Table of Contents

Space Medicine

Can Electrical Muscle Stimulation Prevent Muscle Loss?

Purpose

The absence of a gravitational load in space results in the breakdown of muscle tissue, which is called muscle atrophy. Muscle atrophy is not necessarily problematic while astronauts are in space, but the loss of muscle strength and function can seriously impede performance during re-entry to the Earth's atmosphere and immediately upon landing. It is particularly dangerous if astronauts must perform a strenuous emergency egress from the shuttle.

Background

The most effective way to minimize muscle atrophy is for astronauts to perform strength training exercises in orbit. However, strength training in microgravity requires complicated equipment and significant amounts of valuable mission time to obtain the required results. The inconvenience of performing strength-training exercises has led scientists to look for other ways to minimize muscle atrophy. One method has been the use of electrical muscle stimulation of the most susceptible muscles.

Previous studies have proven the efficacy of Neuromuscular Electrical Stimulation (NMES) protocols that stimulate muscle through skin surface electrodes in order to cause muscle contraction. Although NMES protocols have proven useful in minimizing muscle atrophy, they cause discomfort to those undergoing treatment and are impractical for spaceflight. CSA's Operational Space Medicine (OSM) group conducted a study to investigate a new type of electrical muscle stimulation called Therapeutic Electrical Stimulation (TES).

Project Description

From 1997 to 1999 the CSA's Operational Space Medicine group, in conjunction with the University of Montreal, evaluated the effectiveness of Therapeutic Electrical Stimulation (TES) in minimizing muscle atrophy in space.

TES could offer a painless and cost-effective alternative to NMES. As TES uses a low-intensity stimulation that does not cause a noticeable muscle contraction, it can be used during sleep without waking the subject. It has the potential to increase mission efficiency by reducing or eliminating the need for astronauts to perform prolonged physical training.

Patients recovering from knee surgery to repair the anterior cruciate ligament (ACL) were selected as subjects for the ground-based research. ACL patients were used because they experience muscle atrophy and decreased function in the quadriceps of the injured leg.

This muscle atrophy is similar to the muscle atrophy that astronauts experience in the anti-gravity muscles of the legs -- the muscles that enable us to stand upright on Earth.

The research subjects were divided into two groups. The control group followed the standard exercise rehabilitation program normally required following reconstructive ACL surgery. The experimental group followed a TES stimulation protocol in addition to the standard rehabilitation program. They received TES to the quadriceps for six to eight hours nightly, five times a week for 12 weeks.

Results

Both groups showed improvements in muscle strength and function over the 12 weeks, but there were no significant differences found between the two groups. The investigators concluded that the lack of statistical significance was due to considerable variation from patient to patient in:

• individual quadricep atrophy and weakness before surgery
• interval between initial injury and surgery
• trauma associated with the surgery

Due to these variations, ACL patients were determined to be unsuitable to simulate space-induced muscle atrophy.

Based on these conclusions and observations the data gained from the study was considered inconclusive. However, TES cannot be discarded as a potential countermeasure for muscle atrophy during spaceflight based on this study. Further studies will be required to determine its potential for alleviating space muscle atrophy.

Related Links

• Percutaneous Electrical Muscle Stimulation -- from ESA's experiment facilities located inside the US "Destiny" Laboratory on the International Space Station.