"You've Got Tight Hip Flexors!" – Trainers
Eh, probably not. Nine times out of ten, "tightness" is really the presentation of weakness elsewhere.
For proper health, we need to pursue structural balance. That means muscles on either side of a load-bearing joint must be strong enough to bear their own cross, so to speak, in order to contribute to a properly functioning, healthy joint.
Here's what's really happening:
This is a common cause of irregular pelvic function. Remember, the glutes are posterior tilters of the pelvis. Once they can contract strongly, they'll help reduce lower back arch and counter the hip flexors, which pull upward on the other side. In a nutshell, properly functioning glutes produce pelvic balance.
Hip Anatomy/Pelvic Structure
You might not be able to squat deep without looking like an invalid trying to get off of the toilet because your hips just weren't built for deep squatting.
Depending on the depth of your hip sockets, angle of your femoral neck, and placement of the hip sockets in the pelvis itself, your own skeleton may be "blocking" you from getting well below parallel for the squat.
If this is the case, your hip flexors have nothing to do with the problem – regardless of whether they're "tight as a rope" or not.
This sounds counterintuitive, but tight muscles can also be weak muscles. That's something that's underappreciated where the hips are concerned.
For a good squat or split squat, the psoas muscles need to shorten eccentrically to help pull the hips down into a deep seated position. No strength, no dice.
The next time someone tells you your ugly squat is due to tight hips, give him an upside tap to the head. Then do this exercise:
Tennis Ball Glute Bridge
This is the money fix for "tight hip flexors." It's surefire way to create or restore pelvic balance by going through a hip extension with engagement on both sides of the pelvis.
Just jam a tennis ball or two into the crease between the top of your thigh and the bottom of your hip and keep it there throughout the movement.
The psoas will have to work very hard to keep the tennis ball in place through end ranges and the glutes have to work just as hard on the planted leg to achieve full hip extension.
If the hips aren't strong enough, the ball pops out of place. Conversely, if the glutes aren't strong enough, your body won't fully extend.