Training 6 days a week doesn't automatically constitute overtraining, just as long as your overall training volume is appropriate for your goals, level of experience, and ability to recover from and adapt to that volume of training. In one trial, the amount of muscle growth generated by training the same muscle groups six times a week was not significantly different to training three times a week. That is, spreading the same amount of volume across six versus three weekly sessions didn't put the brakes on gains in size or strength.