TONIC MUSCLES YOGA

Forward bend in feet is an exercise that provides a deep relaxing and lengthening of legs, back and neck. 
To achieve this you must stretch the muscles of the posterior thigh and the quadriceps contract. The femoral biceps, muscle semitendinoso and semimembranoso, namely the posterior thigh muscles, bones ischiatic arise from the base of the basin and fit below the knees, the lower portion of the legs. Their contraction causes the approach of their points of origin: action that determines the bending of the knee joints ol'estensione, or both. In the process of elongation, however, the opposite happens: the knee is straight el'anca flexes. And that's what happens in Uttanasana. 

Contraction: THE THREE TYPES 

Isometric, concentric and eccentric are the types of contractions involved in the performance of the position. When you lift, steps from bending the extension of the hips, while the posterior muscles of the legs perform a concentric contraction (the muscle contracts and shortens). 
When, instead, we fold in Uttanasana, we speak of eccentric contraction (the muscle contracts and stretches): stretch the muscles but at the same time working hard to control the descent of the upper body while the bone ischiatic rotate gradually upwards . 
Finally, if you decide to stop half way during the bend with your fingers several inches of the floor, the rear thigh muscles contract isometric (contract but neither stretched nor shortened). If not, the basin is completely reverse cadresti and on land. 
Therefore, these muscles allow you to remain in the posture without shorten or allungarsi.Qui but problems arise for those with stiff muscles and is unable to tap with your fingers on the floor. The back of the thighs, rather than lie down, remain in tension to maintain the stability of the basin. This will submit the muscles and discs of the lumbar spine in a great effort with no improvement in flexibility. To avoid this, a system or a brick covered in hand so that the weight of the body is discharged through the hands on support and then on the floor. Thus the muscles of the legs can freely stretch and melt. 

FRIENDS Antagonist 

In Uttanasana is essential that your knees remain straight. To do this it is necessary to contract the quadriceps (large side, huge media extensive intermediate retto femoral) that are used to straighten the joints. So the first step is to verify the proper contraction with a simple exercise. Sit on the floor with both legs stretched in front. Supports the thumb on one side of the patella and the other fingers of the hand on the other side. If the quadriceps are relaxed, the patella can move up and down, left and right. If I live, however, the patella is locked and you can not move: this is what should happen in Uttanasana. 
The quadriceps act as "antagonists" of the posterior muscles of the thighs, when contracts are each other and relax automaticamente.su down. Other muscles involved in posture are the spinal erettori: forming the bulk beam that extends on the back, up parallel to the backbone. When you bend to the ground, the spinal erettori contract eccentrically to control the descent of the bust. Unrolls when the back and you raise, contract concentrically to allow you to summarize the upright. When you bend and lift you in Uttanasana, the pelvis rotates in the right direction thanks to the spinal erettori. 
If you take the lower back straight, these muscles contract in order to maintain the isometric possible elongation of the spinal curves, while the thigh muscles contract in an eccentric way to rotate the pelvis forward. If you lift with your back straight, the posterior thigh muscles pull the bones ischiatic down, rotating the pelvis to allow it to assume an upright position. 

The secret to performing well Uttanasana is to understand the interplay of muscle contraction and relaxation. For you to enjoy all the benefits of this relaxing bend. 

MICRO-DETAILS 

While perfect alignment even be sure that they are above, not behind the ankles. If the hips are unbalanced, the legs go back and you lose the lengthening of the muscles of the calf (gastrocnemial and sun). When the legs, however, are perpendicular to the floor, ankles forming an angle of about 90 degrees with the feet, and this lengthens and relaxes the muscles of the calf.