Tilman Engel

Stumbling reactions during perturbed walking: Neuromuscular reflex activity and 3-D kinematics of the trunk - A pilot study

Reflex activity of the lower leg muscles involved when compensating for falls has already been thoroughly investigated. However, the trunk׳s role in this compensation strategy remains unclear. The purpose of this study, therefore, was to analyze the kinematics and muscle activity of the trunk during perturbed walking. Ten subjects (29 ± 3 yr;79 ± 11 cm;74 ± 14 kg) walked (1m/s) on a split-belt treadmill, while 5 randomly timed, right-sided perturbations (treadmill belt deceleration: 40 m/s(2)) were applied. Trunk muscle activity was assessed with a 12-lead-EMG. Trunk kinematics were measured with a 3D-motion analysis system (12 markers framing 3 segments: upper thoracic area (UTA), lower thoracic area (LTA), lumbar area (LA)). The EMG-RMS [%] (0-200 ms after perturbation) was analyzed and then normalized to the RMS of normal walking. The total range of motion (ROM;[°]) for the extension/flexion, lateral flexion and rotation of each segment were calculated. Individual kinematic differences between walking and stumbling [%; ROM] were also computed. Data analysis was conducted descriptively, followed by one- and two-way ANOVAs (α=0.05). Stumbling led to an increase in ROM, compared to unperturbed gait, in all segments and planes. These increases ranged between 107 ± 26% (UTA/rotation) and 262 ± 132% (UTS/lateral flexion), significant only in lateral flexion. EMG activity of the trunk was increased during stumbling (abdominal: 665 ± 283%; back: 501 ± 215%), without significant differences between muscles. Provoked stumbling leads to a measurable effect on the trunk, quantifiable by an increase in ROM and EMG activity, compared to normal walking. Greater abdominal muscle activity and ROM of lateral flexion may indicate a specific compensation pattern occurring during stumbling.

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

Background Back 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. Methods Eighty 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. Results No 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 higher flexed posture (UTA (p = 0.02); LTA (p = 0.004)) during normal walking (Amean). Trunk posture (Amean) during perturbation showed higher trunk extension values in LTA segments for H/Hmatched compared to BPP (p = 0.003). Matched group (BPP vs. Hmatched) analysis did not show any systematic changes of all results between groups. Conclusion BPP present impaired muscle response times and trunk posture, especially in the sagittal and transversal planes, compared to H. This could indicate reduced trunk stability and higher loading during gait perturbations.

Neuromuscular trunk activation patterns in back pain patients during one-handed lifting

AIM To analyze neuromuscular activity patterns of the trunk in healthy controls (H) and back pain patients (BPP) during one-handed lifting of light to heavy loads. METHODS After assessment of back pain (graded chronic pain scale according to von Korff) all subjects (n = 43) performed a warm-up (treadmill walking). Next, subjects were instructed to lift 3 × a 20 kg weight placed in front of them (with both hand) onto a table (height: 0.75 m). Subsequently, all subjects lifted with one hand (left-side, 3 repetitions) a weight of 1 kg (light), 10 kg (middle) and 20 kg (heavy) in random order from the ground up onto the table left of them. Trunk muscle activity was assessed with a 12-lead EMG (6 ventral/6 dorsal muscles; 4000 Hz). EMG-RMS (%) was averaged over the 3 repetitions and analyzed for the whole one-handed lifting cycle, then normalized to RMS of the two-handed lifting. Additionally, the mean (normalized) EMG-RMS of four trunk areas [right/left ventral area (VR/VL); right/left dorsal area (DR/DL)] was calculated. Data were analyzed descriptively (mean ± SD) followed by student’s t-test comparing H and BPP (α = 0.05). With respect to the unequal distribution of subjects in H and BPP, a matched-group analysis was conducted. Seven healthy controls were gender- and age-matched (group Hmatched) to the 7 BPP. In addition, task failure was calculated and compared between H/Hmatched vs BPP using χ2. RESULTS Seven subjects (3m/4f; 32 ± 7 years; 171 ± 7 cm; 65 ± 11 kg) were assigned to BPP (pain grade ≥ 2) and 36 (13m/23f; 28 ± 8 years; 174 ± 10 cm; 71 ± 12 kg) to H (pain grade ≤ 1). H and BPP did not differ significantly in anthropometrics (P > 0.05). All subjects were able to lift the light and middle loads, but 57% of BPP and 22% of H were not able to lift the heavy load (all women). χ2 analysis revealed statistically significant differences in task failure between H vs BPP (P = 0.03). EMG-RMS ranged from 33% ± 10%/30% ± 9% (DL, 1 kg) to 356% ± 148%/283% ± 80% (VR, 20 kg) in H/BPP with no statistical difference between groups regardless of load (P > 0.05). However, the EMG-RMS of the VR was greatest in all lifting tasks for both groups and increased with heavier loads. CONCLUSION Heavier loading leads to an increase (2- to 3-fold) in trunk muscle activity with comparable patterns. Heavy loading (20 kg) leads to task failure, especially in women with back pain.

Neuromuscular response of the trunk to sudden gait disturbances: Forward vs. backward perturbation.

The study aimed to analyse neuromuscular activity of the trunk comparing four different perturbations during gait. Thirteen subjects (28±3yrs) walked (1m/s) on a split-belt treadmill, while 4 (belt) perturbations (F1, F2, B1, B2) were randomly applied. Perturbations differed, related to treadmill belt translation, in direction (forward (F)/backward (B)) and amplitude (20m/s(2) (1)/40m/s(2) (2)). Trunk muscle activity was assessed with a 12-lead-EMG. EMG-RMS [%] (0-200ms after perturbation; normalized to RMS of normal gait) was analyzed for muscles and four trunk areas (ventral left/right; dorsal left/right). Ratio of ventral:dorsal muscles were calculated. Muscle onset [ms] was determined. Data analysis was conducted descriptively, followed by ANOVA (post hoc Tukey-Kramer (α=0.05)). All perturbations lead to an increase in EMG-RMS (428±289%). F1 showed the lowest and F2 the highest increase for the flexors. B2 showed the highest increase for the extensors. Significant differences between perturbations could be observed for 6 muscles, as well as the 4 trunk areas. Ratio analysis revealed no significant differences (range 1.25 (B1) to 1.71 (F2) between stimuli. Muscle response time (ventral: 87.0±21.7ms; dorsal: 88.4±17.0ms) between stimuli was only significant (p=0.005) for the dorsal muscles. Magnitude significantly influences neuromuscular trunk response patterns in healthy adults. Regardless of direction ventral muscles always revealed higher relative increase of activity while compensating the walking perturbations.

Reproducibility of scapular muscle activity in isokinetic shoulder flexion and extension

Repetitive overhead movements have been identified as a main risk factor to develop shoulder complaints with scapular muscle activity being altered. Reliable assessment of muscle activity is essential to differentiate between symptomatic and asymptomatic individuals. Therefore, the present study aimed to investigate the intra- and inter-session reliability of scapular muscle activity during maximal isokinetic shoulder flexion and extension. Eleven asymptomatic adults performed maximum effort isokinetic shoulder flexion and extension (concentric and eccentric at 60°/s) in a test-retest design. Muscle activity of the upper and lower trapezius and serratus anterior was assessed by sEMG. Root Mean Square was calculated for whole ROM and single movement phases of absolute and normalized muscle activity. Absolute (Bland-Altman analysis (Bias, LoA), Minimal detectable change (MDC)) and relative reliability parameters (Intraclass correlation coefficient (ICC), coefficient of variation (CV)/test-retest variability (TRV)) were utilized for the evaluation of reproducibility. Intra-session reliability revealed ICCs between 0.56 and 0.98, averaged CVs of 18% and average MDCs of 81mV. Inter-session reliability resulted in ICCs between 0.13 and 0.93, averaged TRVs of 21%, average MDCs of 15% and systematic and random error between -8±60% and 12±36%. Scapular muscle activity assessed in overhead movements can be measured reliably under maximum load conditions, though variability is dependent on the movement phase. Measurement variability does not exceed magnitudes of altered scapular muscle activities as reported in previous studies. Therefore, maximum load application is a promising approach for the evaluation of changes in scapular control related to pathologies.

Unexpected walking perturbations: Reliability and validity of a new treadmill protocol to provoke muscular reflex activities at lower extremities and the trunk

Instrumented treadmills offer the potential to generate standardized walking perturbations, which are particularly rapid and powerful. However, technical requirements to release adequate perturbations regarding timing, duration and amplitude are demanding. This study investigated the test-retest reliability and validity of a new treadmill perturbation protocol releasing rapid and unexpected belt perturbations to provoke muscular reflex responses at lower extremities and the trunk. Fourteen healthy participants underwent two identical treadmill walking protocols, consisting of 10 superimposed one-sided belt perturbations (100ms duration; 2m/s amplitude), triggered by a plantar pressure insole 200ms after heel contact. Delay, duration and amplitude of applied perturbations were recorded by 3D-motion capture. Muscular reflex responses (within 200ms) were measured at lower extremities and the trunk (10-lead EMG). Data was analyzed descriptively (mean±SD). Reliability was analyzed using test-retest variability (TRV%) and limits of agreement (LoA, bias±1.96∗SD). Perturbation delay was 202±14ms, duration was 102±4ms and amplitude was 2.1±0.01m/s. TRV for perturbation delay, duration and amplitude ranged from 5.0% to 5.7%. LoA reached 3±36ms for delay, 2±13ms for duration and 0.0±0.3m/s for amplitude. EMG amplitudes following perturbations ranged between 106±97% and 909±979% of unperturbed gait and EMG latencies between 82±14ms and 106±16ms. Minor differences between preset and observed perturbation characteristics and results of test-retest analysis prove a high validity with excellent reliability of the setup. Therefore, the protocol tested can be recommended to provoke muscular reflex responses at lower extremities and the trunk in perturbed walking.

BACK PAIN RISK FACTORS IN ADOLESCENT ATHLETES: SUITABILITY OF A BIOMECHANICAL SCREENING TOOL?

Background Back pain (BP) is already a relevant injury site in adolescent athletes. A valid screening is essential for BP prevention. Objective To investigate whether a biomechanical screening tool (BST) is suitable to predict BP in adolescent athletes. Design Longitudinal analysis with 1.9±1.0 yrs between both measurement days. Setting Medical center of the German Olympic Sports Federation. BST was implemented in the annual (pre-participation) examination of elite athletes. Patients (or Participants) 343 athletes (195 males/148 females, 13±1 yrs, 164±12 cm, 53±13 kg, 5±3 training years, 8±6 training hours per week) out of 20 sport disciplines were included in the study. Interventions (or Assessment of Risk Factors) Subjective BP was assessed using a faces-pain-scale (FPS 1–5: 1=no pain; 2–5=slight- to maximum pain). In addition, postural control (one-legged stance), jumping performance (counter movement/drop jump), and maximum isokinetic trunk extension/flexion strength (60°/sec) was assessed for all athletes. Main Outcome Measurements Athletes were classified into 4 groups with respect to the course of back pain [(A) no BP (n=206); (B) BP-developers (n=34); (C) persisting BP (n=71); (D) diminishing BP (n=32)]. Outcomes included center of pressure displacement COP [mm], jump height [cm], peak jumping force [N], contact time [ms] and peak torque for trunk extension/flexion [Nm]. Descriptive analysis was followed by two-way ANOVA (repeated measures; α=0.05). Results Overall, the athletes enhanced trunk strength, jump performance and postural control across the evaluation period. Pain free athletes (A) showed statistically significant higher trunk strength gains (extension/flexion: +45/+37%) compared to athletes developing BP (B: +20/+9%; p<0.05). No differences were observed for jump performance and postural control (p>0.05). Conclusions Analysing biomechanical variables is valid to identify significantly impaired trunk strength development in athletes with BP incidence. In contrast, jump performance and postural control are of minor relevance. Therefore, poor trunk strength development could serve as back pain risk factor in athletes. Trunk strength training interventions should be recommended.

Ultrasound Applied to Subcutaneous Fat Tissue Measurements in International Elite Canoeists.

Subcutaneous adipose tissue (SAT) measurements with ultrasound have recently been introduced to assess body fat in elite athletes. However, appropriate protocols and data on various groups of athletes are missing. We investigated intra-rater reliability of SAT measurements using ultrasound in elite canoe athletes. 25 international level canoeists (18 male, 7 female; 23±4 years; 81±11 kg; 1.83±0.09 m; 20±3 training h/wk) were measured on 2 consecutive days. SAT was assessed with B-mode ultrasound at 8 sites (ISAK): triceps, subscapular, biceps, iliac crest, supraspinal, abdominal, front thigh, medial calf, and quantified using image analysis software. Data was analyzed descriptively (mean±SD, [range]). Coefficient of variation (CV%), intraclass correlation coefficient (ICC, 2.1) and absolute (LoA) and ratio limits of agreement (RLoA) were calculated for day-to-day reliability. Mean sum of SAT thickness was 30.0±19.4 mm [8.0, 80.1 mm], with 3.9±1.8 mm [1.2 mm subscapular, 8.0 mm abdominal] for individual sites. CV for the sum of sites was 4.7%, ICC 0.99, LoA 1.7±3.6 mm, RLoA 0.940 ( *  /÷1.155). Measuring SAT with ultrasound has proved to have excellent day-to-day reliability in elite canoe athletes. Recommendations for standardization of the method will further increase accuracy and reproducibility.

Reliability of Evaluating Achilles Tendon Vascularization Assessed With Doppler Ultrasound Advanced Dynamic Flow

The reliability of quantifying intratendinous vascularization by high‐sensitivity Doppler ultrasound advanced dynamic flow has not been examined yet. Therefore, this study aimed to investigate the intraobserver and interobserver reliability of evaluating Achilles tendon vascularization by advanced dynamic flow using established scoring systems.

Differences in neuromuscular activity of ankle stabilizing muscles during postural disturbances: A gender-specific analysis

The purpose was to examine gender differences in ankle stabilizing muscle activation during postural disturbances. Seventeen participants (9 females: 27 ± 2yrs., 1.69 ± 0.1 m, 63 ± 7 kg; 8 males: 29 ± 2yrs., 1.81 ± 0.1 m; 83 ± 7 kg) were included in the study. After familiarization on a split-belt-treadmill, participants walked (1 m/s) while 15 right-sided perturbations were randomly applied 200 ms after initial heel contact. Muscle activity of M. tibialis anterior (TA), peroneus longus (PL) and gastrocnemius medialis (GM) was recorded during unperturbed and perturbed walking. The root mean square (RMS; [%]) was analyzed within 200 ms after perturbation. Co-activation was quantified as ratio of antagonist (GM)/agonist (TA) EMG-RMS during unperturbed and perturbed walking. Time to onset was calculated (ms). Data were analyzed descriptively (mean ± SD) followed by three-way-ANOVA (gender/condition/muscle; α = 0.05). Perturbed walking elicited higher EMG activity compared to normal walking for TA and PL in both genders (p < 0.000). RMS amplitude gender comparisons revealed an interaction between gender and condition (F = 4.6, p = 0.049) and, a triple interaction among gender, condition and muscle (F = 4.7, p = 0.02). Women presented significantly higher EMG-RMS [%] PL amplitude than men during perturbed walking (mean difference = 209.6%, 95% confidence interval = -367.0 to -52.2%, p < 0.000). Co-activation showed significant lower values for perturbed compared to normal walking (p < 0.000), without significant gender differences for both walking conditions. GM activated significantly earlier than TA and PL (p < 0.01) without significant differences between the muscle activation onsets of men and women (p = 0.7). The results reflect that activation strategies of the ankle encompassing muscles differ between genders. In provoked stumbling, higher PL EMG activity in women compared to men is present. Future studies should aim to elucidate if this specific behavior has any relationship with ankle injury occurrence between genders.