If the iliopsoas and other hip flexors are tight, they pull down and forward on the pelvis, which tilts the pelvis forward and compresses the lower back. Picture a man standing with the front of his pelvis tilting forward and his tailbone lifting. To stand upright, he has to overarch his lower back. Anatomically, this is called hyperextension; commonly, it's called "swayback." Prolonged standing or sitting in this position increases pressure on the facet joints of the lower spine, which can contribute to arthritis in those joints.
People eat way too many carbs and keep their glycogen levels full for too long. They are always turning sugar into fat because they are always eating carbs. The body wants fats to make fat, not carbs. The body doesn’t even like storing carbs as fat, that’s because we have fat to do that. It’s less stressful to store fat as fat rather carbs as fat. People are stressing themselves out by always eating carbs which always keep their glycogen levels full. They need to carb cycle so that they aren’t gaining fat from BOTH fats and carbs. This is how combining fats and carbs in a meal CAN lead to more fat, only if glycogen is full.
Note that this recommendation is for total weekly volume, which means it would need to be divided up based on how many times you’re training each muscle group per week. So, for example, someone training everything twice per week would do 30-70 reps for each bigger muscle group in each of those workouts, and 15-35 reps for each smaller muscle group in each of those workouts.