The effect of lumbar spine manipulation on the muscle activity of the quadriceps femoris and hamstring muscle groups
Authors:   , Parkes Jenna-Leigh 
Published: May 2022

Background: The clinical use of spinal manipulative therapy is becoming increasingly evident in the treatment of musculoskeletal conditions. However, the exact neurophysiological mechanisms behind spinal manipulative therapy and its effects on muscle activity require further investigation. Fixated joints within the spine have been shown to cause changes in muscle activity in both segmentally related muscles and extremity muscles. When present in symptomatic or asymptomatic individuals, fixations in the spine may not only lead to local neurophysiological changes but may affect global neurophysiology. Chronic lower back pain has been associated with the presence of arthrogenic muscle inhibition in lower limb musculature which prevents an individual from fully activating the affected muscle. Although this form of inhibition is predominately present in symptomatic individuals, there is evidence to suggest that asymptomatic individuals undergo a similar neuromuscular change. However, further research is needed to determine if the extent of the effects of arthrogenic muscle inhibition differs between symptomatic and asymptomatic subjects. Aim: This study aims to determine and compare the effects of a lumbar spine manipulation on the muscle activity in the quadriceps femoris and hamstring muscle groups in asymptomatic and symptomatic participants. Method: This study was a randomised controlled trial which utilised a pre- and postexperimental design. A total of 48 participants between the ages of 18-45 years of both genders and all races were recruited. The sample population included a symptomatic and asymptomatic clinical group. Each clinical group had a treatment and control group. Once placed into their respective groups, individuals were randomly allocated to the intervention or control group. Muscle activity readings of the quadriceps femoris and hamstring muscles were obtained during sets of maximum voluntary contractions that occurred at the pre-intervention/control, post-intervention/control and post 10- minute intervention/control. IBM SPSS version 26 was used to analyse the data. Repeated measures ANOVA tests were used to compare each outcome between preand immediate post-treatment between the intervention and control groups for immediate effects, and pre- and 10-minute post-treatment between the intervention and control groups for short-term effects. This was initially done within the asymptomatic and symptomatic participants separately. Results: There were no statistically significant differences between the age and gender of the symptomatic and asymptomatic groups. With regards to muscle activity, no significant changes in the quadriceps femoris or hamstring muscle groups were identified in the asymptomatic group. Significant changes were detected in the right rectus femoris of the quadriceps muscle demonstrating evidence of a treatment effect (p=0.047). However, this change did not persist in the 10-minute readings. Although not statistically significant, there was clear evidence of a clinical trend that presented in the quadriceps femoris muscle (rectus femoris and vastus medialis) of the symptomatic group, as the overall muscle activity of the participants who received the intervention increased bilaterally. There were no statistically significant differences found when comparing the data between the symptomatic and asymptomatic clinical groups. Conclusion: The results showed that lumbar spine manipulation did not produce significant differences in the immediate post-readings and the 10-minute readings in the quadriceps femoris and hamstring muscles of the symptomatic and asymptomatic groups. When comparing the clinical groups, there was no significant difference between the asymptomatic and symptomatic groups in terms of the pre-intervention readings of muscle activity and the post-intervention measures immediately and at the 10-minute interval following lumbar spine manipulation.