what's the difference between "ups and downs"and "highs and

what's the difference between "ups and downs"and "highs and lows"?
At the beginning of the century,medical scientists make a surprising discovery:that we are built not just of flesh and blood but also of time.They were able to demonstrate the rise and fall of body energies,making us different from one day to the other.The forces became known as biorhythms:they create the _______in our everyday life.
呵呵~~~诸位~~我的第一感觉就是ups and downs,答案不是这个,是highs and lows~~~谁能解释下啊?