I already wrote a blog about the health benefits of exercise but what about strength training? I have heard that lifting weights raises your metabolism higher and longer than aerobic exercise. I was skeptical to say the least. Think of it like this. Most people go to the gym for an hour or so. But they are not lifting weights for an hour. They do a set of lifts which takes 20 seconds or so then they talk to their friends for a minute or two followed by another 20 second set of lifting. If I had to guess I would say we only lift weights for a total of 10-15 minutes per a one hour gym session. How many calories could that possibly burn?
This topic raised my curiosity. I was hopeful that lifting weights does raise your metabolism and helps burn more calories. I have been a runner my whole life (a slow one but one that could run for hours) but I always wanted to avoid the runner’s build- lanky with no muscle definition. I have lifted weights off and on since high school. The idea of lifting iron plates never thrilled me. I do it just to maintain muscle mass. Listening to audio books has made lifting weights more tolerable. Okay, back to the topic. Turns out strength training offers many health benefits besides raising your metabolism!
Strength training in minimal time
Strength training activities involve body weight workouts, free weights, resistance training equipment, or elastic bands. Most people assume that strength training requires a lot of time every week. Research has shown that this is not the case. A thorough review concluded that most of the benefits from strength training can be accrued from two 15-20 minutes sessions per week (1). Better yet, strengthening the lower back only requires 75-90 seconds per week!
Aerobic exercise alone may not lower body fat long term
As I mentioned in the introduction runners that do not lift weights usually become skinny with little muscle mass or become “fat” skinny where they are skinny overall but may have a little gut. There is a reason for this. In order to lose weight we must create a calorie deficit. Reducing our caloric intake and engaging in cardiovascular activity like jogging help create a calorie deficit and hence weight loss. Initially, you will lose body fat. But there is little evidence showing that after 3-6 months body fat will continue to be reduced or that fat loss will be maintained (1).
If your goal is simply to lose weight than this approach may work. But if you want to change your body composition or put on muscle mass this approach will fail. With continued calorie deficit and weight loss lean body mass will be lost along with fat which will lower your metabolic rate overall (more muscle mass requires more energy to maintain than fat mass and raises your metabolic rate). With less muscle mass and a lowered metabolic rate fewer calories are needed to maintain weight. In order to avoid subsequent weight gain you will have to consume fewer and fewer calories which is difficult and unrealistic.
Because it is so hard to continue on a diet where you must consume so few calories weight gain is likely. And since you are not lifting weights the weight gain will be fat. Muscles are not just cosmetically attractive. Higher amounts of body fat have been associated with various diseases. Body fat around the organs acts like a biologically active mass which negatively influences hormone levels and increases risk of heart disease.
The need to add weight training to weight loss programs
Resting metabolic rate, or RMR, is the amount of energy expended by the body at rest (to maintain such processes as breathing, circulation, organ functions, brain activity, etc.)
Adding weight training to a weight loss program can increase resting metabolic rate by increasing our muscle mass. Research has shown however that we cannot increase our muscle mass if there is a severe calorie restriction. If we are consistently losing weight from a low calorie diet we will not be able to put on muscle mass. An ideal solution would be to reduce caloric intake to the point where you lose a pound a week but weight train a few days each week. This way you can increase muscle mass and decrease body fat in a way that has proven to result in sustained weight loss and maintenance over time.
Typically, the slower you lose weight, the better chance you have of keeping the weight off long term. That is why crash diets are such a bad idea. It is not just a low body weight that confers health benefits, it is also a low body fat. As I mentioned in my protein blog, eating adequate protein is necessary to gain muscle AND helps maintain muscle even when you stop lifting weights! Key word is adequate, not excessive protein.
Weight training affects the metabolic rate of men and women differently
It seems that an increased metabolic rate associated with strength training is more complicated than previously thought. A study involving subjects of both genders and ages (men and women 20-30 years old and men and women 65-75 years old) found that the effects of 24 weeks of strength training increased strength in all participants equally but only the men had a significantly increased metabolic rate (2). Although this is but one study researchers suggested that men may have experienced larger proportional increases in hypertrophy (increase in size of muscle mass) and sympathetic nervous system activity than women. This is only a hypothesis and more studies need to be conducted to confirm or refute the results of this study.
You can become lean without losing weight
So many people in the United States are too focused on losing weight at any cost. From personal experience I can tell you that I had a much higher body fat percentage when I was twenty pounds lighter. As I began a weight training routine I put on fifteen pounds but my body fat continued to decrease. That’s why the scale can be deceiving; to tell if you are losing fat go by how well your clothes fit and how you look in the mirror, not just how much you weigh. Remember, muscle weighs more than fat per volume (muscle is denser) so increasing muscle mass while losing fat can cause an increase in weight!
To illustrate this point let’s look at a study involving men 61-77 years old who engaged in 26 weeks of resistance training. At the end of the study the subject’s body weights did not significantly change but their percent body fat decreased by 3.4%, their fat mass significantly decreased by 6.83 pounds and fat free mass (most likely muscle) significantly increased by 4.4 pounds (3). A major issue with this study is a lack of control group.
Resistance training increases resting metabolic rate (RMR)
To repeat myself, RMR is the amount of energy expended by the body at rest (to maintain such processes as breathing, circulation, organ functions, brain activity, etc.) and accounts for 70% of our daily energy expenditure (4). It is the minimum amount of calories needed to maintain life-so if your RMR is 2,400 calories you would need to consume 2,400 calories a day just to maintain life. The RMR is unrealistic however and is measured for someone that just sits all day and does not move- movement would require additional calories above the RMR. Obviously, increasing our RMR would be beneficial for weight loss as our body would require more calories to maintain its current weight and eating calories under this increased need would result in weight loss. Having an extremely low RMR, say 1200 calories day, means that eating more than 1200 calories a day would result in weight gain. This is why having a high RMR can help with weight loss and a low RMR can cause weight gain.
Two ways strength training may increase resting metabolic rate (RMR)
Let me preface this section by saying the two ways strength training may increase RMR are based mostly on human physiology and not on actual studies. The two ways are highly controversial and we may find out one day that strength training does not have a significant impact on RMR. I like keeping an open mind about different theories so I will talk about them anyway.
Resistance training is believed to increase RMR through two means: 1) increasing fat free mass and 2) through acute or postexercise effects (4).
Fat free mass – our RMR is highly correlated with fat free mass- which is our mass accounted for by bone, organ tissue and muscle. We cannot change our bone or organ tissue but we can change the amount of muscle we have so any increase in fat free mass is mostly muscle since our organs and bones do not change. Muscle mass contributes about 22% to our RMR (4). So increasing our muscle mass while decreasing our fat mass will likely result in an increased RMR…but the big question is if it increases RMR enough to result in weight loss over time? It may indeed raise our RMR but not enough to cause significant weight loss. There needs to be more studies on this topic.
Acute or postexercise effects – following exercise our body’s metabolic rate is maintained above resting values due to excess postexercise oxygen consumption (EPOC) (4). It appears EPOC can increase our energy expenditure but studies suggest for this to occur a person must perform strenuous exercise (moderate resistance exercises with a large number of sets).
One postexercise effect may be an increase in using our body fat for energy, or fat oxidation. During exercise our muscles use glucose (sugar) for energy. Our body pulls glucose from its stored form called glycogen. After exercise our body replenishes our glycogen stores and in this time of glucose storing we may draw on fat to use as energy. This is a common theory at least.
Using weight training to preserve muscle mass while dieting
There has been debate around whether or not weight training combined with a very low calorie diet can help prevent loss of muscle. In one study researchers assigned twenty obese subjects to one of two groups: a very low calorie liquid diet plus aerobic exercise or a very low calorie liquid diet plus strength training and then compared the groups in regards to loss of lean body weight and change in resting metabolic rate (RMR) (5). After 12 weeks researchers found that although the aerobic exercise group lost more weight than the resistance exercise group the lean body weight did not decrease in the resistance exercise group but did decrease in the aerobic exercise group. Also found was that the resting metabolic rate significantly increased in the resistance exercise group but decreased in the aerobic exercise group.
This study showed that although the aerobic group lost more weight, the resistance exercise group maintained lean body mass and increased their resting metabolic rate which may be a more effective and healthier weight loss strategy long term. Slowly losing weight while maintaining lean body weight and increasing resting metabolic rate is a more effective long term strategy than losing weight quickly but losing lean muscle mass and decreasing your resting metabolic rate, both of which would make losing more weight more and more difficult as the resting metabolic rate keeps decreasing.
Another study compared weight loss, fat-free mass and resting metabolic rate among obese subjects assigned to one of three groups: diet plus strength training, diet plus aerobic exercise and diet alone (6). After the eight week study amount of weight lost did not differ between the groups but the strength training group lost significantly less fat free mass than the other two groups. The resting metabolic rate decreased similarly between the three groups.
Both of the previously mentioned studies used similar methodology and similar diets. It is odd that the subjects in the second study performing aerobic exercise did not lose more weight than the other two groups. As I mentioned, there is debate about every topic in nutrition and health, and this is no exception. At least both studies showed that strength training was able to preserve lean body mass better than aerobic training. Also remember that both of these studies used obese subjects whose metabolism may respond differently to dieting and exercise than their leaner counter parts.
Using weight training to preserve muscle mass while drastically reducing caloric intake
A study by Donnelly took fourteen obese female subjects and assigned them to a severe energy restriction diet plus weight training or severe energy restriction diet and sedentary (7). At the end of the 90 day trial, the females in both groups lost the same amount of weight, body fat percentage and fat free mass (7). The only difference between the groups was that the females that weight trained gained strength and experienced muscle fiber growth while the sedentary females lost strength by the end of the study. So it seems that even when on an extremely calorie restricted diet weight training offers some benefits over being sedentary.
Large study comparing resistance training and aerobic exercise
I would like to discuss this study last as it is the largest and most recent study comparing resistance training and aerobic exercise that I could find. A 2012 study recruited 119 subjects that were sedentary, overweight or obese adults (ages 18-70) and randomly assigned them to one of three groups: 1) Resistance training (RT) 2) Aerobic training (AT) 3) or a combination of resistance training and aerobic training (AT/RT) (8). The study lasted eight months. When the study was over researchers found that there was a significant decrease in body weight in the AT and AT/RT groups but a significant increase in the RT group (8).
Fat mass and waist circumference did not change in the RT group but significantly decreased in the AT group and the AT/RT group (8). Lean body mass significantly increased in the RT group and the AT/RT group but did not change in the AT group (8). Body fat percentage dropped the most in the AT/RT group. RT was better at increasing muscle mass while aerobic training was better at reducing fat and body mass. The strengths of this study were the large sample size and long trial length.
These results are slightly different than the other studies that I mentioned. The group that benefited most was the aerobic and resistance training combined group. Surprisingly, there was no change in fat mass or waist circumference in the resistance training group. As I have said, the effect of strength training on body fat and body weight is controversial. Perhaps light cardio plus weight training produces the best results on weight loss and lowering body fat percentage.
Unfortunately most of the studies on this topic were from the early 2000’s. I am not sure why there has not been more recent research in this area. Also, almost all of the studies mentioned were relatively short (a few months) and involved obese subjects which may differ from more fit or leaner people. The effect of strength training on weight loss, body fat percentage and resting metabolic rate has proved difficult to unravel with many studies finding conflicting results. It is extremely hard to say with certainty if strength training raises resting metabolic rate, if the effect levels off after a long length of time and if it raises metabolic rate enough to actually result in weight loss.
If you want to lose weight and are not concerned about gaining or maintaining muscle mass you could get away with reducing your calories and engaging in aerobic exercises. If you want to put on muscle mass and loss fat you should slowly lose weight (about a pound a week), engage in strength training activities and engage in aerobic exercise but not to the point where you produce a large calorie deficit as it will prevent you from putting on muscle mass. If you want to lose weight and maintain muscle mass you should do strength training, lower your calories and do light aerobic exercise. I am far from an expert in this area and these are just general guidelines. Whether or not you should do strength training revolves around your goals.
Personally, I would not neglect aerobic training. Weight lifting is great for putting on muscle mass and gaining strength but aerobic training offers many additional benefits on your health such as reducing heart disease, reducing blood pressure, improving blood sugar levels and reducing risk of dementia. But I have already covered this topic in my physical activity blog!
- Winett, R. A., & Carpinelli, R. N. (2001). Potential health-related benefits of resistance training.Preventive medicine,33(5), 503-513.
- Lemmer, J. T., Ivey, F. M., Ryan, A. S., Martel, G. F., Hurlbut, D. E., Metter, J. E., … & Hurley, B. F. (2001). Effect of strength training on resting metabolic rate and physical activity: age and gender comparisons.Medicine and science in sports and exercise,33(4), 532-541.
- Hunter, G. R., Wetzstein, C. J., Fields, D. A., Brown, A., & Bamman, M. M. (2000). Resistance training increases total energy expenditure and free-living physical activity in older adults.Journal of Applied Physiology,89(3), 977-984.
- Alexander, J. L. (2002). The Role of Resistance Exercise in Weight Loss.Strength & Conditioning Journal,24(1), 65-69.
- Bryner, R. W., Ullrich, I. H., Sauers, J., Donley, D., Hornsby, G., Kolar, M., & Yeater, R. (1999). Effects of resistance vs. aerobic training combined with an 800 calorie liquid diet on lean body mass and resting metabolic rate.Journal of the American College of Nutrition,18(2), 115-121.
- Geliebter, A., Maher, M. M., Gerace, L., Gutin, B., Heymsfield, S. B., & Hashim, S. A. (1997). Effects of strength or aerobic training on body composition, resting metabolic rate, and peak oxygen consumption in obese dieting subjects.The American journal of clinical nutrition,66(3), 557-563.
- Donnelly, J. E., Sharp, T., Houmard, J., Carlson, M. G., Hill, J. O., Whatley, J. E., & Israel, R. G. (1993). Muscle hypertrophy with large-scale weight loss and resistance training.The American journal of clinical nutrition,58(4), 561-565.
- Willis, L. H., Slentz, C. A., Bateman, L. A., Shields, A. T., Piner, L. W., Bales, C. W., … & Kraus, W. E. (2012). Effects of aerobic and/or resistance training on body mass and fat mass in overweight or obese adults.Journal of Applied Physiology,113(12), 1831-1837.