A comparison of different measures of the soleus Ia-motoneuron pathway in people with incomplete spinal cord injury

Measures of the Ia-motoneuron pathway, including ratio of the maximum H-reflex and M-wave (H max /M max ), rate-dependent depression of H-reflex (RDD) and clonus, are often used to quantify hyperreflexia after spinal cord injury (SCI). However, conflicting reports exist regarding the effect of SCI on these measures. In addition, the reliability of these measures is unknown for people with SCI. This study explored the potential effects of group (SCI or Control), age and sex, on H max /M max , RDD and clonus, as well as the reliability of each measure. Fifteen individuals with motor-incomplete SCI and 18 uninjured participants completed the study. All measures were recorded twice on two separate days. Reliability was quantified by the Intraclass Correlation Coefficient. Effects of group and age were explored by Linear Mixed Models or non-parametric methods as appropriate. Compared to Controls, those with SCI showed less RDD (Mann-Whitney U=-130, p=0.001) and more clonus (LMM Group main effect p=0.005), but no difference in H max /M max . In Controls, Sex affected the H max /M max (LMM main effect p<0.001), with females showing higher values than males. The small number of female SCI participants made it impossible to explore sex differences after SCI. In those with SCI, the test-retest reliability was moderate for the H max /M max and clonus, but low for RDD, suggesting reliability should be considered when comparing the changes of these measurements over time. Potential age and sex differences in H max /M max may have contributed to conflicting reports in the past.