Mars mahadasha lasts for 7 years. Mars in Vedic astrology represents our will power, ability to fight, anger, stamina, energy, impulsivity, military, martial arts, sports, conflicts, knife, weapons, sharp objects, fire, cuts & burns. When one goes through the mahadasha of Mars, they will be far more active than before. There would be a great need to use the body for pleasurable pursuits like sports, yoga, hiking or taking some kind of a training. One finds the need to take action towards their goals. Mars is the warrior within us and he is ready to defend what we believe in. So any unfinished goals we had in the past would suddenly see the light of day. There are possibility of being injured while playing sports, getting small cuts & burns or it can prompt surgery. But, it's not a bad thing because surgery means you might taking care of an alignments that could've become dangerous for you if you never took such actions. There would be great enthusiasm of being a patriot where people even join the military or police force.
It's seen that most fire fighters and policemen have Mars in the 1st, 3rd, 6th and 10th house, which represents battleground houses where one needs to take action as in physical action, fight enemies and rise to a high status of government. Bruce Lee had Mars in the sixth house which led him to become the world's greatest martial artist and he reached such heights during his Mars mahadasha. Wherever Mars is placed in your horoscope it will suddenly become lit during it's mahadasha period like a light bulb, but not only that, the houses ruled by Mars will also become activated like Aries and Scorpio. But, there is another factor to consider: nakshatra. During the period of a mahadasha lord, not only the planet and the sign it rules becomes activated, but also the planets sitting in the nakshatra of the mahadasha lord also become activated and live. In our case, Mars rules the nakshatra of Mrigshirsha, Chitra and Dhanishta. Any planet sitting in such nakshatra will also become active and provide things related to the house where they are sitting in. This is why our live is never one dimensional, we always experience different aspect of our life during a dasha, this is also because of the concept of antra dasha as well. But Mars usually makes the person bold and gives them will power to take action and risk during the 7 year time period. But judging a dasha is not only seen from the ascendant, but also the moon sign, d9 chart and putting the maha dasha lord as the ascendant.