Sunday, 11 October 2015

The Myth of the "Workout Weight Loss"

Some folks like to weigh themselves before a workout/run/ride and again afterwards.
Today I did this.
I weighed in at 92.5 kg (203 lbs) when I got up, then I had a single cup of tea (no sugar, as always), and went for a pre-breakfast ride,
I came back and weighed-in again at 90.6 kg (199 lbs)

So I lost almost 2 kg (or about 4 lbs) in weight this morning.
Few more workouts/rides like that and I'll soon be thin again!

Or not.

Lets analyse the ride.
Here it is on Strava.
Turns out I set three "personal records".
I might add that there was a slight tailwind on all of those sections!
But, overall, I would describe my performance as "sluggish".
With no carbs to draw on (no breakfast, remember) I was struggling the whole way.
I couldn't get my heart rate up (normally I can get past 170 with no problems - indeed, I got a max of 182 only last Sunday, after breakfast, of course!). Today I couldn't get past 165.
Like I said - "sluggish".
Had to keep forcing myself to up the pace, as I fought my body's desire to slack off a bit.
Decent bit of sweat after the first hill climb, however.

So, if I lost almost 2 kg (about 4 lbs) how many calories did I burn?
Strava says 360 calories burnt during the ride, with 87m of climbing
But Strava loves missing out the small climbs if you don't have a barometric altimeter on your recording device, and my Garmin 310xt doesn't have one.
The Garmin Connect site has an "auto-correct" option, so the heights recorded in a ride are matched against a known height map (e.g. if my course went through a bit with a 5 metre (16 foot) drop then a 5 metre climb, Garmin Connect makes sure the the position data from my ride reflects this. Strava misses out anything less than about a 10 metre climb to compensate for the variability of GPS altitudes, and even strips the "Garmin Connect" height corrections back out of a data file transferred from Garmin Connect to Strava!
Enough background - what does Garmin Connect, with its "height correction" say about calories used?
Garmin Connect says 707 calories with 98m of climbing.
Which is right?
707 calories or 360 calories?
they BOTH use the same data file!
oddly enough, exercise only uses about 20-25% of daily calories - with about 70-75%% being "basal metabolic rate" - in other words, if I am fit, I use extra calories just sitting down :-)
(the other few percent of daily calorie use is down to ther stuff like the type of fat cells and whether you exercise before or after breakfast and stuff like that).

So lets have a look at typical calorie usage for typical folks.
Of course, these are "average" figures, and folks with a high metabolic rate will use more, while folks with a low metabolic rate will use less.
But let's just assume I am "average".
How fast was I cycling?
Strava says 19.8 km/h (12.3 mph), while Garmin Connect says 19.7 kph (notice that Strava use different units that are equivalent!), which works out at about 12.2 mph.
At least both sites have me going about the same average speed!

So let's see how that looks on the "Harvard" table.
Cycling at 12 to 13.9 mph uses about 355 calories for half-an-hour for a 185lb person.
OK, but I weigh just over 200lbs.
Look at how the extra weights for the three examples in the table adds some calories each time.
The 125lb person uses 240 calories, the 155lb person uses 298 calories and the 185lb person uses 355 calories.
So each extra 30 lbs of weight of the person results in (approx.) an extra 57 or 58 calories being burnt per half-hour.
Well, I am just over 200 lbs, so we will add about HALF of a 30 pound unit to the weight (bring it up from 185lbs to 200lbs), so we need to add about half of 57 or 58 calories to the calories burnt as well.
So let's say the I (weighing about 200 lbs) use about 384 calories per half-hour while riding at about 12 (and a bit) miles per hour.

The ride took about 1 hour, so I should have used about 768 calories (Garmin Connect was therefore closest with 707 calories).
Perhaps I have a VERY efficient pedalling action, and a VERY well-developed energy usage system - far better than "average"?
Well I did complete a 232km (145 mile) ride about 7 weeks ago, and that certainly isn't average! It also turns out, that although on balance, a pedalling cadence of about 90 is the best mix for balancing muscle tiredness and energy usage, a pedalling cadence of about 70 is actually more efficient as regards energy usage (higher muscle fatigue, though!).
So maybe I really do pedal more efficiently than "average".

Looks like that Garmin Connect figure of 707 calories looks as good as any to use.
Since I lost 1.9kg (4 lbs) on the ride, how much weight does 707 calories work out as?
Given that body fat varies in energy density from between about 2800 calories per pound (454g) to about 3700 calories per pound (454g), my ride this morning has lost not much more than about a quarter-of-a-pound (call it 110 grammes) of body fat/

So where did the "rest" of the weight go?
What happened to the missing 1.8kg (3.75 lbs) of weight loss?

Well, I sweated a bit, and, to be honest, I perhaps didn't even use as much fat as I mentioned above.
Some of the energy I used will have come from my gycogen stores (in muscles and in the liver), but let's just assume that my body does a 100% "Dr Atkins" thing, and restocks the glycogen entirely from fat.
But that doesn't help.
Where did the missing weight go?
Remember I said I sweated? ...

... Well ...

... So my hydration levels fell during the ride.
That's why you are supposed to drink after exercising heavily.
Remember I was lightly dressed on a cool day, so I am going to sweat a bit, but not as much as you will in a hot gym (unless they have the air-con turned to "super-cold"!).

So when you weigh yourself before and after a ride/workout/run a good part of what you are measuring is dehydration, not weight loss.
Have a drink of water and you weigh almost the same as before ...

I actually aim to finish super-long rides weighing pretty much the same as when I started. I finished my 232km (145 mile) ride with not much change in weight, despite having burnt far more calories than you will ever do so in an hour in the gym (Strava called that ride at 4600 calories with 1238m of climbing, while Garmin Connect (with the height corrections, remember) called the ride at 7350 calories and 1496m of climbing). The reason I didn't lose weight - well, I drank a lot, and I ate as I went!
But even if I hadn't eaten, and even if we take the biggest number (Garmin Connect at 7350 calories), that still only works out at about 2 to 3 lbs of fat (about a kilo to about 1.4 kilos).

So there you have it - most of what you measure as "weight loss" if you weigh yourself before and after a workout is merely a change in body water (hydration). As soon as you drink, most of the "weight" comes back.

"Dehydration symptoms generally become noticeable after 2% of normal euhydration water volume has been lost."
Ok, so let's see how much that might be for me?
I have fancy weighing scales that use bio-impedance to measure such things, and my figure comes out at about 59% water, with a weight of about 92kg - not that unusual for a man of 50 (which I am).
59% of 92 kg is about 54 kilos (about 119lbs).
So I have about 54 kilos of water "on board" - excluding anything I have recently drunk that is making its way through my "plumbing" from my mouth to my butt (remember, if I pee out the water, it has to pass through my body's organs - specifically my kidneys, which will send some of it to other parts of my body for usage, and dump the rest).
2% of 54kg is about a kilo (2.2 lbs).
So I could lose up to about a kilo of water without even noticing any effect.

"The symptoms of dehydration become increasingly severe with greater water loss. Heart and respiration rates begin to increase to compensate for decreased plasma volume and blood pressure, while body temperature may rise because of decreased sweating. At around 5% to 6% water loss, grogginess or sleepiness, severe headaches or nausea, and a tingling in the limbs (paresthesia) may all be experienced."
So, as we are only looking for 1.9kg of "missing weight", we need to work out what 1.9kg is as a percentage of 54 kg. 1.8kg comes out as 3.3% of 54 kg, while 1.9kg comes out as 3.5%.
Just 3.3% to 3.5% dehydration. therefore, would explain the weight loss - enough to be slightly dehydrated, but not enough to be showing grogginess, sleepiness, headaches, nausea or tingling.

And there you have it.
The "missing weight" is easily explained as water, which will be replaced when I have a drink (yep, I had a post-ride drink and banana!)

Of the 1.9kg (4 lbs) I appeared to lose in weight on this morning's ride, only about 100g (a quarter of a pound) was ACTUAL weight loss - the rest was just sweat, which will be replaced by proper hydration.

Weighing yourself before and after a workout may make you happy, but it is not a reliable measure of weight loss.
To get closer to the "truth", why not weigh youself when you get up in the mornings, trying to keep things like restroom visits and drinks as constant as you can (I get up, then go to the restroom, then weigh myself, then have a cup of tea. Same pattern, as near as I can, every morning).
There will be weight fluctuations, but anything "real" will show up when measured over a decent length of time.
Here is 9 months of my "morning" weight data:

9 months of almost daily weight data - a much better method than weighing yourself before and after workouts!
Blue line is the data from my scales, the green line is a 3-day average of that data, and the red line is a "trend" line, using the 90/10 formula from The Hacker's Diet.
Why not weigh YOURSELF every day in the mornings for a few months. If you have to miss the odd day, then don't worry. As long as you weigh yourself on MOST days, the data will still be sound. It is not really the day-to-day weight that matters either - it is the weight trend (shown as the "red" line in the graphic above.
My chart shows steady weight loss for about 5 months, then a rise in the Summer, then some more weight loss after that. Probably flattening off about now. But I'm pleased - I am still down by about 5 kg (11 lbs) since January 1st. If you are interested, I have already posted on the reasons behind the "Summer rise" in the chart.

Update, 17th October 2015:
Of course, having "proved" that exercise loses very little weight, why do I do it?
Well, exercise loses a BIT of weight.
100 grammes (about a quarter of a pound) from that ride.
Then, of course, one could always do some MORE exercise.
Anna and I did four short runs this week - only just over two miles each time (about 3.5 km).
Each run used about another 300 claories - so that is another 1200 calories used up, so that's a bit more weight gone.
And so it goes on, a bit of weight most weeks. Only losing, at most, about a kilo (2.2 lbs) a month.
Not that impressive, perhaps.
But nine-and-a-half month into the "exercise" diet, and I am still about 6 kilos (13lbs) lighter than when I started.

How many diet plans have you tried, which lost loads of "weight" (most of which was almost certainly water anyway!) in the first few weeks, but six months later, you weighed as much as when you started?

Exercise has a few "extra" benefits, too.
  • General health is just one of them.
  • Turns out that if you do "high-intensity" exercise, your body runs at a slightly higher metabolic rate for a while afterwards - up to 48 hours! This results in a "bonus" calorie usage that can be up to about 30% of the amount that the "original" exercise used.With lower-intensity exercise, the "bonus calories" effect is still there, but it is smaller.
  • Also turns out that if you exercise regularly, most days or every other day, the "bonus" effects seem to merge to give an effectively higher basal metabolic rate - so you use extra calories even when you are asleep!
  • Further more, the exercise will build up your muscles a bit, and although replacing fat with muscle won't make you directly lighter, muscles have extra mitochondria which use more calories again, which results (again) in an increased metabolic rate. This increased metabolic rate means you can eat more for the same weight, or if you eat the same as before, you lose weight.
Win, win.

But there's more ...
  • Regular exercise makes you feel happier, too. Part of that is purely psychosomatic, in that if you feel less fat, you feel better, but part of it is "chemical", and it has to do with endorphins.
    Exercise-induvced endorphins are credited with reducing stress, warding off depression, and inproving sleep.
So stop reading this, and go and do some exercise?

I've cycled two miles, walked about 4 1/2 miles and run about 2 miles today. Climbed about 10 flights of stairs, too!
Have you done more? (in which case, congratulations!)
Or less?
It's your life and your future.
Change it for the better.

Go do some exercise!

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