UK Space Agency project

Our team at the University of Birmingham is responsible for assessing muscle strength, endurance, force steadiness, and neuromuscular control of astronauts' neck muscles pre- and post-flight. These assessments include:

• Maximal voluntary contractions: measuring neck flexion, neck extension, and shoulder shrug strength
• Force control assessment: evaluating accuracy in tracking submaximal force targets
• Endurance testing: sustained shoulder abduction for 60 seconds to monitor fatigue-induced adjustments

We use state-of-the-art equipment, including High-Density Surface Electromyography (HDsEMG) to capture these measurements. HDsEMG involves placing grids of tiny, closely spaced electrodes on the skin over specific neck muscles. Unlike conventional EMG, which uses only a few electrodes, HDsEMG provides a detailed "map" of muscle activity, allowing us to see how different regions of the same muscle work together, adapt over time, and coordinate with other muscles. A key advantage of HDsEMG is that it allows us to decompose the signals into the activity of individual motor units - the fundamental building blocks of muscle function, consisting of a single motor neuron and all the muscle fibres it controls. Through specialised signal processing techniques, we can track the same motor units across different recording sessions before and after spaceflight, providing unique insight into how the nervous system adapts to microgravity at its most fundamental level.

Force output during these tasks is measured using a specialised handheld dynamometer, which precisely quantifies the force exerted during different neck movements. For submaximal contractions, participants receive real-time visual feedback displayed on a monitor, where they attempt to match target force levels represented graphically. This sophisticated feedback system enables precise assessment of force steadiness and motor control, allowing identification of subtle deficits in neuromuscular coordination that might contribute to increased injury risk following spaceflight.

Our consortium employs multiple imaging technologies to assess structural changes:

Magnetic Resonance Imaging (MRI)

MRI uses powerful magnets and radio waves to create detailed images of soft tissues without radiation. This non-invasive imaging allows us to examine:

• Intervertebral disc morphology and composition: measuring changes in the size, shape, and water content of the discs between vertebrae
• Vertebral body analysis: assessing structural changes in the neck vertebrae
• Muscle size, water, and fat content: evaluating whether muscles atrophy (shrink) or undergo fatty infiltration during spaceflight

Dual-Energy X-ray Absorptiometry (DXA)

DXA is a specialised form of X-ray that precisely measures bone mineral density in the cervical spine. This helps determine whether bone loss occurs in the neck vertebrae during spaceflight, which could affect spinal stability and potentially contribute to disc herniation risk.

This component involves detailed analysis of neck movement patterns using an infrared-based motion capture system with reflective markers placed on the head and trunk. This technology measures:

• Range and speed of movement: how far and how quickly astronauts can move their necks in different directions
• Movement precision: the accuracy and smoothness of neck movements
• Aberrant motions: unusual movement patterns that may indicate instability or compensation

By examining how astronauts move their necks before and after spaceflight, we can identify potential mechanisms that might increase the risk of injury upon return to Earth's gravity.

NIRS is a non-invasive technique that uses light waves to measure oxygen levels and blood flow in neck muscles during activity. This technology helps us understand:

• Muscle metabolism: how efficiently the muscles use oxygen during activity
• Fatigue resistance: how quickly muscles become fatigued and recover
• Blood flow dynamics: whether microgravity affects the delivery of blood and oxygen to neck muscles

These measurements provide important information about physiological changes that may not be visible through structural imaging alone.

Our measurements follow a structured timeline:

• Pre-flight: 180-90 days and 60-30 days prior to spaceflight
• Post-flight: 1-7 days, 8-14 days, 45-60 days, and 160-190 days after spaceflight