Calories or Kilojoules?

Like many of us, I’m engaged in a constant struggle to maintain a healthy weight and fitness level, and being an economist, I naturally like to think about this in quantitative terms (I’m not alone in this).

The basic equation is simple[1]: Energy used – energy consumed = fat burnt. But to make sense of this equation, we need units, and that raises the immediate questions:

Calories or kilojoules? and
How much do I have to burn to lose 1kg of fat?

The short answers are: Calories and 9000 Cal[2]

More over the fold

Calories (more precisely, kilogram calories, Cal in SI) are familiar and widely used, but Kilojoules are the Standard International Unit, and are more prominently displayed on food. 1 calorie is approximately equal to 4 kilojoules, which is discouraging, because Australian food labels report kilojoules (calories in small print) while most exercise programs only give you calories. Looking at how the unit are derived, this is the wrong way around.

A calorie is a unit of heat: the amount required to raise the temperature of a kilogram (or litre) of water by 1 degree Kelvin (or Celsius). That makes sense as a measure of food energy, since we burn it. A Kilojoule is a measure of work done: it’s what’s needed to generate one kilowatt of power for one second. So, if you’re concerned with running or cycling, the question of interest is how many kilojoules you can generate in torque, overcoming resistance and so on.

So, we might say that Calories are input and Kilojoules are output. If you want to lose weight, it’s calories burnt that matter. But it turns out, quite by chance, that calories are also a pretty good output measure. That’s because, considered as engines, our bodies are only about 25 per cent efficient, which roughly cancels the ratio of kilojoules to calories. So, one calorie (= 4Kj) consumed translates to about 1Kj of useful work.

That makes sense to me. At top pace, I burn around 1000 Cals an hour. At 25 per cent efficiency, that amounts to an output of 250 watts, which is about right, given that I weigh 70kg, am travelling at 3.5m/s and would decelerate to zero in a couple of seconds if I stopped pushing. (The efficiency figure is just for conversion of food to mechanical energy – there’s a whole lot more to consider in terms of the mechanical efficiency of running. Measurement is much easier in the case of cycling).

On the second question, the energy content of fat is around 37Kj/g, or 9Cal/g. Exercise will also result in fluid loss, but since fat doesn’t contain much water, this is all temporary.

So far, I’ve talked only about the difference between calories in and out, but what about the levels? It’s surprisingly hard to get good estimates, but it appears that a moderately active man of my age should be consuming 2000-2500 Cals/day. I’d say I’m burning an extra 1000/day, but on the other hand, I’d like an energy deficit of 500/day at the moment, since I’m trying lose a few kilos I put on at the end of last year. However, I’m not measuring calorie intake with any precision, relying for the moment on more activity and cutting down on a few obvious items, like alcohol.

fn1. Exploiting it is not so simple. I’m not an expert, but it seems pretty clear that, if you have been at a given weight for a long time, your body will try to keep you there, by slowing down metabolism, sending hunger signals to your brain and so on. Still, having lost 15 kilos over a couple of years, and kept all but 2 or 3 off for a couple of years more, I don’t accept the fatalist view that there’s nothing to be done about this.

fn2. My earlier understanding was 7500, and since posting, I’ve seen some sources to support this. YMMV

66 thoughts on “Calories or Kilojoules?

  1. Also, as you get lighter, you have to work harder to maintain a consistent weight loss.

    Smartphones are really a wonder for doing all this type of data tracking. I use myFitnessPal to monitor calorie intake, although sometimes the calorie estimate are inconsistent or way off. Still, it allows me to see what works well with my exercise rate.

  2. John are you using a power meter for cycling?
    I’ve been thinking of trying those new cleat-based systems for this years training for my annual target ride around Lake Taupo; but I’m not sure how much better it is than heart rate. In particular it occurs to me that heart rate might be a better measure of how the engine is running than just how much energy it is producing (so on ‘bad’ days maybe you are better off training to HR rather than putting in extra to meet target output levels)

  3. 70 kilos!!! I dream of being 70 kilos.

    Currently, I am 85.2 kg having dropped from 87.8 on 1/1/2013. Thus a weight loss of 2.6 kilos but let’s “round” it to 2.1 kilos to allow for random variations, mainly in water content in my body. This is convenient as it indicates I have lost about 2.1 kilos in 21 days or 100 grams a day.

    However, when I check my chart all this loss occurred in the first week of my diet. And I have marked time for 2 weeks since. This is despite working physically hard (for me) most days. This means a couple of hours gardening work in the hot sun or a brisk 45 minute walk also usually in the hot sun. The weight loss in the first week could hardly have been all fat. And it is not water as I have kept myself properly hydrated (at least over the full 24 hour cycle). So what was the weight I lost? My waist is smaller by about 3 cms so that suggests some was fat. Was the rest glycogen in the liver and muscles (over-stored as I pigged out over Xmas)? This suggests that I have done some good in burning away that excess glycogen which would have been laid down as my next “installment” of fat.

    Any thoughts?

  4. John,I’ve been undertaking an overhaul of my diet and exercise over the past year, and while a calories in/calories out approach is great start I think some further ‘tailoring’ would help most people. I’ve seem to be getting large benefits from cutting down on meat (and hence, probably fat as % of my diet) AND/OR doing high intensity cardio excercise for short durations. Some links you might find interesting:

    A great little doco on genetically determined responsiveness to exercise:

    And, the benefits of HIIT (High Intensity Interval Training):

    On dieting, the two cults which manifest in various forms seem to be the high-protein diets(paleo-primal, Atkins) and the plant-based, high carbohydrate school ( vegetarianism, and veganism). Apart from the fact that no endurance athlete is on a high-protein diet (ketosis will cripple your performance) the vegan/veg folk might be on to something with this book looking at epidemiological data from China:

    My prescription, as a base, is high intensity 20 min workouts (2-3 a week), five meals with meat per week (maximum), 3+ serves of fruit a day. And of course, early nights, and lots of water.

    Would be interested to hear people’s thoughts/experiences….

  5. For information about UNSW’s research on interval training see transcript of Radio National’s Health Report of Monday 2 July 2012 – “Quick sprints can cut abdominal fat in men.”

    Steve Boutcher (UNSW) speaking of their 12 week program: “The warm up is 5 minutes just like a 30 walk thing like steady state, just to get the legs moving and so forth and then the music kicks in, 8 second sprint, 12 second easy and they do 60 sprints. So 68 seconds, 60, 12 seconds, so there’s actually 8 minutes of sprinting in each session and 12 minutes of really easy exercise. So in this study we actually did 12 hours of exercise to reduce that visceral fat, a 70% decrease in visceral fat.”

    This contrasts with steady moderate exercise requirement of “about an hour a day, about 3,700 kilocal a week” to achieve a comparable result.

    As for caloric restriction, there seems to something to be said for an “interval” approach to that too. Not only does intermittent fasting avoid adaptation and lowering of metabolic rate, the later stages of say a 24 hour fast may stimulate stem cell growth. See New Scientist 22 November 2012 “Deprive yourself: The real benefits of fasting” by Emma Young. The full article is pay-walled. There is a suggestion that humans are better adapted to a feast/famine regime than to unremitting abundance.

  6. “There is a suggestion that humans are better adapted to a feast/famine regime than to unremitting abundance.” – rsp.

    That is why I am on the “one meal a day diet”. I now eat a normal evening meal and then an hour later substitute a high fibre breakfast cereal with low fat milk and fruit for any dessert. In the morning, I have half a glass of fruit juice with water added to fill the glass, plus 1 cup of tea or coffee. Then I live on coffee, tea and water through the day. Currently there is a dash of low fat milk but no sugar in my beverage.

    In the past, when I kept to this diet and had only water and/or black, unsweetened tea through the day, it was highly effective. I am working back to that regimen. What one has to say to oneself is that this dietry style is for life. I am trying to make that mental adjustment this time round. I only kept it up for 8 mths last time. If one has to lunch out to be social this is fine. One simply has no evening meal other than the cereal and fruit.

    I find this diet unleashes extra energy in me. I can work physically and/or formally exercise without eating through the day. In fact, I feel more like doing the hard work and exercise not less like doing it on this diet.

    Doctors throw up their hands in horror at this diet and offer all the standard saws about large breakfasts and eating regularly (meaning three times a day). They may be right for some people. This diet would not suit diabetics or people prone to low blood sugar or other blood sugar regulation issues.

    The hardest thing about this diet is the social pressure to conform to other people’s eating habits. ‘Tis amazing how people are so loathe to let another march to his/her own drum. They always want you to conform to their ways of thinking and acting. I don’t think there is anything inherently natural about breakfast, lunch, dinner with morning tea and afternoon tea in between. These are IMO aristocratic eating habits then adopted by the middle classes.

    Hunter-gatherers, which is how we evolved, probably ate sparingly if at all through the day and shared the fruits and meats of hunter-gathering at the end of the day around the group or tribal fire. Sounds like a one meal a day diet to me.

  7. I gave the sugar a rest since new year’s. I notice my baseline energy has really picked up, which I assume is a result of not spiking my blood glucose all the time.

  8. I think we should stop using nonmetric units because it’s a) simpler and b) another sign to to the US their cultural dominance is waning. I gave the example on an earlier thread about the statement ‘ gas is $4’. We are forced to think through gaseous gas, gasoline, litres, US gallons and Imperial gallons. In my opinion (shared by Dr Sheldon Cooper) the US should adopt the metric system before they are left behind. Fortunately a gigajoule and a million British Thermal Units are about the same. It would be nice if more blog software used UK spelling as the default.

    I note at least two US origin fast food chains have wall signs stating that 8,750 kj is the average adult allowance. With fat if we X1,000 we get 37,000 kj or 37 MJ per kg. The thermal energy of petrol is usually given as about 35 MJ per litre. That’s a bit under a kilogram and also includes latent heat of condensed water vapour from burning. Therefore fat is ‘hotter’ than petrol albeit powering a less efficient engine.

  9. I found the “granny diet” successful: don’t eat anything your great grandmother wouldn’t recognise as food.

  10. @Sancho

    Using one hand I can literally bound to my feet from a floor sitting position (in about 1.5 seconds I think), despite being 58.5 years and easily 10 kg to 15 kg overweight.

    However, with no hands I am stuck unless I do a swivelling knee lever and even sometimes a secondary elbow to knee lever. I can feel weight and lack of flexibility causing problems here. In addition, the flabby gut reduces the ability to bend forward from the waist in a floor seated position. I suspect the key move for those who can do it is to be able to tuck the feet close to the buttocks with knees still well raised and pointing mostly forwards, bend well at the waist, rock forward, arms stretched forward and bound up.

    Looks like I have a lot of work to do.

  11. Afterthought. Crossing the legs just above the ankles can help. I reckon with another 5kg loss I could do it that way without hands or knees. Excess weight means my COG is too far behind the feet. A slimmer person can lean the torso, head and arms forward and get the effective seated COG over the feet.

    JQ, you should be able to do it easily at 70 kg. It will just be a matter of technique for you.

    1. Cross the legs just above the ankles.
    2. Tuck the crossed heels as close to your hams or buttocks as possible.
    3. Throw the arms forward, rock forward and reverse squat upwards.

  12. 3rd footnote. Obesoklast can do it easily now. It’s just technique, practice and balance.

    My son, nearly 19, 183 cm and a very light 52 kg (he hasn’t filled out yet) can rise from a floor seated position using a single leg. Don’t you hate the young? I do. :s (Just joking.)

  13. Another sidenote to this is looming Peak Oil and svelteness. Apparently there were few fat people in the UK during World War 2 thanks to rationing of bread, butter and so on. Someone said this week even in the high sugar diets of the 1970s people disco danced the weight away.

    Our current food production and distribution uses massive fossil fuel inputs. Urea fertiliser made from gas, diesel for farm machines, electricity and gas for canneries, more diesel for delivery trucks then big display fridges at Coles and Woolies powered by coal fired electricity. Authors like Hall, Pimental and others claim that 10 energy units go into food production for every energy unit of food value. That is the EROEI is 0.1 as opposed to about 80 for coal.

    When fossil fuel depletion (also phosphorus) and carbon taxes make the current food system unviable we’ll have to eat less or burn more personal kilojoules obtaining that food. Since we’ll all telecommute c/- the NBN we can spend that saved commuting time in the garden. Dinner will have a lot of spuds and turnips because petrol is just too dear to go to Maccas.

  14. @Hermit

    Just have a look at photos of streetscapes and lunch hour crowds in Australian cities in the 1960s. Just about all the people are like posts, straight up and down. There is the odd old fellow with a gut (maybe 1 in a 100) and that’s about it.

    And yes, food shortages are about to bite the whole world. In Australia, we will be able to buy enough foof, just, but it will be very, very expensive. I would not be surprised if food prices double every five years from now on. In fact, I am a bit conflicted about my current weight loss effort. By the time I lose it, food will be so dear that I would have soon lost it anyway due to necessary economising.

  15. If the economic approach suggested by Jessica Irvine actually worked, homo sapiens would have died out long ago and we wouldn’t be here to discuss weight loss. Fortunately or unfortunately, we include a set of sophisticated homeostatic mechanisms that regulate energy usage in a way that is optimised to maintain and slightly increase our weight in a variety of conditions.

    If you don’t eat, your body slows down: your resting metabolic rate slows, your brain activity decreases, you tend to limit exertion, you sleep more, and so on. All this stuff happens unconsciously. You may experience feeling of loss of vitality or mental sharpness which eating actually improves. Maintaining a diet regime requires use of willpower. People have a limited willpower resource and there may other demands on willpower, eg, processing advertising. Willpower uses brain energy and your available willpower will decrease when you are hungry. Experiments have shown that a carbohydrate mouth rinse will improve your performance in restrain tests requiring “willpower” without any energy ingestion. This parallels similar results showing that muscle output will increase after a carbohydrate mouth rinse. This demonstrates some of what you are up against. The body systems are performing a sophisticated calculation to preserve your internal energy stores for survival.

    When your weight decreases below it’s recent running mean the levels of about eight “hunger” hormones increase which make you feel like eating. They are also likely to play a few cognitive tricks like making portions appear smaller and forgetting what you have just eaten. These hormonal changes have been demonstrated to persist for months after weight loss but may persist for years.

    These factors make weight loss very difficult. It is unpleasant and demanding. This is why yoyo dieting is so common and why the emphasis needs to be more on weight maintenance and less on weight loss. Once you can do the maintenance with equanimity, try to add a little slow weight loss. The Catch 22 is that before attempting something as demanding as weight loss, you would want to be fit and healthy – and probably young and mentally robust as well.

    My general strategy is to eat well, eat small, eat slow and try to burn it off regularly, all without killing yourself. It’s a balancing act. Try to maximise the enjoyment your get from every joule. Spend as little time as possible in the junk-food energy overload zone when the body will lay down fat for future use. On the use side, try to get your resting metabolic levels up, exercise regularly, and, spend time in the high energy use zone. High energy use periods, especially the interval training mentioned above, have been found to actually mobilise fat where moderate activities like walking won’t. If you can make intense exercise enjoyable enough – sport! – you will actually want to spend time in the fat burn zone. This seems infinitely preferable to me to signing up to a life-depleting calorie restriction program. The object should not be to simply loose weight but to maintain a good weight without feeling depleted. It is quite possible to take up a calorie restricted diet, feel letargic and morose and remain overweight.

  16. 1) Calories in/out, wrong. Gary Taubes achingly documented histories of where the science went wrong make for interesting reading.
    2) The idea that ketosis is bad for endurance athletes performance was disproved in the 70’s Peter Attia, MD site, The Eating Academy has reams of stuff on this.
    Come on guys, your nutrition science is quaint.

  17. @Alex
    Totally wrong on ketosis and endurance athletics, the oft cited studies on this were disproved by more thorough studies in the late 70’s (see Stephen Phinney’s work). And this should not be a surprise, all human cultures prior to agricultural got the bulk of their calories from fats (and they were no vegetarian cultures). If indeed, carb diets were optimal in some way (they actually do seem to have advantages for high powered, explosive types of performance) given the epoch long evolutionary selection pressures, it would be a major scientific conundrum.

  18. @Jim Birch

    A lot of what you say about willpower and yo-yo dieting is right. Last time I used the one meal a day diet I lasted about 8 months and lost about 16 kg. It was very tough mentally in the end. After getting injured and losing the exercise and diet habit I put the 16 kg and a couple more back on over about 18 to 24 mths.

    What makes me think it will be different this time? Blind optimism and stupidity I guess plus a little more experience about how I approach it. Even if I fail again, I feel that yo-yoing is better then going ever and ever upwards which people seem to do after a certain “gross failure” point in lifestyle, diet and exercise is reached and passed. Cruelly, there seems no almost hope for people after that point without major outside assistance.

  19. @Sancho I think there maybe a misconception, it can’t be standing up from sitting on the floor it must be standing up from a seat using the floor (ie use your feet not the arms of the chair).

    The study used quite old people and it would be unreasonable to expect any of them to rise from the floor without using their hand(s).

  20. @John Quiggin

    Nothing beats the empirical approach. That’s my motto. I set the problem “get up from a seated position on the floor without using hands, knees or elbows” for my wife and 18 y.o. twins and watched their attempts carefully.

    My daughter was the one who crossed her legs just above the ankles. As she is light also but not as athletic as my son I figured that it was an intuitive, instinctive or personally learned method from a younger age. As soon as I saw it, I thought there might be a lever advantage in it so I tested it on myself. I think there is all of a levering advantage, the advantage of bringing more muscles into play and a compensating geometry for lack of range and mobility in joints.

  21. @rog

    I think in the original post/link it was made clear that at least one hand could be used from the floor. Some of us just wanted to take it further and do it without hands or knees.

  22. @Ikonoclast As a kid everything I did was physical and all work was by hand. We even used to shovel sand soil etc onto the truck. I marvel at old industrial chimneys and buildings because I know how much effort went into making the bricks, hauling them up and then laying them. Not an engine in sight. Same with old split post fences and slab huts, made with elbow grease.

  23. I’d like to state that using calories instead of joules, or worse calories instead of kilojoules, or even calories instead of kilocalouries makes Jesus cry. Mind you, this particular Jesus has a physics degree and is a bit of a pedant.

  24. @pjm

    I didn’t say any cultures were vegetarian actually. There is undoubtedly a strong correlation btw slimness and health with low proportions of animal products as seen in Asian diets (compared to Western ones) and within Chinese populations (see the China Study). And why should we take dietary habits (there wasn’t one pre-agricultural diet) as the perfect template for eating? We also evolved to bash neighbours to death because they weren’t in our tribe. Yes, we’ve evolved to survive on a massive range of dietary intakes. Move on.

    Gary Taubes and his followers had better get on to every Tour de France rider and marathon runner with the high protein/paleo/fasting fad ASAP. They’re ALL doing it wrong! Right now, what do the pro teams in the Tour Down Under in Adelaide munch on all day? Bananas and coke. Not steak. Five hours in the saddle, burning 5000-8000 calories a day eating pasta, vegies, lean meat, pasta, rice, coke, energy bars, and more pasta. Oh and Taubes has also said that exercise won’t slim you down, it’ll just increase your appetite and if you’re slim you’re just born that way. He’s a scam artist.

    Carb up and I’ll see you out on the road running and cycling. Not in the gym looking like a puffy unfit Michelin man with high cholesterol.

  25. my first job was in a bank. standing up all days does amazing things for your fitness.

    after 4 weeks annual leave, I was exhausted by the end of my first day back.

  26. I think physics Jesus was traumatized by a calorie when he was little. I have to admit I don’t like them myself. Anything that isn’t SI makes me feel like I should have 12 fingers.

  27. @rog

    Hang on rog, how old are you? Nearly 300 or maybe 1000 or more? Steam engine invented in 1712, the Newcomen. First practical application about the same year for pumping water. Don’t give me this no engines stuff. πŸ™‚ Even you said you shovelled sand onto a truck. An internal combustion engine truck I dare say.

    Cranes existed in the middle ages, the treadwheel crane (a machine tho powered by human or animal muscle) not to mention good old block and tackle. Also, windlasses, windmills, water wheels etc etc. All machines, and many in fact used renewable energy.

  28. Oh dear… Both are units of energy, and as such interchangeable with the appropriate constant (if you can work out exactly which Calorie you’re using), so forget the units of heat and units of work – same thing. Apart from that, as Ronald pointed out, the calorie is simply an evil unit.

    As I remember 1Cal ? 4.2J, which combined with it’s definition (the amount of energy needed to raise the temperature of 1g of water by 1Β°C (ignoring the details)) leads to its only advantage: idly working out in your head how much water you could heat from room temperature to 100Β°C with a Mars Bar (?250kCal). About 3L. And a circa factor 4 in there isn’t too much extra work to do it in Joules…

    So if you’re not into mental combustion of food, we’re left with a pointless unit with a dubious definition πŸ™‚

  29. @Jim Rose
    Arranging a standing desk is a priority for me this year. Elevating desks are expensive, but there’s a range of hydraulic arms that can mount monitors and workspaces, which are useful for transferring between desks.

  30. @John Quiggin Why settle for less?

    Like most economic equations, there is always a gap between the pen and reality

    Energy used – energy consumed = fat burnt.

    Or is it:

    Energy used – energy consumed = change in muscle + fat burnt.

    Then someone may like to point out that energy used = energy consumed, and that you only get more muscle and fat if you import surplus food – an externality – and run into deficit when the supermarket is closed.

  31. A calorie is a unit of heat: the amount required to raise the temperature of a kilogram (or litre) of water by 1 degree Kelvin (or Celsius)??????????????

  32. IIRC, a degree is the same unit in celsius or kelvin. They just index from different temparatures: celsius from the boiling point of water and kelvin from true zero.

  33. This a.m. I went to Woolies and Subway. A sign in the Woolies delicatessen said our energy intake should be 8,700 kJ and Subway said 8,750 kJ. I presume that’s for a semi-sedentary adult.

  34. @aidee

    It can be a bit hit and miss with it’s calorie counting, but generally it keeps me thinking more about food, which is my primary burden. I can run a half marathon no problem, but it’s the food that the toughest part of staying fit!

  35. I’ve now lost 4 kg in 23 days. The scary thing is I can see no difference although my belt has easily gone in one notch. My BMI is now 26.5 – still way too high – and my waist is 103 cm when a healthy waist for me would be about 93 cm down to 91 cm.

    I am suffering some continuous leg weariness from outdoor work and long walks each day (50 minutes plus) combined with my obvious calorie deficiency. (Some of this leg weariness I put down to being 58.5 years.)

    Another scary thing is that dressed casually I don’t really look fat compared to a lot of other people my age. I think the general large expansion of waistlines has given many of us a false idea of what constitutes being overweight. I noticed this in the past when I dropped 10 to 15 kg. People I had used to think were quite trim started to look chubby and overweight to me. It’s an interesting distortion of perception that occurs. Whatever our weight we tend to regard our own appearance as the norm, at least for our own age group.

    I am thinking my goal should be 70 kg. That’s the only way I could break even 60 minutes for a 10 k run. Not sure of my chances in reaching and maintaining it though. 75 kg would be acceptable if I can increase muscle mass. A bit of mass is handy for yard work, cutting and lifting logs, leaning on crowbars etc.

  36. @Ikonoclast
    70-75 is a good goal – IIRC you are similar height 1.75m to me. As you say, 4kg is perceptible in tightness of clothes, but not otherwise

  37. It seems I am about 178.5 cm. 70 kg would give me a BI of about 22 which is healthy but not low by any means. My wife starts to complain that I look “gaunt” below 76 kg. Without the subcutaneous fat in the face the wrinkles show more, ’tis all.

    If I want to actually run again, 70 kg is the first benchmark. 65 kg might be the benchmark if I get fanatical. I don’t call jogging running, I call it plodding. My theory is that there is a genuine difference between running and plodding. There is a distinct (qualitative) difference in the feeling. In plodding one runs “on” the ground. In running one runs “over” the ground.

    In quantitative terms, I think proper running involves (apart from just going faster than mere jogging);

    (a) significant glide time mid-stride when both feet are off the ground.
    (b) significant storage of energy in elastic tissues (mainly tendons) such that push-off is only partly muscle powered as it is also signicantly powered by stored energy in the elastic tendons.
    (c) toe landing on each stride rather than heel-toe landing or flat foot landing.

    I think (b) and (c) are difficult for older runners. Elasticity is lower the older you get. I was never a natural toe-lander even as a young runner. I got away with it at that time as I was extremely light. However, studies show (I believe) that toe-landers are several times less likely to get running injuries.

    I used to sail a bit once and there is an analogy I make between sailing and running. A small boat with a correctly shaped hull can proceed slowly by displacement movement or more rapidly by planing. A large plodder is working like a displacement boat in a sense. A large proportion of his energy goes straight down in the plod to arrest and prevent his whole bulk falling to earth. A lesser proportion of his energy is used to propel him forward. He would be better off walking briskly for his exercise at least until he gets to true running weight.

    A proper running gait mean you are “up on the plane” with a greater proportion of your energy now pushing you forward. Tendon elasticity (if you are still blessed with it) is used to store part of the the energy of falling and then it is employed it to push you back up and forward for the next stride. This bounciness and energy saving constitutes the feeling of gliding over the ground rather than just plodding on it. Such is true running.

  38. Footnote:

    More accurately walking is analogously equal to displacement movement and running is analogously equal to planing. Jog-plodding is the transition phase and a jog-plodder is stuck in the transition phase. A boat that does not have quite enough energy to rise to a proper plane will go a little faster but drag a larger and larger displacement wave. With a feel for sailing you can feel this displacement wave holding you back and preventing the boat rising on to a true plane.

    A jog-plodder has an analogous power-drag ratio or power-weight ratio problem and he/she can’t rise to a true running position and gait and is thus stuck in what it is really a transition gait.

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