TY  - JOUR
A1  - Müller, Steffen
A1  - Baur, Heiner
A1  - Hirschmueller, Anja
A1  - Mayer, Frank
T1  - Validität des COP-Verlaufes zur Quantifizierung der funktionalen Gangentwicklung bei Kindern
N2  - Functional gait development in children is discussed controversially. Differentiated information about the roll- over process of the foot, represented by the "Center of Pressure" (COP), are still missing. The purpose of the study was the validation of the COP-path to quantify the functional gait development of children. Plantar pressure distribution was measured barefoot with an individual speed on a walkway (tartan) - in 255 children aged between 2 and 15 years. The medial and lateral area enclosed between the COP-path and the bisection of plantar angle (A(med), A(lat), Sigma: A(ml)) was calculated from plantar pressure data. Furthermore, the duration of the COP-path in the heel (COPtimeF), midfoot (COPtimeM) and forefoot (COPtimeV) was analysed. The load distribution under the medial and lateral forefoot was also calculated. The variation coefficient (VC) was calculated as a measure of interindividual variability. The medio-lateral divergency of the COP (Aml) initially decreases with advancing age (-20.2%), followed by a continuous increase (+27.2%). No changes in VC (A(med), A(lat), and A(ml)) appeared during age-related development. COPtimeM remains constant in all children over time. In contrast to COPtimeM, Cop(time)F decreases from youngest to oldest children (-31.0%), and COPtimeV increases (+41.7%). After initial descent up to 8 years of age, VC (COPtimeF, COPtimeM, COPtimeV) remains constant. The mediolateral load under the forefoot did not change. The COP-Path is able to characterise the functional gait development of children. VC values indicate high individual variability of gait pattern. In this context, age-based standard values should be critically discussed
Y1  - 2006
ER  - 
TY  - JOUR
A1  - Carlsohn, Anja
A1  - Scharhag-Rosenberger, Friederike
A1  - Schapp, Lukas
A1  - Fusch, Gerhard
A1  - Mayer, Frank
T1  - Validity of the determination of energy input from a dietary record in persons of normal weight - dependence on the level of energy input comparison between elite sportsmen with very high energy intake and a control group of persons of normal weight
JF  - Ernährungs-Umschau : Forschung & Praxis
N2  - Dietary records are often biased, especially those of overweight individuals. The purpose of the study was to investigate underreporting among persons of normal weight with a very high energy intake (El).
 The total energy expenditure (TEE) of 16 elite athletes (BMI 24 +/- 2 kg/m(2)) and 17 controls (BMI 23 3 kg/m2) was measured using the doubly-labeled water technique (DLW, 14d). El was estimated using 2 x 3-day dietary records. Underreporters were identified by BLACK'S cut-off (El:TEE < 0.76). 44% of athletes (El: 3584 824 kcal/d; TEE: 4621 1460 kcal/d) and 29% of controls (El: 2552 680 kcal/d; TEE: 3151 822 kcal/d) were identified as underreporters. TEE explains 52% of underreporting. In summary, a high energy intake seems to strongly predict underreporting. Prevalence and magnitude of underreporting increase with increasing energy intake.
KW  - energy intake
KW  - dietary records
KW  - bias
KW  - underreporting
KW  - athletes
Y1  - 2012
U6  - https://doi.org/10.4455/eu.2012.958
SN  - 0174-0008
VL  - 59
IS  - 10
SP  - 572
EP  - 577
PB  - Umschau-Zeitschriftenverl.
CY  - Frankfurt, Main
ER  - 
TY  - JOUR
A1  - Müller, Steffen
A1  - Stoll, Josefine
A1  - Müller, Juliane
A1  - Mayer, Frank
T1  - Validity of isokinetic trunk measurements with respect to healthy adults, athletes and low back pain patients
JF  - Isokinetics and exercise science : official journal of the European Isokinetic Society
N2  - Background: Isokinetic measurements are widely used to assess strength capacity in a clinical or research context. Nevertheless, the validity of isokinetic measures for identifying strength deficits and the evaluation of therapeutic process regarding different pathologies is yet to be established. Therefore, the purpose of this review is to evaluate the validity of isokinetic measures in a specific case: that of muscular capacity in low back pain (LBP).
 Methods: A literature search (PubMed; ISI Web of Knowledge; The Cochrane Library) covering the last 10 years was performed. Relevant papers regarding isokinetic trunk strength measures in healthy and patients with low back pain (PLBP) were searched. Peak torque values [Nm] and peak torque normalized to body weight [Nm/kg BW] were extracted for healthy and PLBP. Ranked mean values across studies were calculated for the concentric peak torque at 60 degrees/s as well as the flexion/extension (F/E) ratio.
 Results: 34 publications (31 flexion/extension; 3 rotation) were suitable for reporting detailed isokinetic strength measures in healthy or LBP (untrained adults, adolescents, athletes). Adolescents and athletes were different compared to normal adults in terms of absolute trunk strength values and the F/E ratio. Furthermore, isokinetic measures evaluating therapeutic process and isokinetic rehabilitation training were infrequent in literature (8 studies).
 Conclusion: Isokinetic measurements are valid for measuring trunk flexion/extension strength and F/E ratio in athletes, adolescents and (untrained) adults with/without LBP. The validity of trunk rotation is questionable due to a very small number of publications whereas no reliable source regarding lateral flexion could be traced. Therefore, isokinetic dynamometry may be utilized for identifying trunk strength deficits in healthy adults and PLBP.
KW  - Isokinetic
KW  - validity
KW  - low back pain
KW  - peak torque
KW  - trunk
Y1  - 2012
U6  - https://doi.org/10.3233/IES-2012-00482
SN  - 0959-3020
VL  - 20
IS  - 4
SP  - 255
EP  - 266
PB  - IOS Press
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Engel, Tilman
A1  - Mueller, Juliane
A1  - Kopinski, Stephan
A1  - Reschke, Antje
A1  - Mueller, Steffen
A1  - Mayer, Frank
T1  - Unexpected walking perturbations: Reliability and validity of a new treadmill protocol to provoke muscular reflex activities at lower extremities and the trunk
JF  - Journal of biomechanics
N2  - 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 (100 ms duration; 2 m/s amplitude), triggered by a plantar pressure insole 200 ms after heel contact. Delay, duration and amplitude of applied perturbations were recorded by 3D-motion capture. Muscular reflex responses (within 200 ms) 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 14 ms, duration was 102 +/- 4 ms and amplitude was 2.1 +/- 0.01 m/s. TRV for perturbation delay, duration and amplitude ranged from 5.0% to 5.7%. LoA reached 3 +/- 36 ms for delay, 2 +/- 13 ms for duration and 0.0 +/- 0.3 m/s for amplitude. EMG amplitudes following perturbations ranged between 106 +/- 97% and 909 +/- 979% of unperturbed gait and EMG latencies between 82 +/- 14 ms and 106 +/- 16 ms. 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. (C) 2017 Elsevier Ltd. All rights reserved.
KW  - Perturbation
KW  - Stumbling
KW  - Gait
KW  - Treadmill
KW  - Reliability
KW  - MiSpEx
Y1  - 2017
U6  - https://doi.org/10.1016/j.jbiomech.2017.02.026
SN  - 0021-9290
SN  - 1873-2380
VL  - 55
SP  - 152
EP  - 155
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Kopinski, Stephan
A1  - Engel, Tilman
A1  - Cassel, Michael
A1  - Fröhlich, Katja
A1  - Mayer, Frank
A1  - Carlsohn, Anja
T1  - Ultrasound Applied to Subcutaneous Fat Tissue Measurements in International Elite Canoeists
JF  - International journal of sports medicine
N2  - 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 (*/divided by 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.
KW  - subcutaneous adipose tissue
KW  - skinfold thickness
KW  - elite athletes
KW  - body composition
KW  - ultrasonography
Y1  - 2015
U6  - https://doi.org/10.1055/s-0035-1555857
SN  - 0172-4622
SN  - 1439-3964
VL  - 36
IS  - 14
SP  - 1134
EP  - 1141
PB  - Thieme
CY  - Stuttgart
ER  - 
TY  - JOUR
A1  - Intziegianni, Konstantina
A1  - Cassel, Michael
A1  - König, Niklas
A1  - Müller, Steffen
A1  - Fröhlich, Katja
A1  - Mayer, Frank
T1  - Ultrasonography for the assessment of the structural properties of the Achilles tendon in asymptomatic individuals: An intra-rater reproducibility study
JF  - Isokinetics and exercise science : official journal of the European Isokinetic Society
N2  - BACKGROUND: Reproducible measurements of tendon structural properties are a prerequisite for accurate diagnosis of tendon disorders and for determination of their mechanical properties. Despite the widely used application of Ultrasonography (US) in musculoskeletal assessment, its operator dependency and lack of standardization influences the consistency of the measurement.
 OBJECTIVE: To evaluate the intra-rater reproducibility of a standardized US method assessing the structural properties of the Achilles tendon (AT).
 METHODS: Sixteen asymptomatic participants were positioned prone on an isokinetic dynamometer with the knee extended and ankle at 90. flexion. US was used to assess AT-length, cross-sectional area (CSA), and AT-elongation during isometric plantarflexion contraction. The intra-rater reproducibility was assessed by ICC (2.1), Test-Retest Variability (TRV, %), Bland-Altman analyses (Bias +/- LoA [1.96*SD]), and Standard-Error of Measurement (SEM).
 RESULTS: Measurements of AT-length demonstrated an ICC of 0.93, TRV of 4.5 +/- 3.9%, Bias +/- LoA of -2.8 +/- 25.0 mm and SEM of 6.6 mm. AT-CSA showed an ICC of 0.79, TRV of 8.7 +/- 9.6%, Bias +/- LoA of 1.7 +/- 19.4 mm(2) and SEM of 5.3 mm(2). AT-elongation revealed an ICC of 0.92, TRV of 12.9 +/- 8.9%, Bias +/- LoA of 0.3 +/- 5.7 mm and SEM of 1.5 mm.
 CONCLUSIONS: The presented methodology allows a reproducible assessment of Achilles tendon structural properties when performed by a single rater.
KW  - Ultrasonography
KW  - Achilles tendon
KW  - reproducibility
KW  - isokinetic
Y1  - 2015
U6  - https://doi.org/10.3233/IES-150586
SN  - 0959-3020
SN  - 1878-5913
VL  - 23
IS  - 4
SP  - 263
EP  - 270
PB  - IOS Press
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Müller, Steffen
A1  - Stoll, Josefine
A1  - Mueller, Juliane
A1  - Cassel, Michael
A1  - Mayer, Frank
T1  - Trunk Muscle Activity during Drop Jump Performance in Adolescent Athletes with Back Pain
JF  - Frontiers in physiology
N2  - In the context of back pain, great emphasis has been placed on the importance of trunk stability, especially in situations requiring compensation of repetitive, intense loading induced during high-performance activities, e.g., jumping or landing. This study aims to evaluate trunk muscle activity during drop jump in adolescent athletes with back pain (BP) compared to athletes without back pain (NBP). Eleven adolescent athletes suffering back pain (BP: m/f: n = 4/7; 15.9 +/- 1.3 y; 176 +/- 11 cm; 68 +/- 11 kg; 12.4 +/- 10.5 h/we training) and 11 matched athletes without back pain (NBP: m/f: n = 4/7; 15.5 +/- 1.3 y; 174 +/- 7 cm; 67 +/- 8 kg; 14.9 +/- 9.5 h/we training) were evaluated. Subjects conducted 3 drop jumps onto a force plate (ground reaction force). Bilateral 12-lead SEMG (surface Electromyography) was applied to assess trunk muscle activity. Ground contact time [ms], maximum vertical jump force [N], jump time [ms] and the jump performance index [m/s] were calculated for drop jumps. SEMG amplitudes (RMS: root mean square [%]) for all 12 single muscles were normalized toMIVC (maximum isometric voluntary contraction) and analyzed in 4 time windows (100 ms pre- and 200 ms post-initial ground contact, 100 ms pre- and 200 ms post-landing) as outcome variables. In addition, muscles were grouped and analyzed in ventral and dorsal muscles, as well as straight and transverse trunk muscles. Drop jump ground reaction force variables did not differ between NBP and BP (p > 0.05). Mm obliquus externus and internus abdominis presented higher SEMG amplitudes (1.3-1.9-fold) for BP (p < 0.05). Mm rectus abdominis, erector spinae thoracic/lumbar and latissimus dorsi did not differ (p > 0.05). The muscle group analysis over the whole jumping cycle showed statistically significantly higher SEMG amplitudes for BP in the ventral (p = 0.031) and transverse muscles (p = 0.020) compared to NBP. Higher activity of transverse, but not straight, trunk muscles might indicate a specific compensation strategy to support trunk stability in athletes with back pain during drop jumps. Therefore, exercises favoring the transverse trunk muscles could be recommended for back pain treatment.
KW  - SEMG-pattern
KW  - back pain
KW  - pre-activity
KW  - drop jump
KW  - neuromuscular
KW  - trunk
KW  - performance
KW  - young athletes
Y1  - 2017
U6  - https://doi.org/10.3389/fphys.2017.00274
SN  - 1664-042X
VL  - 8
SP  - 124
EP  - 132
PB  - Frontiers Research Foundation
CY  - Lausanne
ER  - 
TY  - JOUR
A1  - Müller, Juliane
A1  - Müller, Steffen
A1  - Stoll, Josefine
A1  - Baur, Heiner
A1  - Mayer, Frank
T1  - Trunk extensor and flexor strength capacity in healthy young elite athletes aged 11-15 Years
JF  - Journal of strength and conditioning research : the research journal of the NSCA
N2  - Mueller, J, Mueller, S, Stoll, J, Baur, H, and Mayer, F. Trunk extensor and flexor strength capacity in healthy young elite athletes aged 11-15 years. J Strength Cond Res 28(5): 1328-1334, 2014-Differences in trunk strength capacity because of gender and sports are well documented in adults. In contrast, data concerning young athletes are sparse. The purpose of this study was to assess the maximum trunk strength of adolescent athletes and to investigate differences between genders and age groups. A total of 520 young athletes were recruited. Finally, 377 (n = 233/144 M/F; 13 +/- 1 years; 1.62 +/- 0.11 m height; 51 +/- 12 kg mass; training: 4.5 +/- 2.6 years; training sessions/week: 4.3 +/- 3.0; various sports) young athletes were included in the final data analysis. Furthermore, 5 age groups were differentiated (age groups: 11, 12, 13, 14, and 15 years; n = 90, 150, 42, 43, and 52, respectively). Maximum strength of trunk flexors (Flex) and extensors (Ext) was assessed in all subjects during isokinetic concentric measurements (60 degrees center dot s(-1); 5 repetitions; range of motion: 55 degrees). Maximum strength was characterized by absolute peak torque (Flex(abs), Ext(abs); N center dot m), peak torque normalized to body weight (Flex(norm), Ext(norm); N center dot m center dot kg(-1) BW), and Flex(abs)/Ext(abs) ratio (RKquot). Descriptive data analysis (mean +/- SD) was completed, followed by analysis of variance (alpha = 0.05; post hoc test [Tukey-Kramer]). Mean maximum strength for all athletes was 97 +/- 34 N center dot m in Flex(abs) and 140 +/- 50 N center dot m in Ext(abs) (Flex(norm) = 1.9 +/- 0.3 N center dot m center dot kg(-1) BW, Ext(norm) = 2.8 +/- 0.6 N center dot m center dot kg(-1) BW). Males showed statistically significant higher absolute and normalized values compared with females (p < 0.001). Flex(abs) and Ext(abs) rose with increasing age almost 2-fold for males and females (Flex(abs), Ext(abs): p < 0.001). Flex(norm) and Ext(norm) increased with age for males (p < 0.001), however, not for females (Flex(norm): p = 0.26; Ext(norm): p = 0.20). RKquot (mean +/- SD: 0.71 +/- 0.16) did not reveal any differences regarding age (p = 0.87) or gender (p = 0.43). In adolescent athletes, maximum trunk strength must be discussed in a gender- and age-specific context. The Flex(abs)/Ext(abs) ratio revealed extensor dominance, which seems to be independent of age and gender. The values assessed may serve as a basis to evaluate and discuss trunk strength in athletes.
KW  - core
KW  - adolescents
KW  - isokinetic
KW  - strength performance
Y1  - 2014
U6  - https://doi.org/10.1519/JSC.0000000000000280
SN  - 1064-8011
SN  - 1533-4287
VL  - 28
IS  - 5
SP  - 1328
EP  - 1334
PB  - Lippincott Williams & Wilkins
CY  - Philadelphia
ER  - 
TY  - JOUR
A1  - Martinez-Valdes, Eduardo Andrés
A1  - Negro, F.
A1  - Laine, C. M.
A1  - Falla, D.
A1  - Mayer, Frank
A1  - Farina, Dario
T1  - Tracking motor units longitudinally across experimental sessions with high-density surface electromyography
JF  - The Journal of Physiology
N2  - A new method is proposed for tracking individual motor units (MUs) across multiple experimental sessions on different days. The technique is based on a novel decomposition approach for high-density surface electromyography and was tested with two experimental studies for reliability and sensitivity. Experiment I (reliability): ten participants performed isometric knee extensions at 10, 30, 50 and 70% of their maximum voluntary contraction (MVC) force in three sessions, each separated by 1 week. Experiment II (sensitivity): seven participants performed 2 weeks of endurance training (cycling) and were tested pre-post intervention during isometric knee extensions at 10 and 30% MVC. The reliability (Experiment I) and sensitivity (Experiment II) of the measured MU properties were compared for the MUs tracked across sessions, with respect to all MUs identified in each session. In Experiment I, on average 38.3% and 40.1% of the identified MUs could be tracked across two sessions (1 and 2 weeks apart), for the vastus medialis and vastus lateralis, respectively. Moreover, the properties of the tracked MUs were more reliable across sessions than those of the full set of identified MUs (intra-class correlation coefficients ranged between 0.63-0.99 and 0.39-0.95, respectively). In Experiment II, similar to 40% of the MUs could be tracked before and after the training intervention and training-induced changes in MU conduction velocity had an effect size of 2.1 (tracked MUs) and 1.5 (group of all identified motor units). These results show the possibility of monitoring MU properties longitudinally to document the effect of interventions or the progression of neuromuscular disorders.
Y1  - 2016
U6  - https://doi.org/10.1113/JP273662
SN  - 0022-3751
SN  - 1469-7793
VL  - 595
SP  - 1479
EP  - 1496
PB  - Wiley
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Quarmby, Andrew James
A1  - Khajooei, Mina
A1  - Engel, Tilman
A1  - Kaplick, Hannes
A1  - Mayer, Frank
T1  - The feasibility of a split-belt instrumented treadmill running protocol with perturbations
JF  - Journal of biomechanics
N2  - Unexpected perturbations during locomotion can occur during daily life or sports performance. Adequate compensation for such perturbations is crucial in maintaining effective postural control. Studies utilising instrumented treadmills have previously validated perturbed walking protocols, however responses to perturbed running protocols remain less investigated. Therefore, the purpose of this study was to investigate the feasibility of a new instrumented treadmill-perturbed running protocol. <br /> Fifteen participants (age = 2 8 +/- 3 years; height = 172 +/- 9 cm; weight = 69 +/- 10 kg; 60% female) completed an 8-minute running protocol at baseline velocity of 2.5 m/s (9 km/h), whilst 15 one-sided belt perturbations were applied (pre-set perturbation characteristics: 150 ms delay (post-heel contact); 2.0 m/s amplitude; 100 ms duration). Perturbation characteristics and EMG responses were recorded. Bland-Altman analysis (BLA) was employed (bias +/- limits of agreement (LOA; bias +/- 1.96*SD)) and intra-individual variability of repeated perturbations was assessed via Coefficients of Variation (CV) (mean +/- SD). <br /> On average, 9.4 +/- 2.2 of 15 intended perturbations were successful. Perturbation delay was 143 +/- 10 ms, amplitude was 1.7 +/- 0.2 m/s and duration was 69 +/- 10 ms. BLA showed -7 +/- 13 ms for delay, -0.3 +/- 0.1 m/s for amplitude and -30 +/- 10 ms for duration. CV showed variability of 19 +/- 4.5% for delay, 58 +/- 12% for amplitude and 30 +/- 7% for duration. EMG RMS amplitudes of the legs and trunk ranged from 113 +/- 25% to 332 +/- 305% when compared to unperturbed gait. This study showed that the application of sudden perturbations during running can be achieved, though with increased variability across individuals. The perturbations with the above characteristics appear to have elicited a neuromuscular response during running.
KW  - Lower-extremity perturbations
KW  - Split-belt treadmill
KW  - Running
KW  - Stumbling
KW  - EMC
Y1  - 2020
U6  - https://doi.org/10.1016/j.jbiomech.2019.109493
SN  - 0021-9290
SN  - 1873-2380
VL  - 98
PB  - Elsevier
CY  - Oxford
ER  -