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Insulin Resistance in the Older Athlete and its Effects on Hypertrophy

As the popularity of bodybuilding has increased, there’s been an influx of athletes into the masters divisions. And for good reason. Science has demonstrated that men and women aged 50 to 100 can make 50 to 60 percent increases in muscle cell size, 60 to 260 percent elevations in isometric (handgrip) and dynamic (free weights/machines) strength1, 2 and 30 percent increases in power in just 12 to 16 weeks.3

While those gains are impressive, research has also shown that masters-aged individuals experience lower mass and strength gains than their younger counterparts.4 Why? During any training protocol your muscle tissue experiences trauma, with the time following training known as the regeneration period. That’s when muscle tissue is repaired and—you hope—increases in size and contractile capability.

The regeneration process itself relies highly on two factors: 1) the nutrients taken in following exercise and 2) the body’s anabolic response to those nutrients. It appears that older persons exhibit a blunted response to the nutrients, which may explain the impaired recovery following exercise.

In the January ’09 IRON MAN we explained that masters-level athletes lose their sensitivity to the essential amino acids responsible for stimulating growth and that, according to research, if they took in enough protein, 30 to 40 grams per meal, or essential amino acids, 15 grams per meal, they could overcome the insensitivity. While amino acids are the major components stimulating skeletal muscle protein synthesis following a meal, they’re only one part of the equation. An additional factor is the release of the hormone insulin.

Insulin’s Role in Protein Synthesis

After you digest carbohydrates, blood glucose is elevated. It then must be stored in cells, such as muscle tissue. That doesn’t happen, though, unless insulin is released from the pancreas, binds to the muscle and signals it to increase the uptake of glucose. Insulin has another role, however. Studies show that in young people eating carbohydrates increases protein synthesis beyond what happens with amino acids alone.

One mechanism behind that increase in protein synthesis is insulin’s ability to increase blood flow to skeletal muscle after a meal.5 Paradoxically, protein synthesis is actually blunted in older people when insulin is increased following the addition of carbohydrates to a protein source!5 It appears that older people become resistant to insulin’s effects, which may explain loss of muscle with age, as well as a decreased ability to recover following training.6 Evidence to support that is found in other conditions that reflect impaired insulin action, such as type 2 diabetes, or low insulin concentrations, such as type 1 diabetes, in which muscle wasting increases.

Insulin’s Actions on Blood Flow—Identifying the Problem in Aged Muscle

In older people blood flow does not increase following insulin or carbohydrate administration.7 Changes in blood flow are a result of signaling molecules that stimulate either vasodilation or vasoconstriction. Nitric oxide enhances blood flow, and endothelin-1 restricts it, either by directly constricting blood vessels or by suppressing NO production. So if your body has more NO than ET-1, blood flow increases. That’s how insulin works: It stimulates capillaries to produce more NO and thus trigger vasodilation and amino acid–rich blood flow delivery to muscles.

A recent study found that older individuals have up to 130 percent more endothelin-1 in their blood than do younger people.8 That suggests that in the elderly, insulin may not be able to overcome elevated levels of the powerful vasoconstrictor ET-1. The result is that masters-aged individuals have an impaired muscle growth response following a carbohydrate-and-protein meal. Given those findings, let’s look at two methods of overcoming insulin resistance in masters-aged athletes.

Method 1: Dietary Modifications

In general the masters athlete should seek to maximize insulin sensitivity, as studies show that taking in carbohydrates in an insulin-resistant state can impede muscle growth. Below are three dietary interventions for increasing insulin sensitivity and anabolism.

Ratio of carbohydrates to protein. The fact that insulin impairs protein synthesis in older muscles has spurred scientists to suggest that aging people need a higher protein-to-carbohydrate ratio. That shifts the reliance away from insulin to stimulate muscle growth. More important is that the technique reverses insulin resistance. Standard nutrition recommendations are to take in 3.5 grams of carbohydrates for every gram of protein. Research from Gabriel’s lab at the University of Illinois, however, has demonstrated that lowering it to 1.5 grams of carb results in improved insulin sensitivity, fat loss and greater increases in muscle during training.9,10 Thus, we recommend eating no more than one to 1 1/2 grams of carbohydrates per gram of protein at a meal.

Type of carbohydrate. The impact that a carbohydrate will have on insulin depends on its fiber content. Eating processed carbohydrates with little to no fiber will result in high releases of insulin following a meal. Chronically elevated insulin counts will only further augment insulin resistance with age. We recommend that people consciously include fibrous carbohydrates in their diet, such as oatmeal, sweet potatoes, leafy green vegetables and other foods high in fiber.

The need for greater amounts of fat. When carbohydrate intake declines, the body begins to rely on muscle tissue for fuel to a greater extent, particularly during a diet. Thus, as one energy source is lowered (carbohydrates), the need to increase an alternative energy source (fats) is elevated. Fat has several anabolic properties, including increasing testosterone production and sparing amino acids from degradation. In general, we recommend that people follow a diet rich in essential fatty acids, particularly omega-3 fatty acids, such as those in fish oil, as well as monounsaturated fatty acids of the kind found in olive oil and avocados.

Method 2: Cardiovascular Exercise—The Final Antidote to Impaired Blood Flow?

Researchers have determined what techniques can actually lower ET-1. Intriguingly enough, it has been shown that three months of aerobic exercise decreases ET-1 concentrations in both young and elderly subjects.6 Moreover, 45 minutes of moderate-intensity treadmill running in 13 men and women 70 years of age completely restored insulin-induced increases in protein synthesis.6 Those changes were associated with a drop in ET-1.

That’s why we recommend that masters athletes perform a minimum of three to five cardiovascular sessions per week at moderate intensity, for a duration of 30 to 45 minutes. That alone should restore ET-1 to youthful concentrations, thereby reestablishing their ability to recover after training pretty much the way younger athletes do.

Practical Applications

We recommend that masters athletes do the following:

• Eat no more than one to 1 1/2 grams of carbohydrates for each gram of protein.

• Eat starchy carbohydrates during the first half to two-thirds of the day, with leafy vegetables the main source in the evening.

• Choose fibrous and unprocessed carbohydrates so you get 25 to 30 grams of fiber per day, with an upper limit of 50 grams.

• For very-low-carb meals or meals that contain only leafy green vegetables, increase your fat intake with such healthful fats as fish oils, olive oil or avocados.

• Perform a minimum of three strenuous 30-to-45-minute aerobic workouts per week.

Decades ago we hadn’t even scratched the surface of researching the differences between older and younger athletes and how they respond to training. Now, with thousands of studies at our fingertips, we can erase the common deficit seen between young and masters athletes. Use the information to become a better, healthier bodybuilder, no matter what your age.

Editor’s note: Gabriel Wilson is completing his Ph.D. in nutrition with an emphasis on optimal protein requirements for muscle growth and is a researcher in the Division of Nutritional Sciences, University of Illinois, Urbana. He is vice president of the Web site Jacob Wilson is a skeletal-muscle physiologist and researcher in the Department of Nutrition, Food, and Exercise Science, Florida State University, Tallahassee. He is president of the Web site

1 Pyka, G., et al. 1994, Muscle strength and fiber adaptations to a year-long resistance training program in elderly men and women. J Gerontol. 49(1):M22-27.
2 Singh, M.A., et al. (1999). Insulinlike growth factor 1 in skeletal muscle after weightlifting exercise in frail elders. Am J Physiol. 277(1 Pt 1):E135-143.
3 Hakkinen, K., et al. (1998). Changes in muscle morphology, electromyographic activity, and force production characteristics during progressive strength training in young and older men. J Gerontol A Biol Sci Med Sci. 53(6):B415-423.
4 Kosek, D.J., et al. (2006). Efficacy of 3 days/wk resistance training on myofiber hypertrophy and myogenic mechanisms in young vs. older adults. J Appl Physiol. 101(2):531-544.
5 Volpi, E., et al. (2000). The response of muscle protein anabolism to combined hyperaminoacidemia and glucose-induced hyperinsulinemia is impaired in the elderly. J Clin Endocrinol Metab. 85(12):4481-4490.
6 Fujita, S., et al. (2007). Aerobic exercise overcomes the age-related insulin resistance of muscle protein metabolism by improving endothelial function and Akt/mammalian target of rapamycin signaling. Diabetes. 56(6):1615-1622.
7 Meneilly, G.S., et al. (1995). Insulin-mediated increase in blood flow is impaired in the elderly. J Clin Endocrinol Metab. 80(6):1899-1903.
8 Maeda, S., et al. (2003). Aerobic exercise training reduces plasma endothelin-1 concentration in older women. J Appl Physiol. 95(1):336-341.
9 Layman, D.K. (2003). The role of leucine in weight-loss diets and glucose homeostasis. J Nutr. 133(1):261S-267S.
10 Layman, D.K., et al. (2003). Increased dietary protein modifies glucose and insulin homeostasis in adult women during weight loss. J Nutr. 133(2):405-410. IM

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