How Much Faster Will I Run If I Lose Weight?

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For runners, weight fluctuation can make all the difference between a good time and a personal best. A few pounds lost can contribute significantly to performance.

And of course, a few pounds gained will slow you down, too.

What is the relationship between weight and running speed? And how much faster can you run if you lose weight?

As a rough estimate, decreasing body mass by one pound decreases the time to run one mile by 1.4 to 3.3 seconds. Fat must be lost and not muscle. Losing muscle results in power reduction, which slows you down instead. The distribution of body weight and the distance run also affect the weight speed ratio.   

Investigating how much faster you can run if you lose weight is a complex question that involves physics and biomechanics.

There are many factors to consider. Each person’s biomechanics and metabolism also play a role.

Let’s take a closer look!

What Physics Tells Us About Weight And Speed

How much faster will I run if I lose weight?

Athletes probably didn’t think their school physics class could be useful in running – but it certainly was!

Physics gives us some basic information about the relationship between mass, acceleration, and force. 

The formula for the relationship between these three elements is as follows: 

                  Force (Newtons) = mass (kg) x Acceleration (m/s2)

This formula tells us that the natural physical laws governing movement show a direct relationship between mass, acceleration, and force.

In other words, the greater the mass, the more force will be needed to maintain the same level of acceleration. If more force cannot be utilized, the acceleration will decrease as mass increases.

In basic terms: the more weight you carry, the harder you’ll have to work to maintain the same speed.

What Does Research Say About Weight And Speed?

For most of us, it makes sense that the heavier you are, the harder it will be to run fast.

We are usually thinking in terms of tens of pounds when we make this assumption. But what about if it is only a few pounds or even only one pound.

How will this affect your running speed?

A study done in 1978 showed that increasing the body weight by 5% reduced the average run performance by 89 meters. Converting this to pounds equates to one pound increased body mass, increasing the time taken to run one mile by 1.4 seconds

That is quite an old study, and it is interesting to see what newer studies say about the relationship between speed and weight. 

Dr. Todd Miller, an exercise professor at Penn State, reviewed the performance of numerous athletes and their weight changes during the preseason, season, and post-season.

He studied multiple different sports in this review.

He devised a study based on what he saw in the statistics.

Dr. Miller found the following results: A 170-pound athlete that gains 2% fat or 3.4 pounds would have an increase of 0.26 seconds in the 40-yard dash.

Although 0.26 seconds may not seem like much time, it is significant in the 40-yard dash. 

If you work out the numbers, Dr. Miller’s research shows that over a one-mile run, the time would increase by 3.3 seconds. This is a meaningful difference for runners looking to shave a few seconds off their personal bests.

At the elite level, it’s the difference between a gold medal and agonising failure.

It must be remembered that these are averages, and not every person will see the same gains from losing one pound of weight. Factors such as height, age, sex, and running style may influence running speed more than weight.  

Is All Weight The Same?

how weight affects speed

In Dr. Miller’s work, he was specifically looking at fat gain. This factor is important as muscle mass is much heavier relative to fat. Gaining muscle mass adds power or force, which is completely different from fat which adds only excess weight.

Athletes can become so obsessed with weight that they neglect to consider whether their weight gain is due to added fat or muscle. 

Many runners with a balanced approach to weight that have been running for a long time note they have an optimal weight. Dropping below this may actually reduce their running times.

If you are a beginner who has only just started running, it’s likely that you will see much greater gains from trimming the belly fat than a seasoned runner who has been in good shape for years.

These experienced runners have inadvertently stumbled on the fact that the body tissue comprising the weight gain or loss is critical. If you lose weight and lose muscle mass, you are effectively reducing your power or force. 

Going back to the basic physics equation, reducing force will lessen the mass that can be moved and the speed with which that can be done. 

Dr. Miller stresses that body composition is essential and must be considered when designing optimal performance programs that include weight loss and gain.

His recommendations are supported by a 2014 study that found that BMI was a better indicator of sporting performance than mass alone.  

How The Body Region Of Mass Gain Affects Speed

Looking at total weight or BMI and the effect on speed is not the whole story. An important factor is whether the region where extra weight is carried in the body makes a difference in speed. 

In other words, if you carry extra fat around your belly, is it the same as having extra weight on your thighs or calves. Will the weight distribution have varying effects on speed?

A study by Myers and Steudel found that carrying extra weight on the feet or legs slows runners down significantly more than if the extra weight is carried around the abdomen. 

They found that adding 100 grams of weight to the athletes’ shoes slowed their performance by 1%.

In a half marathon, that would change a time of 2.00 hours to 1:58:45. This could make a difference in the athlete’s placement in a competition – and is one of many factors why runners obsess over whether they have the right shoes!

The logical conclusion would be that running shoes should be as light as possible. Effectively running barefoot should produce faster running times. But is this true, and should all runners be hardening their feet to run barefoot and increase their running times? 

Running barefoot to lose weight
Running barefoot is a canny way to drop weight instantly!

Fortunately, and to the relief of most athletes, laboratory results do not always hold true in real life. This anomaly is mostly because scientific studies cannot take all the variables into account. 

Colorado study showed that shoes with cushioning reduced the metabolic power required for running.

A reasonable amount of cushioning, which would increase the weight of the shoe, will increase the runner’s speed as the power required is less.

A runner must achieve the optimal balance between the weight of the shoe and the benefit of cushioning. This would probably be different for each athlete.  

The fact remains that reducing weight on your shoes can have a much greater effect on your running time than losing the same amount of body weight

Which Running Distance Is Best for My Physique?  

Runners may choose to run sprints, middle distance, and long-distance events. An interesting question is whether weight and BMI influence runners the same when they compete in events of different distances.

A study done in 2014 showed some interesting and surprising results. Sprinters in the 100m, 200m, and 400m events are usually taller and heavier than middle and long-distance runners. 

Elite runners of the 400m events were the heaviest and tallest. For a 400m event, sustained power and stride length make a difference which explains the finding. 

As the distance increased, the average mass of the runners decreased. Runners of marathons and ultra-marathons were the shortest with the lowest BMI. 

The most successful long-and-middle distance runners had the lightest mass compared to their counterparts. In sprinting events, the most successful athletes were heavier than their competitors. 

This study shows that the optimal individual running distance may be predetermined by your height and physique. 

Can You Be Too Thin To Run Fast?

There is a temptation, especially amongst competitive runners, to lose as much weight as possible.

It is critical to realize that weight loss does not guarantee time gains that result in success. As we have seen, there is more to performance-enhancing weight management than simply losing weight.

Inadequate pre and post-run fuelling can result in:

  1. weight loss
  2. an inability for muscles to repair and recover
  3. generalized long-lasting fatigue
  4. increased risk of injuries
  5. a weakened immune system.

These are all symptoms of overtraining syndrome when the body is pushed beyond its capabilities and begins failing. In severe cases, overtraining syndrome has even resulted in death.   

A runner that is underweight stands a much higher risk of developing overtraining syndrome. It is vital to work with coaches, nutritionists, and your doctor if you wish to lose weight to improve your performance. 

Changing the distance you run may be better if your physique is not suited to the current distances you run. 

Our Verdict on Losing Weight to Run Faster

Losing weight to have a lower BMI can result in faster run times for middle and long distances.

Sprinting has different physical requirements. While it is true that carrying excess fat will slow down performance times, it is important that weight management is related to appropriate fat loss.

The basic message is to lose fat without losing muscle.  

Changing running style or technique may be a better way to improve running times if you have little spare fat to lose.

It is wise to consult a sports coach and nutritionist before embarking on drastic weight loss programs. 

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