Do you all have any opinions about a hip belt on which a barbell attaches between the legs? The belt itself fits around the waist. Supposedly the benefits are to relieve pressure from the back and even it out around the pelvic girdle, especially when doing heavy squats. Please advise.
Once again, I'll start by mentioning that in the fitness/performance industry it is important to try to keep "opinions" or "GYM SCIENCE" out of the picture, as they are usually based on nothing scientifically sound. Rather, one should rely purely on the practical sciences (I.E. biomechanics, functional anatomy, physiology, etc.). That being said, let's look at this device from a practical point of view... ...
Yes, I do know of the hip belts you are referring to. They are, as you mentioned, designed to remove most/all of the load from the spine there by applying it more directly to the hips/lower appendages. Rather than offering my opinion, my question to you and anyone else curious about this device is this:
"WHAT'S THE GOAL?"
If the goal is increased hypertrophy (increased cross-section of muscle tissue), of the legs, than this is a valid option. THIS IS ASSUMING ADEQUATE MUSCLE BALANCE/FLEXIBILITY/NEUROMUSCULAR EFFICIENCY, as well as proper volume, intensity, rest and nutrition are all present, (which is a BIG assumption!).
If you're goal is sports specific, (I.E. increasing vertical leap, or overall lower extremity strength/power), than this tool may/can help to do so when used appropriately. However, not loading the spine may NOT be adequately preparing the spine for the future sports/performance environment from a neurological standpoint.
Gray Cook, creator of the "Functional Movement Screen" reported results from a similar situation. He found that with the goal of increasing vertical leap by performing squat jumps (total body power with emphasis on the lower extremities), there was a better over all training effect when he placed extrinsic load (elastic tubing in this case), in the hands while the shoulders/arms were overhead (shoulder flexion & abduction), thus placing the load through the entire body VS. attaching the resistance around the hips.
Now, this is not to say that everyone should be squatting with loads on their backs! In fact, many people probably should not be performing loaded squats at all, AT LEAST NOT INITIALLY. Which brings me to my last and most important point.
If and individual chooses this tool as an option BECAUSE he/she is experiencing pain, discomfort, or excess "pressure" in the spine as you stated in your question, than a red flag goes up here. Performing loaded squats on top of what ever musculoskeletal imbalance or dysfunction is causing the pain/pressure/restriction can only result in disaster. This is why a thorough kinetic chain assessment must be performed on all clients/fitness enthusiasts/athletes prior to exercise and training. Proper progression with the goal of adding extrinsic load must follow. This involves flexibility, core stability, and balance progressions, as well as proper basic nutritional requirements.