Christoph Anders

The influence of foot posture on the cost of transport in humans

SUMMARY Although humans appear to be specialized for endurance running, the plantigrade posture of our feet, in which the heel contacts the substrate at the beginning of a step, seems incompatible with economical running. In this study, we tested the hypothesis that plantigrade foot posture reduces the energetic cost of transport (COT) during walking in humans. When human subjects walked with their heels slightly elevated in a ‘low-digitigrade’ posture, COT increased by 53% above that of normal plantigrade walking. By contrast, there was no difference in COT when subjects ran with digitigrade versus plantigrade foot posture. Stride frequency increased and stride length decreased when subjects switched to digitigrade walking; however, this change did not influence the COT. Additionally, we found that possible reductions in postural stability appear not to have caused the elevated cost of digitigrade walking. Digitigrade walking, however, did (1) increase the external mechanical work performed by the limbs; (2) reduce the pendular exchange of kinetic and potential energy of the center of mass; (3) increase the average ground reaction force moment at the ankle joint; and (4) increase the recruitment of major extensor muscles of the ankle, knee, hip and back. These observations suggest that plantigrade foot posture improves the economy of walking. Relative to other mammals, humans are economical walkers, but not economical runners. Given the great distances hunter-gatherers travel, it is not surprising that humans retained a foot posture, inherited from our more arboreal great ape ancestors, that facilitates economical walking.

The musculoskeletal system of humans is not tuned to maximize the economy of locomotion

Humans are known to have energetically optimal walking and running speeds at which the cost to travel a given distance is minimized. We hypothesized that “optimal” walking and running speeds would also exist at the level of individual locomotor muscles. Additionally, because humans are 60–70% more economical when they walk than when they run, we predicted that the different muscles would exhibit a greater degree of tuning to the energetically optimal speed during walking than during running. To test these hypotheses, we used electromyography to measure the activity of 13 muscles of the back and legs over a range of walking and running speeds in human subjects and calculated the cumulative activity required from each muscle to traverse a kilometer. We found that activity of each of these muscles was minimized at specific walking and running speeds but the different muscles were not tuned to a particular speed in either gait. Although humans are clearly highly specialized for terrestrial locomotion compared with other great apes, the results of this study indicate that our locomotor muscles are not tuned to specific walking or running speeds and, therefore, do not maximize the economy of locomotion. This pattern may have evolved in response to selection to broaden the range of sustainable running speeds, to improve performance in motor behaviors not related to endurance locomotion, or in response to selection for both.

A topographical analysis of spectral electromyographic data of the human masseter muscle under different functional conditions in healthy subjects

In 20 healthy subjects, 16-channel surface electromyograms (EMG) were recorded with the mandible in its postural position, during compensation for forces applied from ipsilateral, contralateral and frontal positions, and during force-constant biting on a unilaterally placed force transducer. After artefact elimination, EMG power spectra were calculated on the basis of the original EMG curves via fast Fourier transformation. Using spectral EMG characteristics, EMG maps were computed by means of an interpolation algorithm and an imaging procedure. Spectral EMG maps were demonstrated for all the test conditions. Significant differences of myoelectrical activity were verified between the 16 electrode positions. Moreover, the levels and/or the topographical distributions of spectral EMG powers differed significantly between the test conditions. During biting as well as with contralaterally and frontally applied forces, the highest EMG activity was found in the inferior third of the masseter and the lowest in the superior third. With ipsilaterally applied forces, the topographical distribution of the total EMG power was completely changed. The power maximum was frequently demonstrated in the superior, especially the posterosuperior, third of the muscle, the minimum in the inferior third. In the postural position of the mandible, EMG activity decreased from the anterior to the posterior regions of the masseter. If the bite force or the horizontally applied forces were enhanced, EMG activity increased significantly but the EMG map structures were only changed in some details. The topographical distribution of myoelectrical activity demonstrated by EMG maps characterizes the intramuscular activation patterns of distinct masseter functions.(ABSTRACT TRUNCATED AT 250 WORDS)

Activation Characteristics of Trunk Muscles During Cyclic Upper-Body Perturbations Caused by an Oscillating Pole

OBJECTIVE To evaluate the effect of a new device on trunk muscle activation. DESIGN Cross-sectional survey of trunk muscle activation characteristics. SETTING Physiologic laboratory at university institute. PARTICIPANTS Thirty healthy subjects (15 men, 15 women) were recruited from a university campus. INTERVENTIONS A simple flexible pole that applies rapidly alternating forces on the trunk when set into motion was used. The device was held horizontally in both hands, in front of the body. It was used at 3 different oscillation frequencies (3, 3.5, 4.5 Hz), in horizontal and vertical plane, respectively. MAIN OUTCOME MEASURES Surface electromyography of 5 trunk muscles was measured and the data were normalized according to relative cycle time. Time dependent (amplitude curve) and time independent (mean amplitude over cycle) parameters were used for analysis. RESULTS Rectus abdominis and external oblique muscle amplitudes were directly proportional with oscillation frequency (analysis of variance), and these effects were independent of sex. Multifidus amplitude levels were subject to oscillation plane with increased levels for vertical oscillation in men but not in the women. All abdominal muscles exhibited continuous activation pattern, independent of oscillation plane. Back muscles changed from a continuous activation in horizontal plane into similarly phasic patterns in vertical oscillation plane. The occurring amplitude peak moved forward in relative cycle with increasing oscillation frequency. CONCLUSIONS Back muscle activation patterns were subject to oscillation plane. Abdominal muscle activation was independent from oscillation frequency and oscillation plane. These normative data may be used to identify disturbed trunk muscle coordination patterns and to control success of functional restoration during rehabilitation interventions of back pain patients.

Influence of delayed muscle reflexes on spinal stability: model-based predictions allow alternative interpretations of experimental data.

Model-based calculations indicate that reflex delay and reflex gain are both important for spinal stability. Experimental results demonstrate that chronic low back pain is associated with delayed muscle reflex responses of trunk muscles. The aim of the present study was to analyze the influence of such time-delayed reflexes on the stability using a simple biomechanical model. Additionally, we compared the model-based predictions with experimental data from chronic low back pain patients and healthy controls using surface-electromyography. Linear stability methods were applied to the musculoskeletal model, which was extended with a time-delayed reflex model. Lateral external perturbations were simulated around equilibrium to investigate the effects of reflex delay and gain on the stability of the human lumbar spine. The model simulations predicted that increased reflex delays require a reduction of the reflex gain to avoid spinal instability. The experimental data support this dependence for the investigated abdominal muscles in chronic low back pain patients and healthy control subjects. Reflex time-delay and gain dependence showed that a delayed reflex latency could have relevant influence on spinal stability, if subjects do not adapt their reflex amplitudes. Based on the model and the experimental results, the relationship between muscle reflex response latency and the maximum of the reflex amplitude should be considered for evaluation of (patho) physiological data. We recommend that training procedures should focus on speeding up the delayed reflex response as well as on increasing the amplitude of these reflexes.

Chronischer unspezifischer Rückenschmerz

ZusammenfassungDer chronische unspezifische Rückenschmerz ist ein zentrales Thema für Patienten, Versicherer und Berufsgenossenschaften. Mit einer Präventivdiagnostik bestünde die Möglichkeit, für einen momentan beschwerdefreien Menschen eine Prognose zu erstellen, mit welcher Wahrscheinlichkeit er einen chronischen unspezifischen Rückenschmerz erleiden wird, wenn er sich nicht einer präventiven Maßnahme unterzieht.Jedes Jahr erleiden 20% der Erwachsenen Rückenschmerzen und 70–80% der Bevölkerung bekommen in ihrem Leben einmal oder mehrmals Rückenschmerzen. Meist reduzieren sich die Beschwerden innerhalb der ersten sechs Wochen ohne medizinische Intervention oder verschwinden ganz. Nur in wenigen Fällen sind sie progredient, chronifizieren und verursachen erhebliche Kosten.Es gilt herauszufinden, ob eine Person zu einer Risikogruppe gezählt werden kann, für die zukünftig eine Chronifizierung des Rückenschmerzes wahrscheinlich wird. Mit dem präventivdiagnostischen Ansatz sollte die Frage beantwortet werden können: Welche Subgruppe von Patienten mit chronischem Rückenschmerz wird besonders von einer Übungstherapie oder von kognitiven verhaltenstherapeutischen Ansätzen profitieren?AbstractChronic low back pain represents an important issue not only for the patients but also for society. Apreventive diagnosis could open the possibility to predict the individual probability of developing chronic low back pain in pain-free persons or persons with sub-acute low back pain if no further preventive interventions would be started.Every year about 20% of adults will suffer from back pain and 70-80% of society will suffer from back pain during their lives. In most cases back pain is alleviated within the first 6 weeks without any medical intervention. Only a few cases are progredient and chronic with immense costs for society and health care systems.It is necessary to find out which individuals will probably suffer from chronic back pain in the future. The diagnostic outcome of the classification should help to answer the question which subgroups of patients with chronic low back pain will especially benefit from exercise therapy or cognitive behavior therapy?

Activation characteristics of shoulder muscles during maximal and submaximal efforts

Determination of individual maximum voluntary contraction (MVC) force is used as the gold standard for normalising surface EMG (SEMG) data. Assuming a linear amplitude–force relationship, individual strain levels are defined according to percentage rates of the measured MVC levels. The purpose of the study was to investigate if the assumed force–strain relationship can be applied without qualification. Therefore, healthy volunteers (nine men, ten women) were investigated during isometric exercises of shoulder muscles at MVC and 50% levels. Tasks were performed at four different angular positions in frontal, sagittal and horizontal planes. In each plane, both possible force directions were investigated. SEMG was taken simultaneously from 13 muscles of the shoulder and upper arms from both sides of the body. At a force level of 50% MVC, SEMG amplitude levels were compared to the expected 50% level. Differences in muscular co-ordination patterns were also determined. During retroversion and horizontal flexion, amplitude levels significantly remained at levels below 50%. This was seen for all the muscles investigated, independent of relative contribution to force production. During horizontal extension and abduction, the main force-producing muscles showed amplitude levels that significantly exceeded the expected 50% level. Co-ordination patterns differed significantly between MVC and submaximal conditions for anteversion, retroversion and horizontal extension. Specifically, four shoulder muscles showed higher proportions at the 50% level compared to MVC. Therefore, certain percentage rates of MVC force levels exhibit quite different strain rates, as identified by SEMG. Depending on force direction, differences in co-ordination patterns exist between MVC and submaximal test conditions. Both findings have implications for therapeutic and training applications.

SEMG activation patterns of thigh muscles during upright standing in haemophilic patients.

Summary.  Although electromyography (EMG) is a common method to evaluate muscle activity, studies utilizing EMG in haemophilic patients are rare. The haemophilic arthropathy, resulting in altered afferent information is expected to cause disturbed activation and inter‐muscular coordination patterns in haemophilic subjects. The aim of this study was to determine differences of selected knee muscles between haemophilic patients and non‐haemophilic subjects during upright standing. Surface EMG (SEMG) amplitudes of rectus femoris, vastus medialis (VM), vastus lateralis (VL) and biceps femoris (BF) muscles of both sides were measured in 27 haemophilic patients (H) and 26 control subjects (C) while standing on an even surface. Data from both sides were pooled in C, but data of H were subdivided further according to major (H‐MA) and minor (H‐MI) affected joints. To normalize the data, amplitude ratios (percentage of cumulated activity) were calculated as well. Regardless of whether H‐MA or H‐MI was compared with C, amplitudes of all extensor muscles reached significantly higher levels in H (P < 0.05). SEMG amplitude ratios also differed between H and C. Independent of subgroup, BF showed significantly reduced activation ratios (P < 0.01). Only the ratios of VM and VL of H‐MA could replicate the observed amplitude differences to C (P < 0.05). These findings show that while standing, haemophiliacs maintain the necessary stability demands through increased extensor activities and modulated coordination patterns. Although all thigh muscles of haemophiliacs are characterized by distinct atrophy, increased amplitude levels could be proved for the knee extensor muscles only. Therefore, general atrophy‐related effects cannot explain these results.

Gender specific activation patterns of trunk muscles during whole body tilt.

Gender specific differences as evidenced in both anthropometric data and physical performance of healthy persons have been broadly demonstrated. Recently advancements in surface electromyography (SEMG) have shown possible differences in men’s and women’s muscle coordination patterns. However, quantitative information about gender related muscle co-ordination patterns are rare. This investigation was carried out to both verify if trunk muscle SEMG amplitude–force relationship differs between men and women and refine techniques of measurement and data analysis using SEMG. Thirty-one healthy volunteers (16 women, 15 men) were investigated during whole body tilt at angles from 5° to 90° (from quasi vertical to horizontal position). Subjects had to maintain body in body axis while their lower body was fixed and the upper body remained unsupported. SEMG was taken from five different trunk muscles of both sides simultaneously. At corresponding tilt angles women exhibited higher amplitude levels of their abdominal muscles in comparison to men, who were characterized by higher back muscle amplitudes. Abdominal muscles showed a non-linear SEMG amplitude–force relationship but differed between genders with more linearity in women. Back muscles showed a linear amplitude–force relationship with no differences between genders. Women were characterized by higher levels of co-contraction of all investigated muscles. The data are in accordance with histological investigations, which already proved specific fiber distribution patterns in both abdominal and back muscles and gender related differences in relative area of Type 1 fibers of back muscles. The observed differences in SEMG–force relationship for the abdominal muscles remain hypothetical because of lack of histological information.

Ankle muscle activation in people with haemophilia.

Since normative surface EMG (SEMG) values for muscles acting at the knee joint are available for people with haemophilia, increasing interest is noticeable for other joints affected by haemophilic arthropathy. Adequate activity of shank muscles is an important key for appropriate postural control. The aim of this study was to determine differences in muscle activation patterns of lower leg muscles between people with and without haemophilia during upright standing. SEMG of tibialis anterior (TA), fibularis longus (FL), lateral (LG) and medial (MG) heads of gastrocnemius, and soleus (SO) muscles of both sides were recorded in 25 haemophilic patients (H) and 25 non‐haemophilic control subjects (C) while standing on even ground. The Gilbert‐Score was used to assign sides to major (H‐MA) and minor (H‐MI) affected ankle joints in H. To normalize the SEMG amplitudes, amplitude ratios (percentage of cumulated activity) were calculated. Compared to controls, TA ratios showed higher and MG reduced levels in both H groups (P < 0.01). In the H‐MA subgroup of H, FL also joined the TA behaviour whereas SO had similar activation direction as MG. Although possible descending influences from the knee joints cannot be excluded, this can be interpreted as a compensational mechanism due to the severity of the orthopaedic status of the ankle, which with increasing heaviness is accompanied by reduced plantar flexion capability. However, ankle joint integrity appears to be reduced in H, with TA and MG seeming to play key roles for neuromuscular control of upright posture.