These are the trend bars. You'll start to see them once Life Cycle has enough data to estimate an average time spent on your activities per day, week, month and year. It'll take a few weeks before you get your first trend bars, but after that, you're good to go.
Life Cycle is aware of your average time spent on any activity. This average is based on your total time since you've started using Life Cycle. This means it changes over time. More data means better accuracy.
The trend bars shows the delta between your average, and your current time spent on that activity. The trend bars focus on what you're doing the most right now, so it's not uncommon that many weeks and months could show the same categories, typically Work (or School), Home and Sleep, for example. But every now and then, you break out from your habits and if you stay consistent, these breakouts will show in these bars. That's when you know you're on to something (or off, depending on your purpose).