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You can use an upper arm rehab bike (UBE) or what people call an arm bicycles for aerobic exercise with no stress on the lower extremities. tai chi is low-impact Yoga is another option You can still do strength training even with arthritis

Typically you have to lose more than 10% of your body weight for people to notice So if you weigh 160 lbs most people won't notice a difference until you are under 145 for example. Second if you are wearing the same clothes they may not see the difference. Try new colors, trimmer fits etc.

If you actually want to see your abdominal muscles you will need to get your body fat down to about the 12% range. You may well be toned as a result of your efforts but to get the look some people have you must reduce body fat to relatively low levels.

It may take up to 2 years for the skin to tighten up after weight loss but 10 lbs does not seem enough to cause a lot of loose skin, If after 1-2 years the skin is stilll loose you can try surgical skin tightening (expensive not covered by insurance) or if less of an issue laser sking tightening $3,000 or so.