In Tadasana one stands firm and tall like a mountain. Tadasana can be practiced as a place to begin when doing standing poses, in between standing poses, or by itself in order to improve posture and groundedness. Standing poses are foundational to yoga, so clearly getting to a strong, well-aligned Tadasana is a large part of your practice. But the benefits of a well-aligned Tadasana aren't just for your yoga practice, once you've mastered what this asana "feels," just can use it to your advantage to lessen fatigue and build awareness of your posture.
When standing in Tadasana, your weight is mainly supported by your skeletal system, not by your muscles. You align your body so as minimize muscular strain. That's the external, or physical, benefit of Tadasana. This is a great asana to practice while you're doing errands that require standing, such as waiting in line. The second benefit is more subtle--an awareness of your body's placement in space. You gain inner focus. Viewed externally, Tadasana is "just standing"; from within the body, Tadasana requirements tiny and constant adjustments.
Tadasana is a very inwardly active and focused posture.
When you're a beginning yoga practitioner, it's surprisingly complicated to master the art of rooting down through the feet while lengthening up through the spine, keeping your chest open without jutting your lower ribs out, and keeping the legs muscles strong and lifted without tensing the belly or jaw. But ultimately, Tadasana demands just one simple thing: that you stand in a way that supports the natural curves of a healthy spine.
In addition to maintaining your spines' natural curves, to function efficiently, your skeletal structure also needs to be aligned vertically. That means when you're standing, your ears should be over your shoulders, your shoulders over your hips, and your hips over your knees and ankles. When any body part falls out of that vertical line, the adjacent support muscles will feel the strain. For example, years of having a forward head will cause the muscles of the upper back and neck to become tired and achy from holding up the weight of the head against the pull of gravity.
So why is Tadasana so difficult? And why do we work so hard to master good posture in yoga—leaving class feeling taller and healthier—only to slump down in the car seat on the way home or revert to a swayback when we heft our overstuffed yoga bags onto our backs?To explore good alignment while standing, use a doorjamb-assessment. You can use this posture/asana check several times a day—without putting on yoga clothes or getting out your mat—to learn "by feel" how to stay vertical and maintain the normal spinal curvature while standing.
Lengthen your spine up the doorjamb by reaching the crown of the head toward the ceiling while your shoulders melt down away from your ears. If you tend to have excessive lordosis, you may find it's much easier to reduce the lumbar curve by bending your knees. If that's the case, your hip flexors are probably tight and your abdominal muscles are weak. To work on strengthening the abdominals, stand at the doorjamb, bend the knees slightly, and draw your tailbone toward the floor and your back waist toward the doorjamb. Don't contract the abdominals so hard that you collapse in the chest or can't breathe—remember that the goal is to have a mild (not excessive or completely flat) curve in your lower back, combined with an open chest and a chin that's level to the ground. (If your chin and gaze tend to go up when you take your head to the doorjamb, kyphosis is probably still causing a forward head. It will take time to reduce the kyphosis; in the meantime, don't force your head to the doorjamb. Keep working to lift your breastbone, without overarching your lower back, and stay in the position in which you can keep your chin and gaze level.) Finally, step away from the doorjamb and train your body to remember the feeling. Focus your mind to remember the cues to good vertical posture. When this happens--ta-dah! you'll be standing in Tadasana. Your back, neck, and shoulder muscles won't have to work so hard and, in the long run, you'll have more energy throughout the day.