Another win for brief intense exercise.

One hard 4 minute session seems to have effects similar to 4 x 4minute sessions. The whole study is available and worth looking through:

Low- and High-Volume of Intensive Endurance Training Significantly Improves Maximal Oxygen Uptake after 10-Weeks of Training in Healthy Men

Conclusion
Our study demonstrated that slightly overweight and healthy individuals only required brief, duration bouts of exercise with good effort three times a week, to produce large increases in VO2max and work economy and reduce blood pressure and fasting glucose levels. Additional studies to examine both adaptations at the molecular level and feasibility for public health appear warranted.

 There is a further write up here.