Ophthalmological Evaluation of Integrated Resistance and Aerobic Training During 70-Day Bed Rest

Abstract

INTRODUCTION We evaluated ophthalmic changes in healthy individuals who underwent integrated resistance and aerobic training (iRAT) during 70-day 6° head-down-tilt (HDT) bed rest (BR). METHODS Participants were selected using NASA standard screening procedures. Standardized NASA BR conditions were implemented. Subjects were randomly assigned to the iRAT protocol or no exercise during HDTBR. Weekly ophthalmic examinations were performed in the sitting (pre/post-BR only) and HDT (BR only) positions. Mixed-effects linear models compared pre and post-HDTBR intraocular pressure (IOP), Spectralis OCT circumpapillary retinal nerve fiber layer thickness (cpRNFLT) and peripapillary retinal thickness observations between groups. RESULTS Six controls and nine exercisers completed the study. There was an overall effect of BR on our outcomes. Except Goldmann IOP (mean pre/post difference in controls and exercisers: −0.47mmHg versus +1.14mmHg), the magnitude of changes from baseline was not significantly different between groups. There was a +1.38mmHg and a +1.63mmHg iCare IOP increase during BR in controls and exercisers, respectively. Spectralis OCT detected a +1.33μm average cpRNFLT increase in both groups, a +9.77μm and a +6.65μm peripapillary retinal thickening post-BR in controls and exercisers, respectively. Modified Amsler grid, red dot test, confrontational visual field, color vision, and stereoscopic fundus photography were unremarkable. CONCLUSIONS Seventy-day HDTBR induced peripapillary retinal thickening and cpRNFL thickening without visible signs of optic disc edema. The magnitude of such changes was not different between controls and exercisers. A slight IOP increase during BR subsided post-BR. Further study should evaluate whether different physical exercise paradigms may prevent/mitigate the risk of space-related visual impairment.

Dietary acid load and bone turnover during long-duration spaceflight and bed rest

“…Although we and others have reported data from this (19) and similar (21,22) bed rest studies, to our knowledge, none of the data reported here have been published previously (and certainly no data pertaining to dietary APro:K effects on bone).…”

“…Comparison data are reported here from a 70-d bed rest study evaluating exercise as a countermeasure to physiologic effects of simulated microgravity (19). These data are from one of a series of bed rest studies conducted at the University of Texas Medical Branch (UTMB) in Galveston, TX (20).…”

Effects of Resistance Exercise with or without Whey Protein Supplementation on Ocular Changes after a 21-Day Head-Down Bed Rest

“…One study demonstrated a small decrease in IOP (−1.61 mmHg) after a short session of weightlifting in 25 healthy volunteers in supine position with 85% top load for 8 repetitions [ 31 ]. Taibbi et al [ 32 ] studied the effects of a 70-day HDBR on ophthalmic changes with some specific countermeasures such as integrated resistance and aerobic training in 6 controls and 9 exercisers. The authors declared that both controls and exercisers exhibited a rise in IOP during HDBR (respectively, +1.38 mmHg and +1.63 mmHg), measured with iCare IOP.…”

“…The authors described a preserved retinal thickness, ganglion cell layer and choroidal thickness after weightlifting. However, Taibbi et al [ 32 ] also studied the effects of integrated resistance and aerobic training on circumpapillary RNFL and peripapillary retinal thicknesses after 70 days of HDBR. In this study, spectralis OCT revealed an increase in circumpapillary RNFLT (+1.33 µm) in 15 subjects (6 controls and 9 exercisers) after HDBR.…”

Head-Down Tilt Bed Rest Studies as a Terrestrial Analog for Spaceflight Associated Neuro-Ocular Syndrome

“…To mitigate the atrophying effect of microgravity on skeletal muscle, astronauts undergo 2.5 h of intensive resistance and aerobic exercise nearly every day onboard the ISS (67). However, implementation of NASA's integrated resistance and aerobic training (iRAT) protocol during 70-day non-hypercarbic strict 6 • HDTBR was not associated with a significant difference in retinal thickening or signs of optic disc edema compared to a control HDTBR group who did not exercise, though IOP was slightly higher (<1 mm Hg) in the exercise group (68). Interestingly, 15 • head down tilt for less than an hour was associated with a decrease in IOP in subjects undergoing either moderate-intensity aerobic, resistance, or high-intensity interval aerobic exercise (69).…”