Effects of 10-week eccentric overload training on kinetic parameters during change of direction in football players.

The aim of the current study was to analyse the effect of 10-week eccentric overload training on kinetic parameters during change of direction (COD) in U-19 football players. The outcome measured included relative peak braking (rPB) and propulsive force (rPF), contact time (CT), time spent during braking (BT) and propulsive phase (PT), relative total (rTOT_IMP), braking (rB_IMP) and propulsive (rP_IMP) impulses. Between-group results showed a substantial better improvement (likely) in CT (ES: 0.72) and BT (ES: 0.74) during side-step cutting, and in rPB (ES: 0.84) and rB_IMP (ES: 0.72) during crossover cutting, in the experimental group (EXP) in comparison to control group (CON). Within-group analysis showed a substantially better performance (likely to almost certain) in CT (ES: 1.19), BT (ES: 1.24), PT (ES: 0.70), rPB (ES: 0.75), rPF (ES: 0.68), rTOT_IMP (ES: 0.48) and rB_IMP (ES: 0.50) in EXP during side-step cutting. Regarding crossover cutting, within-group analysis showed a substantial better performance (likely to almost certain) in CT (ES: 0.75), rPB (ES: 0.75), rPF (ES: 1.34), rTOT_IMP (ES: 0.61), rB_IMP (ES: 0.76) and rP_IMP (ES: 0.46) in EXP. In conclusion, the eccentric overload-based programme led to an improvement in kinetic parameters during COD football tasks.

Influence of football match time-motion parameters on recovery time course of muscle damage and jump ability.

We analysed the time course of recovery of creatine kinase (CK) and countermovement jump (CMJ) parameters after a football match, and correlations between changes in these variables and match time-motion parameters (GPS-accelerometry) in 15 U-19 elite male players. Plasma CK and CMJ height (CMJH), average concentric force (CMJCON) and average eccentric force (CMJECC) were assessed 2 h before and 30 min, 24 h and 48 h post-match. There were substantially higher CK levels 30 min, 24 h and 48 h (ES: 0.43, 0.62, 0.40, respectively), post-match. CMJECC (ES: -0.38), CMJH (ES: -0.35) decreased 30 min post, CMJCON (ES: -0.35), CMJECC (ES: -0.35) and CMJH (ES: -1.35) decreased 24 h post, and CMJCON (ES: -0.41) and CMJH (ES: -0.53) decreased 48 h post. We found correlations between distance covered at velocities ≤21 km · h(-1) and changes in CK at 24 h (r = 0.56) and at 48 h (r = 0.54) and correlations between CK and distance covered >14 km · h(-1) (r = 0.50), accelerations (r = 0.48), and decelerations (r = 0.58) at 48 h. Changes in CMJCON 30 min and 24 h post (both r = -0.68) correlated with impacts >7.1·G. Decelerations >2 m · s(-)(2) correlated with changes CMJCON (r = -0.49) at 48 h and CMJECC (r = -0.47) at 30 min. Our results suggest that match GPS-accelerometry parameters may predict muscle damage and changes in components of neuromuscular performance immediately and 24-48 h post-match.

Analysis of the acceleration profile according to initial speed and positional role in elite professional male soccer players.

BACKGROUND: The aim of the current study was to analyze the acceleration profile in elite professional soccer players according to their initial speed but also considering players' position. METHODS: Players' accelerations profiles were analyzed using a relative acceleration profile according to the initial speed (S1, from 0 to 7 km/h; S2, from 7.1 to 14.3 km/h; and S3, ≥14.4 km/h) and the maximum acceleration. RESULTS: Within-group analyzes showed that center backs (CB) performed more high intensity accelerations (likely) when they started in S1 than S2 (effect size [ES] 0.50). Strikers (S) and wide midfielders (W-MD) achieved more accelerations (likely to almost certain) starting in S3 than S1 (ES=0.80 and ES=0.59, respectively) and S2 (ES=0.67 and ES=1.09, respectively). Full backs (FB) completed more accelerations (almost certain) starting in S1 and S3 than S2 (ES=1.39 and ES=1.36, respectively). Finally, midfielders (MD) executed a greater number of high intensity accelerations (likely to almost certain) when they started in S1 than S2 (ES=0.83) and S3 (ES=0.66), and in S3 than S2 (ES=4.72). Between-group analyzes showed that S, W-MD, and FB performed a greater total number of high intensity accelerations (very likely to almost certain) than CB (ES=1.94, ES=1.57, and ES=1.51, respectively) and MD (ES=1.23, ES=0.92; and ES=0.81, respectively). Furthermore, MD performed substantially greater total number of high intensity accelerations (likely) than CB (ES=0.56). CONCLUSIONS: Results suggest that CB achieved more high-intensity accelerations starting in low and moderate speed, S and W-MD in high speed, and FB combined low and high speed.

Is strength-training frequency a key factor to develop performance adaptations in young elite soccer players?

The aim of this study was to analyse the effects of a combined strength-training programme (full-back squat, YoYoTM leg curl, plyometrics and sled towing exercises) on performance in elite young soccer players and to examine the effects when this training programme was performed one or two days per week. Thirty-six male soccer players (U-17 to U-19) were recruited and assigned to experimental groups (EXP1: 1 s w-1; EXP2: 2 s w-1) or a control group (CON). Performance was assessed through a countermovement jump (CMJ) test (relative peak power [CMJPP] and CMJ height [CMJH]), a 20-m linear sprint test with split-times at 10-m, and a change of direction test (V-cut test) 1 week before starting the training programme and also 1 week after performing such training programme. Within-group analysis showed substantial improvements in CMJ variables (ES: 0.39-0.81) and COD (ES: 0.70 and 0.76) in EXP1 and EXP2, while EXP2 also showed substantial enhancements in all linear sprinting tests (ES: 0.43-0.52). Between-group analysis showed substantially greater improvements in CMJ variables (ES: 0.39-0.68) in experimental groups in comparison to CON. Furthermore, EXP2 achieved a substantial better performance in 20-m (ES: 0.48-0.64) than EXP1 and CON. Finally, EXP2 also showed greater enhancements in 10-m (ES: 0.50) and V-cut test (ES: 0.52) than EXP1. In conclusion, the combined strength-training programme improved jumping ability, independently of training frequency, though the achievement of two sessions per week also enhanced sprinting abilities (linear and COD) in young soccer players.

Effects of Traditional Versus Horizontal Inertial Flywheel Power Training on Common Sport-Related Tasks.

This study aimed to analyze the effects of power training using traditional vertical resistance exercises versus direction specific horizontal inertial flywheel training on performance in common sport-related tasks. Twenty-three healthy and physically active males (age: 22.29 ± 2.45 years) volunteered to participate in this study. Participants were allocated into either the traditional training (TT) group where the half squat exercise on a smith machine was applied or the horizontal flywheel training (HFT) group performing the front step exercise with an inertial flywheel. Training volume and intensity were matched between groups by repetitions (5-8 sets with 8 repetitions) and relative intensity (the load that maximized power (Pmax)) over the period of six weeks. Speed (10 m and 20 m), countermovement jump height (CMJH), 20 m change of direction ability (COD) and strength during a maximal voluntary isometric contraction (MVIC) were assessed before and after the training program. The differences between groups and by time were assessed using a two-way analysis of variance with repeated measures, followed by paired t-tests. A significant group by time interaction (p=0.004) was found in the TT group demonstrating a significantly higher CMJH. Within-group analysis revealed statistically significant improvements in a 10 m sprint (TT: -0.17 0.27 s vs. HFT: -0.11 0.10 s), CMJH (TT: 4.92 2.58 cm vs. HFT: 1.55 2.44 cm) and MVIC (TT: 62.87 79.71 N vs. HFT: 106.56 121.63 N) in both groups (p < 0.05). However, significant differences only occurred in the 20 m sprint time in the TT group (-0.04 0.12 s; p = 0.04). In conclusion, the results suggest that TT at the maximal peak power load is more effective than HFT for counter movement jump height while both TT and HFT elicited significant improvements in 10 m sprint performance while only TT significantly improved 20 m sprint performance.

Two new indexes for the assessment of autonomic balance in elite soccer players.

PURPOSE: The application of Poincaré-plot analysis to heart-rate variability (HRV) is a common method for the assessment of autonomic balance. However, results obtained from the indexes provided by this analysis tend to be difficult to interpret. In this study the authors aimed to prove the usefulness of 2 new indexes: the stress score (SS) and the sympathetic:parasympathetic ratio (S:PS ratio). METHODS: 25 professional Spanish soccer players from same team underwent 330 resting measurements of HRV. All subjects experienced 10 min of HRV monitoring through an R-R-interval recorder. The following parameters were calculated: (1) Poincaré-plot indexes: SD1 (transverse axis), which is proportional to parasympathetic activity; SD2 (longitudinal axis), which is inversely proportional to sympathetic activity; and the SD1:SD2 ratio; (2) time-domain parameters: standard deviation of R-R intervals (SDNN), root-mean-square differences of successive heartbeat intervals (rMSSD), and percentage of successive R-R-interval pairs differing in more than 50 ms in the entire recording divided by the total number of R-R intervals (pNN50); and (3) the proposed 2 new indexes: the SS and the S:PS ratio. RESULTS: The study found a high negative correlation between the SS and SDNN (R2=.94). The S:PS ratio correlated inversely to rMSSD (R2=.95), SDNN (R2=.94), and pNN50 (R2=.74). The S:PS ratio showed a strong correlation with SD1 (R2=.95) and SS (r=.87, R2=.88). CONCLUSIONS: The application of the SS as sympathetic-activity index and the S:PS ratio as a representation of autonomic balance (SS:SD1) provides a better understanding of the Poincaré-plot method in HRV.

Effects of a 10-week in-season eccentric-overload training program on muscle-injury prevention and performance in junior elite soccer players.

PURPOSE: To analyze the effect of an eccentric-overload training program (ie, half-squat and leg-curl exercises using flywheel ergometers) with individualized load on muscle-injury incidence and severity and performance in junior elite soccer players. METHODS: Thirty-six young players (U-17 to U-19) were recruited and assigned to an experimental (EXP) or control group (CON). The training program consisted of 1 or 2 sessions/wk (3-6 sets with 6 repetitions) during 10 wk. The outcome measured included muscle injury (incidence per 1000 h of exposure and injury severity) and performance tests (countermovement jump [CMJ], 10-m and 20-m sprint test). RESULTS: Between-groups results showed a likely (ES: 0.94) lower number of days of absence per injury and a possible decrement of incidence per 1000 h of match play in EXP than in CON. Regarding muscle performance, a substantial better improvement (likely to very likely) was found in 20-m sprint time (ES: 0.37), 10-m flying-sprint time (ES: 0.77), and CMJ (ES: 0.79) for EXP than for CON. Within-group analysis showed an unclear effect in each variable in CON. Conversely, substantial improvements were obtained in CMJ (ES: 0.58), 20-m sprint time (ES: 0.32), 10-m flying-sprint time (ES: 0.95), and injury severity (ES: 0.59) in EXP. Furthermore, a possible decrement in total injury incidence was also reported in EXP. CONCLUSIONS: The eccentric-based program led to a reduction in muscle-injury incidence and severity and showed improvements in common soccer tasks such as jumping ability and linear-sprinting speed.