Recently Sephus Le Roux asked:
Q: When it comes to loosing fat Is it better to jog at a moderate pace for 45 minutes or to run at your max for say 5 minutes?

A: This is an important question to ask because there is still debate in the scientific community about which exercise intensity is required for optimizing fat usage. In recent times, many “new-age” training regimens have become popular – High Intensity Interval Training (HIIT), for example. It is generally believed that such methods can be superior in terms of fat burning capacity as compared to normal aerobic-based exercise. The answer isn’t so clear cut however, so I will present an argument and advantage for each of these types of exercise. The importance of COMBINING the two, and not performing either in isolation, cannot be overstressed. Your body is remarkably adaptive, so you need to constantly keep things new and fresh, in order to avoid a dreaded fitness-plateau.

Under normal resting conditions, your muscles prefer to use fats as a fuel source. Fat is far more energy-dense than other types of fuel (carbohydrates or protein), and so is the most efficient to use when the body is not under heavy load. As you become engaged in light (walking) to moderate exercise (jogging), the relative amount of carbs being used increases at the expense of fat. This is due to the fact they can provide energy more rapidly for the exercising muscle tissue. Further increasing the intensity, causes the muscles to enter anaerobic (“without oxygen”) mode. This means they switch over exclusively to burning carbohydrates rather than fat or protein.

So technically lower intensity, more prolonged exercise is better suited to fat burning. The important distinction to make however, is that while more fat is being used during the activity itself, the TOTAL caloric expenditure for the same duration of activity is a lot lower. This is really what matters in the long term. And so in this regard short length, high intensity exercises tend to use more energy in a given unit of time than the endurance type discussed above. Even though all of this energy wasn’t initially derived from fat itself, the body will use its fat stores later on, recovering the used energy in the hours following the exercise (up to 72 hours after very strenuous high intensity exercises like sprinting, lunges, squats and compound lifts). Further in favour of high-intensity vs. endurance, is the fact that anaerobic exercise has been shown to cause notably higher muscle growth. This extra lean mass then uses more energy at rest to sustain itself, further speeding up your overall metabolic rate.

In summary, the answer isn’t 1-dimensional, and ultimately you should work to incorporate both types into your fitness regimen. Aim for 3-4 anaerobic sessions per week. These can include, but aren’t limited to: isolated weight training; compound training (multiple muscle groups), progressive sprints (100m > short rest > 90m > short rest > 80m > …- or the other way around to mix things up); lunges; squats; fast swimming; high-intensity spinning classes and weighted or unweighted sets of body-weight exercises (pull-ups, pushups, situps, ‘jumping jacks’ in combination). A 30 minute workout in which you push your body close to its limit, with less than 60 seconds rest between sets, is enough to cause a massive energy deficit, which the body must then work at replacing following the exercise (remember that this is when the fat will be used).

On weekends, when you have a bit more time, aim to do a 3-5km jog for example, working at improving either your distance or time every 1 or two weeks. Try to increase general, everyday walking where possible too. Keep in mind that more time exercising at lower intensity is required to burn the same amount of calories than during a shorter, high-intensity burst. So you should be aiming at more than an hour of activity at this intensity, at least 2 times a week.

A final point to remember is that diet is a far greater contributor to overall body composition than exercise. Both types of exercise are very beneficial, but more emphasis must be placed on improving one’s diet if permanent results are to be achieved.

-K

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