Posted by on Sep 30, 2015 | No Comments

37146_487681796048_218142676048_7179466_7224958_nPurpose & limits in improving running performances through weight reduction.

Optimizing body weight (body fat, bulky upper body muscles) is a common strategy amongst endurance athletes to improve running and cycling performances. However, excessive body weight reduction can impair health and performance.

Your body requires nutritions for growth, maintenance (immunystem) and repair. Therefore,not every weight reduction makes sense and delivers positive performances.

Excessive weight loss could mean that you are not only lose body fat but also impair muscle tissues (repair & growth) and energy stores which are two significant areas that are obviously important to performing well and remain healthy.

  • Key word: “optimizing training performances“. During a workout our focus must be on optimizing training results with a constant energy supply coming mostly from glycogen stores (liver,muscles), blood glucose and fat burning. I always say to my athletes “if you want quality results you need to put quality into the engine”! In other words, if you want to train consistently strong and/or enjoy a life filled with ongoing action & activities (performing as a parent, as a friend & family member, at work etc) I advise you to eat well and eat at the right time!


  • Key word: “Speeding up recovery“. The time after a workout must be used to replenish glycogen stores, and to drink lots of water.  Eat a mixture of high quality carbs & proteins which are needed for muscle repair. I noticed when I ate enough proteins I wasn’t hungry all the time.  Micronutrients found in natural food, such as vitamins and minerals, are also very important. Pay attention to what you eat after a training workout.


  • Key word: “timing“. If your are thinking to lose some extra body fat it is important to know when to do it. There is a fine line in making sure you are eating enough to train & recover well and to reduce body weight. Therefore, I advise against a too fast body weight reduction. Start well ahead of your A-race (i.e 6 months). Reduce your body weight slowly. Certainly, no more then 1/2 kg per week and change elements in your diet one step at a time. I think that this is a good & healthy approach. You will probably find a “sweet spot” or optimum body weight range where your health and training performances aren’t compromised. The consumption of the right amount of calories (not overeating!) metabolized from the right food source matters greatly in order to feel strong in your next training workout, to speed up restoration and recovery from workouts and to pull the handbrakes on weight gain.

Food sources:

  •  High in complex carbs coming from natural foods such fruits,vegetables, greens, legumes and beans.
  •  Quality proteins for example: Salmon, chicken, dairy (yogurt), lean meat, legumes, beans, tofu.
  •  Healthy fats (I have fats in my diet and aim at 20-25% of total calorie intake) like avocado oil, olive oil, nuts, and even butter.

Running economy

Doesn’t it feel harder to move when we carry extra weight? I’m convinced that a lot of athletes can relate to this very well. Indeed, as we carry more weight our body requires more oxygen or energy at a given speed or watts.

For example:

A 3:45 hour marathon equals 187 meters per minute {42,200m /225min}. American College of Sports Medicine developed a formular and based on that the horizontal energy cost of running is 0.2 milliliter of oxygen per kilogram of body weight per meter per minute (ml
O2/kg/m/min). Now, let’s say your bodyweight is 85kg ( = 187 pounds, 1kg = 2.2lbs) and your V02max is 4.2l/min (4,200ml/min) then V02max is 49.4ml O2/kg/min ( 4200ml O2/85kg). After a 5k weight reduction (80kg) this would mean your V02max increased to 52.5ml O2/kg/min (4200ml O2/80kg) and assuming that your V02max of 4200ml/min is still the same and didn’t change. That’s a 6.2% increase.

The oxygen requirements to run a 3:45hr marathon would be 37.4ml O2 / kg / minute  (0.2ml O2 x 187 pounds). For our  85kg runner that totals about 3,179ml O2 /min which is running at  75% of V02max (3,179 x 100/4,200ml). If this 85kg runner lost 5k (now 80kg) his/her oxygen cost would drop to 2,992ml O2/min (37.4ml O2/kg x 80kg). Her/his running economy would improve and a 3:45h Marathon would require less oxgyen (3,170-2,992ml O2= 187ml O2) to complete.

Since the cost of running one meter (0.2ml O2/kg/meter/min) for our 80 kg runner is 16ml/O2 (0.2ml x 80kg), running speed would increase approx. 11.68m/min (187 ml/min /16ml O2) to a speed of 198.7 meters per minute. Hence, our runner would improve his/her marathon time by 12:37mins (or 3:32hrs) or about 5.6%.

  • 1% bodyweight reduction yields 0.66% to 1.0% increase in running speed.

*Disclaimer* – a bodyweight reduction isn’t always desired and in particular if you are a long-distance open water swimmer who is passioned about swimming in cold water. For example, if you are planning to swim across the English Channel (22.5miles) I would advice to actually add an extra layer of body fat. For more information on open water swimming please contact my friend Tim Denyer (an experienced open water swim coach from London, England,UK) and visit his website


“transition to the next level”



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