CON/ECC leads to significantly greater muscle hypertrophy compared with CON/ECC, but without the hypothesized enhancing effect on SC activation. At the same time, CON/ECC+ induces a less favorable slower muscle phenotype for strong and fast movements.
Objective Recovery of the quadriceps femoris muscle after anterior ligament reconstruction is impaired. The aim of this study was to investigate satellite cell content and function of the vastus lateralis muscle after anterior ligament reconstruction. Methods Biopsies were obtained from the vastus lateralis muscle of 16 recreational athletes immediately before and again 12 weeks after anterior ligament reconstruction. Total satellite cell number (Pax7 + ), activated (Pax7 + /MyoD + ), differentiating (Pax7 – /MyoD + ), and apoptotic (Pax7 + /TUNEL + ) satellite cells, myofibers expressing myosin heavy chain (MHC) I and II, and neonatal MHC (MHCneo) were determined immunohistochemically. Results After anterior ligament reconstruction, the number of apoptotic satellite cells was significantly ( p = 0.019) increased, concomitant with a significant ( p < 0.001) decrease in total satellite cell number, with no change in activated and differentiating satellite cell number. MHCneo + myofibers tended towards an increase. CONCLUSION Satellite cell apoptosis and the reduction in the satellite cell pool might provide an explanation for prolonged quadriceps muscle atrophy after anterior ligament reconstruction. LAY ABSTRACT Protracted muscle atrophy is common after anterior ligament reconstruction, even if athletes adhere to a structured rehabilitation programme. Satellite cells, the stem cells of skeletal muscle, play an important role in recovery of an atrophied muscle. Exercise can activate satellite cells, induce their proliferation, and probably also differentiation of these stem cells. The current study evaluated satellite cell content and function in biopsies from the vastus lateralis muscle of 16 recreational athletes immediately before and 12 weeks after anterior ligament reconstruction. After anterior ligament reconstruction, an increased number of satellite cells showed signs of apoptosis (cell death). Furthermore, total satellite cell number was decreased, with no change in the numbers of activated and differentiating satellite cells. The number of regenerating myofibers expressing neonatal myosin tended to increase. In conclusion, satellite cell apoptosis and the reduced satellite cell number might provide an explanation for the impaired muscle recovery after anterior ligament reconstruction.
Impaired muscle regeneration has repeatedly been described after anterior cruciate ligament reconstruction (ACL-R). The results of recent studies provided some evidence for negative alterations in knee extensor muscles after ACL-R causing persisting strength deficits in spite of the regain of muscle mass. Accordingly, we observed that 12 weeks of concentric/eccentric quadriceps strength training with eccentric overload (CON/ECC+) induced a significantly greater hypertrophy of the atrophied quadriceps muscle after ACL-R than conventional concentric/eccentric quadriceps strength training (CON/ECC). However, strength deficits persisted and there was an unexpected increase in the proportion of slow type I fibers instead of the expected shift towards a faster muscle phenotype after CON/ECC+. In order to shed further light on muscle recovery after ACL-R, the steady-state levels of 84 marker mRNAs were analyzed in biopsies obtained from the vastus lateralis muscle of 31 subjects before and after 12 weeks of CON/ECC+ (n = 18) or CON/ECC strength training (n = 13) during rehabilitation after ACL-R using a custom RT2 Profiler PCR array. Significant (p < 0.05) changes were detected in the expression of 26 mRNAs, several of them involved in muscle wasting/atrophy. A different pattern with regard to the strength training mode was observed for 16 mRNAs, indicating an enhanced hypertrophic stimulus, mechanical sensing or fast contractility after CON/ECC+. The effects of the type of autograft (quadriceps, QUAD, n = 19, or semitendinosus tendon, SEMI, n = 12) were reflected in the lower expression of 6 mRNAs involved in skeletal muscle hypertrophy or contractility in QUAD. In conclusion, the greater hypertrophic stimulus and mechanical stress induced by CON/ECC+ and a beginning shift towards a faster muscle phenotype after CON/ECC+ might be indicated by significant gene expression changes as well as still ongoing muscle wasting processes and a negative impact of QUAD autograft.
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