The weight-training sweet-spot
Never train more than 60-90 minutes (this doesn’t include a warm-up, or a cool-down) at a time. Excessing training negatively affects hormones and increases the risk of getting sick. Listen to your body. If you feel too tired to go on after a three minute break, after 30-45 minutes of exercise, cool-down and call it a day. You will work up to longer training periods, over time, if consistent, when your body has adapted. If you’re in the gym for two hours or more at a time and are not seeing results, this is why.
P.S. I have a detailed guide to exercise and weight-training, and provide my one-week workout plan in my book The High-Five Diet. To read a few chapters of the book and order your copy, click here: https://www.amazon.com/High-Five-Diet-Easiest-Weight-Loss-ebook/dp/B01HSIM6NA/ref=sr_1_1?s=books&ie=UTF8&qid=1468641914&sr=1-1&keywords=the+high-five+diet
Want more information, go to https://www.thehighfivediet.com/
Source: Clark, M., Sutten, B., and Lucett, S., NASM Essentials of Personal Fitness Training. MA: Jones & Bartlett Learning. 2014. Print. 362-365.