Muscle growth: Don’t overlook the role of blood flow

When talking about muscle growth, people typically focus on protein turnover and the various aspects that influence both protein synthesis and breakdown. However, the importance of blood flow and the role it plays in muscle hypertrophy (muscle cell increase/growth) are often underemphasized and overlooked. Understanding the mechanics of how the body transports nutrients, and then how these nutrients interact with hormones and vasodilators to produce physiological change, is not easy. Examining some of the science surrounding blood flow and exercise as relates to, and intersects with, nutrition can provide meaningful background on what has become a category within sports nutrition.

After resistance exercise to failure (typically many repetitions), intramuscular adenosine triphosphate (ATP) and creatine phosphate (CP) levels become depleted while adenosine diphosphate (ADP), adenosine monophosphate (AMP), adenosine, lactate and nitric oxide (NO) increase. These metabolites either directly or indirectly increase blood flow to the muscle. This contributes to muscle hypertrophy along with cellular swelling and changes in metabolites, referred to as “metabolic stress.”^1,2 In addition, enhanced blood flow to an exercising muscle may delay fatigue, and allow for increased training volumes and/or recovery, therefore potentially leading to enhanced muscle growth and function indirectly. Due to the increased awareness of the role blood flow plays in muscle hypertrophy, several supplements have been marketed to enhance blood flow through various mechanisms.

Perhaps the most popular are the ingredients related to enhancing blood flow via NO, which stimulates vasodilation and is formed from L-arginine.² Therefore, supplementation with arginine is said to increase NO and thus, blood flow. Arginine supplementation has been shown to enhance exercise performance in athletes and active adults through an increased time to exhaustion,³ improved recovery⁴ and delayed muscular fatigue.^5,6 The bioavailability of arginine has been questioned and therefore, in order to enhance absorption, inositol-stabilized arginine silicate (ASI, as Nitrosigine from Nutrition 21), a sports nutrition ingredient, has been tested and shown to increase blood levels of arginine and NO.⁷

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Susan J. Hewlings, Ph.D., R.D., is the co-founder of Substantiation Sciences, a professor at Central Michigan University, director of scientific affairs for Nutrasource Diagnostics Inc. and chief science director for IgY Nutrition. Hewlings specializes in substantiation from study design to publication. She has over 15 years of experience in the industry, and has published in multiple peer-reviewed journals, textbooks and trade publications.

Douglas Kalman, Ph.D., R.D., has been involved in over 250 clinical trials and projects within the pharmaceutical, medical and nutrition fields. He has published more than 75 abstracts and 30 peer- reviewed manuscripts. He is co-editor of the scientific journal The International Society of Sports Nutrition (ISSN) and serves on the editorial board of three others. Kalman is one of the co-founders of ISSN. He has worked in collegiate and Olympic sports nutrition, as well as being an adjunct professor at Nova Southeastern University in Davie, Florida. Kalman recently joined Nutrasource as the vice president of scientific affairs.

References

1. Gundermann DM et al. "Reactive hyperemia is not responsible for stimulating muscle protein synthesis following blood flow restriction exercise." Journal of Applied Physiology. 2012;112(9):1520-1528.

2. Cholewa J et al. "Effects of dietary sports supplements on metabolite accumulation, vasodilation and cellular swelling in relation to muscle hypertrophy: A focus on 'secondary' physiological determinants." Nutrition. 2019;60:241-251.

3. Yavuz HU, Turnagol H, Demirel AH. "Pre-exercise arginine supplementation increases time to exhaustion in elite male wrestlers." Biology of Sport. 2014;31(3):187-191.

4. Rector TS et al. "Randomized, double-blind, placebo-controlled study of supplemental oral L-arginine in patients with heart failure." Circulation. 1996;93(12):2135-2141.

5. Schaefer A et al. "L-arginine reduces exercise-induced increase in plasma lactate and ammonia." International Journal of Sports Medicine. 2002;23(6):403-407.

6. Dong JY et al. "Effect of oral L-arginine supplementation on blood pressure: a meta-analysis of randomized, double-blind, placebo-controlled trials." American Heart Journal. 2011;162(6):959-965.

7. Kalman DS et al. "A clinical evaluation to determine the safety, pharmacokinetics, and pharmacodynamics of an inositol-stabilized arginine silicate dietary supplement in healthy adult males." Clinical Pharmacology : Advances and Applications. 2015;7:103-109.