The influence of alcohol on physiologic processes and exercise

Introduction 

Ethanol or alcohol is one of the most commonly used/abused drugs in human history. Alcohol can have many effects on exercise physiological performance, so it is important to distinguish between chronic use, moderate use, and abuse. Alcohol is a mind-altering drug that reduces thinking ability, distorts judgment, and acts as a depressant on the body. Research has suggested that alcohol leads to increased dopamine release in the human brain, bringing on feelings of relaxation and happiness. Although this drug is often used during recreation for the purpose of feeling good, it should not be used in combination with exercise because of the serious negative physiological effects it has on the body.

Endocrine System Effects

One of the most easily observable effects of alcohol on the body is dehydration. When alcohol is consumed, anti-diuretic hormone (ADH) is inhibited, causing less water to be absorbed back into the nephrons in the kidneys when urine is cycling through. This causes urine levels to increase, leading to more frequenct urination. With higher levels of water exiting the body, dehydration is likely to occur. This is especially a problem during exercise, when the body is also expelling water in the form of sweat. It is important to be fully hydrated for a workout; therefore, it is dangerous to consume alcohol before or during exercise. Research has suggested that beverages containing up to 4% alcohol can delay the recovery process from dehydration to rehydration. This prevention from reaching rehydration in a timely manner could be deadly in a situation regarding exercise.

Cardiovascular System Effects

Another important physiological effect that alcohol has on the body deals with blood pressure. Alcohol consumption increases blood and plasma volume, which in turn increases blood pressure. Exercise has a similar effect; the sympathetic immune system is stimulated, leading to vasoconstriction and ultimately increasing blood pressure. To practice safe exercise, it is important to not have an elevated blood pressure beforehand. Research has recommended that alcohol consumption be reduced in order to maintain healthy and safe blood pressure levels. Likewise, it is unsafe to consume alcohol before or during exercise because blood pressure levels may rise to dangerous levels.

Perhaps the most important physiological effect that alcohol has on the body is that which concerns the heart. Research has shown that intoxication by alcohol directly relates to impairment of cardiac contractility. Depending on how much alcohol was consumed, cardiac contractility was impaired at varying levels; a lighter intoxication lead to minimal impairment, while higher levels of intoxication lead to greater impairment. Exercise causes heart rate to increase, requiring a great deal of cardiac contractility. If the heart is impaired because of alcohol intoxication, blood may not be pumped sufficiently throughout the body during exercise. Therefore, if a person plans on exercising, they should either drink lightly or not at all in an attempt to keep their heart working properly. 

Alcohol can also induce oxidative stress resulting in cardiac dysfunction. However, with exercise the oxidative damage can be reduced by use of the antioxidant system. Most of the negative effects of increased oxidative stress can be seen in aerobic exercise (800m/1500m). 

According to O'Brien and Lyons, medical hazards for athletes can be related to alcohol consumption prior to an exercise activity or performance. A specific health hazard created by alcohol is the reduction in the contraction strength of the left ventricle of the heart resulting in a decreased ability to pump blood to the body. In addition, alcohol consumption has also been found to potentially cause cardiac arrhythmias, which could lead to a major health issue for an athlete.

Muscular System Effects 

Additionally, alcohol negatively affects the skeletal muscle substrate utilization. By decreasing glucose and amino acid utilization, there is decreased energy supply available to the muscle. Alcohol has also been shown to prevent muscle function by impairing the excitation/contraction coupling because the inhibition of calcium channels in the sarcolemma. Furthermore, post-exercise alcohol intake, an activity often celebrated amongst team sport athletes, has been shown to inhibit the necessary recovery and adaptation process. For muscles to hypertrophy (enlarge) and generate adaptations following exercise, production of myofibrillar proteins must supersede the breakdown of myofibrillar proteins. Research shows that consuming large amounts of alcohol inhibits the synthesis of myofibrillar proteins during recovery from resistance, continuous, or intermittent high-intensity exercise. This suppression of the skeletal muscle's anabolic response necessary for muscle adaptation, repair, and regeneration is likely caused by the oxidative stress and inflammation generated by alcohol consumption. This stress disturbs the endoplasmic reticulum's homeostasis, therefore disrupting its ability to properly fold and ship proteins around the cell.

The American College of Sports Medicine (ACSM) maintains a position related to alcohol consumption and exercise, stating that alcohol use will not increase exercise performance. Use of alcohol before performing a physical activity can affect an athlete by decreasing "reaction time, hand-eye coordination, accuracy, balance, and complex coordination." While some athletes partake in alcohol consumption to help with reducing nervousness or increasing confidence before an athletic performance, the ACSM argues that an athletes psychomotor skills and ability to process information, for rapid adaptations, will be negatively affected. Ingestion of alcohol will also affect many of the body's natural response mechanisms to exercise. Blood glucose levels can be affected during exercise due to consumption of alcohol prior to activity, which can lead to hypoglycemia. According to the ACSM, alcohol "will not improve and may decrease strength, power, local muscular endurance, speed, and cardiovascular endurance." There is evidence suppporting ACSM's proposal that alcohol may decrease power in exercise. Lecoultre and Schutz (2009) studied a group of well-trained male cyclists to determine the effects of an acute consumption of alcohol on cyclists during a 60-minute cycling endurance performance test. The results showed a significant decrease of power output (PO) in the ethanol group from the second 10-minute mark to the end of the test when compared to the PO of the control group.

Implications for Physical Therapy 

When working with a patient that consumes alcohol, it is important to keep in mind its effect on blood pressure, blood glucose, heart rate, and skeletal muscle substrate utilization. Hydration is also critical for those patients who drink alcohol to avoid becoming dehydrated, particularly if working out in hot or humid environments. Blood pressure should be checked before exercise to ensure it is within appropriate limits, and monitored throughout the bout of exercise. Athletes should also be informed of the negative effects on performance that alcohol elicits, as well as the hindrance post-exercise consumption has on muscular adaptation and repair.  .