Here is some evidence why runners don’t like hills. First of all, going uphill means that you're going against the earth’s gravitational pull. This is also more difficult for heavier people, having to use more muscles. Also, the heart has to pump more blood to the cells and as a consequence, lungs have to do more work to remove the carbon dioxide from the heart and replenish it with oxygen.
Running hills can make you sick, this is more of a problem if someone had to run in the middle of a hot, summer day. To begin with, many people have reported illnesses such as nausea, lightheadedness, headaches, and even heat strokes. Especially, since you’re higher up on the ground, you are closer and exposed to the sun more. In addition, Trees usually don’t grow on an incline.
Muscle soreness is a common problem for all runners, and it is more of a problem for hill runners. Even though aches and pains mean that you have to push yourself hard, it is not fun to have. To begin with, in most cases it is mild, emerging shortly after a workout, and it can last up to one to two days. On the other hand, known as delayed-onset muscle soreness (DOMS), is a rare condition of serious pain. These pains usually occur after a long and intense workout. (Which is basically what hill day is, long and