Rocco Di Michele

Comparison of Physiological Responses to an Incremental Running Test on Treadmill, Natural Grass, and Synthetic Turf in Young Soccer Players

Di Michele, R, Di Renzo, AM, Ammazzalorso, S, and Merni, F. Comparison of physiological responses to an incremental running test on treadmill, natural grass, and synthetic turf in young soccer players. J Strength Cond Res 23(3): 939-945, 2009-This study aimed to compare the physiological responses to a running test often used to assess lactate thresholds in soccer players when performed with an identical protocol on treadmill (Tr), natural grass (Nat), and synthetic turf (Synt). Eighteen young soccer players (mean ± SD: age, 17.4 ± 0.8 years; body mass, 66.2 ± 6.7 kg; height, 175.8 ± 5.7 cm) performed on each surface a multistage running test, including 4-minutes stages separated by a 1-minute rest, with initial speed set at 8 km·h−1 and increased of 2 km·h−1 after each stage. Blood lactate concentration (La) and heart rate (HR) were assessed. The test ended when La exceeded 4 mmol·L−1. At each of the stages completed in the three conditions by all the subjects (8, 10, 12, and 14 km·h−1), La was higher in Synt vs. both Nat and Tr with differences of at least 0.6 mmol·L−1 (p < 0.05), whereas HR was higher (p < 0.05) in Synt vs. Nat with differences from 4.3 b·min−1 (at 10 km·h−1) to 6.4 b·min−1 (at 8 km·h−1). Running speed at the 4 mmol·L−1 La threshold was lower (p < 0.05) in Synt (13.1 ± 1.1 km·h−1) than in Nat (13.9 ± 1.2 km·h−1) and Tr (14.4 ± 1.3 km·h−1). The La/HR curve obtained in Synt was shifted upward compared with the Nat and Tr curves, indicating higher La values at given HRs. These results could be mostly explained by adaptations of running mechanical patterns to surface properties that affect the energy requirements of running. This study emphasized the importance of testing soccer players on the specific surface used for training activities when assessing lactate threshold indices to prescribe and monitor field training.

Seasonal Training-Load Quantification in Elite English Premier League Soccer Players

PURPOSE To quantify the seasonal training load completed by professional soccer players of the English Premier League. METHODS Thirty players were sampled (using GPS, heart rate, and rating of perceived exertion [RPE]) during the daily training sessions of the 2011-12 preseason and in-season period. Preseason data were analyzed across 6×1-wk microcycles. In-season data were analyzed across 6×6-wk mesocycle blocks and 3×1-wk microcycles at start, midpoint, and end-time points. Data were also analyzed with respect to number of days before a match. RESULTS Typical daily training load (ie, total distance, high-speed distance, percent maximal heart rate [%HRmax], RPE load) did not differ during each week of the preseason phase. However, daily total distance covered was 1304 (95% CI 434-2174) m greater in the 1st mesocycle than in the 6th. %HRmax values were also greater (3.3%, 1.3-5.4%) in the 3rd mesocycle than in the first. Furthermore, training load was lower on the day before match (MD-1) than 2 (MD-2) to 5 (MD-5) d before a match, although no difference was apparent between these latter time points. CONCLUSIONS The authors provide the 1st report of seasonal training load in elite soccer players and observed that periodization of training load was typically confined to MD-1 (regardless of mesocycle), whereas no differences were apparent during MD-2 to MD-5. Future studies should evaluate whether this loading and periodization are facilitative of optimal training adaptations and match-day performance.

A notational analysis of shot characteristics in top-level table tennis players

Abstract This study aimed to analyse selected shot characteristics in top-level table tennis matches, with a special focus on comparing the playing style of Asian and European players. Ten mens matches played by 20 top-ranked players (14 Asians and 6 Europeans) were analysed. The indicators examined were the area of ball bouncing for serves (n =918), and the stroke type, footwork type and shot outcome for other shots (n=3692). The interrelationships between variables were analysed using chi-squared tests, log-linear modelling and multiple correspondence analysis. A strong association was found between strokes and footwork types, with most stroke types executed each after specific footwork types. Furthermore, a clear tendency to have a positive, negative or neutral outcome was observed for each stroke type. When compared to Europeans, Asians used more frequently the most aggressive strokes and footwork types, confirming anecdotal claims on their particularly offensive playing style. Asians showed also a better serving effectiveness, often sending the ball in those areas of the table from which a counterattack is difficult to make. In summary, this study gives a systematic description of highly relevant technical and tactical characteristics in top-level table tennis, thus providing valuable information for coaches and performance analysts.

The concurrent effects of strike pattern and ground-contact time on running economy

OBJECTIVES Running economy is a key determinant of endurance performance, and understanding the biomechanical factors that affect it is of great theoretical and applied interest. This study aimed to analyse how the ground-contact time and strike pattern used by competitive runners concurrently affect running economy. DESIGN Cross-sectional. METHODS Fourteen sub-elite male competitive distance runners completed a 6-min submaximal running trial at 14kmh(-1) on an outdoor track using their habitual strike pattern (n=7 rearfoot strikers: average age, 25.3 years old (SD=2.4); average weight, 64.7kg (SD=5.6); average height, 175.3cm (SD=5.2); n=7 midfoot strikers: average age, 25.0 years old (SD=2.8); average weight, 69.6kg (SD=4.0); average height, 180.1cm (SD=5.1). During the run, the oxygen uptake and ground-contact time were measured. RESULTS Midfoot strikers showed a significantly shorter (p=0.015) mean contact time (0.228s (SD=0.009)) compared with rearfoot strikers (0.242s (SD=0.010)). Conversely, there was no significant difference (p>0.05) between the groups with respect to mean oxygen uptake (midfoot strikers: 48.4mlmin(-1)kg(-1) (SD=5.3); rearfoot strikers: 49.8mlmin(-1)kg(-1) (SD=6.4)). Linear modelling analysis showed that the effect of contact time on running economy was very similar in the two groups, with a 1ms longer contact time involving an approximately 0.51mlmin(-1)kg(-1) lower oxygen uptake. In contrast, when controlling for contact time, midfoot striking involved an approximately 8.7mlmin(-1)kg(-1) lower oxygen uptake compared with rearfoot striking. CONCLUSIONS When adjusting the foot-ground contact biomechanics of a runner with the aim of maximising running economy, a trade-off between a midfoot strike and a long contact time must be pursued.

Kinematic analysis of the braking and propulsion phases during the support time in sprint running

The contact time (CT) and the ratio between the duration of braking (BP) and propulsion phase (PP) during the support are two mechanical parameters that are relevant for the performance in sprinting. Several different kinematic methods have been used to estimate the BP-PP transition point, with some disagreements among studies. The purpose of this study was to compare three criteria to individuate that point: the maximum knee flexion (KNEEFLEX), the maximum fall of the COM (COMVERT) and the horizontal COM acceleration (COMHORIZ). It was hypothesized that these three events would take place in different instants, representing different moments of the step cycle. The kinematic analysis was performed through stereophotogrammetry on seven male middle-level sprinters (mean + or - SD height: 180 + or - 5 cm; body mass: 75 + or - 11 kg; personal best on 100 m: 10.96 + or - 0.45 s). The COMVERT expressed as percentage of CT (mean + or - SD 31.73 + or - 8.29%) was on average strongly anticipated compared to both KNEEFLEX (45.07 + or -3.60%, p < 0.01) and COMHORIZ (56.86 + or - 8.56%, p < 0.01). The approximately 12% difference between KNEEFLEX and COMHORIZ was also statistically significant (p < 0.01). The 40-60% relative proportion of BP and PP considered to be optimal in the literature, was reflected in this study only by the KNEEFLEX criterion. Given the importance of BP time as a reference parameter to assess the training status and efficacy of training interventions, it looks necessary both from a scientific and applied perspective to consider a standardized criterion to identify the BP-PP transition point.

Quantification of training load during one-, two- and three-game week schedules in professional soccer players from the English Premier League: implications for carbohydrate periodisation

ABSTRACT Muscle glycogen is the predominant energy source for soccer match play, though its importance for soccer training (where lower loads are observed) is not well known. In an attempt to better inform carbohydrate (CHO) guidelines, we quantified training load in English Premier League soccer players (n = 12) during a one-, two- and three-game week schedule (weekly training frequency was four, four and two, respectively). In a one-game week, training load was progressively reduced (P < 0.05) in 3 days prior to match day (total distance = 5223 ± 406, 3097 ± 149 and 2912 ± 192 m for day 1, 2 and 3, respectively). Whilst daily training load and periodisation was similar in the one- and two-game weeks, total accumulative distance (inclusive of both match and training load) was higher in a two-game week (32.5 ± 4.1 km) versus one-game week (25.9 ± 2 km). In contrast, daily training total distance was lower in the three-game week (2422 ± 251 m) versus the one- and two-game weeks, though accumulative weekly distance was highest in this week (35.5 ± 2.4 km) and more time (P < 0.05) was spent in speed zones >14.4 km · h−1 (14%, 18% and 23% in the one-, two- and three-game weeks, respectively). Considering that high CHO availability improves physical match performance but high CHO availability attenuates molecular pathways regulating training adaptation (especially considering the low daily customary loads reported here, e.g., 3–5 km per day), we suggest daily CHO intake should be periodised according to weekly training and match schedules.

Power production of the lower limbs in flutter-kick swimming

This study aimed to compare the power produced by the flutter-kick action at different swimming velocities. Eighteen high-level male swimmers completed a maximal 15-m flutter-kicking sprint and underwent two tests (one passive and one with maximal flutter-kicking) in which they were towed at six velocities ranging from 1.0 to 2.0 m/s. Power values were computed for each velocity, and selected kinematic indices were evaluated at 1.2 and 2.0 m/s. The highest power (54 ± 8 W) was observed at the velocity at which the drag equaled the propulsive force (1.27 ± 0.08 m/s), which was similar to that recorded in the flutter-kicking sprint (1.26 ± 0.09 m/s). Thereafter, power decreased significantly with increasing velocity, up to 17 ± 10 W (at 2.0 m/s). The angle between the horizontal and the line connecting the highest and lowest points of the malleolus trajectory was significantly wider at 1.2 m/s than at 2.0 m/s (75 ± 4° vs. 63 ± 6°). This could explain the change of power with velocity because all the other kinematic indices considered were similar at the two velocities. These results suggest that the propulsive role of the flutter-kick increases as the swimming velocity decreases.

Assessment of three-dimensional joint kinematics of the upper limb during simulated swimming using wearable inertial-magnetic measurement units

ABSTRACT The analysis of the joint kinematics during swimming plays a fundamental role both in sports conditioning and in clinical contexts. Contrary to the traditional video analysis, wearable inertial-magnetic measurements units (IMMUs) allow to analyse both the underwater and aerial phases of the swimming stroke over the whole length of the swimming pool. Furthermore, the rapid calibration and short data processing required by IMMUs provide coaches and athletes with an immediate feedback on swimming kinematics during training. This study aimed to develop a protocol to assess the three-dimensional kinematics of the upper limbs during swimming using IMMUs. Kinematics were evaluated during simulated dry-land swimming trials performed in the laboratory by eight swimmers. A stereo-photogrammetric system was used as the gold standard. The results showed high coefficient of multiple correlation (CMC) values, with median (first–third quartile) of 0.97 (0.93–0.95) and 0.99 (0.97–0.99) for simulated front-crawl and breaststroke, respectively. Furthermore, the joint angles were estimated with an accuracy increasing from distal to proximal joints, with wrist indices showing median CMC values always higher than 0.90. The present findings represent an important step towards the practical use of technology based on IMMUs for the kinematic analysis of swimming in applied contexts.

Energy Intake and Expenditure of Professional Soccer Players of the English Premier League: Evidence of Carbohydrate Periodization

In an attempt to better identify and inform the energy requirements of elite soccer players, we quantified the energy expenditure (EE) of players from the English Premier League (n = 6) via the doubly labeled water method (DLW) over a 7-day in-season period. Energy intake (EI) was also assessed using food diaries, supported by the remote food photographic method and 24 hr recalls. The 7-day period consisted of 5 training days (TD) and 2 match days (MD). Although mean daily EI (3186 ± 367 kcals) was not different from (p > .05) daily EE (3566 ± 585 kcals), EI was greater (p < .05) on MD (3789 ± 532 kcal; 61.1 ± 11.4 kcal.kg-1 LBM) compared with TD (2956 ± 374 kcal; 45.2 ± 9.3 kcal.kg-1 LBM, respectively). Differences in EI were reflective of greater (p < .05) daily CHO intake on MD (6.4 ± 2.2 g.kg-1) compared with TD (4.2 ± 1.4 g.kg-1). Exogenous CHO intake was also different (p < .01) during training sessions (3.1 ± 4.4 g.h-1) versus matches (32.3 ± 21.9 g.h-1). In contrast, daily protein (205 ± 30 g.kg-1, p = .29) and fat intake (101 ± 20 g, p = .16) did not display any evidence of daily periodization as opposed to g.kg-1, Although players readily achieve current guidelines for daily protein and fat intake, data suggest that CHO intake on the day before and in recovery from match play was not in accordance with guidelines to promote muscle glycogen storage.

Assessment of handedness using latent class factor analysis

Recently several studies in which handedness was evaluated as a latent construct have been performed. In those studies, handedness was modelled using a qualitative latent variable (latent class models), a continuous latent variable (factor models), or both a qualitative latent variable and a continuous latent trait (mixed Rasch models). The aim of this study was to explore the usefulness and effectiveness of an approach in which handedness is treated as a qualitatively scaled latent variable with ordered categories (latent class factor models). This aim was pursued through an exploratory analysis of a dataset containing information on the hand used by 2236 young Italian sportspeople to perform 10 tasks. For comparison purposes, a latent class analysis was carried out. A cross-validation procedure was implemented. The results of all the analyses revealed that the best fit to the observed handedness patterns was obtained using a latent class factor model. Through this model, individuals were assigned to one of four ordered levels of handedness, and a quantitative index of left-handedness for each individual was computed by taking into account the different effect of the 10 tasks. These results provide support for the use of the latent class factor approach for handedness assessment.