How would the stimulation of muscarinic receptors in cardiac muscle affect the heart?

Ricardo notices that when he plays soccer in the rain, his ball does not seem to go as far after a kick. what is the best scientific question that ricardo could ask about this observation? is soccer better played in the rain or sun? how does rain affect the distance a soccer ball can travel? how does rain affect the speed of a soccer ball? is soccer affected by the rain?

Which would be the most useful source of evidence to support mcneill's contention?

What substance acts to prevent sudden ph changes in bodily fluids?