Each interval in the 4 x 4 HIIT protocol lasts how long?

• A. One minute
• B. Two minutes
• C. Four minutes
• D. Thirty seconds

Answer: (C)

In this HIIT approach, the work interval is four minutes long. That duration is chosen to sustain a high level of effort long enough to push oxygen uptake toward its maximum and engage both aerobic and anaerobic systems, creating a strong training stimulus. Shorter intervals (like thirty seconds or one minute) don’t maintain the intensity long enough to fully stress VO2 max, and two minutes may not consistently reach the same high-demand zone across repeats. The rest between intervals is typically three to four minutes of lighter activity, allowing partial recovery so you can repeat the four-minute efforts effectively.