Before we even get into testing flexibility, the question is: does it matter? The simple answer is yes, but as I'll explain it depends on what you need that flexibility for. To test it:
A good level of flexibility is hitting around 90 degrees straight in the air. But I find it alright if someone gets to 80 degrees depending on their sport and activity.
But when I do this test what I really look for is on the opposite die. When the leg goes up , what's the pelvis doing? If there's a lot of tilting and bending happening, this is more my concern. It means in a functional task like a soccer kick or sprint you're probably compensating and don't have TRUE flexibility of that hamstring.
For movement geeks it means you have poor extension or tight hip flexors on the opposite side. It can also mean poor hip mobility on the same side.
Hamstring 'inflexibility' is related to injury (Clarke, 2008). But it depends on WHY inflexibility is happening. You can't just stretch your hamstrings forever, you have to address core stability issues, other muscle balances as well.
Do this simple test yourself, do you have good active hamstring flexibility?
Dead Bug Exercises For Core Control
Ok let's be honest, there are a thousand ways to train your abs and mid-section. But building off our most 2 weeks ago, we need to build a foundation of control for our low back and pelvis before progressing to dynamic movements.
'Dead Bug' exercises are an absolute staple of improving core control. It ensures proper activation of the local muscles like Multifidi and TrA (pictured above). This stabilizes each spinal segment so that when huge movements occur, shearing forces to the low back are limited.
Shown below is a basic dead bug exercise:
Notice my legs and arms move independently of my pelvis. Your back should not change position and your pelvis should not tilt when you move your limbs. It needs to be done SLOWLY to get the benefit. You can also use a rolled up towel or band behind your back to tell if your spine changes position.
These become pretty easy with practice, so there are countless variations (ex. perform with both arms extended). Driving home the point, this does not give you jacked abs, it is to retrain the brain to get co-ordination of the spine and pelvis when doing other movements.
Milner Chiropractic and Sports Injury Clinic