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This Article Full Text Full Text (PDF) All Versions of this Article: 583/3/1079    most recent jphysiol.2007.135392v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by de Boer, M. D. Articles by Narici, M. V. Search for Related Content PubMed PubMed Citation Articles by de Boer, M. D. Articles by Narici, M. V. Related Collections Skeletal Muscle and Exercise

¹ Manchester Metropolitan University, Institute for Biophysical and Clinical Research into Human Movement, Alsager ST7 2HL, UK
² University of Nottingham, Graduate Medical School, Derby City General Hospital, Derby DE22 1HX, UK

Muscles and tendons are highly adaptive to changes in chronic loading, though little is known about the adaptative time course. We tested the hypothesis that, in response to unilateral lower limb suspension (ULLS), the magnitude of tendon mechanical adaptations would match or exceed those of skeletal muscle. Seventeen men (1.79 ± 0.05 m, 76.6 ± 10.3 kg, 22.3 ± 3.8 years) underwent ULLS for 23 days (n = 9) or acted as controls (n = 8). Knee extensor (KE) torque, voluntary activation (VA), cross-sectional area (CSA) (by magnetic resonance imaging), vastus lateralis fascicle length (L_f) and pennation angle (), patellar tendon stiffness and Young's modulus (by ultrasonography) were measured before, during and at the end of ULLS. After 14 and 23 days (i) KE torque decreased by 14.8 ± 5.5% (P < 0.001) and 21.0 ± 7.1% (P < 0.001), respectively; (ii) VA did not change; (iii) KE CSA decreased by 5.2 ± 0.7% (P < 0.001) and 10.0 ± 2.0% (P < 0.001), respectively; L_f decreased by 5.9% (n.s.) and 7.7% (P < 0.05), respectively, and by 3.2% (P < 0.05) and 7.6% (P < 0.01); (iv) tendon stiffness decreased by 9.8 ± 8.2% (P < 0.05) and 29.3 ± 11.5% (P < 0.005), respectively, and Young's modulus by 9.2 ± 8.2% (P < 0.05) and 30.1 ± 11.9% (P < 0.01), respectively, with no changes in the controls. Hence, ULLS induces rapid losses of KE muscle size, architecture and function, but not in neural drive. Significant deterioration in tendon mechanical properties also occurs within 2 weeks, exacerbating in the third week of ULLS. Rehabilitation to limit muscle and tendon deterioration should probably start within 2 weeks of unloading.

(Received 20 June 2007; accepted after revision 24 July 2007; first published online 26 July 2007)
Corresponding author M. D. de Boer: Instititute for Biophysical and Clinical Research into Human Movement (IRM), Manchester Metropolitan University, Alsager ST7 2HL, UK. Email: m.deboer{at}mmu.ac.uk

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