The effect of unloading on protein synthesis in human skeletal muscle

Abstract

Atrophy of skeletal muscle is observed in response to immobilization and lack of weight-bearing. The aim of this study was to investigate the effect of immobilization on muscle protein synthesis and associated biochemical parameters in skeletal muscle of healthy volunteers employing a standardized model of lower limb unloading. One leg was unloaded for 10 days, and percutaneous muscle biopsies were taken before and at the end of the unloading period. The capacity for protein synthesis, as reflected by the concentration of RNA, decreased by 16% (P < 0.05) although the fractional synthesis rate (FSR) of protein was not significantly changed after 10 days of unloading. Furthermore there was an increase in the concentration of the free branched chain amino acids in muscle by 48% (P < 0.05).

Protein synthesis rates in human muscles: neither anatomical location nor fibre‐type composition are major determinants

“…First, despite evidence of a wide variance in the proportional contribution of Type-1 and Type-2 fibres to total fibre content in vastus lateralis (∼30-70%, see Table 1), the most frequently studied human muscle, the published basal rates for muscle protein synthesis in human vastus do not show a similar variability. Second, the published basal rates of muscle protein synthesis in other human muscles (Bennet et al 1989;Chesley et al 1992;MacDougall et al 1995;Tipton et al 1996;Gamrin et al 1998;Fowles et al 2000) are fairly similar despite their markedly different fibre-type composition, although the use of different analysis techniques weakens this comparison, especially if the differences between muscles are (as we have shown) of a smaller magnitude than those in animals. This is why we designed our studies to achieve greatest possible power to detect differences: (1) we chose […”

“…Muscle protein turnover in human muscles other than the quadriceps and with distinctly different fibre-type composition (i.e. tibialis anterior, soleus, biceps brachii, deltoid) has been measured in very few studies, with varying experimental conditions (Bennet et al 1989;Chesley et al 1992;MacDougall et al 1995;Tipton et al 1996;Gamrin et al 1998;Fowles et al 2000) but no studies have compared basal rates of protein turnover and/or the response of protein turnover to various anabolic/catabolic stimuli in different muscles simultaneously. Hence, it is not known if the observations made in animals are mirrored in human beings.…”

Effect of passive stretching on the immobilized soleus muscle fiber morphology

“…In addition to alterations in muscle length, a significant decrease in muscle strength and mass is also induced by immobilization, and can be observed within the first 48 h (5,6). It has been shown that soleus muscles held in the shortened position lose 37% of their mass after being immobilized for 7 days, whereas immobilization in the stretched position does not cause muscle fiber atrophy (7)(8)(9).…”

Diacutaneous fibrolysis versus passive stretching after articular immobilization: Muscle recovery and extracellular matrix remodelling

“…Articular immobilisation leads to muscle atrophy and rigidity, characterised by decrease in muscle fibre protein content and size 1 and increase in their connective tissue 2 . Data show that during the first 6 hours of articular immobilisation, the synthesis of muscle protein is reduced, and within 72 hours, it might reduce the muscle mass up to 30% of its original size 3,4 . Seven days of immobilisation results in loss of muscle fibres, reduces the number of serial and parallel sarcomeres and leads to muscle atrophy and shortening 5,6 .…”