A300 ZERO-G Airbus
Over the past decade, our research group has developed a novel form of NMES technology, which we call NMES-EX. This system generates repeated rhythmical co-contractions of the large muscles in the legs without undue discomfort by delivering pulse trains at low frequencies (4-6 Hz) to the large leg muscle groups via large surface electrodes. This creates a demand for oxygen in the tissues and results in activation of a cardiovascular response that is consistent with that observed during physical activities such as walking, cycling or running. Increases in the stimulation intensity result in stronger contractions and consequently increased loading on the cardiovascular system. The application of this technology in microgravity may assist astronauts in the prevention of cardiovascular and physical deficiencies following missions. This potential countermeasure needs to be validated in a microgravity environment in order to observe its efficacy and physiological effect is similar to that in ground based experiments. Thus the primary objective of this experiment is to demonstrate that there is no attenuation of the acute physiological effect of NMES-EX during simulated microgravity compared to the 1g effect. A secondary objective of this experiment will be to ensure the application of NMES-EX is functional, safe and effective in a microgravity environment.
TECHNICAL DESCRIPTION OF THE EXPERIMENT
NMES is long established in the literature as a tool to optimize motor performance, increasing muscle mass (Cabric et al, 1987, Gondin et al, 2005), strength (Gondin et al, 2005, Maffiuletti et al, 2002), power (Maffiuletti et al, 2002), activation (Gondin et al, 2005) and endurance (Kim et al, 1995). It has also been demonstrated that NMES has a potential role in the maintenance of bone mineral density in spinal cord injured patients (Chen et al, 2005, Griffin et al, 2009). In recent years investigators have directed attention to the use of NMES technology to elicit a cardiovascular response. Muscular integrity is needed for emergency manoeuvres, high-performance duties such as extravehicular activities (e.g., space walks), using tools, mobility, and, possibly, to limit the degree of PSOI upon return to Earth (Payne et al, 2007). Current countermeasures on board a space flight to target the cardiovascular and musculoskeletal systems range from bungee-cord assisted treadmills to ‘Penguin’ or ‘Regent’ suits, as well as dietary and pharmaceutical interventions. However, many of these measures fail to protect bone, muscle, orthostatic intolerance and fitness fully (Hargens and Richardson, 2009). One way to counteract the general physiological deterioration experienced on a mission is by exercising regularly during the entire duration of the microgravity exposure. An optimal countermeasure intervention should deliver effective maintenance of muscle strength and function, cardiovascular exercise capacity, and bone mineral density without taking up large amounts of physical space on the ISS. Researchers have tried many approaches to this problem but current state of the art involves the use of bulky piece of equipment being carried into space to achieve the desired effect (Hargens and Richardson, 2009). This is not an optimal solution in an environment like the ISS where physical space is at a premium. Previous efforts at solving the problem using surface electrical stimulation of the large muscle groups in the legs have not been very successful. These efforts mainly revolved around use of tetanic contractions of single muscle groups at frequencies of 30-50 Hz. Our novel form of NMES delivers significant training effects to the cardiovascular and muscular systems across a range of populations. It achieves these effects without the need for extensive equipment, needing only a hand held battery operated stimulator and a garment containing surface electrodes. Furthermore, the fact that the system employs a co-contraction of the quadriceps and hamstring muscle groups means that it may have a positive effect on bone health. However, we have yet to have an opportunity to test this hypothesis.
APPLICATIONS OF THE RESEARCH
This research will help inform the further development of the NMES system as a commercially viable exercise modality for different clinical populations and in the wellness market.
M. Cabric, H.J. Appell, A. Resic, (1987), "Effects of electrical stimulation of different frequencies on the myonuclei and fiber size in human muscle", International Journal of Sports Medicine, 8, 5, pp. 323-326.
N.A. Maffiuletti, S. Dugnani, M. Folz, E. Di Pierno, F. Mauro, (2002), "Effect of combined electrostimulation and plyometric training on vertical jump height", Medicine and Science in Sports and Exercise, 34, 10, DOI: 10.1249/01.MSS.0000031481.28915.56, pp. 1638-1644.
P. Banerjee, A. Clark, K. Witte, L. Crowe, B. Caulfield, (2005), "Electrical stimulation of unloaded muscles causes cardiovascular exercise by increasing oxygen demand", European Journal of Preventive Cardiology (formerly European Journal of Cardiovascular Prevention & Rehabilitation), 12, 5, pp. 503-508.
P. Banerjee, B. Caulfield, L. Crowe, A. Clark, (2005), "Prolonged electrical muscle stimulation exercise improves strength and aerobic capacity in healthy sedentary adults", Journal of Applied Physiology, 99, 6, pp. 2307-2311.
P. Banerjee, B. Caulfield, L. Crowe, A. Clark, (2009), "Prolonged electrical muscle stimulation exercise improves strength, peak VO2, and exercise capacity in patients with stable chronic heart failure", Journal of Cardiac Failure, 15, 4, pp. 319-326.
N.A. Maffiuletti, M. Pensini, A. Martin, (2002), "Activation of human plantar flexor muscles increases after electromyostimulation training", Journal of Applied Physiology, 92, 4, DOI: 10.1152/japplphysiol.00884.2001, pp. 1383-1392.
B. Caulfield, L. Crowe, G. Coughlan, C. Minogue, (2011), "Clinical application of neuromuscular electrical stimulation induced cardiovascular exercise", Engineering in Medicine and Biology Society, EMBC, 2011 Annual International Conference of the IEEE, ISBN: 978-1-4244-4121-1, DOI: 10.1109/IEMBS.2011.6090887, pp. 3266-3269.
N.A. Maffiuletti, T. Hortobágyi, (2011), "Neural adaptations to electrical stimulation strength training", European Journal of Applied Physiology, 111, 10, doi: 10.1007/s00421-011-2012-2, pp. 2439-2449.
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Photo 1: Experimental set-up for the "NMES-EX (NeuroMuscular Electrical Stimulation - EXercise): A potential countermeasure in microgravity" experiment during the 55th Parabolic Flight Campaign in the A300 ZERO-G airbus. Credit: ESA - C. Dekker
Dr. Brian Caulfield is explaining the experiment during the 55th ESA Parabolic Flight Campaign.