Types of athletic training affect how brain communicates with muscles

Date:September 18, 2015

Source:University of Kansas

Summary:The brains of endurance trainers communicate with muscles differently than those of strength trainers or sedentary individuals, new research shows. While it is not immediately clear why the communication between the brain and muscle was different as a result of different types of exercise, one researcher said it offers leads for new means of research into neuromechanical differences in muscle function, muscle performance, muscle stiffness and other areas.

A University of Kansas study shows that the communication between the brain and quadriceps muscles of people who take part in endurance training, such as running long distances, is different than those who regularly took part in resistance training and those who were sedentary. The findings may offer clues to the type of physical activity humans are most naturally suited to.

Trent Herda, assistant professor of health, sport and exercise sciences, and Michael Trevino, a doctoral student, conducted studies in which they measured muscle responses of five people who regularly run long distances, five who regularly lift weights and five sedentary individuals who regularly do neither. The studies have been published in the Journal of Sports Sciences and Muscle and Nerve.

Among the findings, Herda and Trevino showed that the quadriceps muscle fibers of the endurance trainers were able to fire more rapidly.

“The communication between the brains and their muscles was slightly different than the resistance trainers and sedentary individuals,” Herda said of endurance trainers. “This information also suggested that resistance trainers and those who are sedentary were more likely to fatigue sooner, among other things.”

Survey participants were 15 healthy volunteers. The endurance trainers had consistently taken part in a structured running program for at least three years prior to the study and ran an average of 61 miles a week and did not take part in resistance training. The resistance trainers had consistently taken part in a weight-training program for at least four years prior to the study. They took part in resistance training four to eight hours per week and reported doing at least one repetition of a back squat of twice their body mass. One reported doing a squat of 1.5 times his or her body weight, but none engaged in aerobic activity such as swimming, jogging or cycling. The sedentary participants did not take part in any structured physical exercise for three years prior to the study.

Participants wore mechanomyographic and electromyographic electrode sensors on their quadriceps muscle and extended their leg while seated. The researchers measured submaximal contraction and total force by having participants extend their leg, then exert more force, attempting to achieve from 40 to 70 percent of total force, which they could see represented in real time on a computer screen.

While it is not immediately clear why the communication between the brain and muscle was different as a result of different types of exercise as evidenced by the difference in rates of muscle fibers firing, Herda said it offers leads for new means of research into neuromechanical differences in muscle function, muscle performance, muscle stiffness and other areas. It also provides several clues into the type of exercise humans are more naturally built for. While not claiming that one type of exercise or sport is superior to another, Herda said the findings suggest that the human body’s neuromuscular system may be more naturally inclined to adapt to aerobic exercise than resistance training for strength as the communication between the brain and muscles was similar between resistance training and sedentary individuals.


Story Source:

The above post is reprinted from materials provided by University of Kansas. Note: Materials may be edited for content and length.


Journal References:

  1. Trent J. Herda, Jacob A. Siedlik, Michael A. Trevino, Michael A. Cooper, Joseph P. Weir. Motor unit control strategies of endurance- versus resistance-trained individuals. Muscle & Nerve, 2015; DOI: 10.1002/mus.24597
  2. Michael A. Trevino, Trent J. Herda. The effects of chronic exercise training status on motor unit activation and deactivation control strategies. Journal of Sports Sciences, 2015; 1 DOI: 10.1080/02640414.2015.1046396

Getting Fit Fast: Inactive People Can Achieve Major Health and Fitness Gains in a Fraction of the Time

Feb. 1, 2013 — With many of us struggling to get enough exercise, sport and exercise scientists at Liverpool John Moores University (LJMU) and the University of Birmingham, under the lead of Professor Anton Wagenmakers, have been working on a time-saving solution.


 

Instead of long stints in the gym and miles of running in the cold, the same results could be achieved in less than a third of the time, according to new research published February 1 in The Journal of Physiology.

The current recommendation of the World Health Organisation (WHO) and UK Department of Health is that people of all ages should do three to five hours of endurance training per week to increase health and fitness and prevent chronic diseases and premature mortality. However, most people find it difficult to set aside this much time in their busy lives.

This study has taken existing research to a new level to prove that replacing endurance training with two types of interval training, High intensity Interval Training (HIT) and Sprint Interval Training (SIT), can make a massive difference to our health and aerobic fitness. In two articles in the 1 February issue ofThe Journal of Physiology, the researchers describe their recent discoveries that three sessions of SIT, taking just 90 min per week, are as effective as five sessions of traditional endurance exercise, taking five hours per week, in increasing whole body insulin sensitivity via two independent mechanisms.

LJMU researcher Matthew Cocks explains: ‘One mechanism involves improved delivery of insulin and glucose to the skeletal muscle and the other involves improved burning of the fat stored in skeletal muscle fibres. Additionally, we found a reduced stiffness of large arteries which is important in reducing the risk of vascular disease.’

On the basis of these novel and earlier findings from other laboratories, Professor Wagenmakers expects that HIT and SIT will turn out to be unique alternative exercise modes suitable to prevent blood vessel disease, hypertension, diabetes and most of the other ageing and obesity related chronic diseases.

LJMU researcher Sam Shepherd describes: ‘SIT involves four to six repeated 30 second ‘all out’ sprints on special laboratory bikes interspersed with 4.5 minutes of very low intensity cycling. Due to the very high workload of the sprints, this method is more suitable for young and healthy individuals. However, anyone of any age or level of fitness can follow one of the alternative HIT programmes which involve 15-60 second bursts of high intensity cycling interspersed with 2-4 minute intervals of low intensity cycling. HIT can be delivered on simple spinning bikes that are present in commercial gyms and are affordable for use at home or in the workplace.’

Lack of time is the number one reason that the majority of the adult population do not meet the current physical activity recommendations. SIT and HIT could solve this problem.

Sam Shepherd comments: ‘A pilot study currently ongoing in the Sports Centre at the University of Birmingham has also shown that previously sedentary individuals in the age-range of 25-60 also find HIT on spinning bikes much more enjoyable and attractive than endurance training and it has a more positive effect on mood and feelings of well-being. This could imply that HIT is more suitable to achieve sustainable changes in exercise behaviour.’

HIT, therefore, seems to provide the ideal alternative to outdoor running, dangerous cycling trips and long boring endurance cycling sessions in health and fitness gyms. That is why the researchers believe that there will be a great future for HIT for obese and elderly individuals and potentially also for patients with hypertension, diabetes and cardiovascular disease.

 

Story Source:

The above story is reprinted from materials provided byWiley, via AlphaGalileo.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.


Journal Reference:

  1. M. Cocks, C. S. Shaw, S. O. Shepherd, J. P. Fisher, A. M. Ranasinghe, T. A. Barker, K. D. Tipton, A. J. M. Wagenmakers. Sprint interval and endurance training are equally effective in increasing muscle microvascular density and eNOS content in sedentary malesThe Journal of Physiology, 2012; 591 (3): 641 DOI:10.1113/jphysiol.2012.239566
Wiley (2013, February 1). Getting fit fast: Inactive people can achieve major health and fitness gains in a fraction of the time.ScienceDaily. Retrieved February 3, 2013, from http://www.sciencedaily.com/releases/2013/02/130201090405.htm

Lose Fat Faster Before Breakfast

Jan. 24, 2013 — People can burn up to 20% more body fat by exercising in the morning on an empty stomach, according to new research from Northumbria University.


 

In a study published online in theBritish Journal of Nutrition on January 24, academics sought to find out whether the known benefits of exercising after an overnight fast were undermined by an increased appetite and eating more food later in the day.

Researchers, led by Dr Emma Stevenson and PhD student Javier Gonzalez, asked twelve physically active male participants to perform a bout of treadmill exercise at 10am, either after they had eaten breakfast or in a fasted state having not eaten since the evening before.

Following the exercise all participants were given a chocolate milkshake recovery drink. Later in the day, participants were provided with a pasta lunch which they were asked to consume until they felt ‘comfortably full’. Their lunchtime consumption of energy and fat was assessed and calculated, taking into account the amount of energy and fat burned during the morning period.

The researchers discovered that those who had exercised in the morning did not consume additional calories or experience increased appetite during the day to compensate for their earlier activity.

They also found that those who had exercised in a fasted state burned almost 20% more fat compared to those who had consumed breakfast before their workout. This means that performing exercise on an empty stomach provides the most desirable outcome for fat loss.

Javier Gonzalez, who is currently undertaking a PhD in Exercise and Metabolism, said: “In order to lose body fat we need to use more fat than we consume. Exercise increases the total amount of energy we expend and a greater proportion of this energy comes from existing fat if the exercise is performed after an overnight fast.

“Our results show that exercise does not increase your appetite, hunger or food consumption later in the day and to get the most out of your session it may be optimal to perform this after an overnight fast.”

Dr Emma Stevenson, Senior Lecturer in Sport and Exercise Nutrition and Associate Director of Northumbria University’s Brain, Performance and Nutrition Research Centre, added: “This research is very important in helping to provide practical guidelines relating to food intake to individuals who are exercising to maximise fat mass loss. It must be highlighted that this is a short-term study and we can only speculate on the longer term outcomes of such nutritional practices.”

 

Story Source:

The above story is reprinted from materials provided byNorthumbria University.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.


Journal Reference:

  1. Javier T. Gonzalez, Rachel C. Veasey, Penny L. S. Rumbold, Emma J. Stevenson. Breakfast and exercise contingently affect postprandial metabolism and energy balance in physically active malesBritish Journal of Nutrition, 2013; : 1 DOI: 10.1017/S0007114512005582
Northumbria University (2013, January 24). Lose fat faster before breakfast. ScienceDaily. Retrieved January 28, 2013, from http://www.sciencedaily.com/releases/2013/01/130124091425.htm

Exercise: Women Must Do More to Reap Same Positive Health Outcomes as Men

Jan. 23, 2013 — More than one-third of Americans are obese, and these individuals often experience accompanying health issues, such as Type 2 diabetes and cardiovascular problems. In response to the so-called “obesity epidemic,” many medical professionals have suggested ways to improve the health outcomes of obese individuals through diet and exercise. Now, research conducted at the University of Missouri suggests certain exercises that benefit obese men may not have the same positive results for obese women. These findings could help health providers and researchers develop targeted exercise interventions for obese women.


“Our results indicate gender may contribute to differences in cardiovascular function of obese individuals with Type 2 diabetes,” said Jill Kanaley, a professor in the Department of Nutrition and Exercise Physiology at MU. “Men saw improvement after aerobic exercise training, but the women did not experience the same benefits.”

Kanaley and her colleagues monitored cardiovascular responses, such as heart rate and blood pressure, of nearly 75 obese men and women with Type 2 diabetes. To monitor cardiovascular responses, the individuals completed an isometric handgrip test, which involves continually and forcefully squeezing an object for a few minutes, at the beginning and end of a structured, 16-week walking program.

“What this research highlights, at least using the handgrip test, is that the advantages we think exercise is going to give individuals may not be the same across genders, particularly for those who have Type 2 diabetes,” Kanaley said. “This is a concern because there are high mortality rates with Type 2 diabetes, especially for women. We’re trying to find successful interventions to help these individuals, and we keep assuming that exercise will do the trick — we think when we tell people to “go train,” regardless of gender, everyone will get the same results. Our research indicates certain exercises may not be enough for women, as our walking program did not show positive improvements for them.”

Obese women with Type 2 diabetes might benefit from longer durations or higher intensities of exercise, Kanaley said. In addition, Kanaley said more concern should be placed on how long it takes cardiovascular function to return to normal after exercise as well as how fast the heart beats during physical exertion.

“A lot of people focus on how high individuals’ heart rates get during exercise, but their recovery rates also should be monitored,” Kanaley said. “When you exercise, you want your blood pressure to rise, but you don’t want it to get too high. Your blood pressure should return to normal relatively quickly after you stop exercise. In our study, the recovery rate for women was not as rapid as for men. After the men trained, they got an even better recovery time, whereas women’s time stayed about the same.”

The study, “Exercise training improves hemodynamic recovery to isometric exercise in obese men with Type 2 diabetes but not in obese women,” was published in the December issue of Metabolism.

 

Story Source:

The above story is reprinted from materials provided byUniversity of Missouri-Columbia.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.


Journal Reference:

  1. Jill A. Kanaley, Styliani Goulopoulou, Ruth Franklin, Tracy Baynard, Robert L. Carhart, Ruth S. Weinstock, Bo Fernhall. Exercise training improves hemodynamic recovery to isometric exercise in obese men with type 2 diabetes but not in obese womenMetabolism, 2012; 61 (12): 1739 DOI: 10.1016/j.metabol.2012.07.014
University of Missouri-Columbia (2013, January 23). Exercise: Women must do more to reap same positive health outcomes as men.ScienceDaily. Retrieved January 28, 2013, from http://www.sciencedaily.com/releases/2013/01/130123115411.htm

Why Good Resolutions About Taking Up a Physical Activity Can Be Hard to Keep

an. 4, 2013 — Physical inactivity is a major public health problem that has both social and neurobiological causes. According to the results of an Ipsos survey published on December 31, the French have put “taking up a sport” at the top of their list of good resolutions for 2013. However, Francis Chaouloff, research director at Inserm’s NeuroCentre Magendie (Inserm Joint Research Unit 862, Université Bordeaux Ségalen), Sarah Dubreucq, a PhD student and François Georges, a CNRS research leader at the Interdisciplinary Institute for Neuroscience (CNRS/Université Bordeaux Ségalen) have just discovered the key role played by a protein, the CB1 cannabinoid receptor, during physical exercise. In their mouse studies, the researchers demonstrated that the location of this receptor in a part of the brain associated with motivation and reward systems controls the time for which an individual will carry out voluntary physical exercise. These results were published in the journal Biological Psychiatry.

Longitudinal section of the mouse brain (top) and diagram of interactions between the endocannabinoid, GABAergic and dopaminergic systems during voluntary physical exercise (bottom). Left: stimulating the CB1 receptors excites the dopaminergic neurons in the ventral tegmental area involved in motivation. Right: the absence of CB1 receptors lowers performance by 20 to 30% owing to reduced motivation. (Credit: ©Inserm/F. Chaouloff)

 

The collective appraisal conducted by Inserm in 2008 highlighted the many preventive health benefits of regular physical activity. Such activity is limited, however, by our lifestyle in today’s industrial society. While varying degrees of physical inactivity may be partly explained by social causes, they are also rooted in biology.

“The inability to experience pleasure during physical activity, which is often quoted as one explanation why people partially or completely drop out of physical exercise programmes, is a clear sign that the biology of the nervous system is involved,” explains Francis Chaouloff.

But how exactly? The neurobiological mechanisms underlying physical inactivity had yet to be identified.

Francis Chaouloff (Giovanni Marsicano’s team at the NeuroCentre Magendie; Inserm joint research unit, Université Bordeaux Ségalen) and his team have now begun to decipher these mechanisms. Their work clearly identifies the endogenous cannabinoid (or endocannabinoid) system as playing a decisive role, in particular one of its brain receptors. This is by no means the first time that data has pointed to interactions between the endocannabinoid system, which is the target of delta9-tetrahydrocannabinol (the active ingredient of cannabis), and physical exercise. It was discovered ten years ago that physical exercise activated the endocannabinoid system in trained sportsmen, but its exact role remained a mystery for many years. Three years ago, the same research team in Bordeaux observed that when given the opportunity to use a running wheel, mutant mice lacking the CB1 cannabinoid receptor, which is the principal receptor of the endocannabinoid system in the brain, ran for a shorter time and over shorter distances than healthy mice. The research published in Biological Psychiatry this month seeks to understand how, where and why the lack of CB1 receptor reduces voluntary exercise performance (by 20 to 30%) in mice allowed access to a running wheel three hours per day.

The researchers used various lines of mutant mice for the CB1 receptor, together with pharmacological tools. They began by demonstrating that the CB1 receptor controlling running performance is located at the GABAergic nerve endings. They went on to show that the receptor is located in the ventral tegmental area of the brain (see diagram below), which is an area involved in motivational processes relating to reward, whether the reward is natural (food, sex) or associated with the consumption of psychoactive substances.

VTA: Ventral tegmental area/NAcc: nucleus accumbens/PFC: prefrontal cortex/DA: dopamine

Based on the results of this study and earlier work, the Bordeaux team suggests the following neurobiological explanation: at the beginning and for the duration of physical exercise, the CB1 receptor is constantly simulated by the endocannabinoids, lipid molecules that naturally activate this receptor in response to pleasant stimuli (rewards) and unpleasant stimuli (stress). Endocannabinoid stimulation of the CB1 receptor during physical exercise inhibits the release of GABA, an inhibitory neurotransmitter that controls the activity of the dopamine neurons associated with the motivation and reward processes. This stimulation of the CB1 receptor “inhibits inhibition,” in other words, it activates the dopaminergic neurons in the ventral tegmental area. The CB1 receptor must therefore be stimulated before the exercise can go on for longer and the body must receive the necessary motivation.

Conversely, without these CB1 receptors, the “GABAergic brake” continues to act on the dopaminergic neurons in the ventral tegmental area, leading to the reduced performance levels observed above.

It is already known that CB1 receptors play a regulatory role in the motivation to consume rewards, whether natural or not. What is original about this research is that it shows that physical exercise can be added to the array of natural rewards regulated by the endocannabinoid system. “If confirmed, this motivational hypothesis would imply that the role played by the CB1 receptor has more to do with ‘staying power’ in the exercise than with actual physical performance levels” explain the researchers.

This work reveals that the endocannabinoid system plays a major role in physical exercise performance through its impact on motivational processes. It thus opens up new avenues of research into the mediators of pleasure — and even addiction — associated with regular physical exercise. “After endorphins, we now need to consider endocannabinoids as another potential mediator of the positive effects that physical exercise has on our mood,” the researchers conclude.


Story Source:

The above story is reprinted from materials provided byINSERM (Institut national de la santé et de la recherche médicale).

Note: Materials may be edited for content and length. For further information, please contact the source cited above.


Journal Reference:

  1. Sarah Dubreucq, Audrey Durand, Isabelle Matias, Giovanni Bénard, Elodie Richard, Edgar Soria-Gomez, Christelle Glangetas, Laurent Groc, Aya Wadleigh, Federico Massa, Dusan Bartsch, Giovanni Marsicano, Francois Georges, Francis Chaouloff. Ventral Tegmental Area Cannabinoid Type-1 Receptors Control Voluntary Exercise PerformanceBiological Psychiatry, 2012; DOI:10.1016/j.biopsych.2012.10.025
 

 

INSERM (Institut national de la santé et de la recherche médicale) (2013, January 4). Why good resolutions about taking up a physical activity can be hard to keep. ScienceDaily. Retrieved January 10, 2013, from http://www.sciencedaily.com/releases/2013/01/130104143615.htm

For Those Short On Time, Aerobic, Not Resistance, Exercise Is Best Bet for Weight And Fat Loss

Jan. 2, 2013 — A new study led by North Carolina researchers has found that when it comes to weight- and fat loss, aerobic training is better than resistance training. The study is believed to the largest randomized trial to directly compare changes in body composition induced by comparable amounts of time spent doing aerobic and resistant training, or both in combination, among previously inactive overweight or obese non-diabetic adults.


 

The study is entitled “Effects of aerobic and/or resistance training on body mass and fat mass in overweight or obese adults”. It is published in the December 2012 edition of the Journal of Applied Physiology published by the American Physiological Society.

Methodology

A total of 234 previously sedentary overweight or obese males and females, age 18-70 years of age, were enrolled in one of three eight-month supervised protocols: aerobic training (AT), resistance training (RT), or a combination (AT/RT). Of the total, 119 participants completed the trials and had complete data for the variables of interest in the article.

Those assigned to aerobic training exercised vigorously, at about 70-85% of maximum heart rate. They exercise approximately 45 minutes three days per week throughout the study period.

Individuals assigned to resistance training also exercised three days a week, completing three sets of 8-12 reps on eight resistance machines that targeted all major muscle groups. Resistance was increased throughout the study to maintain a steady level of challenge as the participants gained strength.

Individuals who were assigned to AT/RT performed all the exercises assigned to both AT and RT groups. At the end of study each enrollee was assessed for weight, body composition, waist circumference, cardiopulmonary fitness and strength compared to their baseline.

Key Findings and Conclusions

The researchers found:

• The groups assigned to aerobic training and aerobic plus resistance training lost more weight than those that did resistance training only. In fact, those who did resistance training only actually gained weight due to an increase in lean body mass.

• Fat mass and waist circumference significantly decreased in the AT and AT/RT groups, but were not altered in RT. However, measures of lean body mass significantly increased in RT and AT/RT, but not in AT. The finding suggest that aerobic exercise is more effective in reducing these measures.

• Lean body mass increased with both RT and AT/RT, but not AT. Having the benefit to of both modes of exercise allowed AT/RT to decrease body fat percent significantly more than either AT or RT due to decreased fat mass combined with increased lean body mass.

Importance of the Findings

According to Leslie H. Willis, an exercise physiologist at Duke University Medical Center and the study’s lead author, “Given our observations, it may be time to seriously reconsider the conventional wisdom that resistance training alone can lead to weight and fat loss.”

Willis added, “If increasing muscle mass and strength is a goal, then resistance training is required. However, the majority of Americans could experience health benefits due to weight and fat loss. The best option in that case, given limited time for exercise, is to focus on aerobic training. When you lose fat, it is likely you are losing visceral fat, which is known to be associated with cardiovascular and other health benefits.”

In addition to Leslie Willis, the study was conducted by Cris A. Slentz, Lori A. Bateman, Lucy W. Piner, Connie W. Bales and William E. Kraus of the Duke University Medical Center; and Joseph A Hourmard and A. Tamlyn Shields of East Carolina University.


Story Source:

The above story is reprinted from materials provided byAmerican Physiological Society (APS), via Newswise.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.


Journal Reference:

  1. L. H. Willis, C. A. Slentz, L. A. Bateman, A. T. Shields, L. W. Piner, C. W. Bales, J. A. Houmard, W. E. Kraus. Effects of aerobic and/or resistance training on body mass and fat mass in overweight or obese adultsJournal of Applied Physiology, 2012; 113 (12): 1831 DOI:10.1152/japplphysiol.01370.2011
 

 

American Physiological Society (APS) (2013, January 2). For those short on time, aerobic, not resistance, exercise is best bet for weight- and fat loss. ScienceDaily. Retrieved January 3, 2013, from http://www.sciencedaily.com/releases/2013/01/130102172945.htm

The Science of Running: Follow the Bouncing Ball

ScienceDaily (Aug. 2, 2012) — Muscle size, genetics and training are among the countless factors that separate Olympic sprinters from the average person. On a fundamental level, however, the mechanics of running are the same for all humans. In fact, they’re basically identical for animals too.

Researchers examined the biomechanics of running and why the joints in the hips, knees and ankles “talk” to each other. (Credit: Image courtesy of Georgia Institute of Technology)


“Science has shown that running is very similar to a bouncing ball,” says Young-Hui Chang, an associate professor who oversees Georgia Tech’s “running lab,” officially called the Comparative Neuromechanics Laboratory. “When humans, horses and even cockroaches run, their center of mass bounces just like a pogo stick.”

This bouncing effect, Chang explains, means that the hip, knee and ankle joints all flex and extend at the same time when the foot hits the ground. Many of the leg muscles are turned on simultaneously, creating force and propelling the runner into the air.

“The greater the force, the greater the speed,” said Chang. “Sprinters and coaches are constantly studying ways to move leg muscles and joints as quickly as possible so that a runner can hit the ground as hard as possible.”

Elite runners and weekend joggers are able to consistently land with the same force, step after step. However, Chang’s research reveals that a stride is just like a fingerprint: no two are exactly alike. The torque generated by each joint is never the same. As a result, your legs have a mind of their own.

“Your knee, for example, automatically adjusts its own torque, each step, based on what the ankle and hip do,” said Chang. “All of this happens without your brain getting directly involved. Your joints ‘talk’ to each other, allowing you to concentrate on other things, like having a conversation or watching for cars.”

By studying how joints adapt to one another, Chang and his team will soon work with amputees to hopefully improve movement for people with prostheses. The researchers are also using their running studies to understand how people walk.

“It may seem backwards to fully understand the nuances of running before we study walking, but walking mechanics are actually more complex. Different muscles are activated at different times in a gait cycle. Joints don’t move in unison. There is no ‘bouncing ball’ phenomenon for walkers.”

Chang is an associate professor in the School of Applied Physiology in the College of Sciences.

 

Link:

http://www.gatech.edu/newsroom/release.html?nid=143521

Citation:

Georgia Institute of Technology (2012, August 2). The science of running: Follow the bouncing ball. ScienceDaily. Retrieved August 4, 2012, from http://www.sciencedaily.com­ /releases/2012/08/120802111336.htm

Running Mechanics, Not Metabolism, Are the Key to Performance for Elite Sprinters

ScienceDaily (Aug. 1, 2012) — Sprinters competing in the 2012 Olympics might assume their championship performance is the result of their fuel-efficient physiology.

Sprinting performance isn’t a factor of conserving energy; rather, forces applied by the foot hitting the ground maximize all-out bursts of sprinting, new research shows. (Credit: © NickR / Fotolia)


But a new study disproves the classic scientific view that conserving energy maximizes performance in a sprinting event.

The study by biomechanics researchers Matthew W. Bundle at the University of Montana and Peter G. Weyand at Southern Methodist University, Dallas, demonstrates that metabolic economy is not an important factor for performance in events lasting 60 seconds or less.

In fact, just the opposite is true.

“That prevailing view is no longer viable,” said Weyand. “Sprinters, if anything, are wasteful of energy. This is due to the biological trade-offs between faster muscle fibers that provide the large and rapid forces needed for sprinting, and slower muscle fibers that maximize metabolic economy.”

Instead, the key to top-flight sprinting is to maximize how hard each foot hits the ground, which allows sprinters to translate musculoskeletal and ground reaction forces into swift motion, said Bundle.

“Saving energy is critically important for endurance, but not for sprinting, which our findings indicate is not energy-limited,” Bundle said.

Metabolic energy available from sustainable, aerobic sources predominantly determines performance during endurance events by setting the intensity of the musculoskeletal performance that can be sustained throughout the effort, the study found.

For sprinters, Bundle and Weyand conclude the opposite is true.

“The intensity of the mechanical activity that the musculoskeletal system can (for a very short time) achieve determines the quantities of metabolic energy released and the level of performance attained,” according to the study.

The authors reported their findings in “Sprint Exercise Performance: Does Metabolic Power Matter?” in the July issue of Exercise and Sport Sciences Reviews.

Sprint performance variations are a function of external forces

The authors write in their study that athletic performance can be analyzed considering either the input to, or the output from, the skeletal muscles that serve as biological engines. Input is the chemical energy that fuels muscular contraction. Output is the force or mechanical power the contractions produce.

To analyze the mechanics of burst-type sprint activities, the authors said they drew on all-out running speeds and cycling power outputs of humans because of the abundance and quality of the data available and because the mechanical and metabolic contrasts between the two provide informative insights. The authors focused on durations of up to five minutes, particularly on efforts of less than a minute.

For both exercises, differences in sprinting performance were predominantly a function of the magnitude of the external forces applied because running contact lengths and cycling down-stroke lengths, as well as stride and pedal frequency, exhibited limited variations. Additionally, for both cycling and running, external forces applied during sprinting are believed to be consistently related to the corresponding muscle forces, regardless of the intensity or duration of the effort.

So what determines the maximum external forces the musculoskeletal system can apply during a brief, all-out sprint? And why do those forces decrease over the duration of the sprint?

The researchers assessed neuromuscular activation using a diagnostic procedure called surface electromyography to measure electrical activity in the activated muscle fibers. That assessment showed that neuromuscular activation increases continuously during all-out sprint cycling and running trials. More rapid increases were typical for the briefest trials that required the greatest forces. That indicates that all-out sprinting performances are highly dependent on duration because of the speed of musculoskeletal fatigue during dynamic exercise requiring large force outputs, the authors reported.

Sprint performance linked to mechanics of applying external force

Bundle and Weyand altered three independent variables to maximize the variation observed in sprint performance: Subjects were individuals with large differences in their sprint performance capabilities; all-out sprint trials spanned a broad range of durations from 2 to 300 seconds; and performance was compared across different modes of sprinting, namely cycling and running.

“The predictive success of our force application model, both within and across modes of sprint exercise, indicates that as efforts extend from a few seconds to a few minutes, the fractional reliance on anaerobic metabolism progressively impairs whole-body musculoskeletal performance, and does so with a rapid and remarkably consistent time course,” the authors wrote. “In this respect, the sprint portion of the performance-duration curve predominantly represents, not a limit on the rates of energy re-supply, but the progressive impairment of skeletal muscle force production that results from a reliance on anaerobic metabolism to fuel intense, sequential contractions.”

Conclusion of study departs from prevailing physiological paradigm

Since the muscular engines of humans and other animals are similar in terms of their metabolic and mechanical function, the findings likely apply to the burst performance capabilities of vertebrate animals in general, say the researchers.

Bundle is an assistant professor of biomechanics at the University of Montana. Weyand is an associate professor of applied physiology and biomechanics in the Annette Caldwell Simmons School of Education & Human Development at SMU in Dallas.

Funding for the study came from the U.S. Army Medical Research and Materiel Command and the Telemedicine and Advanced Technology Research Center.

 

Link:

http://blog.smu.edu/research/2012/08/01/new-study-mechanics-of-running-not-metabolism-is-key-to-performance-for-elite-sprinters/

Journal Reference:

  1. Matthew W. Bundle, Peter G. Weyand. Sprint Exercise Performance. Exercise and Sport Sciences Reviews, 2012; : 1 DOI: 10.1097/JES.0b013e318258e1c1

Citation:

Southern Methodist University (2012, August 1). Running mechanics, not metabolism, are the key to performance for elite sprinters. ScienceDaily. Retrieved August 3, 2012, from http://www.sciencedaily.com­ /releases/2012/08/120801132723.htm