That said it’s not a very satisfactory answer. Let me do better.
I must share first that I almost always go with heavy weights. If you can safely, we all need to go there for a percent of the time we spend lifting weights. The instance when heavy is not appropriate – a joint issue, or a chronic condition – then I advocate plan B. The goal is always, the right plan for the right now in your life, not a blueprint someone else has developed based on “average.” Which, of course, you are not!
Recent research has shown that as long as you lift to fatigue lifting lighter weight can result in changes in hypertrophy. That means you will still gain some size. Don’t let that scare you. As a female, and particularly a female over 50 you don’t have enough testosterone to get big. Bulk, even if it was a challenge for you in younger years (possibly due to the protocol you were following being a mismatch for your body type and goals).
If seeing the baby bicep bump on your upper arm is your primary goal, then light weights may be your end game. However, if you also want to be stronger or do something about belly fat, it’s going to take heavier weight training regularly.
A recent study published in the Journal of Strength and Conditioning found that lifting at 80% of 1-rep max (you would fatigue at 10) and 30% (you would fatigue at approximately 35) increased hypertrophy (size) but muscular strength in only the subjects that lifted 80%.
Strength is required for a range of daily activities from opening jars and climbing stairs to lifting heavy bags of groceries. You use it in recreational activities like hiking inclines, digging in your garden, and riding your bike up a hill.
Strength is a component of getting out of a chair. Though you may be far from thinking that’s a workout move, keeping what you’ve got now in planning for the future is important. It’s easier to build strength now than it will be in 10 years or 20 no matter what your (adult) age is now.
Considering all that, a reasonable progression is required to safely bring you to a point where lifting a weight so heavy you would fatigue at 10 repetitions is possible.
*There is also some evidence of bone density improvements with light weights during the first six months of resistance training. Once you’ve adapted to any stress, it will take additional stress to continue progress. Minimal Effective Stress (MES) refers to the fact that if you for example walk regularly, simply walking more does not increase bone density or prevent further losses. You need additional stress on the bones in order for them to positively respond. Lifting light weights compared to not lifting weights will work for a period of time. Then you’ll need to increase the weight, if you safely can, to overcome your new MES.
Share your personal habits with me! Are you lifting weights? Are you using heavy or light weights or both? Have you noticed more results since you’ve been lifting than if you had a time when you did cardio alone?