Biomechanics means the study of how forces act on the body and how the body moves in response. In plain terms, it's the physics of movement: how your joints, muscles and tendons share load when you walk, run, lift or throw. It's a useful tool for physios, but here's what most explanations leave out: "bad biomechanics" explains far less pain and injury than people think. Research shows that many movement "faults" we were told to fear, such as flat feet or a rounded back when lifting, don't reliably predict injury.
Key takeaways
- Biomechanics meaning: the science of forces and movement in living bodies. In sport and physio, it's about how load is shared across your body.
- Movement "faults" are weak predictors of injury. A 2019 review of 16 running studies found the evidence "sparse and inconsistent".
- Flat feet aren't a death sentence for runners. In 927 novice runners, pronated feet were not injured more often.
- Lifting with a bent back hasn't been shown to cause back pain (low-quality evidence from a 2020 review).
- But technique can matter. In one trial, 2 weeks of gait retraining cut running injuries over the next year.
What is biomechanics? A simple definition
The word combines bio (life) and mechanics (the physics of forces and motion). Biomechanics applies the same principles engineers use for bridges and machines to people.
It has two main branches:
| Branch | What it describes | Everyday example |
|---|---|---|
| Kinematics | How you move: joint angles, speed, timing, range of movement | How far your knee bends as you land from a jump |
| Kinetics | The forces that cause or result from movement | How hard your foot hits the ground, or the load through your Achilles |
When people say a movement or tissue is biomechanical (or talk about a single "biomechanic" factor, like knee angle), they mean it relates to these forces and movements.
What is biomechanics in sport?
In sport, biomechanics is used to improve performance and, in theory, to reduce injury risk. Examples include:
- analysing a sprinter's start or a golfer's swing to make it more efficient
- measuring how much load a runner's legs take with each step
- designing footwear, bikes and equipment
At elite level this can involve motion-capture cameras and force plates. In a physio clinic it's usually simpler: watching you squat, hop, lift or run, and asking how symptoms change as you move.
Myth: "Your biomechanics are why you're injured"
For years, injuries were explained by spotting a movement "fault" and correcting it: flat feet, knees caving in, a rounded back. The idea is intuitive. The evidence is much weaker than the confidence it's usually delivered with.
Myth vs evidence
Myth: Flat or "over-pronating" feet cause running injuries, so you need corrective shoes.
Evidence: A Danish study followed 927 novice runners in neutral shoes for a year. Runners with pronated feet were not injured more than those with neutral feet, and actually had slightly fewer injuries per 1,000 km run.
That study was well designed: it followed people forward in time and measured exactly how far each person ran using GPS. But very highly pronated feet were rare (only 18 feet), so we can't be sure about extreme cases.
The wider picture is similar. A 2019 systematic review of 16 prospective studies looked for biomechanical risk factors for running injuries. It found that the evidence was "sparse and inconsistent" and depended heavily on who was studied and which injury was measured. The most consistent finding was limited evidence that female runners with more inward hip movement were more likely to develop kneecap pain or IT band syndrome.
What about lifting with a "straight back"?
"Lift with your legs, keep your back straight" is one of the most repeated pieces of health advice. A 2020 review and meta-analysis in JOSPT tested whether bending your lower back when lifting is linked to back pain. It found low-quality evidence that it is not a risk factor. In fact, people who already had back pain tended to bend their back slightly less when lifting.
The authors rated the studies as low quality, and most were cross-sectional (a snapshot, not a follow-up over time), so this isn't the final word. But it's a good reason to stop fearing a rounded back. Your spine is built to bend, and it gets stronger when you load it gradually.
So does technique ever matter?
Yes. Biomechanics isn't useless; it's just not the whole story. One of the strongest pieces of evidence that changing technique can help comes from a randomised controlled trial of 320 novice runners in Hong Kong.
Half had 2 weeks of gait retraining, using real-time feedback on a treadmill to land more softly. The other half ran on the treadmill for the same time without feedback. Over the next 12 months:
- 16% of the gait-retrained runners were injured
- 38% of the control group were injured
That's a 62% lower injury risk.
How much weight should we give this? It's a large, well-run trial, but it's one trial, in novice runners, using specialist lab equipment, with injuries reported through an online system. It hasn't yet been widely repeated in other groups. It suggests that targeted changes can help in the right person, not that everyone needs their running style rebuilt.
What's more important than "perfect" movement?
A helpful way to think about overuse injuries is load versus capacity: how much stress you put on a tissue compared with how much it can currently handle. Biomechanics affects where the load goes. Training changes, sleep, stress and strength affect how much load you can tolerate.
That's why physios usually look at both:
- Load: recent changes in training, a new job, a sudden jump in mileage or gym sessions.
- Capacity: strength, conditioning and how well the tissue has adapted.
- Movement: whether a particular pattern is making a painful area worse right now.
Changing how you move is one option. Getting stronger and building load more gradually is often the bigger lever. See our posts on increasing running mileage safely and why strength training is part of physio.
What happens in a biomechanical assessment?
A biomechanical assessment looks at how you move during the activities that bring on your symptoms. At a physio appointment, that might include:
- watching you walk, squat, step down, hop or run
- checking strength, range of movement and balance on each side
- testing which movements bring on or ease your pain
- asking about your training, work and any recent changes
What to wear: shorts and a T-shirt or vest top, plus the trainers you usually run or train in.
The useful question isn't "is this movement perfect?" but "is this movement linked to this person's pain, and is changing it worth it?" Sometimes the answer is a small technique change. More often it's a strength programme and a smarter training plan.
When should you see a professional?
See a physio if pain:
- has lasted more than 2–3 weeks, or keeps coming back
- is changing how you walk, run or lift
- is stopping you training or working normally
Get urgent help (GP, NHS 111, or 999 in an emergency) if you have pain after a significant fall or injury and can't put weight on the limb, a hot, red, swollen joint with fever, calf swelling and redness, numbness or weakness in a leg, or back pain with changes in bladder or bowel control or numbness around the saddle area.
How we help at Athos Physio
Our clinic is inside F45 Manchester NQ, at 77 Piccadilly. We'll assess how you move as part of the bigger picture, explain what's likely to be driving your symptoms, and build a custom rehab and strengthening plan around your sport, training or work. You don't need a GP referral, and we work with Bupa, WPA, Vitality and Aviva. Book an assessment.
FAQs
What is biomechanics in simple terms?
Biomechanics is the physics of how living bodies move. It looks at the forces acting on your body, such as gravity, ground impact and muscle pull, and how your joints, muscles and tendons respond. Physios use it to understand how load is shared during movement.
What is biomechanics in sport?
In sport, biomechanics analyses technique and forces to improve performance and help manage injury risk. Examples include analysing a running stride, a golf swing or a jump landing. At elite level it uses cameras and force plates; in clinic, it's usually careful observation and testing.
What is a biomechanical assessment?
It's an assessment of how you move during activities that matter to you, such as walking, running or lifting. A physio watches your movement, tests strength and range, and checks how movements affect your symptoms. The aim is to find changes that are actually linked to your pain.
What should I wear to a biomechanics assessment?
Wear shorts and a T-shirt or vest so your hips, knees and ankles can be seen, and bring the trainers you normally run or train in. If a particular activity brings on your pain, bring the kit you'd use for it.
Do flat feet cause injuries?
Not on their own, in most people. A one-year study of 927 new runners found that pronated (flatter) feet were not injured more often than neutral feet. Very flat feet were too rare in that study to draw conclusions, so get anything painful checked.
This article is general information, not a substitute for an individual assessment.
Sources
- Ceyssens L, et al. Biomechanical risk factors associated with running-related injuries: a systematic review. Sports Med 2019;49(7):1095–1115. https://doi.org/10.1007/s40279-019-01110-z
- Nielsen RO, et al. Foot pronation is not associated with increased injury risk in novice runners wearing a neutral shoe: a 1-year prospective cohort study. Br J Sports Med 2014;48(6):440–447. https://doi.org/10.1136/bjsports-2013-092202
- Saraceni N, et al. To flex or not to flex? Is there a relationship between lumbar spine flexion during lifting and low back pain? A systematic review with meta-analysis. J Orthop Sports Phys Ther 2020;50(3):121–130. https://doi.org/10.2519/jospt.2020.9218
- Chan ZYS, et al. Gait retraining for the reduction of injury occurrence in novice distance runners: 1-year follow-up of a randomized controlled trial. Am J Sports Med 2018;46(2):388–395. https://doi.org/10.1177/0363546517736277
Related: The 5 most common running injuries · Increasing running mileage safely · Strength training in physio · Does bad posture cause desk pain? · All conditions we treat
Reviewed by Nick Chatziviltsos, PgDip, HCPC-registered physiotherapist (PH114351).