Hi, Marielle! Like you, I am 47, and within the past 1-2 years I put on a fairly tiresome layer of pure fat around my midsection as well as the outer hips and thighs despite maintaining a fairly intense (for me) program of land cardio, free weights and water training. I have drained off most of that fat within the past 4-6 weeks by, believe it or not, emphasizing cardio workouts that make me sweat as much as they make me puff and pant. I do not use a heart rate monitor (I tend to value breathing rate and rating of perceived exertion more than strict HR), but I know my body well enough to know when I'm working hard in an HR sense. I also do not weigh myself, because I know that maintaining or increasing lean muscle mass will offset fat loss measurements on the bathroom scale; I simply go by how my clothes fit.
It's very weird, though - paying attention to Sweat Rate and emphasizing that has made all the difference. I tend to sweat more when my land cardio workouts include a really good mix of floor plyo work (plyo jacks, plie jacks, plyo lunges, squat jumps; the cardio drills from Drill Max, Boot Camp Original, 4DS-Boot Camp, Kick Max, etc. - clearly more drill-y than dancy), step plyo work (think power drills from Body Max 1, Body Max 2, CTX Power Circuit, HSTA, the I-Maxes, and so on) with some new fangled fast-foot drills, good old fashioned hi/lo, and Cathe kickbox (KPC and 4DS-Kickbox are my faves, with the power drills from Cardio Kicks close behind them) thrown in for good measure. Not to mention cardio drills holding a weight plate (these you have to be very careful selecting, based on your leg power capacity and your shoulder stability).
I come from a long line of fat-storers on both sides of my family tree, so although I try to avoid becoming obsessed with every fat gram I'm ingesting, I do pay attention to fat gram accumulation because of the health risks involved.
The Sweat Rate Strategy has had great dividends, at least for me, but it's a good thing that I'm a home exerciser. When I'm shooting for having the sweat literally pouring off me and flinging droplets Hither And Thither, you practically need a HazMat team to clean up after me - not so great if I were in a studio group-fitness class.
Just my own experience! HTH -
A-Joc