Rest days need to be a day for you to get out of the gym. Recharge your battery and rest your mind. When you constantly stress the body the mind will follow. These days have to be for you go on hike, do yoga….yes I did a lot of yoga and still do a ton of stretching on my days off. When you’re 20 -25 you can get away with not stretching by you want to keep up and not play catch up down the road. Read a book and be present with your friends and loved ones. You sacrafice a lot of time to be in shape and to reach your on rest days don’t think about what you could be doing in the gym have fun with your friends do something other then go to a gym. And then be ready to attack those next sessions the next couple days.