Coffee and Caffeine
Caffeine ingestion is linked to increase anaerobic performance and muscle endurance. In an study, pre-workout caffeine increased maximum muscular strength. Caffeinated pills, mixes and drinks are the most common pre-workout supplement among bodybuilders, athletes, and gym-goers. Strong black coffee and cream is a great idea. Adding sugar is a bad idea.
Many people who follow intermittent fasting take black coffee during the fast. Black coffee taken before exercise, just before the fast ends is great way of depleting glycogen levels and burning fat.
Caffeine and testosterone
Logic would suggest that caffeine would slightly decrease testosterone levels due to elevated cortisol (the stress hormone). However this might be mitigated by a testosterone raising effect at a cellular level. Hard exercise, particularly heavy lifting, boosts testosterone, so anything that can improve athletic performance should boost testosterone levels. Caffeine taken 1 hour before exercise is able to raise testosterone levels by 10%+.
A substance in our bodies called cAMP (cyclic adenosine monophosphate) is a messenger between cells and hormones. So higher cAMP levels are associated with higher testosterone levels. cAMP is broken down by an enzyme called PDE-4, it's been found that caffeine inhibits PDE-4. In medicine, doctors use PDE inhibiting drugs to treat a range of ailments. On October 26, 2009, The University of Pennsylvania reported that researchers at their institution had discovered a link between elevated levels of PDE4 (and therefore decreased levels of cAMP) in sleep deprived mice. Treatment with a PDE4 inhibitor raised the deficient cAMP levels and restored some functionality to memory functions. The cAMP-dependent protein kinase A (PKA) is an essential regulator of hormone production.
Sources: anabolicmen.com, ncbi.nlm.nih.gov