For individuals with bad knees, the best cardio exercises prioritize low-impact movements that minimize joint stress while still delivering cardiovascular benefits. Medical and fitness experts consistently recommend activities that avoid repetitive pounding on the knees, such as running or jumping, and instead focus on fluid, controlled motions or non-weight-bearing exercises. Swimming emerges as the most universally praised option across sources, as it provides a full-body workout with zero impact on the knees, while elliptical machines, cycling, and rowing are frequently cited as gym-based alternatives that mimic natural movement patterns without excessive strain.

Key findings from the research include:

• Swimming and water-based exercises are the top recommendation due to their zero-impact nature and ability to engage multiple muscle groups simultaneously ^{[1][3][6][7][9]}
• Elliptical trainers and stationary bikes are the most knee-friendly gym machines, offering adjustable resistance and controlled motion ^[2][3][6][9]
• Rowing machines provide a full-body, low-impact workout but require proper form to avoid knee strain ^[3][6][7]
• Walking (short, brisk sessions) and step-ups are accessible at-home options that strengthen knees when performed correctly ^[1][2][9]

Best Low-Impact Cardio Options for Bad Knees

Water-Based Exercises: The Gold Standard for Knee Protection

Swimming and pool exercises are the most consistently recommended cardio options for individuals with knee pain across all reviewed sources. The buoyancy of water eliminates gravitational impact entirely, allowing for fluid movement without compressing the knee joints. This makes aquatic exercise uniquely suitable for both rehabilitation and fitness maintenance. Swimming engages the entire body—including the heart, lungs, and major muscle groups—while the water’s resistance provides a strength-training component without the need for weights.

Key advantages of water-based cardio include:

• Zero joint impact: Water supports up to 90% of body weight, reducing stress on knees, hips, and ankles ^[3][6]
• Versatility: Activities range from lap swimming to water aerobics, resistance training with pool noodles, or even aquatic jogging for those who miss running ^[1][7]
• Therapeutic benefits: Warm water (typically 83–88°F in therapy pools) can ease stiffness and improve circulation, which is particularly beneficial for arthritis sufferers ^[6]
• Caloric burn: A 155-pound person can burn approximately 223–400 calories per hour swimming at a moderate pace, comparable to land-based cardio ^[9]

For those new to swimming, sources recommend starting with 20–30 minute sessions 2–3 times per week, focusing on strokes like freestyle or backstroke that emphasize smooth, controlled movements. Water aerobics classes are also highlighted as a social and structured way to incorporate pool exercise, with many gyms offering shallow-water options for beginners ^[1].

Gym and Home Equipment: Ellipticals, Bikes, and Rowers

When water-based exercise isn’t accessible, elliptical machines, stationary bikes, and rowing machines are the next best options for knee-friendly cardio. These machines are designed to mimic natural movement patterns while reducing impact, making them staples in physical therapy and rehabilitation settings.

Elliptical trainers are frequently cited as the safest alternative to treadmills. They allow for a running-like motion without the joint jarring that occurs when feet strike the ground. Studies referenced in the sources note that ellipticals can burn 270–400 calories per hour while maintaining a knee flexion angle that minimizes strain ^[2][3]. Key tips for elliptical use include:

• Keeping resistance low to moderate to avoid overloading the knees ^[9]
• Maintaining an upright posture to distribute effort evenly between the legs and arms ^[3]
• Using the moving handles to engage the upper body and reduce lower-body fatigue ^[6]

Stationary bikes (both upright and recumbent) are another top recommendation, particularly for those with arthritis or post-injury stiffness. Cycling improves knee flexibility and strengthens the quadriceps and hamstrings, which support knee joint stability ^[2][7]. Sources emphasize:

• Starting with low resistance and gradually increasing as tolerance improves ^[2]
• Opting for recumbent bikes if sitting upright causes discomfort, as they distribute weight more evenly ^[3]
• Avoiding "mashing" the pedals (pushing down too hard) to prevent knee strain ^[7]

Rowing machines offer a full-body workout but require caution. While they are low-impact, improper form—such as over-bending the knees or jerking the handle—can exacerbate knee pain. Correct technique involves:

• Pushing through the legs first, then engaging the core and arms ^[3]
• Keeping the knees aligned with the toes during the drive phase ^[6]
• Starting with short, 5–10 minute sessions to assess knee tolerance ^[9]

For home workouts, step-ups (using a low bench or sturdy platform) are a practical alternative. They mimic stair climbing without the downward impact and can be adjusted for intensity by changing step height or speed ^[1][9].

Additional Considerations and Precautions

While the above exercises are generally safe for bad knees, sources uniformly stress the importance of individualization and professional guidance. Knee pain can stem from various conditions—such as osteoarthritis, ligament tears, or patellofemoral syndrome—each requiring tailored approaches. For instance:

• Osteoarthritis sufferers may benefit more from warm-water pool exercises to reduce stiffness ^[6]
• Post-surgical patients should avoid resistance-based machines until cleared by a physical therapist ^[2]
• Those with patellar tracking issues may need to modify step-ups or cycling to avoid excessive knee flexion ^[7]

Sources also warn against common mistakes, such as:

• Overtraining: Gradually increasing duration and intensity is critical. Harvard Health recommends starting with 5–10 minutes of activity and adding 1–2 minutes per session ^[2]
• Poor footwear: For walking or step-ups, supportive shoes with cushioning are essential to absorb shock ^[1]
• Ignoring pain: Discomfort during exercise should subside within 30 minutes; persistent or sharp pain signals the need to stop and consult a professional ^[7]

Finally, combining cardio with strength training (e.g., partial squats, calf raises, or Pilates) is encouraged to build muscle support around the knees ^[1][7]. Strengthening the quadriceps, hamstrings, and glutes can reduce knee pain long-term by improving joint stability.