High-intensity interval training has been on the American College of Sports Medicine (ACSM) list of top fitness trends for the past. To generalize the definition of a HIIT workout, it combines short, anaerobic bursts of exercise with shorter rest periods.
On a podcast featuring cardiologist Dr. John Higgins, he reviewed new research that shows that men see more benefits to their level of fitness including decreased body fat and increased aerobic capacity after about six weeks of training. Women, on the other hand, did not show as much improvement.
An very important asterisk to this research is that the population of women that showed lesser results were those who are post-menopausal and nearing retirement age. Younger and middle-aged women actually did see similar results as the men. This suggests that the difference for older women is related to hormonal changes or an overall ability to perform high intensity workouts.
One important bulletpoint to consider is that HIIT workouts were created to cater to those busy people who only had 20-30 minutes to sneak in a workout. Meaning, this type of workout might work best for them only because that's all they have time for.
Although men do see greater results from HIIT workouts than women, personal trainers will admit that they watch men closer because of their higher risk for a cardiac event, such as a heart attack. For the older population, both men and women, fitness programs will still benefit from some HIIT workouts, but the "foundation" should be more moderate exercise to protect themselves from both injury and a significant health event.