Karim Chamari

Publications (145) View all

• Source

  Available from: Monoem Haddad

  Article: Effects of ramadan on the diurnal variations of repeated-sprint performance.

  Asma Aloui, Anis Chaouachi, Hamdi Chtourou, Del P Wong, Monoem Haddad, Karim Chamari, Nizar Souissi
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  ABSTRACT: Purpose: This study examined the effects of Ramadan on cycling repeated-sprint ability (RSA) and corresponding diurnal variations. Methods: Twelve active men performed an RSA test (5 × 6-s maximal sprints interspersed with 24 s passive recovery) during morning and afternoon sessions 1 wk before Ramadan (BR), during the second (R2) and the fourth (R4) weeks of Ramadan, and 2 wk after Ramadan (AR). Maximal voluntary contraction was assessed before (MVCpre), immediately after (MVCpost), and 5 min after the RSA test (MVCpost5). Moreover, hematocrit, hemoglobin, and plasma sodium and potassium (K+) concentrations were measured at rest and after the RSA test and MVCpost. Results: Overall, peak power (Ppeak) during the RSA test decreased throughout the 5 sprints. Ppeak measured in the first sprint and MVCpre were lower during Ramadan than BR in the afternoon (P < .05) and higher in the afternoon than the morning BR and AR (P < .05). However, this diurnal rhythmicity was not found for the last 4 sprints' Ppeak, MVCpost, and MVCpost5 in all testing periods. Furthermore, the last 4 sprints' Ppeak, MVCpost, MVCpost5, and morning MVCpre were not affected by Ramadan. [K+] measured at rest and after the RSA test and MVCpost were higher during Ramadan than BR in the afternoon (P < .05) and higher in the afternoon than the morning during Ramadan (P < .05). Conclusions: Fatigability is higher in the afternoon during Ramadan, and, therefore, training and competition should be scheduled at the time of day when physical performance is less affected.
  International journal of sports physiology and performance 05/2013; 8(3):254-62. · 1.80 Impact Factor
• Source

  Available from: Monoem Haddad

  Article: Static Stretching Can Impair Explosive Performance For At Least 24 Hours.

  Monoem Haddad, Amir Dridi, Chtara Moktar, Anis Chaouachi, Del P Wong, David Behm, Karim Chamari
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  ABSTRACT: The aim of this study was to compare the effects of static versus dynamic stretching on explosive performances and repeated sprint ability (RSA) following a 24-h delay. Sixteen young male soccer players performed 15-min of static stretching (SS), dynamic stretching (DS), or a no stretch control condition (CC) 24-h before performing explosive performances and RSA tests. This was a within-subject repeated measures study with SS, DS, and CC being counterbalanced. Stretching protocols included 2 sets of 7-min 30-sec (2 repetitions of 30-sec with 15-sec passive recovery) for five muscle-groups (quadriceps, hamstring, calves, adductors, and hip flexors). 24-h later (without any kind of stretching in warm up), players were tested for 30-m sprint test (with 10- and 20-m lap-times), 5 jump-test (5JT), and RSA test. Significant differences were observed between CC, SS and DS with 5JT (F=9.99, p<0.00, ES=0.40), 10m sprint time (F=46.52, p<0.00, ES=0.76), 20m sprint time (F=18.44, p<0.000, ES=0.55) and 30m sprint time (F=34.25, p<0.000, ES=0.70). The significantly better performance (p<0.05) was observed after DS as compared to CC and SS in 5JT, and sprint times for 10m, 20m and 30m. In contrast, significantly worse performance (p<0.05) was observed after SS as compared to CC in 5JT, and sprint times for 10m, 20m and 30m. With RSA, no significant difference was observed between different stretching protocols in total time (F=1.55, p>0.05), average time (F=1.53, p>0.05), and fastest time (F=2.30, p>0.05), except for the decline index (F=3.54, p<0.04, ES=0.19). Therefore, SS of the lower limbs and hip muscles had a negative effect on explosive performances up to 24-h post-stretching with no major effects on RSA. Conversely, DS of the same muscle groups are highly recommended 24-h before performing sprint and long-jump performances. In conclusion, the positive effects of DS on explosive performances seem to persist for 24-h.
  The Journal of Strength and Conditioning Research 04/2013; · 1.83 Impact Factor
• Source

  Available from: Dellal A

  Article: The effects of a congested fixture period on physical performance, technical activity and injury rate during matches in a professional soccer team.

  Alexandre Dellal, Carlos Lago-Peñas, Ezequiel Rey, Karim Chamari, Emmanuel Orhant
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  ABSTRACT: BACKGROUND: In modern professional soccer, the ability to recover from official match-play and intense training is often considered a determining factor in subsequent performance. OBJECTIVE: To investigate the influence of playing multiple games with a short recovery time between matches on physical activity, technical performance and injury rates. METHODS: The variation of physical (overall distance, light-intensity, low-intensity, moderate-intensity and high-intensity running) and technical performance (successful passes, balls lost, number of touches per possession and duels won) of 16 international players was examined during three different congested periods of matches (six games in 18 days) from the French League and Cup (n=12), and the UEFA Champions' League (n=6) during the 2011-2012 season and compared with that reported in matches outside these periods. Data were collected using a computerised match analysis system (Amisco). Injury rate, time loss injuries, as well as the mechanism, circumstances and severity of the injury were also analysed. RESULTS: No differences were found across the six successive games in the congested period, and between no congested and the three congested periods for all the physical and technical activities. The total incidence of injury (matches and training) across the prolonged congested periods did not differ significantly to that reported in the non-congested periods. However, the injury rate during match-play was significantly higher during the congested period compared with the non-congested period (p<0.001). The injury rate during training time was significantly lower during the congested period compared with the non-congested periods (p<0.001). The mean lay-off duration for injuries was shorter during the congested periods compared with the non-congested periods (9.5±8.8 days vs 17.5±29.6 days, respectively p=0.012, effect sizes=0.5). CONCLUSIONS: Although physical activity, technical performance and injury incidence were unaffected during a prolonged period of fixture congestion, injury rates during training and match-play and the lay-off duration were different to that reported in matches outside this period.
  British journal of sports medicine 02/2013; · 2.55 Impact Factor
• Article: Time-of-day effects on biochemical responses to soccer-specific endurance in elite Tunisian football players.

  Omar Hammouda, Hamdi Chtourou, Anis Chaouachi, Henda Chahed, Hlima Bellimem, Karim Chamari, Nizar Souissi
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  ABSTRACT: Abstract This study aimed to investigate footballers' diurnal variation of performance during the Yo-Yo intermittent recovery test and the associated biochemical responses. Fifteen male footballers (17.3 ± 0.3 years, 69.1 ± 4.2 kg, 179.7 ± 3.6 cm) performed two randomised Yo-Yo tests at 07:00 h and 17:00 h. Blood samples were collected before and 3 min after each test for the assessment of metabolic responses. Resting oral temperature and rating of perceived exertion (RPE) after and peak heart rate during the Yo-Yo test were recorded at both times-of-day. Core temperature and performances during the Yo-Yo test increased from the morning to the evening (P < 0.0005 and P = 0.01, respectively) without significant time-of-day effects on peak heart rate and RPE. Moreover, pre- and post-Yo-Yo test biochemical parameters (high-density lipoprotein, triglycerides, glucose, creatine-kinase) were higher at 17:00 h than 07:00 h (160.45 ± 18.68 vs. 173.73 ± 14.48 before and 191.18 ± 21.13 vs. 219.27 ± 27.74 IU · L(-1) after the Yo-Yo test at 07:00 h and 17:00 h, P = 0.032 and P < 0.0005, respectively for creatine-kinase). Only post-exercise lactate levels were higher in the evening (9.82 ± 0.65 vs. 10.86 ± 0.33 mmol · L(-1), P < 0.0005) with all biochemical variables being increased after the exercise (P < 0.0005). These findings suggest a possible link between the diurnal fluctuation of metabolic responses and the related pattern of specific-endurance performances in footballers. Therefore, the higher biochemical responses observed in the evening could explain, partially, the greater performance and metabolic solicitation at this time-of-day.
  Journal of Sports Sciences 01/2013; · 1.93 Impact Factor
• Source

  Available from: Jacques Prioux

  Article: Effects of recovery mode (active vs. passive) on performance during a short high-intensity interval training program: a longitudinal study.

  Abderraouf Ben Abderrahman, Hassane Zouhal, Karim Chamari, Delphine Thevenet, Pierre-Yves de Mullenheim, Steven Gastinger, Zouhair Tabka, Jacques Prioux
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  ABSTRACT: The aim of this longitudinal study was to compare two recovery modes (active vs. passive) during a seven-week high-intensity interval training program (SWHITP) aimed to improve maximal oxygen uptake ([Formula: see text]), maximal aerobic velocity (MAV), time to exhaustion (t (lim)) and time spent at a high percentage of [Formula: see text], i.e., above 90 % (t90 [Formula: see text]) and 95 % (t95 [Formula: see text]) of [Formula: see text]. Twenty-four adults were randomly assigned to a control group that did not train (CG, n = 6) and two training groups: intermittent exercise (30 s exercise/30 s recovery) with active (IE(A), n = 9) or passive recovery (IE(P), n = 9). Before and after seven weeks with (IE(A) and IE(P)) or without (CG) high-intensity interval training (HIT) program, all subjects performed a maximal graded test to determine their [Formula: see text] and MAV. Subsequently only the subjects of IE(A) and IE(P) groups carried out an intermittent exercise test consisting of repeating as long as possible 30 s intensive runs at 105 % of MAV alternating with 30 s active recovery at 50 % of MAV (IE(A)) or 30 s passive recovery (IE(P)). Within IE(A) and IE(P), mean t (lim) and MAV significantly increased between the onset and the end of the SWHITP and no significant difference was found in t90 VO(2max) and t95 VO(2max). Furthermore, before and after the SWHITP, passive recovery allowed a longer t (lim) for a similar time spent at a high percentage of VO(2max). Finally, within IE(A), but not in IE(P), mean VO(2max) increased significantly between the onset and the end of the SWHITP both in absolute (p < 0.01) and relative values (p < 0.05). In conclusion, our results showed a significant increase in VO(2max) after a SWHITP with active recovery in spite of the fact that t (lim) was significantly longer (more than twice longer) with respect to passive recovery.
  Arbeitsphysiologie 12/2012; · 2.15 Impact Factor