Five days of bed rest in young and old adults: Retainment of skeletal muscle mass with neuromuscular electrical stimulation

Abstract

The consequences of short-term disuse are well known, but effective countermeasures remain elusive. This study investigated the effects of neuromuscular electrical stimulation (NMES) during 5 days of bed rest on retaining lower limb muscle mass and muscle function in healthy young and old participants. One leg received NMES of the quadriceps muscle (3 × 30min/day) (NMES), and the other served as a control (CON). Isometric quadriceps strength (MVC), rate of force development (RFD), lower limb lean mass, and muscle thickness were assessed pre-and post-intervention. Muscle thickness remained unaltered with NMES in young and increased in old following bed rest, while it decreased in CON legs. In old participants, mid-thigh lean mass (MTLM) was preserved with NMES while decreased in CON legs. In the young, only a tendency to change with bed rest was detected for MTLM. MVC and early-phase RFD decreased in young and old, irrespective of NMES. In contrast, late-phase RFD was retained in young participants with NMES, while it decreased in young CON legs, and in the old, irrespective of NMES. NMES during short-term bed rest preserved muscle thickness but not maximal muscle strength. While young and old adults demonstrated similar adaptive responses in preventing the loss of skeletal muscle thickness, RFD was retained in the young only.

Keywords: aging; atrophy; disuse; muscle strength.

FIGURE 1

Schematic illustration of the study timeline. Prior to the bed rest period, young (n = 16) and old (n = 16) healthy participants were included and familiarized to testing procedures. Following this, on Day −3, participants were pre‐intervention tested. On Day 0, participants arrived in the fasting state in the morning where blood samples were collected, and hereafter the bed rest was initiated. Throughout the 5 days of bed rest, NMES leg received 3 × 30 min NMES. The last NMES session was in the evening on Day 4. On Day 5, blood samples were drawn in the fasted state in the morning, following which participants were transported by wheelchair to the Lab for post‐intervention testing.

FIGURE 2

Changes in blood analyte concentrations and HOMA IR index during 5 days of bed rest. Data are presented as absolute values: Mean ± SD. n = 16 (young), 16 (old). (a) Changes in plasma glucose concentrations. (b) Changes in fasting insulin concentrations. (c) Changes in HOMA IR index. (d) Changes in fasting c‐peptide concentrations. (e) Changes in fasting cortisol concentrations. *Significant difference in concentrations between days (p < 0.05).

FIGURE 3

Percentage change from pre‐ to post 5 days of bed rest in muscle mass. CON, control leg, bed rest only. NMES: Stimulation leg, bed rest + daily NMES. Data are presented as mean ± SD with individual data points indicated. n = 16 (young), 16 (old) (a) changes in leg lean mass assessed by DXA scan. (b) Changes in mid‐thigh lean mass assessed by DXA scan. (c) Changes in vastus lateralis muscle thickness assessed by ultrasound imaging. *Significant difference between legs (p < 0.05). No difference between delta values (pre‐ to post bed rest) of young and old was detected.

FIGURE 4

Percentage change from pre‐ to post 5 days of bed rest in mechanical muscle function. CON, control leg, bed rest only. NMES: Stimulation leg, bed rest + daily NMES. Data are presented as mean ± SD with individual data points indicated. n = 16 (young), 16 (old). (a) Percentage change in maximal muscle strength. (b) Percentage change in rate of force development (RFD) from 0 to 50 ms. (c) Percentage change in RFD from 0 to 200 ms. No difference between delta values (pre to post bed rest) of young and old was detected.