Ever since my accident, my primary source of aerobic exercise has been a recumbent stationary bike. In terms of my lower body, and especially my left leg, the ability to sustain an increased heart rate in any other way is pretty slim. I can lift weights and such, especially those using just the abs and arms, but good cardio is a trick.
Working Out Just to Stay Alive
I fell in May 2022. Through the rest of the summer, I was mostly on bed rest with only short excursions. By September, I was able to be more active and was returning to work several days a week. I was starting to figure out stairs. Through October and November 2022, I was getting better at navigating slopes and ramps as long as I had assistance (be it mobility aids or someone assisting me).
As we got into 2023, there became an increased need for me to get more mobile in general. In January of that year, Kaz and I ordered a recumbent bike. It took a moment to get it and get it set-up but early on the idea was just to get on it and move. At this point, I could move using just a cane, later using a pair of Nordic walking sticks, though had to be very careful with any kind of obstacles or changes in height.
Early workouts on the bike were usually just me getting to something like 10-11ish mph (16-18km/h) and keeping that going for 10-15 minutes with nearly no resistance. Even that was wiping me out.

Getting into Trackable Patterns
I have been steadily improving while trying to not stress my legs so much that it leaves me too tired to move. In the last couple of years I have worked out two general loops: sprints and uphill jogs.
Sprints will be roughly 20 minutes, give or take, and will be pushing for speed with lower degrees of resistance. 20-22mph (32-40 km/h). Hitting somewhere around the 100w and up (I’ve seen 180w). The idea is to hit the 10km mark as soon as possible and then go past it.
This involves a lot of sweating. A lot of sweating.
I probably look like I have been crying in the rain after I get done.

The “uphill jog” will have moderate to high resistance but a slower overall speed, centered around the 16-17mph (25ish km/h) for half an hour with the focus on strength building.
Trying to Up Endurance
Today I worked in the first cycle of a distance-as-in-time. Pedal as fast as I want, or as slow as I want. Just keep going for the whole time. Keeping the resistance in the upper-low-to-lower-moderate range (for now). Began with just 40 minutes, but it went well enough that I’ll up the time to an hour next time.

Not too bad. Not great. Somewhere in between.

Ends up being an average of ~26km/h over ~17km. It’ll be interesting to see how it goes as I increase it to a full hour.
By the way, yes that image of my final results (and the image I took for the header) are a bit dark. Keep in mind that this is roughly what it looks like outside as I start my workout:

It’s dark. I could turn on a light but there’s something about being out of breath and sweating bullets in the pre-dawn light that is kind of meditative.