The rule of thumb among most fitness professionals regarding the ideal number of times per week to train a particular muscle group, is actually only once per week. That’s right, you should only be targeting a specific muscle one time during an entire week of training for the best results in building up overall muscle mass and increasing strength levels.
For all the people out there who train chest 3 days per week while being confused why they are not making any gains, its comes down to something called overtraining. Your body just does not have the amount of energy and resources to completely recover if you are working a muscle group so many times during the week. You should be focused on hitting the muscle hard with maximum intensity in a limited time period (45-60 minutes) for the best possible results. If your weight lifting workouts are getting into the range of 1.5 to even 2 hours, you are either chatting way too much or doing way too many exercises, sets and reps. Either way, you are not only wasting your time in the gym but you are negatively impacting your overall muscle building results!
Have you ever done a certain exercise that you haven’t done in a while only to wake up the next morning barely able to move because your muscles are so sore? This is due to the way your muscles react to new stimuli and this way of training should be your goal when training to build maximum muscle mass. Just think about it for a moment. If you train the exact same way day in and day out with the same exercises, the same routine and the same repetition range, what do you think your muscles will do? That’s right, they will become accustomed to the repeated stimulation and stop growing and getting stronger. So, always try to mix it up and confuse your body for optimal growth!
In terms of your question about fatigue during your actual workout, this comes right back to the optimal amount of time per workout I touched upon earlier. You always want to train super hard and intense but you need to also train smart. Long 2 hour workouts are not ideal for packing on the most amount of muscle and building strength. A great tip is to buy an inexpensive stopwatch and actually time your workouts. Make sure you are totally finished with your workout within 60 minutes to ensure you’re on track. Doing this provides a continual source to check the status of the length of your training but it also helps with time management and forces you to get your butt in gear in the gym so you can finish up and do the work you need to in order to accomplish everything before the time is up. Having a stop watch is also great for timing your rest periods to make sure you are getting enough recovery between sets. The bottom line is to get into the gym, take care of business in the shortest amount of time and then get out of there so you can rest, recover and grow!