September Edition: This Month In Journals

FasterSkier is starting a new, once-a-month series looking at new research in the field of sports science. Periodically, we’ll flip through some of the world’s best peer-reviewed medical journals and summarize, in plain English, studies that we think will be of interest to skiers. Here’s our first installment – enjoy!

* Those dopers who claim that their blood measurements were funny because they just did a really hard workout might actually have a point. A team of Australian researchers showed in a paper in the International Journal of Sports Medicine that hemoglobin mass (Hb Mass) does, in fact, increase after an endurance race effort.

Back in 2008, a German group led by Dr. Nicole Prommer at the University of Bayreuth suggested in Medicine and Science in Sports and Exercise that Hb Mass, which unlike the Hemoglobin concentration (Hb) measurement used in biological passport programs by anti-doping organizations is not influenced by fluctuations in blood and plasma volume, should be used in anti-doping efforts.

But the Australian team followed up on previous work done since 2008 and put 18 sub-elite triathletes through their paces in an Ironman, and then compared them to 8 control athletes who hadn’t done the race. They found that the racers’ Hb Mass increased by 3.2 % from before the race to directly afterwards, while the control subjects showed no significant change.

Noting that this increase corresponds to the illicit benefit of the infusion of one bag of blood, the researchers discouraged WADA from including Hb Mass in their biological passport program, at least until further work can be done to determine how long the effect lasts after a hard effort.

More information: Gough, C.E., Eastwood, A., Saunders, P.U., Anson, J.M., and Gore, C.J., (2012) Spurious Hb Mass increases following exercise. International Journal of Sports Medicine 33:691-695.

* In the September 1 issue of the British Medical Journal, a team of researchers from several Boston-area hospitals and medical schools published a meta-analysis (review of past studies) of the effects of progestin-only contraception on the risk of thrombosis, a condition in which a blood clot forms in a vein or artery; 300,000 Americans die from venous thrombosis each year. As FasterSkier reported last summer, the use of hormonal birth control appears to have an indirect, if not necessarily direct, impact on athletic performance in female skiers. In addition, U.S. star Kikkan Randall suffered a scary run-in with Deep Vein Thrombosis (DVT), which she attributed to her use of birth control.

As the Boston team wrote, when hormonal birth control became available in the 1960’s, the corresponding increase in thrombosis incidence was pinned on estrogen, the first of two hormonal elements in the typical birth control pill (progestin being the other). Over the last 50 years, pills have gradually decreased in their estrogen concentration, and the types of synthetic estrogen and progestin used in birth control have also changed. It has been assumed that progestin-only pills, which were put on the market beginning in the 1970’s, carried a smaller risk of thrombosis.

But as FasterSkier found last summer, there hasn’t been much in the way of controlled, high-quality testing on this issue. The team led by Drs. Simon Mantha of the Lahey Clinic and Jeffrey Zwicker of Beth Israel and the Harvard Medical School encountered a similar problem. A search using terms like “progestin”, “progesterone”, and “thromboembolism” in the top three scientific search engines returned over 2,000 papers, but after screening, only eight addressed the question of progestin and thrombosis.

Not a single one of the studies was randomized, one of the cornerstones of strong scientific and medical research, to compare outcomes for women taking the progestin and those in a control group. Instead, all eight studies used existing groups of patients. Five of the eight studies were case-control, taking patients with known outcomes (thrombosis, no thrombosis) and looking back at their histories to examine the cause. The other three studies were cohort studies, which take groups of patients with known risk factors (for example, progestin vs. not) and then examing the prevalence of a disease (for example, thrombosis) going forward.

The Boston team then effectively combined all of the women in the various studies and ran a global test, determining that the relative risk factor for thromboembolism (either venous or pulmonary) for progestin-only users compared to the general population was 1.03, deemed an insignificant risk (this would mean that progestin users would have a three percent greater chance than the general population of developing thrombosis). Interestingly, the relative risk factor for women using an injectable progestin (rather than a pill of IUD) was 2.67.

Mantha and Zwicker’s team concluded that the lack of increased risk might be due to the fact that progestin-only “mini-pills” contain much lower doses of the hormone than do the more common combined estrogen-progestin pills. But they also called for more studies, saying that the small amount of research on this subject could mean that some studies were biased.

More information: Mantha, S., Karp, R., Raghavan, V., Terrin, N., Bauer, K.A., and Zwicker, J.I., (2012) Assessing the risks of venous thromboembolic events in women taking progestin-only contraception: a meta-analysis. British Medical Journal 345:4944.

* Do girls drop out of sports more frequently than boys, and when children or teenagers of either gender quit athletics, why is it? These are a few of the questions addressed by Dr. Jose Francisco Guzman of the University of Valencia and Dr. Kieran Kingston of the University of Wales in a recent paper in the European Journal of Sports Science.

Following a group of 857 Spanish children ages 11 to 19, all of whom participated in some kind of organized sports, for 19 months, the researchers tried to determine why athletes quit using a model called “self-determination theory.” They looked at how self-motivated the athletes were, how they perceived sports to impact their studies, and how satisfying they found athletics, among other metrics, and pooled athletes by age and gender.

They found that there was a correlation between an athlete’s level of motivation and their perception of how their sport might hamper their studies; taking it one step further, the researchers guessed that motivated athletes were less likely to consider athletics a drawback to their academic success. Regardless, they found that this combination led athletes to stay in their sports longer.

Interestingly, the team saw that dropout rate did not change significantly with age or gender, and concluded that their model could be applied generally to assess and predict how many children would stay in sport.

More information: Guzman, J.F., and Kingston, K., (2012) Prospective study of sport dropout: a motivational analysis as a function of age and gender. European Journal of Sports Science 12:431-442.

* Summer may be basically over, but a study published in the October issue of the European Journal of Applied Physiology suggests a way for athletes to better cope with heat during training: pre-cooling. But was does that mean? If you’re running a race in the summer, do you have to sit in an ice bath before hitting the start line?

Because heat stresses the body in many ways and can athletic performance, previous research had suggested preemptively cooling the body to try to curb heat stress. A paper by researchers at Charles Sturt University in Australia, led by Dr. Geoffrey Minett, examined various durations of pre-cooling and their effects not only on athletic performance but also on neuromuscular function.

The Australians used eight subjects in their study, all men in their mid-20’s who were club-level athletes in team sports. At roughly 91 ºF and 33 % relative humidity, the men were asked to perform two 35-minute exercise sessions separated by 15 minutes of rest. Each session included both maximal sprints and “shuttle running” intervals of 50 seconds, with jogging and walking recovery in between, measuring how far the athletes ran in each 50-second interval.

Each subject did the workout three times, with randomly assigned pre-cooling treatments: either no cooling, ten minutes of cooling, and twenty minutes of cooling. The treatment itself was complex and comprehensive: an iced towel over the head, neck and shoulders, dunking the hands in cold water up to the wrists, placing ice packs on the thighs, and wearing an ice vest.

The treatments did have their desired effect. Core body temperature was significantly lower in the 20-minute pre-cooled group compared to the others, and that effect lasted the entire workout. Other physiological variables, such as heart rate and blood pH or glucose levels, were unaffected. Muscles, however, also showed the benefits of pre-cooling: the maximum voluntary contractions (MVC), in this case the force applied by the right knee extensor in response to an electric stimulus, were higher both mid- and post-exercise in the pre-cooled athletes.

All of this led to performance increases for the 20-minute pre-cooling treatment. The times of the maximal sprints in the second bout of a session declined more drastically in athletes having only the control (8.82 %) or ten-minute (6.95 %) pre-cooling treatment, whereas the 20-minute pre-cooled athletes declined a modest 6.09 % during the second bout. Distances covered during the shuttle-running portion of the workout were significantly higher for the 20-minute athletes as well.

The researchers concluded not only that pre-cooling was beneficial, but that the dose was important: ten minutes of the treatment did not produce the same performance increase shown by twenty minutes of cooling.

More information: Minett, G.M., Duffield, R., Marino, F.E., Portus, M., (2012) Duration-dependent response of mixed-method pre-cooling for intermittent-sprint exercise in heat. European Journal of Applied Physiology 112:3655–3666.

* Publishing in the same journal online ahead of the print edition, ew: score one for icky science. In an attempt to understand why athletes so often exhibit signs of asthma or general bronchial constriction, a Madrid-based research team looked at what the athletes coughed up. Sputum!

Lead author Dr. Beatriz Sastre of the IIS-Fundacion Jimenez-Dıaz Immunology Department and five Spanish colleagues rounded up 68 subjects, divided between athletes and non-athletes and asthmatics and non-asthmatics; the athletes were Spain’s Olympians from 2008. All the subjects were put through breathing “challenges”, which meant chemically inducing a constricted airway. Between the asthmatic and non-asthmatic athletes, the researchers actually didn’t find any difference in inflammation of the airways.

In the sputum samples, the researchers found that athletes had expelled more bronchial skin cells – meaning that there were injuries to their airways that left them spewing tissue. They also tested the presence of several kinds of white blood cells, finding that healthy control subjects expelled fewer of three different kinds of white cells (eosinophils, neutrophils, and basophils) than athletes and asthmatics; athletes showed higher levels of neutrophils and basophils than even asthmatic non-athletes. Basophils, for example, initiate inflammation.

Given the lack of inflammation difference between asthmatic and non-asthmatic athletes, and the fact that athletes seem to have more epithelial airway injuries and also more white blood cells which promote inflammation, the study concludes that exercise can induce airway difficulties in all athletes – even the best-trained ones.

More information: Sastre, B., Fernandez-Nieto, M., Rodriguez-Nieto, M.J., Aguado, E., Sastre, J., and del Pozo, V., (2012) Distinctive bronchial inflammation status in athletes: basophils, a new player. European Journal of Applied Physiology