Personally I don't believe in overtraining.
What if I told you this: If your family was captured and you were told you needed to put 100 pounds onto your max squat within two months or your family would be executed, would you squat once per week? Something tells me that you'd start squatting every day. Other countries have this mindset. America does not.
This can apply to anything, your squat, sprinting, jumping, whatever it is.
You can train everyday, and you can train hard, your body is magical, it will adapt. Yes there will be that dark period, where you dont feel like doing anything, your sore, lethargy strikes, you dont feel like talking to anyone.
How your body feels is a lie. Yes you can have sore legs, but you can still hit a personal best squatting that day, its happened to me a shit ton. Here's a nice quote I have from John Broz the coach from the U.S.A's national weightlifting team.
If you got a job as a garbage man and had to pick up heavy cans all day long, the first day would probably be very difficult, possibly almost impossible for some to complete. So what do you do, take three days off and possibly lose your job?
No, you'd take your sore, beaten self to work the next day. You'd mope around and be fatigued, much less energetic than the previous day, but you'd make yourself get through it. Then you'd get home, soak in the tub, take aspirin, etc. The next day would be even worse.
But eventually you'd be running down the street tossing cans around and joking with your coworkers. How did this happen? You forced your body to adapt to the job at hand! If you can't' squat and lift heavy every day you're not overtrained, you're undertrained! Could a random person off the street come to the gym with you and do your exact workout? Probably not, because they're undertrained. Same goes with most lifters when compared to elite athletes.
– John Broz 2002
This is true, you see this with anything.
Most people dont get over the dark period, where you feel like shit, thats why most people fail and never reach that elite category of lifters. Personally I squat heavy 3x a week, whether I am sore, in pain. Unless I am injured, and physically unable, I will continue this. I play on a rep basketball team with 2 practices a week, rugby for school with 3 practices a week, lift weights, and do cardio.
What people need to realize that training is not an all or nothing thing, it is obvious that it isn't healthy to train 6-7x a week with high intensity right away, you need to build up to it. Why do you think track athletes have a base training period, or most athletes run a GPP phase? Building up conditioning and work capacity is very important in terms of injury prevention and recovery. Slowly, they up the intensity as their season progresses and peak when its contest time, these cycles are important in reaching a "high" phase and just being successful in sport.
Obviously your nutrition needs to be right, and you should be drinking enough water, getting enough sleep, stretching, foam rolling to ensure proper recovery, but if you are doing everything properly, dont be a fucking pussy and just train for whatever it is.