Half-time re-warm up increases performance capacity in male elite soccer players

Transcription

1 Scand J Med Sci Sports 215: 25: e4 e49 doi: /sms John Wiley & Sons A/S. Published by John Wiley & Sons Ltd Half-time re-warm up increases performance capacity in male elite soccer players P. Edholm 1, P. Krustrup 2,3, M. B. Randers 2 1 School of Health and Medical Sciences, Örebro University, Örebro, Sweden, 2 Department of Nutrition, Exercise and Sports, Copenhagen Centre for Team Sport and Health, University of Copenhagen, Copenhagen, Denmark, 3 Sport and Health Sciences, College of Life and Environmental Sciences, St. Luke s Campus, University of Exeter, Exeter, UK Corresponding author: Peter Edholm, School of Health and Medical Sciences, Örebro University, Fakultetsgatan 1, 7282 Örebro, Sweden. Tel: , Fax: , peter.edholm@oru.se Accepted for publication 19 March 214 This study investigated the acute effects of a half-time re-warm up on performance and movement patterns in soccer match play. Using a crossover design, 22 professional male players performed traditional passive rest (CON) or a low-intensity re-warm up (RW) during the half-time period of two soccer matches. Before and after the first half and before the second half, maximal sprint and jump performance were evaluated. Time motion analysis of the first 15 min of each half was conducted. Sprint and jump performance were reduced (P <.5) by 2.6% and 7.6%, respectively, during the half-time period in CON, whereas sprint performance was maintained and the decrement in jump performance (3.1%; P <.5) was lower after RW. No significant interaction for highintensity running was observed, but less defensive highintensity running was observed after RW than CON (.14 ±.6 vs.22 ±.7 km; P <.1). Moreover, RW had more possession of the ball in the beginning of the second half. In conclusion, traditional passive half-time rest leads to impaired sprint and jump performance during the initial phase of the second half in professional soccer players whereas a re-warm up effectively attenuates such deteriorations. Less defensive high-intensity running and more ball possession were observed after RW, indicating a game advantage at the onset of the second half. The ability to perform large amounts of high-intensity running is generally considered as an important performance marker in soccer, and most (Reilly & Thomas, 1976; Ekblom, 1986; Bangsbo et al., 1991; Carling et al., 28; Ingebrigtsen et al., 212) but not all (Di Salvo et al., 29; Rampinini et al., 29) studies have shown that professional soccer players perform more high-intensity running during all stages of a match compared with lower level soccer players. Interestingly, several studies have reported that soccer players at all levels including professional players perform less highintensity running during the initial phase of the second half compared with the first half of a match (Mohr et al., 23, 25; Bradley et al., 29; Weston et al., 211). In fact, Mohr et al. (25) showed that as much as 2% of elite soccer players have their least intense 15-min period in a match during the initial part of the second half. This is remarkable, especially as the players just before this period have had a 15-min half-time period, aiming to give the players time to rest and recover so that they can resume the second half of the game with renewed vigor. The reason for this significant reduction in high-intensity running is unknown. However, several hypotheses have been suggested, including tactical aspects, accumulated fatigue, half-time length, ambient temperature, and lack of physical preparation prior to the second half (Mohr et al., 24; Mugglestone et al., 213; Zois et al., 213). In addition to high-intensity running, soccer players capacity to produce explosive actions such as maximal sprint and jump performance is also an important performance marker (Stolen et al., 25). Even small differences might be crucial in the critical duels influencing the results of the game and a difference of only.5 s in a 1-m sprint equals.25.5 m depending on the running speed. In line with this, professional soccer players have repeatedly been reported to have higher sprint and jump capacity than nonprofessionals (Stolen et al., 25). Before a match professional soccer players usually perform a warm up routine typically lasting 3 min and consisting of low- to high-intensity exercises (Towlson et al., 213). This type of physical preparation has been shown to elevate muscle temperature, which in turn is associated with enhanced sprint and jump performance (Sargeant, 1987; Stewart & Sleivert, 1998; Bishop, 23; Mohr et al., 24). Thus, the warm up regime performed by professional soccer players before matches induces physiological changes assuring that players are well prepared to perform maximal efforts directly from the start of match. Given the above discussion, it is interesting to e4

2 Half-time re-warm up and soccer performance note that re-warm up regime specifically set up to prepare the players for the second half of the game are rarely used (Towlson et al., 213). Indeed, the dominating routine during the half-time period in professional soccer is traditionally restricted to passive seated recovery, rehydration, and brief tactical advice from the coach (Towlson et al., 213). Such half-time regimes are probably not optimal as it has been shown that both core and muscle temperature decreases during a passive half-time period (Mohr et al., 24; Lovell et al., 27, 213). Moreover, those studies also reported that as a consequence of the decrements in core and muscle temperature, the soccer players exercise capacity was impaired including sprint, jump, and dynamic strength performances. Thus, this sequence of event with passive seated half-time recovery, decreased muscle temperature, and impaired exercise capacity might at least, in part, be the cause of the reduced amount of high-intensity running seen during the initial phase of the second half in soccer matches. The issue of re-warm up before the second half during 9-min soccer matches is poorly studied and has been addressed in only two reports (Mohr et al., 24; Lovell et al., 213). Nevertheless, both of these two novel papers suggest that a short-active re-warm up regime (7 min of low-to-moderate aerobic running exercises at approximately 7% of HR max as a component of the latter part of the 15-min half-time period) is an efficient method to maintain elevated muscle temperature and preserve sprint and jump performance over the half-time period. However, both of these studies have some limitations that need to be considered. First, both studies were conducted on amateur players. Second, the study design included either a friendly match where the players repeatedly were replaced by substitute players during muscle temperature sampling or a soccer game simulation agility course aiming to replicate a competitive match. Thus, it is still unknown whether the proposed impairments in sprint and jump performance after the half-time period also are present in well-trained professional players during real soccer matches and subsequently if a half-time re-warm up regime outlined as above is an effective method to attenuate such potential decreases in performance capacity. Finally, it is also unknown whether there are any connections between the reduced performance capacity (i.e., sprint and jump performance) and the reduced amount of high-intensity running that are often observed during the initial part of the second half, and whether a re-warm up during the half-time period also results in an increased amount of high-intensity running performed in the initial phase of the second half. Therefore, the aims of this investigation were to study the effect of an active re-warm up program as a part of the half-time period during match play in professional soccer players. More specifically we investigated (a) changes in maximal sprint performance and countermovement jump (CMJ) performance and (b) movement pattern and technical skill during the initial 15 min of each half. Methods Participants Twenty-two male professional soccer players with a mean age of 25 (range: 18 33) years, an average height of 182 ( ) cm, and a mean body mass of 78.6 ( ) kg playing in the same team in the top league in Sweden (Allsvenskan) participated in the study. The players participated in two 9-min matches separated by 6 days of regular training. Only field players with complete test data from both matches were included in the statistical analysis. Three players were not able to complete both matches due to injuries (one during the first match and two during training between the matches). Thus, a total of 17 players were included in the analysis. All players were informed of the experimental procedures and possible discomforts associated with the study before giving their written consent to participate. The study was conducted in accordance with the guidelines set by the Swedish Central Ethical Review Board. Experimental design The players were divided into two teams according to playing position and coach-evaluated skill level. The selection of the two teams was made in close collaboration with the head coach to make sure that the teams were of equal skill level. Thereafter, two 9-min matches separated by 6 days of training were completed with the same subjects playing the same field position in the same team during both matches. During the 3 days preceding each match, training was standardized and consisted of low-intensity soccer training. Before the start of each match, players performed a 3-min standardized warm up, consisting of low-to-moderate speed running, light individual calisthenics, and stretching exercises followed by short bursts of high-speed running and different playing exercises with the ball at a moderate intensity. During the first match, the control group (CON) had a traditional 15-min half-time period in the break between the first and the second half of the game (including seated passive recovery, rehydration, and coaching instructions), whereas the experimental group performed a re-warm up regime (RW) essentially as described by Mohr et al. (24). Thus, the RW protocol consisted of 7 min of traditional passive rest (as described above), followed by 7 min of low-/moderateintensity jogging and light calisthenics at 7% of maximal heart rate. The RW regime ended 1 min before the start of the second half. The study was conducting using a crossover design, so that the team who had the traditional half-time rest in the first match performed the RW regime in the second game and vice versa. To mirror a real competitive match as much as possible, the two teams were separated during the matches, using separate dressing room, test stations, and performed the half-time activities separately. In addition, the two matches were supervised by official referees with extensive experience from the top Swedish soccer league. To minimize the influence of match tactics on individual movement patterns, the playing system and tactics were standardized in close collaboration with the head coach, as defensive/ offensive tactics might result in large inter-individual variation in the amount of high-intensity running among players (Bradley et al., 211). During the matches the teams only had support of an assistant coach, whose role was to assist and remind the players of the preordained tactics. e41

3 Edholm et al. The player s net fluid loss during the matches was determined by weighing the players without clothes immediately before and after the matches, using a digital scale (Seca 78, Seca Ltd., Birmingham, UK). The players were allowed to drink water ad libitum during the matches and their fluid intake was measured. The fluid loss was calculated as fluid loss =Δbody weight + fluid intake. The players wore soccer boots and clothing during all trials, and were instructed to refrain from consumption of caffeine (24 h) and alcohol (48 h) before each trial. The players maintained their usual diet throughout the study period. We noted similar weather conditions (5 vs 6 C, 87% vs 84% humidity and 3 vs 2 m/s wind) when the two matches were played. Performance tests The players completed performance tests on three occasions: (a) after the pre-match warm up, before start of the first half; (b) after the first half, before start of half-time period; and (c) after the half-time period just before the start of the second half (Fig. 1). All the players were familiarized to all of the testing procedures 1 week before the first experimental day. Each test occasion included two maximal 1-m sprints and two maximal CMJs. The tests were always performed in the same order during all test occasion. The 1-m sprint tests were performed on grass at the side of the field with players wearing soccer boots. Each player performed two trials separated by a 9-s walk back recovery and the best result was used for data analysis. The players were instructed to start with their feet in a parallel position standing behind a mark, which were placed.5 m behind the first set of photocells. The players were also instructed not to do any kind of backward movement with the upper body or the feet, as such procedure allowed the player to break the first photocell with a forward acceleration movement and thereby reducing the sprint time. Sprint time was recorded by infrared light sensor, with a precision of.1 s and placed at a height of 1. m (Musclelab 4, Ergotest, Oslo, Norway). Immediately after the sprint test, the players performed two maximal CMJs separated by 9 s of rest. The jumps were performed indoors on a 25-mm hard tartan rubber carpet, which allowed the player to perform the jumps while wearing soccer boots. The best result was used for data analysis. The CMJ started from a standing position with hands fixed to the hips. To make sure that the player landed on their toes (with ankles in a dorsal flexion position), the players were instructed to perform a small post-jump direct after landing (not measured). This procedure ensured that the players were jumping and landing on the ground with their toes first and with straight legs, consequently giving a correct time in the air. Jumping height was measured using portable MicroMusclelab (Ergotest) units connected to infrared light rails. Jumping height was calculated as h = t f2 g 8 1 where h = jump height, t = time in air, and g = gravity. Each team had their own test station (sprint and jump) to make sure that the performance test took a minimum amount of time. Movement patterns and heart rate During both matches all field players were filmed close up throughout the first 15 min of each half (Fig. 1) using 2 digital video cameras (Canon DM-MV 6, Canon Inc., Tokyo, Japan). An additional camera was used to follow the ball. The cameras were positioned at the side of the pitch, at the level of the midway line, at a height of about 15 m, and at a distance of 3 4 m from the touchline. The recordings were later replayed on a monitor for computerized coding of activity pattern as described in detailed by Bangsbo et al. (1991). The following locomotion categories were used: standing ( km/h), walking (6 km/h), jogging (8 km/h), lowspeed running (12 km/h), moderate-speed running (15 km/h), high-speed running (18 km/h), sprinting (3 km/h), and backward running (1 km/h). The locomotion categories were chosen in accordance with previous studies (Bangsbo et al., 1991; Mohr et al., 23). High-intensity running was defined as all runs with speeds above 15 km/h (encompassing moderate-speed running, high-speed running, and sprinting). The number of occurrences of each activity was recorded in each of the first 15 min of each half in both matches. The distance covered in each activity for each interval was determined as the product of the total time spent in that activity category and mean speed for that activity. The total distance covered during the first 15 min of each half was calculated as the sum of the distance covered during each type of activity. The number of shoots, dribbles, and passing was counted and possession of the ball was analyzed. Offensive high-intensity runs were defined as high-intensity runs while the team had possession of the ball. The pitch was divided into three zones (defending zone (team 1)/attacking zone (team 2), neutral zone, and attacking zone (team 1)/defending zone (team 2). The neutral zone was defined as 19 m on each half of the pitch from the halfway line. Effective playing time was defined as the total playing time minus time used for stoppages. Data from each 15-min period were subsequently divided into 5-min periods. All recordings were analyzed by the same experienced observer. Prior to the present analysis the experienced observed analyzed the same matches not related to the present study with 6 months between the analysis and a coefficient of variation for test retest analysis of < 5% for each locomotion activity was found. The observer was blinded for re-warm up regimes in both matches. The recordings from the first and the second half of each match as well as players from both teams were analyzed in a random order. Heart rate was monitored in 5-s intervals throughout the games including the half-time periods using Polar System heart rate monitors (Polar Electro OY, Kempele, Finland). Statistical analysis Statistical analysis was performed using SigmaStat software (version 12., Systat Software Inc., San Jose, California, USA). Changes in sprint and jump performance, movement pattern, and ball skill and technical standards were evaluated by a two-way analysis of variance with repeated measures. When a significant Video filming 15 min Video filming 15 min Warm up 3 min 1st half 45 min Half-time rest 15 min (CON/RW) 2nd half 45 min Test 1 Test 2 Test 3 Heart rate monitoring Fig. 1. Schematic view of the experimental design during the two matches. Sideward arrows denote end of filming; upward arrows denote test of sprint and jump performance. e42

4 Half-time re-warm up and soccer performance (a) 11 (b) 14 RW CON RW CON % of pre-match sprint performance # # * % of pre-match jump performance # * Pre 1st half Pre 2nd half Pre 1st half Pre 2nd half Post 1st half Time (min) Post 1st half Time (min) Fig. 2. Ten-meter sprint performance (a) and countermovement jump performance (b) during soccer matches. Closed bars ( ) represent re-warm up (RW) condition and open bars ( ) represent control (CON) condition during half-time rest. N = 17. Data are presented as means ± standard error of the mean. #P <.5 post first half vs pre second half. *P <.5 RW vs CON. interaction was detected, data were subsequently analyzed using a Newman Keuls post-hoc test. Effect sizes (ESs; η 2 ) were calculated and values of.1,.6, and >.15 were considered small, medium, and large, respectively (Cohen, 1988). Test retest analysis revealed high-reliability coefficient for both CMJ and 1-m sprint (α =.97 and.93), respectively. The differences in heart rate between the matches and the first and second half were tested with Student s paired t-test. Correlation between two variables was assessed using Pearson s correlation coefficient. P-values <.5 were considered statistically significant. Data are presented as mean ± standard deviation unless otherwise stated. Results Sprint performance A significant time condition interaction was found for 1-m sprint performance (P =.14; η 2 =.5, i.e., small ES). Post-hoc test revealed that no differences in the player s 1-m sprint performance were found before the first half between re-warm up (RW) and control condition (CON) (1.89 ±.4 vs 1.88 ±.6 s). After the first half sprint performance was reduced by 3% during both RW and CON to 1.95 ±.6 and 1.93 ±.5 s, respectively (P <.5). Immediately after the half-time period, sprint performance was further reduced by another 2.6% during CON (1.98 ±.6 s), whereas no further change was observed after RW (1.94 ±.5 s, P <.5 vs CON; Fig. 2(a)). Jump performance Also for CMJ a significant time condition interaction was found (P =.43; η 2 =.5, ES = small). Post-hoc test revealed that before the start of matches, there were no differences in the players CMJ performance between RW and CON (38.7 ± 3.7 vs 39. ± 2.9 cm) and after the first half CMJ performance was still unchanged during both RW and CON (38.7 ± 3.8 and 39.4 ± 3.8 cm, respectively). However, directly after the half-time period CMJ performance was significantly reduced by 3.1% during RW (37.5 ± 3.7 cm) and 7.6% during CON (36.4 ± 3.9 cm), with a larger (P <.5) reduction in CON than in RW (Fig. 2(b)). Before the start of match, there was a significant correlation between sprint and CMJ performance during both RW and CON (r =.52, P <.5 and r =.58, P <.5 for RW and CON, respectively), whereas no such correlations were observed after the first half or after the half-time period. Heart rate The mean heart rate for the players during the two matches were 162 ± 1 and 164 ± 1 beats/min for RW and CON, respectively, which corresponded to 84% ± 2% (RW) and 85% ± 2% (CON) of maximal heart rate. The average heart rate was higher (P <.5) during the first half compared with the second half of the matches during both RW (167 ± 7vs157 ± 12 beats/ min) and CON (167 ± 8vs161 ± 11 beats/min). Moreover, the average heart rate was also higher (P <.5) during the first 5 and 15 min of the first half compared with the second half both in RW (163 ± 7vs159± 1 and 168 ± 8vs161 ± 12 beats/min) and CON matches (164 ± 9vs158± 14 and 168 ± 9 vs 163 ± 12 beats/ min). Immediately before start of the second half, the heart rate was higher (P <.5) after RW compared with CON (117 ± 1 vs 19 ± 12 beats/min), and the time for the heart rate to increase to values taxing average heart rate of the second half was faster (P <.5) after RW (71 ± 34 s) compared with CON (129 ± 44 s; Fig. 3). Weight loss The average body weight loss for the players was.9 ±.3 and 1. ±.3 kg during RW and CON e43

5 Edholm et al. (a) 18 (b) * Heart rate (beats/min) Mean RW Mean CON Heart rate (beats/min) Mean RW Mean CON Time (s) Time (s) Fig. 3. Mean heart rate kinetics response during the initial 3 min of (a) first half and (b) second half. Dashed line ( ) represent re-warm up (RW) condition and dotted line ( ) represent control (CON) condition during half-time rest. N = 17. Data are presented as means ± standard error of the mean. *P <.5 RW vs CON. condition matches, respectively. The fluid intake was.3 ±.2 kg (RW) and.3 ±.2 kg (CON); thus, the calculated total fluid loss was 1.2 ±.4 kg (1.5% ±.3% of body weight) and 1.3 ±.3 kg (1.7% ±.3% body weight) during RW and CON, respectively. There were no significant differences between RW and CON condition matches regarding fluid loss. Match activities, distance covered, and technical skill Total distance covered during the initial part of the second half was significantly shorter than during the first half for both RW (9%, P <.1) and CON (4%, P <.5), with a larger drop in RW compared with CON (P <.5, η 2 =.2, ES = small). No significant interaction was observed for distance covered with highintensity running (P =.294) or sprinting (P =.84). Re-warm up during half time had no effect on the number of high-intensity runs or sprints as no time condition interaction was found. When focusing on the initial 5 min of each half the statistical analysis showed no significant time condition interactions (Table 1). Defensive and offensive high-intensity runs For the distance covered with defensive high-intensity running, a significant time group interaction was observed (P <.5, η 2 =.6, ES = medium) and posthoc tests showed that this distance was lower in the initial 15 min of the second compared with the first half (.14 ±.6 vs.21 ±.7 km, P <.1) in RW but not in CON (.22 ±.7 vs.21 ±.11 km). The defensive high-intensity running distance was different between the two conditions in the second (P <.1) but not in the first half (P =.937). These differences between the two conditions were due to the number of defensive high-intensity runs, which decreased (P <.5) in the second half for RW (13.9 ± 5.7 vs 22.3 ± 7.8) but not for CON (21.1 ± 4.8 vs 22.9 ± 1.6), whereas no difference was observed in the mean length of the defensive high-intensity runs for either RW (1 ± 2 vs 1± 2 m) or CON (1 ± 2 vs 9 ± 2 m). No difference was observed in offensive high-intensity running in the initial 15 min of each half. In the initial 5 min of each half, a significant interaction was found for the distance covered with defensive high-intensity running (P <.5, η 2 =.6, ES = medium). Post-hoc tests showed that the distance tended (P =.95) to be lower in the second half compared with the first half in RW (.5 ±.4 vs.8 ±.3 km) but not in CON (.8 ±.4 vs.8 ±.4 km) with a significant difference between RW and CON in the second (P <.1) but not in the first half (P =.683). No difference was observed in the number of defensive high-intensity runs or the mean distance of those runs. Moreover, no significant interactions were found for the distance covered with or the number of offensive high-intensity running during the initial 5 min of each half. Effective playing time The effective playing time was 69% ± 1% for the initial 15 min of the second half and 8% ± % for the similar period in the first half. Also for the initial 5 min of each half less effective playing time was observed for the second half compared with the first half (67% ± 1% vs 75% ± 6%). e44

6 Table 1. Distance covered with and number of occurrences of sprinting, high-intensity running, and in total during the initial 5- and 15-min periods in the first and second half after active half-time re-warm up (RW) or a passive half-time period (CON) Distance (km) Sprinting High-intensity running Total RW CON RW CON RW CON First half 5 min.3 ±.2.3 ±.2.13 ±.5.15 ±.7.64 ±.7.68 ± min.3 ±.2.4 ±.4.14 ±.6.16 ±.8.68 ±.7.7 ± min.3 ±.2.3 ±.2.11 ±.4.1 ±.6.63 ±.5.63 ±.6 15 min.8 ±.3.1 ±.4.37 ± ± ± ±.18 Second half 45 5 min.3 ±.2.5 ±.3.13 ±.5.15 ±.6.6 ±.7.67 ± min.2 ±.2.2 ±.2.9 ±.4.12 ±.5.58 ±.7.63 ± min.3 ±.2.4 ±.2.12 ±.5.15 ±.6.59 ±.7.63 ± min.8 ±.3.1 ±.4.34 ±.3.42 ± ± ±.18* No. of occurrences (n) First half 5 min 1.8 ± ± ± ± ± ± min 1.8 ± ± ± ± ± 9 12 ± min 1.9 ± ± ± ± ± 8 93 ± min 5.4 ± ± ± ± ± ± 3 Second half 45 5 min 2. ± ± ± ± ± ± min 1.1 ± ± ± ± ± ± min 1.9 ± ± ± ± ± 1 9 ± min 5.1 ± ± ± ± ± ± 34 N = 17. Distance covered (km) and number of occurrences (n) are expressed as average per player. Data are presented as means ± standard deviation. *Denotes significantly different from RW (P <.1). Denotes significantly different from first half (P <.5). Denotes significantly different from first half (P <.1). Half-time re-warm up and soccer performance Table 2. Possession of the ball during the initial 15 min of both halves in game with active half-time re-warm up (RW) or a passive half-time period (CON) in total and possession of the ball in defending, neutral, and attacking zone RW CON Total possession Defending Neutral Attacking Total possession Defending Neutral Attacking 15 min first half min second half min first half min second half Match activities adjusted for effective playing time When the match activities were related to effective playing time and analyzed as distance covered per min effective playing time (MEPT), a significant time condition interaction was observed for total distance covered (P <.5, η 2 =.2, ES = small) and post-hoc test showed that a significant longer total distance was covered in the first 15 min of the second half compared with the same period in the first half for both RW (.17 ±.2 vs.16 ±.1 m per MEPT, P <.5) and CON (.19 ±.2 vs.17 ±.2 m per MEPT, P <.1), with a shorter distance covered in RW than CON in the first 15 min of the second half (P <.1) but not in the first half (P =.12). In accordance with the main analysis, high-intensity runs (P <.5, η 2 =.5, ES = small) and sprinting (P <.5, η 2 =.2, ES = small) were performed less frequent in RW than in CON (3.3 ±.7 vs 3.8 ± 1.3 and.5 ±.2 vs.6 ±.2 times per MEPT). Ball possession and specific actions Ball possession increased in RW in both the initial 5 and 15 min in the second half compared with the corresponding period in the first half. Moreover, the ball possession increased in both the attacking and defending zone, whereas ball possession in the neutral zone decreased in both periods (Table 2). The number of ball entries into the attacking zone was 12 and 11 in RW and 8 and 11 in CON in the first 15 min of the second half compared with the similar period of first half. In the initial 5 min of the second half and the first half, the number of ball entries into the attacking zone was 4 and 3 in RW and 2 and 3 in CON, respectively. The number of passes and dribbles was lower in the second half compared with the first half for RW (1 ± 4 vs 113 ± 13 and 2 ± 2vs26± 11, respectively) and CON (89 ± 7vs18± 9 and 17 ± 4vs22± 11), whereas 2 ± 1 shots on goal in the second and 1 ± 2 shots on goal in the first half were observed in both conditions. e45

7 Edholm et al. Discussion The main findings of the current study were that an active half-time re-warm up (RW) regime attenuated the decreases in sprint and jump performances observed after traditional passive half-time period (CON) in professional soccer match play. These findings are in line with previous results obtained for sub-elite players (Mohr et al., 24; Lovell et al., 213) and emphasized that these types of performance decrements also occur in well-trained professional soccer players during actual match play. The magnitude of the impaired sprint performance after passive half-time period in this study (CON, 2.6%) was similar to that reported by Mohr et al. (24) (2.6%) but lower than Lovell et al. (213) (6.2%). These differences might be attributed to several different factors, including the fact that Lovell et al. (213) used a soccer match simulation agility course to mimic a soccer game instead of investigating changes in the player s physical performance capacity in relation to a real soccer match play. Thus, the players movement pattern and exerciseinduced fatigue might have differed from actual soccer match play. However, other factors such as starting procedure during the sprint test (3. vs.5 m rolling start) and differences in the player s physical capacity (subelite vs professional soccer players) might also contribute to differences in sprint performance deteriorations. In the study by Mohr et al. (24), sprint performance was measured through a repeated sprint test (3 3 m, rest 25 s). However, movement analysis has revealed that the mean distance of a single sprint during a soccer game is m and it is very seldom that players performed high-intensity running over 3 m or longer (Reilly & Thomas, 1976; Bangsbo et al., 1991; Valquer et al., 1998; Mohr et al., 23; Di Salvo et al., 29). Previous studies have also shown that while professional soccer players have a significantly better sprint capacity over short distances (e.g., 1 m) than sub-elite soccer players, such patterns do not seem to exist at longer distance (e.g., 3 m) (Cometti et al., 21; Stolen et al., 25). This suggests that long sprint distances such as a 3-m dash do not mirror actual game situations. Thus, from a physiological point of view it might be argued that data on performance capacity over shorter distance such as 1 m that were used in the current study are more relevant if the aim is to examine professional soccer players maximal sprint performance capacity. Nevertheless, result from the current study supports the previous findings by Mohr et al. (24) and Lovell et al. (213) in that a short, low-intensity re-warm up program is an efficient method to limit the decrements in sprint performances observed during traditional passive halftime period in soccer players. In the present study, jump performance was significantly reduced after the half-time period during both RW and CON condition (pre half-time period vs post half-time period). However, the RW regime was associated with a reduction in the CMJ performance deterioration as the decrease jump height was significantly lower after RW compared with CON condition (3.1% vs 7.6%). This indicates that the RW regime at least to some extent also had a positive effect on preserving jump capacity over the half-time period in professional soccer players. Studies investigating the effect of different warm up protocols on jump performance in well-trained athletes have shown that warm up protocols, which include some brief but high-loading exercises such as jumping or squats with heavy load, are more efficient in improving the jumping ability than a traditional warm up (5-min jogging and some half-squats with low load) (Saez Saez de Villarreal et al., 27). In line with this, Gullich and Schmidtbleicher (1996) suggest that in addition to elevated muscle temperature, the warm up-induced increases in jump performance might also be ascribed to an increased recruitment of higher order motor units. Thus, it might be that the RW regime, which consisted of low-intensity jogging and light calisthenics, should be modified to contain some brief but more neuromuscularly challenging stimuli such as squat jumping in order to increase its efficiency regarding preservation of the players jump performance. After RW players restarted the game with higher heart rate levels than after CON condition (+7.3%) and were able to reach mean second half heart rate values faster than after CON (Fig. 3(b)). Previous studies have reported that a close relationship exists between heart rate and oxygen uptake responses during varying nonsteady states activities (Bot & Hollander, 2) and faster oxygen uptake kinetics and the ability to maintain sprint performance during repeated sprints (Dupont et al., 21). Therefore, the association between RW and both faster recruitment of the aerobic system and reduced contribution of anaerobic metabolism to meet the metabolic demand appears to be a reasonable hypothesis. In this study, the muscle temperature of the players was not measured and this could be regarded as a limitation. The reason for not including such measurement was that this procedure would have either required an extended half-time period or that the players were temporarily taken out of the game for sampling, as performed in the study by Mohr et al. (24). As one of the aims of the present study was to investigate the re-warm up concept during real match play and to evaluate its potential effect on movement pattern both of those options were excluded. Moreover, previous studies have repeatedly shown that muscle temperature decreases during passive half-time rest and that a RW regime such as that utilized in this study inhibits such decreases (Mohr et al., 24; Lovell et al., 213). Mohr et al. (24) also reported that there was a correlation between changes in muscle temperature and repeated sprint performance over the half-time period, suggesting that e46

8 Half-time re-warm up and soccer performance muscle temperature has a key role in the reduced physical performance capacity seen in soccer players after the half-time period. However, other mechanisms such as increased neuromuscular function, elevated blood flow in working muscle, and oxygen uptake kinetics could also be involved (Hodgson et al., 25). Nevertheless, the exact mechanism through which soccer players performance capacity is compromised during passive halftime rest, and consequently that a RW regime effectively attenuates remains unclear, thus warrants further research. The second key finding of this study was that the total distance covered was lowered from the initial 15 min of first half to the initial 15 min of the second half in both RW and CON, but to a higher extent in RW (9% vs 4%, respectively). Interestingly, no significant interaction was found for distance covered with high-intensity running and sprinting; thus, high-intensity running was not lowered in the initial 15 min of the second half as often observed (Mohr et al., 23, 25; Bradley et al., 29; Weston et al., 211) in neither RW nor CON. The lower physical match performance observed in RW may be related to lower physical demands as it was observed that ball possession was higher in RW. A previous study has shown that a team s physical performance is related to the level and performance of the opposing team (Rampinini et al., 27). Moreover, another study by the same research group showed that successful teams covered less total distance, highintensity running, and very high-intensity running than less successful teams, but covered significantly more distance with possession of the ball in the same categories (Rampinini et al., 29). Similar findings have been shown in another study (Di Salvo et al., 29), indicating that high-intensity running distance covered with or without the ball may be a better indicator of performance although it should be noticed that ES were small to moderate. Thus, the shorter distance observed in RW in this present study may simply be a consequence of their higher percentage of ball possession and therefore higher physical demands put on CON chasing and trying to regain possession of the ball. It should however be noted that the ES on almost all workload parameters were only small. Although the used design tries to limit confounding variables, match-to-match variation in workload, especially high-intensity running and sprinting, between consecutive soccer matches has been shown to be high, which complicates the use of real matches when evaluating interventions and therefore possibly resulting in small ESs (Gregson et al., 21). Few studies have highlighted the importance of relating workload to the effective playing time instead of only total playing time as these parameters may vary from game to game and throughout the periods of the game (Castellano et al., 211; Dellal et al., 213). In this study, the effective playing time was 11% and 8% lower in the initial 15- and 5-min period of the second half compared with the corresponding periods in first half. However, as most high-intensity running is performed during effective playing time (Castellano et al., 211), we divided distances covered with the effective playing time in the respective periods as applied by others (Lago-Peñas et al., 212; Dellal et al., 213). When related to the effective playing time, more total distance was covered in the first 15 min of the second half compared with the similar period in the first half, which is in contrast to when analyzed as total time. Moreover, when related to effective playing time more high-intensity running and sprinting was performed in the initial phase of the second half than in the first half. Although relating workload to effective playing time changed the results regarding differences between the first and second half, no shift was observed in the relation between RW and CON. Thus, CON had a higher workload than RW during the initial part of the second half. This may also be explained by the higher ball possession in RW, and thereby more ball chasing by CON. Moreover, these results highlight the importance of taking effective playing time into account when comparing workload between different periods of a match or between matches. It might be argued that the type of RW regime used in this study could result in accumulated fatigue and thus compromise the player s ability to perform maximally during the later stage of the game (e.g., through accelerated glycogen depletion (Gollnick et al., 1973), dehydration (Edwards et al., 27), and/or increased thermal heat strain (Nadel et al., 198). However, results from both Mohr et al. (24) and Lovell et al. (213) contradict this speculation as no differences in muscle temperature or sprint performance were observed during the later stage of the game when comparing traditional passive half-time period and an active re-warm up regime. Moreover, although HR was elevated after performing RW, no differences in HR were observed during the later part of the second half and no differences in fluid loss (1.5% vs 1.7% of body weight) were seen between RW and CON matches. Accordingly, this type of short-to-moderate intensity RW regime does not induce additional fatigue and therefore does not compromise the player s performance capacity during later stage of match. Although outside the scope of this study and accordingly not investigated here, it is very interesting to note that several researchers have reported an increased risk of muscle injury (i.e., non-contact injuries) during the initial stage of the second half of match play in soccer (Hawkins & Fuller, 1996; Rahnama et al., 22). As it is well known that a decrement in muscle temperatures such as those typically reported after passive half-time period in soccer players ( C) (Mohr et al., 24; Lovell et al., 213) is associated with an increase risk of muscle injuries (Safran et al., 1989), and that a re-warm up regime such as that utilized in this study attenuates such decrements (Mohr et al., 24; Lovell et al., 213), e47

9 Edholm et al. it might be speculated that half-time re-warm up also is an effective method to prevent muscle injuries during the initial phase of the second half. Thus, the potential of half-time re-warm up regimes as an injury prevention tool in professional soccer warrants further research. In summary, the present study demonstrates that a traditional passive half-time period during soccer match play results in impaired sprint and jump performance during the initial phase of the second half in professional soccer players and that a re-warm up protocol effectively attenuates such deteriorations. Despite an increased physical work capacity, RW did not increase the amount of high-intensity running performed by the players during the initial phase of the second half. Nevertheless, time motion analysis did reveal a higher ball possession and less defensive high-intensity sprints after RW, which indicates a game advantage at the onset of the second half. Perspectives This study adds to the growing body of evidence showing that a traditional passive half-time period during soccer match causes temporary impairment in the players physical performance capacity and, accordingly, is not an optimal procedure to prepare the players for the second half of the game. The study also shows that if a short-duration low-intensity re-warm up regime is performed during the second part of the half-time period, such deteriorations in performance capacity are diminished or neutralized. Moreover, time motion analysis revealed that inclusion of such a re-warm up regime might result in game advantages as players increased their ball possession and reduced their amount of defensive high-intensity running during the initial phase of the second half after re-warm up. Taken together, the enhanced performance capacity in professional soccer players after an active re-warm up regime might contribute to decisive actions during the initial phase of the second half of the game. As the initial phase of the second half during soccer match also has been identified as a period of increased vulnerability to injuries (Reilly & Hardiker, 1981), the results from this study provide a strong rationale for professional soccer team to evaluate and adapt their half-time period regime so that the players are optimally physically prepared to perform during the first part of the second half in competitive matches. Key words: Football, high-intensity exercise, sprint performance, countermovement jump, time motion analysis. 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