Effects of sudden walking perturbations on neuromuscular reflex activity and three-dimensional motion of the trunk in healthy controls and back pain symptomatic subjects

Abstract

BackgroundBack pain patients (BPP) show delayed muscle onset, increased co-contractions, and variability as response to quasi-static sudden trunk loading in comparison to healthy controls (H). However, it is unclear whether these results can validly be transferred to suddenly applied walking perturbations, an automated but more functional and complex movement pattern. There is an evident need to develop research-based strategies for the rehabilitation of back pain. Therefore, the investigation of differences in trunk stability between H and BPP in functional movements is of primary interest in order to define suitable intervention regimes. The purpose of this study was to analyse neuromuscular reflex activity as well as three-dimensional trunk kinematics between H and BPP during walking perturbations.MethodsEighty H (31m/49f;29±9yrs;174±10cm;71±13kg) and 14 BPP (6m/8f;30±8yrs;171±10cm;67±14kg) walked (1m/s) on a split-belt treadmill while 15 right-sided perturbations (belt decelerating, 40m/s2, 50ms duration; 200ms after heel contact) were randomly applied. Trunk muscle activity was assessed using a 12-lead EMG set-up. Trunk kinematics were measured using a 3-segment-model consisting of 12 markers (upper thoracic (UTA), lower thoracic (LTA), lumbar area (LA)). EMG-RMS ([%],0-200ms after perturbation) was calculated and normalized to the RMS of unperturbed gait. Latency (TON;ms) and time to maximum activity (TMAX;ms) were analysed. Total motion amplitude (ROM;[°]) and mean angle (Amean;[°]) for extension-flexion, lateral flexion and rotation were calculated (whole stride cycle; 0-200ms after perturbation) for each of the three segments during unperturbed and perturbed gait. For ROM only, perturbed was normalized to unperturbed step [%] for the whole stride as well as the 200ms after perturbation. Data were analysed descriptively followed by a student´s t-test to account for group differences. Co-contraction was analyzed between ventral and dorsal muscles (V:R) as well as side right:side left ratio (Sright:Sleft). The coefficient of variation (CV;%) was calculated (EMG-RMS;ROM) to evaluate variability between the 15 perturbations for all groups. With respect to unequal distribution of participants to groups, an additional matched-group analysis was conducted. Fourteen healthy controls out of group H were sex-, age- and anthropometrically matched (group Hmatched) to the BPP.ResultsNo group differences were observed for EMG-RMS or CV analysis (EMG/ROM) (p>0.025). Co-contraction analysis revealed no differences for V:R and Srigth:Sleft between the groups (p>0.025). BPP showed an increased TON and TMAX, being significant for Mm. rectus abdominus (p = 0.019) and erector spinae T9/L3 (p = 0.005/p = 0.015). ROM analysis over the unperturbed stride cycle revealed no differences between groups (p>0.025). Normalization of perturbed to unperturbed step lead to significant differences for the lumbar segment (LA) in lateral flexion with BPP showing higher normalized ROM compared to Hmatched (p = 0.02). BPP showed a significant ...

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“…Twelve pairs of EMG electrodes are positioned over the ventral and dorsal muscles (Fig. 3 ; [ 4 ]). All participants undergo a general physical warm-up of at least 5 min prior to testing.…”

“…dorsi (LD) of left and right sides) muscles (Fig. 3 ) [ 4 ]. Muscular activity will be analyzed using bipolar surface EMG (band-pass filter: 5 Hz to 500 Hz, gain: 5.0, overall gain: 2500, sampling frequency: 4000 Hz; RFTD-32, myon AG, Baar, Schweiz).…”

“…Neuromuscular activity serves as secondary outcome: MVC-normalized EMG amplitudes (EMG-RMS (%)) are calculated for each test condition and all single muscles. Furthermore, the mean EMG-RMS is calculated for four areas of the trunk (right and left ventral area: grouping of RA, EO, IO on right side and grouping of RA, EO, IO on left side, right and left dorsal area: grouping of LD, UES, LES on the right side and grouping of LD, UES, LES on the left side) [ 4 ]. Within the time domain, the onset of muscular activity (ms) will be detected and measured for the first active ventral and dorsal muscles, representing a response to the perturbation.…”

“…Trunk stability, led by neuromuscular activity, is required to control trunk motion during repetitive (dynamic) loading situations and to avoid overloading. Importantly, reduced trunk stabilization, mainly characterized by an increased muscle response time, higher co-contraction and an altered muscle activity pattern, could contribute to overload and injury [ 4 , 5 ]. Consequently, inadequate neuromuscular control during dynamic loading is discussed as an explanatory model in back pain etiology [ 6 , 7 ].…”

“…Potential factors underlying back pain have been discussed, including repetitive micro traumas and insufficiency of the muscle-tendon complex based on inadequate postural and neuromuscular control, reduced maximum trunk-strength capacity and trunk-muscle fatigue during dynamic loading [ 9 ]. Hence, optimizing neuromuscular core stability is considered beneficial for protection against sudden, repetitive and excessive overloading of the trunk [ 2 – 4 , 8 ].…”