Muscular Force Generation in Microgravity

The findings from water immersion indicated that some motor tasks, such as plantarflexion (25), but not others, such as the leg-press (7), appear to be affected. Thus, it would be relevant to test a number of motor tasks and body regions. On the other hand, parabolic flight requires that methodologies can be performed in a quick efficient fashion. Hence, we propose examining ankle plantarflexion, leg-press and grip-force.

The primary hypothesis is that plantarflexion MVC will be reduced in the microgravity phase of parabolic flight.

As secondary parameters will be assessed parameters of muscle function that can be easily implemented in parabolic flight, such as electromyography and ultrasound measurements of the musculotendinous unit. To assess the muscular system more deeply, for plantarflexion superimposed twitches will be performed (16) during MVC and at rest. An additional experimental condition placing foam (unstable surface; standard size) under the foot during plantarflexion will be included. This approach increases the challenge for the neuromuscular control system and, under such conditions, MVC is reduced (29).

These secondary investigations, which do not prohibitively complicate the practical implementation of the project, will help to understand what is happening in the musculature should we indeed find impediments of muscle force generation in microgravity.

The aim of this study is to evaluate the applicability of high-load resistance training as a countermeasure for long term space flights, the current project has two scientific goals.

The main objective is to perform a deeper examination of muscle function and MVC in weightlessness (parabolic flight).

The secondary objective is to gather further insight into the underlying mechanisms and structures based on investigations targeting the neuromuscular and musculotendinous systems and their interaction.

The main judgment criteria is the MVC tested during three different tasks: (1) leg press, (2) plantarflexion and (3) grip strength.

As secondary criteria, we will assess parameters of muscle function that can be easily implemented in parabolic flight:

• Rate of force development
• Electromyographic activity
• Ultrasound measure: fascicle length and pennation angle of the gastrocnemius medialis muscle
• Superimposed twitch torque (M-waves at rest and V-waves in MVC conditions)
• Maximum voluntary activation capacity (%VA): %VA = (1-[torque superimposed twitch/torque resting twitch])*100%.

The primary hypothesis is that plantarflexion and knee extension force generation capacity will be reduced, but not grip-force, in the microgravity phase of parabolic flight.