A Christmas HIT – guest blog on fat loss by David Kingsbury PT (Part 1)
A High Intensity Christmas can Reduce your Body Fat
With the festive season upon us, there‘s no better time to explore the science behind exercise and fat loss. For many years, aerobic exercise has been considered one of the most effective ways to reduce total body fat and maintain a healthy weight. Now, however, evidence is growing that high intensity training (or HIT), which involves relatively short bursts of exercise at all out intensity, may be a more efficient exercise protocol for inducing fat loss.1
Reducing body fat
Consider this Australian study evaluating the effect of different exercise intensities on fat mass in young women of relatively normal weight.2 Researchers compared low-intensity exercise (consisting of up to 40 minutes of steady cycling at 60% of VO2 max, three times a week) with a high intensity protocol which involved performing a series of cycle sprints of just 8 seconds duration, followed by 12 seconds of rest, for periods of between 5 and 20 minutes. Cardiovascular fitness improved in both groups over the 15-week study, but only those following the HIT programme achieved a significant fat loss in both total and abdominal fat even though they exercised for only half the time of the other group.
A similar study - this time in a group of overweight young men - found that 20 minutes of HIT three times a week significantly reduced abdominal, visceral and trunk fat over a 12-week period.3
While the exact mechanisms underlying HIT-induced fat loss have yet to be determined, it seems that hormones released by the adrenal glands called catecholamines (for example, adrenalin) play a part.1,3 Catecholamines are involved in releasing stored fat for use as energy, and significant levels are generated during high intensity exercise.
Another way HIT might influence fat loss is by its impact on appetite and food intake. By altering the subjective reward value of food in the brain, it seems that high intensity exercise might encourage us to choose lower calorie foods.
Such a mechanism would fit with the findings of a study published this month that used MRI scanning to image activation of the brain.4 Researchers from around the UK showed pictures of high calorie and low calorie foods to volunteers after they had completed high intensity exercise (running on a treadmill for 60 minutes at 70% of V02 max). They found that HIT increased neural responses in reward-related regions of the brain in response to images of low-calorie foods and suppressed activation during the viewing of high-calorie foods. This finding is particularly meaningful when devising fat loss programs.
Evidence for HIT’s impact on subsequent energy intake includes a study of obese adolescent boys that compared cycling at low intensity (40% of V02 max) and high intensity (75% of V02 max). HIT had a beneficial impact on 24-hour energy balance, mainly due to a spontaneous decrease in energy intake during lunch and dinner following the exercise bout. Energy intake at dinner, for example, was not only 20.5% lower after HIT compared with no exercise, it was also 19.7% lower after HIT compared to low intensity exercise.
David goes on to give exercise workout ideas in the next blog http://weightmatters.co.uk/2013/12/12/a-christmas-hit-guest-blog-by-david-kingsbury-pt-on-hit-training/
Boutcher SH. High intensity intermittent exercise and fat loss. J Obes 2011; 2011: 868305
Trapp EG. The effects of high-intensity intermittent exercise training on fat loss and fasting insulin levels of young women. Int J Obes (Lond) 2008; 32: 684-91.
Heydari M et al. The effect of high-intensity intermittent exercise on body composition of overweight young males. J Obes 2012; 2012: 480467.
Crabtree DR et al. The effects of high-intensity exercise on neural responses to images of food. Am J Clin Nutr 2013 [Epub ahead of print].
Thivel D et al. The 24-h energy intake of obese adolescents is spontaneously reduced after intensive exercise: a randomized controlled trial in calorimetric chambers. PLoS ONE 2012; 7: e29840
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