The role of muscle tone in healthy body composition and metabolic health

Muscle tone is traditionally defined as the residual tension that exists in a relaxed muscle, or the passive partial contraction of the muscle during a resting state. Physical activity, especially resistance training, is considered an integral part of maintaining muscle tone by stimulating muscle protein synthesis and increasing or maintaining muscle mass. Muscle loss, on the other hand, has been associated with delayed recovery from illness, impaired wound healing, reduced resting metabolic rate, physical disability, poorer quality of life, and higher health care costs.

Body composition can be measured in multiple ways, but in general it refers to the amount and distribution of body fat and lean body mass. For example, people of the same height, gender, and weight may have different body types and different body composition depending on their percentage distribution of fat, bone, water, and muscle. Body composition measurement, in the form of lean body mass loss, has been included in the diagnostic criteria for malnutrition by the Academy of Nutrition and Dietetics. Optimal body composition has been associated with numerous health outcomes and may play an integral role in healthy aging and the risk factors for several diseases, such as cardiovascular disease, metabolic syndrome, diabetes, chronic obstructive pulmonary disease, osteoporosis, and osteoarthritis. 

Exercise, and increasing muscle mass and tone, can be an effective way to improve body composition. It has been shown to decrease body fat and increase lean body mass, thus improving overall body composition. There is support for a variety of different exercise modalities being able to improve body composition. A randomized control trial (n = 89) showed that all types of exercise can improve the body composition of individuals with a sedentary lifestyle; however, strength training programs that develop the entire body may show the greatest impact. Another randomized control trial (n = 45) found that high-intensity interval training based on running can improve the physical health of obese adolescents by improving their body composition, decreasing body fat, visceral adipose tissues, low-density lipoprotein cholesterol, and insulin resistance. A meta-analysis comparing the effectiveness of several different types of exercise for overweight and obese individuals found that combined aerobic and resistance training improved body composition and inflammatory status the most. Finally, an overview of 12 systematic reviews and 149 controlled trials concluded that exercise favorably impacted body composition by reducing total and visceral fat.

Metabolic health refers to how well the body generates and processes energy, taking into consideration cardiovascular risk, blood sugar regulation, blood pressure, and waist circumference. According to a study based on the National Health and Nutrition Examination Survey, the prevalence of metabolic health in American adults is alarmingly low, posing serious individual and public health concerns. Muscle tone, maintained through physical activity, can be a powerful regulator of insulin sensitivity and overall metabolic health, with short-term benefits stemming from each individual training session and long-term adaptations that improve overall body composition. The skeletal muscle is the largest metabolic tissue in the human body and an important site for glucose metabolism, both during exercise and while at rest. It is also regarded as an endocrine and paracrine organ, where muscle-derived proteins, called myokines, facilitate interactions between the muscles and other organs, such as the liver, pancreas, skeletal system, adipose tissues, and the cardiovascular system. During exercise, the muscles use as a source of fuel both muscle-stored glycogen and circulating plasma glucose, activating glucose metabolism through insulin-dependent mechanisms and optimizing insulin response and glucose oxidation. Routine exercise further increases skeletal muscle tone, oxidative capacity, and mitochondrial biogenesis, which in turn leads to even greater glucose uptake. Muscles also influence energy and protein metabolism throughout the body by acting as a reservoir of amino acids, which can be released when needed elsewhere in the body. An observation study found that, among people over 65 years old with normal body mass index, lower muscle mass was a risk factor for metabolic syndrome. Regular exercise and improved muscle tone may improve metabolic health and reduce the risk for metabolic disease, including type 2 diabetes, obesity, metabolic syndrome, and non-alcoholic fatty liver disease. 

What are some nutrients that can support muscle tone and healthy body composition?

Collagen peptides have been shown to support the maintenance of collagen, which is the primary structural component of connective tissues, accounting for as much as 30% of the body’s total protein. Collagen is responsible for muscle flexibility and adaptation and provides structure, support, and strength to muscles, helping them function properly. A randomized controlled trial (n = 53) found that male subjects with sarcopenia who were supplemented with collagen peptides following resistance training achieved improved body composition by increasing lean body mass more than the control group, who completed the same resistance training but without the collagen peptide supplementation. Another randomized controlled trial (n = 77) investigated the effect of collagen peptide supplementation on the body composition and muscle strength of premenopausal women and found that subjects who received the collagen peptides increased lean body mass, hand-grip strength, and leg strength significantly more than the control group.

Creatine is primarily stored in skeletal muscle and involved in muscular contractions. Both muscle strength and creatine levels naturally decline with age. Supplementation has been shown to increase intramuscular creatine concentrations, high-intensity exercise capacity, and lean body mass. A meta-analysis showed that older adults who receive creatine supplementation had increased lean body mass and muscle strength during resistance training. 

Leucine is the essential amino acid that is considered to be the most anabolic. For effective muscle stimulation and muscle protein synthesis, the International Society of Sports Nutrition recommends resistance exercise and adequate protein consumption in the range of 1.4 to 2 grams of protein per kilogram of body weight per day (g/kg/d). Higher protein intake of 2.3 to 3.1 g/kg/d may be needed to maximize the retention of lean body mass in resistance-training individuals, where the protein source should contain 700 to 3,000 mg of leucine, in addition to a balanced content of all essential amino acids. A systematic review of 16 randomized controlled studies found that individuals 65 years or older supplemented with leucine experienced beneficial effects on body weight and lean body mass.

In addition to a balanced whole foods diet rich in vitamins, minerals, phytonutrients, essential amino acids, and essential fatty acids, some other nutrients that may support muscle tone and a healthy body composition include β‐hydroxy β‐methylbutyrate, Vitamin D, and geranylgeraniol pyrophosphate.

What about weight-loss medications?

Weight-loss medications, such as glucagon-like peptide-1 receptor agonists (GLP-1 RAs), work by mimicking the GLP-1 hormone, which is released by the gastrointestinal (GI) mucosa after consuming a meal and signals to the pancreas to produce more insulin, while suppressing glucagon secretion. This may help keep the blood sugar within a normal range, reduce food intake, and slow down gastric emptying. A meta-analysis examining the effect of GLP-1 RAs on weight loss reported a modest effect in overweight and obese patients with or without type 2 diabetes mellitus; however, it also reported associated GI disturbances, such as nausea, diarrhea, and vomiting, which in certain cases could lead to acute kidney injury. Gastrointestinal issues are the most common adverse effect of the GLP-1 RAs, but others may include injection site reactions, headache, infections, abdominal pain, and pancreatitis.

With GLP-1 RAs weight loss, there is also concern about the effects on muscle mass, health, and function. In addition to the aforementioned adverse effects, GLP-1 RAs can also be associated with losing lean body mass up to 40% to 60% of total body weight, which may have an adverse effect on muscle tone, body composition, and metabolic health. While medications can be helpful in achieving weight loss, they may also be associated with considerable side effects. A regular exercise routine, together with a healthy diet and nutritional supplementation when needed, may help support body composition and metabolic health, while minimizing potential adverse effects.

Learn more about muscle tone, body composition, and metabolic health: 

Collagen Peptides to Promote Skeletal Muscle

Beyond Protein: Nutrition for Muscle Health

Impacts of Beef Protein Supplementation on Body Composition and Performance

By Antonia Toupet, PhD