| Yhteenveto: | Aquatic rehabilitation is a widely used tool for injury prevention or rehabilitation. The
underlying neuromuscular mechanisms during immersion are less known due to
methodological issues. The following study main purpose to assess neuromuscular functions
and muscle architecture changes within immersed condition. The physical properties of water
to the human body are well understood, as well as its effect on the cardiorespiratory system.
While the Hoffmann reflex, as a tool to assess neuromuscular changes on dry land is widely
examined, it has been rarely used during immersion. The effect of water immersion on
muscle behavior is also unknown. In this study control values were recorded in sitting
position for one hour on dry land. This recording period was needed to mimic the similar
protocol as in water and to compare the two conditions. The dry land recording showed no
changes in the recorded parameters over time. Unaltered reflex and muscle architecture
parameters on dry land indicate that the changes during immersion are due to the altered
environment. During the first 15 minutes of immersion maximal M-wave and muscle
thickness decreased significantly. Maximal H/M ratio showed no significant changes in water
immersed condition. The decreased potentiation of the muscle due to the architecture changes
is reflected by the decreased maximal M-wave; however the unaltered H-reflex indicates
background compensatory mechanisms. Possibly the activation of peripheral
mechanoceptors and the effect of weightlessness decreased the tonic presynaptic inhibition
which leads to compensated H-reflex response. Repeating the protocol showed good
reliability of the maximal H/M ratio, and good inter-session reliability of the muscle
thickness. The thesis indicates that with adequate precaution, H-reflex and ultrasound
recording is possible during prolonged immersed condition, while the results raise the
possibility of acute peripheral and central neuromuscular activation during immersion. With
the current protocol the precise mechanisms cannot be addressed, it rather raises the
importance for future studies to measure muscle architecture and presynaptic inhibition.
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