Yoga will increase your concentration this is from my personal experience .

It will refresh our mind and thoughts ..

Yoga gives many many benifits. practcing yoga regularly will result into more cocentration, increase in flexibility, Complete Detoxification, Muscle tonning, calmness of mind, ridhdhi & sidhdhi etc. etc. many many more.

one has to clear about what is yoga?
its a sanskrit word derived from dhatu "Yuja" meaning to unite, and Yoga means "the union". Union of individual prana to cosmic energy.

Doing Asana is only one part of yoga. and called as Hatyoga.
Astang Yoga consists of
1. Yama - Attitudes towards society
2. Niyama - Attitudes towards ourselves
3. Asana - Correct way to using the body
4. Pranayam - Science of breathing
5. PRATYAHARA - Restraintment of our senses
6. Dharana - Ability to direct our minds
7. Dhyana - Ability to maintain direction
8. Samadhi - Complete integration with object

Similarly there are many streams of yoga e.g. Sankhya yoga, Gyan Yoga, Bhakti Yoga, Karma Yoga etc. (you can read Bhagavat geeta to know more abot thease streams or paths)
Practicing all thease 8 part of yogic action will give proper benifits. Only doing Asana & pranyam is not sufficient for all gains. now a days many many people have started teaching only asanas & pranayama in name of yoga.

Find yourself a right teacher or path who can take you to 8 parts of Yoga & right yogic stream

so if any one claims as yoga teacher don't forget to ask about all 8 parts of yoga & stream of yoga.

--
Love Moves the world.

Bhakti yoga is a term within Hinduism which denotes the spiritual practice of fostering loving devotion to God, called bhakti. Traditionally there are nine forms of bhakti-yoga. Bhakti yoga is generally considered the easiest of the four general paths to liberation, or moksha (the others being Karma, Raja and Jnana Yoga), and especially so within the current age of Kali yuga (according to the Hindu cycle of time). In scriptures such as the Bhagavata Purana, bhakti is described as a perfectional stage in itself which surpasses even moksha as a level of spiritual realisation. Hindu movements in which bhakti yoga is the main practice are called bhakti movements.

http://hubpages.com/_jzccc9vgz55/hub/Bhakti-Yoga_

Yes, it does increase our concentration. download the complete book on yogasan from
http://www.myfullneeds.com/health.htm