Is there an allowance for hips rising in the squats when you are going heavy.
It's hard to say without seeing your Squat.
Not the the extent that it becomes a good morning type movement but in general is a little hip rise allowed when reaching your 5 rep max or is any hip rise at all an indication that you have one too heavy and are losing form?
How You Squat
It has to do with how you are built. Such as if you have a long or short torso, etc.
Tom Purvis, Physical Therapist, goes more into this in the video's below.
Squats Part 1: Fold-Ability and Proportions
Squats Part 2: Fold-Ability and Proportions (Examples and Adjustments)
Another factor is...
Vertical Bar Path
Dr Tom McLaughlin's (PhD Exercise Biomechanics) research determined that regardless of the amount of forward lean you have in a Squat, the bar needs to remain in a vertical path; the bar need to travel up.
The bar should not have a...
Horizontal Bar Movement
This means turning the movement into more of a
Good Morning.
The predominate reason that the Good Morning Squat occurs is weak Quad and a strong back. The body's natural survival mechanism automatically shift the load to the strong muscles to ensure you get up in the Squat.
Ironically, most individual who see a Good Morning Squat believe the back is the weak link. Many then increase lower back training which makes it worse.
In a Good Morning Squat, the key is to increase Quad Strength.
Also, greater emphasis needs to be on Abdominal Training; which enable you to maintain a move Vertical Bar Path in the Squat.
As someone once said, "Increasing Abdominal Strength is like adding another set of Erector Back Muscles.
This brings back to...
Your Hips Rising
Again, it hard to say without seeing your Squat.
However, the hips rising is usually an indication the load is being shifted from the weaker Quads to the strong Lower Back.
Bench Press For Reps Contest Example
Years ago, i was helping at a Powerlifting Meet where they had a Bench Press For Reps Contest.
Most of the individuals Benching were right handed. As muscle fatigue set in, their right arm would lag in driving the weight up.
One of the lifters commented to me that it was strange that right handed individuals had weaker right arms, since the right lagged behind; which was incorrect.
Allowing the weaker left arm to go up first, shifted more of the load to the strong right arm. The same occurred with left handed individual.
The dominate/stronger left arm lagged behind, literally picking up more of the load.