Previous research has reported that plyometric training improves running economy (RE) and ultimately distance-running performance, although the exact mechanism by which this occurs remains unclear. This study examined whether changes in running performance resulting from plyometric training were related to alterations in lower leg musculotendinous stiffness (MTS). Seventeen male runners were pre- and post-tested for lower leg MTS, maximum isometric force, rate of force development, 5-bound distance test (5BT), counter movement jump (CMJ) height, RE, VO(2max), lactate threshold (Th(la)), and 3-km time. Subjects were randomly split into an experimental (E) group which completed 6 weeks of plyometric training in conjunction with their normal running training, and a control (C) group which trained as normal. Following the training period, the E group significantly improved 3-km performance (2.7%) and RE at each of the tested velocities, while no changes in VO(2max) or Th(la) were recorded. CMJ height, 5BT, and MTS also increased significantly. No significant changes were observed in any measures for the C group. The results clearly demonstrated that a 6-week plyometric programme led to improvements in 3-km running performance. It is postulated that the increase in MTS resulted in improved RE. We speculate that the improved RE led to changes in 3-km running performance, as there were no corresponding alterations in VO(2max) or Th(la).

Johnston, RJ, Watsford, ML, Kelly, SJ, Pine, MJ, and Spurrs, RW. Validity and interunit reliability of 10 Hz and 15 Hz GPS units for assessing athlete movement demands. J Strength Cond Res 28(6): 1649-1655, 2014-The purpose of this study was to assess the validity and interunit reliability of 10 Hz (Catapult) and 15 Hz (GPSports) Global Positioning System (GPS) units and investigate the differences between these units as measures of team sport athlete movement demands. A team sport simulation circuit was completed by 8 trained male participants. The movement demands examined included: total distance covered (TD), average peak speed, and the distance covered, time spent, and the number of efforts performed low-speed running (0.00-13.99 km$h 21 ), high-speed running (14.00-19.99 km$h 21 ), and very highspeed running (.20.00 km$h 21 ). The degree of difference between the 10 Hz and the 15 Hz GPS units and validity was assessed using a paired samples t-test. Pearson's correlations were also used for validity assessment. Interunit reliability was established using percentage typical error of measurement (%TEM) and intraclass correlations. The findings revealed that 10 Hz GPS units were a valid (p . 0.05) and reliable (%TEM = 1.3%) measure of TD. In contrast, the 15 Hz GPS units exhibited lower validity for TD and average peak speed. Further, as the speed of movement increased the level of error for the 10 Hz and 15 Hz GPS units increased (% TEM = 0.8-19.9). The findings from this study suggest that comparisons should not be undertaken between 10 Hz and 15 Hz GPS units. In general, the 10 Hz GPS units measured movement demands with greater validity and interunit reliability than the 15 Hz units, however, both 10 Hz and 15 Hz units provided the improved measures of movement demands in comparison to 1 Hz and 5 Hz GPS units.

The purpose of this research was to investigate the validity and the reliability of 5-Hz MinimaxX global positioning system (GPS) units measuring athlete movement demands. A team sport simulation circuit (files collected from each unit = 12) and flying 50-m sprints (files collected from each unit = 34) were undertaken, during which the total distance covered; peak speed; player load; the distance covered; time spent and number of efforts performed walking, jogging, running, high-speed running, and sprinting were examined. Movement demands were also separately categorized into low-intensity activity, high-intensity running, and very high-intensity running. The results revealed that GPS was a valid and reliable measure of total distance covered (p > 0.05, percentage typical error of measurement [%TEM] < 5%) and peak speed (p > 0.05, %TEM 5-10%). Further, GPS was found to be a reliable measure of player load (%TEM 4.9%) and the distance covered, time spent, and number of efforts performed at certain velocity zones (%TEM <5% to >10%). The level of GPS error was found to increase along with the velocity of exercise. The findings demonstrated that GPS is capable of measuring movement demands performed at velocities <20 km·h(-1), whereas more caution is to be exercised when analyzing movement demands collected by using GPS velocities >20 km·h(-1).

This study examined the relationship between coaches' perception of match performance and movement demands in Australian Football. Movement demands were collected from 21 professional players over 12 matches during one Australian Football League season, with 69 player files collected. Additionally, match events relative to playing time and distance covered, along with player physical characteristics were collected. Based on coaches subjective rating of match performance (out of 20), relatively high calibre (HC) players (≥ 15/20) were compared with relatively low calibre (LC) players (≤ 9/20) for all variables. The HC players were older (+17%, p=0.011), spent a greater percentage of time performing low-speed running (+2%, p=0.039), had more kicks (38%, p=0.001) and disposals (35%, p=0.001) per min and covered less distance per kick (- 50%, p=0.001) and disposal (- 44%, p=0.001) than the LC group, with the effect sizes also supporting this trend. Further, HC players covered less distance (- 14%, p=0.037), spent less percentage of time (- 17%, p=0.037) and performed fewer (- 9%, p=0.026) efforts per min high-speed running than LC players, which was further confirmed by the effect sizes. Movement demands and match events are related to coaches' perception of match performance in professional Australian Football. Further, high levels of involvement with the football appeared to be more important to performance than high exercise speed.

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