2007, Piran, Slovenia

Gravitational Physiology
Contractile properties
Isometric twitch contraction time of five skeletal muscles (biceps brachii – BB; vastus
medialis – VM; erector spinae – ES; gastrocnemius medialis – GM; biceps femoris –
BF) was recorded using tensiomiography (TMG), a mechanomyographic method
(Valenčič 1990; Dahmane et al., 2000 and 2005; Pišot et al. 2002). Twitch contraction
time of the mechanical response was measured in relaxed pre-defined positions
(Delagi et al. 1975) with fixed joint angles. From the supramaximal twitch response
we obtained the maximal amplitude of the response (Dm, mm) and the contraction
time (Tc, ms) from 10% to 90% of Dm. Measurements were performed 30 minutes
before, and after 35 days of horizontal bed rest.
Muscle thickness
The thickness of the GM, TA, VL, and BB were measured at mid muscle belly along
the mid-sagittal plane by ultrasound imaging using a digital ultrasonographer (Esaote
Mylab 25) fitted with a 7-10 MHz linear probe. The examination was performed at
rest with the subject in the horizontal position. In each ultrasound image so obtained,
muscle thickness was measured at mid length as the vertical distance between the
superficial and deep tendon aponeuroses in the central portion of the muscle. The
reliability of this technique in detecting changes in muscle size induced by bed rest
has been previously documented (Reeves et al. 2002).
RESULTS
Contraction time
Whole muscle Tc for all measured muscles are presented in Table 1. Whole muscle
Tc for ES was reduced by 13% (P < 0.05) and for GM increased by 17% (P < 0.01).
In other muscles changes were not significant (Table 1).
Maximal displacement
Whole muscle Dm for all measured muscles are presented in Table 2. Whole muscle
Dm for VM was increased by 25% (P < 0.01), for BF by 30% (P < 0.01) and for GM
by 31% (P < 0.01). In other two muscles changes were not significant (Table 1).
Table 1: Whole muscles Tc and Dm changes before (Pre) and after (Post) 35 days bed-rest.
Tc / ms Dm / mm
Muscle Pre Post %∆ Pre Post %∆
BB 29.2 ± 4.1 27.5 ± 2.2 -5 15.8 ± 2.0 15.0 ± 1.8 -3
ES
19.6 ± 4.5 16.5 ± 2.2*
-
13
5.1 ± 1.4 5.1 ± 2.3 2
VM 25.2 ± 2.0 25.1 ± 2.5 0 8.7 ± 1.6 10.8 ± 1.5** 25
BF 31.0 ± 7.6 29.8 ± 6.1 -2 5.3 ± 1.0 6.6 ± 1.0** 30
GM 26.4 ± 3.1 31.0 ± 6.0** 17 4.2 ± 0.8 5.5 ± 1.1** 31
%∆, percent change. *P < 0.05 from Pre. **P < 0.01 from Pre.
Muscle thickness
After 35 days of bed rest, muscle thickness decreased in all tested muscles. The
greatest atrophy was observed in GM (15-17%) and the least atrophy in the BB
muscle (n.s.)
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