The Best Low-Impact Cardio When Running Hurts Your Knees

First, why running hurts

Every running stride is a small collision. Measured on force plates, the ground pushes back with about two to three times your body weight, and more as you speed up. (Frontiers in Bioengineering and Biotechnology 2024; ledger.) Your knees take a good share of that, a few thousand times per run. Plenty of people are fine with it. If you're carrying extra weight, an old injury, or cartilage with a few decades on it, that collision is why a run that felt fine at 25 needs negotiating at 45.

The answer isn't to stop moving. Cardio fitness comes from sustained effort with your heart rate up, and your heart can't tell whether the effort came from pavement. So the question is which activities give you the effort without the collision.

What "low impact" actually means

Low impact describes the load, not the effort. An activity is low impact when nothing lands hard, or when something else absorbs the landing, so the force travelling up through your ankles, knees and hips stays close to your own body weight instead of multiplying.

Running is the reference point at the other end: the ground pushes back with roughly two to three times your body weight on every stride, and more as you speed up. (Frontiers in Bioengineering and Biotechnology 2024; ledger.) Walking, cycling and swimming sit well under that, which is why they head the list below. A sprung floor or trampoline sits in the low-impact group for a different reason: the surface gives way and takes the landing, which is why rebounding is generally described as a low-impact aerobic workout with far less joint load than running. (Cleveland Clinic; ledger.)

Two things the label does not mean:

• Not low effort. Your heart rate doesn't know what your knees are doing. An hour of coached bouncing or a hard session on the bike will leave you as puffed as a run.
• Not automatically safe for every joint. Low impact means less load per step. If a specific movement hurts, that's still a reason to ask a physio or your GP about that movement.

So the useful question isn't "is this low impact", it's "where does the force go". If it goes into water, a saddle, or a sprung surface instead of your knees, you're in the right part of the list.

Low-impact cardio, ranked by joint load

1. Swimming and water-based aerobics. The water carries most of your weight, so your joints get the effort and almost none of the impact. And it works. A 2026 systematic review and meta-analysis of 15 trials in older adults found water-based aerobic exercise improved cardiorespiratory capacity by about 5 ml/kg/min compared with doing nothing, with gains in muscle strength as well, and the fitness gains were similar to land-based aerobic exercise. (Journal of Aging and Physical Activity 2026.) The catch is access. You need a pool, and lap swimming has a technique barrier that an aqua class doesn't.

2. Cycling. You're seated, there's no landing, and the pedal stroke moves the knee through its range without loading it. The fitness evidence is strong. A 2026 meta-analysis of seven randomised trials compared people who trained only on a bike with people who trained only by running, and found no significant difference in VO2max, or even in running time-trial performance. (Frontiers in Sports and Active Living 2026.) The bike kept people as fit as running did, running included. If your knee complains on the bike, get the seat height checked first; a saddle set too low is the usual culprit.

3. Rowing and the elliptical. Both machines exist to take the landing out. Rowing works most of your body at once; the elliptical is running without the impact. Neither has been studied as thoroughly as swimming or cycling, so I won't put a number on them, but both let you hold a high heart rate for a long time with your feet planted or your backside on a seat.

4. Bouncing on a sprung surface. A trampoline or sprung floor absorbs the landing so your joints don't have to, which is why rebounding is generally described as a low-impact aerobic workout with far less joint load than running. (Cleveland Clinic; ledger.) Low impact isn't low effort, though. An hour of coached bouncing is genuinely hard work. The trial evidence I can point to is on balance and mobility rather than cardio: a 12-week mini-trampoline programme improved balance, gait, strength and functional mobility in older women with low bone density. (Posch 2019.) That's why it sits here and not at the top of the list. It's on the list at all because it's the one people look forward to.

5. Brisk walking, especially uphill. The lowest bar and the most underrated. Walking loads the knees at a fraction of running, and a hill or a weighted vest gets the heart rate up without adding impact. It won't build the top end of your fitness the way the options above will, but it holds the base.

How to choose

Pick the one you'll do three times a week. That's the whole rule. Every trial above ran for weeks or months, and the fitness they measured belonged to the people who kept turning up. A programme you skip does nothing, however good it looked on paper.

If you want one suggestion: cycle or swim for the base, and add a session a week of something you enjoy enough to laugh at. Ours is coached, adults-only, and over before you check your watch.

FAQ

What counts as low-impact cardio?

Anything that keeps the force through your joints close to your body weight: walking, cycling, swimming and water aerobics, rowing, the elliptical, and bouncing on a sprung surface. Running is the contrast, at roughly two to three times body weight per stride.

Should I stop running completely?

Not necessarily. Plenty of people run less rather than never, and fill the gap with one of the options above. If your knee hurts during or after runs, see a physiotherapist before you push through it. A physio can tell you what the pain means and what to do about it. I can't.

Is low-impact cardio as good as running for fitness?

For aerobic fitness, the cycling trials say yes: no significant difference in VO2max after weeks of training. Water-based exercise improves fitness measurably too. What you give up is running-specific: the tendon and bone loading that only impact provides. That's a real trade, and for a sore knee it's usually the right one.

Is trampolining bad for your knees?

On a proper trampoline or sprung floor, the surface does the absorbing that pavement makes your joints do, which is why it counts as low impact. It's still exercise, so if you have a current knee injury, ask your physio or GP before your first session. We start everyone on the floor and on the wall, with a coach, before any big jumps.

How much should I do?

Australian guidelines suggest 150 to 300 minutes of moderate activity a week, or 75 to 150 minutes of vigorous. Three sessions of 30 to 45 minutes of anything above gets you into that range.

Knees ready for something more fun than a bike? Guided sessions at Run The Wall in Brookvale are adults-only, groups of four, on a surface built to take the landing for you. Book a session, or read what bouncing does for your body in 7 health benefits of trampolining for adults.

References

• Comparison of ground reaction forces as running speed increases. Frontiers in Bioengineering and Biotechnology (2024). Claim ledger entry rtw-running-grf-2to3x.
• Effects of Water-Based Aerobic Exercises on Physical Fitness in Older Adults: A Systematic Review With Meta-Analysis of Randomized and Nonrandomized Trials. Journal of Aging and Physical Activity (2026). doi:10.1123/japa.2024-0182 (PMID 41633352)
• Cross-training between running and cycling: effects on VO2max and running performance, a systematic review and meta-analysis. Frontiers in Sports and Active Living (2026). doi:10.3389/fspor.2026.1843803 (PMID 42267259)
• Cleveland Clinic. Trampoline workout benefits. Claim ledger entry rtw-rebound-lowimpact.
• Posch, M., et al. (2019). Effectiveness of a mini-trampoline training program on balance and functional mobility, gait performance, strength, fear of falling and bone mineral density in older women with osteopenia. Clinical Interventions in Aging, 14, 2281-2293.