Wolff’s Law: Why Bone Builds Where You Load It, And What That Means For Your Yoga

Wolff’s law: the short answer

Wolff’s law says that bone adapts to the loads put through it. Load a bone in the right way and it lays down more material. Stop loading it and the body slowly takes away what it no longer needs. A German surgeon, Julius Wolff, described the idea in the 1890s, and it is the reason exercise can say anything useful about bones at all.

Chris Lalor, Flametree’s Senior Iyengar Yoga Teacher, sums up the practical side in one line: the load has to be above habitual, or nothing happens. Bone stops answering a load it has already got used to.

• The rule: bone builds where it is loaded, and nowhere else.
• The catch: the load must be more than that bone is used to.
• The good news: the dose is small. A few well-chosen loads a day is the idea, not hours.
• For yoga: standing poses, single-leg poses and weight through the hands ask for more than a normal day does.
• The limit: the rule is solid. Whether a yoga class changes a bone scan is still being studied.
• New students: 12 classes for $59.50 in Darwin or LIVE online.

Last updated: 25 October 2026

Who was Wolff, and what did he notice?

Julius Wolff was a German surgeon. Looking at bones, he noticed that their inner structure and their shape followed the forces they carried. Bones that carried more got stronger in the right places. Bones that carried less faded.

Today we know why. Bone is living tissue, not a dead frame. Two teams of cells work on it all your life:

• Osteoclasts are the clearing crew. They dissolve old bone.
• Osteoblasts are the builders. They lay down new bone.

Think of a building site that never closes. The instruction it waits for is load. When a bone is loaded, the builders get to work. When it is not, the clearing crew slowly wins.

What kind of load does bone listen for?

Not every load counts. In her masterclass paper on bones, Chris Lalor gathers decades of research into four points. Bone answers a load that is:

• Changing. A load that comes and goes is a signal. A steady push that never changes soon stops being one.
• Big enough. A bigger strain gets a bigger response, once it passes a minimum.
• Quick to arrive. How fast the load comes on matters as much as how big it is.
• New and varied. A direction the bone does not often meet gets a stronger answer than a familiar one.

A well-made yoga pose can give you several of these at once, which is why the variety in a class is part of the plan.

Why does the load have to be “above habitual”?

Here is the part most people miss, and it changes how you look at every pose.

Your thigh bone has carried your weight thousands of times a day for decades. It has fully adapted. Just standing up is not a signal any more. It is the baseline.

To get any response, the load has to be more than that bone is used to. This cuts two ways.

• In the legs, the bar is high. Walking already loads the legs a lot, so you need something more to beat it.
• In the arms, the bar is very low. In an ordinary day your arms carry hardly anything. Almost any real weight through the hands is a big step up.

Walking, for all its good points, does little for the wrists and shoulders. That is why a pose on the hands is such a big deal. We look at that in our post on weight bearing exercises for osteoporosis.

Does bone build everywhere, or only where you load it?

Only where you load it. Sport has run this experiment for us.

In 1995 a Finnish team measured the arm bones of 105 national-level women tennis and squash players. They compared the playing arm with the other arm. They did the same in 50 women who did not play. In the players, the playing arm held about 8 to 16 percent more bone mineral, depending on the site measured. In the women who did not play, the difference between the two arms was about 3 to 5 percent. Same person, same diet, same genes. The only difference was which arm swung the racquet.

The gap was also two to four times bigger in women who started playing around or before puberty. Young bone answers load best, but that does not mean older bone stops answering.

So a practice that loads the whole body from many directions has an edge over one that loads only the legs. Our post on how to increase bone density goes further into this.

How much load does bone need?

Much less than people think.

In 1984, two researchers, Rubin and Lanyon, studied a forearm bone of a bird (a chicken), in a way that let them control the load exactly. When they took the load away, bone was lost. When they gave the bone just four loads a day, it held steady. When they gave it 36 loads a day, new bone formed. Over six weeks the bone mineral content rose to between 133 and 143 percent of where it started. And when they raised the loads from 36 to 1,800 a day, nothing extra happened.

This was a bird, in a laboratory, so the numbers do not carry over to a person. The idea does: a small dose of the right kind gets the response, and a huge number of repeats adds nothing. That is why a handful of well-held poses can matter more than a long, busy session.

What does Wolff’s law mean for your yoga practice?

It tells you what to look for in a class. A well-taught Iyengar class gives bone several kinds of load at once.

• Standing poses, held. Warrior 2, Triangle and Half Moon put weight through the legs and hips, and the hip is loaded from the side, a direction walking never uses.
• Muscles pulling on bone. Your muscles attach to your bones and pull on them. In a held pose, muscles on both sides of the limb work at the same time, like the guy ropes on a tent.
• Single-leg poses. On one foot, the standing leg and hip carry the whole body.
• Weight on the hands. Downward Dog and Plank load the wrists and arms, which an ordinary day almost never does.

Props do not water this down. A chair or a wall lets you hold a pose accurately and for long enough to count.

What Wolff’s law does not tell you

It is a rule about how bone behaves. It is not a promise about a bone scan.

Here is what the research shows so far. A 2026 review pooled 74 trials of exercise in 5,331 women after menopause. It found that mind-body exercise, a group that includes yoga, Tai Chi and Pilates, combined with strength work was the most effective kind for bone density at the spine and the neck of the thigh bone. Programmes of a year or longer gave the more consistent gains. Another study, by Dr Loren Fishman and colleagues, looked at 227 volunteers who kept up a 12-minute daily yoga routine. Their bone density rose in the spine and thigh bone, and no yoga-related serious injuries were reported. It compared people with their own earlier results and had no separate comparison group, so it is a signal and not proof.

No study has yet tested a full Iyengar practice, with weight on the hands, for bone density. Not yet tested is not the same as wrong. In yoga we call this the three ways of knowing: known from long practice, supported by research, and still being studied. Wolff’s law sits in the second group. How much a yoga class adds to it sits in the third.

Start with the free ebook and the bones and balance pass

Chris Lalor teaches this in her Yoga For Bones masterclass, and our free ebook, Strong Bones, Steady Feet, explains it in plain words. The ebook explains yoga. It does not teach it, because classes do that.

New to Flametree, or away for three months or more? The Yoga For Bones And Balance pass gives you 12 classes for $59.50 (10 at half price plus 2 free). Use them at our Woolner and Coolalinga studios or LIVE online. Props are supplied, and there is a money-back guarantee on your first class. Studio classes are for permanent NT residents, and online is open from anywhere.

Want to see the times first? Look at the beginner timetable. Or read our post on how to improve balance.

Wolff’s law questions

What is Wolff's law in simple terms?

Bone adapts to the loads placed on it. Load it in the right way and it builds more bone where the load goes. Take the load away and the body slowly removes bone it no longer needs.

Who discovered Wolff's law?

A German surgeon, Julius Wolff, described it in the 1890s, after studying how the inner structure of bones followed the forces they carried.

Does Wolff's law apply to older people?

Bone is alive at every age, so it can still answer load. Young bone answers best, and a 1995 study found the playing-arm advantage in tennis players was two to four times bigger if they started around puberty. That does not mean older bone stops responding, but the changes are small and slow.

Does Wolff's law mean exercise can fix thin bones?

It means exercise is one of the things bone responds to. It does not promise a result on a scan. Trials of yoga for bone density so far are small and mixed, and the larger recent reviews are the most encouraging, especially when strength work is part of the practice.

How many loads a day does bone need?

In a famous bird-bone experiment, 4 loads a day held bone steady and 36 loads a day built it. Adding many more built no more. That is a laboratory result, but it supports the idea that short, regular bouts do the job.

Sources

• Rubin CT, Lanyon LE. Regulation of bone formation by applied dynamic loads. J Bone Joint Surg Am 1984. PubMed
• Kannus P, Haapasalo H, Sankelo M, et al. Effect of starting age of physical activity on bone mass in the dominant arm of tennis and squash players. Ann Intern Med 1995. PubMed, DOI
• Zhou Z, Wei X, Zhang X, et al. Effects of different types of exercise over 24 weeks on bone mineral density in postmenopausal women: a systematic review with pairwise and network meta-analysis. J Sport Health Sci 2026. PubMed, DOI
• Lu YH, Rosner B, Chang G, Fishman LM. Twelve-minute daily yoga regimen reverses osteoporotic bone loss. Top Geriatr Rehabil 2016. PubMed, DOI
• Lalor C. Yoga For Bones: What, Why And How. Flametree Sunday Arvo Masterclass paper, 2026.

This post is general information about yoga. Flametree Yoga Studio, Darwin, Northern Territory.