takayama spent a month analyzing the results.compared the amounts of perspiration generated during three types of exercise of different intensity. walking, bicycling, and jumping rope. even in areas with low index numbers, subjects who jumped rope perspired enough to become dehydrated, placing them more at risk of heatstroke. takayama says olympic organizers should take note. >> translator: the amount of heat the body creates depends on the kind of sport one is doing. we should come up with comprehensive measures taking that into account. >> reporter: planners will need to keep many factors in mind to ensure that the 2020 olympics are remembered for the number of medals won and not the number of visits to emergency rooms. kazuaki hirama, nhk world, tokyo. >> the summer heat is a concern here in tokyo. people in northern japan are dealing with the after affects of the storm that blew through. >> lion -- since recordkeeping began in 1951. this is the imagery when the center is about to make landfall. the system typhoon and a large