As a parting thought, we can’t emphasize enough the importance of consistency and staying focused. Your workouts shouldn’t be two-hour affairs—each visit to the gym needs to be fast-paced and intense. With that as your guide and following the heavy-duty blueprint laid out here, we can’t promise it’ll be easy, but the results should be worth every drop of sweat. Just think, 10 more muscular pounds may be a mere month away.
Aim to eat roughly 250 to 500 extra calories per day. To make sure that any weight gained is from muscle, Fitzgerald recommends that the bulk of those calories come from protein. In a 2014 Pennington Biomedical Research Center study, people who ate a high-calorie diet rich in protein stored about 45 percent of those calories as muscle, while those following a low-protein diet with the same number of calories stored 95 percent of those calories as fat.
The hip flexors help balance the posterior pelvic muscles. Three key muscles often become tight and shortened as a result of activities of daily living. These are the iliacus, psoas major, and the rectus femoris. The iliacus and the psoas major are often referred to as the iliopsoas because they share the same insertion at the lesser trochanter of the femur. The psoas minor inserts on the superior ramus of the pubis bone and mainly supports the natural lordotic curvature of the spine, but is only found in about 40% of the population. The psoas major originates on the anterior surface of the lumbar vertebrae and runs over the pubis bone and inserts into the lesser trochanter of the femur. This muscle not only helps to flex the hip, but also has an effect on the lordotic curvature of the lumbar vertebrae. The rectus femoris has a proximal attachment at the acetabulum and inserts into the tibial tuberosity. This long muscle plays a role in both hip flexion and leg extension (Figure 9-4).
Your questions kinda ties everything together. You are already aware of “nutrient density” which is AWESOME. This is important because I believe one food may be more “healthier” over another due to its “nutrient density”. The other food is still healthy because it still contains nutrients, but the nutrients could be more dense…so this is why I think one food may be “healthier”, while the other just isn’t as “healthy”. It’s not, not healthy.. Make sense?
Another common reason I see glutes that aren’t working properly is due to injury. Often an injury happens that changes the mechanics and motor programming of a person’s body. This can lead to some muscle groups becoming overactive, while others become underactive (think: compensation). This can alter things for a long time without the person even knowing it. 
How to do it: Lie on your back with both feet planted firmly against the flat base of a Bosu ball, knees bent. Stabilize your body. If you’re feeling a bit wobbly, your arms can hover on either side of you in case you fall in one direction. If you feel balanced, raise your arms straight up above your chest, hands clasped to challenge and work your stability. Drive your hips toward the ceiling, then lower and repeat.