[Relationship between the changes of surface electromyographic signal of thigh muscle and balance function in stroke patients].

Objective: To explore the relationship between the changes of surface electromyography (sEMG) signal of thigh muscles and balance function in stroke patients during maximum isometric voluntary contraction (MIVC) of knee extension and flexion so as to provide rationales for rehabilitation.

Methods: Twenty-one stroke patients and 18 age- and sex-matched normal controls were recruited for this study. The surface electromyographic signals of of vastus medialis (VM), rectus femoris (RF), vastus lateralis (RL) and biceps femoris (BF) were recorded during MIVC of knee extension and flexion. Root mean square (RMS) and co-contraction ratio (CR) of both groups were compared and analyzed. The balance function was assessed by Berg balance scale (BBS).

Results: There were significant differences in RMS of VM, RF, VL and BF of ipsilateral [(136 +/- 63) microV, (107 +/- 24) microV, (154 +/- 19) microV, (91 +/- 63) microV], thigh during knee extension and flexion (P < 0.05). There were significant differences in CR on ipsilateral thigh muscles than the unaffected (43% +/- 13% vs 37% +/- 20%) and controls (43% +/- 13% vs 32% +/- 10%) during knee flexion (P < 0.05). The RMS of RF and BF on ipsilateral thigh was significantly positively correlated with the score of BBS (rRF = 0.53, P = 0.01 vs rBF = 0.51, P = 0.02); The CR of knee extension and flexion on ipsilateral thigh had a significantly negative correlation (CRE = -0.59, P = 0.005 vs. CRF = -0.41, P = 0.046).

Conclusion: The strength of bilateral thigh muscles decreases in stroke patients. The spasticity of thigh extensor still exists. Besides reducing the spasticity of hemiplegic limb extensor, rehabilitation should also focus upon bilateral thigh muscles, particularly ipsilateral RF and BF strength training to improve the knee joint stability and improve the balance function.