Energy for Activity: Why some activities might impact asthma more than others?
Last Spring, I wrote about activities that may be more or less compatible with asthma. Of course, there are various reasons why some activities may be better for asthmatics than others—many are linked to environment, such as how hockey may be more difficult because of cold air, arena fumes combined with the constant cardiorespiratory exertion required on ice. However, sometimes, the activity itself just means that you might have more issues breathing—take something like yoga versus running, or weight lifting versus cycling. Both cardiorespiratory activities, which get your muscles moving and your heart beating harder and lungs working faster, and muscular activities (weight lifting, yoga, etc.) are important to your overall health and fitness, but when offered the dichotomy of a strength/resistance based activity or a cardio based one, most of us would probably consider the resistance type activity to be easier on our lungs. One day, of course, I began wondering if this was perhaps due to the type of energy system used by our bodies to do these types of activities—and pulled out the textbooks to see what I could dig up.
Energy systems: An extreme oversimplification
The foods we eat, specifically carbohydrates and fat, are turned into energy by our bodies (which in turn keeps us alive, yay!). Of course, that same piece of food we ate doesn’t go directly into our cells (think muscles in terms of physical activity). It is first converted to a usable form of energy by the body (if you care to know, it’s called ATP—or adenosine triphosphate).
When we exercise, the ATP (energy) is used by our bodies in one of three ways (or a combination) depending on what we’re doing—these are called the energy systems.
We’re going to stick to the basics for today because this is totally a series of lectures I’d never volunteer to present ;).
Cardiovascular/Cardiorespiratory Activities: The Aerobic System
The aerobic system is the one we are most familiar with, so I will start here. The aerobic system takes over after about 2-3 minutes of continuous activity,1 providing energy for endurance-type “cardio” activities—swimming, cycling, running, and the like. This also includes sports (team or individual) that includes these activities at their core—think basketball and soccer (or triathlons!). These activities will have your heart pumping harder and your lungs working to breathe faster to deliver oxygen to your muscles, which allows both carbohydrates and fats to be used by muscles (“oxidative” reactions).2 Oxygen is the key to energizing these activities. Aerobic actually means “requiring, involving or relating to free oxygen”. The aerobic system has a relatively slow response, which is why anaerobic systems “kick in” before it does.
Of course, the only way to get more oxygen where it’s needed is to breathe faster.
The aerobic system and asthma
Without pre-medicating, exercise-induced asthma usually onsets 5-15 minutes into exercise.3 Some people will begin to have exercise-induced symptoms at earlier or later points into their activity, of course. But if we consider that the aerobic system takes over and will have our bodies needing increased oxygen by our 3rd minute of exercise, this might explain why it is these sorts of endurance activities that can be more difficult for people with asthma.
Resistance/Strength Activities: The Anaerobic Systems
Now, here’s where it gets a bit confusing. If you’re doing a short sprint type activity—like 100-meter swim, 800 m track or 1000 m (1 km) speed skating or cycling—anything that lasts under about 3 minutes—you’re working with the anaerobic system. The depletion of the ATP and glucose stores (glucose becomes ATP, remember!) in the muscles does not occur before the activity’s completion. These systems rely on ATP/glucose and lactic acid (a byproduct of the quick use of ATP) for energy.
What’s missing? Oxygen. Anaerobic means “without oxygen”. That means that while you still have to breathe during these activities, of course, oxygen isn’t fueling your activity. (Also this is likely why the “warm up mode” on treadmills and stationary bikes are 3 minutes long). Other substances stored or synthesized within the muscles are used for energy are used until these stores are depleted (under 10 seconds for the “phosphagen” or “creatine phosphate” systems, about 3 minutes for the lactic acid system.1 The problem with this is that lactic acid produces lactate as a byproduct of its use for energy—this is what builds up in the muscles during endurance events and causes burning and pain (cramps) in the muscles. If you’ve ever wondered why it’s not exactly a rare occurrence for endurance athletes or some sprinters to puke during a big event, lactic acid is the culprit as the body tries to get rid of lactic acid.4
The anaerobic system and asthma.
Shorter activities or ones that require bursts of power (weight lifting or shot put for example) may be easier for people with asthma because they don’t have an extended requirement for oxygen—shot put for example requires a short sprint and spin to gain power, and then the push of the shot. These quick activities are not easier, but some people with exercise-induced asthma find them easier to do.
To further complicate things...
Most activities are neither purely anaerobic or aerobic—energy systems are switched between at different points in the sport. However, if anaerobic (ATP) stores aren’t replenished by the time they are needed again, performance may be sluggish. In soccer or basketball, shooting, sprinting and dodging are anaerobic, but jogging down the court or field is aerobic.5 When anaerobic energy stores are depleted, the aerobic system kicks in—it’s a team effort.
The role of intensity.
Did you know that yoga is actually an aerobic activity5? Just like how running may be more difficult, or high-intensity, than walking, the intensity of your activity will impact your breathing. A walk will get you breathing quicker, but not as much as running might—just like it’ll take longer for a walker to burn calories than a runner, the intensity of the activity will impact how quickly your asthma might affect you during exercise. This might explain, though, how you might be able to do a 30-minute yoga session with no asthma issues or walk forever, but if you—like me—try to run for more than a few minutes, you can’t breathe.
A final note...
While these people may or may not have asthma, it was interesting to me to watch the athletes give interviews after competing this past summer in Rio. I noticed that the swimmers were usually much less out of breath than the runners were—I’m curious, but I presume that the runners I caught had been engaged in activity longer than the swimmers, and had switched over to the aerobic energy system, while the swimmers had yet to hit their anaerobic threshold.
What are your thoughts? Does my thought process on why different activities might be better or worse for asthma based on how energy is used make sense? Let me know in the comments.
Do you get muscle cramps caused by your asthma medicine?