Caffeine is a harmless drug for most people, and exercise is a positive activity for those who are physically able to incorporate it into their routines. These two practices can usually be combined without any problems -- although caffeine and physical exertion both cause effects on your body. Exercise after drinking coffee is dangerous to a small segment of the population, but most people face no risk.

Physical Effects

Caffeine affects your central nervous system within minutes of drinking coffee. The drug is a stimulant, so it makes you more alert, reduces fatigue and wakes you up if you were sleepy. While those effects are often desirable, caffeine can also cause unpleasant symptoms, like agitation, dizziness and nervousness in people who are very sensitive to the chemical. The stimulating effects may facilitate exercise after drinking coffee, but the negative effects may prevent exercise for people who are prone to those reactions.

Amount

Consuming excessive amounts of coffee causes unpleasant symptoms that may impair exercise even in people who are not overly sensitive to caffeine. Your heartbeat quickens, muscles tremble, you feel nervous and your stomach gets upset. All of these issues can impair physical activity. Exercise makes your heart beat faster because of the exertion, so drinking large amounts of coffee before your workout may be dangerous if you have heart problems if caffeine magnifies that effect.

Considerations

Caffeine is a diuretic, which means that it increases your urine output, according to TeensHealth.org. This raises your dehydration risk unless you replenish the fluid output promptly. Exercise makes you sweat to help keep your body cool. If you work out after drinking coffee, make a special effort to drink enough water or other hydrating beverages to balance the increased fluid loss from perspiration and urination.

Warning

About 2 percent of the population has an aneurysm, or bulging spot on an artery wall, in the brain. Sometimes this condition is harmless, but it can lead to a stroke if the weak spot bursts. Both exercise and coffee raise the chance of a rupture, according to a 2011 study of 250 rupture survivors by researchers in the Netherlands, published in the journal "Stroke." Exercise was linked to 8 percent of the stokes, and coffee was linked to 1 percent. Twenty-eight other risk factors were studied. When combined together, they were still only linked to 5 percent of the cases. Beware following coffee with exercise if you have an aneurysm because of the increased rupture chances.