Christoph Anders

Although surface electromyography (SEMG) is widely used in research, it remains unclear whether systematic differences in SEMG amplitudes are sensitive to sex, age, or individual force capacity. To address this issue, the present study conducted a re-evaluation of SEMG amplitude values of back muscles in a total of 239 healthy participants (115 women) aged 18–52 years. SEMG data were obtained during static submaximal and maximal (MVC) tasks. Across the subgroups defined by sex, age, BMI, and force capacity, no relevant differences in amplitude were identified, with the following exceptions M. iliocostalis: young > older and all muscles low BMI > high BMI. In contrast, during MVC, amplitude differences were consistently detected: men > women, young > older, low BMI > high BMI, and strong > weaker. Analysis of the amplitude-force relationship using values normalized to MVC revealed nearly perfectly linear relation-ships across all subgroups. Although the data points were in different positions along the range of origin, the slopes were nearly identical. These findings suggest that, within the submaximal range, SEMG amplitudes of the back muscles may be analyzed jointly without adjustment for sex, age, or force capacity. By contrast, SEMG data obtained during MVC should be evaluated separately for the respective subgroups.

Background: In this study, trunk extension strength was compared between healthy female and male participants. Methods: Overall, 115 women and 124 men underwent isometric maximal voluntary contraction (MVC) testing in an upright standing position. Upper body weight was additionally assessed. The primary outcome variables were maximal torque, upper body weight expressed as torque, and the MVC-to-upper-body-weight ratio. In view of the large sample size, interpretation of the results was based not only on statistical significance but also on clinical/practical relevance, as reflected by effect size (ES) and the relationship between the difference in mean values (DMV) and the minimal important difference (MID). Results were classified as relevant only when all three predefined criteria were met (p < 0.05, ES > 0.5, and DMV > MID). Results: Men showed significantly higher MVC values than women (241 Nm vs. 162 Nm; p < 0.0001; ES = 1.974; DMV > MID). Likewise, upper body torque was significantly greater in men than in women (115 Nm vs. 80 Nm; p < 0.0001; ES = 2.119; DMV > MID). However, after normalization for upper body torque, the between-sex difference in relative strength was no longer considered relevant (2.16 vs. 2.00; p = 0.0055; ES = 0.364; DMV < MID). Conclusions: These findings indicate that although absolute trunk extension strength differs markedly between sexes, relative strength adjusted for upper body weight is broadly comparable. Both women and men demonstrated a physiological strength reserve of approximately 100% relative to upper body weight.

In the present study, data were compiled to compare trunk extension strength between healthy female and male participants. Participants (124 females, 115 males) performed isometric maximal voluntary contraction (MVC) tests in an upright standing position. In addition, upper body weight was determined. Outcome parameters included maximal force values, expressed as torque, as well as upper body weight (also in torque values). Furthermore, the ratio between MVC and upper body weight was calculated. Highly significant differences were observed for MVC (men: 241 Nm, women: 162 Nm, p< 0.0001) and for upper body torque (men: 115 Nm, women: 80 Nm, p< 0.0001). After normalization to upper body torque, no relevant differences between sexes were detectable (men: 2.16, women: 2.00, p=0.0055, Effect size: 0.364). Despite substantial sex-related differences in absolute force capacity, relative strength—when adjusted for upper body weight—does not differ meaningfully between men and women. Both sexes are characterized by a physiological strength reserve of approximately 100% of their upper body weight.

Abdominal muscles play a crucial role in spinal stability which may be altered by muscular fatigue. To assess the extent of current fatigue, subjective and objective parameters can be used. The aim of the present study was to investigate whether different perceived exertion levels correspond with changes in fatigue-associated electrophysiological parameters of abdominal muscles. For this, 34 healthy participants (17 women) underwent a 10 min static endurance task of their abdominal muscles at 50% upper body weight. Every elapsed minute, perceived exertion was assessed together with changes in electro-physiological parameters. Based on the perceived exertion levels, participants were divided into a “good end” and a “bad end” group. Independent of group, muscular fatigue was identified in all abdominal muscles. In the rectus abdominis muscle this was most pronounced, with different levels between groups and satisfactory correlations between perceived exertion levels and electrophysiological parameters. Thus, electrophysiological signs of fatigue and RPE levels are interchangeable for the rectus abdominis. In contrast and therefore of utmost importance, fatigue of the oblique abdominal muscles is largely unrelated to perceived exertion. Given the key role of these muscles in maintaining trunk stability, prolonged submaximal loads appear to affect their function regardless of mild or intense exertion level.

Measurement data serve as an objective basis for scientific findings. Therefore, their reliability in repeated measurements is a crucial prerequisite. The repeatability of measurements is quantified using various reliability parameters. Often, data are subjected to normalization procedures to reduce inter-individual variability or to improve interpretability. In our study, we aimed to investigate the extent to which the application of normalization has impact on the determined reliability parameters. This was examined using the example of maximum force values for trunk extension and flexion. For this purpose, 85 healthy individuals (42 women) were subjected to maximum isometric force tests of the trunk muscles at two-weeks intervals. The calculated reliability and agreement parameters included the intraclass correlation coefficient (ICC), the standard error of measurement (SEm), the standard error of the mean (SEM), and the coefficient of variation of the method error (CVME). The ICC values consistently indicated good reliability for the original data (Extension: 0.889, Flexion: 0.882). Within the subpopulations of women and men, lower but still good ICC levels were observed (Women Extension: 0.671, Flexion: 0.826; Men Extension: 0.819, Flexion: 0.680). For the anthropometrically normalized force values, lower ICC levels were found for the entire group (Extension: 0.803, Flexion: 0.768) although the deviations in the subpopulations were different (Women Extension: 0.747, Flexion: 0.805; Men Extension: 0.852, Flexion: 0.642). Thus, normalization of measured values leads to varying deviations of calculated ICC levels compared to the original data, which is why the use of standardized data is not recommended for reliability calculations.

Zusammenfassung: Während der bipeden Lokomotion des Menschen müssen permanent externe oder interne Störungseinflüsse kompensiert werden. Dies geschieht sehr effizient, indem praktisch ein Schritt ausreicht, um diese Kompensation auszuführen. Im Falle interner Störeinflüsse ist damit eine Dauerbelastung der der gestörten Seite gegenüberliegenden Seite zu konstatieren. Da niemand ideal symmetrisch ist, wirken also auch bei Gesunden derartige Einflüsse, die solange das sensomotorische System nicht dekompensiert permanent ausgeglichen werden. Das erfordert aber immer zusätzlichen kompensatorischen Aufwand. Ziel der vorliegenden Studie war es, zu untersuchen ob das beidseitige Einbringen einer Gangjustierhilfe im vorderen medialen Knöchelbereich zu einer Symmetrisierung von pedobarographischen Kennwerten führt.Dazu gingen 16 gesunde Probanden (7 Frauen) auf einem 10 m Walkway in selbst gewählter langsamer, normaler und schneller Gehgeschwindigkeit. Die Druckmessung erfolgte über in die Schuhe eingebrachte größenangepasste Druckmesssohlen. Als Hauptzielparameter wurde der Symmetrieindex für die mittleren Drücke, die Maximaldrücke, den Quotienten der Fläche unter der Druckkurve zwischen Mittelfuß und gesamtem Fuß (Impulsquotient), sowie die Kraftrate (steilster Anstieg der Druckkurve) bestimmt. Für die zeitunabhängigen Druckwerte konnte generell eine verbesserte Symmetrie gesehen werden, die teilweise signifikante Differenzen aufwies. Die Kraftrate zeigte ein entgegengesetztes Verhalten. Damit konnte eine symmetrisierende Wirkung der Gangjustierhilfe auf Druckwerte, sowie eine durchaus differenzierte Wirkung auf die Anstiegssteilheit der Druckkurven nachgewiesen werden. Diese Befunde stehen nicht im Widerspruch und geben somit Hinweise auf eine funktionell symmetrisierende Wirkung der Gangjustierhilfe.

Objective: While psychological factors are known to influence physical performance, responses to unexpectedly extended endurance tasks remain unclear.Methods: In a crossover-randomized study, 37 participants performed an isometric endurance task twice, with a 14-day interval, compensating for 50% of upper body weight for 10 min. Muscular fatigue was measured via EMG of the back muscles, and perceived exertion (RPE; Borg scale 6–20) was recorded every minute (Real). In the experimental condition (Fake), RPE was recorded every 50 s without participants’ awareness. After the tenth query, participants were told a technical error occurred and were asked to continue for two additional minutes with two extra RPE queries. Participants were grouped by RPE and Fatigue Index (FI) into “good-end” and “bad-end” groups. FI and RPE were compared between Real and Fake conditions.Results: RPE-based grouping showed no significant FI differences. FI-based grouping revealed significantly higher RPE in the “good-end” group during the Fake condition (+0.9 at 540/550 s; +1.0 at 600 s). No significant differences were found in the “bad-end” group.Conclusion: Extending a task beyond its expected endpoint increases perceived exertion, which may lead to task termination despite unchanged muscular fatigue.

Hysteresis refers to a physical phenomenon in which the response or state of a system depends on both the input variable and its history. Hysteresis phenomena are also observed in biological systems and have been described for the sensorimotor system. The aim of the present study was to determine whether hysteresis phenomena can also be detected in trunk muscles during isometric load-varying situations. To this end, 40 healthy individuals (19 women) were subjected to isometric tests, where the applied load was systematically altered by complete rotations of the entire body in the Earth’s gravitational field. The study was conducted with 25%, 50%, and 75% of the upper body weight. Additionally, we varied the starting point (forward tilt and backward tilt) and the direction of rotation. The activity of a total of six trunk muscles was recorded using surface EMG (sEMG). The sEMG amplitudes were compared between the phases of increasing and decreasing load levels for each test situation. Hysteresis behavior was observed in all examined muscles, with the movement half-phase with increasing load showing higher amplitudes than the half-phase with decreasing load. However, this was consistently verifiable only for the multifidus muscle. For the abdominal muscles, the longissimus, and the iliocostalis muscle, the occurrence of hysteresis depended on the starting position: it could only be demonstrated if the starting point was chosen to correspond with the muscles’ main force direction. Thus, only the multifidus muscle exhibits a situation-independent hysteresis, whereas all other examined trunk muscles only show this phenomenon if subjected to load already at a loading situation. This indicates a physiologically determined functional weakness for load impacts on primarily unloaded muscles, posing a potential injury risk.

Zusammenfassung: Hintergrund Trotzdem der Mensch auf ca. 3 Millionen Jahre Evolution des aufrechten Ganges zurück blicken kann ist dieser Prozess, wie auch alle anderen evolutionären Prozesse nicht als abgeschlossen zu betrachten. Dies gilt insbesondere unter sich ständig ändernden Umweltbedingungen. Um hier zu optimieren wurde eine Orthesen-ähnliche Einlage, die so genannte Gangjustierhilfe (GJH), die medial im Bereich des Fersenbeines appliziert wird entwickelt. Die vorliegende Studie evaluiert die Auswirkung der GJH beim beschuhten Gehen auf die Gehgeschwindigkeit und die Oberkörperbewegung beim Gehen. Materialien und Methoden Dafür wurden 40 gesunde Probanden (20 Frauen, 19–35 Jahre) während des Gehens über festen Boden bei selbst gewählter normaler, sowie betont langsamer und schneller Gehgeschwindigkeit untersucht. Die Messung der Gehgeschwindigkeit erfolgte über ein Lichtschrankensystem, die Oberkörperbewegungen wurden über Inertialsensoren, die verwackelungsfrei am Sternumbefestigt waren erfasst. Zur Auswertung kamen dabei die Beschleunigung, sowie die Winkelgeschwindigkeiten in jeweils drei Achsen. Ergebnisse Die mittleren Gehgeschwindigkeiten waren bei Anwendung der GJH für normales und betont schnelles Gehen signifikant höher als ohne GJH (Normal, ohne GJH 1,41±0,05 m/s (MW±95% CI), mit GJH 1,47±0,04 m/s; schnell, ohne GJH 1,79±0,06 m/s, mit GJH 1,82±0,05 m/s). Für die Oberkörperbewegungen konnte während der Lastübernahme (0–5% normierter Gangzyklus) eine signifikant schnellere Extensionsbewegung des Oberkörpers nachgewiesen werden. Schlussfolgerungen Die GJH bewirkt somit einen lokomotionsaktivierenden Effekt und unabhängig davon eine erhöhte Aufrichtbewegung des Oberkörpers, die zu einer Rückverlagerung des Körperschwerpunktes und damit zu einem verbesserten funktionellen Gangbild beiträgt. Diese verstärkte Aufrichtung kann darüber hinaus als Baustein zur Sturzprophylaxe unserer immer älter werdenden Bevölkerung beitragen.