Ubhaya Padangusthasana is  a seated posture, where both big toes are held with both hands while balancing on your sitting bones. The posture strengthens the abdominal muscles, lengthens the hamstrings as the legs are held straight reaching up diagonally and it is a good chest opener. Its main goal though is the balance improvement. When achieved the steadiness of the posture your blocked energy (prana) from the base of the spine is released and can freely flow upwards. 

• The posture strengthens abdominal muscles and internal organs
• It improves digestion
• It releases the blocked energy in your spine so it rejuvenates the back
• It stretches the whole spinal cord as the legs are raised upward 
• Stretches your arms  and improves flexibility in your legs
• It is a good chest opener
• Stimulates the nervous system and activates the brain
• Improves concentration skills

Urdhva Mukha Paschimottanasana is the same posture as the first seated posture in Ashtanga yoga except you are balancing on your sitting bones, while holding the outer sides of your feet and pulling your legs toward your torso. This is also very similar to Ubhaya Padangusthasana, only the stretch is even more intense. It lengthens the entire backside of the body and it improves circulation from head to toe. 

• Intensely lengthens the leg muscles
• By stretching the entire spine it can help relieve back aches
• It tones the internal organs
• Stimulates the digestive organs and improves digestion
• Calms the mind and improves concentration
• Improves balancing skills 
• Strengthens the hip flexors