A researcher is very interested in stress and decides to study how it might effect one's blood pressure. Four stress tests are created:

Test 1 - running on a treadmill as fast as you can for 90 seconds,

Test 2 - trying to solve as many increasingly difficult brain teasers in 90 seconds,

Test 3 - trying to hold one's breath for 90 seconds,

Test 4 - typing a 1000 word passage accurately in 90 seconds