when you run graded fitness tests, you usually look for ‘steady state’ during which the heart rate settles into a certain zone. In the tests I have done, I had to have the subject achieve a steady state heart rate before progressing to the next level. In that scenario, a 30 second or 1 minute effort would not have accomplished that. I found another link that describes that quite well http://www.sfu.ca/~leyland/Kin343%20Files/Bike%20Lab.pdf.
I am not quite sure about your question. A MET (Metabolic equivalent) level is simply a unit of energy expenditure. After fitness assessments, exercise recommendations may be made in terms of MET levels based on established tables that link those levels to certain activities.
Here is an excellent article called “Metabolic Equivalents (METS) in Exercise Testing, Exercise Prescription, and Evaluation of Functional Capacity” http://onlinelibrary.wiley.com/doi/10.1002/clc.4960130809/pdf.
Hope this helps.