What can I do to counter bad posture from sitting all day?

from J.McGarrison

Answer:

Stand!

And I'm not (just) being a smart ass.  The seated workplace environment is killing us.  As I say in an earlier post, you can't spell OBESITY without S-I-T (http://triumphtraining.com/blogs/blog/6364524-365-ways-341-can-t-spell-obesity-without-s-i-t).  The one "real" job I had was my freshman summer in college when I worked at an office as a temp.  Doesn't sound glorious, I know.  But I had my very own cubicle and even wore a tie (which someone tied for me, of course).  And even though I wasn't deep into the study of health back then, I knew the office chair was doing me no favors.  So I drank a LOT of water and made lots of trips to the bathroom--on a different floor--just to have an excuse to get up and move around.

As a cyclist who spends countless hours in the seated position, I have personal experience with trying to counter the effects of excessive hip flexion.  As a therapist whose clientele spends a large majority of the day in the seated workplace environment, I spend a large portion of my time reversing the postural aberrations which are incurred by sitting in an office from 9 to 5. 

In general, you want to stretch what's tight and strengthen what's weak.  For those who sit for long durations, this would likely entail:

STRETCH

--sub occipitals
--levator scapulae
--pec major/minor
--latissimus dorsi
--hamstrings
--hip flexors (psoas/TFL/rectus femoris)
--probably any of the "deep six"

STRENGTHEN

--deep cervical flexors
--scapular adductors
--lumbar erectors
--abdominals
--glutes

The above could be detailed into a small book, but you asked for some simple movements.  The first would be a McKenzie Press Up:

--In prone position with hands at shoulder level, palm down, extend arms to push the torso up.
--Move into (spinal) extension while keeping the lumbar erectors relaxed.
--Only move as far into extension as possible while keeping the (anterior superior iliac spine) ASIS on the ground.
--Take a breath in (through the nose) at the top of the movement and then exhale on the way down. 
--Repeat 10 times.

This movement stretches some of the muscles mentioned above while, more importantly, mobilizing the lumbar spine and re-centralizing the discs.  Lumbar curvature should be between 30-35 degrees.  However, extended periods of hip flexion/sitting can decrease the curvature and create dysfunction/pain due to loss of optimal orthopedic alignment.

A second exercise would be to simply keep your head on the head rest when driving a car.  This will train the deep cervical flexors which counter the pull of muscles such as the sternocleidomastoids (SCM).  When overdeveloped in proportion to their antagonists (thru sitting, excessive flexion exercises, etc) the SCM's pull the head forward.  Where the head goes, the entire kinetic chain follows.  This can and often does lead to excessive rounding of the thoracic spine (which should again be between 30-35 degrees), resulting in concomitant changes (i.e. pain/dysfunction) in the lumbar spine and associated musculature.  So position the rear view mirror where you can use it while your head is on the head rest.  Anytime your view is sub-optimal, you'll know your driving position is, too.