Can Losing Weight Make You Run Faster?

Drawing of one runner that is faster than three others

The authors of a recent study looked at how, among other things, shaving 100g off the weight of the runner’s shoes could contribute to a sub-2. That idea got a lot of runners thinking: if 100 grams is important enough that Nike developed new shoes for the job, how much could losing a few pounds off my actual body weight help me break my own speed records?


When considering this, the first question to ask is: can you lose weight without sacrificing performance? The balance between weight loss and maintaining performance comes with a mixed message. Yes, you can lose weight while training for a race. No, it’s not an easy thing to do. But we are talking about people who run 42.2km (26.2 miles) for fun, so let’s not sell them short.

The Science Behind Weight and Running Times

A new study on body mass reduction and running performance took a fresh look at this idea. During the past 40 years the majority of studies have been centered mainly on the effect of adding external load to the energy cost of walking and running. But in this study, the researchers took eleven trained club level runners (eight male, three female) and had them participate in a series of four maximal trials four to six days apart.

During the first trial, the subjects completed an exhaustive incremental peak VO2 test on the treadmill. On the second visit they completed a three kilometer race time trial on the treadmill running with their normal body mass (BM).

What’s really interesting about this test is that instead of adding weight to the runners (like the previous test), they subtracted five or ten percent of the runners’ body mass using a system of pulleys that lifted the runners up slightly, making them weigh less, in a sense.

In the series of three kilometre race trials, they found that the runners “being lighter” by five or ten percent resulted in improvements of 3.1 and 5.2 percent in their run time. If we do the math, that is a race time improvement of 0.64 percent per pound lost. For the particular subjects of the study, that equalled an improvement of 2.4 seconds per mile per pound. Which we can project would become even more significant over the marathon distance of 26.2 miles. Even a single pound lost could result in slightly more than a minute shaved off their marathon race time.


The study concluded that “the reduction of five and ten percent of inactive body mass may improve significantly 3km performance time … and are supportive of the notion that one way to maximize further running performance is to reduce inactive body mass.” Which means the lighter they made the runner, the faster they could run.

I want to draw attention to the language they used: inactive body mass. In other words, body fat. Not muscle. We’ll talk about that a little more later but for now, I just want you to keep this in mind.

Back in 1978, one study did the opposite of the study we just discussed. They actually added an extra 5, 10, or 15 percent to the body weight of their subjects using a crazy looking harness that was attached around their waist and across their shoulders.

In that study, the runners performed a 12-minute run with no extra weight. Then they ran the same 12 minutes with added weight and found that the distance the runners were able to cover was reduced by an average of 89 meters for each additional five percent of added weight. Again, if we do some math, that equals an extra 1.4 seconds per mile per pound.

This study concluded that “changes in excess body weight can influence VO2 max expressed relative to body weight and distance run performance independent of any change in cardiovascular capacity.” Which means, they ran slower when they weighed more even though their fitness level stayed the same.

Why Does Weight Affect Running Speed?

A paper on body mass and the metabolic cost of running suggest that the running motion can be thought of as a series of movements that fight directly against gravity. Each stride is essentially an upward and forward push against the pull of the earth and that is what uses most of your energy when you run.


The authors conclude that, “Our results show that generating force to support body weight is the primary determinant of the metabolic cost of running.” Which means that we expend the majority of our energy by simply supporting the weight of our own body.

But not all body weight is created the same and if you’re going to carry extra weight, apparently your belly or hips is the best location for that weight (mechanically speaking, not metabolically).

In a 1985 study on the effect of limb mass on running showed that having two four-pound weights attached to your waist will increase energy cost by about four percent, while having the same eight pounds of weight strapped to your feet or ankles will increase energy cost by 24 percent. That is an incredible difference but it is not hard to imagine how that might feel, like trying to run in a shallow swimming pool.

The study’s authors concluded, “We found that the cost of adding a given mass to the limbs is significantly greater than adding it to the centre of mass and that this effect becomes more pronounced as the limb loads are moved distally.” Meaning, it is harder to move heavy limbs than it is to move a heavy torso.

Even if you aren’t into the physics of all this, you might find it interesting that losing weight from your body is only about thirty percent as effective as losing weight from your shoes. Apparently extra shoe weight requires much more energy to heave forward each and every time you take a stride. In comparison, your muffin-top basically gets to go along for the ride.

Losing weight from your body is only about thirty percent as effective as losing weight from your shoes.

Inactive Body Mass

Ok, now the important part. So far all these studies have made an unrealistic assumption that the weight you are lugging around is completely inactive body mass. As I hinted at earlier, if you go and lose a bunch of muscle, you will likely end up slowing your run time down regardless of how much the bathroom scale is displaying. Whereas if you gain the right type of muscle weight in the correct locations, you will instead have the potential to speed your run up. Plus, as you may have learned in a previous Get-Fit Guy episode about body fat, even fat can come in handy.


How to Find Your Perfect “Running” Weight

Ideally, nailing our perfect race weight would be a natural result of training and eating well, rather than an arbitrary number you choose and obsess over. I would say that before you dive into any weight loss strategy, you should ask yourself if you are currently at a healthy weight for your height, muscle mass, and bone structure. Then look at what would happen if you were to lose X amount of weight. Would this leave you in an unhealthy BMI or more importantly at too low a Body Fat Percentage?

If so, you may want to reconsider that goal or at very least be extremely strategic about when and for how long you maintain that particular weight. Dipping into that range to see how it feels can be an interesting experiment but is one you probably shouldn’t attempt right before the Olympic trials.

Way too often runners read some of the studies I mentioned earlier and assume that weighing less will lead them to running faster but this is not always the case. Our human meat-sacks crave homeostasis and each one of us has a healthy weight range where we will perform at our absolute best. Sadly, this weight may not match what you picture for yourself and certainly won’t match what we see on the covers of magazines. We’ve seen enough Photoshop exposés at this point to know that even the athletes in the photo didn’t look like that in the studio.

Our human meat-sacks crave homeostasis and each one of us has a healthy weight range where we will perform at our absolute best.

Most sports doctors with say that our healthy weight range is usually your weight, plus or minus three pounds at a time when you are nailing your diet, working out consistently, and ideally not paying any attention to the bathroom scale. That is when homeostasis kicks in naturally.

My friend, The Nutrition Diva, has a great article called Diet Strategy to Lose Fat and Gain Muscle, and in it she says, “If you’re within 5 or so pounds of your goal weight, you might want to focus more on improving your body composition. To do this, you’d challenge your muscles while adjusting your food intake to keep your weight more or less steady…. incorporating high quality protein into every meal can help build lean muscle tissue and may also help with weight maintenance.”

In a past Get-Fit Guy episode we talked about how it seems counterintuitive that you can have the body in a “loss” state and a “gain” state at the same time. But it turns out that if you do the right things, this is actually possible.


The Strategies

  • Combining calorie restriction with weight training
  • Giving yourself specific days of the week to “re-feed” with higher calorie intake (also known as “calorie cycling”)
  • Avoiding excessive aerobic cardio, which breaks down the muscle you’re trying to build which can be tricky when you are at the peak of your marathon training.

Which is why, I suggest doing this in three phases, instead of all at once a few weeks before the big race.

The Steps

  • Step 1: Have a Fat Loss Phase (ideally in the off-season) where you get yourself to your healthy weight.
  • Step 2: Start a Muscle Gain Phase (which should also incorporate pre-hab and some base training).
  • Step 3: Hardcore run training (where your weight should achieve its own homeostasis through consistent training and a good diet).

Be Careful

While yes, the typical citizen these days may be out of shape and heavier than any doctor would advise, highly-motivated runners are their own physical (and psychological) breed. A breed that all too often falls for the “if one is good then ten must be better” mentality.


Many runners I know have fallen into the trap of aiming to lose too much weight and ending up injured or sick or they lost the weight too late in the season and thus had a disappointing A-Race. Overdoing it or not getting the timing right can lead to various injuries, illnesses, fertility problems, or at least the opposite of what was intended—racing slower instead of faster. Let’s face it, you can nail your “race weight” and still come in last, and there’s no medal for that.

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