Although I would agree that pool or aquatic exercises are probably the easiest on the body, I think many important factors have been neglected.
1. Most obese individuals are low-income individuals and, therefore, normally lack accessibility to such facilities
2. Most obese individuals are not comfortable wearing clothing necessary to get into a pool. Making an obese person put on a bathing suit or even t-shirt and shirts can be stressful, emotional and embarrassing.
3. Keeping body temp down may help obese individuals to exercise longer in the pool. However, a slight increase of body temp with land exercises helps curb appetite temporarily, whereas aquatic exercises usually do not.
Taking all of these into consideration, I would not put aquatic exercises as a general recommendation for mobile obese individuals [unless I knew they had access to a pool and were open to wearing a bathing suit]. Instead I would say walking. This requires no gym membership, no equipment, no bathing suits and it will directly translate into improving their activities of daily living. To reduce joint and muscle pain, make sure they wear appropriate footwear [and replace when worn], ice after workouts and stretch before and after walking.
The first thing I would add onto walking would be functional low-impact exercises, such as diagonal chops, which can be performed with no resistance or with a band, med ball, dumbbell or soup can.
When it comes to exercises for obese individuals simplicity is key because if they are not compliant with your exercise program it will not be successful no matter how good you think it is.
I want to take the spin on the question of what is best for them. I think in a way the best thing for them isn’t the workout itself you do with them, but the habits you create. It’s going to take these people a very very long time before they can start doing many movements the rest of us take for granted. So my best advice is doing whatever will get them in a new habit that they can enjoy and stick to for years. I know everyone is always looking for a quick fix. As fitness professionals we know the quick fix will never work out long term. So just start them off walking, maybe doing some tai chi to just make them move. Then refer them to work with a registered dietitian.
I also agree with the water training, I have been a swim coach for the past 5 years and do Hydro training at Lifetime Fitness. The problem with this though is a lot of them won’t put in the effort in the water. They think they can hide and call bouncing for an hour a workout. So just keep an eye on them and don’t let them cheat!
I am making the assumption that you have a physician’s okay and that you are knowledgeable about possible diseases that are often correlated with morbid obesity. I also assume that you have – as well as is possible – did a screening and therefore have a rough idea what the person can and cannot do.
My first recommendation would be aquatic exercise if a pool is accessible.
If it is not, I would begin with strengthening, particularly the lower extremeties. Very obese people often have painful knees because of their weight which in turn prevents them from doing any cardiovascular exercises. What you can do as exercise may initially be very limited, and if the person is very deconditioned, you may encounter painful muscle cramps with even light exercises.
I found the first few weeks to be marked by trial and error because you will probably encounter limitiations you were not aware of (and neither was the client).
At times, just some assisted stretching may be helpful. I always tell people in that situation that the training has to be interactive and that you have to rely on their candid input to see what works and what does not.
I have a bodywedge which I like to use because a regular bench is often too narrow and therefore scary. Fortunately, I also have a Feldenkrais treatment table with is wide enough to be done for floor exercises if the client cannot get up from the floor. I put the Bodywedge on that table, and that works really well.
I wish you good luck with your client. You can only make a precarious situation better.