • Improving strength by putting muscle tissue in optimal state for reorganization
  • Reorganize the lipids (fat) in the muscular structure”

How do you actually keep from overheating?

A lesson on thermoregulation is warranted. When you exercise, you generate energy, which is released as heat. Excess core heat, a complex result of muscle activation, is transported from your core to your skin, where it is lost to the environment via several methods – radiation, conduction, convection, and evaporation.

Radiation. When your body is hotter than your surroundings, which it almost always is, then a greater quantity of heat radiates from your body than to it. In a thermal comfortable room, about 60% of heat loss occurs as radiant heat.

Conduction. The transfer of heat from your body to an object, say your mat in yoga. In a normally heated room, 3% of heat loss occurs due to conduction.

Convection. Heat transfer via moving gas/liquid, which is almost always occurring. In a reasonably temperatured room, 15% of heat loss occurs via convection.

Evaporation. Heat loss that occurs through ventilation/diffusion and sweating. This accounts for 25% of heat loss in a comfortable environment.

Metabolic heat is transported to the skin while activation of sweat glands causes sweat to be secreted onto skin surface, promoting heat loss by evaporation of the water portion of sweat, which does not contain toxins, by the way.

Body cooling by radiation and convection, which is about 75% of heat loss, depends on a significant difference between your core temperature and the air around you. When that air exceeds 98.6°, heat exchange is reversed and your body now gains heat by radiation and convection instead of losing it. Read that sentence again.

Now you are left with only one mechanism to cool your core temperature – evaporation of your sweat. Sweat can only cool you if it is allowed to evaporate. When the surrounding air is dry, sweat readily evaporates, cooling your skin. However, if the humidity is high as it is in hot yoga studios, evaporation is impeded, resulting in sweat accumulating on your skin and insufficient cooling of your body. You now have no way to lower your core temperature other than leaving the room. Ironically, ignorantly, and inexplicably, many hot yoga studios discourage you from leaving the room and instead suggest you lie down on your mat, where you are now at the mercy of gaining more body heat from conduction of heat from your mat to your body. Double jeopardy for studios with floor heating systems. You are now in a position of experiencing a critical heat load and developing the mother of all heat illness – heat stroke.

If you have not experienced a hot yoga class, I cannot impress upon you enough how much sweating happens. Many participants are soaked and dripping with sweat before the end of the first breathing exercise at the start of class. When sweating becomes your last resort to cool your core temperature, it must be matched by water intake or dehydration occurs.  Ironically, ignorantly, and inexplicably, many hot yoga studios discourage drinking outside one or two sanctioned water breaks.

When your core temperature reaches 104°, which happened to one of the study’s male participants (interestingly, male participants experienced significantly higher heat-induced heart rates and core temperatures), heat stroke becomes a real possibility. The Mayo Clinic defines heat stroke as “a condition caused by your body overheating, usually as a result of prolonged exposure to or physical exertion in high temperatures. This most serious form of heat injury, heatstroke can occur if your body temperature rises to 104 F (40 C) or higher.” Heatstroke can result in a number of complications including permanent damage to your brain and other vital organs and/or death. Heatstroke requires emergency treatment. Damage worsens the longer treatment is delayed, increasing your risk of serious complications or death.

What should hot yoga studios and teachers do?

I know enough hot yogis to also know it is futile to preach to them about the risks of the practice they love, so I offer, instead, best practices for minimizing that risk.

The ACE study made several recommendations for improving safety of hot yoga classes.

  • Shorten classes to 60 minutes. Study participants began experiencing dangerous core temperatures at the 60 minute mark
  • Lower the room temperature
  • Encourage students to stay hydrated by reminding them to drink water throughout the class
  • Stress to students that toweling off sweat undermines evaporative cooling in an already gravely compromised evaporation system

I would go bolder and say:

Hot yoga studios should reject the Bikram heat/humidity standard and implement a temperature cap of 98.6°, which would hopefully keep core temperatures below the 104° heat stroke threshold.  Humidity levels should also be lowered to allow for more efficient evaporative heat loss. I would hope to see further research that explores a range of lower temperatures and humidities as well include a greater number of participants, including novices and those unacclimatized, and an active control group.

New students should be offered a shortened, modified class to allow them to acclimatize. This study used regular practitioners of Bikram Yoga, who were acclimatized to 90 min at  105°/40%. However it takes up to 14 days to fully acclimate to these excessive conditions.

Hot yoga studios should provide ongoing training to its staff and students on how to recognize heat illness and what to do about it.

Namaste, Michele

bikram-yoga-safety-infographic

 

 

 

 

 

Yoga and bone density – another myth?

Raise your hand if you believe that yoga promotes bone health and helps prevent osteoporosis. Keep your hand raised if you think research has shown this to be true. Hold that hand high if you’ve read this research. Look Ma, no hands.  In fact, there are no randomized, controlled trials to support claims of many yoga teachers, including me, that practicing yoga promotes healthy bones and prevents osteoporosis. We don’t actually know yogasana’s effect on bone mineral density nor has anyone studied how much force specific yoga postures generate, which is thought to be important to bone density  – until now.

Exercise benefits bones in two ways. 1) Ground reaction force (GRF) is the ground pushing back back into a body with equal force. For example, walking has a GRF of 1 to 1.5  times your body weight. Running is 3-4 X body weight. When you are standing or walking in alignment, gravity compresses bones of your spine, pelvis, and lower extremities, which respond to these loads by laying down more minerals, thus increasing bone density   2) Muscle contractions load bones, again signaling them to lay down more minerals, thus increasing bone density. This bone mineral density (BMD) is used as a measurement of bone health. Research shows that both high and low impact exercise increases BMD in the spine and femoral neck, which are the areas most studied. In non-seated, non-supine yoga postures, one to four of your limbs support your body against gravity. Force is generated as you move into, hold, and move out of postures; and as you shift weight between your extremities. The nature of yoga suggests that it is a low-impact exercise that uses the body’s own resistance to generate force, but very few studies even measure GRF in exercise and none in yoga – until now.

In the first study of its kind, Sylvia Wilcox, a yoga teacher and lead researcher, measured GRF for 28 weight bearing Hatha yoga poses in a study published in 2012 in the International Journal of Exercise. Her research team used parameters from the only known previous study that divided exercises into either high-impact or low-impact GRF, where high impact was equal to or greater than 2 times body weight and low impact was less than two times body weight.

My favorite part of the study is a table that lists GRF measurements for a sample of the 28 poses studied. But, I wanted to see them all, so I located the lead author’s Master’s thesis that did indeed report GRF for all 28 asanas. The intention of this study was not to compare asanas and rank/recommend those with the greatest potential for bone building, as tempting as that may be for someone like me scanning the list. It’s main purpose was to obtain ground reaction force data from common yoga postures to see how their generated forces compare to activities like running, walking, dancing, jumping jacks, etc. As expected, Wilcox’s study was able to define yoga as a low-impact practice in terms of measured GRF.  In fact, yoga measures lower forces than any activities measured in previous studies.

Age, Weight, & Gender and Force Generation

Analysis showed no significant differences between test participants due to weight or age. For five of the 28 postures, there were significant differences between men and women explained by differences in centers of mass between the sexes. For postures connecting upper & lower body to the ground (think plank) force through the arms is greater for men than women because men’s center of mass is concentrated on the upper-body; conversely, force through the feet is greater for women than for men, because women’s center of mass is in the pelvis. In virabhadrasana/crescent, as part of Surya Namaskar (Sun Salutation), as subjects transitioned from Adho Mukha Svanasana (downdog) men generated more force in the front leg than women. It was theorized, based on researchers’ observations that because many of the males used momentum to swing the back leg forward into the lunge that they landed with greater force as opposed to the slower, more steady transition by female participants.

Upper Extremities and Force Generation

Almost nothing is written about low-impacts generated through the upper extremities. Where as handsprings done by gymnasts measure forces at 3 x body weight, yoga’s chataranga, updog, and pincha myurasana generate forces less than 1 x body weight, with only plank and crow generating maximum vertical forces of 1.08 and 1.05 body weight respectively. The researchers designed a small six month intervention with one non-yoga exercise that produced a similar range of forces in the upper extremities as those in the yoga study. In the intervention, changes in bone mineral content were recorded. It is entirely possible to replicate the magnitude, rate, and frequency of such impact forces using yoga postures instead of the non-yoga exercise as performed in the intervention study, thus showing that yoga may influence bone mineral density.

Can You Optimize Your Yoga Practice for Increased Bone Mineral Density?

Wilcox observes that in prior animal studies, low impact exercise with rest intervals produced similar bone building results as high-impact forces. If these findings apply to humans, could Hatha yoga, which is an excellent specimen of low impact applied loads with rest intervals between postures, be sufficient to stimulate bone cells in practitioners? Remember, no study, including this one, has attempted to show that yoga does or does not increase bone mineral density. However, it is known that resistance training in the form of concentric and eccentric loading of muscles, not only increases tendon stiffness that makes them stronger and able to withstand greater loads, but is also osteogenic, or bone mineral producing.  You can make your own yoga practice potentially more osteogenic by finding opportunities to turn static, passive stretches into dynamic postures that explore active mobility, use your own body as resistance, and include isometric, concentric, and eccentric muscle work so that you are generating force at all ranges of motion. I go into more detail about these methods in an earlier blog post, called Strong at Any Length.

If you want to play now, check out these free video shorts (less than 3 min each) that demonstrate how to potentially bone up your asanas.

Uttanasana Strong

Natarajasana Strong

Figure 4 Strong

Malasana Strong

Don’t Cheat Your Twist

Hamstring Training with Partner

Hamstring Training without Partner

Ustrasana Prep

Squatting on a Block

Oh, and if you are interested in learning about other unsubstantiated yoga claims and myths, check out the hard hitting new e-book Exposing Yoga Myths from the gals over at Smarterbodies.

Namaste, Michele

 

 

 

Busting other yoga myths with biomechanics

Unlike some of the improbable myths that the gals over at Smarterbodies take on in their new ebook Exposing Yoga Myths, yoga teachers could be forgiven for their misconceptions about demands placed on joints and muscles in common balancing asanas. In fact, nobody was more surprised at what is actually happening than Dr. George Salem, lead researcher for the Yoga Empowers Senior Study (YESS). Dr. Salem is Director of the Musculoskeletal Biomechanics Research Laboratory, Director of the Human Anatomy Program, directs the Exercise and Aging Biomechanics research program; and is Associate Professor in the Division of Biokinesiology & Physical Therapy at the University of Southern California.

In the study that is the subject of this post, Dr. Salem and his team used standard biomechanical analysis (joint moments of force and EMG measurements of muscle activation patterns) to examine physical demands placed on older persons, average 70 years old, performing three common variations each of Vrksasana (Tree) and Uthitta Hasta padangustasana (single leg balance).  Here’s what they discovered.

Vrksasana (tree pose)

Because it can become confusing, use this key for translating beginner, intermediate, and advanced vrksasana. You can see a visual here.

  • beginner = toes of non-stance leg touching the floor; hands on wall
  • intermediate = only stance foot touches ground; hands on wall
  • advanced = only stance foot touches ground; no wall support

They hypothesized that the beginner variation, which was done with toes on the floor and heel against the inside of the shank (lower leg) of the stance leg and using a hand on the wall for support, would be the least physically demanding . The intermediate variation, which had the entirety of the foot on the stance shank, but still holding the wall, would be more physically demanding. The advanced variation, which was classic vrksasana, with foot on shank and no wall support would be the most physically demanding. They hypothesized that the increase in physical demands would be linear. They were wrong.

Progressing

What they found was that there was a large increase in demand going from tree with the toes on the ground and wall support (beginner tree) to tree with the foot off the ground and wall support (intermediate tree). And there was not much change at all between having or not having wall support, when only the stance foot was grounded. Providing wall support doesn’t lessen demand nearly as much as lifting the toes from the mat.  This suggests that more time may be needed practicing the beginner variation before transitioning to the intermediate variation. Because older persons have diminished strength and balance, reduced joint range of motion, and a greater prevalence of osteoarthritis, some variations of what are seemingly appropriate asanas may place them at risk for musculoskeletal and neurological pain and injury. And while increased muscle loading may improve strength and endurance, excessively high joint moments of force may lead to damaging loads to joint structures and exacerbate osteoarthritis and other pathological joint issues.

Recommendation: In working with older persons in vrksasana, when they are ready to progress from the beginning variation, have them keep their toes on the floor and move away from the wall, rather than having them lift their toes while staying at the wall.

Hip Strength

Another finding was that advanced tree and intermediate tree (both with non-stance foot off the ground) were nearly identical in the physical demands of the lateral hip musculature aka abductors aka gluteus medius. Thus, there appeared to be no adaptive benefit to stepping away from the wall, when you are already balancing on one leg (toes of non-stance leg not on the ground). Thus, for students who feel safer holding onto a wall, they are gaining as much improvement in strength and endurance as those not holding the wall. Strong abductors are associated with better balance and reduced fall risk.

Recommendation: Let your students know that holding onto the wall does not undermine hip strength and will  effectively assist them in achieving better balance, decrease fear of falling and performance anxiety in class, and build confidence. 

Knee Safety

A really important finding has implications for students with knee issues. Intermediate and advanced tree pose increases loading of joint structures. Unfortunately, such loading characteristics are associated with knee osteoarthritis and joint pain, thus could exacerbate preexisting conditions. Importantly, and in contrast to commonly held conceptions, the use of a wall for support during these variations of Vrksasana does not offer protection for the knee joint.

Recommendation: For senior students with existing knee problems, suggest they stick with the beginner version of Vrksasana.

Uthitta Hasta Padangustasana (single leg balance)

Follow this key, when visualizing the beginner, intermediate, and advanced variations of padangustasana. Here is a visual.

  • beginner = extended leg supported on blocks
  • intermediate = extended leg supported on chair
  • advanced = extended leg unsupported aka supported by the strength of the student

Progressing with Props…maybe not

Again, researchers were surprised, when their hypotheses were not supported. It turns out that extending your leg onto a chair is not much of a progression over stepping onto a stack of blocks, although it appears quite a bit more demanding. (I interject that there is likely more balance anxiety for some older students to place their leg on the higher chair.) The real progression comes with the advanced variation, which uses active mobility – you holding your own leg up. What is striking to me is that while the leg may be higher on the chair, the effort is larger in the advanced variation – even though the leg is barely off the ground (see link to visual) because the student is generating internal force (muscle force) rather than relying on external force (chair) to assume the posture. It matters how you get there. It matters how you stay there.

Hamstrings

In the advanced variation, co-contraction of the hamstrings and quadriceps occurs, stiffening the joint and increasing stability, however, this increased loading may exacerbate existing knee osteoarthritis symptoms.

Recommendation: For senior students with existing knee problems, suggest they stick with the beginner or intermediate variations of Vrksasana.

Ankles

This study found Padangustasana to be an excellent posture for improving plantar flexor (think rising up onto the ball of your feet) strength and performance, which is associated with balance and postural control, gait, and fall risk in older persons. However, it’s not until students are confidently performing this one legged balance that they appreciatively load the plantar flexor muscles.  This asana is also excellent for ankle inverter strength (think sole of the foot facing in towards the midline of your body), which, like strong plantar flexor muscles, is critical for balance but also in agility and walking proficiency.

Recommendation: encourage your appropriate older students to work towards the advanced variation o Uthitta Hasta Padangustasana for improving ankle strength and agility.

Conclusions

This study’s biomechanical insights provide evidence that can be used by yoga instructors, when selecting modifications for their older students.

Here are three points to remember:

  1. Posture variations that have long been considered introductory may actually induce higher demands at some joints and planes of motion, than pose variations considered advanced.
  2. Pose variations can produce forces that are in the opposite direction of those generated during the classical variation.
  3. Use of props, such as a wall, to reduce contraindicated joint loading may have little or no effect.

As a yoga and movement teacher, my biggest take away is that there are few well-designed studies in the area of biomechanical forces and yogasana. In fact, the authors’ state that this is the first study to quantify the physical demands of yoga pose variations, using biomechanical methodologies. I will continue to seek more research like this so that I can replace time-honored ideas about what I think or what I’ve been told might be happening in yoga with what is actually happening in yoga.

The Physical Demands of the Tree (Vriksasana) and One-Leg Balance (Utthita Hasta Padangusthasana) Poses Performed by Seniors: A Biomechanical Examination. Sean S.-Y. Yu,  Man-Ying Wang,  Sachithra Samarawickrame,  Rami Hashish,  Leslie Kazadi,  Gail A. Greendale, and George J. Salem. Evidence-Based Complementary and Alternative Medicine. 2012.  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3437689/

Namaste, Michele

Welcome to your shoulder girdle – shoulder extension

Q. When I extend my arms, called shoulder extension in yoga, with a strap looped around my hands (or just hands clasped), I have significantly more range of motion than when I do the same action but holding a block. What is the difference?

These are the kinds of questions that I ponder at 3:30 am, when I should be sleeping. I don’t have enough tacit knowledge (yet) to answer such questions, so I get out my anatomy books and play, trying to puzzle it out. It is in this way that I’ve layered functional, contextual understanding on top of fuzzy recollections and ineffectual memorization. As always, what is happening is way more complex than my summation, but you’ll get the drift.

What are the similarities?

Let’s first look at the similarities. In both examples of shoulder extension, the primary movers or agonists – being the posterior deltoids and triceps – are contracting with help from latissimus dorsi aka lats, while the anterior deltoids, pectoralis major aka pecs and biceps are stretching.

And now the differences.

shoulder_extension_strap

In the strap example, because my hands have to push outward against the strap to keep it taut, my arms are therefore attempting to abduct or move away from my body, which means my lateral deltoids are also contracting. Were the strap removed, continuing to abduct my arms would eventually bring them into the arm position of Virabhadrasana 2. The loads are different, but the result would look about the same if I were clasping my hands instead of using a strap.

shoulder_extension_block2

In the block example, because my hands have to push into the block to keep if from falling to the floor, my arms are thus adducting or moving towards my body, meaning my lats and pecs are also contracting. By contracting my chest muscles, I effectively put the break on further extension of my arms behind me because I am now co-contracting muscles that both cause and keep me from extending. And that is why I cannot lift my arms as high with the block. 

Which method is better?

Is one method – strap or block – better than the other? It depends…

If you want to increase strength and integrity of your tendons, which is my goal in yoga, the bock technique is better for two reasons:

Co-contracting provides greater resistance for the primary movers – posterior deltoids and triceps. I don’t need to tell you this as you can experience it yourself, when you attempt to extend further.

  • the technique I use is to place a block behind me with elbows extended (straight), press firmly into the block (~75% of maximum effort) and try to lift it higher – just like in the picture above.

Adding  an isometric contraction at end range of motion signals collagen production in your tendons thus increasing their stiffness and their capacity to withstand greater loads. Relax already, stiffness as a biomechanical concept is not the same as that feeling of “tight” or “stiff” often exclaimed in yoga; tendon stiffness is a desirable thing. This kind of muscular work in yoga will make your tendons and ligaments more resilient against injury and ultimately may improve your flexibility.

  • One technique I use is to place a block behind me with elbows extended, and barely holding the block, lift my arms until I hit my end range and then press my hands firmly (~75% of maximum effort) into the block, holding for 10 seconds. This technique differs from what I described previously in that I lift my arms first  and press the block second; whereas previously, I pressed first and lifted second. It makes a difference how you get there. 
  • Another technique would be to press the block down onto a counter/table which is essentially trying to move into shoulder flexion and will fire the stretching anterior deltoid. At the same time, press your hands into the block (adduct) to isometrically contract your pectoralis major. It’s a lot of work!

shoulder_extension_blocktable

  • And yet another technique would be to clasp your hands and push them into a block positioned against your sacrum – here you get concentric work in the posterior deltoids, triceps, and lats as well as isometric contraction in your anterior deltoids while they are stretching at what may or may not be your end range. It doesn’t matter – you want to be be able to generate force at all ranges of motion.

shoulder_extension_block3

Think of this work in shoulder extension as prep work for puvottonasana aka reverse table top/plank. Ray Long, whom I introduce in an earlier post, is a master at knowing what muscles are working in just about any yoga pose you can think of. Once you know which muscles are contracting and which are stretching in a pose, you can manipulate variables to increase active mobility. He cues to isometrically attempt to scrub or drag the hands towards the hips, but without actually moving them. This simulates shoulder flexion,  and just like in the examples above using the table or the block against the sacrum, it causes an isometric contraction in the muscles that are stretching, and that makes them strong, more resilient at that range of motion. You can read more here in his book Yoga Mat Companion 3: Anatomy for Backbends and Twists.
Try it.

purvottonasana_RL

Purvottonasana by Ray Long

Or, you could just go back to passively flopping your arms overhead, which may increase your flexibility, but won’t increase strength and resiliency of your tissues. I like to think of passive, yummy poses as junk food yoga, a nod to Katy Bowman’s junk food walking. It’s really yummy and pleasurable, but should only be consumed in small amounts, not that often, and never in place of nutritious, connective tissue loving active mobility.

shoulder_extension_yummy

Namaste, Michele