We all like to keep our ISO as low as possible to get high-quality shots, but that often means lowering the shutter speed to the point where we're toeing the line of sharp photos. This helpful video will give you a good rule for making sure you can still get sharp images.
Coming to you from Tony Northrup, this helpful video talks about the rule of doubles, Northrup's own modern version of the reciprocal rule. The reciprocal rule is a holdover from the film days and provides a general guideline for the minimum shutter speed needed for sharp images, generally seen as the reciprocal of the focal length (for example, 200mm would require a 1/200 s shutter speed). However, as high-resolution sensors have proliferated, faster shutter speeds have been needed, but this is also offset by the image stabilization capabilities of many modern bodies and lenses. Furthermore, since there isn't a tangible cost associated with each digital exposure like there is with film, we can afford to fire off lots of frames, which is what Northrup takes advantage of. If your subject allows you the time to do this, it's a great trick. Just remember that even if you pull it off with a slow shutter speed, that speed still needs to be fast enough for any movement of the subject itself.