Rowing machines are good for upper and lower body....BUT you need to be sure you're doing absolutely correctly, and probably have a reasonable level of fitness to do so.....it's very easy to get carried away, lose your form, and get injured. Also not good for immediately after THR as you slide forward, bend your knees and your hips bend up towards the body, bit like a lying or semi-recumbent leg press......both make you bend more than 90 degrees,, and you have to be concentrating to make sure you're in control, not doing it ballistically (ie letting momentum carry you). Take advice from a physio if you want to use it, but I would suggest not before at least 6mths (I used to be a gym instructor, helping GP and Physio referrals in a former life, and worked with physios)