Episode #362: Weighted Vests

0:00Dr. Jordan Feigenbaum:Welcome back to the Barbell Medicine Podcast. I'm Dr. Jordan Feigenbaum. I hope you had a great weekend. In this podcast, I wanted to talk about one of the most recent trends in the fitness scene, weighted vests. Influencers on social media have been promoting the use of weighted vests while walking and other forms of exercise in order to burn more calories, build muscle, and maintain strong bones. Heck, there's even a new Equinox fitness program centered around using their$375 weighted vest. With all of this interest in weighted vests, I thought it might be useful to do a deep dive into the topic to see if the hype is warranted.

0:32Dr. Jordan Feigenbaum:In this episode, I'll review the factors that determine how many calories we use during exercise, along with what the scientific evidence says about using weight vests for weight management, muscle strength, muscle growth, bone density, and more. All that and more on this episode of the Barbell Medicine Podcast. But before we get into that, I wanted to mention that we have tickets available for our two-day health and performance seminar, where myself, Dr. Baraki, Leah Lutz, and Tom Campitelli will provide in-depth lifting instruction and education on a variety of topics ranging from cardiovascular health and sarcopenia to nutrition and programming.

1:04Dr. Jordan Feigenbaum:Now, the seminar is gonna be in San Antonio, Texas on September 20th and 21st. We'll be training with the attendees on Friday evening before the seminar and having dinner with everyone on Saturday. So come hang out with the Barbell Medicine crew. We'd love to see you there. Click the link in the description below to get your ticket today. Okay, I think a good place to start here is with what is probably the main reason people are wearing weighted vests to burn more calories when they're exercising in order to aid in weight management. Now, these are actually two separate outcomes that are not really the same.

1:35Dr. Jordan Feigenbaum:In other words, it is totally possible that using a weighted vest during exercise does indeed increase the amount of energy being used, which we measure in calories, but also at the same time not help with weight management. Now to understand this a bit better, let's talk about energy expenditure during exercise in general, and then focus on how wearing a weighted vest affects it. First off, let's start with total daily energy expenditure. Now this is the total amount of energy used per day, which again is measured in calories. The three components of total daily energy expenditure, which is abbreviated TDEE, are resting energy expenditure, diet-induced energy expenditure, and activity-induced energy expenditure.

2:15Now, resting energy expenditure is the amount of energy used to sustain basic life processes such as breathing, heart function, and other essential tissue functions while an individual is awake, and it accounts for about 60 % of total daily energy expenditure. This is just keeping the lights on in the body. Now, diet-induced energy expenditure, which is also known as the thermic effect of food, describes the energy required to digest, absorb, transport, and store energy from food, and it represents about 10 to 15 % of total daily energy expenditure. Lastly, activity-induced energy expenditure refers to the calories used during exercise and non-exercise activity.

2:53Exercise activity would be things that are purposeful, repetitive, and goal-directed towards improving health and fitness, whereas non-exercise activity includes occupational activity, chores, and involuntary activities such as fidgeting, twitches, frequent standing, and other subconscious movements. Sometimes those are called spontaneous physical activities or spa. Now, activity-induced energy expenditure is the most variable component of total energy expenditure, and it's typically between about 20 % to 40 % of the total amount of calories you burn per day, or your TDEE. Again, we measure the energy expenditure or, quote, cost of an activity in calories.

3:31And if you ever wanted to know how many calories that you need in a day, well, we have a free calculator on our website that can help you out. It's linked in the show notes below. Now, the energy cost of exercise has a dose-dependent relationship with activity-specific factors such as intensity, duration, the amount of muscle mass used, and the economy of movement. Increases in exercise intensity, increases in exercise duration, and the amount of muscle mass being used increase the amount of calories being used during exercise. In contrast, improvements in movement economy decrease the energy cost of movements as the individual adapts to the exercise that they're doing because they become more efficient.

4:14Now, in one study, and this is one of my favorites, the energy cost of individuals training for a half marathon did not increase when the weekly running distance was increased from 25 to 50 kilometers per week. They doubled the distance that they were doing per week, but the amount of energy it cost them on a weekly basis to do all this running didn't go up. Yeah, check that one out. Now, environmental factors such as ambient conditions, training surfaces, etc. can also influence an activity's energy cost by altering the metabolic requirements for force production by the muscles during a specific task.

4:49For example, running on a soft sandy beach into a headwind requires additional force production to maintain a given velocity compared to running on a track with calm winds. It should be noted, however, that changes in temperature do not appear to have a significant effect on energy cost during exercise, though they do appear to influence eating behaviors after a workout. When it's colder outside, eating tends to be increased, so there's an increase in energy intake, and with warmer temperatures, those are associated with a decrease in post-workout energy intake. Whether or not this has an effect on body weight long-term, well, that still remains yet to be proven.

5:27Now, in addition to the energy used during a workout, exercise increases energy demands post-workout in order to support recovery and other associated processes when an individual is at rest. For example, increases in muscle protein synthesis rates in the post-workout period are thought to represent a significant increase in resting energy expenditure. The increase in energy demands necessitates additional oxygen consumption, which is known as excess post-exercise oxygen consumption, or the acronym EPOC. The energy used during EPOC increases with intensity, training volume, and the amount of muscle mass being used, and it decreases as individuals become more adapted to training.

6:10A number of studies have suggested that resistance training increases EPOC to a higher level than aerobic training, but this isn't the whole story. It mostly seems to be true that EPOC is higher after lifting weights in training naive individuals. They're relatively untrained or new to lifting weights. However, when you compare trained individuals from aerobic training or even interval work compared to resistance training, it's not so clear that there's a big benefit or advantage of resistance training when it comes to the amount of energy used during EPOC or for EPOC. It also appears that the overall effect of EPOC on 24-hour energy expenditure, so how many calories you burn in a day, well, it's relatively modest for most workouts and training schedules.

6:53This brings up at least two big, important points regarding exercise and energy expenditure. So point one, the amount of energy used by the body due to exercise is not purely additive to total daily energy expenditure. In other words, if I personally have a baseline total daily energy expenditure of 3 ,000 calories per day without exercise, and then the exercise that I complete costs another 1 ,000 calories, my total daily energy expenditure is unlikely to be 4 ,000 calories. You can't just add the two numbers together. Instead, it'll be something a little bit less than that due to the body compensating and subsequently using less energy for other components of metabolism.

7:38How much less varies amongst individuals due to their genetics, their weight change history, particularly recent weight change history, their current nutritional status, the type of exercise they're doing, the amount of exercise they're doing, and more. Now, this constrained energy expenditure model, as it's known, is still an active area of research, also controversy, though the majority of individuals who exercise will experience it on some level. The crux of this first point is simply this. Whether someone is in a research setting or the real world, weight loss from exercise is usually less than what would be predicted purely from the calorie deficit calculated by adding someone's exercise on top of their total daily energy expenditure.

8:18Now for more on the constrained energy expenditure model, check out the podcast with Dr. Herman Ponzer, author of the book Burn and Adaptable, and it's linked in the show notes below. Now the second point here, and one that I think is more important than arguing over additive versus constrained energy models of exercise? Well, it's that the benefits of exercise are far more worthwhile than anything having to do with weight loss and calories. Exercise benefits virtually every organ system in the body, from your brain to your bones and your muscles to your metabolic function. Exercise improves the form and function of virtually everything, regardless of whether someone loses weight or not.

8:56Using exercise to burn calories misses the forest for the trees. Yes, exercise costs energy, but most of its benefits on health and fitness are independent of changes in body weight. Now, with all that in mind, does wearing a weighted vest increase the amount of calories used during exercise? By wearing a weighted vest during exercise, we would predict that an individual would burn more calories for the same amount of exercise activity, like the duration or the volume, and if it's done at the same intensity. The muscles have to create more force to deal with the added weight, and that costs more calories.

9:30That's pretty straightforward. However, one might predict that exercising with a weighted vest is harder, perhaps reducing the time that one exercises for, or making them otherwise reduce the intensity of their exercise by going slower, thereby reducing the total calorie cost of exercise. Let's take a look here at some science. One study on nine young healthy women had them do a graded exercise test on a treadmill, unloaded, or carrying a 70-pound rucksack, or wearing a 70-pound weighted vest until exhaustion. In the unloaded test, they exercise for about 20 minutes before exhaustion, whereas they quit after only 11 minutes with the weighted vest and six and a half minutes with the rucksack.

10:11It does seem like wearing one of these weighted vests or adding weight to the activity does tend to decrease the amount of time that people will exercise for. Now, in another study, 20 healthy adults walked on a treadmill unloaded or carrying 22%, 44%, or 66 % of their body mass in a weighted vest. The treadmill test included an increase in speed every two minutes until the person could no longer maintain the pace without jogging or running. Energy expenditure was measured during these tests. The results? Well, while energy costs went up with increased loads being carried, the total amount of calories burned was not that different between each condition, as it is affected by other variables like speed, terrain, and grade.

10:53For example, a 75-kilo adult walking at 3 miles an hour on level pavement is predicted to burn 282 calories per hour. If we add a vest that weighs 5 % of their body weight, well, yeah, the number goes up, but only to 290 calories per hour. and if we increase the weight of the vest even more to 10 % of the individual's body weight with the same speed, the same terrain, etc., well, that would cost 300 calories per hour. To put this into perspective, if you're 165 pounds and you walk for an hour with a 16-pound vest, you are likely to only burn an extra 18 calories in that hour compared to walking without a vest, and that's assuming you are walking at the same speed and for the same duration.

11:37You don't call it in early. If speed and or time spent exercising goes down, it's probably a wash. To summarize, wearing a weighted vest does seem to increase the amount of energy or calories used compared to being unloaded, provided the exercise is performed at the same pace and for the same duration or volume. However, the amount of additional calories being burned is modest, and the additional weight from the vest does tend to make the exercise more difficult to complete at the same pace and duration, perhaps limiting its utility for this purpose. Okay, so now on to the next question. Does this potential increase in calorie cost during exercise from wearing a weighted vest, does it lead to greater weight loss or greater ability to manage someone's weight?

12:20Let's take a look at some research. One study looked at 18 older adults with osteoarthritis who were losing weight. During the six-month trial, all subjects consumed a shake-based diet of around 1 ,200 calories per day in order to lose weight. Half of the subjects were randomly assigned to wear a weight vest up to 10 hours per day, with the weight of the vest gradually increasing up to 15 % of the individual's starting weight. Over the six-month study, both groups lost about the same amount of weight, right at about 11 kilograms, despite the vest wearers carrying around extra weight for an average of 6.6 hours per day.

12:56Both groups also lost about the same amount of lean body mass, about 3 kilos. In the subsequent 18 months, however, there was much less weight regain in the group who wore the weighted vests. However, it's not clear that they were actually wearing the vest after the initial 6-month study period, so we don't know if this is due to continued use of the weight vests, or if maybe wearing the weight vest during the weight loss period did something unique. Hmm, that's interesting. Maybe there's something to the effect of loading the body for extended periods of time and subsequent weight management.

13:27This has actually been discussed before, even on this podcast. We call this the gravidostat theory. Now, researchers from Sweden hypothesize that the body uses gravity as a regulator of body weight and body fat. This so-called gravidostat theory, it's this idea that there are specific cells in the bones and elsewhere that sense the amount of weight being carried around. One of the first studies on this was actually done in rodents. So in this study, they implanted capsules weighing 15 % of the rodents' body weight into their abdomens, whereas the control rodents had an empty capsule of equal size implanted.

14:05After two weeks, about 80 % of the added capsule weight was lost in the rodents with the heavy capsule implanted, and these rodents weighed about the same as the controls, despite still having the heavy capsule implanted. Now, that was like 2018. So subsequently, has there been any research in humans? Yes, there has. One study had 10 adult humans wear a weighted vest weighing about 13.5 % of their body weight for a week, followed by not wearing the vest for the following week. They wore the vest for just over eight hours each day. Mean hourly ratings for hunger and snack cravings, as well as daily peak hunger, were marginally lower in those wearing the vest.

14:46But the researchers didn't measure changes in weight or energy intake to see if these differences really meant anything. So did they actually eat less because they rated their hunger as lower? Did they lose more weight because of these changes in appetite and feelings of fullness or satiety? We'll never know. Another study compared 36 adults with obesity who were wearing a weight vest that weighed about 11 % of their body weight for eight hours per day, with 33 adults wearing a weighted vest that weighed about 1 % of their body weight over three weeks. Those wearing the heavier weight vest lost three and a half pounds during the study period, while the light vest group only lost a half a pound.

15:25The heavy vest wearing group also lost 4 % more fat mass, though fat-free mass was unchanged between groups. A longer-term human study showed no weight or fat loss benefits to wearing a vest that was 10 % of the individual's body weight for nearly seven hours a day over five months as compared to not wearing a vest at all. In one of the largest single studies done on wearing weight vests, they took 150 older adults with obesity who were enrolled into a study that was designed to help them lose 10 % of their body weight through dietary changes. Now, the subjects were randomized into one of three groups, where group one just did the diet only, diet only intervention.

16:04Group two did the diet and they wore a weighted vest. And group three did the diet, they wore the weighted vest, and they lifted weights three times per week. At the end of a year, 12 months of follow-up, the amount of weight loss was about the same in all groups at about 9 kilograms, despite the weighted vest groups wearing the vest for an average of 7 hours per day. There were no differences in resulting bone mineral density measurements either. In fact, the biggest differences between the groups were loss of body fat and changes in muscle strength. Unsurprisingly, the group lifting weights three times per week lost more fat mass and gained more muscle strength than the other groups.

16:42Now, for those of you keeping score at home, there were no differences between the diet-only group and the diet and weight vest group for amount of body fat loss or muscle strength, so it didn't really seem like the weighted vest had much of an effect on that. So overall, it does not appear that wearing a weighted vest improves weight loss or body composition as compared to doing the same amount of exercise at the same intensity but not wearing a vest. Whether or not wearing a weighted vest reduces the propensity of an individual to regain weight after weight loss is mostly speculative and would need to be tested further to feel confident about this finding.

17:17Weight vests also do not appear to increase bone mineral density in vulnerable populations. You'd expect older folks with osteoarthritis who previously hadn't been loaded that much to respond relatively well if there was an effect here, but they didn't. We'll still need more evidence here to comment confidently one way or the other, however. Between the very small potential increase in calorie expenditure and the non-existent benefit on weight or fat loss from wearing a weighted vest during exercise, I think it's pretty safe to say this theory has been debunked for the moment. If new data comes out, I'm open to changing my mind, but that's where I'm at for now.

17:52But that doesn't mean that weighted vests are all bad. When we come back from this break, I'll cover the best use cases for a weight vest based on the current science. Increasing intensity.

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23:52So let's start with conditioning. In conditioning, intensity refers to the metabolic demand of the activity. There are many ways to express exercise intensity. You can use oxygen consumption, power output, heart rate, speed, and more. But whether it's expressed in absolute or relative terms, intensity determines the nature of the physiological stress that an individual experiences during exercise, which influences the type of fitness and health adaptations obtained from exercise. Now, in a recent meta-analysis on weighted vests used during conditioning or cardio, the average increase in heart rate while walking at a self-selected pace is about 7%.