Feasability of An Eccentric Isokinetic Protocol to Induce Trunk Muscle Damage: A Pilot Study.

Eccentric exercise is discussed as a treatment option for clinical populations, but specific responses in terms of muscle damage and systemic inflammation after repeated loading of large muscle groups have not been conclusively characterized. Therefore, this study tested the feasibility of an isokinetic protocol for repeated maximum eccentric loading of the trunk muscles. Nine asymptomatic participants (5 f/4 m; 34±6 yrs; 175±13 cm; 76±17 kg) performed three isokinetic 2-minute all-out trunk strength tests (1x concentric (CON), 2x eccentric (ECC1, ECC2), 2 weeks apart; flexion/extension, 60°/s, ROM 55°). Outcomes were peak torque, torque decline, total work, and indicators of muscle damage and inflammation (over 168 h). Statistics were done using the Friedman test (Dunn's post-test). For ECC1 and ECC2, peak torque and total work were increased and torque decline reduced compared to CON. Repeated ECC bouts yielded unaltered torque and work outcomes. Muscle damage markers were highest after ECC1 (soreness 48 h, creatine kinase 72 h; p<0.05). Their overall responses (area under the curve) were abolished post-ECC2 compared to post-ECC1 (p<0.05). Interleukin-6 was higher post-ECC1 than CON, and attenuated post-ECC2 (p>0.05). Interleukin-10 and tumor necrosis factor-α were not detectable. All markers showed high inter-individual variability. The protocol was feasible to induce muscle damage indicators after exercising a large muscle group, but the pilot results indicated only weak systemic inflammatory responses in asymptomatic adults.

Neuromuscular shoulder activity during exercises with different combinations of stable and unstable weight mass.

BACKGROUND: Recent shoulder injury prevention programs have utilized resistance exercises combined with different forms of instability, with the goal of eliciting functional adaptations and thereby reducing the risk of injury. However, it is still unknown how an unstable weight mass (UWM) affects the muscular activity of the shoulder stabilizers. Aim of the study was to assess neuromuscular activity of dynamic shoulder stabilizers under four conditions of stable and UWM during three shoulder exercises. It was hypothesized that a combined condition of weight with UWM would elicit greater activation due to the increased stabilization demand. METHODS: Sixteen participants (7 m/9 f) were included in this cross-sectional study and prepared with an EMG-setup for the: Mm. upper/lower trapezius (U.TA/L.TA), lateral deltoid (DE), latissimus dorsi (LD), serratus anterior (SA) and pectoralis major (PE). A maximal voluntary isometric contraction test (MVIC; 5 s.) was performed on an isokinetic dynamometer. Next, internal/external rotation (In/Ex), abduction/adduction (Ab/Ad) and diagonal flexion/extension (F/E) exercises (5 reps.) were performed with four custom-made-pipes representing different exercise conditions. First, the empty-pipe (P; 0.5 kg) and then, randomly ordered, water-filled-pipe (PW; 1 kg), weight-pipe (PG; 4.5 kg) and weight + water-filled-pipe (PWG; 4.5 kg), while EMG was recorded. Raw root-mean-square values (RMS) were normalized to MVIC (%MVIC). Differences between conditions for RMS%MVIC, scapular stabilizer (SR: U.TA/L.TA; U.TA/SA) and contraction (CR: concentric/eccentric) ratios were analyzed (paired t-test; p ≤ 0.05; Bonferroni adjusted α = 0.008). RESULTS: PWG showed significantly greater muscle activity for all exercises and all muscles except for PE compared to P and PW. Condition PG elicited muscular activity comparable to PWG (p > 0.008) with significantly lower activation of L.TA and SA in the In/Ex rotation. The SR ratio was significantly higher in PWG compared to P and PW. No significant differences were found for the CR ratio in all exercises and for all muscles. CONCLUSION: Higher weight generated greater muscle activation whereas an UWM raised the neuromuscular activity, increasing the stabilization demands. Especially in the In/Ex rotation, an UWM increased the RMS%MVIC and SR ratio. This might improve training effects in shoulder prevention and rehabilitation programs.

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.

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/Hmatchedvs 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.