When a planet is retrograde, it appears to be moving backward in the sky from the perspective of the Earth. Of course, the planet is actually continuing in its usual orbit, and the retrograde effect is a kind of optical illusion. Since perspective is so important in astrology, however, retrograde planets do correspond to recognizable meanings.
Mars is the planet associated with the Warrior archetype. It is therefore the planet we look to when we want to know about assertiveness, aggression, determination, and action. Mars is also closely associated with sexuality - not the love and romance aspect of sex, but the more instinctual, desire-driven side of it.
Mars does not go retrograde very often. The Warrior only backpedals through the zodiac once every two years, for about ten weeks. Astrologers often caution that activities signified by a planet are best avoided when the planet is retrograde, but what does that mean for Mars? Ten weeks of celibacy? Yikes!
Well, it is usually is considered to be a poor time to begin a new sexual relationship, but there is no reason to abstain altogether for ten weeks. The underlying meaning of Mars retrograde is that energy is lacking - and that's why new sexual relationships are seen as being doubtful: the desire may not last.
It is also thought to be a poor time to begin a new job. Now, with a down economy, it is unlikely that many people who are looking for work would refrain from taking a job that was available, and that is not necessary. However, jobs that begin on Mars retrogrades often fail to live up to expectations and energy seems to be dissipated: Bill Clinton was sworn into office for both his terms with Mars retrograde.
Mars retrograde probably isn't the best time to begin a new exercise program, either. Again, the underlying meaning is that energy is lacking for external activity, so a program that begins under Mars retrograde may fizzle quickly (gym membership, equipment costs, clothing, and other expenses may continue, however!). It probably isn't the best time to buy new exercise equipment for your home, either (treadmills make for expensive clothing racks).
Engines, anything made of iron, and cutting things are all ruled by Mars, so the retrograde period is not the best time to go buy a new set of kitchen knives, nor the electric sharpener for them. Surgeons are also associated with Mars, and the retrograde is considered a poor time for elective surgery. For that matter, it isn't a good time to find a new barber.
One of the ironies of a planet's retrograde time is that although we "know better" we are often pulled towards the activity symbolized by the planet. When Mercury is retrograde, we can find ourselves really wanting that new software, and when Venus is moving backward through the skies, we really want a relationship. Similarly, Mars retrogrades can make us really want a new sexual experience, or can increase our desire for a new job. No, we're not all horny job seekers for ten weeks, but you may feel the pull of Martial activity in your life.
That's because when a planet is retrograde, its energy moves inwards. It isn't a great time to externalize that energy in the world, but internally we become more in touch with the planet's symbolic meaning. So it really is a very good time to find what it is you want with respect to Mars-related activity, even if waiting a bit is a good idea.
Waiting is good because the intense internal energy may be somewhat transient. Our attention is brought to something, but that doesn't mean we really want to act on it, at least not as a permanent change of direction in our lives. A new job can seem great, but impulsively jumping to a new career should probably be something that we consider more carefully than when under the influence of the retrograde.
Mars makes a circuit of the zodiac about every two years, which means that on average he spends about two months in each sign. However, because of his retrograde movement, one of those signs actually gets a visit for about six months. People with strong planetary placements in those signs can feel the effect much more strongly, and we will all feel it more in the houses affected by the retrograde.
source = http://www.integralastrology.net/page15/page26/page26.html