A limited number of studies has investigated the gastrocnemius and soleus in patients undergoing anterior cruciate ligament reconstruction (ACLR). This study investigated the muscle strength (Nm kg-1 × 100) and reaction time (acceleration time (AT), milliseconds) of thigh and calf muscles in patients undergoing ACLR. Thirty-two patients with ACLR and 32 normal control subjects were included. One year postoperatively, the strength of thigh muscles was significantly reduced after ACLR compared with that of controls (hamstring: 80 ± 31.3 vs. 142 ± 26.4, p < 0.001, quadriceps: 159 ± 63.7 vs. 238 ± 35.3, p < 0.001). However, the strength of calf muscles was not significantly different compared with that of controls (gastrocnemius: 77 ± 22.9 vs. 81 ± 22.5, p = 0.425, soleus: 54 ± 15.9 vs. 47 ± 16.1, p = 0.109). The AT of calf muscles was significantly faster after ACLR than that of controls (gastrocnemius: 26 ± 9.8 vs. 31 ± 9, p = 0.030, soleus: 18 ± 6.7 vs. 22 ± 8.5, p = 0.026). The AT of thigh muscles was significantly elongated after ACLR than that of controls (hamstring: 72 ± 18 vs. 55 ± 12.4, p < 0.001, quadriceps: 63 ± 17.6 vs. 47 ± 17, p < 0.000). The strength of thigh muscles was reduced, and the ATs of thigh muscles were slower one year after ACLR. However, the AT of the triceps surae was faster than that of controls. This may implicate a compensatory mechanism of the triceps surae for the weakness and delayed activation in hamstring and quadriceps muscles.
Keywords: anterior cruciate ligament reconstruction; muscle reaction time; muscle strength; triceps surae.