B737-500 CREW PLANNED A FLAPS 5 DEGS TKOF BECAUSE OF PERFORMANCE LIMITATIONS. BECAUSE OF A SHORT TAXI; RWY CHANGE; AND A MISSED BEFORE TKOF CHKLIST ITEM; THE CREW BEGAN TKOF WITH FLAPS 1 DEG. THE CREW DID NOT ABORT THE TKOF; BUT INSTEAD SELECTED FLAPS 5 DEGS DURING TKOF ROLL.

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PRIOR TO TKOF; THE FO AND I WERE TYRING TO DETERMINE WHETHER WE WOULD BE ABLE TO TAKE OFF WHEN WE REACHED THE DEP RWY; AS WE WERE OVER GROSS AND NEEDED TO BURN DOWN THE PLANNED 900 LBS ON TAXI OUT. THE GND TFC WAS LIGHT. THE FO HAD PULLED UP TKOF DATA FOR RWY 22L USING FLAPS 5 DEGS. WHEN WE WERE CLRED TO TAXI; IT WAS FOR DEP FROM RWY 32L AT T10; THERE WERE ABOUT 3 ACFT IN FRONT OF US. HE GOT DATA FOR THE NEW RWY AND CALLED LOAD PLANNING WITH A KID COUNT AND RECEIVED A NEW LOWER ZERO FUEL WT THAT BROUGHT US UNDER MAX TKOF GROSS WT. JUST AS WE WERE CLRED FOR TKOF; THE BEFORE TKOF CHKLIST WAS COMPLETED. AS WE STARTED THE TKOF ROLL; THE FO NOTICED THAT HE HAD FLAPS 5 DEG DATA IN FRONT OF HIM (FOR RWY 22L) AND THE FLAPS WERE SET TO 1 DEG. OUT OF CONCERN THAT WE WOULD NOT MEET TKOF PERFORMANCE CRITERIA; HE MOVED THE FLAPS TO 5 DEGS AND TOLD ME SO. I HAD ASSUMED THE FLAPS WERE ALREADY AT 5 DEGS (WE MUST HAVE INCORRECTLY DONE THE BEFORE TKOF CHK) AND ELECTED TO CONTINUE THE TKOF. I LOOKED DOWN AND SAW THAT WE WERE IN; OR RAPIDLY APCHING; THE HIGH SPD REGIME. I NOTICED THE FLAPS MOVING PAST 2 DEGS AND I WAS SURE THEY WOULD REACH 5 DEGS BEFORE V1. V SPDS WERE CALLED BY THE FO FOR FLAPS 5 DEGS AND A NORMAL TKOF PROFILE WAS ACCOMPLISHED FROM THAT POINT ON. I FEEL THE HIGH WORKLOAD AND TIME COMPRESSION (AS WE HAD A SHORT TAXI) EXPERIENCED BY THE FO WERE THE CONTRIBUTING FACTORS THAT HAD THE FO HEADS DOWN DURING THE TKOF ROLL AND UNAWARE OF HOW FAST OR FAR WE HAD TRAVELED DOWN THE RWY AT THE TIME HE MOVED THE FLAP HANDLE. WE HAD A THOROUGH DEBRIEFING AFTER THE INCIDENT AND BOTH AGREE THAT HE SHOULD HAVE CALLED FOR AN ABORT WHEN THE CONFUSION AROSE RATHER THAN CHANGE THE RECONFIGN OF THE ACFT.