What Your Gym/ Exercise Class Doesn’t Tell You…

‘The Exercise Equation’

Exercise sessions in themselves don’t actually result in appreciable fat loss. That’s a pretty bold, counterintuitive, and almost heretical statement, but it’s actually closer to the truth than you would’ve been told. Here are the approximate energy expenditures for a range of activities (please remember I’m only using Calories as a measurement as it will be the most familiar to most people):

During 1 hr of Exercise an average sized person will expend:

- Aerobics 414 Cal
- Running @ 8mph 1098 Cal
- Weight Training (40s btw Sets) 898 Cal
- Weight Training (90s btw Sets) 450 Cal

So if we were to just look at the ‘Eat Less, Move More’ simplistic premise, which activity would we choose? Running right? After all we expend over twice as much ‘energy’ as both aerobics (low intensity) and weight training (90 second rest between sets). Even if we drop our rest periods to less than half (40 seconds) during weight training, running still expends 120% more energy. However, as you’re beginning to appreciate there’s nothing simple about the Human body. Here’s why just looking at Caloric expenditure is insufficient when approaching exercise for losing body-fat.

‘The First Kicker’

The first 20-30 minutes of any exercise primarily uses carbohydrate as a fuel source due to hormonal restraints. So no matter what exercise type you choose or how you structure these sessions, hardly any fat is used in the first half an hour. After this initial point depending on the intensity, duration, and ingested nutrients, the relative percentage of fat used changes. Let’s have a quick look at the above activities in light of this knowledge and what it means for fat loss:

Aerobics

- 414 Cals
- (-first 20 mins) = 276
- 40% fat = 110 Cals from fat
- To use 1 lb of fat would require around 32 of these sessions

Running

- 1098 Cals
- (- first 20 mins) = 732 Cals
- 25% fat = 183 Cals from fat
- To use 1 lb of fat would require around 19 of these sessions

Weight Training

- 898 Cals
- (-first 20 mins) = 598 Cals
- 25% fat = 150 Cals from fat
- To use 1 lb of fat would require around 23 of these sessions


In fact it’s even worse than this; if you had just sat on your bum for an hour, an average sized man would’ve still used 72 Kcal worth of Energy; and because the intensity is low, a fairly large percentage (47 Kcal worth) would be from fat. So you have to take this away from the above equation which would lower the fat loss from each session further.

So a 1 hour aerobics class only puts you ahead by 63 Kcal worth of fat, running only 136 Kcal from fat and weight training only 103 Kcal from fat. Or put another way: 1, 3, and 2 teaspoons of fat, respectively.

‘Putting the Boot In’

And these are in situations specifically set up to tilt the balance in favour of fat oxidation. If you’re performing them in the morning after an overnight fast and you’re metabolically healthy then, you ‘may’ approach these numbers. If you’re doing it in the evening in a non-fasted state and you’re metabolically ‘damaged’, then the entire dynamic is altered away from fat usage.

One final wrinkle is your current conditioning; to be able to achieve the above sessions you need to be in fairly good shape already. For example, the running workout requires you to run at 8 miles per hour outdoors; that is not an easy pace especially when factoring in the weather and terrain. On a treadmill you’d need to be clipping along at 13kph at a minimum 2-4% incline for an entire hour. If you’re well conditioned you can do this and your body will start incorporating fat into the mix after 20 min’s. If you are not currently in great condition then you’d struggle to complete the workout, and even if you could, because the relative intensity would be higher for you, then your body cannot incorporate fat into the fuel mix.

So am I saying exercise is ineffective for fat loss? Not at all, but it’s nothing to do with the fat (or even the ‘Calories’) used during the workout, nor is it really to do with the raised metabolic rate outside of the workout either. So if your gym or exercise class is belabouring the Calorie ‘burn’ or even ‘After-burn’ of a particular workout then consider what they do actually know, because it certainly isn’t exercise science.