2007, Piran, Slovenia

Gravitational Physiology
SKELETAL MUSCLE STRUCTURAL AND FUNCTIONAL
ADAPTATIONS TO 35-DAY BED REST:
RESULTS OF THE 2006 VALDOLTRA BED REST CAMPAIGN
Marco Narici 1 , Olivier Seynnes 1 , Maarten de Boer 1 , Guglielmo Antonutto 2 , Rado
Pisot 3 , Igor Mekjavic 4 , and Pietro Enrico di Prampero 2
1 Institute for Biophysical and Clinical Research into Human Movement, Manchester
Metropolitan University, United Kingdom; 2 Sezione di Fisiologia Umana
Dipartimento di Scienze e Tecnologie biomediche, Universita’ di Udine, Italy;
3 Institute of Kinesiology Research, University of Primorska- Science and research
centre of Koper, 4 Slovenia, Institute of Josef Stefan, Ljubljana, Slovenia
Contact person: m.narici@mmu.ac.uk
INTRODUCTION
Exposure of humans to actual or simulated microgravity leads to muscle wasting and
weakness (di Prampero and Narici, 2003). However, the loss of muscle force,
typically observed in these conditions, exceeds that of muscle size: that is to say,
muscles become intrinsically weaker. The causes of this phenomenon are known to
involve several mechanisms of muscular, neural (in the case of voluntary contractions,
Antonutto et al. 1999), and tendinous origin (Reeves et al. 2005). In addition to a
decrease in single fibre specific tension (Larsson et al. 1996), recent evidence
suggests that human muscle architecture undergoes substantial remodelling with
disuse (Narici & Maganaris, 2007). Thus the aim of the present study was to
investigate the changes in muscle architecture induced by chronic disuse (bed rest)
and their potential role in the disproportionate loss of muscle strength, compared to
that of muscle size, observed in these conditions.
METHODS
Ten healthy males (age 22.3 ± 2.2 years) underwent 35-day bed-rest (BR) in the
clinical facility of the Orthopaedic Hospital Valdoltra, Ankran, Slovenia. Each
participant gave written informed consent to this investigation that was approved by
the local Ethics Committee.
Three days before bed rest (BR-3) and on the first day of recovery (R+0) the
following measurements were performed:
(1) maximum isometric contraction of the knee extensors of the dominant leg at 80
degrees of knee flexion, assessed using an isometric chair dynamometer (Udine
University)
(2) muscle thickness of the gastrocnemius medialis (GM), vastus lateralis (VL),
tibialis anterior (TA) and biceps brachii (BB), evaluated along the mid-sagittal plane
of the muscle belly by ultrasound imaging (Fig. 1)
(3) muscle architecture of the VL muscle (fibre fascicle length and pennation angle)
assessed by ultrasound imaging (Fig. 1.)
RESULTS
MVC: maximum isometric force of the knee extensors decreased on average by
20.7% (P