Inertial effects are the resistance a particle has to changes in acceleration. The best way to think of this is when you are in a car. If you accelerate fast you get pushed into the back of your seat, while if you stop fast you move forward and press against the seat belt. This is your body resisting changes in motion. This in turn will cause a force to press against you. So if the car accelerates to fast or decelerates to fast the human body could get damages due to large forces being placed on it. This is why cars have crumple zones; because those crumple zones will cause a lower deceleration of the car, which will put less force on the human body.