Abstract
As astronauts prepare to undertake new extra-terrestrial missions, innovative diagnostic tools are needed to better assess muscle deconditioning during periods of weightlessness and partial gravity. Electrical impedance myography (EIM) has been used to detect muscle deconditioning in rodents exposed to microgravity during spaceflight or using the standard ground-based model of hindlimb unloading via tail suspension (HU). Here, we used EIM to assess muscle changes in animals exposed to two new models: hindlimb suspension using a pelvic harness (HLS) and a partial weight-bearing (PWB) model that mimics partial gravity (including Lunar and Martian gravities). We also used a simple needle array electrode in lieu of surface or ex vivo EIM approaches previously employed. Our HLS results confirmed earlier findings obtained after spaceflight and tail suspension. Indeed, one EIM measure (i.e., phase-slope) that was previously reported as highly sensitive, was significantly decreased after HLS (day 0: 14.60 ± 0.97, day 7: 11.03 ± 0.81, and day 14: 10.13 ± 0.55 | Deg/MHz|, p < 0.0001), and was associated with a significant decrease in muscle grip force. Although EIM parameters such as 50 kHz phase, reactance, and resistance remained variable over 14 days in PWB animals, we identified major PWB-dependent effects at 7 days. Moreover, the data at both 7 and 14 days correlated to previously observed changes in rear paw grip force using the same PWB model. In conclusion, our data suggest that EIM has the potential to serve as biomarker of muscle deconditioning during exposure to both micro- and partial- gravity during future human space exploration.
Highlights
It has long been known that the muscular system is profoundly impacted by weightlessness (Edgerton et al, 1995; Baldwin, 1996), resulting in rapid and significant atrophy (LeBlanc et al, 1995; Fitts et al, 2001) that is especially pronounced in the weight-bearing triceps surae muscles (Desplanches et al, 1990; Desplanches, 1997)
We demonstrate that Electrical impedance myography (EIM) detects muscle alterations in both micro- and partial- gravity rat analog models, and that these changes correlate with our earlier data showing alterations in Rear Paw Grip Force (RPGF) in these two conditions (Mortreux et al, 2018, 2019a,c)
We were able to confirm that the data obtained using a small intra-muscular EIM needle array yielded similar results to those previously acquired with a surface electrode (Li et al, 2013) or during ex vivo measurements (Sung et al, 2013) after spaceflight and HU
Summary
It has long been known that the muscular system is profoundly impacted by weightlessness (Edgerton et al, 1995; Baldwin, 1996), resulting in rapid and significant atrophy (LeBlanc et al, 1995; Fitts et al, 2001) that is especially pronounced in the weight-bearing triceps surae muscles (i.e., gastrocnemius and soleus) (Desplanches et al, 1990; Desplanches, 1997). Numerous countermeasures have been investigated and refined in such analog models, including exercise (Swift et al, 2010; Fujita et al, 2011), nutraceuticals (Momken et al, 2011), pharmacological agents (Tipton and Sebastian, 1997), or a combination of several of these approaches (Li et al, 2012; Dillon et al, 2018), in order to lessen muscle loss and dysfunction during periods of microgravity These findings led to the establishment of strict and tailored exercise regimens for astronauts (Trappe et al, 2009; Petersen et al, 2016, 2017; Lambrecht et al, 2017; Lang et al, 2017), rendered possible by the exhaustive equipment available for all crewmembers onboard the ISS (Korth and Reeves, 2015). These exercises, in combination with pre-flight conditioning and post-flight rehabilitation, help ensure muscle function upon return to terrestrial gravity
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