Re-thinking Triathlon Death

During last triathlon season, there were a string of deaths in the water.  Fourteen deaths in races were largely from swimming (one death occurred on the bike)

These unfortunate events led a Washington Post writer to postulate that the deaths during the swim were the result of panic attacks.  I have also heard medical personell postulate that these events were the results of heart attacks and heat stroke.

Of the deaths, the mean age was 44 and 11 were men.  6 deaths were in sprint triathlon (1/4-1/2 mile swim, 12 mile bike, 3.1 mile run), 4 in Olympic distance (1.5k swim, 40k bike, 10k run) and 3 in the longer distances (half Iron distance or Iron distance 2.4mile swim, 112mile bike, 26.2mile run) 

The cause of these deaths has been ruled drowning, but no matter what the cause of death, if it occurs in the water, chances are it will lead to drowning.  Feelings of panic are commonplace in open water, mass start events, but they do not mean that they are panic attacks.

You can feel panicky from too much coffee, a rapid heart rate, feelings that you can't breathe, etc.  It is the things that cause the rapid heart rate and rapid breathing that can lead to metabolic problems which can lead to fatal problems.

Let's examine what happens when you jump into a cold lake.  Most swims are in bodies of water that are at least 10 degrees colder than body temperature.  Cold water immersion leads to a phenomenon known as the Mammalian Diving Reflex.  This reflex decreases breathing and slows the need for oxygen and is life saving for non-swimmers and children who fall into water .  

The more dangerous response is the Cold Shock Reflex. This reflex will cause you to take a deep breath, followed by uncontrolled hyperventilation.  A triathlete who jumps into cold water, or at least puts their face in cold water, will have a temporary breath-holding reflex.  If this same triathlete starts swimming quickly, they would be out of breath before even starting.  Imagine running down the block while holding your breath; you would feel out of breath very quickly.  

Hyperventilation will happen immediately following and is one of the components of feeling panicky.  A rapid rise in heart rate will also accompany the Cold Shock Reflex and can also lead to a feeling of panic.  A tight wetsuit can make breathing difficult as well.  It is these heart and lung changes, not panic, that are responsible for many open water deaths.

In a 2010 review of triathlon swim deaths, 7 of 9 patients were found to have cardiac abnormalities.  However, 6 of the 7 were found to have left ventricular hypertrophy, which is a common finding in endurance athletes and is expected in trained endurance athletes.  One of the patients had abnormal coronary arteries, which may have contributed to the death.  This is not compelling evidence that there is a cardiac cause of sudden death in the water.

Hyperventilation can have a negative impact on the lungs.  It is not uncommon for hyperventilation to have an effect on the airways and lead to coughing or even spasm of the vocal cords.  This makes it harder to breathe and leads to increased hyperventilation.  Which can in turn lead to increased anxiety.  Anxiety worsens the cold shock response.

With repeated cold water immersions (4 days apart), the amount of hyperventilation is shorter and not as much.  Less frequent immersions diminish the length but not the magnitude of the response. One way to reproduce this habituation to the cold shock reflex is taking repeated cold showers at 50 degrees fahrenheit for 3 minutes.

3 minute showers at 50 degrees may save your life

Finally, how can we screen for the ill-effects of the cold shock reflex?  One way is to perform maximum hyperventilation while monitoring lung changes.  This is a regular component of the cardiopulmonary exercise testing. If changes in measured lung volumes or coughing is present, perhaps these changes should be treated.  Standard cardiac stress tests will probably not be useful for screening for the cold shock reflex.  If we are to prevent triathlon swim death, other tests and decreasing the response to cold water are essential.

Caffeine and Cycling time trials

I'm a big fan of caffeine. A caf-fiend, some might say. It is rumored that ethiopian shepherds first noticed the effects of caffeine after observing energetic behavior in their goats who had just eaten coffee.

Athletes are looking for that same energy.

Two recent studies on caffeine are worth mentioning.  In the first, a caffeine related improvement in performance was seen, but not in everyone.  Although 7 out of 9 individuals had improved performance, the overall improvement in performance was 1.6-1.9%. 

The dose of caffeine used was 5mg/kg, taken 90 minutes before exercise.  Caffeine doses between 3 and 6 mg/kg have also shown improvement in performance.

The same authors also found that caffeine, caused an improvement in cycling performance in trained individuals, which might help explain why only 7 of 9 individuals did better.

Caffeine increases heart rate and decreases mood, two side effects that you might not want.

Caffeine works by increasing adrenaline which, in turn increases circulating fatty acids that can be used as fuel.  If you are using predominately slow twitch fibers, then you will have more of an effect from the caffeine than if you are using predominately fast twitch fibers.  Of course, everyone has a different muscle fiber profile, so if you don't know yours, then it will be hard to determine if caffeine ingestion will work for you.

Some other interesting caffeine facts:

• Eating green leafy vegetables will lessen breakdown and clearance of caffeine , giving an extra kick (Kale latte, anyone?)
• Taking Zantac (cimetidine) will also keep the caffeine from being broken down
• You don't need to withdraw from caffeine to have it make a difference
• Repeated small doses of caffeine (1-2g/kg) during prolonged exercise can also help

References:

Astorino TA, Cottrell T, Lozano AT, Aburto-Pratt K, Duhon J. Effect of caffeine on RPE and perceptions of pain, arousal, and pleasure/displeasure during a cycling time trial in endurance trained and active men. Physiol Behav. 2012 May 15;106(2):211-7. Epub 2012 Feb 12.

Astorino TA, Cottrell T, Lozano AT, Aburto-Pratt K, Duhon J. Increases in cycling performance in response to caffeine ingestion are repeatable. Nutr Res. 2012 Feb;32(2):78-84.

Graham TE. Caffeine and Exercise; Metabolism, Endurance and Performance. Sports Med. 2001. 31(11); 785-807

Matty Reed in the Performance Lab: Part 2

The Bike Fit

One of the most important things to remember about bike fit is that power output depends not only upon angles, but also upon the rider’s strengths and weakness and how to make a rider stronger.

After series of single leg squats, planks, and joint mobility measures, it was clear that the position of comfort and maximal power would depend upon further stabilizing Matt’s core muscles.  His aerodynamic position was already  tested in the wind tunnel, so I was more concerned with keeping his frontal area minimized while changing his core stability

Because riding position changes with different power outputs, it is important to use a point on the power curve that approximates race-pace wattage.  The point that we chose was where lactic acid starts accumulating.  By testing the bike fit at this point, we could see how the changes were affecting him.

After a few changes to his elbow pads, we did another trial at race wattage.  His exhaled carbon dioxide dropped, meaning that he was not accumulating lactic acid.  

Moving the elbow pads further forward let Matt use his aero bars as levers to pull back and activate some of his core muscles which gave him more power as he pedaled.  My big concern was that this position might lead to more acid accumulation, since he was using more muscles, but the changes resulted in less lactic acid accumulation, meaning he could pedal harder before the burn of the lactic acid would cause muscle fatigue.

Using stop motion video, I was able to measure and maintain his hip and knee angles that he was comfortably using. 

He had two weeks until his next race the Boulder, Colorado 5150, in which he got second place.

Matty Reed in the Performance Lab: Part 1

A project about making a great triathlete better.

I got an email about helping out Fuji sponsored rider Matt Reed with a bike fit.  It seems that even though he was having great results all season, including a frigid win in Boise 70.3, he felt as though he wasn’t getting the power output he wanted and it was harder on the bike than in previous years.

Matt came to the Performance Lab following a 5th place in the Philly Olympic Triathlon.  I felt a little bad knowing that he raced just the day before and was now going to be doing a maximal test.  VO2max testing would help us establish his muscle fiber profile and would also give us some good power benchmarks to use for bike fitting.  On the way to reaching VO2max we can figure out how the heart lungs and muscles work together.  By analyzing the data we are able to identify where he maxed out his slow twitch fibers, his anaerobic threshold and his VO2max.

Many of the elite/pro half iron distance triathletes that I have tested have a similar profile, that is they are largely aerobic machines, using their slow twitch fibers to move them.  Once we were done with our testing, I knew that Matt was different--he has a lot more anaerobic fibers than most, which is where he gets his power.  The anaerobic fibers (also called fast twitch or Type II) are 5-10 times more powerful than slow twitch fibers.  The drawback is that fast twitch fibers can fatigue faster.

Once we know where Matt is getting his power, I gave him specific wattage based intervals to use which will help him target his strengths.  On review of the testing I was able to give Matt his nutrition requirements for the different muscle fibers that he is using when he races.

At the end of the test, I asked how he felt.  His answer? “If I knew I was going to be doing a VO2 max test, I might not have had the Ahi Tuna for lunch.”

Decreased Body Fat, Improved Mood

Let's face it, dieting is pretty brutal.  Calorie restriction not only leaves us feeling empty, but also makes us grumpy.  Furthermore, trying to lose weight in season leaves little energy to burn for training.  


Athletes who try to lose weight in season, especially if they are trying to "make weight," frequently resort to some extreme measures that leave them dehydrated, more susceptible to heat and lacking appropriate energy.


One strategy was recently reported for a jockey.


His resting metabolic needs were met by being broken down into six meals.  He maintained this regimen while continuing his daily exercise routine.  After 9 weeks, he had a 17.5 pound weight loss (8kg).  


Knowing and meeting basic metabolic needs prevents metabolic slowing which can actually result in weight gain and more difficulty in losing fat.  Using 6 daily meals helps prevent hunger which will lead to over-eating--especially when compared to the two daily meals the jockey was eating before this trial. Resting metabolic rates express the amount of calories that are burned at rest as grams of fat, carbohydrate and protein.


More importantly, aside from the loss of body fat, the jockey had an improved mood, which might help him keep up his diet and exercise routine.


source: Int J Sport Nutr Exerc Metab. 2012 Jun;22(3):225-31

Running adds years to your life and life to those years

Danish researches presenting the results of the Danish Central Register found that regular running as exercise live an average of 6 years longer than their non-running (non-exercising) counterparts. 

Jogging was associated with a 44% reduction in the risk of death over 35 years, which translates into an age-adjusted survival benefit of 6.2 years in men and 5.6 years in women.

Joggers reported an overall sense of well-being, which isn't just about extending life, but living better.

The benefit was found in 3 cumulative sessions a week, totaling one to 2.5 hours a week.

European Association for Cardiovascular Prevention & Rehabilitation
Source reference:
Schnohr P "Jogging -- healthy or hazard symposium: Assessing prognosis: a glimpse of the future" EuroPRevent2012.

Nutrition Notes

Here are the notes from a presentation that I recently gave on endurance nutrition.  While these are general guidelines and recommendations, specific numbers that apply to individuals can be calculated during exercise testing with calorimetry.  


Calorimetry lets us measure how many calories as fat, carbohydrate and protein one burns with any given exercise intensity.


Here are my nutrition guidelines for endurance events:

Nutrition Notes

Pre-Exercise

The closer to the start of exercise, the smaller amount of food needed

Choose rapidly digestible, low fiber foods (gels, liquids applesauce)

During Exercise

Energy intake for sustained high-level activity

Intake should match expenditure for maximum carbohydrate use or race pace

30-60g carbohydrate per hour

Recovery

Replace used up muscle glycogen

Prepare for the next training day/race

0.5g carbohydrate per pound of body weight & 0.16g protein per pound of body weight

Race Day Plan

24 Hours to Go

Carbohydrate-load: 2.5 minute threshold effort followed by 30 seconds at VO2max

10g/kg carbohydrate (5g/lb) over next 24 hours

Carbohydrate should be low glycemic and low fiber

3 hours to go

Last solid meal.  Meal should be mostly low glycemic carbohydrate

Protein should be 10% of total calories

2 hours to go

4-6% Carbohydrate solution (4-6 grams of carbohydrate per 100ml water)

30 minutes to go

High glycemic index snack (gel, applesauce)

Race Time

Fluid consumed to limit sweat loss to 1% of body weight

Carbohydrate if racing for more than 1 hour

Running Stride Frequency

One of the best changes to come out of the minimalist running movement has been an increase in stride frequency.  By increasing frequency, the "over-stride" is prevented as runners have to decrease the stride length as they increase their foot turnover speed.  Higher foot turnover can also decrease impact forces on the leg compared with a higher stride frequency (longer stride length) at any given speed.

The study found that increasing stride frequency by 17-18% decreased impact.  For example if your foot cadence is 160 strides/minute, increasing by 18% (160 x 1.18 = 188) would yield a stride frequency of 188 strides/minute.

In this study, a metronome was used to help the subjects keep in step with their selected foot cadence.

To count your foot cadence, keep track of the number of times your foot hits the ground in 1 minute.  Multiply by 1.18 to find your ideal cadence for decreasing impact forces.  

Not everyone needs to decrease impact forces, however.  Most running injuries are not directly impact related, but rather, are related to how well we deal with impact.

Beware of Brown Rice Syrup?

In a study published in Environmental Health Perspectives, researchers question the safety of Organic Brown Rice Syrup (OBRS) as a sweetener in gels.  There are no current regulations regarding Arsenic in food, however bars and high energy foods containing OBRS also had higher As concentrations than equivalent products that did not contain OBRS.  I doubt that occasional gel use will become a problem, but taking a gel every 30minutes during a 140.6 event could, theoretically, result in increased arsenic levels in the body.

What I learned from a VO2max Test

Using CardioPulmonary Exercise Testing as a training tool

I have been trying to increase my speed over the 5k-8k distances.  No matter how hard I think I can go or how hilly the course is, my pace over this distance didn’t seem to change much this season.  

I decided to look into why this could be.  After all, if I can do intervals faster than this pace, shouldn’t I be able to race at a faster pace?  This season I started doing threshold intervals that were slightly faster than my threshold intervals last season, but was unable to complete a full set of 6, usually getting tired by number 3.

I decided it was time to check if my heart, lungs and muscles were doing everything that they should be doing.

Using a ramp protocol (increasing speed by 1 mile/hr every 2 minutes), I ran on the treadmill while collecting the usual data (Heart rate, oxygen, carbon dioxide, breathing rate and volume).  While my VO2max was increased from 1.5 years ago, the real story is what happened on the way to my VO2max.

I topped out my slow twitch fibers at 8 mph.  I could theoretically keep this pace for ever, assuming I could continue fueling my body.  Beyond this point, the acid from lactic acid was affecting me.

My Anaerobic Threshold occurred at 9 mph (6:40 min/mile pace).  This is a pace I can sustain for about 5 minutes.

My VO2max occurred at 11mph and I was able to hold it for 90 seconds

What do these numbers mean?

My marathon pace would be 8mph, assuming I could remember to fuel during the marathon.

My 6:55 pace for my last few races is explained by my Anaerobic Threshold pace of 6:40.  For shorter distance races, I tend to use all of my slow twitch (type I) and some of my fast twitch fibers (type IIA) when I race.  

Starting the first two kilometers of an 8k at a 6:30 pace is definitely too fast.  I’d be much better off running just below my Anaerobic Threshold and kicking up the pace at the last half mile or so.  I now realize that my tendency is to start out too fast which leaves me struggling to recover during the middle part of a race.

To increase my Anaerobic Threshold pace, I plan on doing 6-8 intervals of 4 or 5 minutes at threshold with either 2 or 1 minutes of rest.  If I can’t maintain this pace for this time, I know that I will have to work harder on replacing my glycogen stores after a workout.

This also explains why I was failing during the second or third 4 minute interval at 11mph.  There’s no way I should be able to sustain my VO2max pace for that long, especially since I could only sustain it for 90 seconds during my test.  I had chalked it up to depleted glycogen and not eating enough during the day, however, now I know that I might actually be eating enough during the day to train after work.

Being seen at night

Blinking lights are commonplace on the backs of commuters and others who are out on the roads training at night.  Well, according to a recent study, that might not be enough.  Twenty four drivers were placed on a road course with a cyclist wearing black clothing with either nothing else, a reflective vest, or a vest plus ankle and knee reflectors.  The bike was outfitted with a steady light, a blinking light, or no light.


Drivers noticed cyclists with a combination of vest, ankle, and knee reflectors.


The light did not make cyclists more conspicuous according to the study.


Lights are easy to mount, however they don't lead to increased visibility.  One take home point is that should be placed on knees and ankles, not on the bike.


Also, look out for expensive SUV's, as they are the number one killer of cyclists.

Recovery for Endurance Athletes

Whether you are riding long and slow or are hammering out some intervals, you need to be recovered to be able to do it all over again the next training day.  There are many components to recovery including removing metabolic waste products (lactic acid,oxidative free radicals), bringing in new amino acids for rebuilding, storing carbohydrates as glycogen, and decreasing muscle soreness.  Recently some high-tech methods that were previously available only to big-budget professionals have come down in price.  Since they have been around for a while, there’s plenty of research into their benefits.

Recovery is the ability to repeat a hard effort again within a short period of time.  When looking at recovery, it is important to ask if the way it makes you feel also goes hand in hand with the ability to exercise again.

Nutrition

Since eating is something with which most endurance athletes are familiar, this should be a good place to start. 

Recovery from exercise, especially from intense exercise, should start with replacing what you’ve lost during exercise.  While many athletes are concerned about staying lean, muscle glycogen should be the focus after exercise, not limiting calories.  A good dose of carbohydrate is 1g per kilogram (1g per 2.2 lbs of body weight).  The insulin that is released to place this carbohydrate into the muscle will also drive protein building blocks into the muscle.  The carbohydrate should be accompanied by 1/3 g per kilogram of body weight.  For the 150lb athlete this translates to:

150lb / 2.2 = 68 g of carbohydrate

68 x 0.3 = 22.67g of protein

While these numbers don’t have to be exact, they are good guidelines as long as you continue to eat between your workouts.  In the face of glycogen depleting workouts, this  amount of carbohydrate and protein should be consumed immediately and one hour following exercise.

How can you tell if your exercise was glycogen depleting?  You shouldn’t be able to replicate your intervals once your glycogen has been depleted.

Another important nutritional concern is maintaining hydration.  After a workout, you shouldn’t be losing a lot of weight.  Any weight loss is from dehydration if you didn’t eat.  You can get a good estimate of sweat loss by weighing yourself before and after a 30-minute exercise session.  The difference in dry/naked weight is your sweat loss (1lb equals 16oz) over 30 minutes.  

It is likely that replacing that much fluid will be very difficult to drink during exercise, so be sure to replace it afterward.

Although nutrition concerns are important for the ability to go hard at the next workout, eating provides fuel, but doesn’t provide relief from soreness.  For that we need to look to some other modalities.

Contrast Temperature Water Immersion

Contrast temperature water immersion involves alternating between soaking in cold (50 degree F/10 degree Celsius) and warm (110 degree Fahrenheit/42degrees Celsius) water baths.  The cold baths were 1 minute and the warm baths were for 2 minutes.  This was repeated for 6-10minutes.

Lactic acid was cleared faster with CTW than with rest, but 4 hours after exercise, there was no difference.  CTW did relieve muscle soreness more than a recovery run (done at 40%).  

Electrical Stimulation

You may have seen infomercials for electrical muscle stimulation.  Usually they are worn  by a large, well-muscled, lean man who is watching TV and getting six-pack abs.  Stim units are also used for recovery.  The theory behind them is that the muscle contractions that occur from the stimulation will act like a pump to move out metabolic waste products and facilitate recovery.

Compression

One doesn’t have to look far to see how quickly compression garments have taken off.  They are nearly ubiquitous in marathons and distance running, and calf compression sleeves are seen on many triathletes.  While their benefits during exercise are important to discuss, improved recovery  is also one of the claims.  Although there was decreased muscle soreness, muscles couldn’t be made to work any harder nor could they be electrically stimulated to work harder.

The effects of compression on performance and decrease in metabolic waste products is largely due to the improvements in the way the muscles feel, however there is some ability to speed lactate clearance.

Graded compression

Graded pneumatic compression boots “space boots” burst onto the endurance scene with their use by several high-profile professional cycling teams.  Before their use in the peloton, the boots were used to help with lymphatic drainage in patients with leg swelling.  There aren’t any studies that look at athletes, but the results for increase blood flow from non-athletic populations are encouraging.  Anyone who has put them on will tell you that they feel great once they have been removed.

Conclusion

Considering the cost range for the listed modalities ranges from free to $5,000, with the same decrease in muscle soreness, it seems like trying Contrast Temperature Water Immersion is a good place to start.  Other modalities, such as foam rolling, high-cadence spins can also be tried to achieve the same mechanism for decreased muscle soreness.

References

Eur J Appl Physiol. 2011 Oct;111(10):2501-7. Epub 2011 Aug 17.

Does electrical stimulation enhance post-exercise performance recovery?

Babault N, Cometti C, Maffiuletti NA, Deley G.

J Sci Med Sport. 2004 Mar;7(1):1-10.

Effect of recovery modality on 4-hour repeated treadmill running performance and changes in physiological variables.

Coffey V, Leveritt M, Gill N.

J Sci Med Sport. 2010 Jan;13(1):136-40. Epub 2009 Jan 7.

The effects of compression garments on recovery of muscle performance following high-intensity sprint and plyometric exercise.

Duffield R, Cannon J, King M.

Int J Sports Physiol Perform. 2008 Dec;3(4):454-68.

The effects of compression garments on intermittent exercise performance and recovery on consecutive days.

Duffield R, Edge J, Merrells R, Hawke E, Barnes M, Simcock D, Gill N.

Br J Sports Med. 2007 Jul;41(7):409-14; discussion 414. Epub 2007 Mar 6.

Comparison of three types of full-body compression garments on throwing and repeat-sprint performance in cricket players.

Duffield R, Portus M.

PLoS One. 2011;6(12):e27749. Epub 2011 Dec 7.

Effects of Whole-Body Cryotherapy vs. Far-Infrared vs. Passive Modalities on Recovery fromExercise-Induced Muscle Damage in Highly-Trained Runners.

Hausswirth C, Louis J, Bieuzen F, Pournot H, Fournier J, Filliard JR, Brisswalter J.

Eur J Vasc Endovasc Surg. 2005 Aug;30(2):164-75.

Improvement of the walking ability in intermittent claudication due to superficial femoral artery occlusion with supervised exercise and pneumatic foot and calf compression: a randomised controlled trial.

Kakkos SK, Geroulakos G, Nicolaides AN.

J Sports Sci. 2005 Jun;23(6):619-27.

The use of recovery methods post-exercise.

Reilly T, Ekblom B.

Eur J Appl Physiol. 2010 Sep;110(2):425-33. Epub 2010 May 30.

Effects of compression stockings during exercise and recovery on blood lactate kinetics.

Rimaud D, Messonnier L, Castells J, Devillard X, Calmels P.

Eur J Appl Physiol. 2011 Jun 28. [Epub ahead of print]

The effect of post-exercise hydrotherapy on subsequent exercise performance and heart rate variability.

Stanley J, Buchheit M, Peake JM.

Int J Sports Physiol Perform. 2011 Dec 12. [Epub ahead of print]

Effect of Contrast Water Therapy Duration on Recovery of Running Performance.

Versey NG, Halson SL, Dawson BT.

Not just for drying laundry...

Many people end up using their treadmills as clothes dryers...


Or so I was warned when purchasing one a few years ago.   Check out this article on Shape.com which features some advice on alternative ways to use the treadmill as an exercise device;
http://www.shape.com/blogs/shape-your-life/5-unique-ways-make-most-your-treadmill

Hand Paddles for Swimming

The other day I decided to buy my own swim paddles.  Being relatively new to the sport, I had been using paddles from my pool.  One of my colleagues at work suggested paddles would be a good investment, especially when traveling as they pack flat.  I was overwhelmed by the choices that exist: big, small, flat, curved, straps, loops.

I went to the medical and exercise science research for some answers.  Here’s what I learned:

• The use of hand paddles did not cause significant changes in hand placement and movement
• Hand paddles increased swim speed, stroke length and stroke time.  These changes increase with bigger paddles
• Hand paddles decreased stroke rate

I had read that hand paddles were to help with getting a feel for the “catch” and “pull”.  I know that if I don’t enter the water with my paddled hand right, it will get caught in the water and pulled in a funny direction.  However, the research doesn’t seem to support any lasting differences.

So, how can we use paddles more effectively?

One of the ways that I have started to use them is to employ Post-Activation Potentiation, or PAP.  I can best explain PAP like this: stand with your right side against a wall.  Lift your right arm to the side, pushing it against the wall.  Continue pushing against the wall for 20 seconds.  Now step away from the wall, you will feel like your arm is floating into the air by itself.

Using paddles, we can achieve the same effect.  Swim 50m with the large paddles, keeping your stroke rate normal.  By pushing your hands through the water, there is a large, almost isometric force across the arms.

Take a short break after the 50m and take off the paddles.

Start swimming again without the paddles and you will be able to turn over your stroke much faster and each stroke will seem easier.

Based upon this use of hand paddles, I opted for larger ones to get more resistance.  

References:

Gourgoulis V. et al. The influence of hand paddles on the arm coordination in female front crawl swimmers. J Strength Cond Res. 2009 May; 23(3):735-40

Gourgoulis V. et al. Hand orientation in hand paddle swimming. Int J Sports Med. 2008 May;29(5):429-34. Epub 2007 Sep 18.

Gourgoulis V. et al. Effect of two different sized hand paddles on the front crawl stroke kinematics. J Sports Med Phys Fitness. 2006 Jun; 46(2):232-7.

Telles T, et al. Effect of hand paddles and parachute on the index of coordination of competitive crawl-strokers. J Sports Sci. 2011 Feb; 29(4):431-8.