Showing posts with label science. Show all posts
Showing posts with label science. Show all posts

Saturday, February 28, 2015

For geeks only

As part of my job as a pediatric nurse practitioner in a busy teaching practice, I get the opportunity to attend weekly Grand Rounds. This is a one hour educational lecture, presented by a resident or attending, with a different topic every week. I love to learn and Grand Rounds is always really interesting. This past week, I attended a lecture by Philip Skiba, DO, PhD, MS, who is the director of our Sports Medicine department. The topic was Assessing Sports Performance. Dr Skiba has done a lot of research and lecturing on this topic. He's also coached many elite and olympic level athletes. So for today's blog post, I put on my science nerd hat and share some of the highlights of his talk--this was a topic near and dear to this runner's heart. Besides, it was fascinating.

Dr Skiba talked a lot of performance of runners. Since this was a medical lecture, the information was pretty scientific. He used a lot of graphs and mathematical formulas. I even heard the term Krebs cycle tossed around! That was a nightmare blast from my biochemistry days! Who knew that I would need to remember that again? But he also talked a lot about some important concepts behind why we train the way we do. I'm going to try to sum it up here without getting too technical, and to prepare this post, I had to do a lot of background reading. Hopefully, I'm able to simplify it enough that it will all make sense and you can apply some of the concepts to your training! I also thought that his lecture helped me understand why we runners train the way we do, and why the work Becky has me doing, in the form of heavy lifting and interval training, is really having a positive impact on my running.

Dr Skiba introduced the concepts of critical power and VO2max. Critical power is the rate at which you can maintain your pace without exhaustion. Some of us refer to this as endurance. If you are very aerobically fit, you will have a high level of critical power. Critical power is a number that can be determined in a lab. Elite athletes train using knowledge of their critical power. If you run beyond your critical power, you start to become fatigued and your performance starts to suffer.

VO2max, also known as aerobic capacity, is the ability of the body to utilize oxygen. Having high critical power and high VO2max means you you can perform at a high level without exhaustion, without going into an anaerobic state (produce lactic acid), or become fatigued. Athletes who have a high VO2 max can perform at a higher level because their bodies have the ability to produce more energy. This explains why a lot of endurance athletes use the banned substance, epo, because this substance helps increase red blood cells, which carry oxygen in the body. More oxygen means increased aerobic capacity. BTW, the maximum allowable hematocrit for professional cyclists is 49.5%. You and I are probably sitting around 36%.

Lactate threshold is another determinant of performance. Lactic acid is a byproduct of metabolism, and begins to build up when you're working hard. Lactate threshold is the level of exercise at which lactate begins to accumulate in the blood. The more fit you are, the longer you can perform at lactate threshold. Lactate threshold is usually about 80-85% VO2max for fit athletes. Lactate threshold is probably the best predictor of performance. And even though conventional wisdom says accumulating lactate is bad, that isn't true. The body can use lactate for fuel and it does during endurance activities. However, increasing lactic acid levels does lead to fatigue.

Economy also plays a role in performance. Running economy is defined as the volume of oxygen consumed at submaximal speeds. An athlete who has a very efficient stride will be able to outrun another athlete who has a higher VO2max, simply because he is using less energy. Body weight is another factor that affects performance. Increased body weight has a negative effect on your VO2max. Also, the heavier your legs are, the lower your running economy. You will run slower than you would with a lower body weight.

There is only so much a runner can do to improve VO2max and critical power. Most of that is genetically determined. But there is some room to improve both parameters. In fact, newer, less conditioned runners can show much more dramatic improvement in these areas that experienced runners. In addition, some of us have more slow twitch muscle fibers (good for endurance events) and some have more fast twitch muscle fibers (good for sprinters). But because no one has 100% of either type, there is some evidence that training can alter this as well. One thing you can really have an impact on is your lactate threshold, though, and that is the focus of a lot of training plans.

Slow vs fast
I need to mention here that just because a person tires out quickly when trying to run long distances doesn't mean they have mostly fast twitch muscles. Keep in mind the concepts of VO2max and critical power. If you run faster than your VO2max you will fatigue very quickly. This has more to do with conditioning than anything else. I had to put this in here because I've actually had non-runners tell me that they "can't run long distances" because they only have fast twitch muscles, that they are more of a sprinter. Girlfriend, please. Pace yourself.

What does all this scientific information mean for the recreational athlete? What if you don't have access to a lab to measure your critical power or your VO2max? How do you know what your lactate threshold is? Can't I just run with my heart rate monitor and be done with it?

There are a few things you can do to improve your VO2max/aerobic capacity. Think intensity, not training volume. That means that stop the madness with the high mileage training. Studies show that HIIT (high intensity interval training) is better at increasing VO2max than endurance training. Some examples are intervals and speed work. A way to increase your lactate threshold is to train at higher volumes of training with your efforts at higher than resting intensity. Think tempo runs. Strength training has also been shown to increase VO2 max, lactate threshold, and running economy. It doesn't have to be all about high mileage.

BTW, while heart rate training has a place in all of this, it is important to know that heart rate monitors do not predict aerobic capacity. All the heart rate monitor tells us is how hard we are working at that moment in time. But monitoring how fast your heart rate goes down after an activity is a predictor of aerobic fitness. A more fit person will recover more quickly.

I walked away from this lecture both awed and overwhelmed. I had no idea that there was so much science behind running and cycling performance. I reflected on this information a lot over the past couple of days. This is the kind of testing and training that is utilized with elite athletes. That's a lot of pressure. I can see why a lot of elites might be tempted to dabble in banned substances, just to see those numbers improve. We mere mortals focus on mile splits. Imagine having your runs broken down into all those numbers and graphs. Seems to me that it kind of takes the fun out of running, doesn't it?

For more information: (includes info on measuring VO2max at home) links to great articles