The use of time-motion analysis has advanced our understanding of position-specific work rate profiles and the physical requirements of soccer players. Still, many of the typical soccer activities can be neglected, as these systems only examine activities measured by distance and speed variables. This study used triaxial accelerometer and time-motion analysis to obtain new knowledge about elite soccer players' match load. Furthermore, we determined acceleration/deceleration profiles of elite soccer players and their contribution to the players' match load. The data set includes every domestic home game (n = 45) covering 3 full seasons (2009, 2010, and 2011) for the participating team (Rosenborg FC), and includes 8 central defenders (n = 68), 9 fullbacks (n = 83), 9 central midfielders (n = 70), 7 wide midfielders (n = 39), and 5 attackers (A, n = 50). A novel finding was that accelerations contributed to 7-10% of the total player load for all player positions, whereas decelerations contributed to 5-7%. Furthermore, the results indicate that other activities besides the high-intensity movements contribute significantly to the players' total match workload. Therefore, motion analysis alone may underestimate player load because many high-intensity actions are without a change in location at the pitch or they are classified as low-speed activity according to current standards. This new knowledge may help coaches to better understand the different ways players achieve match load and could be used in developing individualized programs that better meet the "positional physical demands" in elite soccer.

The aim of this study was to characterise the acceleration and sprint profiles of elite football match play in one Norwegian elite football team (Rosenborg FC). Fifteen professional players in five playing positions took part in the study (n = 101 observations). Player movement was recorded during every domestic home game of one full season (n = 15) by an automatic tracking system based on microwave technology. Each player performed 91 ± 21 accelerations per match, with a lower number in the second compared with the first half (47 ± 12 vs. 44 ± 12). Players in lateral positions accelerated more often compared to players in central positions (98.3 ± 20.5 vs. 85.3 ± 19.5, p< 0.05). Average sprint distance was 213 ± 111 m distributed between 16.6 ± 7.9 sprints, with no differences between first (106 ± 60 m, 8.2 ± 4.2 sprints) and second halves (107 ± 72 m, 8.3 ± 4.8 sprints). Players in lateral positions sprinted longer distances (287 ± 211 m vs. 160 ± 76 m, p < 0.05) and tended to sprint more often (21.6 ± 7.8 vs. 13.0 ± 5.7, p = 0.064) compared to players in central positions. We found more walking and less of the more intense activities during the last third of the season compared to the first. The main finding in this study was that Norwegian elite players had substantially less number of accelerations and fewer but longer sprints than previous studies reported for higher-ranked leagues. Also, less high-intensity activity was found towards the end of the season. Ultimately, these data provide useful information for the fitness coach (1) in planning of position-specific football training and (2) to avoid the decline in high-intensity activities the last third of the competitive season.

This study examined the ability of the Acti4 software for identifying physical activity types from accelerometers during free-living with different levels of movement complexity compared with video observations. Nineteen aircraft cabin cleaners with ActiGraph GT3X+ accelerometer at the thigh and hip performed one semi-standardised and two non-standardised sessions (outside and inside aircraft) with different levels of movement complexity during working hours. The sensitivity for identifying different activity types was 75.4-99.4% for the semi-standardised session, 54.6-98.5% outside the aircraft and 49.9-90.2% inside the aircraft. The specificity was above 90% for all activities, except 'moving' inside the aircraft. These findings indicate that Acti4 provides good estimates of time spent in different activity types during semi-standardised conditions, and for sitting, standing and walking during non-standardised conditions with normal level of movement complexity. The Acti4 software may be a useful tool for researchers and practitioners in the field of ergonomics, occupational and public health. Practitioner Summary: Being inexpensive, small, water-resistant and without wires, the ActiGraph GT3X+ by applying the Acti4 software may be a useful tool for long-term field measurements of physical activity types for researchers and practitioners in the field of ergonomics, occupational and public health.

We examined performance, heart rate response and construct validity of the Yo-Yo IR2 test by testing 111 elite and 92 sub-elite soccer players from Norway and Denmark. VO₂max, Yo-Yo IR1 and repeated sprint tests (RSA) (n = 51) and match-analyses (n = 39) were also performed. Yo-Yo IR2 and Yo-Yo IR1 performance was 41 and 25% better (P < 0.01) for elite than sub-elite players, respectively, and heart rate after 2 and 4 min of the Yo-Yo IR2 test was 20 and 15 bpm (9 and 6% HRmax), respectively, lower (P < 0.01) for elite players. RSA performance and VO₂max was not different between competitive levels (P > 0.05). For top-teams, Yo-Yo IR2 performance (28%) and sprinting distance (25%) during match were greater (P < 0.05) than for bottom-teams. For elite and sub-elite players, Yo-Yo IR2 performance was correlated (P < 0.05) with Yo-Yo IR1 performance (r = 0.74 and 0.76) and mean RSA time (r = -0.74 and -0.34). We conclude that the Yo-Yo IR2 test has a high discriminant and concurrent validity, as it discriminates between players of different within- and between-league competitive levels and is correlated to other frequently used intermittent elite soccer tests.

To reduce athlete testing time, the aim of this study was to investigate the relationship between the Yo-Yo intermittent recovery test levels 1 (IR1) and 2 (IR2) performances, maximal sprinting speed (10, 20, and 35 m), repeated sprint ability (RSA; 7 × 35 m), and submaximal heart rates (HRs) after 2 and 4 minutes of the Yo-Yo IR tests by testing 57 high-level soccer players. All players played regularly in one of 3 highest levels of Norwegian soccer and were tested during 3 sessions on 3 consecutive days. Large correlations were observed between Yo-Yo IR1 and IR2 test performances (r = 0.753, p ≤ 0.05). Small and moderate correlations were found between 20- and 35-m sprinting speed and Yo-Yo IR1 performance (r = -0.289 and -0.321, respectively, p ≤ 0.05), whereas 35-m sprinting speed correlated moderately to Yo-Yo IR2 performance (r = -0.371, p ≤ 0.05). Repeated sprint ability at 10, 20, and 35 m all showed moderate to large correlations to Yo-Yo IR1 performance (r = -0.337 to -0.573, p ≤ 0.05). Repeated sprint ability at 20 m (r = -0.348, p ≤ 0.05) and 35 m (r = -0.552, p ≤ 0.01) correlated moderately and largely to Yo-Yo IR2 performance. In addition, moderate and large correlations were found between submaximal Yo-Yo IR1 HRs after 2 (r = -0.483, p ≤ 0.01) and 4 minutes (r = -0.655, p ≤ 0.01) and Yo-Yo IR1 performance, and 2 minutes Yo-Yo IR2 HR and Yo-Yo IR2 performance (r = -0.530, p ≤ 0.01). Intraclass correlation measures of submaximal HR after 2 and 4 minutes of Yo-Yo IR1 test and after 2 minutes of the Yo-Yo IR2 were 0.92 (coefficient of variation [CV] = 4.1%, n = 33), 0.93 (CV = 3.8%, n = 33), and 0.72 (CV = 2.9%, n = 10). Adjusted ordinary least square (OLS) regressions revealed associations (p ≤ 0.05) between sprint speed at 20 and 35 m and Yo-Yo IR1 test performance, but only between 35 m and IR2 test performance (p ≤ 0.05). Further, OLS showed that RSA at 35 m was related to both levels of the Yo-Yo IR test (p ≤ 0.01), and that submaximal HRs after 2 and 4 minutes were independently associated with Yo-Yo IR1 and IR2 performances (p ≤ 0.01). In conclusion, Yo-Yo IR1 and 2 test performances, as well as sprint and RSA performances, correlated very largely, and it may therefore be considered using only one of the Yo-Yo tests and a RSA test, in a general soccer-specific field test protocol. The submaximal HR measures during Yo-Yo tests are reproducible and may be used for frequent, time-efficient, and nonexhaustive testing of intermittent exercise capacity of high-level soccer players.