One of the touchiest subjects in any type of fitness is weight. While many of us exercise to maintain or even lose weight, the fitness community also strives to support positive body image, and to de-emphasize the need to lose weight to become someone’s idea of the “right” size.
But if optimal performance, rather than casual exercise, is your goal, then at some point you will need to answer whether being lighter will translate into being faster. It can be a difficult question to answer effectively – and healthily.
Generally speaking, yes, weight loss will make you run faster. You’ll have less weight that you have to move, which means you’ll either work less hard to run the same speed, or work at the same effort and be faster.
But somewhere in there, an obsession with weight loss can be both mentally and physically unhealthy, and comparing your body to elite runners at the front of the pack is likely unrealistic. In this article, we’ll discuss how weight loss (or the other side, weight gain) affects your running pace.
We’ve set it up as a question-and-answer guide so that you’ll be able to find answers quickly to different questions you might have about weight loss and running.
Does weight affect running speed?
Yes, it does, whether you gain or lose weight. Imagine two runners with identical levels of fitness and ability. Let’s suppose that one of those runners is 10 pounds heavier than they should be. Of course, the lighter runner will run faster without the 10 extra pounds of mass.
Think about it this way. Weighing 10 pounds more means you have 10 more pounds of body to move. Whether that mass comes from fat or muscle, it takes more energy to move more mass. You will still be able to run the same speed, but it will be somewhat harder.
Remember that when you’re running, your legs must support your body weight and propel your body forward, which takes a substantial amount of energy. As a result, the more you weigh, the more your body will have to work when you run.
This all comes down to VO2 max, the calculation of how much oxygen your body can absorb when as its aerobic limit. The number is calculated by dividing the volume of oxygen your body can absorb in a minute by your mass in kilograms. In general, there are two ways to improve VO2 max: increase your oxygen absorption, or decrease your mass (i.e., lose weight). A good training plan will actually do both.
But this makes sense because you have less mass to carry around as you pound the pavement, but your heart and lungs are still at their same proficiency of pumping blood to the muscles.
Everyone isn’t the same.
Remember that everyone is different. Each individual has unique body constitutions and metabolic rates. No matter how much you run, some individuals will never be as lean as others, and your maximum VO2 max number is, to a certain extent, limited by genetics.
According to a recent study by researchers at the University of Zaragoza, runners who have a natural ability to achieve a very low body fat percentage have a performance advantage over others.
Additionally, the food you consume can also impact your body weight. If you’ve had a salty meal, for example, you might weigh a pound or two more than your normal weight on account of retaining more fluid.
How much faster will someone run if they lose weight?
Experts note that you’ll be able to run about two seconds faster per mile for every pound that you lose. This means that if you lose 15 pounds, you’d run about 30 seconds per mile faster, cutting a 5k time by a minute and a half just from your weight loss or a marathon time by 13 minutes.
Again, it is important to keep in mind that there are healthy limits here. Too much weight loss (see below) can have a negative impact on strength, which will slow you down.
You can use this weight vs pace calculator to figure out how much faster you’ll likely run if you lose weight healthily. It allows you to input your weight, distance, and pace/speed. Once you input that information, you’ll be able to see how much faster (or conversely, how much slower) you’ll run if you lose (or gain) a few pounds.
Is it possible to lose too much weight?
Yes, it is. As can be the case in other sports, eating disorders can be prevalent among the running community. If runners struggle with eating disorders, they can actually start to run slower when they lose weight, because they are restricting calories.
Additionally, if you’re already slim, even if you’re not struggling with an eating disorder, dropping more pounds could lead to muscle loss, which will impact your ability to run. Remember that it is possible to become too thin.
Muscles contribute to performance in distance running, so muscle loss means performance loss. And your body does, indeed, need some amount of body fat – and women need more than men to maintain good health. Thus, it is always going to be helpful to achieve an optimal body fat level while not losing muscle.
Your Ideal Racing Weight
Your ideal racing weight is the weight that with the lowest body fat percentage that you can healthily achieve. This tends to be 3 – 9% for males under 40, or 5- 12% for males over 40, and 12 – 17% for females under 40 or 15 – 20% for females over 40.
But these are just estimates. The only way to figure out your lowest healthy body fat percentage is to get there yourself. You need to make sure, though, that you’re not overtraining or under-nourishing your body.
Your running performance should improve as your body fat percentage decreases, but if it starts to get worse, this means that you’ve gotten too lean and need to make sure that you are getting the nutrients and rest that you need.
Make the right decisions for your body. This may mean that if you’re a serious runner, your ideal racing weight is slightly higher than you anticipate. Being slimmer doesn’t always mean that you’ll run faster if your body isn’t getting what it needs.
Focus on having a consistent running program and eating healthy, and let your body do the rest. Chances are that you’ll find yourself PRing and happier than if you just think, “leaner and skinnier is always better.”
At the end of the day, remember that weight loss will make you run faster, but you need to do it in a healthy way. And remember that some people will naturally be able to become leaner than others, so there will be an endpoint to your weight loss.
Once you reach your ideal body fat percentage, you should aim to stay around that number if you want to be the most efficient runner you can be. If you’re consistent with your running program, your body will lose the weight that it needs, and you’ll be at your ideal weight.