According to the textbooks, in terms of the energy you burn it makes little difference whether you walk or run. It’s the distance that determines how much energy your body burns, not your speed. Sounds logical, but it’s actually a little more complex. Obesity researchers at the French Institut Louis Bugnard discovered that people who want to lose weight benefit more from a more upbeat cardio session than an hour of gentle physical exercise.
If you want to lose weight there’s something to be said for extended low-intensity physical exertion. Exertion at 30-50 percent of your maximal oxygen uptake [your VO2max] results in optimal fat burning. More intensive exercise burns more energy per minute, but that extra energy comes from your glycogen reserves, not from your fat cells. An advantage of more intensive exertion is not only that it saves time, but also that you get a raised EPOC – excess post exercise oxygen consumption. So in the end you burn a bit more energy with more intensive training than you do with low-intensity training.
The problem with most EPOC studies is that the test subjects don’t eat after their training. If test subjects eat after their training, which is then more effective: high-intensity or low-intensity training? That’s the question these researchers wanted to answer.
The researchers used ten somewhat overweight teenagers for their study. On one occasion the subjects did nothing [Cont], and on two other occasions they burned 300 kcal on a bike. On one of those two occasions the intensity at which the subjects cycled was 35 percent of their VO2max [E35]. Doing this meant it took the subjects an average of 54 minutes to burn the 300 kcal. On the other occasion the test subjects cycled at 70 percent of their VO2max [E70]: they were done in 26 minutes.
Half an hour after completing the training the subjects were given a lunch containing as much energy as they normally ate and – in the case of the E35 and E70 occasions – the 300 kcal they had burned.
The half hour after finishing cycling is called ‘immediate recovery’. The 6 hours after the lunch is the ‘postprandial recovery’.
During the half hour after the E35 training the subjects burned 47kcal. For E70 the figure was 56kcal. After the meal, E35 burned 642 kcal and E70 664 kcal. The total energy expenditure after the E35 training was 689 kcal, and after E70 it was 720 kcal. That’s a difference of 31 kcal.
The researchers also looked at their subjects’ fat burning. During the exercise, E35 resulted in a slightly higher amount of fat burnt than E70, but after the exercise fat burning was consistently higher for E70 than for E35.
When the researchers calculated how many grams of fat the test subjects burned after their training, they discovered that E35 only burned 3 g more fat than the control group. E70 burned 11 g more fat than the control group.
The researchers regard their research results as being “of particular interest in the treatment of excessive body weight”. Their results show clearly that people who want to lose weight by exercising will benefit more from half an hour of jogging than an hour of walking.
Lipid oxidation in overweight men after exercise and food intake.
Fat oxidation (FO) is optimized during low- to moderate-intensity exercise in lean and obese subjects, whereas high-intensity exercise induces preferential FO during the recovery period. After food intake during the postexercise period, it is unknown if FO differs according to the intensity exercise in overweight subjects. Fat oxidation was thus evaluated in overweight men after low- and high-intensity exercise during the recovery period before and after food intake as well as during a control session. Ten healthy, sedentary, overweight men (age, 27.9 +/- 5.6 years; body mass index, 27.8 +/- 1.3 kg m(-2); maximal oxygen consumption, 37 +/- 3.9 mL min(-1) kg(-1)) exercised on a cycloergometer (energy expenditure = 300 kcal) at 35% (E35) or 70% (E70) maximal oxygen consumption or rested (Cont). The subjects were fed 30 minutes after the exercise with 300 kcal (1256 kJ) more energy in the exercise sessions than in the Cont session. Respiratory quotient and FO were calculated by indirect calorimetry. Blood samples were analyzed to measure plasma glycerol, nonesterified fatty acid, glucose, and insulin. During exercise, mean respiratory quotient was lower (P < .05) and FO was higher (P < .01) in the E35 than in the E70 session (FO [in mg min(-1)]: E35 = 290 +/- 12, E70 = 256 +/- 38, and Cont = 131 +/- 7). Conversely, FO was higher in the E70 than in both the E35 session and the Cont session during the immediate recovery as well as during the postprandial recovery period (P = .005 for all; FO from the end of the exercise to the end of the session [in grams]: E70 = 45.7 +/- 8.9, E35 = 38.2 +/- 6.8, and Cont = 36.0 +/- 4.3). Blood parameters did not differ between the 3 sessions but changed according to the absorption of the nutrients. In overweight subjects, high-intensity exercise increased FO during the postexercise period even after food intake compared with the low-intensity exercise and the control session.
PMID: 19796778 [PubMed - indexed for MEDLINE]