djiledesign/Getty ImagesFor decades, people exercising have been told one simple rule: never let your knees go over your toes. During lunges, squats and many other exercises, well-meaning coaches, trainers and physiotherapists repeated this advice so often it became fitness folklore. More recently, however, social media has pushed back. Popularised by fitness influencer Ben Patrick – better known as the “Knees Over Toes Guy” – millions have embraced a training style that focuses on building lower limb strength. Among the tenets is the idea that letting your knees travel further forward is a key part of “bullet proofing” your knees. So who’s right? Like most health and fitness debates, the answer lies somewhere in the middle. It’s not about whether your knees move forward beyond your toes, but what happens when they do.Knees like to be usedIn everyday life, your knees move well beyond your toes all the time. Think about walking downstairs, crouching down to play with kids, and kneeling in the garden. Imagine doing a squat. As your knees bend further, your thigh muscles work harder to stop your knees from collapsing to the floor. This extra muscle tension increases the force between your kneecap and thigh bone – what we call joint loading.Now think of exercises like the knees over toes split squat, which look a bit like this.This movement deliberately allows the knees to travel further forward, increasing this joint loading compared to shallower squats. For some people, this can be painful. For most, however, loading your knees like this is normal and perhaps even a good thing. Your bones, muscles and articular cartilage (the lining that covers the end of your bones that makes joint movement smooth) are living tissues that need loading to stay healthy. In this context, loading means making them bear weight.Weight bearing exercise – such as lifting weights – is one of the best ways to keep bones strong (and prevent osteoporosis).The opposite happens in space, where astronauts rapidly lose bone and muscle because their bodies are no longer exposed to gravity. On Earth, bedrest results in similar changes. Our bodies, including our knees, were designed to be used.The exercises aren’t actually newThe “knees over toes” approach hasn’t yet been well scientifically tested, so we don’t know whether it performs better than other well-designed strength programs. However, many of the exercises it promotes, such as split squats and deep squats, have been used for decades. The branding is new, the movement principles are not. Many of these exercises deliberately bend the knee through a larger range of motion, increasing the work done by your thigh muscles. This may promote greater muscle growth and strength than shallower exercises. Strength training also improves bone health and helps maintain healthy cartilage.Where caution is neededThe same feature that makes these exercises so useful, their ability to load the knee, is also why they should be progressed gradually. About one in four people have kneecap pain (sometimes called patellofemoral pain). If that’s you, pain often occurs during activities that place high loads on the knee, such as squatting and walking downstairs. But pain doesn’t automatically mean damage. In fact, progressively rebuilding your knees’ ability to tolerate heavy loads is one of the most effective treatments we have.Exercise therapy isn’t simply considered safe – it is the cornerstone of treatment when appropriately prescribed to build back the muscle strength and regain function.Should you try knees over toes exercises?The unsatisfying answer is: it depends.If you’re new to strength training, it’s normal for your muscles to feel worked and even a little sore afterwards. If you already have knee pain, start with a smaller knee bend, less weight, or fewer repetitions. For example, one of the signature “knees over toes” exercises is the split squat. Rather than trying to copy the deep versions shown on social media, begin with a comfortable knee bend and gradually increase how far your knee travels forward as your symptoms and strength allow. If you want to try a split squat, begin with a comfortable knee bend. martin-dm/Getty Images Mild discomfort can be acceptable, but pain that steadily builds during exercise, or leaves your knee much worse the next day, usually means you’ve progressed too quickly. That doesn’t necessarily mean you need to stop – try doing a little less before gradually building back up. If you’re unsure, consult a physiotherapist or doctor.If the exercises are working, you should notice them becoming easier, and everyday activities (such as walking downstairs, getting out of a chair) becoming more comfortable.Our knees don’t need to stay behind our toes, but they don’t need to be forced past them either. Whether you choose “knees over toes” exercises or another strengthening program matters less than progressing gradually and consistently. One exercise from social media is unlikely to be the holy grail for every knee problem or training goal.The goal is to build a knee that’s strong enough for the life you want to live.Matt Savage is the recipient of a La Trobe University Graduate Research Scholarship, and works as a musculoskeletal physiotherapist in private practice.Adam Culvenor receives funding from the National Health and Medical Research Council and Medical Research Future Fund.