Modulation of the nociceptive withdrawal reflex in walking is not changed by the presence of tonic pain

Figures

• 

  Fig. 1. Threshold testing to identify a reflex response. Top panel shows the stimulus channel. Bottom panel shows the EMG recorded from the biceps femoris. Stimulus was delivered at time zero (green circle). A response was established if the interval peak z-score was ≥ 10. The z-score was calculated as the difference between the peak amplitude in the interval 60–200 ms post stimulation (pink box) and the mean baseline amplitude (yellow box), divided by the standard deviation of the baseline amplitude

• 

  Fig. 2. Pain ratings over time (n = 16) in the tonic pain trial. Coloured lines represent individual participants. Dashed black line represents the mean

• 

  Fig. 3. Reflex response in the vastus lateralis muscle of the stimulated leg during a control trial from one example participant in a terminal stance and b mid-swing phase. The black lines represent EMG during non-stimulated trials and magenta dashed lines represent EMG during a stimulation trial. Time 0 indicates when the stimulus was delivered. There is a large reflex response (magenta dashed lines) evident in mid-swing (77% of gait cycle) that is absent in terminal stance (37% of gait cycle)

• 

  Fig. 4. Mean relative reflex response in the leg ipsilateral to the stimulation across the gait cycle for: a vastus lateralis (n = 15); b biceps femoris (n = 14); c tibialis anterior (n = 16); d soleus short loop (60–120 ms post stimulation, n = 14); and e soleus long loop (120–200 ms post stimulation, n = 14). Dark blue circles represent control condition and red diamonds represent the tonic pain condition. Error bars represent the standard deviation. * denotes significant difference in phase (p < 0.05), ** denotes significant difference in phase (p < 0.001)

• 

  Fig. 5. Mean relative reflex response in the leg contralateral to the stimulation across the gait cycle for: a vastus lateralis (n = 15); b biceps femoris (n = 14); c tibialis anterior (n = 16) and d soleus (n = 14). Dark blue circles represent control condition and red diamonds represent the tonic pain condition. Error bars represent the standard deviation. * denotes significant difference in phase (p < 0.05), ** denotes significant difference in phase (p < 0.001)

• 

  Fig. 6. Example response to stimulation at the a hip, b knee and c ankle in the leg ipsilateral to the stimulation, normalised to the gait cycle (time zero is heel strike of the stimulated leg). Data are shown from the hip and ankle of one participant and the knee of another participant. Black lines with grey shading represent mean ± SD strides in the control condition without stimulation. Red lines with lighter red shading represent mean ± SD strides in the tonic pain condition without stimulation. Blue dashed lines represent strides in the control condition with stimulation and magenta dashed lines represent strides in the tonic pain condition with stimulation (both from average stimulation time plus 20% of the gait cycle). Stimulation shown for 0%, 40%, 60% and 80% to maintain visual clarity

• 

  Fig. 7. Kinematic response of the contralateral leg to stimulation of the ipsilateral leg during the ‘loading response’ phase of the gait cycle. Top panel shows plantarflexion/dorsiflexion angle of the strides in the control condition without stimulation (mean black line and standard deviation grey shading) and strides in the control condition when stimulation was delivered in the loading phase of the ipsilateral leg (mean red line and standard deviation pink shading). Middle panel shows SPM in the range of interest. Bottom panel shows Cohen’s d (black line) and difference between angles (grey line)