Muscle Strength is one of eleven International Bedrest Standard Measures conducted on healthy subjects at the :envihab facility in Cologne, Germany. Muscle strength will be assessed through isometric and isokinetic muscle testing. Isometric maximum voluntary contractions will provide a very fast and reliable measurement of isometric strength of the knee and ankle. Isokinetic muscle testing will assess the strength of the knee, ankle, and trunk musculature. The purpose of the standard measures project is to populate a repository with data that enables high-level monitoring of countermeasure effectiveness and meaningful interpretation of health and performance outcomes. These standard measures will support future, hypothesis-driven research that enables planetary missions by providing an optimized minimal set of measures captured from subjects. These measures will be available to other studies under data sharing agreements as well as undergo analysis to understand risk posture.
Isometric Knee Strength:
Subjects will be seated and positioned in the dynamometer with the knee flexed at 60 degrees. Subjects will then perform three sets of maximum contractions alternating between flexion and extension muscle contractions. Each muscle contraction should last five to seven seconds with 30 seconds of rest between flexion and extension contractions.
Isometric Ankle Strength:
Subjects will be placed in the prone position with the ankle positioned at 90 degrees. Subjects will perform three sets of maximum contractions, alternating between plantar flexion and dorsiflexion muscle contractions. Muscle contraction should last five to seven seconds with 30 seconds of rest between plantar and dorsiflexion contractions.
The highest value of toque (Nm) obtained for both isometric tests are considered to be subjects’ maximum. If a subject continues to improve at the third contraction, testing will continue until no further improvement is observed.
Before isokinetic muscle testing is conducted, subjects will warm up muscles by completing five contractions with increasing force levels. A two to three-minute rest period will be provided between testing of each muscle group. For standardization purposes, knee and ankle testing will be performed on the right lower extremity.
Isokinetic Knee Testing:
Subjects will be placed in a seated position and knee range of motion on the dynamometer will be set for 20 degrees to 95 degrees. The weight of the limb will be assessed with the knee positioned at 30 degrees. Isokinetic peak torque (Nm) will be assessed at a speed of 60 degrees per second. The subject will perform three repetitions of continuous concentric extension and flexion motion at maximal effort.
Isokinetic Ankle Testing:
Subjects will be in the prone position. Range of motion of the dynamometer will be adjusted to 5 degrees less than the subject's maximum position of dorsiflexion and 5 degrees less than the subject's maximum position of plantar flexion. Weight of the limb will be assessed with the ankle positioned at 15 degrees. Isokinetic peak torque (Nm) will be assessed at a speed of 30 degrees per second. Three repetitions of continuous concentric dorsi- and plantar flexion contractions will be performed at maximal effort. A rest period of about two minutes will be provided before testing is repeated to assess peak torque (Nm) for eccentric muscle contractions.
Isokinetic Trunk Strength:
Subjects will be in the standing position and range of motion on the dynamometer is set for 0 degrees to 90 degrees of motion. Weight of the trunk is not required. Peak torque (Nm) will be assessed at a speed of 60 degrees per second. Subjects will perform three repetitions of continuous concentric flexion and extension motion at a maximal effort.
Muscle Endurance Testing:
To warm up, subjects will complete five minutes of light exercise (50 Watts) on a cycle ergometer. Endurance testing of the knee will be assessed at a speed of 180 degrees per second. Subjects will perform 20 repetitions of continuous flexion and extension motion at maximal effort. Total work in Nm will be recorded.
The scheduled days of collection are as follows:
The :envihab International Bedrest Standard Measures Test Battery is not a hypothesis-driven study, but rather a collection of data made available to future researchers and for trend analysis. As such, there are no specific hypotheses, outcome measures, or statistical analyses associated with the skeleton of the project. The questionnaire will capture a "snapshot" of optimized data that can be investigated by researchers in the future.
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