Writers and researchers have been busy lately over at the British Medical Journal. They just released not one but seven articles basically debunking many long held beliefs about exercise, sports drinks, hydration, performance and recovery. In the article I’m discussing today, the BMJ presents evidence that either refutes or calls into question several things that athletes have taken as fact for many years by taking a deeper look at the studies and evidence long thought to support them. Here follows a list of myths that the BMJ claims to have busted.
1. The Color of Urine Accurately Reflects Hydration
I have to say that I have used this idea for years, instructed my athletes, and judged my own hydration by this measure. Think about it. It makes sense. If you don’t have enough water in your system, your urine is a dark yellow. Add water, get your system hydrated so that now you can produce more waste, the color of your urine is either very light or clear.
What we’ve been told. Antidiuretic hormone is secreted by the posterior pituitary gland as a result of dehydration, resulting in increased water absorption in the collecting ducts of the kidneys. This decreases urine output and concentrates the solutes (including urea, uric acid, creatinine), leading to a darker color of urine. After fluid ingestion less water needs to be reabsorbed to maintain homeostasis so larger quantities of pale urine are produced. (source)
What the BMJ says. They found only eight low-quality studies that have different conclusions. Because there is no objective measure of hydration, and there is no way to determine over-hydration, three studies stated that urine color was not a useful tool for determining hydration, while three studies decided that is was useful when accurate results were not required. Two other said that urine color can be useful, but only in certain situations and at certain times (like the first morning void).
Because certain medications can interfere with urine color, untrained people are less likely to distinguish their urine color than investigators, and because none of the studies looked at the possibility of overhydration which can lead to hyponatremia, the BMJ’s conclusion is that urine color is not a consistently useful, or even safe way to determine adequate hydration.
2. You Should Drink Before You Feel Thirsty
We’ve been told for years that by the time we feel thirsty we are already dehydrated, therefore it is important to drink before we have the urge. Sports drink makers tell us that we must drink before, during and after sport in order to enhance or maintain performance levels, and that if we do this, we may be able to “teach” our system to tolerate even more fluids.
The idea behind this is that when we sweat, our concentration of sodium rises, causing an increase in osmotic pressure and intracellular dehydration. All this works to stimulate thirst, but, according to the theory, we are already partially dehydrated.
What we’ve been told. When the body loses fluid due to sweat, the extracellular concentration of sodium rises leading to a subsequent increase in osmotic pressure and intracellular dehydration. Osmoreceptors in the hypothalamus detect dehydration and signal other parts of the brain to stimulate the sensation of thirst. In extreme conditions such as malnutrition or when children are left in hot cars failure to react to thirst sensations by consuming fluid can have fatal consequences. (source)
What the BMJ says. Reviews of the performance of elite athletes showed better performance when their drinking was driven by thirst. One study found that performance levels were maintained provided loss of body water was between 1.8% and 3.2% of body weight. One study even showed that performance was improved with sweat induced dehydration of up to 2.3 percent, with the explanation that the athlete carries less body weight and exercise doesn’t have to be interrupted.
For the average person, it was mentioned that while the BMJ was unable to find any reports of death directly from dehydration, there are several reports of death from overhydration. By following advice to drink before thirst, many athletes are drinking too much, which doesn’t help performance and puts them at risk.
#3 Energy Drinks with Caffeine and Other Compounds Improve Performance
Many energy drinks make claims that scientific studies prove that carbohydrate drinks that contain stimulants such as caffeine, guarana, and taurine improve performance. Caffeine has long been used for such purpose, and when combined with the other compounds we are told that the combination is uniquely performance enhancing.
What we’ve been told. Caffeine has long been used to enhance sports performance, and energy supplements containing caffeine, in addition to other compounds, are purported to be uniquely performance enhancing when taken together. These include taurine, a sulphonic amino acid that is thought to increase skeletal muscle contractility while decreasing systemic vascular resistance; and guarana, which contains caffeine and related xanthines. Caffeine acts as a competitive inhibitor of adenosine on central nervous system receptors, and an inhibitor of phosphodiesterase. It increases heart rate and induces glycogen sparing, and is believed to enhance available energy stores. (source)
What the BMJ says. They found nine studies that investigated the effects of energy drinks. Four studies noted positive effects, including increased aerobic and anaerobic endurance, with another trial noting increased endurance in trained athletes. Three studies found that energy drinks did not improve running time to exhaustion among physically active college students, mean sprint time among female collegiate soccer players, and sprint performance or anaerobic power in college football players. The BMJ did not find any research comparing the effectiveness of energy drinks versus caffeine alone.
On the negative side, caffeine can cause insomnia, headaches, and gastrointestinal bleeding. The dangers of energy supplements include nausea and vomiting, tachycardia, tremors, seizures, and sleep disturbances, particularly in adolescents. There are several reports of cardiac arrhythmia and death, as well as hospital admissions as a result of energy drink use.
The bottom line is that very little evidence supports the use of energy drinks to enhance performance, and what evidence exists is of poor quality. They found no studies that suggest that there are benefits from the ingredients in energy drinks beyond caffeine, and that there are important concerns regarding harm.
#4 Carbohydrate and Protein Combinations Improve Post-Workout Performance and Recovery
I know already that this will be a hard one for many athletes to let go. For the past decade or so, we have been told that carbohydrates alone are not the best solution for recovery, and that we need added protein in a specific ratio (4:1, four grams carbohydrates to 1 gram protein), for optimal results. The combination is supposed to stimulate increased uptake of glucose by the cells, resulting in faster glycogen storage, than either carbohydrate or protein alone.
What we’ve been told. After exercise, 24 hours of rest are usually sufficient to replenish glycogen stores alongside a regular diet. Ingesting carbohydrate during recovery from exercise may improve subsequent sports performance by increasing the rate of glycogen synthesis. However, combined ingestion of both protein and carbohydrate has been shown to synergistically influence the release of insulin, increase the rate of muscle glycogen storage, and reduce markers of exercise induced muscle damage. (source)
What the BMJ says. They found 21 trials, fewer than half of which reported any benefit from protein and carbohydrate ingestion compared to carbohydrate alone. One review concluded that the available evidence fails to show a relation between increased muscle glycogen synthesis and improved sports performance.
Studies varied widely in the ratio of carbohydrate to protein required, all the way from 2:1 to 6:1, and all the studies using the different ratios had contrasting results. Six studies looked at whether carbohydrate and protein improved muscle recovery. Only one found that carbohydrate and protein resulted in smaller decreases in muscle performance than carbohydrate alone.
The BMJ concluded that for the general public, there is a lack of evidence to support carbohydrate and protein supplements after exercise to improve muscle recovery and performance. For professional athletes, their conclusions are that such supplements show inconsistent and generally small benefits in some measures of sports performance, but generally do not show benefits beyond what is supplied by a nutritious and balanced diet.
#5 Compression Garments Improve Performance and Enhance Recovery
In recent years, compression garments, from shorts to socks to arm sleeves have been touted as the ultimate tool to improve performance and speed recovery. The skin tight garments are made of body hugging fabric that exerts various degrees of pressure. They are said to improve circulation and help remove lactic acid, which will shorten recovery time and lead to better performance. We are encouraged to wear these items during exercise, told that the compression will support muscles and tendons during movement and thus reduce fatigue and pain.
What we’ve been told. Wearing compression garments during exercise is thought to improve venous return and increase removal of metabolites such as lactic acid. Additionally the garments are claimed to work by reducing the oscillation (or “wobble”) of muscles and tendons that occurs during repetitive exercise, thus reducing muscle pain and fatigue. By reducing damage the garments may reduce the predisposition to serious injury later. Finally, for contact sports such as rugby or American football, compression garments may cushion direct trauma to the body. (source)
What the BMJ says. They found three trials that tested the effect of compression garments on sporting performance, all of which had negative results. A further 10 studies found no benefit from compression garments on various exercise protocols in controlled or laboratory settings.
On the other side, four small studies found improved performance and reduced lactic acid levels in participants wearing compression garments. Six studies reported a beneficial effect on muscle soreness by athletes who wore compression garments either during or after exercise. Finally, three studies compared using compression garments to other forms of recovery treatment, such as massage, hot and icy cold water treatment and low level exercise, and found compression garments had a similar effect to the other treatments.
The BMJ concluded, that for the general public, there is a lack of evidence to support that compression garments will improve performance. They may reduce muscle soreness if worn for 24 hours after an exercise session. For professional athletes there is no consistent evidence that compression garments improve sporting performance. Muscle soreness seems to be reduced if worn for 24 hours after an exercise session, but objective measures of recovery are less consistent and are no better than other methods used to assist recovery as mentioned above. Potential adverse effects of these garments are increased skin temperature and reduced range of motion.
So there you have it, five tried and true fitness “facts” mythbusted either partially or completely by this latest British Medical Journal Report. (There is one more, Branched Chain Amino Acids Improve Performance and Recovery After Exercise, which can be read on the BMJ site.)
For the complete results and complete citations for all the studies mentioned, as reported by the British Medical Journal click here. The report also lists further research that needs to be done to find conclusive evidence, if any exists, for each item in this list.
As I said in my opening paragraph, the BMJ was exceptionally busy today, publishing seven reports related to fitness and exercise, performance and recovery. The other six are listed, along with the links, below.
The evidence underpinning sports performance products: a systematic assessment
The truth about sports drinks
How valid is the European Food Safety Authority’s assessment of sports drinks?
Commentary: role of hydration in health and exercise
Forty years of sports performance research and little insight gained
Miracle pills and fireproof trainers: user endorsement in social media
So, what do you think? Did the BMJ’s report make you question any long held beliefs? Do you want to research further? Let’s discuss!