Running is a high-impact activity. The defining feature of high-impact exercise is that both feet leave the ground simultaneously during each stride, creating a significant jolt when you land. During running, your body absorbs between 2.0 and 2.9 times your body weight with every footstrike, compared to just 1.0 to 1.5 times body weight during walking. That force is what earns running its high-impact classification.
What Makes an Exercise “High Impact”
Impact level in exercise refers to the ground reaction force your skeleton and joints absorb during movement. Activities are generally grouped into three tiers: low impact (swimming, cycling, elliptical), moderate impact (walking, hiking), and high impact (running, jumping, plyometrics). The key distinction isn’t intensity or how hard you breathe. It’s whether there is a flight phase where both feet are airborne, because landing from that phase multiplies the force traveling through your bones, cartilage, and tendons.
This means a slow jog is still high impact, even though it feels easy. A person jogging at a relaxed pace still generates roughly twice their body weight in ground reaction force per step. And because a typical runner takes around 160 to 180 steps per minute, those forces accumulate quickly over the course of a session.
How Running Loads Your Tendons and Joints
The Achilles tendon, the thick band connecting your calf muscles to your heel, is one of the structures most affected by running’s impact. Research measuring Achilles tendon strain found that it stretches about 4.0% during walking and up to 4.9% during fast running, reaching roughly 62% of its maximum capacity. More notable is the loading rate: during the stance phase of running, the Achilles tendon absorbs force at 16.5 to 20.0 kilonewtons per second. That’s roughly 15 to 19 times faster than the rate during a slow, controlled muscle contraction. This rapid loading is what makes running fundamentally different from slower movements, even when the total force is similar.
Your knees, hips, and spine experience analogous forces. Each landing compresses cartilage and loads the bones beneath it. For healthy tissue, this is a stimulus. For tissue that’s already damaged or for someone ramping up mileage too quickly, it can become a source of pain.
The Bone Density Payoff
High impact is not inherently bad. In fact, it’s one of the most effective stimuli for building stronger bones. A study comparing runners to cyclists of similar age, weight, body composition, and activity level found striking differences in bone health. Sixty-three percent of the cyclists had low bone density (osteopenia) in the spine or hip, compared to just 19% of the runners. Cyclists were seven times more likely to have osteopenia of the spine than runners, even after controlling for age, body weight, and bone-loading history.
The reason is straightforward: bone responds to mechanical stress by adding density. Running’s repeated impact signals your skeleton to reinforce itself, particularly in the hips, spine, and legs. Low-impact activities like cycling and swimming don’t provide that signal, which is why athletes in those sports sometimes have weaker bones than people who don’t exercise at all.
Running and Knee Arthritis Risk
One of the biggest concerns people have about high-impact exercise is whether it wears out your joints. The research here is surprisingly reassuring for recreational runners. A large meta-analysis published in the Journal of Orthopaedic & Sports Physical Therapy found that the prevalence of hip and knee osteoarthritis was 3.5% in recreational runners, compared to 10.2% in sedentary controls. That’s a lower rate of arthritis in the runners. Recreational runners actually had a slightly reduced association with knee osteoarthritis specifically (odds ratio of 0.83 compared to non-runners).
Competitive runners told a different story. Their osteoarthritis prevalence was 13.3%, higher than both recreational runners and sedentary people. The difference between the two groups likely comes down to volume and intensity: moderate, consistent running appears to keep cartilage healthy through regular loading, while extreme mileage or decades of competitive training may exceed the tissue’s ability to recover.
Who Should Be Cautious
Running’s high-impact nature is beneficial for most healthy adults, but certain groups need to approach it carefully. People with existing joint injuries, stress fractures, or advanced osteoarthritis may find that the repeated loading aggravates their condition. Those with osteoporosis face a paradox: their bones need the loading stimulus, but weakened bone is more vulnerable to fracture from that same stimulus. In these cases, a gradual progression from walking to walk-run intervals can bridge the gap.
Bodyweight also matters. A 200-pound runner generates roughly 400 to 580 pounds of force per step. For someone new to exercise or carrying significant extra weight, starting with lower-impact options and transitioning to running over weeks or months reduces the risk of overuse injuries in tendons, shin bones, and joint surfaces.
Reducing Impact While Still Running
If you want to keep running but lower the forces involved, several strategies help. Increasing your step rate (cadence) by 5 to 10% shortens your stride and reduces the braking force at each landing. Running on softer surfaces like trails, grass, or a track distributes impact differently than concrete. Wearing shoes with adequate cushioning absorbs some of the peak force before it reaches your skeleton. And alternating running days with low-impact cross-training like cycling or swimming gives your tissues time to repair between sessions.
None of these changes turn running into a low-impact activity. They simply lower the magnitude of each impact, which can be enough to keep you running comfortably if you’re managing a nagging injury or easing back after time off.