Q: is there a way to measure how fast you burn calories (to compare how much this increases after certain stages of your workout regimine)?

A: There is no practical way of doing it directly. There are consumer devices to claim to do that but they are more or less junk (which is unfortunately typical of most approaches that aim to count calories). A laboratory setup is able to measure calories burned fairly precisely by fitting you with an oxygen mask and measuring the amount of carbon dioxide that you breathe out -- this works because the carbon in carbon dioxide comes directly from burning calories. Many elite-level athletes use such devices to monitor and optimize their training. But needless to say this setup is both expensive and cumbersome.

Good news is if you have strict control over your diet and regularly measure your weight, you can get a very good approximation of how many calories you're burning on average over longer periods of time (several weeks or longer).

For example, you may be following a strict 3000-calorie diet daily, and every morning for two weeks you measure your weight first thing in the morning after using the bathroom on empty stomach. Your weight may go up and down day-to-day, but over two weeks time there should be a clear trend emerging over time and let's say you find that the trendline is that you've lost 1.6 pounds in those 14 days. Then you can do a simple calculation:

• Calories consumed = 14 days * 3000 calories/day = 42,000 calories consumed during these 14 days.
• Calories burned = Calories consumed + 3500 calories for every pound lost = 42,000 + 3500 * 1.6 = 47,600 calories burned during these 14 days.
• Calories burned per day = 47,600 / 14 = 3400 calories.

So in this particular case you find that you've been burning about 3400 calories per day during these 14 days.