October 12, 2012
Effects of Dehydration during Cycling on Skeletal Muscle Metabolism in Females

Exercising in a dehydrated state can hurt performance.  That really is nothing new.  However, what is not known is how dehydration can effect substrates being used by the  muscle during exercise, particularly in women.  So, this one is for you ladies.

Introduction:  Did you know that a 2% loss in body mass because of dehydration can elevate HR, core temperature, and the osmolarity of blood plasma?  Did you also know that it is said that women thermoregulate less effectively because of a higher core temperature during the same exercise load as men?  In fact, females usually experience a quicker rise in core temperature during exercise.  Depending on core temperature during exercise, the body can switch between using muscle glycogen or fat.  Therefore, you could say that depending on hydration status (which effects core temperature) the body will switch between these two fuel sources as well.  But which one?  The hypothesis in this study states that women will rely more heavily on whole body carbohydrate oxidation as well as the breakdown of glycogen from muscle during dehydrated exercise.

Methods:  Nine women underwent cycling at 65% VO2peak for 120 min.  Some received fluids during the exercise and the others did not.  It is important to note that before the exercise trial, both groups were properly hydrated.  Thus, this study is just examining the consequences of not drinking water during prolonged endurance exercise.

Results: One way to measure whether or not you are using carbohydrates or fat during exercise is by a method called indirect calorimetry, which can provide you with a RER.  RER, as I’ve described before, is the respiratory exchange ratio.  A RER of 1 means you are using primarily carbohydrates and a RER closer to 0.75 means you are using primarily fat.  With that said, the RER of the dehydrated group was significantly higher than the hydrated group, meaning that they were using more carbohydrates during exercise.  Likewise, carbohydrate oxidation and total body carbohydrate oxidation was higher in the dehydrated group whereas fat oxidation was lower.  The dehydrated group had a significantly higher core temperature and heart rate as well.

Discussion:  At this point you would probably like to know why being dehydrated makes the body rely more on carbohydrates rather than fat.  There currently is no answer to that; however, the authors suggest three theories behind it.

  1. An augmented nervous system response from the adrenal glands leading to activation of an enzyme that uses glycogen.
  2. Low energy levels that are sensed in cells
  3. Higher intramuscular temperature (which appears to be the primary mechanism)

My input:  It is now being understood a little more why dehydration causes performance deficits.  Clearly, if you are going to tap into your muscle glycogen faster, you will not be able to perform as long as if you were using primarily fat, which is very energy rich.  Still, more needs to be done to understand the exact mechanism for the switch.

Logan-Sprenger et al Med Sci Sports Exerc. 2012 Oct;44(10):1949-57.

May 3, 2012
Cold-water immersion for preventing and treating muscle soreness after exercise.

Taking ice baths post-exercise seems to be the most popular method of reducing delayed onset muscle soreness for novice and elite athletes.  This method, known scientifically as cryotherapy, is growing to be more popular than traditional ones such as massage, stretching, or taking non-steroidal anti-inflammatory drugs (NSAIDs).  The most popular forms of cryotherapy are cycling 1 min in ice water (5 degrees Celsius) followed by 1 minute out for a total of three times or a longer duration of 15 minutes at 15 degrees Celsius.  Now that you have the background, I’ve went out and found an enormous extensive review on the subject to make clear whether or not this technique is useful or useless at combating muscle soreness and aiding recovery.

The scientific claims:  You know that you treat sprains, strains, or any swelling in the body with ice.  The mechanisms for why cryotherapy works are similar; reduce pain, swelling, and inflammation.  There is also vasoconstriction (decreasing the diameter of the blood vessel) which stimulates blood flow and nutrient and waste transfer as well as decrease in nerve transmission speed, which could alter the threshold of pain receptors.

The studies used:  The review included 17 small trials (published from 1998-2009) of 366 participants.  No restrictions were placed on age (16-29), gender female, or type of level of exercise.  Also, no restrictions were placed on duration or frequency of immersions or depth of immersion.  The studies were all of small sample size (20 participants or less) except for one that used 54.

The exercises used:  All exercise used were designed to produce delayed onset muscle soreness (DOMS) under laboratory controlled conditions.  Repetitions for resistance exercise ranged from 50-100 of eccentric or alternative concentric and eccentric contractions.  The other studies used running or cycling in single bout efforts (for the bike) or steady state efforts.  Few actually included team sport exercise (basketball and soccer).

The cryotherapy used:  The most common for the studies was 10-15 degrees Celsius with an average immersion of 12.6 minutes.  This was employed in almost all of the studies immediately after exercise.  The different methods of cold-water immersion were compared to nothing/rest (the most common), cold-water immersion vs. contrast immersion (switching between hot and cold), cold-water immersion vs. warm water, and cold-water immersion vs. active recovery.

Enough with the technicalities.  Let’s go to the results. 

Cold-water immersion vs. nothing:  In terms of muscle soreness, there is no significant difference immediately between the two conditions but at 24, 49, 72, 96 hours later the cold-immersion group reported a significantly lower amount of muscle soreness than the group that just rested.  This effect seems to be more prevalent after running based exercises than resistance exercises but the authors not that due to the various types of exercises that were performed between all the studies, plus the sample sizes being small, it is difficult to find whether or not this is truly significant.  There were no significant differences in strength, power, functional performance, swelling, or biomarkers of muscle damage.

Cold-water immersion vs. contrast immersion:  In terms of muscle soreness, there was no significant differences between the groups.  Also, there was no significant differences in strength, power, functional performance (time to fatigue), swelling, range of movement, or biomarkers of muscle damage.

Cold-water immersion vs. warm-water immersion:  There was significant lower levels of muscle soreness reported only for the cold-water immersion group at time-point 96 hours with no differences in strength, power, functional performance, swelling, or biomarkers of muscle damage.

Cold-water immersion vs. active recovery:  There are no significant differences in reports of muscle soreness, strength, power, functional performance, swelling, or biomarkers of muscle damage.

Discussion/Conclusions:   Cold-water immersion did significantly reduce muscle soreness at time points 24, 48, 72, and 96 hours post-exercise.  However, it is important to note that these were all subjective reporting (self-reports) and the authors state it is hard to draw true conclusions from the data due to poor methodological quality.  There were high risks of bias due to the fact that blinding was performed poorly as well as concealment of group assignments (only 1 study did this effectively).  There were also large differences in the types of exercises used and subjects were a mix between trained and untrained.  The effectiveness very well may rely on the specificity of the exercise performed as well as the athletic level of the individual.

My input:  Did you know that in the 1920s, cyclists in the Tour de France would smoke during the race because they believed that smoking opened up the blood vessels and oxygen transport machinery of the lungs?  Ridiculous, right?  I’m not saying ice-baths are as crazy as this, but are they truly beneficial to aid recovery in the muscle?  I’m not so sure.  From the most basic laws of chemistry, we know that when something is heated up the molecules in it move faster and when something is cooled down the molecules in it slow down.  If you are exposing your muscles to cold, all of the molecular processes will slow down.  You need enzymes (which function effectively at specific temperatures) and proteins moving post-exercise to begin the repair process and signal inflammation, and if you’ve read my previous posts on muscle hypertrophy, you know inflammation is necessary.  It is the same reasoning to avoid NSAIDs in hopes of reducing muscle soreness.  For this reason, I’m always heading for the exact opposite after training, a hot shower.  The reason I do this is not only to continue normal biochemical processes in the muscle but also to incorporate the activation of what are called heat shock proteins.  Heat shock proteins are proteins in the body that respond to stress or elevated temperatures.  They function as chaperones for other proteins by aiding them to conform to a certain shape and stabilize proteins that are not shaped properly.  Basically, they can clean up the mess inside of the muscle cell and help with repair.  This is another reason why I’m not on the ice-bath bandwagon.  You might feel that it has helped you before in the past and it possibly could have helped, but I just want to let you know there is no scientific evidence supporting it.  The studies are low quality studies.  If you truly want a good study on this, take a group of at least 35 people, train their legs or their arms simultaneously with the same protocol and put one limb in the ice and one limb not in the ice or in warm water, take muscle biopsies, and see the differences between the conditions (Anyone want to take this on as a nice Master’s or PhD project? I’ll be glad to give advice for it).  To my knowledge this has not been done and this would be the best way to see if cold-immersion truly helps.  Although there was some evidence in a decrease in self-reported muscle soreness, I’m still not convinced and higher quality studies are necessary before I’ll be convinced.

Bleakley et al Cochrane Database Syst Rev. 2012 Feb 15;2:CD008262.

February 29, 2012

Great, great, great video.  John Hawley is a big time name in exercise metabolism research as well as a good friend of our lab.  He came to visit us a few months back on a tour of speaking throughout Europe.  I got to spend two days with him and I must tell you I gained a month’s worth of knowledge in those two days. If you’re an endurance athlete, you need to watch this.

I’ve been spending a lot of time finishing a manuscript for publication and the head of our lab put me on a new project so that is why I haven’t been posting much.  There are some good articles saved in my drafts right now that I’ll post later this week.  For now, take some time out of your day, enjoy this video, and most importantly, learn something that will help you with your fitness endeavors.  

June 27, 2011
Dehydration Reduces Left Ventricular Filling at Rest and During Exercise

Introduction:  Research suggests that the combination of increased body temperature and dehydration leads to decreased cardiac functionality during exercise.  The main factor leading to this is a decline in cardiac stroke volume (SV), that is the volume of blood pumped through the left ventricle of the heart during one beat.  Exercises physiology 101 tells us stroke volume is the difference between the end diastolic volume (EDV) (period when the ventricle relaxes and fills) and the end systolic volume (ESV) (period when the ventricle contracts and pushes blood throughout the entire body).  Therefore, the researchers wished to elucidate the effect of dehydration on left ventricular volume and mechanics at rest and during exercise (bouts of cycling in the heat)

Hypothesis:  dehydration would reduce left ventricular mechanics at rest and during exercise.

Results:  Dehydration caused a reduction in EDV, ESV, and SV during exercise.

Conclusion:  The decline in SV is clearly due to a decrease in left ventricular filling of approximately 20ml.  The factor attributed to this is a lower venous return which adds to the EDV in the stroke volume equation (SV = EDV - ESV) as well as a reduced time for the ventricle to fill with blood.

My input:  The take home message is simple here, runners and cyclists, drink your water!

Stohr et al. J Appl Physiol June 23, 2011

April 1, 2011
Fructose and Galactose Enhance Postexercise Human Liver Glycogen Resynthesis

It is believed that strategies that enhance liver glycogen post-exercise will increase exercise capacity in a subsequent exercise bout, and that the liver restores glycogen as a first priortiy over skeletal muscle when carbohydrates are available post-exercise.  Similar to my previous post, researchers wished to sort out which combinations of carbohydrate sources better replenished liver glycogen stores.

Conclusion:  This study demonstrates that ingestion of ~70 g·h-1 of maltodextrin + fructose (2:1) or maltodextrin + galactose (2:1) drinks consumed during the short-term post-exercise recovery results in a two-fold increase in the rates of liver glycogen replenishment compared to an iso-energetic, iso-osmotic maltodextrin + glucose control.

My input:  This is the first study of its kind to look at liver glycogen resynthesis with novel MRI tracer techniques.  They did note that galactose does cause some stomach upset in the cyclists.  However, whole body glycogen storage seems to be more effective when fructose is present, possibly making it the best carbohydrate source.

Practicality:  Carbohydrate drinks containing fructose and galactose could help in situations where athletes have to exercise twice in one day with relatively little recovery.

Décombaz et al MSSE March 2011

March 31, 2011
A low carbohydrate-protein supplement improves endurance performance in female athletes.

So, carbohydrates alone or in combination with protein for endurance performance enhancements?  That is the question.  Researchers at the  Department of Kinesiology and Health Education, The University of Texas at Austin, sought after the answer.   Supplements were provided every 20 minutes during exercise and were composed of a CHO mixture (1% each of dextrose, fructose, and maltodextrin) + 1.2% PRO (CHO + PRO) or 6% dextrose only (CHO).  The TTE was significantly greater with CHO + PRO in comparison to with CHO mean that the group given the mixture performed longer.

Conclusion:  ”Results from the present study suggest that the addition of a moderate amount of PRO to a low mixed CHO supplement improves endurance performance in women above that of a traditional 6% CHO supplement.Improvement in performance occurred despite CHO + PRO containing a lower CHO and caloric content. It is likely that the greater performance seen with CHO + PRO was a result of the CHO-PRO combination and the use of a mixture of CHO sources.”

My input:  The conclusion about the different mixture of CHO sources makes sense in light of their different times of digestion in the body.  For instance, that is why I always eat an apple pre-workout because fructose is a slower digesting CHO sugar than dextrose (which I would subsequently take post-workout).

The practicality: Maybe you’re asking, “Nick, I don’t know how to mix up 1% each of dextrose, fructose, and maltodextrin.”  My answer to that is simple.  Check the backs of the labels of your favorite sports drink (Gatorade, Powerade, Accerlerade, etc…) and see if they contain a mix of all 3 sugars.  Beware of real high amounts of fructose; however, because this can upset the stomach during exercise.  See which ones work best for you.

McCleave et al J Strength Cond Res. 2011 Apr;25(4):879-88.

March 29, 2011
Effect of increased dietary protein on tolerance to intensified training.

A brand new study published in MSSE studied the effect of protein intake during high-itensity training for endurance purposes.  The researchers found that increased dietary protein intake led to a possible attenuation in the short-term decrement in time trial performance after a block of high-intensity training compared with normal training.  This study was a counterbalanced crossover experimental design in which the cyclists participated in all three of the different experimental protocols.

CONCLUSIONS:  Additional protein intake reduced symptoms of psychological stress and may result in a worthwhile amelioration of the performance decline experienced during a block of high-intensity training.


Witard et al Med Sci Sports Exerc. 2011 Apr;43(4):598-607.

March 1, 2011
"Pain is temporary. It may last a minute, or an hour, or a day, or a year, but eventually it will subside and something else will take its place. It I quit; however, it lasts forever."

— Lance Armstrong