The ultimate builder of health and fitness in my opinion is the bridge. Here is a very basic list of the benefits of the bridge-
1. It strengthens the spine in a manner which no other exercise can. This is because of the range of motion involved. During a traditional back squat or a deadlift, the primary function of the spine is to not collapse and round. Yes, the spine does get stronger, but it never goes through any real range of motion, because of which the transfer of strength is limited, because in actual movement, the spine has to move through a large ROM.
2. The spine is designed to be flexible and needs to be strong in every part of that ROM. That is why a movement which takes the spine from reasonable flexon to full extension is indispensable. The floor bridge done properly, takes the spine through the full ROM, with full contraction of the spinal muscles at the top of the movement. It does so in a safe fashion. Even though the weight is limited, due to the extended range of motion, and the full contraction and the traction of the anterior chain, the strength benefits are enormous. Also the bridge is fairly easy to make harde.
3. The bridge strengthens the entire spine, not just the lower back, but the dorsal, lumbar and cervical spine. This is critical, as all other spinal exercises tend to zero in on one area.
4. The bridge also has both the qualities required to develop tendon and ligament strength- full extension and full contraction. Thus, it strengthens the tendons as well as muscles.
5. It strengthens the hip muscles and the glutes and the hamstrings. The bridge is a great glute strengthener as it fills the gap left by squats and trains hip hyper extension.
6. It strengthens the postural muscles of the body. The muscles between the shoulder blades, the external rotators, the glutes, all these need to be strong to prevent conditions like lardosis, kyphosis and the hollowed chest look. The bridge strengthens all those muscles, and stretches out their antagonists- the hip flexors, the pecs, the lats. It is the ultimate postural exercise.
7. It builds great active flexibility in the hip flexors, the spine and the pecs and lats. And almost everyone today needs added flexibility in those muscles. It builds shoulder mobility as well.
8. It realigns the vertebra. Even if the exercise did just all of the above, it would be great, but it does all of it without any spinal compression- the normal effect of weight training.
9. It increases the flexibility of the rib-cage.
Even if I have not convinced you that the bridge is the ultimate exercise, you will at least agree that it is one hell of an exercise and should definitely be a part of your routine. Between squats and bridges, you have the whole package covered.
Alright, now to the exercise.
Start with the basics and build up to the hardest variation.
1. Hip Thrusts-
Lie supine on the ground. Your knees should be tucked in with your heels flat, with your feet shoulder width, toes pointing outwards. Keep your hands on your stomach were they cant assist you. Clench your glutes to raise your hips until your body forms a straight line. Think of moving your hips not arching your spine. Hold this position for a seconds, before going back to the start position. Repeat as desired.
Master for 3 sets of 50 before you consider yourself done with this movement.
This will have to be done on a slippery surface. Sit in an L shape on the ground. Your palms should be by your hips on the ground, pointing towards your toes. Your feet should be together. Now press your hips off the floor with your arms, but keep your feet on the floor. Press backwards by extending your shoulders. Think of contracting your posterior deltoids. This will teach you to contract your shoulder blades.
By contracting your shoulder blades, your feet will slide forward. Keep your legs straight. As you start moving forward, contract your glutes and move your hips up and forward, until your body is straight. Hold this position.
Place your shoulders on a bench a little lower than your knee. Your feet should be in the same position as for hip thrusts. Place your palms in line with your shoulders on the bench with your fingers pointing downwards. Your hips should be only slightly lower than your shoulders. Clench your glutes and move your hips upwards until your body forms a nice tight arch at the top. The ROM is not too high, your head should just clear the bench. Hold the top position for a second, fully contracting your bridging muscles and your glutes. Lower yourself back to the start position and repeat.
Get into the hip thrust position, with your palms by your head as in the previous step. Clench your glutes and raise your hips upwards, until you forma nice tight arch. Your limbs must be fully extended and your hips must be the highest point of your body. Arch your cervical spine as well. Hold the top position for a second, and then lower your shoulder, which maintaining this arch, by bending your arms and shoulders, until the crown on your head touches the ground. Hold this for a second, before pressing back up.
This movement is easier than the full bridge because of the reduced ROM, but it build the shoulder mobility and strength required for full bridges.
This is the same as the last technique, except you will lower yourself all the way down to the start position and press back up. Spend a lot of time on this movement, at least 6 months before moving to the next movement. It is essential to ingrain the movement and allow it to take its full effect on your muscles and joints.