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Does dehydration impair endurance exercise performance? ~ Félix-Antoine Savoie & Eric Goulet

Most major sports and nutrition organizations support the notion that loss of body mass through dehydration (i.e., hypohydration) impairs endurance exercise performance [1-4]. For example, in their latest stance regarding fluid intake during exercise, the American College of Sports Medicine states that “the goal of drinking during exercise is to prevent excessive dehydration (greater than two percent body weight loss from water deficit) … to avert compromised exercise performance”[1].

Photo by Nelson Minar. Used with permission. All rights reserved. Source: flickr

Photo by Nelson Minar. Used with permission. All rights reserved. Source: flickr

Most studies have used exercise protocols, including fixed-intensity or incremental exercise bouts to investigate the effects of dehydration on endurance performance [5,7]. Although it makes sense to use imposed-intensity exercise protocols, athletes have the freedom to choose and alter their pace at will. Conclusions regarding endurance performance are better derived therefore from studies that use time-trial type exercise protocols [6].

Goulet demonstrates in a recent meta-analysis [7] that the impact of exercise-induced dehydration on cycling performance depends on an athlete’s ability to control his or her pace. Goulet’s results show that when intensity is imposed, dehydration-induced body mass loss as low as 1.75 percent impairs performance; whereas body mass deficits of up to four percent have no bearing on cycling time-trial performance. These results agree with several field studies that have found significant relationships between body mass loss and endurance performance, such that athletes who lose the most weight during an endurance competition are often those who perform the best [8-11].

It must be clear to athletes and coaches alike that these results should not be taken as an incentive to voluntarily restrict fluid intake during exercise. However, it does signify that body mass losses due to water deficit are less meaningful to endurance performance than previously thought.

How much should an athlete drink during exercise?

In 2006, the International Marathon Medical Director Association (IMMDA) issued their own position statement on fluid intake during exercise. They recommend that athletes refer to the sensation of thirst to determine fluid intake [12]. The foundation beneath this recommendation was that plasma hyperosmolality, as occurs with exercise-induced sweat loss [13], is far more detrimental to endurance performance than is body water loss.

Drinking according to thirst suffices to maintain plasma osmolality within homeostatic range.  Albeit no direct scientific evidence supports the IMMDA’s claim, a recent meta-analysis has shown that gauging fluid intake with thirst optimizes endurance performance; drinking below it meaningfully decreases endurance performance [14]. We contend that athletes should drink according to the dictates of thirst with no need for more.

Dr. Eric Goulet, PhD, has been an adjunct professor of exercise physiology and a researcher at the Research Center on Aging of the University of Sherbrooke since 2009. Eric has authored twelve peer-reviewed publications related to endurance performance and hydration and is on the editorial board of the Journal of Exercise Physiology online.

Félix-Antoine Savoie (BSc) is a graduate student at the University of Sherbrooke and currently under the supervision of Dr. Goulet. 


1.         Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS. American College of Sports Medicine position stand. Exercise and fluid replacement. Medicine and science in sports and exercise. 2007 Feb;39(2):377-90.

2.         Casa DJ, Armstrong LE, Hillman SK, Montain SJ, Reiff RV, Rich BS, et al. National athletic trainers’ association position statement: fluid replacement for athletes. Journal of athletic training. 2000 Apr;35(2):212-24.

3.         International Olympic Committee Consensus Statement on Sports Nutrition.  2010  [cited; Available from:

4.         Rodriguez NR, Di Marco NM, Langley S. American College of Sports Medicine position stand. Nutrition and athletic performance. Medicine and science in sports and exercise. 2009 Mar;41(3):709-31.

5.         Cheuvront SN, Carter R, 3rd, Sawka MN. Fluid balance and endurance exercise performance. Current sports medicine reports. 2003 Aug;2(4):202-8.

6.         Mundel T. To drink or not to drink? Explaining “contradictory findings” in fluid replacement and exercise performance: evidence from a more valid model for real-life competition. British journal of sports medicine. 2011 Jan;45(1):2.

7.         Goulet ED. Effect of exercise-induced dehydration on endurance performance: evaluating the impact of exercise protocols on outcomes using a meta-analytic procedure. British journal of sports medicine. 2012 Jul 4.

8.         Zouhal H, Groussard C, Minter G, Vincent S, Cretual A, Gratas-Delamarche A, et al. Inverse relationship between percentage body weight change and finishing time in 643 forty-two-kilometre marathon runners. British journal of sports medicine. 2011 Nov;45(14):1101-5.

9.         Sharwood KA, Collins M, Goedecke JH, Wilson G, Noakes TD. Weight changes, medical complications, and performance during an Ironman triathlon. British journal of sports medicine. 2004 Dec;38(6):718-24.

10.       Kao WF, Shyu CL, Yang XW, Hsu TF, Chen JJ, Kao WC, et al. Athletic performance and serial weight changes during 12- and 24-hour ultra-marathons. Clinical journal of sport medicine : official journal of the Canadian Academy of Sport Medicine. 2008 Mar;18(2):155-8.

11.       Zouhal H, Groussard C, Vincent S, Jacob C, Abderrahman AB, Delamarche P, et al. Athletic performance and weight changes during the “Marathon of Sands” in athletes well-trained in endurance. International journal of sports medicine. 2009 Jul;30(7):516-21.

12.       Hew-Butler T, Verbalis JG, Noakes TD. Updated fluid recommendation: position statement from the International Marathon Medical Directors Association (IMMDA). Clinical journal of sport medicine : official journal of the Canadian Academy of Sport Medicine. 2006 Jul;16(4):283-92.

13.       Shirreffs SM, Sawka MN. Fluid and electrolyte needs for training, competition, and recovery. Journal of sports sciences. 2011;29 Suppl 1:S39-46.

14.       Goulet ED. Effect of exercise-induced dehydration on time-trial exercise performance: a meta-analysis. British journal of sports medicine. 2011 Nov;45(14):1149-56

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Exercising during pregnancy reduces the risk of high birth weight newborns and of caesarean delivery ~ Jonatan Ruiz

Taking moderate-intensity exercise three times a week during the second and third trimester of pregnancy halves the risk of having a high birth weight newborn (babies with macrosomia, that is, weighing over four kilos) and, therefore, the risk of needing a caesarean delivery.

Photo by Serge Melki. Used with permission. All rights reserved. Source: flickr

Photo by Serge Melki. Used with permission. All rights reserved. Source: flickr

These findings come from research led by Rubén Barakat of the Polytechnic University of Madrid, Alejandro Lucía of the European University of Madrid, and Jonatan Ruiz of the University of Granada. Together with Sports Science graduates, they ran a series of programmed training sessions for a sample of 510 sedentary pregnant women. The results of their study have been published in the British Journal of Sports Medicine.

The researchers contacted a total of 780 Spanish pregnant women attending two primary health care centres in Leganés (Madrid). Finally, 510 gave their consent to participate in the study. They all recognized they were sedentary—that is, that they exercised for less than twenty minutes on fewer than three days a week.

55 minutes exercise

The intervention group followed a training program that consisted of fifty-five minute sessions of aerobic, muscle strength and flexibility exercises on three days a week from weeks 10-12 to weeks 38-39 of pregnancy, while the control group received standard recommendations and care.

The results showed the training sessions did not reduce the appearance of gestational diabetes mellitus but did diminish the incidence of two major associated risks: macrosomia (down by fifty-eight percent) and caesarean delivery (which fell by thirty-four percent).

These findings “reinforce the need to encourage more supervised exercise interventions during pregnancy to combat the negative effects of gestational diabetes mellitus”, says Jonatan Ruiz, researcher in the University of Granada Department of Physical and Sports Education and corresponding author of the study.

Post published originally in CANALUGR.

Jonatan R Ruiz is a Ramón y Cajal Research Fellow at the School of Physical Activity and Sport Sciences at the University of Granada (Spain). Ruiz has a PhD in Exercise Physiology from the University of Granada (Spain), and a second PhD in Medical Sciences from the Karolinska Institutet (Sweden). His research combines physical activity epidemiology with clinical physiology to study the interaction between physical activity, fitness, features of the metabolic disorders, and genetics.

Barakat R, Pelaez M, Lopez C, Lucia A, Ruiz JR. Exercise during pregnancy and gestational diabetes-related adverse effects: a randomised controlled trial. Br J Sports Med 2013 47: 630-636 doi: 10.1136/bjsports-2012-091788

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When should an Achilles tendon be injected? ~ Dr. Jill Cook

Many treatment options exist for recalcitrant Achilles tendinopathy, as detailed in Clinical Sports Medicine, including sclerosing, autologous blood and corticosteroid injections. What is lacking in most research reports is a clinical decision-making algorithm –when, and in whom, should I use these various interventions?

As interventions are investigated in isolation the literature does not enlighten us at all; so we are left to clinical guidance. This does not necessarily help us either, as many clinicians become advocates for certain treatments, convinced of its efficacy, and are not thoughtful about selecting interventions for different clinical presentations.

Photo by texmex5. Used with permission. All rights reserved. Source: flickr

Photo by texmex5. Used with permission. All rights reserved. Source: flickr

So what to do? Aside from being well informed on the pathology and presentation of Achilles tendinopathy, clinicians should consider the answers to at least some of the following questions before recommending invasive Achilles tendon treatments:

  1. Is the premise underlying the treatment defensible??
  2. Are there comprehensive pre-clinical data?
  3. Are there comprehensive supportive clinical data?
  4. What is the quality of the clinical data?
  5. Is it economically reasonable and are there any practitioner competing interests?
  6. Does the treatment have a clinical reasoning process?
  7. Are the risks reasonable compared to the projected benefits?

So many of the uni-modal treatments for Achilles tendinopathy fail first at Point 1, where the pathology of tendinopathy and the proposed treatment effect cannot be reconciled. They then fail at many of the subsequent points as well: this is when the thoughtful clinician will look for other more logical alternatives.

Few of the current injections offered for tendinopathy can be justified if we ask the hard questions about the treatment. So the answer to the original question “when should an Achilles tendon be injected?” is “rarely.” Or at least that is the answer until there is more clinical research that improves the background understanding of these treatments.

Jill Cook is a Professor in musculoskeletal health in the School of Primary Health Care, Monash University in Australia. Cook’s research areas include sports medicine and tendon injury. Cook currently supplements her research by conducting a specialist tendon practice and by lecturing and presenting workshops both in Australia and overseas.

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“Fortunes favour the prepared mind.” Being prepared for sporting emergencies ~ Shane Brun

Fortunes favour the prepared mind” and making assumptions can sometimes help…

Emergencies in the sporting context are something we hope will never happen; unfortunately they do and are happening more frequently. In healthcare we are constantly reminded never to assume and always confirm our clinical suspicions. Managing emergencies in sports is no different, or is it?

Unfortunately, too many people die unnecessarily because those around them are ill prepared or ill equipped to deal with the emergency in front of them. Sadly, this situation occurs far too often in the sporting context as well. In some cases, when managing the severely injured athlete making some assumptions may be lifesaving. Here are a few:

Situation Assumption Response
If an athlete collapses and becomes unconscious during training or competition and the cause of the collapse did not result from contact or a collision. The cause of the collapse is a cardiac arrest unless proven otherwise. Commence Basic Life Support (BLS) and obtain an AED immediately. (
If an athlete collapses and becomes unconscious during training or competition and the cause of the collapse did result from contact or a collision. The athlete has sustained a spinal injury as well as a head injury. Whilst assessing and managing Airway, Breathing and Circulation, ensure inline spinal immobilisation. This involves the entire spine and not just the neck; immobilising only the neck may worsen the problem.
Someone is unconscious. Their airway is blocked and the most likely cause is their tongue and soft tissues at the back of the throat. Head tilt and chin lift is the most effective immediate way of clearing an airway(1).
Someone who is unconscious and not breathing normally. This person is in cardiac arrest. Whilst applying BLS principles, apply and use an AED as soon as possible. For every one minute delay in defibrillation there is a 10% reduction in survival(2). Extrapolation of conservative data suggests that in a population the size of Australia anywhere from 125-5,000(3-7) people per year will have a Sudden Cardiac Arrest. An AED will save many of them, (road traffic incidents account for about 1,500 deaths per year).
You are confronted by an emergency situation. Chances are you may be the only one with the skills to manage the situation. Ensure you and your support team practice your emergency drills regularly.
An explosion, fire or stadium collapse occurs. The nearest emergency exit is blocked. Ensure you and your team are aware of all emergency exits and the best way to get to them. You should be familiar with the contents of chapter 47 of CSM4(8).
An athlete is experiencing an itch and lip and facial swelling, redness, you hear them wheezing and they are finding it difficult to breathe shortly after taking some anti-inflammatory medication. This person is having an anaphylactic reaction and they will become much worse very quickly. Administer adrenaline intramuscularly immediately(9); this person will die of an airway blockage, shock or both unless they are treated immediately.

Shane Brun is Associate Professor of Musculoskeletal and Sports Medicine at James Cook University Queensland Australia. He is also Visiting Professor to the Sports Medicine unit of the University Malaya and an elite medical officer with the Asian Football Confederation (AFC) and Fédération Internationale de Football Association (FIFA).


  1. Koster RW, Sayre MR, Botha M, Cave DM, Cudnik MT, Handley AJ, et al. Part 5: Adult basic life support: 2010 International consensus on cardiopulmonary resuscitation and emergency cardiovascular care science with treatment recommendations. Resuscitation. 2010 Oct;81 Suppl 1:e48-70. PubMed PMID: 20956035.
  2. Sunde K, Jacobs I, Deakin CD, Hazinski MF, Kerber RE, Koster RW, et al. Part 6: Defibrillation: 2010 international consensus on cardiopulmonary resuscitation and emergency cardiovascular care science with treatment recommendations. Resuscitation. 2010 Oct;81 Suppl 1:e71-85. PubMed PMID: 20956034.
  3. Van Camp SP, Bloor CM, Mueller FO, Cantu RC, Olson HG. Nontraumatic sports death in high school and college athletes. Medicine and science in sports and exercise. 1995 May;27(5):641-7. PubMed PMID: 7674867.
  4. Maron BJ, Gohman TE, Aeppli D. Prevalence of sudden cardiac death during competitive sports activities in Minnesota high school athletes. J Am Coll Cardiol. 1998 Dec;32(7):1881-4. PubMed PMID: 9857867.
  5. Atkins DL, Everson-Stewart S, Sears GK, Daya M, Osmond MH, Warden CR, et al. Epidemiology and outcomes from out-of-hospital cardiac arrest in children: the Resuscitation Outcomes Consortium Epistry-Cardiac Arrest. Circulation. 2009 Mar 24;119(11):1484-91. PubMed PMID: 19273724. Pubmed Central PMCID: 2679169.
  6. Harmon KG, Asif IM, Klossner D, Drezner JA. Incidence of sudden cardiac death in national collegiate athletic association athletes. Circulation. 2011 Apr 19;123(15):1594-600. PubMed PMID: 21464047.
  7. Maron BJ, Doerer JJ, Haas TS, Tierney DM, Mueller FO. Sudden deaths in young competitive athletes: analysis of 1866 deaths in the United States, 1980-2006. Circulation. 2009 Mar 3;119(8):1085-92. PubMed PMID: 19221222.
  8. Brun S. Medical Emergencies in the Sporting Context. In: Peter Brukner KK, editor. Clinical Sports Medicine. 4 ed. Sydney: The McGraw-Hill Companies; 2012. p. 972-95.
  9. Brown SG, Mullins RJ, Gold MS. Anaphylaxis: diagnosis and management. Med J Aust. 2006 Sep 4;185(5):283-9. PubMed PMID: 16948628.



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Core Training: Considering Anatomy and Function in Spinal Flexion Exercises ~ Johann Windt

Up to eighty-five percent of the population will experience low back pain at some point during their lives.(1) In response to this potentially debilitating condition, the link between low back pain and core training has long been investigated. Numerous investigations have demonstrated that various core training regimes may help mitigate chronic low back pain.(2-4)

Optimal core training in the treatment of lower back pain is beyond the scope of this post, and has been written of elsewhere.(5) Instead, this post will serve as a brief reminder to consider a couple concerns associated with repeated spinal flexion exercises (ie. sit-ups and crunches) in core training and low back rehabilitation before encouraging or prescribing them.

Photo by The U.S. Army. Used with permission. All rights reserved. Source: flickr

Photo by The U.S. Army. Used with permission. All rights reserved. Source: flickr

Many people still consider spinal flexion exercises as a primary mode of core training. Dr. Stuart McGill, in particular, has highlighted two primary concerns with these exercises, especially if done for treatment or prevention of low back pain. One concern is anatomical, another functional.

First, data has demonstrated that unlike spinal compression, repeated spinal flexion consistently contributes to the deterioration of the intervertebral discs and increases the risk for disc herniation.(6-7) Furthermore, the execution of full sit-ups exacerbates this problem by placing a large compressive load in the lumbar spine in its flexed position.(8-9)

From a functional perspective, such exercises emphasize the production of power from abdominal muscles initiating the movement. However, in the majority of everyday situations and in most sporting instances, the core musculature is braced and transmits the force produced by the hips and legs.(10-11)

For both these reasons, it may be wise to replace exercises that emphasize spinal flexion with those whereby the core resists motion through the bracing of the abdomen.(12) Variations of the crunch, such as the curl-up, help to recruit the rectus abdominis adequately while sparing the lumbar spine.(11-12)

This is not a call to completely abandon spinal flexion exercises, but simply a reminder of one component of making wise, evidence-based decisions regarding core training for low back pain. Given the popularity of these exercises, understanding the above concerns can help inform practice and improve patient outcomes.

For more information on core-training and its role in injury prevention, rehabilitation and performance read Chapter 14 “Core Stability” and Chapter 26, “Low Back Pain” in Clinical Sports Medicine.

Johann Windt is a graduate student at the University of British Columbia under the supervision of Dr. Karim Khan. Windt’s experience as a strength and conditioning coach and trainer empowers his belief that exercise is medicine, the message that his current research promotes.


1      Press J, Dvorak J. Low back pain. In Brukner P, Bahr R, Blair S, et al. eds. Brukner & Khan’s Clinical Sports Medicine. McGraw Hill 2012. 463–91.

2      Saal JS, Saal JA, Yurth EF. Nonoperative Management of Herniated Cervical Intervertebral Disc With Radiculopathy. Spine 1996;21:1877–83.

3      Manniche C, Lundberg E, Christensen I, et al. Intensive dynamic back exercises for chronic low back pain: a clinical trial. Pain 1991;47:53–63.

4      O’Sullivan PB, Phyty NDM, Twomey LT, et al. Evaluation of Specific Stabilizing Exercise in the Treatment of Chronic Low Back Pain With Radiologic Diagnosis of Spondylolysis or Spondylolisthesis. Spine 1997;22:2959–67.

5      McGill S. Low back disorders: evidenced-based prevention and rehabilitation. 2nd ed. Champaign, IL: : Human Kinetics 2007.

6      Callaghan JP, McGill SM. Intervertebral disc herniation: studies on a porcine model exposed to highly repetitive flexion/extension motion with compressive force. Clin Biomech 2001;16:28–37.

7      Tampier C, Drake JDM, Callaghan JP, et al. Progressive Disc Herniation. Spine 2007;32:2869–74.

8      McGill SM. The mechanics of torso flexion: situps and standing dynamic flexion manoeuvres. Clin Biomech 1995;10:184–92.

9      Juker D, McGill SM, Kropf P, et al. Quantitative intramuscular myoelectric activity of lumbar portions of psoas and the abdominal wall during a wide variety of tasks. Med Amp Sci Sports Amp Exerc 1998;30:301–10.

10   McGill S. Core Training: Evidence Translating to Better Performance and Injury Prevention. Strength Cond J 2010;32.

11   McGill S. Ultimate back fitness and performance. Backfitpro Inc 2009.

12   McGill SM. Low Back Exercises: Evidence for Improving Exercise Regimens. Phys Ther 1998;78:754–65.


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