The bars over top of your health bar shows the current boost level from using consumables. Each bar corresponds to a different level of boost:

 - **Level 1**:+1% Health Regen per 8 Seconds
 - **Level 2**:+2% Health Regen per 8 Seconds
 - **Level 3**:+3% Health Regen per 8 Seconds and +2.5% Movement Speed Bonus
 - **Level 4**:+1% Health Regen per 8 Seconds and +6.2% Movement Speed Bonus

You can increase the your boost level by using the following consumables (See image below more more detail):

 - **Energy Drinks**: 1.5 bars of boost (40% of total boost)
 - **Pain killer**: 2 bars of boost (60% of total boost)
 - **Adrenaline Shot**: 4 bars of boost (100% of total boost)

One thing to keep in mind is that the effects of using the consumables is cumulative, so drinking two energy drinks will get you to around 80% of your boost bar (slightly less, as the bar degrades while you drink the second energy drink).

[![More detail on boosts][1]][1]
[Boost amount source][2]


  [1]: https://i.sstatic.net/XA5au.jpg
  [2]: https://forums.tiny-spaceship.com/t/playerunknowns-battlegrounds-an-ocd-thread/25?u=magnumdopus