In this episode of MASS Office Hours, Dr. Eric Trexler and Dr. Mike Zourdos answer questions submitted by listeners and viewers in the live chat. Topics include lifting recommendations for endurance athletes, heart rate zones for lifting, lower back training, finding the right amount of set volume, troubleshooting training plateaus, sacrificing sleep to increase training frequency/volume, and much more. The MASS crew goes live for Office Hours every Wednesday night at 7pm eastern time. Be sure to join us for a future episode!  Our next episode will begin at 7pm on January 17. If you'd like to submit a question ahead of time, please use this link:  https://forms.gle/9Ah39mefs8cuVa9H7 Time stamps:  0:00 Intro 1:48 Lifting recommendations for endurance athletes 9:53 Heart rate zones for lifting 18:39 Glycine and water retention 21:44 Direct lower back training 26:45 Optimal body-fat range for building muscle 32:20 Spinal erector training (proximity to failure) 34:14 Lifting for bone density 39:22 Finding the optimal set volume for you 43:40 Troubleshooting a plateau in the gym 48:28 Bodybuilding posing for beginners 52:17 Is total workout time a good proxy for managing volume, intensity, and rest periods? 1:00:31 Sacrificing sleep to increase training frequency/volume 1:11:14 Training around a foot injury