Q:

Why do Muslims run slowly in the first 3 Tawaf in Hajj?

When muslims go to Umrah they have to perform the tawaf around the Kabah, why does the first 3 have to be at a faster pace? Also why is the Ihraam showing parts of the musculin body?

A:

why does the first 3 have to be at a faster pace?
The reasoning behind doing this is to show strength and endurance, and the reason it lives on until today is to commemorate the event behind this as well as to remember the blessings Allah has given us.

Allah's Messenger (ﷺ) and his Companions came to Mecca and the fever
  in Medina had weakened them. Thereupon the polytheists (of Mecca)
  said: There would come to you a people whom the fever has made weak
  and they have suffered severely from it. They sat in Hatim. Thereupon
  Allah's Apostle (ﷺ) commanded them to walk quickly ift three circuits
  and walk (in four) between the two corners. so that the polytheists
  should. see their endurance. The polytheists then said (to one
  anothery You were under the impression that fever had emaciated them.
  whereas they are stronger than so and so. Ibn Abbas said: He (the Holy
  Prophet) did not command them (the Muslims) to walk quickly in all the
  circuits out of kindness to them.

صحيح مسلم
Also why is the Ihraam showing parts of the masculine body?
We do this so that it is more inviting to faster walking, and it livens up the person.  The wisdom behind this, and Allah knows best, is that one should always be ready for Jihad at all times, for one should choose cloths whether in peace or war that would help him work without laziness. 
Source (Arabic), Source (Arabic)

