# Reduced postural stability in men and women aged 55–65 following 14 days of head-down bed rest

## TL;DR

A 14-day head-down bed rest reduced postural stability in middle-aged men and women, with effects similar to aging and no benefit from exercise.

## Contribution

This study evaluates the effects of HDBR on postural stability in late middle-aged individuals, a group often overlooked in prior research.

## Key findings

- Postural stability decreased significantly after HDBR, especially in the medio-lateral axis with eyes open.
- Deconditioning effects were reversible within four weeks after HDBR.
- Exercise did not mitigate the effects of HDBR on postural stability.

## Abstract

Aging and head-down bed rest (HDBR) decrease postural stability. Chances of being bedridden increase with age, but HDBR studies usually focus on young men. Here, we evaluate the impact of HDBR on postural stability among late middle-aged individuals. Twenty-two healthy participants (55–65 years old, 11 women) were exposed to 14-day HDBR. Eleven participants performed daily exercise. Static posturography data were collected before, 5 h after, and 4 weeks after HDBR. No time×group or time×sex effects were observed, but women had lower postural stability. With eyes open, the root mean square of the center of pressure was larger immediately after HDBR only in the medio-lateral axis (median [interquartile range]: +53% [+ 15%; +129%], p = 0.002). The mean velocity was increased on both axes (+ 20% [+ 8%; +46%] for medio-lateral and + 19% [+ 13%; +36%] for antero-posterior, both p < 0.001). The complexity features and the critical time were left unchanged. The effects of HDBR were more visible in the eyes open condition and the deconditioning was reversible after four weeks. 14-day HDBR decreased postural stability in individuals aged 55–65, with no impact of the chosen countermeasure. While the deconditioning was equivalent to two decades of aging for some features, additional research is required to determine whether age was an aggravating factor.