High-intensity interval training HIIT has been in the exercise new a lot in recent years.  It has been highlighted as an exercise that can be done in a shorter period of time, works better for reducing central body fat, and is in the spotlight as an option for aerobic training.  Prior studies found that HIIT had a greater effect than continuous moderate-intensity training on fat loss, especially a decrease in truncal adiposity or central obesity and this has been well documented in multiple studies.  The sad thing is it is not much different than the circuit training we did in high school gym class.  HIIT is a great exercise for an individual to perform because it has a smaller time requirement and requires less equipment.  

As a physician, I have been approached by a lot of patients asking for weight loss and exercise advice.  A lot of them are looking for that a magic pill or exercise to be able to lose weight in a specific area.  Outside of surgery, physicians have limited tools to help with spot fat loss.  Prior to this recent 2017 study, I would have told

them that it was a waste of time, but that might be changing if further research backs up the results of this new study.  

The study was published in The Journal of Sports Medicine and Physical Fitness in 2017[1].  The researchers sought to examine whether long-term HIIT preferentially modulates truncal adiposity rather than peripheral adiposity.  They specifically looked at thigh adiposity because local muscle energy consumption is increased profoundly during HIIT in these muscles.  They also examined the association between changes in adipose tissue distribution and serum adiponectin (a potential satiety hormone) level.  The subjects were twelve healthy male participants from 28-48 years of old.  The subjects were assigned to a group that performed HIIT using only a leg ergometer or to a group that performed HIIT using both leg and arm ergometers twice weekly for 16 weeks.  The training programs consisted of 8 to 12 sets with 1 min of very light active recovery between sets.  Body composition analyses, aerobic fitness, and measurements of serum adiponectin were performed at baseline and after the intervention.  The results of the study found a decrease in leg fat or thigh adiposity with improvement in aerobic fitness in the combined group.  Visceral adiposity was decreased in the leg HIIT and regional fat loss near the main active muscles was observed during the 16-week HIIT program. 

The bottom line:  Regional fat loss rather than fat across the whole-body fat was observed after a 16-week HIIT program.  This study is promising that spot fat loss is possible, but the low number of subjects and single-sex participants necessitates more research to confirm the result in a more diverse population.  I would also like to see other areas outside of the thighs examined.