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Walking Two Ways at Once: A research study experience on a split belt treadmill
Participating in this movement study at the Kennedy Krieger Institute was such unique experience. While the physical location of the lab was in KKI, The Motion Analysis Lab of Johns Hopkins School of Medicine conducted the study. I walked into the building, signed in, and found the lab through a door in the lobby, which was very convenient and one of the easier places to get to in my study participation career. After reading and signing the consent form, I changed into a tight tee shirt, compression shorts, and sneakers that I was instructed to bring with me. The research team had some clothing for participants who didn’t remember to bring tight fitting clothing.
The researcher then marked specific locations on my body with small balls as though I were going to be in a video game simulation. The small ball sensors had a sticky side which adhered to my body and clothing. The researcher used a measuring tape to place the balls at precise distances from landmarks on my body, like my hip-bones, knees, and shoulders. Between placements, he would run back to his computer to calibrate the sensors and ensure they were receiving data from the proper locations. I was also given a mouthpiece connected to a tube to wear to measure VO2 (volume oxygen). It was similar to getting a VO2 Max, which measures oxygen use and carbon dioxide output. As Elizabeth Quinn states, “VO2 max, also known as maximal oxygen uptake, is the measurement of the maximum amount of oxygen a person can utilize during intense exercise. It is a common measurement used to establish the aerobic endurance of an athlete prior to or during the course of training. It is one of several tests used to determine an athlete's cardiovascular fitness and performance capacity.”
Next, I got onto a split belt treadmill, a type of treadmill that has a separate platform and belt for each leg. Both sides moved at the same speed for a while as I walked at a steady pace. The researcher had given the treadmill a steep incline, which made the walking more difficult. I was breathing very hard at this point, and breathing into the tube wasn’t enjoyable. At times, it was somewhat hard to breath and I felt out of breath.
We did multiple trials, each about 5 to 10 minutes long with different speeds and inclines. Then the incline came back down to 0 and the real fun began! One of the sides of the split belt treadmill began going slower or faster than the other side. One of my legs had to walk faster than the other without my falling off of the treadmill. I had to adjust my gait so that it looked and felt like I was walking normally. I was surprised how quickly I adjusted and learned the new movements. It almost felt as though I had to mimic a limp to not fall off the treadmill. The foot on the faster side would touch the belt for less time than the foot on the slower side. The researcher put me through various trials where each leg went through variations of slowing one side down and speeding one side up. Eventually, a new wrinkle was added as the treadmill was given a steep incline like before.
The Step Length Asymmetry results from a portion of my walking were provided to me via email and can be seen here. This was what the research said about my results:
“-The blue markers indicate your step length asymmetry during baseline in which both belts were moving together at 0.7 m/s
-The green markers indicate your step length asymmetry during initial adaptation in which the left belt gradually sped up from 0.7 m/s to 1.4 m/s and the right belt moved at 0.7 m/s
-The red markers indicate your step length asymmetry during de-adaptation in which both belts again moved together at 0.7 m/s
-The pink markers indicate your step length asymmetry during re-adaptation in which the left belt suddenly moved at 1.4 m/s and the right belt moved at 0.7 m/s (exactly the same speed configuration as you experienced during initial adaptation - the green markers)
A value of 0 indicates that your step lengths are symmetric (as is the case during baseline). You can see that you remain relatively close to symmetry (zero) during initial adaptation (green) and then drastically move away from symmetry during the de-adaptation period (red) as your brain has learned to walk normally in the asymmetric environment and then is suddenly forced to adapt back to a normal, symmetric environment. Upon re-adaptation to the same conditions (left belt at 1.4 m/s, right belt at 0.7 m/s) a second time (pink), you again see a large change in the symmetry because, although your brain has walked under these conditions before, you hadn't previously experienced the abrupt change in the belt speeds and so your brain does not seem to immediately recognize the condition as being the same speed configuration as before.”
Adjusting to the different speeds of the belts when one belt was going much faster than the other was not very difficult for my nervous system as I was a healthy adult when I did this study. I was a little confused by the researcher’s interpretation that I drastically moved away from symmetry during de-adaption as the red dots are generally closer to zero than the green dots are, but maybe he meant that I wasn’t as close as the blue dots are during my de-adaption period. The purple dots show that by the end of the trial, I had gotten pretty close to 0, meaning there was little asymmetry in my step length. To me, being able to adjust that quickly in one re-adaption session on a split belt treadmill is mind-boggling.
Understanding how healthy humans learn to adapt to walking challenges like these has major implications for individuals who need to relearn to walk. The mechanisms observed from the various body sensors of how my gait was adjusting to the varying patterns can be applied to re-teaching individuals who have lost the ability to walk due to stroke, neurological problems, or physical issues. The researcher explained this with specific details:
“We use this information to develop training protocols to reduce step length asymmetry in persons who have experienced a stroke. For instance, if a person post-stroke takes a shorter step with their left leg than their right, we may configure their legs on the split-belt treadmill such that we induce asymmetry in the opposite direction to make their left leg step longer than their right in an attempt to even out the step lengths.”
The oxygen and carbon dioxide measurements through the mouthpiece can be used to inform other things related to mobility or be used separately to inform other related fields. Researchers collecting various modalities of data during studies like these allows for a richer wealth of knowledge to pull from for future scientific literature and further study investigations.
I was paid $15 per hour, and the study was about 2 hours long. I believe I got the check a week later in the mail. Participating in this study was enjoyable and it was awesome to know I had helped with research that is useful to people facing the challenge of relearning mobility. I had never been on a split belt treadmill before and have not been on one since. One could say it was a once in a life-time opportunity, especially if I never walk on a split belt treadmill again!