Muscle – It’s Not Just For Bodybuilders!
by Monica Mollica ~ trainergize.com
To most people outside the gym, the word “muscles” brings to mind huge bulging muscle bellies and bodybuilders. The importance of muscle mass, strength, and metabolic function in the performance of exercise and sports, has never been questioned. However, muscles aren’t just for show. Here I will explain why.
Role of muscle in the body’s metabolism
Skeletal muscle is the most abundant tissue in the human body, and the maintenance of its mass is essential to ensure basic function as locomotion, strength and respiration (1). In order for us to survive, certain tissues and organs, like the brain, heart, liver and skin, need to maintain their protein content. These essential tissues and organs rely on a steady supply of amino acids via the blood to serve as precursors for the synthesis of new proteins to balance the persistent rate of protein breakdown that occurs in all tissues.
In the absence of nutrient intake (for example in between meals and during sleep) muscle protein serves as the principal reservoir to replace blood amino acid taken up by other tissues (2-4). In the fasting state, blood amino acids serve not only as precursors for the synthesis of proteins but also as precursors for hepatic gluconeogenesis (5). Consequently, the protein mass of essential tissues and organs, as well as the necessary plasma glucose concentration, can be maintained relatively constant despite the absence of nutritional intake, provided muscle mass is adequate to supply the required amino acids.
The primary fate of ingested amino acids is incorporation into muscle protein to replete the reserves of amino acids lost in the fasting state. Under normal conditions, gains in muscle protein mass in the fed state balance the loss of muscle protein mass in the fasted state. The ability of muscle protein breakdown to maintain plasma amino acid concentrations is remarkable, provided adequate muscle mass is available.
Role of muscle in chronic disease
Chronic diseases related to poor lifestyle behaviors account for more than two-thirds of deaths in the United States (6), and alterations in muscle and loss of muscle mass (muscle wasting) play an important role in the most common diseases and conditions (7). Heart disease and cancer are the major chronic diseases suffered in the Western world (6), and both cardiac failure and cancer are often associated with rapid and extensive loss of muscle mass, strength, and metabolic function (cachexia) (1, 8, 9). With cardiac and cancer cachexia, the loss of muscle mass is an important determinant of survival. In these conditions these are notable alterations in muscle metabolism (1), among all an increased expression of muscle catabolic pathways and myostatin (which inhibits muscle growth) (10).
Another chronic condition that is caused by muscle loss is sarcopenia, which is a progressive loss of muscle mass and function that occurs with aging and causes frailty (11-14). Sarcopenia is a widespread syndrome that has a devastating effect on quality of life, activities of daily living and ultimately survival (11-14). Muscle loss isn’t just negative for the elderly, is also occurs in younger people, and is then called myopenia (15).
Exercise training has been proven to be beneficial in chronic diseases and conditions that cause, or are caused by, muscle wasting (1, 8, 9, 11, 13, 14). Another chronic disease where muscle mass (and exercise) is of importance is osteoporosis.
Mechanical force on bone is essential for increasing and maintaining bone strength and mass (16). Whereas body weight and weight-bearing exercises provide a direct mechanical force on bones, the largest loads on bone are proposed to come from muscle contractions (16). Correlations between grip strength and bone area, bone mineral content, and bone mineral density in both healthy athletes (17) and stroke patients (18) support the notion that muscle contractions play a significant role in bone strength and mass. Even the correlation between body weight and bone mass can be explained on the basis of the force exerted on bone by muscle contractions, in that it takes more force per unit area to move heavier bodies.
Furthermore, changes in bone mass and muscle strength move in the same direction over the life span (16). Although it is debatable whether it is muscle strength or simply muscle mass that is important in determining bone strength and mass, is has been shown that muscle mass correlates positively with bone mineral content and bone mineral density (19). Thus, maintenance of adequate bone strength and density with aging is highly dependent on the maintenance of adequate muscle mass and function.
Role of muscle in the prevention of obesity
Whereas the role of muscle is central and obvious in syndromes such as sarcopenia and cachexia, which are defined—at least in part—by loss of muscle mass and strength, the potential role of muscle in the prevention of obesity is less well appreciated.
The development of obesity results from an energy imbalance over a prolonged time, which means that energy intake exceeds energy expenditure.
An effect on energy balance can therefore be achieved by altering either energy intake or energy expenditure. In our diet focused society, the energy intake side of the energy balance equation gets almost all the attention. This is unfortunate since variations in our energy expenditure are at least as important. After all, it is called “energy balance” which means that both sides need to be balanced at a healthy level. Just cutting back on our caloric intake will not put our energy balance at a healthy level. Instead it will just cause deprivation and frustration.
Total energy expenditure is the sum of resting energy expenditure (REE), the thermic effect of food, and the activity energy expenditure related. Our muscle mass, and the energy expenditure related to muscle metabolism, affects both resting and activity energy expenditure. The energy expenditure caused by physical activity is obvious; the more muscle we have, the higher workloads we can move, and the more calories we’ll expend. However, the energy expenditure caused by our resting metabolism can be quite significant too if we have an enlarged muscle mass. Let’s take a look at a simple calculation to illustrate this:
The mass and protein turnover rates of the body’s organs and tissues is pretty constant (4). In contrast, large variations in muscle mass are possible, and the rate of muscle protein turnover (ie, muscle protein synthesis and breakdown) may vary as well. The synthesis and breakdown of muscle protein are principally responsible for the energy expenditure of resting muscle.
The average muscle mass of young, healthy males to range from 35 to 50 kg (20). In contrast, an elderly woman may have less than 13 kg muscle. While the exact energetic of muscle protein turnover aren’t known, a conservative estimate can be done on the basis of muscle protein synthesis. For our male and old woman, the energy expenditure per day as a result of muscle protein synthesis may range from 485 kcal/d to 120 kcal/d (21-24). This is a quite large difference, and doesn’t even consider any increase in protein turnover caused by physical activity. Note that in this example the male is not a bodybuilder. Extremes in muscle mass, for example male body builders to frail elderly, would cause even greater differences in resting energy expenditure.
In terms of whole-body energy balance, a difference in resting energy expenditure of 365 kcal/d, stemming from a difference in muscle protein turnover, would lead to a gain or loss of 47 g fat mass/day, because 1 kg (2.2 lb) of fat stores 7700 kcal (25). If activity and diet remained constant, this would mean a gain or loss of 1.4 kg (3.1 lb) fat mass/month. This effect on energy balance is particularly striking when it is realized that the estimate given above for the energy expenditure associated with muscle protein turnover is likely an underestimate, because protein breakdown also requires energy. It is evident from these estimations that, when a long-term perspective is considered, even relatively small differences (eg, 10 kg = 22lb) in muscle mass could have a significant effect on energy balance. Every 10-kg difference in lean mass translates to a difference in energy expenditure of ≈100 kcal/day, assuming a constant rate of protein turnover. In considering the magnitude of energy imbalances leading to obesity, it is reasonable to view the situation over long periods of time, because obesity often develops over months and even years. A difference in energy expenditure of 100 kcal/day translates to ≈4.7 kg (10.3 lb) fat mass/year. Thus, the maintenance of a large muscle mass and consequent muscle protein turnover can contribute to the prevention of obesity.
The expanded muscle mass can be capitalized on to facilitate fat loss. It is evident from the calculations presented above that a stimulation of muscle protein turnover in the setting of increased muscle mass could have a significant effect on resting energy expenditure and thereby energy balance. This can be accomplished through nutrition, because increasing amino acid availability, through and increased protein intake, increases muscle protein turnover (26).
What’s interesting is that the calories used to provide energy for muscle protein turnover is largely derived from stored fat, because this is the preferred energy source of resting muscle (27). This has been confirmed in studies of testosterone injection in hypogonadal elderly men, in which increases in muscle protein synthesis and lean body mass over time was accompanied by a decrease in fat mass (28).
Bottom Line
Now you have some good and scientifically supported arguments to present when your friends and family members start complaining about your high protein intake and passion for training and growing muscle!
I will leave the related topic of “how much muscle is adequate muscle” for another article and discussion. Hopefully studies will start to pop up in the near future on the relation of the fat free mass index (FFMA) and obesity and chronic diseases, and its importance for health and well being.
About the Author:
———————
Monica Mollica has a Bachelor’s and Master’s degree in Nutrition from the University of Stockholm, Sweden, and is an ISSA Certified Personal Trainer. She works a dietary consultant, health journalist and writer for www.BrinkZone.com, and is also a web designer and videographer.
Monica has admired and been fascinated by muscular and sculptured strong athletic bodies since childhood, and discovered bodybuilding as an young teenager. Realizing the importance of nutrition for maximal results in the gym, she went for a BSc and MSc with a major in Nutrition at the University.
During her years at the University she was a regular contributor to the Swedish bodybuilding magazine BODY, and she has published the book (in Swedish) “Functional Foods for Health and Energy Balance”, and authored several book chapters in Swedish publications.
It was her insatiable thirst for knowledge and scientific research in the area of bodybuilding and health that brought her to the US. She has completed one semester at the PhD-program “Exercise, Nutrition and Preventive Health” at Baylor University Texas, at the department of Health Human Performance and Recreation, and worked as an ISSA certified personal trainer. Today, Monica is sharing her solid experience by doing dietary consultations and writing about topics related to health, fitness, bodybuilding, anti-aging and longevity.
References:
1 Lenk K, Schuler G, Adams V. Skeletal muscle wasting in cachexia and sarcopenia: molecular pathophysiology and impact of exercise training. Journal of cachexia, sarcopenia and muscle. 2010 Sep;1(1):9-21.
2 Biolo G, Zhang XJ, Wolfe RR. Role of membrane transport in interorgan amino acid flow between muscle and small intestine. Metabolism: clinical and experimental. 1995 Jun;44(6):719-24.
3 Felig P, Owen OE, Wahren J, Cahill GF, Jr. Amino acid metabolism during prolonged starvation. The Journal of clinical investigation. 1969 Mar;48(3):584-94.
4 Matthews DE. Proteins and Amino Acids. In: Shils ME, Shike M, Ross AC, al e, editors. Modern Nutrition in Health and Disease. 10th ed; 2006.
5 Felig P. The glucose-alanine cycle. Metabolism: clinical and experimental. 1973 Feb;22(2):179-207.
6 Anderson RN, Smith BL. Deaths: leading causes for 2002. National Vital Statistics reports. : National Center for Health Statistics, 2005. (No. 17.); 2005.
7 Zamora E, Galan A, Simo R. [Role of myostatin in wasting syndrome associated with chronic diseases]. Medicina clinica. 2008 Nov 1;131(15):585-90.
8 Kung T, Szabo T, Springer J, Doehner W, Anker SD, von Haehling S. Cachexia in heart disease: highlights from the ESC 2010. Journal of cachexia, sarcopenia and muscle. 2011 Mar;2(1):63-9.
9 Lenk K, Erbs S, Hollriege R, et al. Exercise training leads to a reduction of elevated myostatin levels in patients with chronic heart failure. European journal of cardiovascular prevention and rehabilitation : official journal of the European Society of Cardiology, Working Groups on Epidemiology & Prevention and Cardiac Rehabilitation and Exercise Physiology. 2011 Mar 14.
10 Bamman MM. Regulation of muscle size in humans: role of myostatin? Journal of musculoskeletal & neuronal interactions. 2008 Oct-Dec;8(4):342-3.
11 Burton LA, Sumukadas D. Optimal management of sarcopenia. Clinical interventions in aging. 2010;5:217-28.
12 Evans WJ. What is sarcopenia? The journals of gerontology Series A, Biological sciences and medical sciences. 1995 Nov;50 Spec No:5-8.
13 Rolland Y, Dupuy C, Abellan van Kan G, Gillette S, Vellas B. Treatment strategies for sarcopenia and frailty. The Medical clinics of North America. 2011 May;95(3):427-38, ix.
14 Waters DL, Baumgartner RN, Garry PJ, Vellas B. Advantages of dietary, exercise-related, and therapeutic interventions to prevent and treat sarcopenia in adult patients: an update. Clinical interventions in aging. 2010;5:259-70.
15 Fearon K, Evans WJ, Anker SD. Myopenia-a new universal term for muscle wasting. Journal of cachexia, sarcopenia and muscle. 2011 Mar;2(1):1-3.
16 Frost HM. On our age-related bone loss: insights from a new paradigm. Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research. 1997 Oct;12(10):1539-46.
17 Ducher G, Jaffre C, Arlettaz A, Benhamou CL, Courteix D. Effects of long-term tennis playing on the muscle-bone relationship in the dominant and nondominant forearms. Canadian journal of applied physiology = Revue canadienne de physiologie appliquee. 2005 Feb;30(1):3-17.
18 Pang MY, Eng JJ. Muscle strength is a determinant of bone mineral content in the hemiparetic upper extremity: implications for stroke rehabilitation. Bone. 2005 Jul;37(1):103-11.
19 Szulc P, Beck TJ, Marchand F, Delmas PD. Low skeletal muscle mass is associated with poor structural parameters of bone and impaired balance in elderly men–the MINOS study. Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research. 2005 May;20(5):721-9.
20 Tipton KD, Borsheim E, Wolf SE, Sanford AP, Wolfe RR. Acute response of net muscle protein balance reflects 24-h balance after exercise and amino acid ingestion. American journal of physiology Endocrinology and metabolism. 2003 Jan;284(1):E76-89.
21 Newsholme EA. Substrate cycles: their metabolic, energetic and thermic consequences in man. Biochemical Society symposium. 1978(43):183-205.
22 Waterlow JC. Emerging aspects of amino acid metabolism. Where do we go from here? The Journal of nutrition. 1994 Aug;124(8 Suppl):1524S-8S.
23 Waterlow JC. Whole-body protein turnover in humans–past, present, and future. Annual review of nutrition. 1995;15:57-92.
24 Waterlow JC. Protein Turnover. 1st ed: CABI; 2006.
25 MaArdle WD, Katch FI, Katch VL. Sports and Exercise Nutrition: Lippincott Williams & Wilkins; 2008.
26 Paddon-Jones D, Sheffield-Moore M, Aarsland A, Wolfe RR, Ferrando AA. Exogenous amino acids stimulate human muscle anabolism without interfering with the response to mixed meal ingestion. American journal of physiology Endocrinology and metabolism. 2005 Apr;288(4):E761-7.
27 Rasmussen BB, Wolfe RR. Regulation of fatty acid oxidation in skeletal muscle. Annual review of nutrition. 1999;19:463-84.
28 Ferrando AA, Sheffield-Moore M, Yeckel CW, et al. Testosterone administration to older men improves muscle function: molecular and physiological mechanisms. American journal of physiology Endocrinology and metabolism. 2002 Mar;282(3):E601-7.