2007, Piran, Slovenia

Lf (mm)
50.0
40.0
30.0
20.0
10.0
Fascicle Length
Lf before
Lf after
Gravitational Physiology
Figure 3. Fascicle length of the VL muscle measured by ultrasound before and after
bed rest.
DISCUSSION
In line with previous observations, bed rest as a model of microgravity leads to
preferential wasting of the postural muscles. The degree of atrophy may be ranked as
follows gastrocnemius m. (16%) > vastus lateralis (9%) > tibialis anterior (6%) >
biceps brachii (2%). Atrophy not only involves a decrease in muscle size but also
marked remodelling of muscle architecture: muscle fibres become shorter and less
pennate. The observed decrease in fibre length implies a loss of sarcomeres in series
(about 1000 sarcomeres) and is expected to shift the sarcomere length-tension relation
to the left, away from the optimum region of force generation, thus contributing to the
decrease in F/CSA. The shorter fibre length may also contribute to the loss of muscle
power observed after bed rest and spaceflight, though this may be partly compensated
by an increased fast myosin heavy chains expression.
REFERENCES
Antonutto, G., Capelli, C., Girardis, M., Zamparo, P. and Di Prampero, P. E., 1999.
Effects of microgravity on maximal power of lower limbs during very short
efforts in humans. J Appl Physiol 86, 85-92.
di Prampero P.E. and Narici M.V., 2003. Muscles in microgravity: from fibres to
human motion. J Biomech 36, 403-412.
Larsson, L., Li, X., Berg, H. E. and Frontera, W. R., 1996. Effects of removal of
weight-bearing function on contractility and myosin isoform composition in single
human skeletal muscle cells. Pflugers Arch 432, 320-328.
Narici, M.V. and Maganaris, C.N., 2007. Plasticity of the muscle-tendon complex
with disuse and aging. Exercise and Sport Science Reviews (in press).
Reeves, N. D., Maganaris, C. N., Ferretti, G. and Narici, M. V., 2005. Influence of 90day
simulated microgravity on human tendon mechanical properties and the effect
of resistive countermeasures. 98, 2278-2286.
Penn Angle (deg)
30.0
25.0
20.0
15.0
10.0
Pennation Angle
Penn Before
Penn after
31