Original Article

European Journal of Applied Physiology

, Volume 97, Issue 6, pp 706-715

First online:

Strength, size and activation of knee extensors followed during 8 weeks of horizontal bed rest and the influence of a countermeasure

  • E. R. MulderAffiliated withInstitute for Fundamental and Clinical Human Movement Sciences918 Department of Clinical Neurophysiology, Institute of Neurology, Radboud University Nijmegen Medical Centre Email author 
  • , D. F. StegemanAffiliated withInstitute for Fundamental and Clinical Human Movement Sciences918 Department of Clinical Neurophysiology, Institute of Neurology, Radboud University Nijmegen Medical CentreFaculty of Human Movement Sciences, Vrije University
  • , K. H. L. GerritsAffiliated withInstitute for Fundamental and Clinical Human Movement SciencesFaculty of Human Movement Sciences, Vrije University
  • , M. I. PaalmanAffiliated withFaculty of Human Movement Sciences, Vrije University
  • , J. RittwegerAffiliated withCenter for Muscle and Bone research, Charité-Campus Benjamin FranklinInstitute for Biophysical and Clinical Research into Human Movement, Manchester Metropolitan University
  • , D. FelsenbergAffiliated withCenter for Muscle and Bone research, Charité-Campus Benjamin Franklin
  • , A. de HaanAffiliated withInstitute for Fundamental and Clinical Human Movement SciencesFaculty of Human Movement Sciences, Vrije UniversityInstitute for Biophysical and Clinical Research into Human Movement, Manchester Metropolitan University

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Abstract

Changes in the quadriceps femoris muscle with respect to anatomical cross sectional area (CSA), neural activation level and muscle strength were determined in 18 healthy men subjected to 8 weeks of horizontal bed rest (BR) with (n = 9) and without (n = 9) resistive vibration exercise (RVE). CSA of the knee extensor muscle group was measured with magnetic resonance imaging every 2 weeks during bed rest. In the control subjects (Ctrl), quadriceps femoris CSA decreased linearly over the 8 weeks of bed rest to −14.1 ± 5.2% (P < 0.05). This reduction was significantly (P < 0.001) mitigated by the exercise paradigm (−3.5 ± 4.2%; P < 0.05). Prior to and seven times during bed rest, maximal unilateral voluntary torque (MVT) values of the right leg were measured together with neural activation levels by means of a superimposed stimulation technique. For Ctrl, MVT decreased also linearly over time to −16.8 ± 7.4% after 8 weeks of bed rest (P < 0.01), whereas the exercise paradigm fully maintained MVT during bed rest. In contrast to previous reports, the maximal voluntary activation remained unaltered for both groups throughout the study. For Ctrl, the absence of deterioration of the activation level might have been related to the repeated testing of muscle function during the bed rest. This notion was supported by the observation that for a subset of Ctrl subjects (n = 5) the MVT of the left leg, which was not tested during BR, was reduced by 20.5 ± 10.1%, (P < 0.01) which was for those five subjects significantly (P < 0.05) more than the 11.1 ± 9.2% (P < 0.01) reduction for the right, regularly tested leg.

Keywords

bed rest Maximum voluntary torque Voluntary activation Atrophy Countermeasure