This is a pose that can be easy to overlook and just roll through it because it's in the Sun Salutations without noticing the benefits. Yet, when we slow it down and focus on the pose we find that there's quite a lot going on and it's great for strengthening the back and improving posture.
We inhale into Ardha Uttanasana (Halfway Lift) before stepping back into Chaturanga or lowering into Uttanasana (forward fold) in the Sun Salutations.
It stretches our calves, knee flexors, hip extensors (glutes), back extensors, chest and shoulder elevators. It also strengthens our back extensors, transverse abdominals and shoulder retractors as we use them to stabilise the pose.
It is important not to compress the back of the neck so be careful not to lift the head too much. If in doubt, keep the neck in line with the spine.
If you hold the pose for three to five breaths you can focus on really feeling into the pose.
Push down into the feet to stabilise whilst concentrating on getting the hips over the heels which will switch on hamstrings, glutes and back muscles. Drawing the navel in towards the spine as you focus on a straight back will engage the transverse abdominals and back extensors. The transverse abdominals are the deep abdominal muscles that help with breathing but also stabilise the pelvis and lower back during most movements.
Depending on your hamstring flexibility your fingertips can be on the mat or on your legs - shins, knees or thighs are all fine, work out what feels best for you. If you are holding it and not just passing through then using blocks or a couple of hardback books is a good way to focus on the back extension without being limited by any hamstring tightness. Try to avoid putting too much weight into the hands; bringing them up inline with the hips, palms facing up can be a nice way of opening up across the front of the chest and focusing on engaging the back muscles.