Jg Morris

The validity of a non-differential global positioning system for assessing player movement patterns in field hockey.

Abstract Nine games players (mean age 23.3 years, s = 2.8; height 1.73 m, s = 0.08; body mass 70.0 kg, s = 12.7) completed 14 laps of a measured circuit that incorporated intermittent running and directional changes, representative of the movements made by field hockey players during match-play. The distances and speeds recorded by a global positioning satellite (GPS) system (Spi Elite™) were compared statistically with speed measurements made using timing gates and distances measured using a calibrated trundle wheel, to establish the criterion validity of the GPS system. A validation of the speed of movement of each participant separately was also made, using data from each timing gate, over a range of speeds. The mean distance recorded by the GPS system was 6821 m (s = 7) and the mean speed was 7.0 km · h−1 (s = 1.9), compared with the actual distance of 6818 m and recorded mean speed of 7.0 km · h−1 (s = 1.9). Pearson correlations (r) among timing gate speed and GPS speed were ≥0.99 (P < 0.001) and the mean difference and 95% limits of agreement were 0.0 ± 0.9 km · h−1. These results suggest that a GPS system (Spi Elite™) offers a valid tool for measuring speed and distance during match-play, and can quickly provide the scientist, coach, and player with objective information about certain movement patterns during competitive games.

Effect of repeated sprints on postprandial endothelial function and triacylglycerol concentrations in adolescent boys

Abstract This study investigated whether repeated, very short duration sprints influenced endothelial function (indicated by flow-mediated dilation) and triacylglycerol concentrations following the ingestion of high-fat meals in adolescent boys. Nine adolescent boys completed two, 2-day main trials (control and exercise), in a counter-balanced, cross-over design. Participants were inactive on day 1 of the control trial but completed 40 × 6 s maximal cycle sprints on day 1 of the exercise trial. On day 2, capillary blood samples were collected and flow-mediated dilation measured prior to, and following, ingestion of a high-fat breakfast and lunch. Fasting flow-mediated dilation and plasma triacylglycerol concentration were similar in the control and exercise trial (P > 0.05). In the control trial, flow-mediated dilation was reduced by 20% and 27% following the high-fat breakfast and lunch; following exercise these reductions were negated (main effect trial, P < 0.05; interaction effect trial × time, P < 0.05). The total area under the plasma triacylglycerol concentration versus time curve was 13% lower on day 2 in the exercise trial compared to the control trial (8.65 (0.97) vs. 9.92 (1.16) mmol · l−1 · 6.5 h, P < 0.05). These results demonstrate that repeated 6 s maximal cycle sprints can have beneficial effects on postprandial endothelial function and triacylglycerol concentrations in adolescent boys.

Motion analysis of U11 to U16 elite English Premier League Academy players

Abstract This study examined (1) the distances and speeds covered during match play for U11 to U16 English Premier League Academy players, (2) the differences in match performance between retained and released players and (3) the effect of calculating speed zones in different ways when analysing match performance. Eighty-one academy outfield players (10–16 years old), competing in 11-a-side matches, were analysed using a 1-Hz global positioning system with three speed zones (absolute, squad and individual). Pitch dimensions were 78.7 × 54.1 m (U11 and U12), 88.0 × 64.2 m (U13) and 100.8 × 68.2 m (U14–U16). Match durations were 20 min × 2 + 15 min × 2 or 25 min × 3 (U11), 25 min × 3 (U12 and U13) and 40 min × 2 (U14–U16). The matches were part of the regular series of inter-academy matches between Premier League Academies during a season. Completion of at least a half of the duration of a match in two separate matches (mean ± s = 3.1 ± 0.8 matches; range: 2–4 matches) was the criterion for inclusion in the study. Total match running distance increased with age from ~5700 (U11) to ~6700 m · h−1 (U15) (P < 0.01). Using the absolute speed zones, it was possible to discern differences in high-intensity (>6.0 m · s−1) distance covered with age (U11: 29 m · h−1, U16: 164 m · h−1, P < 0.01). Using the squad speed zones, it was possible to discern differences between retained and released players in the U11/U12s (moderate-speed running) and in the U15/U16s (walking, jogging and low-speed running) (P < 0.01). Thus, total and high-intensity running distances increase with age, and walking, jogging, low-speed running and moderate-speed running distances are greater in retained than in released players and these differences are best identified through the use of absolute and squad speed zones, respectively.

Longitudinal development of match-running performance in elite male youth soccer players [forthcoming]

This study longitudinally examined age‐related changes in the match‐running performance of retained and released elite youth soccer players aged 8–18 years. The effect of playing position on age‐related changes was also considered. Across three seasons, 263 elite youth soccer players were assessed in 1–29 competitive matches (988 player‐matches). For each player‐match, total distance and distances covered at age group‐specific speed zones (low‐speed, high‐speed, sprinting) were calculated using 1 Hz or 5 Hz GPS. Mixed modeling predicted that match‐running performance developed nonlinearly, with age‐related changes best described with quadratic age terms. Modeling predicted that playing position significantly modified age‐related changes (P < 0.05) and retained players covered significantly more low‐speed distance compared with released players (P < 0.05), by 75 ± 71 m/h (mean ± 95% CI; effect size ± 95% CI: 0.35 ± 0.34). Model intercepts randomly varied, indicating differences between players in match‐running performance unexplained by age, playing position or status. These findings may assist experts in developing training programs specific to the match play demands of players of different ages and playing positions. Although retained players covered more low‐speed distance than released players, further study of the actions comprising low‐speed distance during match play is warranted to better understand factors differentiating retained and released players.

longitudinal development of match-running performance in elite male youth soccer players

This study longitudinally examined age‐related changes in the match‐running performance of retained and released elite youth soccer players aged 8–18 years. The effect of playing position on age‐related changes was also considered. Across three seasons, 263 elite youth soccer players were assessed in 1–29 competitive matches (988 player‐matches). For each player‐match, total distance and distances covered at age group‐specific speed zones (low‐speed, high‐speed, sprinting) were calculated using 1 Hz or 5 Hz GPS. Mixed modeling predicted that match‐running performance developed nonlinearly, with age‐related changes best described with quadratic age terms. Modeling predicted that playing position significantly modified age‐related changes (P < 0.05) and retained players covered significantly more low‐speed distance compared with released players (P < 0.05), by 75 ± 71 m/h (mean ± 95% CI; effect size ± 95% CI: 0.35 ± 0.34). Model intercepts randomly varied, indicating differences between players in match‐running performance unexplained by age, playing position or status. These findings may assist experts in developing training programs specific to the match play demands of players of different ages and playing positions. Although retained players covered more low‐speed distance than released players, further study of the actions comprising low‐speed distance during match play is warranted to better understand factors differentiating retained and released players.

The effect of playing status, maturity status, and playing position on the development of match skills in elite youth football players aged 11–18 years: a mixed-longitudinal study

Abstract This mixed-longitudinal study examined the development of match skills in elite male youth footballers (aged 11–18 years), while considering the effect of playing status, maturity status, and playing position. Across two seasons, 126 elite male youth footballers were assessed in 1–10 competitive matches (401 player-matches). For each match, the on-the-ball actions of each player were recorded using a notation system. The match skills observed were frequencies of successful passes, on-target shots, dribbles, crosses, clearances, and tackles/blocks/interceptions. Multilevel Poisson analysis was used to model the development of players, with regard to each match skill. Modelling revealed significant (p < .05) age-related changes in the frequency of several match skills. That is, dribbles increased, on-target shots, crosses and tackles/blocks/interceptions decreased, whereas changes in successful passes were position-specific. Players retained by an academy performed more dribbles compared to released players (p < .05) (e.g. retained vs. released 18-year-old centre forward = 4.1 vs. 2.0 dribbles per hour), and retained defenders performed more tackles/blocks/interceptions than released defenders (p < .05) (e.g. retained vs. released 18-year-old, on-time maturing centre back = 12.5 vs. 10.2 tackles/blocks/interceptions per hour). Moreover, compared to on-time maturing players, early maturing players performed more tackles/blocks/interceptions (p < .05) (e.g. on-time vs. early maturing retained 18-year-old centre back = 12.5 vs. 15.2 tackles/blocks/interceptions per hour). Playing position affected all match skills (p < .05). The developmental profiles of match skills presented here may support experts in identifying and developing talented footballers across a wide age range, while considering the influence of maturity status and playing position.