David C. Nieman, Dr.P.H.
Appalachian State University

Prolonged and intensive exertion causes numerous changes in immunity in multiple body compartments. These exercise-induced immune changes occur at the same time the human body is experiencing physiologic and oxidative stress, inflammation, and suppressed function against foreign pathogens. Risk of upper respiratory tract infection (URTI) is 2-6 times higher in endurance athletes compared to controls during the 1-2 week period following competitive race events. URTI risk may be compounded when the endurance athlete goes through repeated cycles of unusually heavy exertion, has been exposed to novel pathogens, and experienced other stressors to the immune system including lack of sleep, severe mental stress, malnutrition, or weight loss.

Although endurance athletes are at increased infection risk during heavy training or competitive cycles, they must exercise intensively to contend successfully. Can athletes use nutrient supplements to counter exercise-induced inflammation and immune alterations? Supplements studied thus far include zinc, dietary fat, plant sterols, antioxidants (e.g., vitamins C and E, beta-carotene, N-acetylcysteine, and butylated hydroxyanisole), glutamine, and carbohydrate. Antioxidants and glutamine have received much attention, but the data thus far do not support their role in negating immune changes after heavy exertion. Most of the focus on nutritional countermeasures has been on carbohydrate.

Research during the 1980s and early 1990s established that a reduction in blood glucose levels was linked to hypothalamic-pituitary-adrenal activation, an increased release of adrenocorticotrophic hormone and cortisol, increased plasma growth hormone, decreased insulin, and a variable effect on blood epinephrine levels. Given the link between stress hormones and immune responses to prolonged and intensive exercise, carbohydrate compared to placebo ingestion should maintain plasma glucose concentrations, attenuate increases in stress hormones, and thereby diminish changes in immunity. Carbohydrate supplementation may also alter immunity following exercise by increasing the availability of energy substrate to immune cells. Glucose is the major energy substrate for immune cells.

Several studies with runners and cyclists have shown that carbohydrate beverage ingestion plays a role in attenuating changes in immunity when the athlete experiences physiologic stress and depletion of carbohydrate stores in response to high-intensity (~75-80% VO2max) exercise bouts lasting longer than two hours. In particular, carbohydrate ingestion (about one liter per hour of Gatorade) compared to a placebo has been linked to significantly lower blood cortisol and epinephrine levels, a reduced change in blood immune cell counts, lower pro- and anti-inflammatory cytokines, and diminished gene expression for IL-6 and IL-8 (two important cytokines) in the muscle. These data demonstrate that the endurance athlete ingesting carbohydrate during the race event experiences a much lower perturbation in hormonal and immune measures compared to the athlete avoiding carbohydrate. Overall, the hormonal and immune responses to carbohydrate compared to placebo ingestion indicate that physiologic stress is diminished.

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Today, I came across a valuable resource with free information on training and injury prevention from Michael Lovegren, MS, NASM-PES, CES who is the Content Development Coordinator for the National Academy of Sports Medicine (NASM). To access the informaiton, check out his website Kinetic Loop Training System.

By: Tyler Wallace, PES, CES

Published: 2008-06-20

 Looking for strong, firm, curved glutes? Based on a muscle activation study performed at the NASM Research Institute at the University of North Carolina, the following exercises were shown to provide the greatest activation of the gluteus maximus. More activation means more results toward your bottom goals! The study looked at what were perceived to be the best exercises for the gluteus maximus and the results showed that these four exercises provided the most recruitment. Read the rest of this entry »

By: Tyler Wallace, CES, PES

Published: 2008-06-20

Based on a muscle activation study performed at the NASM Research Institute at the University of North Carolina, the following exercises were shown to provide the greatest activation of the gluteus medius. The study looked at what were perceived to be the best exercises for the gluteus medius and the results showed that these four exercises provided the most recruitment.   Read the rest of this entry »

By: Michael Lovegren

Published: 2008-07-31

Introduction 

As gas prices continue to soar, more Americans are parking their SUVs and purchasing a bicycle to ride to and from work as an alternative way of spending money on fuel.  By bicycling to work, commuters will be able to reach their daily physical activity needs and help fight the problem of America being an obese nation.  But what if I told you that by riding your bicycle, you might be susceptible to repetitive knee injuries?   Read the rest of this entry »