Hi Anna,
So, let's just get this clear:
- 15min xtrainer >> +intensity every 5min
- 15min treadmill >> 5min run, 10min incline walk
- 2km row
So that'd add up to ~40min every time you train, which is 3 days per week.
The equipment used for monitoring your heart rate is something that needs consideration before taking into account the 178bpm HR. If you have a HR monitor attached to your chest, that'll give you much more reliable feedback than if you're using the HR monitors built into the handles of the xtrainer. Anyway, 178 is very close to your theoretical max HR (which may or may not be your actual max HR), so you're probably getting the intensity up pretty high, which will obviously burn more calories and demand more of your muscles per minute, which is better for far loss on paper, provided you don't give yourself a heart attack while you're at it.
Now, some maths. The average person, training at a sustainable rate, can burn about 5kcal/min. The average person really pushing themselves can push their sustainable rate up to maybe 10kcal/min. Generally, going beyond that threshold will put you into an anaerobic zone, where you burn more kcal/min, but may not even be able to last 1min before having to reduce the intensity.
So, let's assume then that you're burning 5-10kcal/min of cardio. That puts your ~40min sessions at a cost of 200-400kcal, give or take. That's not bad. If you've been at weight maintenance (ie staying at 80kg +2kg for more than a month) and change nothing else, this will put you at a calorie deficit of 600-1,200kcal/week (200-400x3 sessions). In theory, 1kg of fat is 9,000kcal, so if this cardio regime is the only thing you change in your lifestyle, it's going to take a long time to lose that 10-15kg. If you want to burn more calories each week, obviously you're going to have to do more to make that happen, such as increased volume (doing another 10min of training each session) or increased frequency (more than 3 sessions per week). I'd particularly recommend including resistance training in your program 2-3 times a week, over and above what you're currently doing if at all possible.
Now, you mentioned you're on a 1,000kcal/day diet. Without knowing what you were eating before, and what changes (if any) were occurring to your body weight and composition over the last couple months, it's hard to give any meaningful feedback on this. However, let's look at nutrition for a moment.
At 80kg, in order to optimise composition by making sure that as much of the weight lost as possible is coming from fat, it's generally recommended that you aim to consume 160g protein and 80g fat per day (2g/kg bodyweight and 1g/kg bodyweight, respectively). With protein being roughly 4kcal/g, and fat being roughly 9kcal/g, that's 640kcal and 720kcal respectively, for a total of 1360kcal. And if you're eating real food, it's inevitable that there's going to be some carbohydrates in there (and, if you drink, some alcohol), so to realistically meet your macronutrient needs you're probably looking at closer to 1,500kcal/day. Planned right according to your appetite, this will obviously be more satsifying than 1,000kcal/day, and will physiologically give better body composition results, even if the weight loss is at a slower pace. It should go without saying, but also eat your vegetables.
So, to be clear, I'm recommending more calories (especially from protein), which will give you slower weight loss, but better weight loss, meaning that you'll look and feel better when you get down to 65-70kg.
