You use therefore to introduce a logical result or conclusion. Muscle cells need lots of fuel and therefore burn lots of calories = thus. as a result of something that has just been mentioned (there + for)
(used to introduce a logical conclusion) from that fact or reason or as a result; "therefore X must be true"; "the eggs were fresh and hence satisfactory"; "we were young and thence optimistic"; "it is late and thus we must go"; "the witness is biased and so cannot be trusted"
as a consequence; "he had good reason to be grateful for the opportunities which they had made available to him and which consequently led to the good position he now held"