Muscle coactivation during knee joint-position sense assessments: the effect of muscle fatigue and implications for the magnitude of errors and directional bias.

PURPOSE: This study aimed to describe muscle coactivation during knee joint-position sense (KJPS) assessments in healthy individuals, before and after muscle fatigue, and to analyse the implications for the magnitude of errors and directional bias.

METHODS

The KJPS of 21 healthy males was assessed in the sitting position through concentric (SIT_CC) and eccentric repositionings (SIT_ECC) to 45° of knee flexion. Two fatigue protocols were tested, consisting of concentric contractions of the knee extensors or flexors. Muscle coactivation indices were calculated based on the normalized mean activation of the vastus lateralis and biceps femoris muscles. Absolute and relative errors were calculated to group participants by magnitude of errors (lower vs. higher errors) and directional bias (extension vs. flexion).

RESULTS

Coactivation indices ranged between 74.92 % - 98.43 %. Significant overall decrease in coactivation indices after both fatigue protocols (p < 0.05). No significant differences in coactivation were found between magnitude of errors groups (p > 0.05), but significant higher coactivation were observed in participants failing the target position into flexion, only in the SIT_CC test (0.001 < p < 0.042).

CONCLUSION

Muscle coactivation between knee extensors and flexors was high in the assessed JPS tests, and decreased after fatigue. Muscle coactivation does not appear to explain the magnitude of errors, while it seems to influence directional bias.