When it comes to indoor cardio workouts, two machines usually top the list: treadmills and stationary bikes. You’ll find them in nearly every gym, fitness studio, or home setup, and for good reason. They’re both effective, accessible, and can give your heart a solid workout.

A treadmill is a machine that lets you walk, jog, or run indoors. It can be motorized (the belt moves for you) or manual (you move the belt with your stride).

Running can improve cardiovascular health, lower blood pressure, and boost endurance. It’s also linked to improved mood and reduced symptoms of anxiety and depression.

Another plus? Treadmill workouts—especially running—can help support bone density, which becomes more important as we age.

A stationary bike mimics the experience of cycling but keeps you in one place. There are several types, like upright or spin bikes, which look similar to traditional outdoor bikes, and recumbent bikes, which have a reclined seat for extra back support. You can even turn a regular bike into a stationary one with a trainer.

Research shows regular cycling improves cardiovascular fitness, lowers cholesterol, and supports weight loss. Cycling is also associated with improved balance and a lower risk of falls, especially in older adults.

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Both machines offer excellent cardio workouts, but the best pick for you depends on several factors:

A comparative study found that treadmill running burns slightly more per minute than cycling. For instance, treadmill use burns around 8.18–10.78 calories per minute, while stationary biking burns 7.98–10.48, depending on your speed and resistance. 

However, if you’re doing a casual ride or walk, the difference might be minimal. But if you’re running on the treadmill versus a low-resistance bike ride, the treadmill pulls ahead.

Another older study found that people burned more calories on a treadmill than on other cardio machines, including an indoor bike, when people worked out at what felt like the same intensity across machines.

Meanwhile, another study found the opposite. While both treadmill and bike workouts increase heart workload as intensity rises, cycling triggered slightly stronger cardiovascular responses. Specifically, participants showed greater increases in blood pressure and heart strain during cycling—especially at low to moderate intensities.

The most effective machine is the one you’ll actually use. The treadmill might be your jam if you enjoy the movement and don’t mind standing, walking, or running. Prefer sitting and zoning out to a playlist or Netflix? Indoor cycling could be a better match.

Also, consider your sport or goal—if you’re training for a run, treadmill training gives you sport-specific conditioning.

Space is a big consideration for home gyms. Stationary bikes typically take up less room than treadmills. However, there are foldable treadmill models that can help minimize their footprint if space is tight.

Both machines are beginner-friendly and versatile enough for seasoned athletes. But your health condition may steer your choice. 

Treadmills, especially when running, may pose more joint strain, particularly for those with knee pain, plantar fasciitis, or other impact-sensitive conditions. If you’re dealing with joint issues or recovering from an injury, the bike’s lower impact may be kinder to your body.

On the flip side, if you’re after intensity, treadmill workouts—especially running—can give you that challenge.  Just keep in mind that improper form, poor posture, or pushing yourself too hard too soon on either machine can lead to injury.

Either works if you’re just trying to meet the recommended 150 minutes of weekly physical activity. But if you’re training for something specific or want to target certain muscle groups, that may guide your pick.

Treadmills offer more of a full-body workout, engaging your core and arms in addition to your legs. Conversely, bikes are more lower-body focused, targeting your quads, hamstrings, and glutes.

If your goal is weight loss, both can help, as long as you’re consistent and match your workouts with intensity and duration.

If you’re recovering from injury or managing joint issues, a stationary bike may be a gentler option thanks to its low-impact nature, making it easier on the knees and hips.

Also, if you’re looking to build strength or improve overall athletic performance, it helps to pair either cardio machine with some strength training or cross-training, like resistance work, Pilates, or even yoga, to keep your routine well-rounded and more effective.

Both treadmills and bikes come in a range of prices, depending on features and build quality. High-end machines with touchscreens, apps, and subscription services will naturally cost more. 

When shopping, consider what features matter to you (e.g., built-in programs, resistance levels, connectivity), maintenance, warranties, and whether you’ll need a subscription for classes or training programs.

Not all machines are built for heavy use or group classes, so set your expectations accordingly.

At the end of the day, both treadmills and stationary bikes are great for cardio and improving your health. The better choice? It’s the one that fits your body, goals, space, and lifestyle—and most importantly, the one you’ll enjoy using consistently.