TY  - JOUR
A1  - Prieske, Olaf
A1  - Mühlbauer, Thomas
A1  - Krüger, Tom
A1  - Kibele, A.
A1  - Behm, David George
A1  - Granacher, Urs
T1  - Sex-Specific effects of surface instability on drop jump and landing biomechanics
JF  - International journal of sports medicine
N2  - This study investigated sex-specific effects of surface instability on kinetics and lower extremity kinematics during drop jumping and landing. Ground reaction forces as well as knee valgus and flexion angles were tested in 14 males (age: 23 +/- 2 years) and 14 females (age: 24 +/- 3 years) when jumping and landing on stable and unstable surfaces. Jump height was found to be significantly lower (9 %, p < 0.001) when drop jumps were performed on unstable vs. stable surface. Significantly higher peak ground reaction forces were observed when jumping was performed on unstable vs. stable surfaces (5 %, p = 0.022). Regarding frontal plane kinematics during jumping and landing, knee valgus angles were higher on unstable compared to stable surfaces (1932 %, p < 0.05). Additionally, at the onset of ground contact during landings, females showed higher knee valgus angles than males (222 %, p = 0.027). Sagittal plane kinematics indicated significantly smaller knee flexion angles (6-35 %, p < 0.05) when jumping and landing on unstable vs. stable surfaces. During drop jumps and landings, women showed smaller knee flexion angles at ground contact compared to men (27-33 %, p < 0.05). These findings imply that knee motion strategies were modified by surface instability and sex during drop jumps and landings.
KW  - stretch-shortening cycle
KW  - ground reaction force
KW  - knee joint angle
KW  - injury risk
Y1  - 2015
U6  - https://doi.org/10.1055/s-0034-1384549
SN  - 0172-4622
SN  - 1439-3964
VL  - 36
IS  - 1
SP  - 75
EP  - 81
PB  - Thieme
CY  - Stuttgart
ER  - 
TY  - JOUR
A1  - Meyer, Ursina
A1  - Ernst, Dominique
A1  - Schott, Silvia
A1  - Riera, Claudia
A1  - Hattendorf, Jan
A1  - Romkes, Jacqueline
A1  - Granacher, Urs
A1  - Göpfert, Beat
A1  - Kriemler, Susi
T1  - Validation of two accelerometers to determine mechanical loading of physical activities in children
JF  - Journal of sports sciences
N2  - The purpose of this study was to assess the validity of accelerometers using force plates (i.e., ground reaction force (GRF)) during the performance of different tasks of daily physical activity in children. Thirteen children (10.1 (range 5.4-15.7)years, 3 girls) wore two accelerometers (ActiGraph GT3X+ (ACT), GENEA (GEN)) at the hip that provide raw acceleration signals at 100Hz. Participants completed different tasks (walking, jogging, running, landings from boxes of different height, rope skipping, dancing) on a force plate. GRF was collected for one step per trial (10 trials) for ambulatory movements and for all landings (10 trials), rope skips and dance procedures. Accelerometer outputs as peak loading (g) per activity were averaged. ANOVA, correlation analyses and Bland-Altman plots were computed to determine validity of accelerometers using GRF. There was a main effect of task with increasing acceleration values in tasks with increasing locomotion speed and landing height (P<0.001). Data from ACT and GEN correlated with GRF (r=0.90 and 0.89, respectively) and between each other (r=0.98), but both accelerometers consistently overestimated GRF. The new generation of accelerometer models that allow raw signal detection are reasonably accurate to measure impact loading of bone in children, although they systematically overestimate GRF.
KW  - bone
KW  - impact loading
KW  - children
KW  - physical activity
KW  - ground reaction force
Y1  - 2015
U6  - https://doi.org/10.1080/02640414.2015.1004638
SN  - 0264-0414
SN  - 1466-447X
VL  - 33
IS  - 16
SP  - 1702
EP  - 1709
PB  - Routledge, Taylor & Francis Group
CY  - Abingdon
ER  -