Wayne Kuznar at MedPageToday.com, has an article about a study from UC San Francisco saying that,
Overall, women with SLE appear to have worse lower extremity muscle strength compared with healthy women.
The UCSF "Lupus Outcomes Study" of 146 SLE patients (women, mean age about 48) showed that Lupus patients, as a group have measurably reduced muscle strength in their lower extremities. I guess this means that if your legs feel weaker than they used to, then this is probably a result of your disease and something to target in your exercise regimen.

You do have an exercise regimen, don't you?

The study is suggesting that this reduced strength, if not payed attention to, could or would result in increased disability -- but also suggests, indeed, that paying attention to it with more exercise to improve and maintain strength in your lower extremities could or would put off that disability.

The bad news; this loss of strength in your legs is real, but the two-fold good news is, the medical PTB are waking up to it as a component of Lupus and, particularly, lower-extremity strength training can probably halt it or put it off.