Health TrialsbyHealthPanel

Unloaded Minds - How Prolonged Unloading Shapes Human Performance in Lunar Gravity

ConditionUnilateral Lower Limb Suspension (Simulated Microgravity)
Trial statusRecruiting
Trial phaseNot applicable
Trial typeInterventional
Biological sexAll
Age18-60
SponsorKarolinska Institutet

About this trial

During spaceflight and lunar missions, reduced gravitational loading causes the muscles and nervous system to decondition rapidly. While muscle wasting is well documented, much less is known about how the brain and spinal cord adapt to the absence of normal mechanical loading - and how these central changes interact with muscle deterioration to impair movement control.

This study investigates how two weeks of simulated lower limb unloading affects the brain's movement programs (motor engrams), the functional connection between nerves and muscles, and overall movement quality. Healthy participants undergo 14 days of Unilateral Lower Limb Suspension (ULLS), a model in which one leg is kept unloaded using a raised shoe and crutches while the other leg functions normally. After the unloading period, participants travel to Bordeaux, France, where they walk on a treadmill for the first time - in lunar gravity - during a parabolic flight.

Before and after the unloading period, participants are assessed with MRI (muscle size), force plate tests (jump performance and balance), nerve stimulation (number of functional motor units), and treadmill gait analysis combining brain activity (EEG), muscle activity (EMG), joint movement, and plantar pressure measurements. The same gait analysis is repeated during the parabolic flight under lunar gravity (0.16G).

The results will shed light on how the brain and muscles adapt to disuse and reactivate under partial gravity - with direct relevance to astronaut safety and rehabilitation, as well as clinical conditions involving prolonged limb immobilization.

Eligibility criteria

This trial accepts healthy volunteers

Qualifiers

None

Disqualifiers

high activity level according to the GLTEQ

contraindications to exercise

pregnancy

contraindications to MRI

Trial design

Design model

Single group

Treatments tested in this trial

  • Unilateral lower limb suspension

    Behavioral

    Unilateral Lower Limb Suspension (ULLS) is a validated spaceflight analog for the lower limbs, which mimics unloading specifically in the lower limbs 3. In ULLS, participants wear a shoe with \~100 mm elevated sole and use short-length crutches aided by a hand grip and forearm support distal to the elbow. This allows the contralateral lower limb to remain unloaded in a straight position and move passively at the hip. The ULLS model specifically targets skeletal muscle unloading in the lower limb with no or minor systemic deconditioning, and it imposes minimal restrictions on participants' daily activities. A key advantage of ULLS is that the contralateral, weight-bearing limb provides a valid inherent control accounting for individual factors such as nutrition, genetics, and lifestyle.

Treatment groups

24 Participants
are divided into 1 treatment group
Group A: ULLSExperimental treatment 1 intervention

Trial outcomes

Primary outcomes

1

Muscle volume

Three days before the initiation of the ULLS intervention, and at day 15 of unloading, all participants will undergo an MRI scan to assess thigh and calf muscle size. Muscle volume will be evaluated using cross-sectional T2-weighted images acquired on a 3-Tesla MR system. Anatomical landmarks and standardized procedures will ensure that the same segment is scanned at both time points. Participants will rest in a supine position for approximately 30 minutes prior to each scan to minimize measurement interference caused by fluid shift. Images will be analysed using manual segmentation to delineate individual muscle boundaries in each cross-sectional slice; muscle volume is then calculated by summing the cross-sectional areas of the target muscles across all slices and multiplying by slice thickness.

Time frame
Three days before the initiation of the ULLS intervention and at day 15 of unloading, for both thigh and calf muscles bilaterally.

Secondary outcomes

1

Gait analysis

Gait analysis will be performed before the ULLS phase and during the lunar gravity phases of a parabolic flight at the two selected gait speeds of 3 km/h and 5 km/h. Kinematic parameters such as knee and ankle joint angles are recorded using 2-dimensional electronic goniometers (Biometrics). Kinematic data will be recorded in the frontal and sagittal plane at a sampling frequency of 500 Hz. Kinetic and spatiotemporal parameters like the force distribution are recorded using pressure insoles with a sampling frequency of 200 Hz. Spatiotemporal parameters are crucial indicators of gait stability and overall mobility. They include variables such as step length, stride length, cadence, step width, and gait cycle duration and their variability.

Time frame
Gait analysis will be performed three-to-five days before the ULLS phase and during the lunar gravity phases of a parabolic flight
2

Electroencephalogram

The data is recorded using a 64-channel electroencephalography (EEG) cap adapted to the size of the head. The electrodes are arranged in the international 10-20 system around the motor cortex. Electrode FCz is used as a reference, AFz as ground. The EEG cap, which is fixed with a chin strap to prevent displacement, is permeable to air to ensure appropriate air ventilation during exercise. The distances between the electrodes are approx. 5 cm to prevent a possible false signal due to salt bridges caused by perspiration. Each electrode is filled with SuperViscTM electrode gel (EasyCap GmbH, Herrsching, Germany) for signal transmission. The use of active EEG electrodes developed by Brain Products (Gilching, Germany) allows the recording of electrocortical activity during exercise without movement artefacts.

Time frame
Three-to-five days before the ULLS phase and during the lunar gravity phases of a parabolic flight, during the gait analysis tests.
3

Electromyography

Surface EMG activity will be continuously recorded for the following 8 muscles of the left and right lower limbs: rectus femoris (RFL and RFR), lateral hamstrings (HL and HR), gastrocnemius lateralis (GASL and GASR), and tibialis anterior (TAL and TAR). These muscles are activated by the Central Nervous System (CNS) to produce the gait. The EMG signals will be collected using a commercial surface wireless EMG system (Delsys, USA).

Time frame
Three-to-five days before the ULLS phase and during the lunar gravity phases of a parabolic flight, during the gait analysis tests.
4

Muscle function and balance

Muscle function will be assessed by a standardized countermovement jump on force plates (MuscleLab, Norway). Balance will be assessed by a sway test where participants will balance on one leg with their eyes closed and eyes open, this is also done on force plates.

Time frame
Three days before initiation of ULLS and immediately after the parabolic flight.

Other outcomes

Sponsors and contacts

Click on the lead sponsor to view all of their trials.

Karolinska Institutet

Lead sponsor

German Sport University, Cologne

Collaborator

Source ClinicalTrials.gov
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