he's training of course - long distance bicycle riding is considered to be quite good sport activity
and on topic - about 'GOROSEI - how did they rise to power' here's my speculative theory:
the Buster Call was announced once as the power able to bring down countries, the strongest military action, etc. but why exactly 5 VA commanding 10 warships
I think that the founders of the WG were bad pirates - epic evildoers trying to bring down the unnamed country of untold riches - the continent/country whose name dr. Clover was about to tell
so if someone uncovers the thruth and bloodshed behind the WG it will be quite shameful for those 'absolute justice defenders'
so the idea is that the buster call is a tradition remaining from the end of the void century - the 5 strongest pirates gathered together their strongest battleships with their strongest men forming a 'power that can bring a country down'. Those 5 pirate captains formed the WG and erased all evidence, changing the history to say that the destroyed country was going to use their super weapons to destroy the world - how convenient >.<
on the Rio Poneglyph is written the real history that the weapons were not going to be used (or something about a treason or other bad thing tarnishing even more the founders of the WG)
so the Gorosei now are descendants of the five pirate captains and of course know everything about this dark governmental secret; that's why they fear a lot from interactions between the Younko or any other really strong pirates - but they also try to keep the balance of the three powers and don't have interest to destroy either the Shichibukai or the Younkou - but why?...
well the shichibukai are like guardians of the first half of Grand Line - if some strong pirates appear there they will bring them down - that's why Mihawk destroyed Don Krieg's Armada of 50 pirate ships because entering the grand line with such a force means only bad intentions, as don Krieg was coming rather to conquer than to have fun adventuring in the Grand Line (like Luffy)
and if the pirates reach the second half of the grand line they either become assimilated in a Younkou's crew (ex. is Rockstar who with a bounty of almost 100 bil beli was a simple underling in Shanks' team) or they get destroyed trying
luffy of course is a special case - they are very small group of strong pirates - everybody would notice a big pirate fleet but will neglect a group of 5-8 people, ne ^^
so the gorosei are free to relax and can simply pull the strings as long as the Younkou are kept separate and the WG secret is hidden deep
...and about the 'are they strong'part:
IMO tho even if they might not be too strong they will have some DF powers - or a DF weapon like Spandam had, at least some of them so that the encounter with them will be more interesting ^^