googlenut, it's called downtraining.
Basically the problem is that the muscles are always slightly tightened and so have no extra hold when under stress, e.g lifting a weight. The therapist compared it to carrying heavy shopping in the crook of your arm, then finding it hard to heft the shopping onto workbench - the arm was knackered holding the weight at such a height.
The exercise she showed me has to be done lying down and twice a day.
Hold and lift the pelvic floor muscles towards belly button, the anus should feel as you're holding in wind. Thighs and buttock muscles should be relaxed - I found this bit hard! Hold for 2-3 seconds then let go breathing out letting the lower abdominal muscles bulge The perineum should this, too. Visualise the PRM relaxing, holding it for 10 seconds. Repeat 10 times. Relaxing for 10 seconds takes some effort because the urge will be to clamp down.
The therapist obviously showed me how to do with her checking the muscles in my fanjo until I got it right.
It felt very weird to be doing something so counter-intuitive; letting go instead of holding on so as to be able to hold on, IYSWIM. Anyway, I've found it very effective, though I should emphasise my incontinence was slight compared to what so many women experience, though of course it was distressing for me.