How much force does exercise actually put through your bones? The research is surprising.

The last post talked about why bones need load and impact — and why walking alone isn't usually enough. But here's a question I find myself thinking about: how much load is actually enough? And how do the things we do every day compare?

It turns out researchers have measured this directly. And the results are worth knowing.

What the research measured

A body of research has looked at peak vertical ground reaction force — the force that travels up through the skeleton when your body meets the ground during different activities. It's measured relative to body weight, which makes it a useful way to compare.

The numbers, adapted from Weeks and Beck and the work of Kukulja et al., tell a clear story.

At the lower end, a lunge puts around 1.1 times your body weight through your skeleton. Walking sits at 1.2 times. Marching on the spot reaches 1.5 times. These are all useful movements. But in terms of the force travelling through bone, they are relatively modest.

Move into running and you reach around 2.6 times body weight. Step-ups at 30 centimetres take you to 2.7 times. A single leg forward leap reaches 3.1 times.

Then things get more interesting. A heel drop — where you rise onto your toes and let the heels fall sharply to the floor — produces 3.6 times body weight. A jump squat reaches 3.8 times. A star jump 4.3 times. A vertical squat jump, at the top of the range, reaches 7.1 times body weight.

The range across the table is striking. Walking and a vertical squat jump are not even in the same conversation when it comes to the signal they send to the skeleton.

What this means in practice

This does not mean everyone should be doing vertical squat jumps. The appropriate level of impact depends enormously on the person — their age, their diagnosis, whether they have osteoporosis, whether they have had fractures, their fitness level and their history.

But it does mean something important: the intensity of the stimulus matters. Bones respond to challenge. They adapt to familiar loads relatively quickly, and after a point, the same movement stops being a particularly meaningful signal for new bone activity. This is why a thoughtfully varied programme, one that gradually increases the demand over time, tends to be more effective than repeating the same comfortable movements indefinitely.

What about weights? Do you still need impact?

This is one of the most common questions I hear, and it is a good one. If you are already lifting weights, do you still need to do any jumping or impact work?

The answer, based on current research, is yes — and here is why.

Strength training works because muscles pull on bones via tendons when they contract against resistance. That pull stimulates the bone-building cells, the osteoblasts, to get to work. It is a powerful signal and an essential part of any bone health programme.

But impact creates a different kind of signal. When your foot meets the ground during a jump or a step, a rapid compressive wave travels through the skeleton. The speed and the brevity of that wave seem to be part of what makes it effective. It is a distinct mechanical stimulus — not interchangeable with the slower, more sustained load of a weighted exercise.

A heavy squat and a jump squat load the same muscles. They send different messages to the bone.

The research points toward a combination being most effective — hip-loading impact activities alongside muscle-strengthening work. Interestingly, jumping has been shown to increase bone density in perimenopausal women, though the evidence is less clear in postmenopausal women, which is one reason why strength training becomes even more central as we move further past menopause.

A note on volume

One more thing worth mentioning. Bone does not seem to respond well to very high volumes of the same stimulus. Research suggests that after around ten minutes of repetitive loading, the response starts to diminish. More is not always better. What matters more is the quality of the stimulus and the variety of the challenge.

This is one reason why I think good Pilates — the kind that includes progressive load, standing work, balance challenge and where appropriate some impact — is genuinely useful. Not because every Pilates class automatically builds bone, but because the principles of attention, progression and precision align well with what bone actually needs.

What this looks like in a class

In my Structural Strength class, the impact section exists for exactly this reason. Heel drops, jump squats, star jumps — these are not there for fitness theatre. They are there because the research supports their use as specific bone stimuli, built into a progressive programme where people work at an appropriate level for their body.

If you are managing osteoporosis or have had a fragility fracture, this approach needs to be more carefully tailored — and there are movements I would modify or avoid. But for many women in midlife with osteopenia or simply a concern about their bone density going forward, progressively increasing impact and load is not only safe with good guidance, it is exactly what the evidence recommends.

Structural Strength is a live online class, Wednesdays at 6.30pm. It is a Pilates-based resistance class designed for midlife bone health — progressive loading, hip strength, and impact work, done with precision and care. DM me if you would like to know more.

Data in this post is adapted from Weeks & Beck and Kukulja et al., as cited in research on peak vertical ground reaction force relative to body weight.