Both "tension/struggle" and "gravity/force" are given in the dictionary tips above, but I found only "tension, struggle" in the translation of mvutano at http://www.elimuyetu.co.tz/subjects/arts/swa-eng/m.html
Since "tension" means stretched tight (or a strained situation) and "gravity" means the force that attracts a body towards the centre of the earth, I was surprised that mvutano could mean both. I suppose you could say that tension pulls in two directions and gravity pulls in one.
Or it is just that words sometimes have two opposite meanings, e.g. "screen" can mean to show (a movie) or to hide (an unsightly view).