Could starting your aerobic session with weights increase fat burning?

Posted on June 12th, 2009 in Exercise, Science, Training

weight For those of us wanting to lose weight, the important aim is to use up our stores of fat. When we think about how to improve our physical condition, aerobic exercises or resistance work are two of the most common choices. But could combining the two exercises in the right order increase our body’s fat burning ability?

Aerobic exercise is effective in improving our cardiorespiratory fitness whilst improving the burning of fat and overall energy use. Weight training or resistance work acts as a stimulus to the muscularskeletal system to increase muscle size and strength. It is therefore recommended that a training routine combines both types of exercise as each has its own advantage. Normally aerobic or resistance exercises are performed in a single training session and if are combined aerobic exercise is often completed first as it is seen as a warm up of the muscle prior to resistance training.

A group of researchers from the College of New Jersey however wanted to examine the impact of resistance training prior to aerobic exercise. The study published in European Journal of Applied Physiology involved 11 males and 21 females who ate a moderate (50%) carbohydrate diet. Six static weight machines were chosen for the resistance exercises: Leg press, lat pull down, leg extension, seated row, shoulder press and chest press. For each subject their 8-RM was determined. This being the maximum amount of weight that could be lifted through a full range motion 8 times. Each subject completed each one of the following trials on different days

Aerobic exercise only (C) (cycle for 20mins at 50% maximum oxygen uptake (VO₂max))
High intensity resistance training (HI) (3 sets of 8 reps at 90% of 8-RM) followed by aerobic exercise
Low intensity resistance training (LO) (3 sets of 12 reps at 60% of 8-RM) followed by aerobic exercise

Throughout each aerobic activity the researchers looked at oxygen uptake and also the oxidisation of carbohydrate and fat. Oxidisation is when the fuel source ie, fat or carbohydrate, combines with oxygen to provide energy. They found that fat oxidisation and oxygen uptake was higher in the HI group than either LO or C in both males and females. Prof Kang, the paper’s author suggests that whilst fat oxidation following LO training was itself higher than aerobic exercise alone it is the intensity of the resistance exercise that is more important than the total volume of exercise completed.

Interestingly after the first five minutes of aerobic exercise they found no difference in carbohydrate oxidation rates. Prof Kang suggests that it appears in training that combines both aerobic and resistance exercises, performing a comparatively higher intensity resistance exercise first would boost the use of fat and energy during any subsequent aerobic activity.

He suggests that the metabolic effect of the resistance work is due to an increase in lipolytic hormones, which may have a short time before they revert back to their resting levels and that the aerobic exercise should ideally start within 5mins of resistance exercise, but after no more than 20mins.

So according to Prof Kang’s research if you really want to burn fat quicker get to the gym half an hour before your aerobics class or run and lift some weights.