Some supplements may help your running. In a 1992 study at the Massachusetts Institute of Technology, choline supplements improved 20-mile race performance.
Many runners report an increased sex drive as they get more fit.
My morning heart rate fluctuates from day to day. Increased aerobic fitness decreases resting heart rate. Over-training can increase pulse. Daily fluctuations may be a reflection of intensity of workouts from the previous day or two- a rebound effect may occur the second day after intense exercise, lowering pulse rate. If pulse variability impacts how you feel or how well you meet training goals, consult your physician.