what are antibiotics and how they affect exercise?

Any substance that inhibits the growth and replication of a bacterium or kills it outright can be called an antibiotic. Antibiotics are a type of antimicrobial designed to target bacterial infections within (or on) the body. This makes antibiotics subtly different from the other main kinds of antimicrobials widely used today:

  • Antiseptics are used to sterilise surfaces of living tissue when the risk of infection is high, such as during surgery.
  • Disinfectants are non-selective antimicrobials, killing a wide range of micro-organisms including bacteria. They are used on non-living surfaces, for example in hospitals.

Of course, bacteria are not the only microbes that can be harmful to us. Fungi and viruses can also be a danger to humans, and they are targeted by antifungals and antivirals, respectively. Only substances that target bacteria are called antibiotics, while the name antimicrobial is an umbrella term for anything that inhibits or kills microbial cells including antibiotics, antifungals, antivirals and chemicals such as antiseptics.

Most antibiotics used today are produced in laboratories, but they are often based on compounds scientists have found in nature. Some microbes, for example, produce substances specifically to kill other nearby bacteria in order to gain an advantage when competing for food, water or other limited resources. However, some microbes only produce antibiotics in the laboratory

How do antibiotics work?

Antibiotics are used to treat bacterial infections. Some are highly specialised and are only effective against certain bacteria. Others, known as broad-spectrum antibiotics, attack a wide range of bacteria, including ones that are beneficial to us.

There are two main ways in which antibiotics target bacteria. They either prevent the reproduction of bacteria, or they kill the bacteria, for example by stopping the mechanism responsible for building their cell walls.

Why are antibiotics important?

The introduction of antibiotics into medicine revolutionised the way infectious diseases were treated. Between 1945 and 1972, average human life expectancy jumped by eight years, with antibiotics used to treat infections that were previously likely to kill patients. Today, antibiotics are one of the most common classes of drugs used in medicine and make possible many of the complex surgeries that have become routine around the world.

If we ran out of effective antibiotics, modern medicine would be set back by decades. Relatively minor surgeries, such as appendectomies, could become life threatening, as they were before antibiotics became widely available. Antibiotics are sometimes used in a limited numbers of patients before surgery to ensure that patients do not contract any infections from bacteria entering open cuts. Without this precaution, the risk of blood poisoning would become much higher, and many of the more complex surgeries doctors now perform may not be possible.


Antibiotics and running performance

Antibiotics work against bacterial infections such as strep throat, ear infections, bladder infections as well as many types of skin infections.

The work “Antibiotic” is derived from the Greek word anti meaning “against” and bios meaning “life” the medicine works by destroying the growth of bacteria.

Antibiotics work in two primary ways:

  1. Bactericidal antibiotics kill bacteria. Penicillin is a very common bactericidal and interferes with the cell wall formation of the bacteria or the contents within the bacterium’s cell.
  2. Bacteriostatic antibiotics prevent the bacteria from multiplying.

Essentially, antibiotics create a war within your body that can seriously affect your running performance. During a long distance race, you need your body to be firing on all cylinders.

If your body is using a lot of its “fighting” power to deal with antibiotics in your system, there are a few symptoms that you can expect to show up in your athletic performance.

Symptom #1: Increased sensitivity to heat/dehydration:

The sulfa-based class of antibiotics add a heightened possibility of increased sun sensitivity.

Given the fact that most endurance events in general and marathons in particular are raced outdoors, on city streets, often with very little cloud cover, this can be a recipe for disaster.

Sunburn and other heat-related health concerns are already high in an outdoor event that takes several hours to complete, but are often increased by the use of sulfa-based antibiotics.

Heat exhaustion, heat stress, and heat stroke are less common but far more dangerous potential consequences of increased sun sensitivity.

A sensible recommendation for athletes on antibiotics is a reduced amount of intensity and volume of exercise as well as increased fluid intake and sun protection.

With the nature of the marathon itself, a notoriously grueling, almost always dehydrating, 26.2 mile event of both incredible volume and intensity, it is almost certain those runners who choose to race a marathon while on antibiotics must take extra precaution and expect significant pace differences.

It is incredibly difficult for a healthy, fit athlete to hydrate properly during a marathon and that difficulty is compounded for the athlete racing while on antibiotics.

Symptom #2: Slower pace

Runners, cyclists, and other endurance athletes alike have reported slower training and racing paces while on antibiotics.

When antibiotics are taken for an illness rather than a skin infection, athletes may blame the decrease in pace (or increase in effort at the same pace) on the illness rather than the antibiotic.

However, even athletes taking antibiotics for an infection of the skin have reported slower racing and training paces.

It is certainly true, however, that certain illnesses may contribute to poor training and racing paces as well.

Another fallacy is assuming that athletes simply “talk themselves out of” running fast while on antibiotics because they expect times to be slower.

A simple example that debunks this theory is the famous story of a horseback rider who reported a 10mph pacing difference for a horse who had been taking antibiotics to clear up a skin rash on his belly.

The horse who normally cantered a morning run at about 25mph dropped instantly to 15mph on the same loop, with the same perceived effort, while on antibiotics.

This disproves the idea that poor racing and training on antibiotics is a mental weakness, as the horse was not aware that he was taking antibiotics.

Symptom #3: Dizziness and stomach upset

Many antibiotics cause diarrhea and stomach upset due to bacterial changes in the intestines and stomach. As the normal bacteria levels in the body are changing, the body’s balance is compromised.

Diarrhea is not only annoying during an endurance event, it can also be dangerous as much more water is lost during diarrhea rather than solid bowel movements. Probiotics, as found in yogurt with live cultures, can help reduce the risk of diarrhea that is caused by the use of antibiotics.

As fluid is lost through sweating associated with increased sun-sensitivity and diarrhea, dizziness and fainting may occur for the endurance athlete, as well as muscle cramping, fatigue, and headache.

These issues are most often seen within the first 2-3 days after starting the use of the antibiotic, but can last much longer in some cases, particularly for athletes.

Symptom #4: Tendon rupture:

One of the common side affects of certain antibiotics is tendon rupture. The class of antibiotics that tendon rupture is associated with is called Fluoroquinolones, one of which is the commonly used antibiotic Levaquin.

The issues associated with this type of antibiotic range from paisn and discomfort in the tendon to complete tears.

Though tendons are most often torn during sprinting and jumping events, long distance runners taking this type of antibiotic should either avoid exercise if it is absolutely necessary to be on the antibiotic, or switch to a different type of antibiotic.

In either case, communication with a doctor and self-research into the topic are absolutely vital.

What if you have no choice but to race while on antibiotics?

If the use of antibiotics is absolutely necessary and you have no intention of giving up a special goal race:

  • Make sure you communicate with your coach, your doctor and your support team out on the course:
  • Your coach may recommend that you decrease your training load by about 25%, but ultimately, the decision to continue training and/or racing is up to you and your doctor.
  • It is important to have a support crew on race day that can provide you with the extra water, electrolytes and sun protection you may need.
  • Consider keeping a journal as you move closer to race day. Tracking your fatigue levels and hydration needs during your training runs may help to give you a good picture about what to expect on race day.

I hope Debra’s story and this research and these recommendations can help you plan and adapt your training and racing should you need to take antibiotics.

source: microbiologysociety.org

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Itoh Z, Suzuki T, NakayaM, et. al. Gastrointestinal motor-stimulating activity of macrolide antibiotics and analysis of their side effects on the canine gut. American Society for Microbiology.1984: 26(6) 863-869

Norrby SR. Side effects of quinolones: comparisons between quinolones and other antibiotics. European Journal of Clinical Microbiology. 1991: 4(6)378-383

McGarvey WC, Singh D, Trevino SG. Partial achilles tendon rupture associated with fluoroquinolone antibiotics: a case report and literature review. Foot and Ankle International. 1996: 17(8)496-498