This Month In Journals: Acetominophen, Huffing O2, and the Difference between Men and Women

Welcome back to This Month in Journals! After catching up with what happened in scientific and social research this winter, we’re back on track. Here is what was published in scientific journals in April.

* At the European Journal of Applied Physiology, a discussion is raging about whether acetominophen should be considered a performance-enhancing drug and places on the WADA Prohibited List.

Several studies in the past few years have found that acetominophen, also called paracetemol, can improve sprint performance and reduce the slowing-down that usually occurs over the course of a race or intervals/heats. It is the main ingredient in Tylenol and is widely available over-the-counter to treat pain, fevers, and colds, and other illnesses.

One such study was published in the journal this winter. A team from the University of Kent and the University of Bedfordshire found that giving active men a 1.3 g dose of acetominophen improved their power output during a series of sprints on stationary bicycles, and reduced the decline in power output from one sprint to the next.

Drs. Giusppe Lippi and Fabian Sanches-Gomar of the University of Parma and the University of Valencia, respectively, voiced concern in a letter to the editor: if this has been shown over and over, why is acetominophen not on the banned list? They pointed out that not only is the drug dangerous in high doses (safety is a common rationale for banning performance-enhancing drugs), but it is easily detectable in urine using a fast and cheap testing technique.

This prompted a response from the original authors, who first hurried to assure readers that though they test the effects of acetominophen on sports performance, they do not condone doping.

Next, they acknowledged that the drug certainly seems to be performance-enhancing. Their research over several years has shown that although it also has effects such as preventing core temperature from shooting up in a hot environment and improving nervous system activation, the main mode of performance enhancement is by reducing the sensation of pain.

The Kent/Bedfordshire team explained that acetominophen is safe at therapeutic doses, and that amateur athletes are widely acknowledged to use many other pain-masking drugs which are much more dangerous. Should those other drugs not be a bigger priority to regulate? Like another common compound which enhances performance – caffeine – acetominophen is possibly not banned because it is so widespread. Furthermore, there are many legitimate reasons to use the drug, so implementing a TUE requirement would likely be tedious.

“Consequently, more robust definitions for what constitutes doping, and clearer criteria for establishing a banned substance are warranted,” the authors concluded in their reply.

This debate is probably not over!

* Next, the debate over xenon gas brought up at the Sochi Olympics is not the only instance of skiers breathing something special to enhance performance. A team of researchers from Switzerland and Germany looked at the effects of the oxygen content of air breathed in between laps of a team sprint on recovery and performance. The results were published in Medicine and Science in Sports and Exercise.

Eight well-trained male skiers did team sprint simulations on a SkiErg, with race distance based on that at the Turin and Vancouver Olympics. The elevation, meanwhile, was simulated at 1800 m (the elevation of the Sochi Olympic venue) via an oxygen mask. Each skier did the team sprint twice. Once, in between laps they breathed air with an excess of oxygen. The other time, they breathed air with very low oxygen. The order of the trials was randomized and the athletes didn’t know which air they were breathing – except by how they felt, of course.

The researchers found that neither power output nor perceived exertion differed between the two trials. However, breathing the oxygen-enriched air did improve the oxygen saturation of the skiers’ hemoglobin. The skiers also didn’t accumulate as much lactate in their blood when they breathed the oxygen-enriched air during their recovery time between laps.

So why was there no performance response? Lead author Anna Hauser of the Swiss Federal Institute of Sport guessed that maybe the recovery time of just 3 minutes in between laps was not long enough for the body to respond to the benefit of extra oxygen.

Or, there might be another explanation. The team did find that there were athlete-specific responses: some skiers did improve when breathing the oxygen-rich air, while others didn’t. With a small sample size of only eight athletes, this likely confounded their ability to find statistically significant results. Individual variation in response to this technique deserves further research.

* Dr. Sandra Hunter of Marquette University took on the task of reviewing research on muscle fatigue in men and women. Writing in Acta Physiologica, she pointed out that it’s difficult to get a clear picture of how male and female athletes differ in terms of fatiguability because the vast majority of sports science research is performed on men.

Then, however, she went on to give an in-depth analysis of what we do know. Men are generally assumed to be stronger than women, but for some muscle groups, women are much less fatiguable. For instance, men are stronger at isometric (static) contractions of knee extensors or elblow flexors, but they also have a shorter time or number of repetitions to failure.

The same is true of repeated dynamic muscle contractions, such as lifting an object. Men also showed a greater relative reduction in the force they were applying, although not necessarily a bigger absolute reduction, because they started off as stronger in the first place.

With repeated dynamic muscle extensions however, such as lowering an object, women were actually more fatiguable than men. Muscle extensions lead to muscle damage and delayed-onset muscle soreness (DOMS), so some researchers hypothesize that the reduction in power output by women is because they have lower pain thresholds and are feeling the burn.

Forget strength – what about power? In sprint repetitions on a stationary bike, men usually experience bigger reductions in power output over a set of intervals than women do, and women recover more quickly between sets.

Hovering around all of these phenomena is the big question: do men tire more quickly because they have higher strength or power to start out with? In many of the studies where pairs of men and women are matched for their initial strength or power, the sex differences disappear. Nevertheless, scientists don’t feel like they have finished answering this question.

There are many other potential explanations, from sex hormones to the sympathetic nervous system. Women have higher lipid metabolism in their skeletal muscle than men do, but men have higher rates of glycolysis; is that it? When generating a force, women have greater vasodilation in their muscles, but men have higher mechanical compression; what about that?

Interestingly, when women are stressed or distracted, their reduced fatiguability goes away. If men and women are asked questions, told to do mental math, or given electric shocks during isometric work, the women’s performance declines at a much faster rate than the men’s. Basically, stress may affect men’s and women’s bodies differently through the sympathetic nervous system.

* Lastly, a quick one. Has your coach ever had you run a bunch of sprints, and then do a set up pushups? If so, they were a smart coach. A study in the European Journal of Applied Physiology compared strength training to combined strength and sprint training. Even though the group doing the combined protocol had half as many sessions a week compared to the strength-only group, the researchers found that both groups got stronger at the same rate – and that the combined training protocol produced improvements in VO₂Max and time to exhaustion, whereas the strength protocol, unsurprisingly, did not.