Muscle Regeneration after Anterior Cruciate Ligament Reconstruction - Effects of Strenght Training Regime and Different Autocrafts

Abstract

PURPOSE: To test the hypothesis that muscle regeneration after ACL-R can be augmented by quadriceps strength training with eccentric overload (CON/ECC+) METHODS: Biopsies from the vastus lateralis muscle were obtained from 37 recreational athletes (25±4 yrs, 181±7 cm, 83.5±15 kg) after 12 weeks (wks) of regular rehabilitation following ACL-R (quadriceps tendon autograft, n=22 or semitendinosus tendon autograft, n=15) and again after 12 wks with 2x/wk either conventional (CON/ECC, n=16) or CON/ECC+ (n=21) supervised leg press training (random assignment). Immunohistochemical analyses were used to determine myosin heavy chain (MyHC) I, II and hybrid fibers to quantify fiber type specific satellite cells (SCs, Pax7+) and active SCs (Pax7+/MyoD+). Magnetic resonance imaging was performed to measure quadriceps cross sectional area (CSA) RESULTS: After 12 wks of one-legged quadriceps strength training CSA was significantly (p=0.000) increased with a significantly (p=0.003) greater increase after CON/ECC+ compared to CON (81.7±13.1 to 96.3±14.7 cm2 vs. 78.5±12.1 to 87.0±11.8 cm2). MyHC I fiber number significantly (p=0.002) increased only after CON/ECC+ (35.7±17.1 to 41.7±15.8 %). The change was significantly (p=0.022) different from CON/ECC (36.6±13.0 to 35.1±10.4 %). MyHC I/II hybrid fibers showed a significant (p<0.001) similar decrease after CON/ECC+ (7.1±6.5 to 4.0±4.5 %) and CON/ECC (7.7±4.9 to 4.8±3.6 %). MyHC II fiber number did not change significantly. While no significant change in SC content was observed (SCs related to MyHC I or II fibers 0.15±0.08 and 0.14±0.07 before, 0.14±0.09 and 0.14±0.07/fiber after training) the number of active SCs per biopsy section was significantly (p=0.007) greater after training (2.42±2.09 vs. 1.08±1.38) without significant difference between the training regimes. No significant differences occurred with regard to the different autografts CONCLUSION: Strength-training induced muscle regeneration after ACL-R lead to an increase in activated SCs and a decrease in MyHC I/II hybrid fibers. After CON/ECC+ the gain in muscle mass was greatest and was accompanied by a significant increase in MyHC I fibers. Supported by the Dietmar Hopp Foundation (23011193)