Not necessarily.
See, intervals are like levels of intensity.
For instance, here is an example of HIIT for a
stationary bike...
First 2 minutes, pedal at an intensity of 5 (50% of full intensity)
Minute 3: Pedal faster or up the resistance on the bike for level 6
Minute 4: Pedal faster or up the resistance on the bike for level 7
Minute 5: Pedal faster or up the resistance on the bike for level 8
Minute 6: Pedal faster or up the resistance on the bike for level 9
Minute 7: Pedal at level 6.
Minute 8: Pedal faster or up the resistance on the bike for level 7
Minute 9: Pedal faster or up the resistance on the bike for level 8
Minute 10: Pedal faster or up the resistance on the bike for level 9
Minute 11: Pedal at level 6.
Minute 12: Pedal faster or up the resistance on the bike for level 7
Minute 13: Pedal faster or up the resistance on the bike for level 8
Minute 14: Pedal faster or up the resistance on the bike for level 9
Minute 15: Pedal at level 6.
Minute 16: Pedal faster or up the resistance on the bike for level 7
Minute 17: Pedal faster or up the resistance on the bike for level 8
Minute 18: Pedal faster or up the resistance on the bike for level 9
Minute 19: Pedal faster or up the resistance on the bike for level 10
Minute 20: Pedal at Level 5 intensity for cool down mode.
Believe me, if you do this right, it will kick your ass. And the best news yet, its only 20 minutes long!!!!!