Cardio sucks but if you have any goals related to health and looking good you gotta do it. The term "cardio" itself instantly gives me images of zombies at a big box gym chain monotonously walking on a treadmill like a hamster stuck on a wheel. I cannot think of a more joyless activity as steady state cardio done time after time in the gym. This boring, zombie-like workout is a reason why so many people quit their self-made workout program. They keep the membership but no longer go because they have turned working out into a chore.
Cardio has obvious benefits as periods of elevated heart rate are required for basic cardiovascular health. If you are a long time weightlifter your joints must have some blood flow that is NOT related to pushing massing weights. The human body was made to move around, to run, sprint or jump. Not to sit in front of a tv or computer for every waking second of your life so having movement in your life is certainly a must.
Fix 1: Kill Cardio Term
First, kill the term Cardio and replace with Energy system work and it instantly seems better and more useful. Go even further with High Intensity Intervals Training, (HIIT) and not only does it sound better that boring cardio, it actually sounds challenging and fun! These workouts are far from monotonous and provide plenty of variety and a change in the word association may provide a subconscious boost.
Fix 2: Make it Competitive
Making energy work fun can be a game changer. Add some competition to compete against yourself, a training partner or a group. Getting more specific, crossfit style workouts where you mix in multiple exercises in circuit fashion while racing against time are a TON more entertaining than straight cardio. Going to a gym to get a treadmill for a set amount of time becomes a boring punishment over time that makes you want to jump off a cliff. It's boring, who wants to purposely do something boring? One big reason Crossfit has taken off is it has taken a typical housewife off of a treadmill, put a barbell in their hands where they lift it over their head and pound it to the ground when done. It is difficult to not feel awesome after such a workout. These types of workouts just make you feel better!
For wheelchair lifters I I would focus on some bodyweight exercises as the primary options. By having a challenge in front of you, say a combination of Dips and Pull Ups with a goal of hitting 100 total pull ups and 200 total dips for a 300 total in a targeted amount of minutes. The first time you attempt this cycle it takes you 25 minutes, track it. The next time you attempt this workout your goal is to beat 25 minutes. Bodyweight Pull UPs and Dips are just two examples of bodyweight exercises that can be used for a circuit style energy session. Pushups are another item that can be used. Add in battle ropes or kettle ball swings. The options are endless on what you can rotate in.
The key to keeping this more of an Energy workout versus a Strength workout is to keep any lift well below a 50% of a max. In other words, the exercise should be something you can at least do 20 reps of. Mix in a couple of exercises in rotating fashion with a goal set of total reps in each, time yourself, then beat it next time. Again, not rocket science but the variety will be a ton more enjoyable than any steady state cardio and this enjoyment will lead to better results.