By Ciarra Ortiz

Patti Grace Smith Fellowship Supervisor: Ariel Ekblaw
Graduate Student Research Supervisor: Rachel Bellisle
Skinsuit Project PI: Dava Newman

Overview

Long duration spaceflight missions eventually begin to affect the muscles that normally keep the human body in an upright position to resist the force of gravity on Earth. These muscle groups are known as postural muscles or antigravity muscles, shown in Figure 1, which include: Erector Spinae, Iliopsoas, Quadriceps Femoris, Hamstrings, and the Soleus (Buckey, 2006).

In Space Physiology, it was noted that an MRI was conducted on astronauts that returned from a long duration space mission to analyze the percentage of muscle loss compared to when the astronauts first left Earth’s atmosphere (Figure 2). 

Two main factors that could lead to these examples of muscle atrophy are the lack of activity and inadequate caloric intake. Essentially, there is less resistance on the body without the effects of gravity and muscles experience disuse because they aren’t standing, running, or walking the same as they would on Earth (Buckey, 2006). The Skinsuit is an intravehicular activity (IVA) suit with the goal of simulating the effects of Earth's gravity through application of static load on the body using material tension (Waldie & Newman 2011a; Waldie & Newman 2011b; Bellisle & Newman 2020). There have been seven versions, shown in Figure 3, of the suit that have been manufactured and one version has even been flown on the International Space Station (Stabler et al., 2017; Kendrick, 2016).

There is a longitudinal material tension administered by the suit determined by calculating the loading regime of an individual’s body in 1-G through anthropometric data. The Skinsuit also provides a skin pressure in order to prevent slippage of the suit material and provides sturdy anchors at the loading stages, the shoulders and the feet. The latest model, the MKVII, was used for this summer’s participant study (Figure 4). The current MKVII provides approximately 20 - 40% load on the body in 1-G, which improves upon previous models of the Skinsuit (Bellisle & Newman 2020; Bellisle et al.,2021, unpublished).

Research Questions

These were the main questions/hypotheses driving our research this summer: 

1. Do lower gravity levels reduce muscle activity on the Moonwalker, a partial gravity simulator?
2. Can Skinsuit loading increase postural muscle activity in reduced gravity environments, partially restoring the muscle activity levels typically seen in 1G?

Moonwalker/Skinsuit participant study

To address the research problems that we were trying to answer, a pilot study was conducted with one participant wearing the Skinsuit with a harness on the Moonwalker (in Figure 5). The Moonwalker is an apparatus that offloads a portion of the participant’s body weight while in the harness to simulate different levels of partial gravity. The Moonwalker was used to help investigate the effects of the Skinsuit loading on postural muscle activity during treadmill running in 1G, 0.7G, 0.38G (Martian Gravity), and 0.17G (Lunar Gravity).

We tested the following environment and condition combinations: 1-G with Harness Suited and Unsuited, 1-G without Harness Suited and Unsuited, 0.7-G Suited and Unsuited, Martian Suited and Unsuited, Lunar Suited and Unsuited. The treadmill speeds used in the study were determined by the Froude Number (Fr), which is a non-dimensional velocity used to determine the walk-run transition for participants with different leg lengths (L) and differing Gravity levels (g).

After using this equation, the speeds calculated were 1.9 mph for 1-G, 2.0 mph for Lunar, 3.0 mph for Martian, and 4.1 mph for 0.7-G. Once the speeds were determined, we started to collect data using surface electrodes to collect electromyography (EMG) data to measure the muscle activity of seven postural muscles on the right side of the participant’s body, which was their dominant side. The muscles, shown in figures 6-12, analyzed were the Vastus Lateralis, Rectus Femoris, Tibialis Anterior, Lateral Head of the Gastrocnemius, Biceps Femoris, Lumbar Paraspinals, and Soleus.

Additionally, we used Novel foot pressure insoles to detect heel strikes through the pressure on the participant’s feet while running on the treadmill. The heel strike timestamps from the novel data was key for sectioning off the novel and EMG data into gait cycles. A full gait cycle would be from when the participant’s one foot contacts the ground with the heel to when that same foot contacts the ground again. Throughout this summer, I created an algorithm to detect the heel strikes and process the EMG data to split into gait cycles.

MATLAB Coding

Heel Strike Detection Algorithm

The code initially imported the foot pressure data collected by the Novel insole sensors and plotted the corresponding data in a force vs time graph for each of the environment and condition combinations (Figure 13). After the data was imported, the code was designed to detect the steepest incline within the force vs time graphs because it was an indication of when the participant’s heel first makes contact with the treadmill. To depict the movement of the participant through the data, I graphed the left and right foot on two separate subplots to visualize the alternating heel strikes. Nevertheless, to ensure that the start trial times matched up with the heel strike timestamps, I watched all the footage from the Go-Pro recordings. In the view of the Go-Pro, a blue LED indicated the start of EMG data collection, and I recorded the time when the LED light blinked and the time when the first heel made contact with the treadmill. By doing this process, I was able to synchronize the time between the pressure data and the EMG data.

EMG Analysis 

Before I started analyzing the EMG Data, I processed the raw EMG data to create a linear envelope, which detrends, filters, rectifies, and normalizes the data (Figure 14). After plotting the EMG data, I began sectioning off data into gait cycles based on the heel strike timestamps from the novel data. This was completed for all seven EMG channels, which correspond to the seven postural muscles we chose to focus on, for each environment and condition.

Nevertheless, to avoid future error in results, I removed the outlier gait cycles based on the lengths of the gait cycles because long durations could be an indication that some heelstrikes were not properly detected by the algorithm. Then, the acceptable gait cycles were interpolated to normalize time across all conditions and environments, which allowed us to calculate the average gait cycle for each channel, environment, and condition that was tested. Finally, I plotted the acceptable gait cycles with the mean curve and the mean curve with the standard deviation for each muscle channel to visualize the muscle activity for further analysis (Figure 9 and 10).

Upcoming Conclusions

The results of the research from this summer will be included in an upcoming conference paper and will therefore not be discussed in depth. Amplitude and frequency metrics will be outputted from the EMG signals to assess our hypotheses. This work will provide preliminary data as a foundation for a larger participant study in the future, which will be used to test the research questions. The Skinsuit has potential to serve as a way to help maintain muscle activity outside of Earth’s gravity, as an alternative or supplement to bulky exercise equipment, like on the International Space Station, or for long-duration space missions. 

Acknowledgements

I just want to thank the Patti Grace Smith Fellowship for allowing me to pursue such a wonderful research opportunity for my first internship in my undergraduate education. I would also like to thank the MIT Space Exploration Initiative Lab and the Human Systems Lab for the knowledge/connections that I have obtained this summer. I thoroughly enjoyed my time working at MIT and I look forward to possible future project opportunities!

References

Bellisle, R. and Newman, D., “Countermeasure Suits for Spaceflight,” in the 50th International Conference on Environmental Systems, 2020. https://ttu-ir.tdl.org/handle/2346/86259 

Buckey, J. C. (2006). Space physiology. Oxford University Press.

Kendrick, D. P., “The Gravity Loading Countermeasure Skinsuit: A Passive Countermeasure Garment for Preventing Musculoskeletal Deconditioning During Long-duration Spaceflight,” Ph.D. Thesis, Dept of Health Sci and Tech, Massachusetts Institute of Technology, Cambridge, MA, 2016.

Stabler, R. A., Rosado, H., Doyle, R., et al., “Impact of the Mk VI SkinSuit on Skin Microbiota of Terrestrial Volunteers and an International Space Station-bound Astronaut,” npj Microgravity, Vol. 3, Sep. 2017, pp. 23.

Waldie, J. M. A., and Newman, D. J., Massachusetts Institute of Technology, Cambridge, MA, U.S. Patent Application for a “Gravity-Loading Body Suit,” No. US 8,769,712 B2, filed Mar. 25 2011.

Waldie, J. M., and Newman, D. J., “A Gravity Loading Countermeasure Skinsuit,” Acta Astronautica, Vol. 68, No. 7-8, 2011, pp. 722-730.

Stabler, R. A., Rosado, H., Doyle, R., et al., “Impact of the Mk VI SkinSuit on Skin Microbiota of Terrestrial Volunteers and an International Space Station-bound Astronaut,” npj Microgravity, Vol. 3, Sep. 2017, pp. 23.