It’s very common to hear things like weight training (resistance training) is critical as part of a weight-loss plan because muscle burns more calories at rest and you get the afterburn effect and so on. How true is this? Are these the best reasons? Let’s take a look.
Muscle Burns More Calories
This is one of the most common reasons I hear that people state for using resistance training to lose weight. While it is true that muscle burns more calories than fat throughout the day, the problem here is two-fold. First, the calorie burn is overhyped, often being stated as high as 50 calories per day for each pound of additional muscle. Thus, if you could manage to gain 4-5 pounds of solid muscle in the next couple of months you’d have a new 200-250 calorie deficit built in to hack your weight loss. It would be great if it worked like this as it would make losing fat a lot easier. Unfortunately, the effect is much smaller. It’s estimated that each pound of muscle burns closer to 7 calories per day, which isn’t nothing by any means, in fact it may be 2-3 times as much energy used by the same fat mass in that time, but it also isn’t all that impressive in terms of shifting the energy equation into a caloric deficit. This brings us to the second reason that stating calories burned by additional muscle helps in weight loss may not be the best reasoning. From a time investment perspective, how much effort needs to be put into building a couple pounds of muscle for a modest caloric benefit compared to simply adding some more cardio which can burn an additional 7 calories in less than two minutes?
Still, don’t throw resistance training out just yet. There are absolutely reasons to do it that help with weight loss (nevermind the many other benefits such as strength, bone health, and so on) and this calorie benefit can be a nice side effect. Just don’t count on it to be as big of a game changer as you may have heard.
The Afterburn Effect
Higher intensity activities use up energy faster than aerobic metabolism can provide it. The body accomplishes this by switching to more anaerobic metabolism which leads to the accumulation of lactic acid in the muscles which gives you the burning sensation from exercise of sufficient intensity and time. After the workout is complete the body still needs to process the lactic acid aerobically and replenish energy stores in the forms of ATP/CP (highly accessible energy molecules) and glycogen (stored sugar-based energy source) in the muscles. This requires energy that isn’t used during the workout itself and is referred to by exercise scientists as Excess Post-exercise Energy Consumption (EPOC) because there is increased oxygen used for a period of time following the workout which means more calories are being used in the rest period after the workout than would have otherwise. This burning calories after exercise is often more commonly referred to as the afterburn effect among fitness enthusiasts and marketers.
Even here, unfortunately, the marketing doesn’t quite live up to the hype though. While the afterburn effect is very real, the total extra calories burned during the afterburn period ranges from negligible amounts to around 150 calories for the first day, diminishing to less and less as time passes possibly lasting up to 72 hours. However, some studies have shown greater promise with as much as 300 additional calories being consumed within a 24-hour period and resting metabolic rates increasing by as much as 5% which rivals the results expected from high intensity interval training. So this can certainly add a meaningful contribution to calories burned, but it’s not the entire story…
Burning Calories Isn’t the Only Goal?!
… at least not directly in the usual ways energy expenditure is calculated. This may sound like heresy since weight loss is still subject to the energy balance equation of energy in vs energy out so surely to help with weight loss the purpose of physical activity is to burn more calories, right? Yes, and no. While the information discussed so far is great news for those wanting to avoid typical cardio and still manage to lose weight, it doesn’t really rise to the level of being reason enough to choose these activities over others on their own, especially for those who don’t enjoy resistance training but do enjoy cardio. (Keep in mind it’s not an either or proposition, both cardio and resistance together yield excellent results, and diet is always a key component of losing fat as well)
Hormonal Shift
Not everyone knows that exercise influences hormones, but it most certainly does. One hormone that is influenced particularly well is insulin. Once again, it’s not that resistance training has a monopoly on exerting effects on insulin, but it does seem to help make improvements from a different way then aerobic exercise does. Both aerobic and anaerobic training improve insulin sensitivity which means that the cells are more responsive to taking up sugar in response to insulin, meaning less insulin is required to regulate blood sugar. This is helpful as insulin is associated with increases in fat storage (it seems to be a vicious cycle of increased fat leading to increased insulin resistance and increased insulin resistance leading to more fat storage). However, where resistance training shines over aerobic training in this arena is that it increases glucose uptake capacity. This is likely a combination of depleting glycogen stores that then have more need to be replenished as well as building up muscle mass and with it glycogen storage capacity. In other words more sugar can be stored and used by the muscles meaning it doesn’t get shunted into fat storage.
Growth Hormone (GH) release appears to be influenced in a linear relationship relative to intensity of the work being done. While moderate aerobic activity will lead to improvements in growth hormone secretion, high intensity intervals will do even better. Resistance training in many ways mirrors the intensity of heavy effort intervals when it comes to metabolic adaptations. Thus it may serve as a less exhausting way to get significant improvements in GH, especially when targeting larger muscle groups that will exert a greater effect throughout the body. It may seem counterproductive at first to increase a hormone that sounds like it’s meant to create growth (which it does in kids), but it actually helps mobilize fat and increase lean muscle mass so it’s helpful for shifting body composition into a leaner state.
Other positive changes include better testosterone to cortisol ratios and so on. The key take away is that there are multiple biochemical interactions and hormonal reactions to exercise that are favorable for having a leaner body composition.
Metabolic Improvements
Beyond the improvements in insulin function mentioned above, resistance exercise also improves sugar regulation independent of insulin function not to mention other changes that improve the muscles capacity to use energy from carbohydrates, fats, and proteins. You can think of this as an upgrade to a more fuel hungry engine. What’s more, these improvements also lead to a greater ability to work harder during more continuous activity such that more calories can be burned than could be with less capable muscles in the same amount of time.
Muscle Building Energy Requirements
Another often overlooked factor is the energy requirement of building muscle. This is not picked up in testing during exercise and since the afterburn effect generally only lasts up to 72 hours, but muscle mass can still increase up to seven or more days following a workout, the energy needed to actually build new muscle on the frame is, in my opinion, an understudied area of interest as it relates to weight loss. From the point of view of someone trying to add muscle they are often told that they need to eat more in order to pack on the meat. It appears to take somewhere between 2500-2800 extra calories to put on a pound of muscle. From a weight loss perspective, this may actually start to make the calorie needle move appreciably in combination with the added metabolic requirements of muscle and the afterburn effect mentioned previously. While in isolation, these different mechanism don’t seem overly impressive, together they start to add up. Consider the case of two reasonably high intensity resistance bouts during the week adding an additional 600 calories of afterburn and assuming a modest gain of 1/4 pound of muscle that week we could add another 700 calories or so that went into that. That adds an additional 1300 calories burned to the week with the following week having the extra muscle to help burn a little more. Every little bit helps.
Injury Prevention
Resistance training also helps foster strengthening of connective tissues and a well designed program will help to keep the body in balance off-setting over-use injuries and those due to poor biomechanics. By avoiding injuries, you can avoid lost workout time slowing down your progress.
Shaping and Transformation
While not actually an aspect of weight loss, this absolutely plays into the reasons most people want to lose weight. While certainly health effects are also an important motivation for many, the fact is that many of us, perhaps you, want to lose weight to increase confidence and sex appeal. Resistance training is the best way to add size and shape to muscles which contributes to a more desirable shape. A nice V-taper in men or an hourglass in women is going to be a result of not only a narrow waist, but also some development of the lats in the back and the muscles of the hips and buttocks. For some people what is accomplished through cardio alone may be enough to satisfy them here, but others will surely want some resistance training to shape these muscles further to achieve these goals. Ultimately, you don’t have to do resistance training to lose weight, but it will make your progress come faster and improve energy and appearance along the way.
Sources
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4038351/
https://pubmed.ncbi.nlm.nih.gov/8300043/
https://pubmed.ncbi.nlm.nih.gov/22240549/
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