Impact training is any form of exercise where your body absorbs force through contact with the ground or another surface. It’s typically categorized as high-impact or low-impact based on how much force your joints experience during the movement. Running, jumping, and plyometrics are high-impact. Walking, swimming, and cycling are low-impact. The distinction matters because the amount of force your body absorbs shapes everything from bone density gains to injury risk.
How High-Impact and Low-Impact Exercise Differ
The simplest way to tell the difference: in high-impact exercise, both feet leave the ground at some point. Running, jumping rope, and most plyometric movements all involve a moment of flight followed by landing. That landing generates force that travels through your feet, ankles, knees, hips, and spine. In low-impact exercise, at least one foot stays on the ground (or your body is supported by water, a bike seat, or the floor), so the forces on your joints stay relatively low.
To put numbers on it, walking produces a ground reaction force of roughly 1.0 times your body weight with each step. Running typically generates 2 to 3 times your body weight, and jumping activities can push that to 4 or 5 times body weight or more, depending on height and landing mechanics. Those forces are the “impact” in impact training, and they’re not inherently harmful. In fact, they’re the primary stimulus behind several important adaptations in your bones, tendons, and muscles.
Common high-impact exercises include running, jump rope, basketball, tennis, hiking on uneven terrain, and CrossFit-style workouts. Low-impact options include swimming, cycling, yoga, Pilates, elliptical training, and walking on flat ground.
Why Impact Builds Stronger Bones
Your skeleton is not a fixed structure. It remodels constantly in response to the forces placed on it. When you land from a jump or strike the ground while running, the mechanical load slightly deforms your bone tissue. Specialized cells embedded deep in the bone detect that deformation and send chemical signals to the cells responsible for building new bone. This process, called mechanotransduction, begins within one minute of the loading stimulus.
The signaling cascade works like a relay system. Sensor cells in your bones detect strain and release signaling molecules that activate bone-building cells. At the same time, mechanical loading suppresses a protein called sclerostin that normally acts as a brake on bone formation. Regions of bone that experience the greatest strain show the most dramatic drop in sclerostin and the greatest new bone growth. The result is a skeleton that reinforces itself precisely where it needs to be strongest.
This is why impact training is so frequently recommended for bone health. The American College of Sports Medicine recommends that healthy adults perform weight-bearing aerobic exercises (like jogging, stair climbing, or tennis) at least 3 to 5 days per week, combined with moderate-to-high intensity resistance exercise 2 to 3 days per week, to maintain bone density. Low-impact activities like swimming and cycling, while excellent for cardiovascular fitness, don’t generate enough skeletal loading to produce the same bone-building effects.
The Critical Window for Children and Teens
Childhood and adolescence represent the most important period for building bone mass. The skeleton accumulates the vast majority of its mineral content before the mid-20s, and the peak bone mass you reach by that age is one of the strongest predictors of osteoporosis risk later in life. A 2025 meta-analysis found that high-impact jumping exercises significantly improved bone mineral content at the lumbar spine and femoral neck in children and adolescents, with especially pronounced effects in girls. Activities like jumping, running games, and court sports during these years essentially set a higher baseline that the body draws on for decades.
How Impact Training Strengthens Tendons
Bones aren’t the only tissue that responds to impact loading. Tendons, the dense cords connecting muscle to bone, also adapt when exposed to high forces. Research on older adults found that high-intensity resistance training increased tendon stiffness by roughly 58%, while low-intensity training produced no meaningful change. Stiffer tendons transfer force more efficiently and are more resistant to injury.
This adaptation is especially relevant for activities that involve rapid changes of direction, jumping, or sprinting, where tendons act as springs that store and release energy. A stronger, stiffer tendon handles those forces with less risk of microdamage. The catch is that tendons adapt more slowly than muscles. Your muscles may feel ready for harder training weeks before your tendons have caught up, which is one reason gradual progression matters so much with impact-based exercise.
Who Should Be Cautious
High-impact training isn’t appropriate for everyone. People with osteoarthritis in the hips or knees need to be selective about impact levels, since repetitive high forces on already-damaged cartilage can worsen symptoms. Joint injuries within the past six months, joint replacement, unstable heart or lung conditions, and significant functional limitations are all reasons to avoid jumping and running until cleared by a healthcare provider. Inflammatory arthritis conditions like rheumatoid arthritis also warrant a cautious approach.
That said, low-impact exercise is almost universally safe and still provides cardiovascular, muscular, and metabolic benefits. The goal isn’t to avoid all impact forever. It’s to match the level of impact to what your body can currently tolerate and recover from.
Progressing From Low-Impact to High-Impact
If you’re new to exercise or returning after a long break, starting with low-impact activities and gradually introducing higher forces is the safest approach. The National Academy of Sports Medicine recommends that beginners avoid doing too much too soon, since jumping straight to running or plyometrics significantly raises injury risk and often leads people to quit entirely.
A practical progression might look like this over four to six weeks:
- Weeks 1 and 2: Walk for 20 to 30 minutes at a comfortable pace on most days. Add bodyweight exercises like squats and lunges that load your joints without leaving the ground.
- Weeks 3 and 4: Introduce interval walks, alternating 30 seconds of fast walking or light jogging with 1 minute at a moderate pace for about 20 minutes. This begins exposing your joints and tendons to slightly higher ground reaction forces.
- Weeks 5 and 6: Extend jogging intervals and begin adding low-level plyometrics like small hops, skipping, or jumping jacks. Keep the volume low and pay attention to any joint soreness that lasts more than 24 hours after a session.
The key principle is that your cardiovascular system adapts faster than your connective tissue. You may feel like you have the endurance to run 30 minutes straight after two weeks, but your tendons, ligaments, and cartilage need more time to handle that load safely. Building up gradually lets all your tissues keep pace with your fitness gains, and it’s the single most effective way to avoid the overuse injuries that sideline so many beginners.