A sandbag is a great form of resistance, especially for outdoor training. Here’s 16-year-old Joseph doing sandbag squats and rows and 61-year-old Jane doing sandbag good mornings: There are so many lower-body options with a sandbag, like bear hug squats, Zercher squats, Romanian deadlifts, split squats, lunges, step-ups, and the list goes on, and there…