Your heart is a muscle which gets stronger each time you work out. But when you are first starting out, it may not be very strong. It might need to beat faster in order to pump the necessary blood and oxygen to the various parts of your body. As you become more fit, it will not need to pump blood as quickly. When you are working out, you will want to work out at about 70 to 85% of your maximum heart rate. You can determine this by subtracting your age from 220 and then multiplying by .70 for the lower end of the heart rate scale and .85 for the upper end. For example, if you are 33, you would take 33 from 220 and get 187. 187 times .70 is 131 (rounded up) and 187 times .85 is 159. So you would want to work out between 131 beats per minute and 159 beats per minute. Yes, you might go over this target heart rate from time to time, and this is okay, but you need to try to stick to this range. If you find your heart rate is too high, slow things down until you are ready to increase your heart rate again.
How Does Your Body Feel - What's its Fitness Level?
In the end, the best way to determine whether you need to slow down is how you feel. If you’re feeling lightheaded or something hurts, you need to slow down to see if the feeling passes. If the feeling does not pass, you need to stop what you are doing to see if the feeling stops. Checking your fitness level after exercise (Fitness Test) makes sense. And if you’re still not feeling well, you need to think about getting medical help.