Performance Level Affects Full Body Kinematics and Spatiotemporal Parameters in Trail Running-A Field Study.

Trail running is an emerging discipline with few studies performed in ecological conditions. The aim of this work was to investigate if and how biomechanics differ between more proficient (MP) and less proficient (LP) trail runners. Twenty participants (10 F) were recruited for a 9.1 km trail running time trial wearing inertial sensors. The MP athletes group was composed of the fastest five men and the fastest five women. Group differences in spatiotemporal parameters and leg stiffness were tested with the Mann-Whitney U-test. Group differences in joint angles were tested with statistic parametric mapping. The finish time was 51.1 ± 6.3 min for the MP athletes and 60.0 ± 5.5 min for the LP athletes (p < 0.05). Uphill sections: The MP athletes expressed a tendency to higher speed that was not significant (p > 0.05), achieved by combining higher step frequency and higher step length. They showed a tendency to shorter contact time, lower duty factor and longer flight time that was not significant (p > 0.05) as well as significantly lower knee flexion during the stance phase (p < 0.05). Downhill sections: The MP athletes achieved significantly higher speed (p < 0.05) through higher step length only. They showed significantly higher knee and hip flexion during the swing phase as well as higher trunk rotation and shoulder flexion during the stance phase (p < 0.05). No differences were found with respect to leg stiffness in the uphill or downhill sections (p > 0.05). In the uphill sections, the results suggest lower energy absorption and more favorable net mechanical work at the knee joint for the MP athletes. In the downhill sections, the results suggest that the more efficient motion of the swing leg in the MP athletes could increase momentum in the forward direction and full body center of mass' velocity at toe off, thus optimizing the propulsion phase.

A forefoot strike pattern during 18° uphill walking leads to greater ankle joint and plantar flexor loading.

BACKGROUND: The ankle joint is one of the most involved joints in uphill walking. Furthermore, it is well known that toe walking increases the external dorsiflexion moment in the first half of stance during level walking. However, the effects of different foot-strike patterns on plantar flexor muscle forces, ankle joint forces, and other lower limb joint and muscle forces are unknown. RESEARCH QUESTION: Do foot-strike patterns during 18° uphill walking affect lower limb sagittal joint angles and moments, as well as joint contact and muscle forces? METHODS: This study was based on a data subset from previous publications, analysing uphill walking on an 18° ramp at a preset speed of 1.1 m/s in 18 male participants (34 limbs analyzed, 27 ± 5 years). Participants were divided into two groups based on their foot-strike pattern at initial contact: heel (HC) and forefoot (FC). Lower limb sagittal joint angles and moments as well as joint contact and muscle forces were assessed. Differences between the groups were assessed using two-sample t-tests. RESULTS: FC showed increased soleus and gastrocnemius muscle forces as well as ankle joint forces during loading response and mid stance compared to HC. The soleus muscle force impulse was 51.1% higher in the FC group than in the HC group (p < 0.001). On the other hand, FC had a lower absolute centre of mass vertical displacement and reduced knee and hip joint, as well as iliopsoas and hamstring muscle force impulses. SIGNIFICANCE: In terms of plantar flexor and ankle joint loading, it is advantageous to exhibit a heel strike pattern. The current results can be used to recommend foot-strike patterns for uphill walking, particularly in the presence or prevention of musculoskeletal issues.

Step-adaptive sound guidance enhances locomotor-respiratory coupling in novice female runners: A proof-of-concept study.

Introduction: Many runners struggle to find a rhythm during running. This may be because 20-40% of runners experience unexplained, unpleasant breathlessness at exercise onset. Locomotor-respiratory coupling (LRC), a synchronization phenomenon in which the breath is precisely timed with the steps, may provide metabolic or perceptual benefits to address these limitations. It can also be consciously performed. Hence, we developed a custom smartphone application to provide real-time LRC guidance based on individual step rate. Methods: Sixteen novice-intermediate female runners completed two control runs outdoors and indoors at a self-selected speed with auditory step rate feedback. Then, the runs were replicated with individualized breath guidance at specific LRC ratios. Hexoskin smart shirts were worn and analyzed with custom algorithms to estimate continuous LRC frequency and phase coupling. Results: LRC guidance led to a large significant increase in frequency coupling outdoor from 26.3 ±â€…10.7 (control) to 69.9 ±â€…20.0 % (LRC) "attached". There were similarly large differences in phase coupling between paired trials, and LRC adherence was stronger for the indoor treadmill runs versus outdoors. There was large inter-individual variability in running pace, preferred LRC ratio, and instruction adherence metrics. Discussion: Our approach demonstrates how personalized, step-adaptive sound guidance can be used to support this breathing strategy in novice runners. Subsequent investigations should evaluate the skill learning of LRC on a longer time basis to effectively clarify its risks and advantages.

Downhill Sections Are Crucial for Performance in Trail Running Ultramarathons-A Pacing Strategy Analysis.

Trail running is an increasingly popular discipline, especially over long-distance races (>42.195 km). Pacing strategy, i.e., how athletes modulate running speed for managing their energies during a race, appears to have a significant impact on overall performance. The aims of this study were to investigate whether performance level, terrain (i.e., uphill or downhill) and race stage affect pacing strategy and whether any interactions between these factors are evident. Race data from four race courses, with multiple editions (total races = 16), were retrieved from their respective events websites. A linear mixed effect model was applied to the full dataset, as well as to two subgroups of the top 10 male and female finishers, to assess potential differences in pacing strategy (i.e., investigated in terms of relative speed). Better finishers (i.e., athletes ranking in the best positions) tend to run downhill sections at higher relative speeds and uphill sections at lower relative speeds than slower counterparts (p < 0.001). In the later race stages, the relative speed decrease is larger in downhill sections than in uphill ones (p < 0.001) and in downhill sections, slower finishers perform systematically worse than faster ones, but the performance difference (i.e., between slower and faster finishers) becomes significantly larger in the later race stages (p < 0.001). Among elite athletes, no difference in pacing strategy between faster and slower finishers was found (p > 0.05). Both men (p < 0.001) and women (p < 0.001), in the later race stages, slow down more in downhill sections than in uphill ones. Moreover, elite women tend to slow down more than men (p < 0.001) in the later race stages, regardless of the terrain, in contrast to previous studies focusing on road ultramarathons. In conclusion, running downhill sections at higher relative speeds, most likely due to less accentuated fatigue effects, as well as minimizing performance decrease in the later race stages in downhill sections, appears to be a hallmark of the better finishers.

Influence of 2 Digital Exercise Modules of a Multimodular System on Balance and Leg Strength Under Consideration of Use Adherence: Prospective Cohort Study.

BACKGROUND: To empower healthy aging, digital solutions embed multiple modules for physical activity, cognitive health promotion, and social engagement. Integrating new empowering technologies such as digital exercise monitoring requires assessment measures and analysis procedures, considering variable compliance of users with different modules. OBJECTIVE: This study aims to assess the influence of a tablet-based and a feedback system-based exercise module on balance and leg strength by considering use adherence instead of the use of the entire multimodular system. METHODS: In the prospective cohort study within the fit4AAL project, 83 users (n=67, 81% women; n=16, 19% men; mean age 66.2, SD 2.3 years) used the 2 digital exercise modules of a multimodular physical activity promotion system for >18 weeks. A data-driven clustering method based on the average use frequency of the exercise modules determined the number of user types that met the World Health Organization-recommended training frequency of at least twice per week. On the basis of this use adherence, statistical analysis was performed with features of functional performance tests (unipedal stance, 30-second chair rise, Y-balance, and hurdle step tests). The tests were conducted 6 months before the intervention, immediately before the intervention, and after the intervention, comparing the baseline phase with the 3 feedback use groups of the study (using only the tablet, the tablet and the feedback system, or only the feedback system). RESULTS: Of the 83 users, 43 (52%) met the World Health Organization-recommended frequency of muscle-strengthening activities. Overall, the feedback use groups achieved, on average, more chair rises in 30 seconds than the baseline group (P=.01; moderate effect size of 0.07). Of the 43 users, 26 (60%) additionally used the feedback system-based exercise module. They improved in balance compared with the users using either the tablet or the feedback system (P=.02). In addition, they improved their leg strength within the group (P=.04) and compared with the baseline (P=.01). CONCLUSIONS: The additional use of a feedback system showed a tendency to positively maintain and influence the already exceptionally high functional performance of older adults. Considering use adherence in future multimodular system studies is crucial to assess the influence of single and combined use of exercise modules on functional performance.

Human Movement Quality Assessment Using Sensor Technologies in Recreational and Professional Sports: A Scoping Review.

The use of sensor technology in sports facilitates the data-driven evaluation of human movement not only in terms of quantity but also in terms of quality. This scoping review presents an overview of sensor technologies and human movement quality assessments in ecologically-similar environments. We searched four online databases to identify 16 eligible articles with either recreational and/or professional athletes. A total of 50% of the studies used inertial sensor technology, 31% vision-based sensor technology. Most of the studies (69%) assessed human movement quality using either the comparison to an expert's performance, to an exercise definition or to the athletes' individual baseline performance. A total of 31% of the studies used expert-based labeling of the movements to label data. None of the included studies used a control group-based study design to investigate impact on training progress, injury prevention or behavior change. Although studies have used sensor technology for movement quality assessment, the transfer from the lab to the field in recreational and professional sports is still emerging. Hence, research would benefit from impact studies of technology-assisted training interventions including control groups as well as investigating features of human movement quality in addition to kinematic parameters.

Simple foot strike angle calculation from three-dimensional kinematics: A methodological comparison.

A simple and accurate method of determining foot strike angle (FSA) during running can simplify data collections and validations of wearable sensors. The purpose of this study was to determine the validity of two simplified methods for estimating FSA and foot angle (throughout the ground contact) from three-dimensional kinematics. Markers were placed on the heel and head of the second metatarsal (HEEL-TOE) or on the lateral side of the head of the fifth metatarsal (HEEL-MET5). When compared to the reference foot segment, the HEEL-TOE method performed similarly with a minimal mean difference (0.28° [0.19°,0.36°], p < 0.001), a high Pearson's r (r = 0.994; p < 0.001), and low bias (-0.20°±1.05°). Alternatively, the HEEL-MET5 method underestimated FSA: mean difference = 4.28° [4.07°,4.91°] (p < 0.001), Pearson's r = 0.968 (p < 0.001), and bias = -4.58°±2.61°. Throughout the contact phase, significant SPM cluster regions were identified, indicating that the HEEL-MET5 method underestimated the angle of the foot for all foot strike patterns in the first 23-34% of the stance (p < 0.025). This study supports the idea that the HEEL-TOE method can be used as a simplified method for determining FSA from 3D kinematics. Researchers should proceed with caution when employing the HEEL-MET5 method, as it is likely underestimating FSA due to foot inversion in the early stance phase.

Breath Tools: A Synthesis of Evidence-Based Breathing Strategies to Enhance Human Running.

Running is among the most popular sporting hobbies and often chosen specifically for intrinsic psychological benefits. However, up to 40% of runners may experience exercise-induced dyspnoea as a result of cascading physiological phenomena, possibly causing negative psychological states or barriers to participation. Breathing techniques such as slow, deep breathing have proven benefits at rest, but it is unclear if they can be used during exercise to address respiratory limitations or improve performance. While direct experimental evidence is limited, diverse findings from exercise physiology and sports science combined with anecdotal knowledge from Yoga, meditation, and breathwork suggest that many aspects of breathing could be improved via purposeful strategies. Hence, we sought to synthesize these disparate sources to create a new theoretical framework called "Breath Tools" proposing breathing strategies for use during running to improve tolerance, performance, and lower barriers to long-term enjoyment.

Thoracolumbar Rotation During Tai Chi Movements-A Biomechanical Analysis of the Entire Peking Style Routine.

The impact of spinal mobility and sagittal spinal shape on the development of balance impairment supports the hypothesis that enhancing spine flexibility results in an improvement in postural balance ability. Therefore, the aim of this study was to investigate whether the range of motion of thoracolumbar rotation during the movements of the Tai Chi Peking style routine is sufficient to improve thoracolumbar flexibility. Three-dimensional kinematic and kinetic data were collected from eight athletes of the German Wushu Federation, while performing all movements of the entire Peking style routine (1) in a competition version corresponding to national/international championships and (2) in a health sport version performed with shorter and higher stances (i.e. a smaller distance between the feet and thus less knee flexion). For each movement the total mean and standard deviation values for the total range of motion of thoracolumbar rotation was calculated. Statistical analysis was performed using the Wilcoxon signed-rank test for paired differences. Eight movements showed major differences (10.12-19.73°) between the two versions. For the remaining movements, only minor differences (0.7-9.56°) were observed. All movements performed on both sides showed no significant lateral differences. Most of the Tai Chi movements, regardless of the performed version, cover a range of motion of thoracolumbar rotation that has the potential to lead to an improvement of thoracolumbal spine flexibility with appropriate training. The most effective single movements (25.97-72.22°) are Brush Knee and Step Forward, Step Back and Repulse Monkey, Grasp the Sparrow's Tail, Wave Hand in the Clouds, and Fair Lady Weaves with Shuttle.

Gait on slopes: Differences in temporo-spatial, kinematic and kinetic gait parameters between walking on a ramp and on a treadmill.

BACKGROUND: Inclined treadmills or static ramp constructions can be used to investigate downhill gait in a standardised laboratory condition. There is a lack of information how the gait patterns are affected when walking on a ramp or an inclined treadmill during uphill and downhill walking. RESEARCH QUESTION: Is there a difference in temporo-spatial parameters, sagittal ankle, knee and hip joint angle as well as ground reaction force when walking uphill and downhill on a ramp and a treadmill. METHODS: Uphill and downhill gait of 15 healthy participants was assessed during walking on a treadmill and on a ramp with slope gradients of 12 °, 6 ° and 0 °. Participants were instructed to walk with the same speed on each slope-system. Kinematic and temporo-spatial paramters were collected using a 3D motion capture system (Qualisys, Gothenburgh, Sweden), kinetic data were collected using pressure insoles (loadsol®, Novel, Germany). Temporo-spatial parameters were analysed using a Friedman ANOVA, time series of kinematic and kinetic data were compared using statistical parametric mapping with a sigificance level of 5%. RESULTS: On the treadmill participants walked with significantly shorter steps and shorter contact times, while they significantly increased step frequency compared to walking on a ramp, regardless of slope gradient. In uphill conditions, treadmill gait increased hip and knee flexion angles during the stance phase and increased the forward tilt of the thorax during the entire gait cycle. During downhill walking a significant decrease in dorsiflexion during initial contact, midstance and the second half of the swing phase was observed. Peak resultant forces remained similar compared to walking on the ramp. These alterations might be due to mechanical and psychological effects. SIGNIFICANCE: Knowledge about these differences is important in future study design and data interpretation from existing literature.

Effect of different walking speeds on joint and muscle force estimation using AnyBody and OpenSim.

BACKGROUND: To be able to use muscluloskeletal models in clinical settings, it is important to understand the effect of walking speed on joint and muscle force estimations in different generic musculoskeletal models. RESEARCH QUESTION: The aim of the current study is to compare estimated joint and muscle forces as a function of walking speed between two standard approaches offered in two different modelling environments (AnyBody and OpenSim). METHODS: Experimental data of 10 healthy participants were recorded at three different walking speeds (self-selected, 25 % slower, 25 % faster) using a ten-camera motion capture system together with four force plates embedded into a ten-meter walkway. Joint compression forces and muscle forces were calculated with a generic model in AnyBody and OpenSim. Trend analyses, mean absolute error (MAE) and correlation coefficients were used to compare joint compression forces and muscle forces between the two approaches. A one-way and two-way ANOVA with repeated measures were used to compare MAE and trend analysis changes, respectively (α = 0.05, Bonferroni corrected post-hoc tests). RESULTS: Trend analyses showed the same speed effect for AnyBody and OpenSim. MAEs increased significantly from slow to fast walking for knee joint compression forces, biceps femoris long head, gluteus maximus, gluteus medius and vastus intermedius. Lower correlation coefficients during slower walking were found for quadriceps muscles, gluteus maximus and biceps femoris compared to normal and faster walking. SIGNIFICANCE: Lower correlation coefficients during slower walking are assumed to be due to a higher amount of solutions solving the muscle recruitment in musculoskeletal models. This indicates that decreasing walking speed is more prone to speed dependent differences regarding variability, while the absolute error increased with increasing walking speed. To conclude, different modelling environments can react differently to changes in walking speed, but overall results are promising regarding the generalization across different generic musculoskeletal models.

Enhanced Breathing Pattern Detection during Running Using Wearable Sensors.

Breathing pattern (BP) is related to key psychophysiological and performance variables during exercise. Modern wearable sensors and data analysis techniques facilitate BP analysis during running but are lacking crucial validation steps in their deployment. Thus, we sought to evaluate a wearable garment with respiratory inductance plethysmography (RIP) sensors in combination with a custom-built algorithm versus a reference spirometry system to determine its concurrent validity in detecting flow reversals (FR) and BP. Twelve runners completed an incremental running protocol to exhaustion with synchronized spirometry and RIP sensors. An algorithm was developed to filter, segment, and enrich the RIP data for FR and BP estimation. The algorithm successfully identified over 99% of FR with an average time lag of 0.018 s (-0.067,0.104) after the reference system. Breathing rate (BR) estimation had low mean absolute percent error (MAPE = 2.74 [0.00,5.99]), but other BP components had variable accuracy. The proposed system is valid and practically useful for applications of BP assessment in the field, especially when measuring abrupt changes in BR. More studies are needed to improve BP timing estimation and utilize abdominal RIP during running.

Step characteristics of international-level skeleton athletes in the starting phase of official races.

The step characteristics of the starting motion of international-level skeleton athletes were investigated in official races as well as the relationship between the start and finish times. The starting motion of 26 male athletes was recorded with four video cameras in Intercontinental and Europe Cups, 2018 and their starting motion was analysed by a three-dimensional direct linear transformation method. The start time showed significant correlation with the finish time (ρ = 0.87, p < 0.001), as well as the sled speed at the 4 m (ρ = -0.43, p = 0.029) and 9 m (ρ = -0.79, p < 0.001) marks. The athletes were divided into two types according to the sled position and the foot for the 1st step: ipsilateral type and contralateral type. The sled speed of the ipsilateral type athletes in the 1st step was higher than that of the contralateral-type athletes. Step length from the 2nd to 5th and 7th steps showed a significant negative correlation with the start time (ρ = -0.70 to -0.46, p = 0.001 to 0.032). The international-level skeleton athletes gained a shorter start time due to a large running speed by acquiring the large SL.

Jumping with barbell load: Assessment of lower limb joint kinematics and kinetics during landing.

Loaded jumps are commonly used to improve leg muscle power. However, the additional load during jump-landing might increase the potential for overuse injury. Therefore, the aims of this study were to evaluate the effect that barbell load has on lower limb joint kinematics and kinetics during jump-landing and to evaluate the effect of arresting the barbell load at flight apex prior to landing on joint kinematic and kinetic variables. Barbell-loaded squat jumps (20, 40, and 60 kg) were investigated during two jump-landing conditions: 1) barbell-loaded (landing with barbell load) and 2) barbell-arrested (barbell load arrested at flight apex prior to jump-landing). Lower body kinematics and joint kinetics were assessed during jump-landing. In the barbell-loaded jump-landing condition, joint angles at initial contact decreased with increasing barbell load. Knee and hip peak power decreased (knee: -38%; hip: -46%), while ankle joint work increased with increasing barbell load. Joint moments, powers and work were decreased in the barbell-arrested condition compared to the barbell-loaded condition. Barbell-loaded jump-landings do not pose increased demands on the knee and the hip joint compared to bodyweight only jump-landings, due to the load-based reductions in jump height and joint kinematic adaptions. However, ankle joint contribution in energy dissipation is increased, possibly resulting in an increased overuse injury risk at this joint. Arresting the barbell load at flight apex prior to jump-landing substantially reduces the joint kinetics, hence serving as valuable training tool for athletes returning to sport after injuries.

Analysis of sloped gait: How many steps are needed to reach steady-state walking speed after gait initiation?

BACKGROUND: Gait initiation in level walking is suggested to take three steps before reaching steady-state walking speed. In sloped gait, it is not clear if the general recommendation of level gait can be used. RESEARCH QUESTION: The aim of this study was to investigate (1) if steady-state walking speed is reached within four steps in sloped gait, and (2) to what extent the number of initial steps cause differences in step length, cadence and ground reaction force (GRF). METHODS: Fourteen healthy participants walked on an instrumented ramp at inclinations of 0°, ±6°, ±12°, and ±18°, covering slight (clinical application) to steep (hiking and mountaineering) slopes. The starting position on the ramp was adjusted to collect each of the first to fourth step using a 12 infrared-camera motion capture system and two force plates. For each slope condition steady-state walking speed was determined using the ratio of the braking and propulsion impulse (ratio pap;pbrakingppropulsion) and the resultant Centre of Mass (CoM) speed (velCoM). Statistical differences between steps were calculated by using a Friedman ANOVA and pairwise post-hoc Wilcoxon tests. RESULTS: In all inclinations, ≥90 % (uphill) and ≥95 % (downhill) of steady-state speed regarding ratio pap and maximum velCoM was reached with the 3rd step. In the level and uphill condition the 4th step showed a slight decrease in velCoM. In uphill and downhill condition, the acceleration was mainly generated due to the increase in cadence with significant increases between the 1st and 2nd step as well as between the 2nd and 3rd step. A significant increase in step length was only observed in the uphill conditions. SIGNIFICANCE: Steady-state walking speed was reached with the 3rd step and thus, walkways which allow for two initial steps seem to be appropriate for uphill and downhill gait analysis for inclinations up to ±18°.

Foot Strike Angle Prediction and Pattern Classification Using LoadsolTM Wearable Sensors: A Comparison of Machine Learning Techniques.

The foot strike pattern performed during running is an important variable for runners, performance practitioners, and industry specialists. Versatile, wearable sensors may provide foot strike information while encouraging the collection of diverse information during ecological running. The purpose of the current study was to predict foot strike angle and classify foot strike pattern from LoadsolTM wearable pressure insoles using three machine learning techniques (multiple linear regression-MR, conditional inference tree-TREE, and random forest-FRST). Model performance was assessed using three-dimensional kinematics as a ground-truth measure. The prediction-model accuracy was similar for the regression, inference tree, and random forest models (RMSE: MR = 5.16°, TREE = 4.85°, FRST = 3.65°; MAPE: MR = 0.32°, TREE = 0.45°, FRST = 0.33°), though the regression and random forest models boasted lower maximum precision (13.75° and 14.3°, respectively) than the inference tree (19.02°). The classification performance was above 90% for all models (MR = 90.4%, TREE = 93.9%, and FRST = 94.1%). There was an increased tendency to misclassify mid foot strike patterns in all models, which may be improved with the inclusion of more mid foot steps during model training. Ultimately, wearable pressure insoles in combination with simple machine learning techniques can be used to predict and classify a runner's foot strike with sufficient accuracy.

Does enhanced footwear comfort affect oxygen consumption and running biomechanics?

Comfort as an essential parameter for running footwear is gaining importance in footwear research and development, and has also been proposed to decrease injury rate and improve metabolic demand in the paradigm of the comfort filter. The aims of this study were to determine differences in oxygen consumption and biomechanical variables associated with lower extremity injuries in response to running shoes of differing comfort. Fifteen male runners attended two testing sessions including an incremental lactate threshold test, a comfort assessment and treadmill running trials for the biomechanical and physiological measurements. Statistical analyses were performed on oxygen consumption, spatio-temporal variables including foot-ground angle and coupling angle variability of 12 couplings in five stride phases. No decrease in oxygen consumption was found in the most preferred shoe condition. Investigation of potential biomechanical contributors to changes in metabolic demands revealed differences in the stride rate between the most and least preferred condition. In coupling angle variability analyses, only one coupling (ankle dorsiflexion/plantarflexion to knee varus/valgus) yielded a significant difference between conditions in the phase including the touch down. Based on the findings of this study, previous suggestions regarding positive effects of enhanced footwear comfort during running cannot be supported - neither on economy nor on injury prevention perspective. However, a prospective study of lower extremity injury combined with measurements of biomechanical and physiological variables seems to be required for a definite support or contradiction of the comfort filter.

Familiarisation of novice and experienced treadmill users during a running session: Group specific evidence, time and individual patterns.

The elimination of familiarisation effects is a recurring topic in biomechanical testing during treadmill running among different experience levels. The two aims of this study were (i) to calculate familiarisation times of novice and experienced treadmill runners on a group level and (ii) to examine individual familiarisation patterns in order to classify those with similar characteristics. Twenty runners participated in this study by performing a treadmill running session with 3D motion capture. Familiarisation times for 9 kinematic variables among both groups (novices and experienced treadmill runners) were statistically analysed. Additionally a qualitative clustering process (supported by quantitative criteria) provided individual familiarisation patterns for all participants and variables. Group mean familiarisation times were inconsistent across variables (ranging from 3 to 14 min), with no general tendency for decreased familiarisation time in experienced compared to novice treadmill runners. The analysis of individual familiarisation patterns revealed that 30.5% were not stable after 15 min. Substantial changes compared to the initial state were observed in data sets with detected familiarisation pattern. Treadmill running experience does not affect familiarisation patterns since this process is highly individual and variable-specific. Consequently, no generalised familiarisation time can be provided and the elimination of familiarisation in biomechanical testing a priori does not seem to be possible in the first 15 min for approximately one third of the individual patterns studied. In conclusion, the common practice of collecting data subsequent to a pre-defined generalised familiarisation time ought to be replaced by measurements at several points in time during trials. This required procedure would allow for checking familiarisation patterns and fluctuations in order to exclude inappropriate data sets in future treadmill studies.

Muscle force estimation in clinical gait analysis using AnyBody and OpenSim.

A variety of musculoskeletal models are applied in different modelling environments for estimating muscle forces during gait. Influence of different modelling assumptions and approaches on model outputs are still not fully understood, while direct comparisons of standard approaches have been rarely undertaken. This study seeks to compare joint kinematics, joint kinetics and estimated muscle forces of two standard approaches offered in two different modelling environments (AnyBody, OpenSim). It is hypothesised that distinctive differences exist for individual muscles, while summing up synergists show general agreement. Experimental data of 10 healthy participants (28 ±â€¯5 years, 1.72 ±â€¯0.08 m, 69 ±â€¯12 kg) was used for a standard static optimisation muscle force estimation routine in AnyBody and OpenSim while using two gait-specific musculoskeletal models. Statistical parameter mapping paired t-test was used to compare joint angle, moment and muscle force waveforms in Matlab. Results showed differences especially in sagittal ankle and hip angles as well as sagittal knee moments. Differences were also found for some of the muscles, especially of the triceps surae group and the biceps femoris short head, which occur as a result of different anthropometric and anatomical definitions (mass and inertia of segments, muscle properties) and scaling procedures (static vs. dynamic). Understanding these differences and their cause is crucial to operate such modelling environments in a clinical setting. Future research should focus on alternatives to classical generic musculoskeletal models (e.g. implementation of functional calibration tasks), while using experimental data reflecting normal and pathological gait to gain a better understanding of variations and divergent behaviour between approaches.

Influence of body segment parameter estimation on calculated ground reaction forces in highly dynamic movements.

The effect of body segment parameter estimation (BSP) on the inverse dynamics modelling results has not yet been demonstrated in specific groups during athletic movements with high segment accelerations. Therefore, the purpose of this study was to analyse this effect in ski-jumpers as representatives of a specific group (i.e. low body mass index) by comparing calculated and measured ground reaction forces during ski-jumping imitation jumps. Full body kinematics and vertical ground reaction forces were recorded of 9 ski-jumpers performing three imitation jumps each. BSP were estimated using three previously published, one individually optimized and one ski-jumper group specific model. Vertical ground reaction forces were calculated using the vertical acceleration of the segments as well as the BSP of the single models in a top-down approach. Statistical analysis revealed a main model effect concerning the root mean square error between the calculated and the measured ground reaction force with deviations between the models of 53%. Individual optimization and the application of the ski-jumper group specific model increased the accuracy of the calculated ground reaction forces by 11 and 7%, respectively, compared to the best performing published model. The results of inverse dynamics modelling are very sensitive to the BSP estimation for specific groups like ski-jumpers during movements incorporating high segment accelerations. This emphasizes the importance of selecting adequate BSP estimation models or methods when analysing specific groups in highly dynamic movements in order to increase the accuracy of the inverse dynamics analyses results.