Hamstrings, glutes and low back could all be contributing culprits in this situation. However, there are other muscles invovled at the hip joint that could be limiting factors as well. If the adductors are tight or glute medius is weak, along with the limitations of the more major culprits, sitting up with legs straight will be challenging.
I am in agreement with both Julie and Karin in this instance. Explore these areas cautiously. Everyone has different degrees of limitations in these areas so finding which ones are the most active in limiting your client’s ability to sit upright should prove to be an interesting journey.
Harold E. Rose, Jr.
Ab-Sutra Health and Fitness Coaches, LLC
Be Healthy, Be Ageless, Be You.
Most likely the limitation is due in large part to inadequate flexibility in hip extensors (gluts and hamstrings, prime movers,) and low back extensors (lower paraspinals, prime movers.)
The answers are great, especially the suggestions to be cautious if the limitation(s) may be the result of previous injury.
Lets think about for a second.
It COULD definitely be any/all of the above mentioned muscles without a doubt. Or it could be something else entirely. I recommend that you do to things to find your answer. My suggestion is take a real good look at it, maybe even compare what you see to others that can perform seated in that position the “ideal” way. If nothing else to get clues. Maybe you will see that the pelvis isn’t completely scooping underneath or that the legs aren’t getting fully extended. You may also see that the lumbar is flexed and the t-spine is kyphotic. So simply, make an observation.
Second, and really the easiest thing to do is ASK. Ask your client, what they feel and what it is that is impeding them.
Putting an observation together with verbal feedback should start you down the road to figuring out what corrective approach you can take to get this “fixed.”
hope this helps,