Tuesday, April 8, 2014

Cardiovascular events during ballroom dancing

Hi everyone! Sorry for the long break in between posts- we had lots of competitions and I had lots of midterms to study for!
One of the competitions we went to this spring was the USA Dance Amateur Nationals. We had lots of fun and did better than I expected. Unfortunately, however, the weekend was not all positive. A fellow competitor collapsed in the ballroom and later passed away (more information here). This is a tragic event, and my thoughts and sympathies are with his family and friends.
This tragedy sparked some interesting discussion on whether AED (automatic external defibrillators) should be mandatory in the ballroom, and I thought that I could better outline my opinion on the issue in a blogpost, with a little more room to prattle on.

First off, lets talk about the cardiovascular demands of competitive ballroom. One study (which I cannot find at the moment) gives the estimated MET load of an elite dancer doing a vigorous dance (V. waltz, quickstep, jive, etc) at about 11 METs. For readers who aren't familiar with METs, they are a unit that tell you how much energy an activity takes. While you are sitting there reading my blog, you are at 1 MET. Running at 6 mph puts me personally at about 10 METs, although this will differ for each person by body weight. Another study found that heart rate during ballroom reaches an average of 175 bpm for males and 178 bpm for females. This is an incredibly high heart rate, considering the calculation to determine predicted maximal heart rate is 208-0.7(age). The average 22 year old (hello, world!) has a max heart rate of 192 bpm, and this decreases with increasing age. All these numbers basically mean that dancesport is incredibly demanding and can require that an individual work at nearly 100% of their maximal workload! (But you all knew this already because we've all been there at the end of jive just wishing the DJ would cut that music out already!)

When the body is exercising at a high intensity, it has an increased demand for oxygen, especially in the muscles (I'm looking at you- legs!). In order to make sure that the tissues get all the oxygen they need, the heart increases a measure called cardiac output. Cardiac output is defined as the stroke volume (how many liters of blood does the heart expel each time it pumps) x heart rate. It is given in liters/minute. Usually this mechanism functions just fine, all the muscles get their oxygen, and we all go on our merry little way. However, when a muscle doesn't get enough oxygen, it becomes ischemic,and after a while, ischemic tissue becomes necrotic (dead). This is certainly bad (and painful!) in skeletal muscle, but becomes really dangerous when we start talking about the heart.

Remember that your heart is basically a giant muscular pump. It needs lots of oxygen to function, just like skeletal muscles. When it starts increasing cardiac output, it does so by working harder (increasing the number of times/minute that it beats, and increasing the stroke volume). When it starts working harder, it needs more oxygen. The heart is supplied with oxygen by the coronary arteries, special blood vessels that wrap around the heart to deliver blood/oxygen and take away waste products. Usually these are able to supply plenty of blood (and therefore oxygen) to keep the heart happy.  However, if for any reason these coronary arteries should become blocked, they aren't able to deliver as much blood (and oxygen!) to the heart, and the heart becomes ischemic. Usually the reason they become blocked is the presence of a thrombus- a blood clot caused by several reasons including atherosclerosis (fatty plaques building up inside the vessels).

As the thrombus occludes (prevents) coronary blood flow, the heart becomes ischemic. This is called a myocardial infarction (heart attack). Heart cells (cardiac myocytes) that are ischemic tend to behave erratically. Cardiac contraction is a very orderly business.. certain cells called pacemaker cells keep the whole thing going along smoothly (using electrical signals) to make sure the different parts of the heart (atria, ventricles) pump in order to make sure that blood is able to be efficiently ejected from the heart and circulated to the rest of the body. When ischemic pacemaker cells stop doing their job, the whole thing falls to bits. There is no longer any coordinated contraction, and the heart ends up just sort of quivering (ventricular fibrillation). This is bad (really, really, really bad). It means that the heart is no longer able to effectively pump blood out to the rest of the body, and other organs (like the brain) become ischemic and die. At this point, the heart basically needs to be rebooted with an outside electrical signal (like a shock from an AED) in order to get everything in sync and pumping normally again. This needs to be done very quickly, as damage to the brain begins at 10 seconds without oxygen, and damage to the heart begins within minutes without oxygen.

This brings me to the second part of the post; should competitions have AEDs on site in case of emergency? I am going to go with a wholehearted yes. Rapid intervention is crucial to good outcomes of myocardial infarctions: AEDs save lives. However, I understand that the issue is slightly more complicated than that. First, someone needs to actually operate the AED. While they are fairly simple to use, especially if you are certified, someone needs to take responsibility and step up. While I certainly hope that no one would sue a bystander trying to help, and there are Good Samaritan laws that protect layperson rescuers in these cases, there may be legal liabilities that the rescuer needs to take on. Secondly, AEDs must be maintained in order to function properly: maintenance can be expensive, especially for a competition that only happens once a year. So, what should be done about this situation? In the thread on Danceforums that I linked to earlier in the post, someone suggested the possibility of renting/borrowing one from a local hospital/healthcare clinic. I think this is a wonderful idea- it takes care of the maintenance issue, but still allows for an AED to be present in the ballroom. As far as trained personnel go, I've encountered many healthcare professionals in my ballroom exploits- I imagine a call for help on the intercom would turn up at least one doctor/nurse/emt/exercise physiologist (wink wink) who would be certified to help.

In conclusion, dancesport is an incredibly aerobic activity which can place extreme demands on the cardiovascular system, sometimes to dire results. Having AEDs on site may help prevent unnecessary deaths during otherwise happy events.

Please check out some of the following links

 CPR/AED certification

Signs and symptoms of a heart attack (just because someone isn't clutching their chest as they collapse on the floor doesn't mean they aren't having an MI). If you or someone you know is experiencing these symptoms, please seek medical attention immediately!



Monday, February 10, 2014

The potential for action observation as a training method for ballroom dancers

This post I'll be looking at a paper entitled "Training the Motor Cortex by Observing the Actions of Others During Immobilization" by Fadiga, et al. published in Cerebral Cortex in July, 2013. If you can get access to the article, I highly recommend it- it is a fairly short, but interesting read. If not, I'll do my best to make this post understandable without reading the paper.

The background science: 
Our brains are "plastic" which means that they are always making (and breaking!) connections between neurons. Repetitive action strengthens these connections, whereas disuse weakens them. Think about sledding: every time you go down a hill and take the same path as before, it becomes more entrenched. This is the same (although grossly simplified way) your brain works. The stronger the neural path, the easier and more automatic the action becomes. This means that you want the neural path for something like a heel turn to be pretty well entrenched, because you have a lot of other things to think about (smile!) when you are competing. One way (probably the best way) to do this, is through lots of (perfect) practice. However, there are some times when we can't always practice. I was on DanceForums earlier this year when one of the members brought up the question about what to do when you are injured. Fadiga, et al. suggest that action observation might be a good thing to try. (Side note- if you haven't been to DanceForums.com and you are a ballroom dancer, you need to go there immediately after reading this post. It is an amazing resource).

The study:
Introduction
The authors wanted to compare two forms of mental practice and their effectiveness at preventing the shriveling/ building up these neural paths. The first method is motor imagery (MI). Motor imagery basically  means thinking about yourself doing the task, and about all the associated feelings. The second is action observation (AO) which involves watching a first person perspective video of the given task (in the paper, they used reaching for an object).

Procedure
First, the subjects underwent  transcranial magnetic stimulation (TMS- a big magnet used to look at neural activity) to look at the activity in the brain area involved in arm reaching. The researchers then immobilized the subjects' arms for 10 hours. After the 10 hours were up, the subjects were assigned to one of three groups- a group that just watched nature documentaries (control group), action observation group where they watched a first person video of an arm reaching for an object, and a motor imagery where the subjects imagined themselves reaching for an object. The researchers then did another TMS to measure how much the neural paths for arm reaching had been depressed through immobilization.

Results
The investigators found that the action observation group had the least amount of cortical activity depression, followed by  motor imagery and then the nature-video control.This means that action observation was the most effective way to keep the skill of arm reaching up while the arm was immobilized.

So what does this all mean, anyways?
Action observation may have potential as a supplementary training method for ballroom dancers. It has shown potential to help prevent loss of skills when practice isn't an option. It is certainly worth a try (it can't hurt, in any case!) However, it is important to note the conditions in which this experiment was conducted. They used a very simple task (reaching for an objects). In case you haven't noticed, most actions in ballroom are much more complex than reaching for an object! Secondly, the researchers used first person videos for the action observation videos. These would be extremely disorienting to watch, in my opinion (especially when the follow is all projected up and left and looking at the ceiling the whole time!) Perhaps someone can try this with one of those little cameras you attach to your head? If you do- send me the result- I'm very curious :) This first person perspective may also provide limited information on the aspect the observer is interested in. My visual perspective as a follow doesn't often include what my feet are doing during a heel turn. Maybe if it was a video of a single step (for example, a heel turn) shot from a first person perspective including the necessary information (e.g. I would wear a camera on my head and look at my feet while performing a heel turn). In any case, this paper certainly provides an interesting starting point for future research to investigate. Maybe someone will even do a study about action observations in dancers...if only I was doing a thesis... (actually, I'm still really glad I'm not doing a thesis....)

TL;DR
Go watch some videos! In all perspectives, but especially first person (if you can find them). They may help, or not, but they certainly won't hurt. Off to youtube for me it is...

Friday, January 31, 2014

Welcome!

Thanks for stopping by!
A little about myself: I am a graduate student working on a master's degree in clinical exercise physiology. I am also an avid dancesport competitor (shout out to all my standard peeps!). While studying how the human body works and adapts to movement, I found that two of my biggest interests in life actually fit together quite nicely.
In this blog, I plan on covering topics that cover the intersection between dance and movement... a few planned topics include maximal aerobic fitness of dancers, neural control of moment, nutrition, how to best train fitness for competitions and so on.  Please note that I am still a student- before engaging in any new exercise program or diet change, consult with a physician, certified health adviser or nutritionist. Please also note that many of my posts will involve academic papers. Unfortunately, I won't be able to make these available to the general public, if you are associated with a university, the papers should be relatively easy to find (I'll post links to Pubmed/Google scholar). If you aren't associated with a university, please know that I will do my best to summarize what is going on so you don't have to pay for the article, however, know that it is an option if you are super interested in the material!