Question Summary:
Is it permissible to do stretching exercises which are not related to yoga?

Question Detail:

 I have been searching online and found out that Yoga is haram in Islam as it imitates the polytheists. I have been getting fat and have brought a fitness program called P90x to get into shape. The program consist of many exercises and also have a Yoga portion in a separate DVD. I am not going to do its yoga. however some of the workout videos contain stretch exercises that are similar to yoga. Like stretching your legs before a leg workout etc.
so I wanted to know if it would be haram to do those stretches, they DO NOT contain any chanting or weird breathing, or facing the sun etc. Can I skip these stretches and do the exercises that are in my knowledge not related to Yoga? and let say a person is performing an exercise but do not know if it is related to any other religion, will he/she be held accountable. This P90X program is very effective and gets you fit but I do not want to erode my faith by doing something that is haram. 

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
Being healthy and active is encouraged in Islam. A Muslim should not be lazy, lethargic and unfit. If one is active and energetic he will have the ability to carry out more ibadah, service the deen more competently and stand to defend Islam when needed. 
On the other hand, being lazy, weak and unhealthy will hold a Muslim back from engaging in ibadah and servicing the deen to ones full potential and capability. It has been reported that Rasulullah صلى الله عليه و سلم would often make the following Dua,
اللهُمَّ إِنِّي أَعُوذُ بِكَ مِنَ الْعَجْزِ، وَالْكَسَلِ، وَالْجُبْنِ، وَالْهَرَمِ، وَالْبُخْلِ، وَأَعُوذُ بِكَ مِنْ عَذَابِ الْقَبْرِ، وَمِنْ فِتْنَةِ الْمَحْيَا وَالْمَمَاتِ
O Allah! I seek your protection from powerlessness (ajz), laziness (kasl), cowardice (jubn), weakness (harem), miserliness (bukhl), I seek your protection from the punishment of the grave (athabul-qabr) and from the trials of life and death¹. 
You stated that you purchased a fitness program CD. If the program CD displays the opposite gender and/or reveals the Satr of the same gender it will not be permissible to view such a program.
In light of the above, if one exercises to remain healthy and to avoid obesity then it is permissible rather commendable as long as no Haram activity is carried out. Also, one must abstain from such exercises which involve other religions rituals and traditions² ; this can be avoided by doing a thorough research before beginning any exercise. If the stretches in reference are free from any other religious rituals or links then it will be permissible to do them. 
And Allah Ta’āla Knows Best
Bilal Ishaq (Issak)
Student Darul Iftaa
Leicester, England, UK
Checked and Approved by,
Mufti Ebrahim Desai.
صحيح مسلم (4/ 2079)[1]
50 - (2706) حَدَّثَنَا يَحْيَى بْنُ أَيُّوبَ، حَدَّثَنَا ابْنُ عُلَيَّةَ، قَالَ: وَأَخْبَرَنَا سُلَيْمَانُ التَّيْمِيُّ، حَدَّثَنَا أَنَسُ بْنُ مَالِكٍ، قَالَ: كَانَ رَسُولُ اللهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ، يَقُولُ: «اللهُمَّ إِنِّي أَعُوذُ بِكَ مِنَ الْعَجْزِ، وَالْكَسَلِ، وَالْجُبْنِ، وَالْهَرَمِ، وَالْبُخْلِ، وَأَعُوذُ بِكَ مِنْ عَذَابِ الْقَبْرِ، وَمِنْ فِتْنَةِ الْمَحْيَا وَالْمَمَاتِ»،
[2] Aap ke Masaa’il aur unka Hal. V 7, Page 334 Maktabah Ludhyanwi