Introduction

It is well documented that aerobic exercises are very healthy for our body and are good ways to burn calories. However, aerobic exercises can also be catabolic, breaking down muscle tissue. A 1995 landmark study revealed that aerobic exercise, including high intensity aerobic exercise, results in muscular atrophy (a decrease in muscle).^I One often overlooked exercise that helps us maintain an active metabolism and healthy bodyweight is progressive resistance training, or just plain old weight lifting for short. Used in conjunction with aerobic exercises and diet and lifestyle modifications, it can help maintain overall health and fitness.

Body Muscle

How Much Do We Have and How Much Can We Lose? Our body is composed of 660 muscles. Skeletal muscle makes up about 40 percent of our body weight and is responsible for storing between 50-75 percent of all proteins found in our body. As we age, our body goes through many physiological processes, including the inevitable loss of muscle. Research has shown that a man who maintains the same healthy weight as he grows older still gains fat and loses muscle tissue and strength.^II,III,IV In general, if no type of resistance training is conducted the following occurs:

• Between 25- 50 years old, one undergoes approximately a 10-15 percent loss of muscle mass.
• Between 50- 80 years old, there is an additional 30 percent loss of muscle mass.
• The total loss muscle mass accounts for roughly 40- 45 percent of our total body muscle mass from age 25- 80 years old.
• Much of this loss in muscle mass can be explained by aging of the neuromuscular system and “inactivity.”

This loss in muscle mass almost mirrors the loss in muscular strength:

• From 45-65 years old, there is a loss of 22 percent in strength.
• Strength loss accelerates after age 70, with a 30 percent decrease between seen between 70 - 80 years old.
• Without strength training, there appears to be a cumulative loss of 50 percent in strength between the ages of 50-80 years old.

Body Muscle

How Does It Contribute to Burning Calories? Such muscle loss translates to about a 2-4 percent reduction per decade in the body’s basal metabolic rate (BMR) which is the calories the body burns at rest.^VI Based on an average BMR of 1,500 calories per day, 2 percent loss results in 30 less calories burned per day. This may not get you excited initially, but consider that over 10 years, it can easily equate to 10 or more pounds gained in body fat!^V

Every pound of body fat contains 3,500 calories. To lose one pound of body fat, the body must burn 3,500 calories. Burning 3,500 calories takes work, for instance, a 140-pound marathoner expends about 110 calories per mile or 2,882 calories to run 26.2 miles!

Previous reports contended that a pound of lean muscle tissue burns between 35-50 calories a day at rest compared with fat which burns approximately 2-4 calories at rest. Recent research is challenging this, contending that muscle only burns 5.7^VII,VIII to 7.2⁹ calories per pound per day at rest. Two classic and very reputable studies^10,11 as summarized in the adapted chart below9 demonstrated that strength training programs can increase the body’s resting metabolism 6.8-7.7 percent and increase lean body muscle mass by three pounds in just 12-16 weeks of 20-30 minutes of strength training per session, regardless of age or sex. Other research supports this and notes that the adult body’s resting metabolic rate can increase 7 percent regardless of age with the use of strength training over a 24 week period.¹²

Study	Strength Training Program	Training Frequency	Training Duration	Change in Tissues	Change in Resting Metabolism
Campbell et al. Tufts University	4 Exercises 3 Sets 8-12 Reps	3 times per week	12 weeks	Muscle gain 3.1 lbs Fat Loss 4.0 lbs	Increased 6.8% or 105 calories per day
Pratley et al. University of Maryland	14 Exercises 1-2 Sets 10-15 Reps	3 times per week	16 weeks	Muscle gain 3.5 lbs Fat Loss 4.2 lbs	Increased 7.7% or 120 calories per day

*Reps=repetition

Body Muscle

How Can You Build More to Maintain a Healthy Weight? Boosting the body’s resting metabolism 7-8 percent may not seem like a lot, but over time, this helps maintain current lean body weight and aides in weight loss, if needed. It also burns an additional 105-120 calories at rest per day, or as much as 3,150-3,600 additional calories burned per month at rest!

So, how can one counteract the slippery slope of weight gain and muscle loss? Unfortunately, we cannot totally reverse this process, but we can slow it down. And, progressive resistive strength training can help. It adds muscle mass through a process called hypertrophy, which increases the actual cross sectional area of the muscle, rather than the number of muscle fibers. When properly conducted, strength training is actually anabolic and can be used to build or maintain muscle mass, increase or maintain bone density, and help with a myriad of other important health and lifestyle issues.

The key to obtaining muscle hypertrophy with strength training is to use a resistance or weight that is equivalent to at least 60 percent of one repetition maximum (1RM). This translates to the maximum amount of weight you should lift one time safely. For example, if your 1RM is 100 pounds, then 60 percent of this would be 60 pounds. In addition, to attain muscle hypertrophy, one also has to consider how many times the resistance or weight is lifted. In general, one would normally set a goal of 6-12 repetitions of lifting 60% of his or her 1RM. If done properly, by the time you reach your last repetition, you really could not do one more repetition without help or using poor form.¹³

Conclusion

Resistance training when combined with other lifestyle modifications such as eating right and doing aerobic exercise is especially effective in maintaining a healthy body weight. Moreover, it is accomplished fairly easily through a simple progressive resistance program of only 20-30 minutes per workout, 2-3 times per week. So, even with a busy person’s weekly time constraints, it can be attainable.

References

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^I Kramer et. al 1995. Compatibility of high-intensity strength and endurance training on hormonal and skeletal muscle adaptations. J Appl Phys 78(3):976-989.
^IIKeys A, Brozek J. Body fat in adult man. Physiol Rev. 1953 Jul;33(3):245–325.
^IIIBooth FW, Weeden SH, Tseng BS. 1994 Effect of aging on human skeletal muscle and motor function. Med Sci Sports Exercise. May;26(5):556-60.
^IVTseng BS, Marsh DR, Hamilton MT, Booth FW. 1995. Strength and aerobic training attenuate muscle wasting and improve resistance to the development of disability with aging. J Gerontol A Biol Sci Med Sci. Nov;50 SpecNo:113-9.
^VWestcott, W. “Keeping Fit: Strength Training Revs Up The Metabolism”: UTICA Observer Dispatch, 7 March 2008.
^VIPaffenbarger, R. and Olson, E. 1996 Lifefit: An effective exercise program for optimal health and a longer life. Champaign, Illinois: Human Kinetics
^VIIBouchard,C. Blair,S., Haaskie, W., 2007. Physical Activity & Health. Champaign, IL: Human Kinetics.
^VIII Mclave, S., Snider, H. 2001 “Dissecting the Energy Needs of the Body” Current Opinion in Clinical Nutrition and Metabolic Care: Mar: 14(2): 143-147.
⁹ Westcott, W. YMCA Article Titled: “Why the Confusion on Muscle and Metabolism?” http://www.ssymca.org/pdf/Health_Articles/Why_The_Confusion.pdf accessed on the internet 5/9/11.
¹⁰ Campbell,w., Crim, M., Young,V. and Evans, W. 1994. Increased energy requirements and changes in body composition with resistance training in older adults. American Journal of Clinical Nutrition, 60:167-175.
¹¹ Prately,R. Nicklas, B., Rubin, M., Miller, J., 1994 Strength training increases resting metabolic rate and noreprinephrine levels in healthy 50 to 65 year old men. Journal of Applied Physiology, 76:133-137.
¹² Lemme,JT., et al. 2001 Effect of strength training on resting metabolic rate and physical activity: age and gender comparisons. Med Sci Sports Exerc. Apr:33(4):532-41.
¹³ Feigenbaum MS, Pollock ML. 1999 Prescription of resistance training for health and disease. Medicine and Science in Sports and Exercise: 31(1):38-45