TY  - JOUR
A1  - Prieske, Olaf
A1  - Demps, Marie
A1  - Lesinski, Melanie
A1  - Granacher, Urs
T1  - Combined Effects of Fatigue and Surface Instability on Jump Biomechanics in Elite Athletes
JF  - International journal of sports medicine
N2  - The present study aimed to examine the effects of fatigue and surface instability on kinetic and kinematic jump performance measures. Ten female and 10 male elite volleyball players (18 +/- 2 years) performed repetitive vertical double-leg box jumps until failure. Pre and post fatigue, jump height/performance index, ground reaction force and knee flexion/valgus angles were assessed during drop and countermovement jumps on stable and unstable surfaces. Fatigue, surface condition, and sex resulted in significantly lower drop jump performance and ground reaction force (p0.031, 1.1d3.5). Additionally, drop jump knee flexion angles were significantly lower following fatigue (p=0.006, d=1.5). A significant fatiguexsurfacexsex interaction (p=0.020, d=1.2) revealed fatigue-related decrements in drop jump peak knee flexion angles under unstable conditions and in men only. Knee valgus angles were higher on unstable compared to stable surfaces during drop jumps and in females compared to males during drop and countermovement jumps (p0.054, 1.0d1.1). Significant surfacexsex interactions during countermovement jumps (p=0.002, d=1.9) indicated that knee valgus angles at onset of ground contact were significantly lower on unstable compared to stable surfaces in males but higher in females. Our findings revealed that fatigue and surface instability resulted in sex-specific knee motion strategies during jumping in elite volleyball players.
KW  - stretch-shortening cycle
KW  - knee joint angle
KW  - exhaustion
KW  - injury risk
KW  - gender
Y1  - 2017
U6  - https://doi.org/10.1055/s-0043-111894
SN  - 0172-4622
SN  - 1439-3964
VL  - 38
SP  - 781
EP  - 790
PB  - Thieme
CY  - Stuttgart
ER  - 
TY  - JOUR
A1  - Negra, Yassine
A1  - Chaabene, Helmi
A1  - Sammoud, Senda
A1  - Bouguezzi, Raja
A1  - Mkaouer, Bessem
A1  - Hachana, Younes
A1  - Granacher, Urs
T1  - EFFECTS OF PLYOMETRIC TRAINING ON COMPONENTS OF PHYSICAL FITNESS IN PREPUBERAL MALE SOCCER ATHLETES: THE ROLE OF SURFACE INSTABILITY
JF  - Journal of strength and conditioning research : the research journal of the NSCA
N2  - Previous studies contrasted the effects of plyometric training (PT) conducted on stable vs. unstable surfaces on components of physical fitness in child and adolescent soccer players. Depending on the training modality (stable vs. unstable), specific performance improvements were found for jump (stable PT) and balance performances (unstable PT). In an attempt to combine the effects of both training modalities, this study examined the effects of PT on stable surfaces compared with combined PT on stable and unstable surfaces on components of physical fitness in prepuberal male soccer athletes. Thirty-three boys were randomly assigned to either a PT on stable surfaces (PTS; n = 17; age = 12.1 +/- 0.5 years; height = 151.6 +/- 5.7 cm; body mass = 39.2 +/- 6.5 kg; and maturity offset = 22.3 +/- 0.5 years) or a combined PT on stable and unstable surfaces (PTC; n = 16; age = 12.2 +/- 0.6 years; height = 154.6 +/- 8.1 cm; body mass = 38.7 +/- 5.0 kg; and maturity offset = 22.2 +/- 0.6 years). Both intervention groups conducted 4 soccer-specific training sessions per week combined with either 2 PTS or PTC sessions. Before and after 8 weeks of training, proxies of muscle power (e.g., countermovement jump [CMJ], standing long jump [SLJ]), muscle strength (e.g., reactive strength index [RSI]), speed (e.g., 20-m sprint test), agility (e.g., modified Illinois change of direction test [MICODT]), static balance (e.g., stable stork bal-ance test [SSBT]), and dynamic balance (unstable stork balance test [USBT]) were tested. An analysis of covariance model was used to test between-group differences (PTS vs. PTC) at posttest using baseline outcomes as covariates. No significant between-group differences at posttest were observed for CMJ (p > 0.05, d = 0.41), SLJ (p > 0.05, d = 0.36), RSI (p > 0.05, d = 0.57), 20-m sprint test (p > 0.05, d = 0.06), MICODT (p > 0.05, d = 0.23), and SSBT (p > 0.05, d = 0.20). However, statistically significant between-group differences at posttest were noted for the USBT (p < 0.01, d = 1.49) in favor of the PTC group. For most physical fitness tests (except RSI), significant pre-to-post improvements were observed for both groups (p < 0.01, d = 0.55-3.96). Eight weeks of PTS or PTC resulted in similar performance improvements in components of physical fitness except for dynamic balance. From a performance-enhancing perspective, PTC is recommended for pediatric strength and conditioning coaches because it produced comparable training effects as PTS on proxies of muscle power, muscle strength, speed, agility, static balance, and additional effects on dynamic balance.
KW  - youth
KW  - football
KW  - stretch-shortening cycle
KW  - athletic performance
KW  - balance
Y1  - 2017
SN  - 1064-8011
SN  - 1533-4287
VL  - 31
SP  - 3295
EP  - 3304
PB  - Lippincott Williams & Wilkins
CY  - Philadelphia
ER  -