Brad's Iyengar Yoga Notebook
Triang Mukhaikapada Pascimottanasana
Triang Mukhaikapada Pascimottanasana is a seated forward bend in the same family as Pascimottansana or Janu Sirsasana, but with it own peculiarities.   Since many of the torso and arm actions are the same for the seated forward bends, I refer you to the more lengthy descriptions of those actions under the Pascimottanasana and Janu Sirsasana sections to avoid repetition here.   The following comments pertain to this pose specifically, as the leg and hip actions differ somewhat from Pascimottanasana, Janu Sirsasana, and the other seated forward bends.
Triang Mukhaikapada Pascimottanasana has traditionally been considered to be an entry level seated forward bend because it is indeed easier to grasp the toes of your forward foot than in other seated forward bends.   But this pose has its own unique asymmetry and challenges that you must confront.
The Sanskrit name of the pose coveys several images.   Triang means "three limbs" literally and can refer to the three limbs that you are extending forward.   Or more loosely the term can refer to three parts of the body in general.   Here it refers to the leg that is in Virasana and describes which three parts should press into the floor -- the upper part of the foot of the Virasana leg, the knee of the Virasana leg, and the buttock bone on the Virasana leg side.   All three of these should be strongly grounding.   Mukhaikapada connotes taking your face down toward one leg or foot.   And Pascimottanasana is the "asana of the intense stretch of the West" (posterior side of the body).
It is good to sit for a few moments in Virasana as a preparation for Triang Mukhaikapada Pascimottanasana.   If you find that your buttock bones do not come easily and firmly to the floor in Virasana, then you need to take some extra height under your buttocks in Virasana, and you will certainly want to sit on some extra height for Triang Mukhaikapada Pascimottanasana.   In Virasana, since you have the tops of both of your feet and shins pressing symmetrically into the floor, it is easier to find balance and you may not be fully aware that you are only lightly sitting on your buttock bones and that some of your weight is still being borne by your knees.   If this is the case for you, it will become obvious when you have one leg straight in Triang Mukhaikapada Pascimottanasana and you find yourself listing toward your straight leg side like a torpedoed battleship.   That is an indication to you that you need to take some height in the form of a blanket underneath the sitting bone of your straight leg in Triang Mukhaikapada Pascimottanasana to level your hips, and it should also cause you to reconsider whether you need more height to sit on in Virasana, since you may have been bearing more weight in your knees in Virasana than you realized and that is unhealthy for the knees.
To come into Triang Mukhaikapada Pascimottanasana, from Dandasana lean over toward one side and take the leg of your other side back into Virasana position.   Adjust your Virasana foot so that it points directly behind you and then place your hand in the pit of your knee and adjust your calf flesh outward and downward.   Just as in Virasana, the inner flesh of your Virasana leg should touch the outer flesh of its thigh.   Be directly on the center of the top of your Virasana foot.   If you are sitting with both of your buttocks on the floor for this pose, press the three parts of your Virasana leg mentioned previously into the floor strongly at this point as well as the buttock bone of your straight leg.
At this point comes the most important aspect of this pose -- you must level your pelvis and hips parallel with the floor no matter what it takes.   Many of us will need to place a blanket under the sitting bone of our straight leg.   If you use a blanket, place it under your sitting bone only, not under your thigh.   Only place as much height under your straight leg hip as it takes to level your pelvis -- don't overdo it -- but use as much as you need because the levelness of the hips is one of the key points of this pose.   There are progressive levels to ensuring that your pelvis is perfectly upright and your hips are level to the floor and you should only do as much as you need:
(1)   If possible, you can sit with both buttock bones on the floor and just draw your buttock flesh back and out to the sides.
(2)   If you need more support, you can place the blanket just underneath the flesh of your straight leg buttock.
(3)   If you need more support, you can place the blanket under the sitting bone of the straight leg side.
(4)   If you need still more support, you can increase the thickness of the blanket.
... but you must do whatever it takes to level your hips before continuing.   Once you have leveled your hips, then again manually adjust the flesh of both your buttocks back and out to the sides.   If you are sitting on some support, the buttock bone of your Virasana leg may not touch the floor now and that is fine.   It is more important that your hips be level.
If you are sitting with both buttocks on the floor, try to sit more on the inner edge of the buttock bone of your straight leg and the outer edge of the buttock bone of your leg in Virasana.   In any event, in this pose you sit with more weight on the buttock of your leg that is extended.   This is an uneven pose, however even in the setting of that unevenness you have to try to bring the spirit of evenness into the sitting.   Press your Virasana leg shinbone down into the floor and descend the groin on the side of your Virasana leg downward a little more toward the floor.
Point the toes of your extended leg straight up toward the ceiling in this pose.   Do not allow your forward leg to roll or tilt outward at all.   Ground both of your thighs.   Roll the thigh of your Virasana leg outward to keep its outer hip moving down toward the floor.   Also rotate the knee of that leg outward so it does not drop.
Before taking your hands to your toes, note that this pose has a twist in the torso, just as in Janu Sirsasana.   So you will begin by twisting from your lower abdomen to try to align your navel toward your straight leg with the goal of bringing the middle of your torso straight down onto the middle of your forward leg.   After turning your torso, take your hands to your extended foot and lift your arms and your torso to come into the concave phase of the pose.   Remember to start Triang Mukhaikapada Pascimottanasana and all seated forward bends from the concave back position, even if you need a belt to reach your feet, and do not go past this stage until your flexibility allows you to lower your torso while keeping the front of your torso long.   It is imperative that you take your back ribs into your body and be concave in your spine before moving deeper into the pose.
As you are able to come into a deeper expression of the pose, exhale while bending forward.   From the buttock of your Virasana side, take your torso forward over the center of your extended leg as you extend through the inner calf of your extended leg forward toward the front of the room.   Bring your torso down directly over your forward leg, not to the inside of it.   In this pose, as in Janu Sirsasana, you strive to center your torso over your straight leg.   It can be tricky at first to bring your torso directly over your extended leg but not allow your weight to roll to that side and cause you to lean or even fall over toward your extended leg side.   Don't let your weight tilt toward the outside of your extended leg and don't let your extended leg tilt outward.   Also keep some weight on the leg of your Virasana side for balance.
As you take your torso forward, you will come light on your buttocks.   Notice also that the shin of your leg in Virasana tends to come away from the floor much more so than in Virasana itself.   You really have to make extra space in your calf and thigh area and press your shin into the floor on the Virasana side to prevent your shin from raising or becoming light on the floor.   As in all seated forward bends, it is important to place awareness in the inner groin and thigh of your straight leg (or legs) and turn it downward toward the floor and also pull it back toward your pelvis as if you are trying to draw it underneath you.
In the deepest expression of the pose, your sternum will be in contact with your forward thigh.   Relax your abdomen throughout the pose -- do not hold any tension there.   Elongate both sides of your chest and waist equally toward your forward foot, though attaining that equal extension is difficult due to the asymmetry of the pose. Pay special attention to keeping the plane of your back level with the floor and not letting it tilt in the direction of your straight leg.   Widen your elbows the sides especially the elbow on the side of your of your straight leg.   If you feel like you need a little more stretch, you can place a block on the sole of your extended leg foot and grasp your hands around the block.
To come out of the pose, inhale while raising your torso to the erect concave position, then lean toward your straight leg side and take your Virasana leg forward to resume Dandasana.