Lifted 30 kg today in the deadlift. I only weigh 60! I am amazed at how good I am feeling after each class. One of the ladies remarked that she feels taller after each session. It is excellent for your posture and not that strenuous.
As one of the coaches put it - this is not about endurance or even fitness. It is purely about using your muscles so they send messages to your bone to grow a bit more. If you don't use those muscles you don't stimulate new (and stronger) bone growth. Each exercise is aimed at using the muscles to encourage bone growth in your hips and spine, where most people have bone loss as we age (and have low estrogen levels). Because of the treatment we are on for preventing recurrence (if you are hormone positive) we are even more at risk of bone loss than the average person unfortunately.
I never thought I would ever do weightlifting but this is actually fun :)