Running is not low impact. It is classified as a high-impact exercise because every stride involves a brief flight phase where both feet leave the ground, followed by a landing that sends force through your joints. That landing generates ground reaction forces of 2.0 to 2.9 times your body weight, depending on speed. For comparison, walking produces only 1.0 to 1.5 times your body weight in force. This distinction matters for your joints, your bones, and how you should think about building a training plan.
What Makes an Exercise “High Impact”
Impact level refers to how much force your body absorbs when it contacts the ground. Low-impact exercises keep at least one foot on the ground at all times (walking, elliptical training, cycling) or remove ground contact entirely (swimming). High-impact exercises include a moment of airtime followed by a landing: running, jumping, dancing, and most court sports.
The key variable is ground reaction force, which is the force the ground pushes back into your body with each step. At a slow jog, you absorb roughly twice your body weight per stride. At faster paces, that climbs toward three times your body weight. Running also increases side-to-side and braking forces by two to four times compared to walking. These forces accumulate over thousands of steps per run, which is why impact management matters so much for runners.
Why High Impact Isn’t Automatically Bad
High impact carries a reputation for being harmful, but the relationship between running and joint health is more nuanced than most people assume. A meta-analysis of over 2,100 adults found that runners actually had lower odds of needing a knee replacement due to osteoarthritis than non-runners, with a pooled odds ratio of 0.46. In practical terms, recreational runners were about half as likely to need a knee replacement as sedentary people.
The reason is that cartilage responds to moderate, repeated loading by adapting and maintaining its health, much like muscle responds to resistance training. Problems tend to arise not from running itself but from doing too much too quickly, or from continuing to train through pain that signals tissue damage.
How Impact Affects Your Bones
One genuine advantage of running’s high-impact nature is what it does for bone density. Exercise research classifies running and jogging as high-impact weight-bearing activities, and these are among the most effective ways to maintain or improve bone mineral density at the hip and spine. Low-impact activities like walking, swimming, and cycling are beneficial for cardiovascular health but provide little stimulus for bone growth. Walking’s loading force simply isn’t large or fast enough to trigger the adaptive response that strengthens bone tissue.
This is especially relevant for older adults and postmenopausal women at risk for osteoporosis. If bone health is a priority, the impact that makes running harder on your joints is precisely what makes it better for your skeleton.
Foot Strike and Loading Rates
Not all running impact is identical. How your foot meets the ground changes the character of the forces your body absorbs. Runners who land on their heels (the most common pattern) produce a distinct spike in force early in each step, with high vertical loading rates. Runners who land on the ball of the foot typically eliminate that initial spike entirely, with loading rates roughly half those of heel strikers.
This doesn’t mean forefoot striking is universally better. It shifts stress from the knee and shin to the calf and Achilles tendon. But it does illustrate that running form can meaningfully change how impact travels through your body, even though the total force remains high.
Surface and Shoe Choices
Running surface makes a smaller difference than most people expect. Concrete produces the highest peak accelerations, but only about 3.6% to 5.6% more than a synthetic track or grass. That’s a real difference over months of training, but it’s not the dramatic reduction many runners hope for when they seek out softer ground.
Shoe cushioning is even more counterintuitive. A study comparing maximally cushioned shoes to traditional neutral shoes found that the extra-cushioned shoes actually increased impact forces and loading rates. Heel-striking runners in the maximalist shoes landed with 1.76 times their body weight, compared to 1.58 times in neutral shoes. The likely explanation is that runners subconsciously adjust their stride when they feel more cushioning underfoot, landing harder because the shoe feels protective. This doesn’t mean cushioned shoes are harmful, but they don’t reduce impact the way their marketing suggests.
Injury Risk and Training Load
The high-impact nature of running does contribute to injury, but the biggest risk factor isn’t the impact itself. It’s how quickly you increase your training. A large cohort study of over 5,200 runners found that 35% sustained a running-related injury, and 72% of those were overuse injuries rather than acute events like ankle sprains.
The clearest predictor of injury was sudden spikes in training distance. Runners who increased a single session’s distance by more than 100% compared to their recent average doubled their injury risk. Even modest spikes of 10% to 30% raised the risk by 64%. The practical takeaway: keeping session-to-session increases below 10% significantly reduces your chances of developing the stress fractures, shin pain, and tendon problems that are hallmarks of high-impact overuse.
Low-Impact Alternatives for Similar Fitness
If you need or prefer low-impact cardio, several options deliver meaningful fitness benefits. For a 160-pound person, running at 5 mph burns roughly 606 calories per hour. Low-impact aerobics and elliptical training burn about 365 calories per hour at moderate effort. You won’t match running’s calorie burn minute for minute, but you can close the gap by exercising longer or at higher intensity.
The elliptical trainer is the closest mechanical match to running because it mimics the leg motion without the landing impact. Cycling and swimming are excellent for cardiovascular conditioning but provide minimal bone-building stimulus. Rowing is another strong low-impact option that adds upper-body work. For most people, mixing high-impact and low-impact sessions throughout the week offers the best combination of bone health, cardiovascular fitness, and joint recovery.