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muscled guy military pressInsulin Causes Vasodilation in Muscle by: Robbie Durand, M.A., C.S.C.S.

Nothing beats a good pump in the gym. Getting a good pump is determined by nitric oxide production in the body, but in addition to taking a nitric oxide precursor; a good insulin spike will also lead to better pumps.

It is well known that insulin is needed for glucose transport into the cells. Insulin can also redirect nutrient blood flow to capillary beds in skeletal muscle leading to enhance blood flow. It has been demonstrated that, within minutes, insulin significantly increases vasodilation in resting skeletal muscle (1). That’s right, if you just drink water during your workouts you may be missing out on insulin’s vasodilating effects on muscle. Insulin enhances both skeletal muscle glucose uptake and total leg blood flow in a dose-dependent fashion (2, 3) (the more insulin is increased, the greater the increase in blood flow.) Studies have shown that insulin-induced increases in total muscle blood flow temporally lag behind the stimulation of muscle glucose uptake (2).

The exact mechanisms by which insulin increases blood flow is unknown but it is speculated to be the result from either a direct vasodilator action of insulin (via receptors on the vascular cells) or indirectly from a signal generated from the stimulation of metabolism within skeletal muscle cells. Insulin could act similar to exercise-induced hyperemia, (Hyperemia describes the increase of blood flow in response to exercise), where muscle blood flow increases to provide sufficient oxygen and nutrients to support muscle contraction. NO is one of many vasodilators found in the vascular system; there is evidence for the involvement of adenosine, potassium, and lactate (6). It is conceivable that any one of these could mediate the increased flow in response to insulin.

Insulin has an effect on increasing NO production, which may be the partial reason for its effects on vasodilation (12). The observation that inhibition of nitric oxide (NO) synthase by the nitric oxide inhibitor (L-NMMA) abolishes insulin-induced increases of leg blood flow in humans and diminishes (~25%) glucose uptake4 suppors a physiological role for insulin action on muscle vasodilation4.

High Intensity Exercise is Key for Nitric Oxide Production

During resistance exercise when skeletal muscle contracts, the number of capillaries that control blood flow open up several-fold – this depends on the exercise intensity. To get a good pump, exercise needs to be performed with high intensity. Higher-intensity exercise both enhances vasodilation and increases total blood flow. Studies have shown that low-intensity forearm exercise increases vasodilation without changing total forearm blood flow, whereas higher-intensity exercise increases both forearm blood flow and vasodilation (5). So to get the most of a muscle pump, use high intensity exercise with large muscle groups, and with short rest periods. Training harder causes physiological adaptations which leads to better pumps and more blood flow.

Trained athletes have elevated basal blood flow to muscle during exercise compared with untrained individuals8. Insulin may be part of the answer to this, as Hardin et al.9 demonstrated that insulin-stimulated blood flow was 31% higher in athletes than in controls.

Being a Porker with Insulin Resistance Causes Reduced Blood Flow

If you have a lot of fat on you, you won’t get the same kind of increase in muscle blood flow as someone who is leaner. Insulin, it has been well documented, increases forearm blood flow, but in obese patients there is impaired forearm blood flow compared to lean individuals. The overweight subjects were also more insulin resistant than their leaner controls. In summary, the reduced increase in muscle blood flow in obese subjects was associated with a decline in skeletal muscle insulin-mediated glucose uptake; this suggests insulin resistance.

Furthermore, Dela et al. (10) found that insulin-stimulated blood flow increased after 10 weeks of one-legged training in both healthy subjects and type 2 diabetic patients. The increase in insulin stimulated blood flow was thought to increase in both healthy and diabetic individuals due to increased insulin sensitivity in muscle. So is it glucose or insulin that causes the vasodilation in muscle endothelium? Both need to be present for optimal vasodilation. Intra-arterial infusion of insulin in physiological doses causes forearm vasodilation, which is increased by co-infusion of glucose, leading researchers to speculate that local insulin-mediated vasodilation may depend on insulin-mediated glucose uptake in muscle (14).

Studies by Vollenweider et al (7). have suggested that increased muscle cell glucose metabolism, needed to generate a metabolic vasodilator response, fails to cause vasodilation in the absence of insulin. Whereas combined insulin and glucose infusion significantly increased calf blood flow, there was no such increase during fructose infusion in which insulin levels remained low, but a similar rise in carbohydrate oxidation was achieved.

NSAIDS and High Fat Diets: Pump Killers

As discussed previously, insulin is needed for a good vasodilatory response in blood vessels. If you want to get a better pump during your workouts you need to spike your glucose levels before exercise to get a good insulin response. Now let’s look at some of the pump killers… NO and cyclooxygenase (COX) produce important mediators of vasodilation. The regulation of these enzymes and their capacity to participate in molecular cross-talk is important for vasodilation. COX-2 is mediated in the pain and inflammation response, with many NSAIDS and prescription drugs targeting the COX-2 enzyme for pain relief.

By taking NSAIDS (which blocks all COX enzymes) muscle vasodilation is reduced. Insulin induces an endothelium-dependent vasodilation in normal arteries; however, it has been demonstrated that the mechanism is primarily COX enzyme dependent (11). Another big mistake is to eat a high fat meal before a workout; a high fat meal before exercise can antagonize insulin-mediated glucose uptake. Additionally, the infusion of fatty acids has been shown to reduce insulin mediated glucose uptake in skeletal muscle (13).

It makes sense to get a better pump in the gym and load up on your nitric oxide supplement; but be sure to wash it down with a high carbohydrate/ amino acid beverage to increase vasodilation.


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2. Baron A: Hemodynamic actions of insulin. Am J Physiol267 :E187 –E202,1994.

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4. Steinberg HO, Brechtel G, Johnson A, Fineberg F, Baron AD: Insulin-mediated skeletal muscle vasodilation is nitric oxide dependent: a novel action of insulin to increase nitric oxide release. J Clin Invest 94 :1172 –1179,1994.

5. Jahn L, Vincent MA, Lindner JR, Barrett EJ: Modest exercise enhances human skeletal muscle perfusion by capillary recruitment in the absence of changes in total blood flow. Diabetes51 (Suppl. 2) :A59 ,2002.

6. Segal, SS. Convection, diffusion and mitochondrial utilization of oxygen during exercise. In: Perspectives in Exercise Science and Sports Medicine Vol 5: Energy Metabolism in Exercise and Sport, edited by Lamb DR, and Gisolfi CV.. Dubuque, Iowa, XX: Brown & Benchmark, 1992, p. 269-344.

7. Vollenweider, P, Tappy L, Randin D, Schneiter P, Jequier E, Nicod P, and Scherrer U. Differential effects of hyperinsulinemia and carbohydrate metabolism on sympathetic nerve activity and muscle blood flow in humans. J Clin Invest 92: 147-154, 1993.

8. Ebeling, P, Bourey R, Koranyi L, Tuominen JA, Groop LC, Henriksson J, Mueckler M, Sovijarvi A, and Koivisto VA. Mechanism of enhanced insulin sensitivity in athletes. Increased blood flow, muscle glucose transport protein (GLUT-4) concentration, and glycogen synthase activity. J Clin Invest 92: 1623-1631, 1993.

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10. Dela, F, Larsen JJ, Mikines KJ, Ploug T, Petersen LN, and Galbo H. Insulin-stimulated muscle glucose clearance in patients with NIDDM. Effects of one-legged physical training. Diabetes 44: 1010-1020, 1995.

11. Miller AW, Tulbert C, Puskar M, Busija DW. Enhanced endothelin activity prevents vasodilation to insulin in insulin resistance. Hypertension. 2002 Jul;40(1):78-82.

12. Scherrer U, Randin D, Vollenweider P, Vollenweider L, Nicod P. Nitric oxide release accounts for insulin’s vascular effects in humans. J Clin Invest. 1994;94:2511–2515.

13. Clerk LH, Rattigan S, Clark MG: Lipid infusion impairs physiologic insulin-mediated capillary recruitment and muscle glucose uptake in vivo. Diabetes51 :1138 –1145,2002.

14. Ueda S, Petrie JR, Cleland SJ, Elliott HL, Connell JM. Vasodilator response to local hyperinsulinemia. Hypertension. 1999 Dec;34(6):e12-3.