When a muscle contracts, it shortens. Take the biceps for example. Without getting too technical, the biceps are attached at the forearm and shoulder. When your biceps contract, they shorten and bring those two points closer together. When you rest, the muscle returns to its normal length, and the two points move farther away. Constantly contracting your biceps over a long period of time would cause them to get shorter, even at rest.
Notice when we are scared or exited that we start to breathe faster. Adrenaline causes this. Which means to calm ourselves we must not breathe fast, we just breathe slower. The slower we can breathe the less stressed we will feel. The slower we can breathe the longer our strokes will be. When we breathe fast, our strokes (breathing in and out) becomes shortened. When we breathe slower we can engage the diaphragm in a way to eventual allow us to breathe longer strokes.
If you are standing, the hip flexors lift your leg when you step up on a stool. If you are lying flat on your back, the hip flexors can either lift your leg or lift your torso into a sit-up. In yoga, Navasana (Boat Pose) is especially good at strengthening the iliopsoas because it demands that the muscle isometrically contract to hold up the weight of the legs and torso.
Alternately, try King Arthur's Pose: Starting on hands and knees with your feet near a wall, put your right shin straight up the wall and bring your left foot forward so it's under the left knee. Place your hands on your knee and lift your spine straight up while taking your tailbone down. You should feel a strong stretch on the front part of your thigh.
There are nutrients within these fat sources which decrease inflammation, improve mental function, improve eyesight, and give you healthier skin, hair, and nails. When I'm crushing the iron in the gym each day, my goal is to be strong and big, but also healthy and mobile. To get that way, I eat all of these generously on a regular basis, and I also take omega-3 supplements daily, in the form of fish oil or krill oil.