Ironman study redefines fine-tuned: Balance training time with blood pressure variability

Exhaustive look at competitive physiology finds complete recovery

BETHESDA, MD (March 6, 2006) -- With thoughts of the Winter Olympics waning, perhaps it's time to turn athletic training preparations toward the November Kona (Hawaii) Ironman competition, the 2008 Summer Olympic triathlon, or your local marathon or 10K.

Worried about the training time commitment involved? Concerned how long it might take you to stand up without fainting afterwards? Fear not.

In a comprehensive study of 25 men competing in an Ironman, Austrian researchers uncovered some startling physiological insights into training and recovery from the combined effects of swimming 3.9 kilometers (2.4 miles), cycling 180.2 km (112 miles) and then running the standard marathon distance of 42.2 km (26.2 miles).

Writing in the Journal of Applied Physiology, the Austrians said faster finishers trained more per week than others, but that contrary to expectations their sympathetic nervous systems were less active than expected, which contributed to a fast recovery.

13 hemodynamic, autonomic measures point to unexpectedly quick recovery

Researchers from the Medical University of Graz, Austria, measured 13 hemodynamic and autonomic parameters from blood pressure changes to heart beat stroke strength, as well as clinical data, including weekly net exercise training (WNET) time.

Knowing that it takes about two weeks for muscles and tendons to recover after an Ironman, the Austrian authors wrote in the Journal of Applied Physiology: "We hypothesized that this extreme endurance exercise would lead to long-standing hemodynamic impairment and sympathetic activation."

Looking at this multitude of parameters from before the competition, they "were prepared to study them for as long afterwards as it would take for full recovery." In addition, they were interested in "the possibility of predicting competition performance from the baseline" or pre-competition measurement levels. The results of time-to-recovery and "predictive factors" were both surprising and deceptively simple. How to train for a faster finish, however, may prove to be very elusive, all agree.

The paper, "Hemodynamic and autonomic changes induced by Ironman: prediction of competition time by blood pressure variability," appears in the Journal of Applied Physiology, published by the American Physiological Society. Research was by Gerfried Gratze, Richard Rudnicki, Wolfgang Urban, Harald Mayer and Falko Skrabal at the Medical University Teaching Hospital, and Alois Schlögl at the Technical University, both in Graz, Austria.

Four major factors recover after only one day, indicating expanded human capacity

"Based on our experience with muscular and tendon recovery of around two weeks, we expected hemodynamic and sympathetic recovery to take at least two weeks," the study leader, Falko Skrabal, said. "In any case, because of muscle recovery time, you couldn't start hard training again for a couple of weeks," added lead author, Gerfried Gratze, who like Skrabal is an active athlete and outdoorsman.

Yet the results showed that one day after the competition four of the most significant parameters were already back to normal: heart beat, cardiac index, mean arterial blood pressure/cardiac index (TPRI, or total peripheral resistance index), and diastolic blood pressure low frequency. Within three days, all the other major hemodynamic/autonomic changes also had returned to their baseline levels.

How to explain the rapid recovery? For a possible answer, the authors reached way back in time – about 5 million years. They conclude: "The rapid recovery after what we consider now to be an extreme endurance exercise may throw some light on the true capabilities of the human body acquired during human evolution. For the largest part, namely for the 5 million years of the hunter-gatherer age, mankind had to perform daily a regimen of 10-30 km of walking and running for survival. This would correspond to up to 4 hours daily exercise time and a WNET of 28 hours. Our ‘well-trained' athletes achieved only between 20%-60% of this duration of training, which demonstrates the change of perspective that occurred with the beginning of the industrial age."

Speed predictors were training time and low frequency blood pressure variability

In their second area of inquiry – how to predict finishing time beforehand – Gratze and Skrabal were equally surprised. After repeated statistical analyses, the only measurements from the day before the Ironman that "contributed independently and significantly to the prediction of competition time were" WNET and DBPLFnu, which stands for diastolic blood pressure low frequency variability in normalized units.

WNET, sure, but what's DBPLFnu, and more importantly, how can one train for it? David K. Spierer, an assistant professor in the Division of Sports Sciences and Director of the Human Performance Laboratory in the School of Health Professions at Long Island University, Brooklyn, New York, explained that the Austrians were measuring the interplay of the body's circulatory and autonomic nervous systems. "The low frequency band of 0.05 to 0.17 Hz of blood pressure variability reported in the paper indicates sympathetic activity (or tone), or simply put, ‘heart rate and blood pressure elevating' activity of the autonomic nervous system," in response to stress, Spierer said.

"Examining blood pressure variability (in this frequency range) gives us a non-invasive foray into the relationship between variations in heart rate as they relate to variations in blood pressure," Spierer noted.

Skrabal said blood pressure variability in this "lower" frequency domain shows the sympathetic regulation of resistance vessel tone. Whereas the heart is innervated by sympathetic (stress) and parasympathetic (recovery) nerves, blood vessels are innervated only by the sympathetic nervous system. "Therefore, they are much better suited for the study of the sympathetic nervous system than heart rate variability," Skrabal observed. What Gratze and Skrabal studied was the relative contribution of the "10 second rhythm" (which is low frequency) to total rhythmic activity of spontaneous vasoconstriction and vasodilation occurring constantly in the arterial vessels responsible for maintaining peripheral resistance and hence blood pressure. The 10 second rhythm is maintained by the sympathetic nervous system.

Low sympathetic activity aids recovery – exactly the opposite of what's expected

"What Gratze and Skrabal demonstrate is that despite their relatively high amount of weekly training, the fast finishers somehow maintain a relatively low level of sympathetic tone, or activity level." In addition to being correlated with fast finishing time, Spierer said, "the low level of sympathetic tone also contributes to the fast recovery time. It is well established that with training comes an increase in parasympathetic tone at rest, the sympathetic counterpart within the autonomic nervous system or the ‘heart rate and blood pressure lowering activity.' However, after an exercise bout like an Ironman requiring such an increase in metabolic demand over a long period of time, it seems that sympathetic tone would predominate for long periods into recovery.

"But the authors found just the opposite to be true. These physiological findings are very interesting and could significantly impact training of athletes in the future. Furthermore, the authors implemented a sound and well controlled protocol to examine physiologic parameters during an extensive recovery period," Spierer added.

The study became feasible by a piece of equipment for automatic and noninvasive hemodynamic and autonomic monitoring called the Task ForceTM Monitor, developed by Skrabal and Gratze. (Information about the Monitor is available at www.cnsystems.at.) It is being used most notably by NASA for the noninvasive investigation of cardiovascular consequences of space flight, Skrabal reported.

Skrabal noted later that their findings support decades of intuitive sports training. "With top sportsmen you always train close to overtraining, which is associated with high sympathetic drive. If we could somehow combine long training regimens without raising sympathetic drive, we could avoid crossing the line between optimal training and counterproductive overtraining," he said.

A look at fainting, and possible relation to POTS

Athletes fainting after such long-distance competition as marathons and Ironman is well-known. Gratze and Skrabal studied this phenomenon at all time points in the study (one day before competition, one hour after competition and one, three and seven days afterward).

They compared the percentage changes of hemodynamic and autonomic parameters from supine rest to active standing, that is standing on "one's own" as opposed to being elevated vertical on a tilting bed. All parameters were similar at all points except one hour after the competition, when subjects "were unable to raise their systolic blood pressure, TPRI, and sympathetic modulation of vasomotor tone, and they showed a paradoxical increase in parasympathetic modulation of the sinus node after active orthostasis," or standing, the paper reported.

"Seven of the 23 subjects fainted in response to active orthostasis [defined by moving from a lying to standing posture] -- and all of the fainters showed significantly higher vagal activation in response to active orthostasis one hour after the race compared with those subjects who did not faint," according to the paper. The authors note that the situation "mimics the low orthostatic tolerance observed in postural tachycardia syndrome (POTS), which is also associated with an increased sympathetic drive to the heart."

Next steps:

  • The "analysis of blood pressure variability in the (low) frequency band domain deserves further study for the prediction of endurance capacity," the paper stated.

  • Regarding POTS, the equipment used didn't allow for measurements that might have helped identify subjects prone to syncope while supine, and this could be added in the next experiment.

  • "Analysis of beat-to-beat blood pressure in the (low) frequency domain could become a valuable additional tool for optimizing the training of athletes," the paper noted. Skrabal added later: "The problem is how to get approvals from trainers and managers of world class athletes to be so intrusive into fixed protocols. But we will start a controlled study in young athletes at the beginning of their career."

Historical perspectives on Gratze-Skrabal et al.

Gratze and Skrabal studied the 2003 Austria Ironman in which there were about 1,500 competitors. Of their 25 subjects (all volunteers from Austrian running clubs), their top finisher in fifth place was Werner Leitner of TC Union Graz in 8 hours 25 minutes and 41 seconds, a personal best; their second-best subject came in 115th, and their last subject came in 1,367th.

To the running public, the 2003 Austria Ironman was most notable because the top woman at Kärnten was Kate Allen, also in a personal best of 8:54.01. The next year, Allen, an Australian turned Austrian, was the Olympic triathlon gold medal winner in 2:04.43. (Compared with an Ironman, the Olympic triathlon comprises a mere 1-mile swim, 25-mile bike ride and 10K run (6.2 miles).

The "average" Kona Ironman athlete trains for seven months (Oct. 14 this year, still plenty of time, if you've registered) and 18-24 hours per week, comprising (in miles/km per week): swimming 7 mi/11.3 km; biking 225 mi/373.3 km; running 48 mi/77.2 km, according to the Kona website.

The first China Ironman has been postponed from April 23, 2006 until 2007.

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Source and funding

The paper, "Hemodynamic and autonomic changes induced by Ironman: prediction of competition time by blood pressure variability," appears in the Journal of Applied Physiology, published by the American Physiological Society. Research was by Gerfried Gratze, Richard Rudnicki, Wolfgang Urban, Harald Mayer and Falko Skrabal at Department of Internal Medicine, Krankenhaus Barmherzige Brüder, Marschallgasse, Medical University Teaching Hospital, Graz, and Alois Schlögl at the Department of Medical Informatics, Institute of Biomedical Engineering, Technical University, Graz, Austria.

Task ForceTM Monitor development was supported by the Austrian Science Foundation (Skrabal) with assistance from the Technical University Graz, Austria.

Editor's note: The media may obtain a copy of Gratze et al. by contacting Mayer Resnick, American Physiological Society, 301.634.7209, cell 301.332.4402 or mresnick@the-aps.org.

The American Physiological Society was founded in 1887 to foster basic and applied bioscience. The Bethesda, Maryland-based society has more than 10,000 members and publishes 14 peer-reviewed journals containing almost 4,000 articles annually.

APS provides a wide range of research, educational and career support and programming to further the contributions of physiology to understanding the mechanisms of diseased and healthy states. In May 2004, APS received the Presidential Award for Excellence in Science, Mathematics and Engineering Mentoring (PAESMEM).


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