You can’t get a proper workout without rest days.
The phrase “too much of a good thing” can be applied to almost all processes of the human body. Too many harmful chemicals, too many vitamins, and too much exercise. Whether you’re purposely trying to slim down for a particular event or just enjoy the act of physical exertion, you have to remember that your body’s muscle-repairing process rely on having enough time to put everything back together. If you go whole-hog at the gym every single day of the week, you’ll work yourself into a pile of mush.
In addition to the obvious physical hazards, though, there are also mental concerns to take into account. Studies show that those who exercise rigorously for five or more days a week exhibited more frequent symptoms of depression and anxiety. It’s not that surprising; when you pummel your body repeatedly like that, your gains are going to gradually diminish. At that point, you’re pretty much just inflicting pain on yourself for its own sake, and guess what? Your body doesn’t like that.
Anxiety and depression can be both a symptom and a cause of overexertion. If you feel like you absolutely have to work out every day, that’s a good sign that something is weighing on you, emotionally speaking. You don’t need to become a body builder to be considered healthy; you should work out because you want to, not because you think you absolutely have to. This is why you need rest days; so your body can have the time it needs to recover, and your mind has the time to indulge in the things that make you happy. According to those aforementioned studies, the best frequency of exercise to avoid mental strain while still getting a proper burn is three to five times a week. Keep it in that range, and you’ll be golden.