First off, congratulations on doing something. Many people would use your condition as an excuse. You should be proud that you aren’t.
There things we must do and things we must not do. This obviously supersedes what we should and shouldn’t do. We have three different types of muscle fibers (slow, intermediate, and fast). With low weight/high rep work, you’re primarily focused on the slow twitch fibers. These are smaller (think marathon runners). The high weight/low rep works builds the intermediate and fast twitch fibers. These are bigger (think sprinters). The work you’re doing can help you maintain some strength but as you age (35 and onward), you’ll likely lose muscle mass.
The only other risk to high rep work is the wear and tear on the joints. This is something John Little goes into great detail in his book: The Time-Saver’s Workout (https://amzn.to/2InGKuW [Affiliate Link]). He and Dr. McGuff, the authors of Body by Science (https://amzn.to/2Xl7Syd [Affiliate Link]) recommend a slow moving protocol that allows you to use a lighter weight and increasing the time under tension. This causes fatigue through all three muscle fiber types, thereby maximizing muscle synthesis and reducing wear and tear.
You might want to look into their protocols and check with your doctor. Their routines will reduce your total workout time and could help you maintain (and even gain) muscle mass and strength. But please talk to your doctor first.
