EBIO 1230 Student Projects Fall 2008

Effects of Increased Heart Rate and Adrenaline on Reaction Time

Alex Fosdick, Justin Diebold, Scott Bailey

Abstract

We tested the effects of an increased heart rate and the increased levels of noradrenaline on a personŐs reaction time. Cardiac muscle can be stimulated by two different types of fibers, inhibitory parasympathetic nerves or excitatory sympathetic nerves. Sympathetic nerve fibers increase heart rate by releasing norepinephrine into the cardiac muscle tissue (Hall 2006). Norepinephrine is a stress hormone that affects the brain and causes a personŐs attentiveness and responsiveness to increase (Hall 2006). Norepinphrine is similar to epinephrine (or otherwise known as adrenaline) and when in use gives humans a fight-or flight response (Hall 2006). Our hypothesis was that heart rate and increased levels of adrenaline affect reaction time.

We tested our hypothesis by comparing reaction times of humans with resting heart rates to the same humanŐs reaction time after a period of exercise which included 30 pushups and 3 short sprints. Three people would perform 3 sets of 10 trials of reaction tests at the normal resting heart rate. Then each person after completing the first set of tests would perform a controlled amount of exercise to increase their heart rate and perform 1 set of the reaction tests. Then each person would repeat this 2 more times to get more data with the increased heart rate. Each reaction trial consisted of one timed response of personŐs ability to push a button to turn of a corresponding light and measuring the time it took them to react to that optical stimulation. The button and light were a part of timer that started counting once the light had been turned on by the test administrator.

Our results indicated that the average personŐs reaction time is faster at an increased heart rate (mean =460 milliseconds) then at a resting heart rate (mean=504 millseconds, P<0.05).

These results are consistent with our hypothesis. However there were some problems with the way we ran our experiment. During testing, our responses were much clumsier during at the fast heart rate. There were multiple outliers in our data due to the participant missing the small buttons on the reaction timers. We could fix this with larger reaction timer buttons. We also had approximately a 45 second period in between exercise and the start of the fast heart rate test. During these 45 seconds we could have had a decrease in heart rate, affecting our data. To fix this we would have to test immediately after exercise and run the test fairly quickly. The last problem is we grouped our data together in groups of high heart rate and low. This grouping could give misleading data because of different heart rates and physiology. To fix this we could measure a personŐs heart rate until they reached a certain rate and test then.

Results of A. Fernandez-Guardiola et al. 1967 of the Institute of Mexico, show that visual motor reaction was influenced by the rate of the heart. From the results of our experiments we can conclude that increased heart rates and adrenaline will increase your reaction. Perhaps we could test the effects of decreasing the heart rate below resting rate and measure the effects to see if that will decrease reaction time.

 

References

Hall, J. 2006. Medical Physiology. Rhythmical Excitation of the Heart 11th Ed. Pgs. 111-122