Nitric oxide concentration and its time change in normal sperm capacitation in vitro. The basal time T1 represents the length of time from the beginning of sperm capacitation to the NO concentration reaching an appropriate level. The duration of time T2 represents the duration of time at this NO concentration (D). Peak represents the appropriate NO concentration fluctuation. From Figure 1, we can see the relationship between changes in concentration of NO and time changes in the normal semen group.