Background. It has been proposed that muscle architecture can be associated with sprint performance and the risk of sustaining a muscle injury. During puberty, sprint performance as well as muscle injury risk increases in young soccer players. In this study, we investigated the changes in m. biceps femoris long head (BFlh) cross-sectional area (ACSA), fascicle length (FL) and pennation angle (PA) and sprint performance as well as their relationship in under 13 to 15 youth soccer players. Methods. In total, we measured 85 youth soccer players in under 13 (n=29, age=12.5 y (SD=0.1), height=155.3 cm (6.2), weight=43.9 kg (7.6)), under 14 (n=25, age=13.5 y (0.3), height=160.6 y (7.7), weight=47.0 kg (6.8)) and under 15 (n=31, age=14.4 y (0.3) , height=170.0 cm (7.7), weight=58.1 kg (8.8) ) teams of three high level soccer clubs. We used ultrasound to measure BFlh ACSA, FL and PA. We performed sprint tests to assess 10m and 30m sprint time, maximal velocity (vmax) and maximal acceleration (amax). We calculated Pearson’s r and 95% compatibility intervals to assess the relationship between sprint ability, maturity ratio, chronological age and architectural parameters. In addition, we calculated the best set of predictors for sprint ability using multiple regression models.Results. All muscle architectural parameters increased from the under 13 to the under 15 age group (BFlh ACSA: 37%, BFlh FL: 11%, BFlh PA: 8%). All sprint performance parameters improved from the under 13 to under 15 age categories (30m time: 7%, 10m time: 4%, vmax: 9%, amax: 7%). BFlh ACSA was correlated with 30m sprint time (r = -0.61 (95% CI = -0.73, -0.45)) and vmax (r= 0.61 (0.45, 0.72)). The correlation for maturity ratio with assessed parameters were larger compared to the correlation for chronological age. A combination of BFlh ACSA, FL, chronological age and height best predicted sprint parameters. Discussion. Parallel to improvements in sprint performance, muscle architectural parame-ters increase from the under 13 to under 15 age groups. BFlh ACSA seems to be related to sprint performance in youth soccer players. BFlh ACSA and chronological age are the main predictors of most sprint parameters.

Background. In addition to generally high levels of physical activity, multi-component exercise training is recommended for the maintenance of health and fitness in older adults, including the prevention of falls and frailty. This training often encompasses serial sequencing of balance, strength, endurance and other types of exercise. Exercise training featuring integrative training of these components (i.e. agility training) has been proposed, as it more likely reflects real life challenges like stop-and-go patterns, cutting manoeuvers, turns and decision-making. In this study, we compared the efficacy of an agility-based training to the traditional strength and balance training approach with regard to selected risk factors for falls and frailty.Methods. We trained twenty-seven community-dwelling healthy seniors (16♂; 11♀; age: 69.5 ± 5.3 y; BMI: 26.4 ± 3.7 kg/m2) for 8 weeks in a group setting with 3 sessions per week, each lasting 50 minutes. Participants were randomized into either the agility group (AGI; n=12), that used the integrative multi-component training, or the traditional strength and balance group (TSB; n=15). TSB performed balance and strength exercises separately, albeit within the same session. The training of both groups progressively increased in difficulty. Outcomes were static and dynamic balance (single leg eyes open stand, Y-balance test, reactive balance), lower limb (plantar flexion and dorsal extension) and trunk flexion and extension maximum strength and rate of torque development (RTD). In addition, we tested endurance by the six-minute walk test (6MWT). We calculated linear mixed effects models for between-groups comparisons as well as effect sizes (ES) with 95 % confidence intervals. Results. Small ES in favor of AGI were found for plantar flexion strength (ES>0.18[-0.27;0.89]) and RTD (ES>0.43[-0.19;1.36]) as well as trunk extension RTD (ES=0.35[-0.05;0.75]). No other parameters showed notable between group differences. Compliance was high in both groups (AGI: 90 ± 8 % of sessions; TSB: 91 ± 7 % of sessions).Discussion. Agility-based exercise training seems at least as efficacious as traditional strength and balance training in affecting selected fall risk factors among community-dwelling healthy seniors. Especially lower limb and trunk extension explosive strength seem to benefit from the agility training.

We evaluated the structure (i.e., the different training parts), contents (i.e., the various activities used), intensity and occurrence of contact situations and headers during training sessions in under-13 football in Switzerland. 242 players from 20 different teams on average aged 11.4 (SD 0.7) years participated. The participants were filmed during a typical training session while they were equipped with a heart rate sensor. The sessions were systematically recorded to allow for detailed analyses. Furthermore, a preliminary and explorative analysis of the influence of the level of play on these results was conducted. The overall findings indicated that training included 33.4% playing forms, 29.5% training forms, 28.4% inactivity time and 8.7% athletics. The highest heart rates were achieved in the playing forms (166 min-1, 83% HRmax) compared to the other two activities (training forms 154 min-1, 77% HRmax; athletics 150 min-1, 75% HRmax). Each player had 12.8 duels and 0.6 headers per training. Overall most duels were conducted from anterior direction. Playing forms induce higher cardio-circulatory load as well as a better learning environment. Potentially dangerous situations like contact with other players or headers occurred in a single player on average every 6 minutes during a training session.