Exercise as potential countermeasure for the effects of 70 days of bed rest on cognitive and sensorimotor performance

Abstract

Background: Spaceflight has been associated with changes in gait and balance; it is unclear whether it affects cognition. Head down tilt bed rest (HDBR) is a microgravity analog that mimics cephalad fluid shifts and body unloading. In consideration of astronaut's health and mission success, we investigated the effects of HDBR on cognition and sensorimotor function. Furthermore, we investigated if exercise mitigates any cognitive and sensorimotor sequelae of spaceflight.

Method: We conducted a 70-day six-degree HDBR study in 10 male subjects who were randomly assigned to a HDBR supine exercise or a HDBR control group. Cognitive measures (i.e., processing speed, manual dexterity, psychomotor speed, visual dependency, and 2D and 3D mental rotation) and sensorimotor performance (functional mobility (FMT) and balance performance) were collected at 12 and 8 days pre-HDBR, at 7, 50, and 70 days in HDBR, and at 8 and 12 days post-HDBR. Exercise comprised resistance training, and continuous and high-intensity interval aerobic exercise. We also repeatedly assessed an outside-of-bed rest control group to examine metric stability.

Results: Small practice effects were observed in the control group for some tasks; these were taken into account when analyzing effects of HDBR. No significant effects of HDBR on cognition were observed, although visual dependency during HDBR remained stable in HDBR controls whereas it decreased in HDBR exercise subjects. Furthermore, HDBR was associated with loss of FMT and standing balance performance, which were almost fully recovered 12 days post-HDBR. Aerobic and resistance exercise partially mitigated the effects of HDBR on FMT and accelerated the recovery time course post-HDBR.

Discussion: HDBR did not significantly affect cognitive performance but did adversely affect FMT and standing balance performance. Exercise had some protective effects on the deterioration and recovery of FMT.

Keywords: bed rest; cognition; exercise; longitudinal; microgravity; sensorimotor functioning; spaceflight analog.

Figure 1

Testing timeline for head down tilt bed rest (HDBR) and normative subjects. The top x-axis shows time in days for the bed rest subjects (e.g., BR -8 = 8 days pre-HDBR). The bottom x-axis shows time in days for normative subjects. The gray background indicates the bed rest period. BR Cognition = Time points at which cognitive assessments (i.e., digit symbol substitution test, Purdue pegboard test, rod and frame test, cube rotation test, and card rotation test) took place for the bed rest subjects; BR Sensorimotor = Time points at which sensorimotor tests (i.e., functional mobility test, and sensory organization test (SOT-5 and SOT-5M)) took place for the bed rest subjects; Normative = Time points during which normative subjects completed cognitive tests in supine and seated position and sensorimotor tests.

Figure 2

Average assessment days for bed rest and normative control subjects. The top x-axis shows time in days for normative subjects. The bottom x-axis shows time in days for the bed rest subjects (e.g., BR -8 = 8 days pre-HDBR). The gray background indicates the bed rest period. Error bars represent standard deviations; Normative = normative control subjects (n = 9); HDBR = head down bed rest subjects (n = 10).

Figure 3

Cognitive and sensorimotor performance as a function of bed rest and in normative non-bed rest subjects in supine position. Graphs show marginal means with pooled standard errors. The top x-axis shows time in days for normative subjects. The bottom x-axis shows time in days for the bed rest subjects (e.g., BR -8 = 8 days pre-HDBR). Blue lines represent data of HDBR control subjects; Red lines represent data of HDBR exercise subjects; Green lines represent data of normative control subjects (in supine position for the Rod and Frame graph); Text printed in brown within the graphs show which main effects are significant for the HDBR analyses (e.g., time, time + group, or group + time + group × time). Dots (e.g., ●) indicate at which time point(s) values differ significantly from their baseline (Δ BR -8 = 8 days pre-HDBR for the total group of HDBR subjects; Δ Day 12: N = day 12 for normative control subjects). In case of a significant group by time interaction effect or group effect of exercise separate lines are presented for HDBR control subjects (in blue; Δ BR -8: C) and HDBR exercise subjects (in red; Δ BR -8: E). Δ G×T indicates time points with significant group by time interaction.