Speed can be defined as the ratio of the distance (d) traveled to the time (t) taken to cover that distance
Speed = distance/time -----(1)
In the given example since the distance is fixed an increase in the time of the trip will increase the denominator in equation(1) thereby decreasing the speed.
I would say the head and heart because if you swim deep in the ocean you will feel pressure in your heart and head because the muscles in your body are closing in on them
