2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
WHOLE MUSCLE CONTRACTILE PARAMETERS AND
THICKNESS LOSS DURING 35-DAYS BED-REST
Rado Pišot 1 , Marco Narici 2 , Boštjan Šimunič 1 and Mihaela Jurdana 1
1 Institute of Kinesiology Research, University of Primorska- Science and research
centre of Koper, Slovenia
2 Marco Narici, Manchester Metropolitan University, UK
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Contact person: rado.pisot@zrs-kp.si
INTRODUCTION
Microgravity is a unique environment imposing major physiological stress to the
human body. Prolonged exposure to such an environment leads to significant
musculoskeletal adaptations resulting in a loss of muscle mass and function.
Skeletal muscle mass and strength are reduced with as little as 7 days of spaceflight
(LeBlanc et al. 1995; Grigoryeva and Kozlovskaya 1987) and continue to decline with
the length of exposure (Adams et al. 2003). Amongst the various muscles affected by
disuse, the extensors are those showing the greatest atrophy. At the single fibre level,
evidence suggests human type II muscle fibres are more, or at least as, susceptible to
atrophy than type I muscle fibres (Edgerton et al. 1995, Fitts et al. 2000, Widrick et al.
1999).
Trappe et al. (2004) found a directional shift from slower contracting fibres to faster
contracting fibres. This slow-to-fast shift in myosin isoform is in agreement with
previous findings in animals (Caiozzo et al., 1994) and humans (Zhou et al. 1995,
Ohira et al. 1999).
Contractile properties of the skeletal muscle in response to disuse change
considerably. Time to isometric twitch peak tension of triceps surae muscle increased
by 13% (Koryak 1995). On the other hand in vitro experiments demonstrated that
maximal shortening velocity (Vo) of the calf muscles increases as a result of space
flight (Caiozzo et al., 1994;1996). The passive tension-strain relationships revealed
that passive tension of both slow and fast soleus fibres increased less steeply with
sarcomere length after hindlimb unloading (Toursel et al. 2002). Increased amplitude
of the mechanomyographic response was linked to decreased muscle stiffness
(Evetovich et al. 1997), where more compliant muscle becomes less efficient in
damping muscle fibre oscillations.
The purpose of this study was to investigate the changes in muscle size, contractile
and stiffness properties following 35 days of horizontal bed rest bed in humans.
METHODS
Subjects and bed rest
Ten healthy males performed 35 days of horizontal bed rest (age 22.3 ± 2.2 years).
The study was conducted at the Valdoltra Orthopaedic Hospital (Ankaran, Slovenia).
The protocol of the study was approved by the National Committee for Medical
Ethics at the Ministry of Health.