This shows that you have exercised too much and are about to reach the limit of exercise, so you will feel very tired and your legs will be as heavy as lead. After all, you have just started fitness, and your body is not suitable for high-intensity exercise. You can't expect yourself to run 10 km at once when you start fitness. It is normal to be tired after running a kilometer. After all, you are still a little tired, your body can't adapt to the pace of running, your body has less energy, consumes faster, and your body function is not good enough.

Don't worry about fitness. If you are too impatient, you won't do anything. Step by step this is the basic principle of fitness. No matter what kind of exercise, the intensity should gradually transition from low intensity to high intensity, the duration should be gradually lengthened, and the amount of exercise should be gradually increased. The natural limit will be completely and thoroughly stimulated.

When you run a kilometer, it belongs to aerobic exercise, and most cells in the body are also breathing aerobic. The speed of metabolism in the blood is accelerated, and the energy will be consumed accordingly. With the decrease of energy and raw materials for cell respiration, people feel tired, and there is not enough raw materials in the body to support the human body to complete running. If you don't have the strength to lift your legs, you will feel as heavy as lead, which is why running is getting more and more tired.

In addition, it may be that you didn't do well in the preparation stage of running. To do stretching well, you must remember to take a deep breath and do enough warm-up exercise before running. You can try to inhale enough air into your lungs through your nose, hold it for a while, then exhale slowly, and cycle this action several times. You may find it a little difficult and tired to breathe, but it is a signal that your body is entering the best exercise state.