Rowing machine or stationary bike

Try each out at a gym a few times before committing.

I have had a lot of success with the rowing machine. I incorporate it into my weekly training. A few years back, I was injured and exclusively rowed for 9 weeks straight (approximately 20,000m a day). 6 weeks after resuming my running schedule, I set a personal best over 10 miles. I'm know the bike will provide good fitness too, but you got to find something you enjoy doing before you can get any benefit. I don't enjoy biking enough to be able to accumulate enough training volume. Pick what you like, and it'll work out.

Rowing is amazing but it’s not for everyone. Lol.

I have two mindsets on that thing. Either the k’s are clicking off and it’s fun or I’m ready to get off after 10min and know I’ve got 35min left or whatever.

Concept 2 is the only option.

In most cases I would say that a rower is a way better choice. If you do it right you're using your legs for 80% of your power anyway.

Unless you are doing this to cross train since you are having back spasms, as your user name implies. In that case a bike might be better. Even then though, the posture of sitting on a stationary bike is not great for your back.

You last three posters have it right, a rowing machine is far better for most.

However, it is the #1 injury in a gym. It is NOT for everyone especially if not done correctly.

Great point. Take it slow and watch some vids on form before going HAM.

Rower > Stationary Bike as a translatable supplement to run training.

With the rower, technique is paramount. Do your research directly from the source, Concept II. Even if you don't purchase or use a Concept II rower, Concept II's online articles are legit. Unfortunately, rowing ergometer training has been hijacked and bastardized by the CrossFit industry, and that S#IT is plastered across all media platforms. Do NOT use a CrossFit source for indoor rowing.

Proper set up (fit) and mechanics are very important with indoor cycling as well, especially if you plan on using it regularly for a training supplement to running. Bike fit can be time consuming, but is absolutely worth it. However, cycling doesn't translate to run fitness anywhere nearly as well as rowing (which uses close to 80% of your muscle mass with each stroke cycle). Yes, you can obviously gain a tremendous amount of fitness and strength from indoor cycling, but there's more to the transition back to running process, and the biomechanics involved with that transition are more difficult to exploit.

Both will work, but the rower is superior when used properly.

Stationary bike with Zwift setup

I'd go with the bike. For me, I just put my "rain bike" up on the indoor bike trainer and ride. It's pretty good. Downside is it is incredibly boring.

Ski-erg