Incidence of Decreased Performance and Heat Illness Related to Inadequate Hydration (N = 276)

Item	Responsea	Race		Sex
		Half-Marathon (n = 158)	Full Marathon (n = 118)	Men (n = 146)	Women (n = 130)
1. Have you ever experienced a major decrease in running performance that you feel was caused from being dehydrated?	No, %	30	24	27	29
	Once, %	32	18	19	35
	More than once, %	37	58	54	37
	Do not know, %	3	7	6	4
	Mean ± SD	2.0 ± 0.8	2.1 ± 0.7	2.1 ± 0.7	1.9 ± 0.8
2. Have you ever suffered heat-related illness symptoms during a run (severe muscle or stomach cramping, light-headedness, dizziness, nausea, or loss of ability to think clearly) while running that you feel were caused from being dehydrated?	No, %	60	50	56	56
	Once, %	21	23	24	19
	More than once, %	19	28	20	26
	Do not know, %	2	1	2	1
	Mean ± SD	2.4 ± 0.8	2.3 ± 0.8	2.3 ± 0.8	2.4 ± 0.8

^a 1, no; 2, once; 3, more than once. Percentages were calculated excluding do not know responses.