▁the ▁circular ▁path . ▁The ▁radius ▁of ▁a ▁circle ▁is ▁the ▁distance ▁from ▁the ▁center ▁of ▁the ▁circle ▁to ▁the ▁outer ▁edge . ▁It ▁is ▁half ▁the ▁length ▁of ▁the ▁diameter . ▁ ▁For ▁a ▁r ider ▁wanting ▁to ▁complete ▁a ▁vertical ▁loop , ▁the ▁minimum ▁speed ▁required ▁of ▁the ▁r ider ▁is : ▁ ▁Where ▁ ▁is ▁the ▁radius ▁of ▁the ▁sphere . ▁ ▁Performance ▁ ▁This ▁ 5 - 8 ▁minute ▁long ▁spect acle ▁can ▁have ▁quite ▁a ▁physical ▁impact ▁on ▁the ▁rid ers ▁as ▁ 3 . 5 – 5 . 5 gs ▁are ▁put ▁on ▁the ▁surface ▁of ▁the ▁glo be . ▁At ▁the ▁a pe x , ▁many ▁rid ers ▁" gre y - out ", ▁which ▁is ▁a ▁trans ient ▁loss ▁of ▁vision , ▁not ▁as ▁severe ▁as ▁a ▁total ▁black out . ▁In ▁addition ▁to ▁grey - outs , ▁for ▁many ▁rid ers ▁vert igo ▁and ▁n ause a ▁is ▁a ▁huge ▁problem ▁as ▁the ▁act ▁is ▁indu cing ▁to ▁such ▁sympt oms . ▁ ▁Because ▁of ▁this , ▁physical ▁fit ness ▁of ▁the ▁rid ers ▁is ▁extremely ▁important . ▁In ▁addition ▁to ▁fit ness ▁keeping ▁a ▁health y ▁di et ▁is ▁just ▁as ▁important ▁because ▁the ▁r ider ' s ▁body ▁mass ▁completely ▁affect s ▁the ▁entire ▁act . ▁Some ▁rid ers ▁will ▁say ▁that ▁they ▁try ▁to ▁concent rate ▁on ▁a ▁particular ▁point ▁in ▁order ▁to ▁" reverse " ▁the ▁effects ▁of ▁the ▁g - for ces . ▁These ▁experienced ▁rid ers ▁say ▁the