The Impact of Bed Rest, Aging and NMES on Skeletal Muscle

The Impact of Bed Rest and Aging on Muscle Mass and Muscle Function: Effects of Neuromuscular Electrical Stimulation

Loss of muscle mass is common phenotypic trait of muscular disuse and ageing. The loss of muscle mass affects, among others, the ability to maintain homeostasis of glucose metabolism and the energy reservoir in catabolic conditions, while also affecting mechanical muscle function which can cause detrimental impairments in general functional status and hence quality of life. However, a limited amount of research has attempted to elucidate molecular regulators of muscle mass loss following bed rest in older individuals and across genders. Consequently, the mechanistic drivers are unresolved and there are currently no effective therapeutic strategies to counteract muscle wasting and loss of function in individuals submitted to bed rest e.g. during hospitalization. Purpose The purpose is to examine the effects of 5 days of bed rest on muscle mass, including myofibrillar protein synthesis and breakdown, and muscle function, and elucidate molecular regulators of muscle mass loss and metabolic pathways, while also investigating if potential negative effects can be counteracted by daily NeuroMuscular Electrical Stimulation (NMES) across different age and genders. Methods The study is designed as a randomized controlled cross-over 5-day bed rest study including a group of healthy young (18-30 years) and healthy old (65-80 years) men and women. Participants will receive daily electrical stimulation (NMES) of the thigh muscles (30 min x 3/day) on one leg (ES), while the other leg serves as a control (CON). Participants will be tested at baseline (pre) and after (post) intervention for muscle strength, muscle power, balance, and muscle activation. Blood samples are collected at several time points and muscle biopsies are sampled pre- and post-intervention along with assessment of whole-body muscle mass and thigh muscle mass. Scientific exposition The results from the study can potentially provide insight into the adaptive mechanisms associated with NMES training and muscular disuse on both cellular- and whole-body level. The understanding of the underlying mechanisms is crucial for the application of NMES in a therapeutic context and will furthermore help us understand the basic mechanism regulating the skeletal muscle mass during both training and muscular disuse. Overall, the results can potentially help establishing treatments to counteract loss of muscle mass, muscle function and muscle health during periods of muscular disuse.

Disuse Atrophy (Muscle) of Lower Extremities, Muscle Function, Neuromuscular Electrical Stimulation, Myofibrillar Protein Synthesis

Participants are subjected to 5 days bed rest. One leg will receive 3/daily neuromuscular electrical stimulation. The contralateral leg will serve as control-leg undergo disuse only.

The assessors will be without knowledge of which leg has received neuromuscular electrical stimulation and which leg was control

One leg will be subjected to disuse by bed rest and will not receive further treatment during the bed rest period.

One leg will be subjected to disuse by bed rest and will in addition receive neuromuscular electrical stimulation of the quadriceps muscle 3 times/day.

Quantification of myofibrillar protein synthesis using the stable-isotope amino acid tracer deuterium oxide (D2O)

Assessed during the period from pre-intervention biopsies (day 0, first day of bed rest) to post-intervention biopsies (day 5, last day and cessation of bed rest)

Maximal isometric voluntary quadriceps strength combined with the superimposed twitch technique to assess maximal strength and voluntary muscle activation

Ultrasound scan of rectus femoris and vastus lateralis muscle thickness and of vastus lateralis pennation angle

Inclusion Criteria: Healthy Age between 18-30 or 65-80 years Injury free in the lower extremities (No previous or current knee injuries or knee pain) Normal weight Consumes normal diet Exclusion Criteria: Cognitive impairment affecting the ability to participate in the study. Health related contraindications to participating in the intervention (i.e., bed rest and/or NMES), such as eczema and rash on the lower extremities Smoker Obesity Not able to speak or understand Danish. Acute or chronic diseases such as diabetes, cancer, embolism, infection, cardio-vascular diseases Use of medication which affects myofibrillar protein synthesis or the skeletal muscle tissue Use of other medication (e.g. anticoagulants, adrenal cortex hormone [within the last 3 months] etc.) Previous or current use of anabolic steroids Previous participation in research trials involving deuterium oxide or another stable isotope tracer