While Brave Frontier's Arena Orbs refresh steadily each hour, you might want to speed up your progress through the Arena ranks. In this case you can use a gem to refresh your Arena Orbs to full.
To refresh your Arena Orbs you can simply do any of the following:
1. Continue on to another arena match when your orbs are empty. You will be asked if you want to refresh your orbs with a gem or;
2. Tap Shop->Restore Arena Energy->Recover