Showing papers by "Karim Chamari published in 2014"

Small-sided games in team sports training: a brief review.

Abstract: Small-sided games (SSGs) incorporating skills, sport-specific movements, at intensities sufficient to promote aerobic adaptations, are being increasingly implemented in professional team sport environments. Small-sided games are often employed by coaches based on the premise that the greatest training benefits occur when training simulates the specific movement patterns and physiological demands of the sport. At present, there is relatively little information regarding how SSG can best be used to improve physical capacities and technical and tactical skills in team sports. It is possible that with some modifications (e.g., number of players, pitch size, coach encouragement, and wrestling), such games may be physiologically beneficial for athletes with relatively high initial aerobic fitness levels. For instance, it has been shown that 3-a-side soccer SSG resulted in higher intensity (i.e., greater overall distance, less jogging and walking, higher heart rate, and more tackling, dribbling, goal attempts, and passes) than 5-a-side SSG. Likewise, when player numbers were kept constant, a larger playing area increased the intensity of the SSG with a smaller playing area having the opposite effect. It has also been demonstrated that energy expenditure was similar between badminton and volleyball courts, but lower than that obtained in a basketball court. Moreover, it has been demonstrated in rugby that wrestling can increase the physical demands of SSG. Consistent coach encouragement can also increase training intensity, although most rule changes have trivial or no effect on exercise intensity. Further research is required to examine the optimal periodization strategies of SSG training for the long-term development of physiological capacity, technical skill, and tactical proficiency, while also minimizing the associated risk of injuries.

Validity and Reliability of New Agility Test among Elite and Subelite under 14-Soccer Players

Abstract: Background: Agility is a determinant component in soccer performance. This study aimed to evaluate the reliability and sensitivity of a "Modified Illinois change of direction test" (MICODT) in ninety-five U-14 soccer players. Methods: A total of 95 U-14 soccer players (mean ± SD: age: 13.61±1.04 years; body mass: 30.52±4.54 kg; height: 1.57±0.1 m) from a professional and semi-professional soccer academy, participated to this study. Sixty of them took part in reliability analysis and thirty-two in sensitivity analysis. Results: The intraclass correlation coefficient (ICC) that aims to assess relative reliability of the MICODT was of 0.99, and its standard error of measurement (SEM) for absolute reliability was <5% (1.24%). The MICODT's capacity to detect change is "good", it's SEM (0.10 s) was ≤ SWC (0.33 s). The MICODT is significantly correlated to the Illinois change of direction speed test (ICODT) (r = 0.77; p<0.0001). The ICODT's MDC95 (0.64 s) was twice about the MICODT's MDC95 (0.28 s), indicating that MICODT presents better ability to detect true changes than ICODT. The MICODT provided good sensitivity since elite U-14 soccer players were better than non-elite one on MICODT (p = 0.005; dz = 1.01 [large]). This was supported by an area under the ROC curve of 0.77 (CI 95%, 0.59 to 0.89, p<0.0008). The difference observed in these two groups in ICODT was not statistically significant (p = 0.14; dz = 0.51 [small]), showing poor discriminant ability. Conclusion: MICODT can be considered as more suitable protocol for assessing agility performance level than ICODT in U-14 soccer players.

Time-motion analysis and physiological responses to karate official combat sessions: is there a difference between winners and defeated karatekas?

Abstract: Purpose: The aim of this study was to measure and compare physiological and time–motion variables during karate fighting and to assess eventual differences between winners and defeated elite karatekas in an ecologically valid environment. Methods: Fourteen elite male karatekas who regularly participated in national and international events took part in a national-level competition. Results: There were no significant differences between winners and defeated karatekas regarding all the studied variables. Karatekas used more upper-limb (76.19%) than lower-limb techniques (23.80%). The kisami-zuki represented the most frequent technique, with 29.1% of all used techniques. The duration of each fighting activity ranged from <1 s to 5 s, with 83.8% ± 12.0% of the actions lasting less than 2 s. Karatekas executed 17 ± 7 high-intensity actions per fight, which corresponded to ~6 high-intensity actions per min. Action-to-rest ratio was about 1:1.5, and high-intensityaction- to-rest ratio was ~1:10. The mean blood l...

Static stretching can impair explosive performance for at least 24 hours.

Abstract: The aim of this study was to compare the effects of static vs. dynamic stretching (DS) on explosive performances and repeated sprint ability (RSA) after a 24-hour delay. Sixteen young male soccer players performed 15 minutes of static stretching (SS), DS, or a no-stretch control condition (CC) 24 hours 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 minutes 30 seconds (2 repetitions of 30 seconds with a 15-second passive recovery) for 5 muscle groups (quadriceps, hamstring, calves, adductors, and hip flexors). Twenty-four hours later (without any kind of stretching in warm-up), the players were tested for the 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 0.05), 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, the SS of the lower limbs and hip muscles had a negative effect on explosive performances up to 24 hours poststretching with no major effects on the RSA. Conversely, the DS of the same muscle groups are highly recommended 24 hours before performing sprint and long-jump performances. In conclusion, the positive effects of DS on explosive performances seem to persist for 24 hours.

Walking and running on treadmill: the standard criteria for kinematics studies.

Abstract: In humans, walking and running represent the most studied locomotion forms. The motorized treadmill has always been a very useful scientific tool, because it allows administer a variety of speed/slope combinations, which is not always easy-to-find in nature. The purpose of this short communication is to help improve the scientific use of the treadmill and explain some simple kinematics variables together with simple ways to measure/calculate them.

Physiological responses according to rules changes during 3 vs. 3 small-sided games in youth soccer players: stop-ball vs. small-goals rules.

Abstract: Small-sided games (SSGs) are effective for soccer-specific aerobic endurance training. To date, no study has investigated the effect of stop-ball (SB-SSG) rule on the physiological responses to SSG. Therefore, the purpose of the present study was to examine the effects of SB-SSG vs. small-goals (SG-SSG) rules on physiological responses during a 3 vs. 3 SSG in young soccer players. Twelve male amateur young soccer players (age, 14.0 ± 0.7 years; body mass, 51.8 ± 8.0 kg; height, 164 ± 7 cm) randomly performed either SB-SSG or SG-SSG for 4 × 4 min separated by 2 min of recovery on a 20 × 15 m pitch. During the SB-SSG, participants were instructed to stop the ball with the soles of their boots in a 15 × 1 m surface behind the pitch bottom line; whereas during the SG-SSG, the participants were instructed to score to a mini-goal (i.e., 1 × 0.5 m). During each test session, the mean heart rate (HR), the post-SSG rating of perceived exertion (RPE) scores and blood lactate concentrations ([La−]) were reco...

Effect of different between-match recovery times on the activity profiles and injury rates of national rugby league players.

Abstract: Professional rugby league competition does not coincide with a standardized amount of recovery between matches; matches can be separated by as many as 10 days and as few as 5 days. These variations in recovery time could influence the match activity profiles and injury rates of players. This study investigated the effect of different between-match recovery times on the activity profiles and injury rates of National Rugby League (NRL) players. Forty-three elite male rugby league players participated in this study. Between-match recovery cycles were defined as short (separated by 5 or 6 days), medium (separated by 7 or 8 days), and long (separated by 9 or 10 days) recovery. Movement was recorded using a commercially available microtechnology unit, which provided information on speed, distance, and repeated high-intensity effort activity. Injuries sustained in either training or match play, which resulted in a missed match, were recorded. Significantly greater (p ≤ 0.05) relative total distance was covered after matches involving short recovery than those involving medium (effect size [ES] = 1.13) or long (ES = 1.08) recovery periods. This difference was because of greater low-speed activity. Injury rates for the adjustables positional group were the highest after short between-match recovery cycles, whereas the injury rates of hit-up forwards and outside backs positional groups were the highest after long between-match recovery cycles. These findings suggest that the activity profiles of NRL match play and the injury rates of specific playing positions are influenced by the amount of recovery between matches. The differences in the activity profiles and injury rates between short, medium, and long between-match recovery cycles should be considered when developing recovery strategies for professional rugby league players.

Anthropometric and physiological characteristics of Melanesian futsal players: a first approach to talent identification in Oceania.

Abstract: This study assessed the anthropometric and physiological characteristics of elite Melanesian futsal players in order to determine the best performance predictors. Physiological parameters of performance were measured in 14 Melanesian (MEL-G, 24.4±4.4 yrs) and 8 Caucasian (NMEL-G, 22.9±4.9) elite futsal players, using tests of jump-and-reach (CMJ), agility (T-Test), repeated sprint ability (RSA), RSA with change-of-direction (RSA-COD), sprints with 5 m, 10 m, 15 m, and 30 m lap times, and aerobic fitness with the 30-15 intermittent fitness test (30-15 IFT). The anthropometric data revealed significantly lower height for MEL-G compared with NMEL-G: 1.73±0.05 and 1.80±0.08 m, respectively; P = 0.05. The CMJ was significantly higher for MEL-G than NMEL-G: 50.4±5.9 and 45.2±4.3 cm, respectively; P = 0.05. T-Test times were significantly lower for MEL-G than NMEL-G: 10.47±0.58 and 11.01±0.64 seconds, respectively; P = 0.05. MEL-G height was significantly related to CMJ (r = 0.706, P = 0.01), CMJpeakP (r = 0.709, P = 0.01) and T-Test (r = 0.589, P = 0.02). No significant between-group differences were observed for sprint tests or 30-15 IFT, including heart rate and estimated VO2max. Between groups, the percentage decrement (%Dec) in RSA-COD was significantly lower in MEL-G than NMEL-G (P = 0.05), although no significant difference was noted between RSA and RSA-COD. Within groups, no significant difference was observed between %Dec in RSA or RSA-COD; P = 0.697. This study presents specific anthropometric (significantly lower height) and physiological (significantly greater agility) reference values in Melanesians, which, taken together, might help coaches and physical fitness trainers to optimize elite futsal training and talent identification in Oceania.

Effects of a short-term in-season plyometric training program on repeated-sprint ability, leg power and jump performance of elite handball players

Abstract: This study examined the effects of 8-weeks of in-season lower limb plyometric training on repeated-sprint ability (RSA), leg power and jumping performance in elite male handball players. Twenty-four participants (age 20 ± 0.3 years, body mass 89.1 ± 2.1 kg, height 1.88± 0.07 m, body fat 13.2 ± 1.3%) were randomly assigned to a control group (CG; n = 10, handball training only) or an experimental group (PG; n = 14, biweekly plyometric training, and handball training). The players were tested for RSA using a protocol of 6 x (2 x 15m) shuttle sprints, separated by 20 s of active recovery. Best time in a single trial (RSAbest), fastest total time (RSATT) and performance decrement (RSAdec) were determined. Leg power was determined by the peak power output (PP) during a 7-second all-out cycling test. Jump heights during the squat jump (SJ) and the countermovement jump (CMJ) were measured. Compared to the CG, PG significantly improved the RSAbest (p < 0.01), RSATT (p <0.01) and RSAdec (p < 0.001), average PP (p < 0.01) and all vertical jump performances (p < 0.001

Effect of two types of partial sleep deprivation on Taekwondo players’ performance during intermittent exercise

Abstract: The purpose of this study was to evaluate the effects of two types of partial sleep deprivation (PSD) on Taekwondo players’ intermittent aerobic performance. Ten male Taekwondo players performed the Yo-Yo Intermittent Recovery Test Level 1 (YYIRTL1) in three conditions in a counterbalanced order, allowing a recovery period ⩾36 h in between them: (A) following a full night of habitual sleep known as a reference normal sleep night (RN), (B) following PSD in the beginning of the night (PSDB), and (C) following partial sleep deprivation at the end of the night (PSDE). No significant difference was observed between the total distance covered inYYIRTL1 (TDYYIRTL1), heart rate peak (HRpeak), plasma lactate concentration, and rating of perceived exertion scale values recorded during YYIRTL1 after (RN), and the two types of PSD (PSDB and PSDE). In summary, the present study indicates that PSDB or PSDE does not alter the intermittent aerobic performance of Taekwondo players in the morning of the following day.

Validity and Reliability of a New Karate-Specific Aerobic Field Test for Karatekas

Abstract: Purpose: This study determined the validity and reliability of a new specific field test that was based on the scientific data from the latest research. Methods: Seventeen international-level karatekas participated in the study: 14 men (age 24.1 ± 4.6 y, body mass 65.7 ± 10.8 kg) and 3 women (age 19 ± 3.6 y, body mass 54.1 ± 0.9 kg). All performed the new karate-specific test (KST) 2 times (test and retest sessions were carried out on separated occasions 1 wk apart). Thirteen men also performed a laboratory test to assess maximal oxygen uptake (VO2max). Results: Test–retest results showed the KST to be reliable. Peak oxygen uptake (VO2peak), peak heart rate (HRpeak), blood lactate concentration, rating of perceived exertion, and time to exhaustion (TE) did not display a difference between the test and the retest. The SEM and ICC for relative and absolute VO2peak and TE were .90, respectively. Significant correlations were found between VO2peak (mL · kg−1 · min−1) and TE measured from the KST (r =...

Importance of muscle power variables in repeated and single sprint performance in soccer players.

Abstract: This study examined the relationship between lower body power and repeated as well as single sprint performance in soccer players. The performance of nineteen male soccer players was examined. The first testing session included the countermovement jump (CMJL) and the progressive full squat (FSL), both with external loads. Power in the CMJL and FSL was measured with each load that was lifted. The second session included a protocol of 40-m repeated sprints with a long recovery period (2 min). The number of sprints executed until there was a 3% decrease in performance for the best 40-m sprint time was recorded as a repeated sprint index (RSI). The RSI was moderately associated with power output relative to body mass in the CMJL and FSL (r = 0.53/0.54, p ≤ 0.05). The most and least powerful players (determined by FSL) showed significant differences in the RSI (9.1 ± 4.2 vs. 6.5 ± 1.6) and 10 m sprint time (p ± 0.01). Repeated and single sprints are associated with relatively lower body power in soccer players.

Eight weeks of dynamic stretching during warm-ups improves jump power but not repeated or single sprint performance

Abstract: There is abundant research involving the acute effects of stretching on subsequent performance; however, there is little information on dynamic stretch training programmes on range of motion (ROM), power and speed measures. It was the objective of this research to examine the training consequences of active dynamic stretching (ADS) and static dynamic stretching (SDS). A repeated measures design compared the effects of 8 weeks of warm-ups incorporating two dynamic stretch modalities: ADS and SDS on squat jump (SJ), countermovement jump (CMJ), 20-m sprint performances and repeated sprint ability (RSA) and hip ROM in 37 male soccer players. SJ height (SDS: 4.6%; ADS: 5.3%; p <0.05), CMJ height (SDS: 5.3%; ADS: 3.4%; p<0.05), CMJ force (SDS: 7.2%; ADS: 12.7%; p<0.001) and CMJ peak power (SDS: 3.9%; ADS: 3.3%; p<0.05) increased significantly after SDS and ADS training compared to the control group (no significant change). Sprint performance and RSA were not affected by either of the dynamic stretch training regimens. The SDS and ADS training programmes elicited similar improvements in flexibility (SDS: 57.6%; ADS: 45.1%; p<0.01) compared to the non-significant changes in the control group. The inclusion of ADS and SDS within the regular warm-up of an 8-week training programme can improve not only flexibility but also jump power measures as well.

The usefulness of session rating of perceived exertion for monitoring training load despite several influences on perceived exertion.

Abstract: Despite various contributing factors, session rating of perceived exertion has the potential to affect a large proportion of the global sporting and clinical communities since it is an inexpensive and simple tool that is highly practical and accurately measures an athlete's outcome of training or competition. Its simplicity can help optimize performance and reduce negative outcomes of hard training in elite athletes.

The effects of one-week training camp on motor skills in Karate kids.

Abstract: AIM The purpose of this study was to evaluate the effects of short-term increased hours of specific high-intensity karate training on motor skills in young karate athletes aged between 8 and 12 years. METHODS Seventy-three children, who regularly trained three karate sessions per-week were divided in two groups: high-intensity karate group (HG=53) and low-intensity karate group (LG=20). HG trained for 7 days: with two sessions per-day (one hour per-session) including specific karate techniques as well as coordination, balance, and flexibility exercises. LG, however, followed the same number of karate training sessions as before the beginning of the study (i.e., three sessions per-week with one hour per-session). Participants performed a battery of tests, 24 hours pre- and one week post-training: a medicine ball throw (MBT), standing long jump (SLJ), active joint flexibility (JM) and lateral/frontal jumps (JLT). RESULTS Significant differences between results of pre and post karate training (ANOVA with repeated measures) included: MBT (P<0.05), SLJ (P<0.0001), JM (P<0.0001), JLT (P<0.0001); whilst the interaction training × time was: MBT (P=0.145), SLJ (P<0.0001), JM (P<0.0001), JLT (P< 0.0001). The HG significantly improved their performance on MBT by 3.23% (P<0.05), SLJ by 5.09% (P<0.001), JM by 1.51% (P<0.001), and JLT by 21.36% (P<0.001). For LG group, there were no significant differences between pre and post-testing in all fitness tests. CONCLUSION Muscular power, flexibility and coordination represent the basics of karate fitness component. In this regard, short term high-intensity karate training represents an effective method for enhancing muscular power and range of motion (i.e. flexibility) in young karate athletes aged between 8 and 12 years. Further studies are needed to support these findings with deeper data.

Does Ramadan fasting affect the diurnal variations in metabolic responses and total antioxidant capacity during exercise in young soccer players

Abstract: The aim of this study was to investigate the effects of Ramadan fasting and time-of-day on biochemical responses to an intermittent exercise [Yo–Yo test level 1, (YYIRT)]. Twenty male soccer players (17.52 ± 0.2 years, 177.4 ± 2.9 cm) completed the YYIRT at 0700 and 1700 hours on three occasions: 1 week before Ramadan (BR), the second week of Ramadan (SWRR2), and the fourth week of Ramadan (ERR4). The total distance covered during the YYIRT (TD) was recorded. Moreover, blood samples were obtained before and after the YYIRT for biochemical measurements. TD was higher BR than during Ramadan in the evening (P < 0.05), but not in the morning. However, there was no significant difference between BR and Ramadan in the morning. While post-exercise values of blood lactate (Lac), glucose (GLC), and markers of muscle injury were greater higher in the evening, resting total antioxidant status (TAS) and uric acid (UA) levels were higher in the morning as compared with the evening BR. These diurnal variations were hidden during Ramadan due to a significant decrease in Lac (P < 0.01), GLC (P < 0.05) and cellular damage (P < 0.05) and an increase in TAS and UA (P < 0.05) values in the evening. No significant difference in biochemical responses was observed in the morning during SWRR2 and ERR4 as compared with BR. In summary, the present study indicates that YYIRT performance was affected by Ramadan fasting only in the evening in young soccer players. The modified diurnal pattern of biochemical responses could explain this performance decrement.

The influence of karate practice level and sex on physiological and perceptual responses in three modern karate training modalities.

Abstract: OBJECTIVE The aim of the present study was to examine the influence of karate practice level (national vs international level) and sex (women vs men) on physiological and perceptual responses in three modern karate training modalities (tactical-technical (TT), technical-development (TD), and randori). METHOD The study included 18 karatekas participating in an eight-session training camp of four TT, two TD, and two randori. During each session, the percentage of maximal heart rate (HR), blood lactate concentration [La(-)], and rating of perceived exertion (RPE) were assessed. RESULTS The main results showed that the percentage of maximal HR was significantly higher in women than in men regardless of practice level or training modality (70.3 ± 4.1 vs 66.2 ± 6.3, respectively). Moreover, [La(-)] and RPE were significantly lower in international-level karatekas compared with their national-level counterparts whatever the sex or training modality ([La(-)] = 11.4 ± 2.6 vs 8.3 ± 2.4 mmol · L(-1) and RPE = 3.6 ± 1.2 vs 4.3 ± 1.5, respectively). Last, physiological and perceptual responses were significantly higher during randori in comparison with TT and TD for both sexes. CONCLUSION The combination of [La(-)] and RPE thus seems to be a good indicator for discriminating between national- and international-level karatekas, and randori seems to be an effective means to reproduce official karate sparring.

Influence of exercise intensity and duration on perceived exertion in adolescent Taekwondo athletes

Abstract: The aim of this study was to examine the influence of exercise intensity and session duration on rating of perceived exertion (RPE) in adolescent Taekwondo (TKD) athletes. Twelve male youth competitive TKD athletes, aged between 13 and 18 years took part in this study. Training data (368 individual sessions) were collected during the 12 weeks of the pre-competitive TKD season. Daily training load was calculated using the heart rate and the session-RPE. Exercise intensity was also classified in five zones [i.e. 50-60%, 61-70%, 71-80%, 81-90% and 91-100% of maximal heart rate (HRmax)] and the time spent in each zone was expressed as percentage of total session time. The analysis of variance showed a significant main effect for zone (p<0.001) with most of the time (69%) spent at intensities between 61 and 90% of HRmax, and only 10% spent above 91% (mean differences compared to the other zones ranging from -6.6% versus zone 1 to -14.8% versus zone 3; p<0.0001). The individual correlation between session-RPE and HR-based methods were moderate to large. The stepwise multiple regression showed that RPE was influenced mainly by the time spent in the high intensity zone that explained 22.1% of the variance in RPE. Session duration accounted for only an additional 3.2%. The results suggest the time spent at high-intensity (i.e. between 91 and 100% HRmax) and only marginally the session duration influences the RPE referred to the whole training session. This seems to confirm that the determination of the TL multiplying the RPE and session duration is acceptable.

The effect of time of day on hormonal responses to resistance exercise

Abstract: The aim of this study was to examine the acute hormonal responses to resistance training performed in the morning or in the evening. Eighteen active men underwent two lower body resistance exercise (RE) sessions (3 × 10 repetitions, maximum of four exercises) on two occasions (07:00 and 17:00 h). Blood samples were collected in the morning and evening before (BT), after (AT), and 60 min after (60-AT) the RE training session for the determination of testosterone (T) and cortisol (C) concentrations. The Δ-changes of T and C concentrations were calculated as the difference between AT and BT, the difference between 60-AT and BT, as well as the difference between 60-AT and AT. The results showed that T increased from BT to AT and decreased from AT to 60-AT at the two times of testing. However, T was higher in the evening and lower in morning at 60-AT compared with BT. C increased from BT to AT and 60-AT in the evening, and decreased from AT to 60-AT at the two times of testing. Likewise, Δ-changes of T and C c...

Effects of Ramadan on physical capacities of North African boys fasting for the first time.

Abstract: Introduction : Most of the literature related to the effects of Ramadan fasting on physical performance has focused on adults, and only three studies have examined its impact on children’s physical performance. Aims : To examine the effects of Ramadan fasting on first-time fasting boys’ performance in short-term explosive exercises [vertical and horizontal jump tests (VJT and HJT), 20-m and 30-m sprints and medicine-ball throw (MBT)], as well as in sub-maximal endurance [6-min walking distance (6MWD) measured during the 6-min walk test (6MWT)]. Methods : Eighteen Tunisian boys [mean±standard deviation (SD) of age and body mass (BM): 11.9±0.8 y and 55.4±18.2 kg, respectively] were included. The experimental design comprised four testing phases: 2-weeks before Ramadan (BR), the end of the second week (R2) and the fourth week (R4) of Ramadan, and 10–12 days after the end of Ramadan (AR). At each phase, boys performed two test sessions in the afternoon (15:00–17:00 h) interrupted by 48 h of recovery (first test session: BM, VJT, HJT, and 20-m and 30-m sprint tests; second session: MBT and 6MWT). The study was conducted during the summer of 2012 from July 5 to August 29. Results : 6MWDs (m) were significantly shorter during R2 (652±101) and R4 (595±123) compared to BR (697±86) and came back to baseline values AR. BM (kg) mean±SD did not significantly change during R2 (52±15) and during R4 (53±15) compared to BR (55±17), and short-term explosive performances were unchanged throughout the study. Conclusion : In non-athletic children, first-ever Ramadan fasting impairs sub-maximal aerobic capacity but has no effect on BM or short-term explosive performance. Keywords: Tunisia; Ramadan fasting; anaerobic exercise; walking distance; child To access the supplementary material for this article please see Supplementary files in the column to the right (under Article Tools) (Published: 24 September 2014) Citation: Libyan J Med 2014, 9 : 25391 - http://dx.doi.org/10.3402/ljm.v9.25391

Acute effects of whole-body vibration on running gait in marathon runners

Abstract: The aim of this study was to investigate the effects of a single bout of whole-body vibration (WBV) on running gait. The running kinematic of sixteen male marathon runners was assessed on a treadmill at iso-efficiency speed after 10 min of WBV and SHAM (i.e. no WBV) conditions. A high-speed camera (210 Hz) was used for the video analysis and heart rate (HR) was also monitored. The following parameters were investigated: step length (SL), flight time (FT), step frequency (SF), contact time (CT), HR and the internal work (WINT). Full-within one-way analysis of variance (ANOVA) of the randomised crossover design indicated that when compared to SHAM conditions, WBV decreased the SL and the FT by ~4% (P < 0.0001) and ~7.2% (P < 0.001), respectively, and increased the SF ~4% (P < 0.0001) while the CT was not changed. This effect occurred during the first minute of running: the SL decreased ~3.5% (P < 0.001) and SF increased ~3.3% (P < 0.001). During the second minute the SL decreased ~1.2% (P = 0.017) and the SF increased ~1.1% (P = 0.02). From the third minute onwards, there was a return to the pre-vibration condition. The WINT was increased by ~4% (P < 0.0001) during the WBV condition. Ten minutes of WBV produced a significant alteration of the running kinematics during the first minutes post exposure. These results provide insights on the effects of WBV on the central components controlling muscle function.

Effect of the number of sprint repetitions on the variation of blood lactate concentration in repeated sprint sessions.

Abstract: The aim of the present study was to examine the effect of number of sprint repetitions on the variation of blood lactate concentration (blood (La)) during different repeated-sprint sessions in order to find the appropriate number of sprint repetitions that properly simulates the physiological demands of team sport competitions. Twenty male team-sport players (age, 22.2 ± 2.9 years) performed several repeated-sprint sessions (RSS) consisting of 1, 2, 3, 4, 5, 9, or 10 repetitions of 30 m shuttle sprints (2 × 15 m) with 30 s recovery in between. The blood (La) was obtained after 3 min of recovery at the end of each RSS. The present study showed that for RSS of 3 sprints (RSS3) there was a high increase (p<0.001) in blood (La), which reached approximately fivefold resting values (9.4±1.7 mmol · l -1 ) and then remained unchanged for the RSS of 4 and 5 sprints (9.6±1.4 and 10.5±1.9 mmol · l -1 , p=0.96 and 0.26, respectively). After RSS9 and RSS10 blood (La) further significantly increased to 12.6 and 12.7 mmol · l -1 , p<0.001, respectively. No significant difference was found between RSS3, RSS4 and RSS5 for the percentage of sprint speed decrement (Sdec) (1.5±1.2; 2.0±1.1 and 2.6±1.4%, respectively). There was also no significant difference between RSS9 and RSS10 for Sdec (3.9±1.3% and 4.5±1.4%, respectively). In conclusion, the repeated-sprint protocol composed of 5 shuttle sprint repetitions is more representative of the blood lactate demands of the team sports game intensity.

Validity of the MarkWiiR for kinematic analysis during walking and running gaits

Abstract: The aim of this study was to validate the MarkWiiR (MW) captured by the Nintendo Wii-Remote (100-Hz) to assess active marker displacement by comparison with 2D video analysis Ten participants were tested on a treadmill at different walking (1<6 km · h -1 ) and running (10<13 km · h -1 ) speeds During the test, the active marker for MW and a passive marker for video analysis were recorded simultaneously with the two devices The displacement of the marker on the two axes (x-y) was computed using two different programs, Kinovea 0815 and CoreMeter, for the camera and MW, respectively Pearson correlation was acceptable (x-axis r≥0734 and y-axis r≥0684), and Bland-Altman plots of the walking speeds showed an average error of 024±052% and 15±091% for the x- and y-axis, respectively The difference of running speeds showed average errors of 067±033% and 126±033% for the x- and y-axes, respectively These results demonstrate that the two measures are similar from both the x- and the y-axis perspective In conclusion, these findings suggest that the MarkWiiR is a valid and reliable tool to assess the kinematics of an active marker during walking and running gaits

Relationship between explosive performance measurements of the lower limb and repeated shuttle-sprint ability in elite adolescent handball players

Abstract: This study investigated the relationship between performance measures of the lower-limb and repeated shuttle-sprint ability (RSSA) in elite adolescent handball players. Twenty-two male handball players (age: 17.7 ± 0.3 years) participated in the study. Subjects underwent measurements of lower-limb maximal strength (1-RM half back squat), explosive power (force-velocity test), jumping ability (squat and counter-movement jumps), sprinting velocities over the first step (VS) and the first 5 m (V5) of a 15 m sprint, and Yo-Yo Intermittent Recovery Test, Level 1. The players were tested for RSSA using a protocol of 6 repetitions of maximal 2 x 15-m shuttle sprints with 180° turns (~6 s) departing every 20 s. RSSA results were evaluated in three ways: best time in a single trial (RSSAbest), decrement (RSSAdec) and total time (RSSATT). The correlations of RSSA with the assorted fitness measures varied considerably. The RSSATT and RSSAdec were positively associated with 1-RM half back squat (r = 0.78 and r = 0.68 respectively; p< 0.01). Significant correlations were also found between RSSATT and

Time interval moderates the relationship between psyching-up and actual sprint performance.

Abstract: This study attempted to test whether the strongest effect of psyching-up (PU) strategy on actual sprint performance can be observed when the strategy is used immediately (or almost) before performance compared with when there is a delay between PU and performance. To do so, 16 male sprinters (age, 20.6 ± 1.3 years; body mass, 77.5 ± 7.1 kg; height, 180.8 ± 5.6 cm) were enrolled in a counterbalanced experimental design in which participants were randomly assigned to 10 sessions (2 [Experimental Condition: imagery vs. distraction] × 5 [Time Intervals: no interval, 1 minute, 2 minutes, 3 minutes, and 5 minutes]). Before performing the experimental tasks, participants rated: (a) the Hooper index, (b) their degree of self-confidence, and (c) after the completion of the experimental test; they rated their perceived effort. Findings showed that the imagery significantly improved sprint performance. Specifically, the imagery enhanced performance on the phase of acceleration (0-10 m) and on the overall sprint (0-30 m) when used immediately before performance and at 1- and 2-minute intervals but not for 3- and 5-minute intervals. These findings support the hypothesis that the potential effect of the PU strategy on performance vanishes over time. The pre-experimental task Hooper and self-efficacy indexes did not change across the 10 experimental sessions, reinforcing the view that the observed performance changes were directly caused by the experimental manipulation and not through any altered status of the athletes (self-efficacy, fatigue/recovery, and stress). The potential mechanisms underlying such a process and practical applications are discussed.

The Relative Age Effect in the 2013 FIFA U-17 Soccer World Cup Competition

Abstract: Purpose: The purpose of this study was to check the eventual existence of any Relative Age Effect (RAE) in the recent 2013’ FIFA Male Under-17 (U-17) World Cup Football tournament. The data pertaining to the players who participated in to that event were collected from the FIFA website. They included the players’ dates of birth (day, month and year) and position (goalkeeper, defender, midfielder or striker).The distributions of birth months were significantly different with more players born in the early months of the year compared with the later months. For the entire cohort of players, 38.7% were born in the first quarter of the year while only 10.5% were born in the last 3 months in the same year. This relative age effect held for all FIFA-designated teams except for the Nigeria and the Cote d'Ivoire having shown a reverse relative age effect. The results of this investigation show that at the highest level of youth soccer, the RAE still exists and is a strong bias toward inclusion of players born early in the concerned year.

Time-of-day effect on dart-throwing performance and the perception of the difficulty of the task in 9–10 year-old boys

Abstract: The aim of this study was to examine the time-of-day effects on dart-throwing performance (at two distances from the dartboard) and the perception of the difficulty of the task in 9–10 year-old boys. In a randomized order, 12 healthy boys (age = 9.8 ± 0.5 years, height = 144 ± 6.2 cm, and body-mass = 32.7 ± 3.4 kg) performed two test sessions, in the morning at 07:00 h and in the evening at 17:00 h. During each test session, performance during the dart-throwing test, oral temperature, and perceived difficulty (PD) of the task were recorded. Performance at throwing darts was scored by three methods: mean distance of the dart from the bulls-eye, number of times the target was missed (number of zeros), and variability of the scores from the darts thrown. Our results revealed that performance at throwing darts was significantly better in the afternoon than the morning, with lowest mean distance of the dart from the bulls-eye around the time of maximal values of oral temperature (p < 0.001). Also, the number o...

Uphill sprint vs. intermittent running in young soccer players: Acute physiological responses

Abstract: Purpose This study aimed to compare the acute effects of uphill repeated sprinting ‘‘with long recovery’’ (RS) and uphill intermittent running (IR) training on heart rate (HR) and blood lactate (BL) responses. Methods Thirteen young male soccer players randomly performed in two separate occasions, on a slope (10 %), an RS and an IR session. RS consisted of three sets of eight maximal uphill 20-m sprints with long (90 s) recovery between sprints, and 8 min passive rest between sets, whereas IR consisted of 24 repetitions of 22-m sub-maximal (95 % of maximum speed achieved in an incremental test) uphill runs interspersed by a 15-s downhill walking recovery, lasting for a total duration of 8 min. Results The mean HR, expressed as the percentage of HRMAX, was significantly higher in IR than in RS (86.1 ± 3.1 vs. 77.0 ± 4.5 %, respectively, p \ 0.05). Conversely, BL measured after 3 min was significantly higher in RS (5.9 ± 1.1 mmol L -1 ) than in IR (2.9 ± 1.2 mmol L -1 , p \ 0.05). Conclusions The differences found between RS and IR may be attributed to the different work/recovery ratios and speed characteristics. Therefore, uphill IR seems more suitable when the target is to tax the aerobic system, while RS may be more suitable when the focus is on stimulating the speed without increasing the metabolic demand.

EEG-Related Changes to Fatigue during Intense Exercise in the Heat in Sedentary Women

Abstract: Purpose: This study examined the possible causal mechanisms of fatigue during intense exercise in the heat in a group of nine sedentary women. Methods: Two strenuous cycling sessions were performed, at 100% of maximal aerobic power, either in neutral (N-Ex, air temperature: 22°C ± 0.4°C, air humidity: 53% ± 8%) or in heat conditions (H-Ex, air temperature: 35°C ± 0.3°C, air humidity: 59 ± 6). Tympanic temperature (Tty), heart rate (HR), body mass loss (BML), lactate concentration [La] and brain electrical activity (EEG: α and β waves and α/β ratio) were recorded. Results: Tty, HR and [La] increases (p ﹣1) than that during N-Ex (0.08 ± 0.02°C·min﹣1), and time to exhaustion (Time Limit at 100%) was significantly (p β waves decreased (p α/β ratio increased (p < 0.05) significantly immediately before exhaustion. Conclusion: During exercise in the heat, the high rate of core temperature rising might be a critical factor triggering faster brain changes.

Diurnal variation of cognitive performance and perceived difficulty in dart-throwing performance in 9–10-year-old boys

Abstract: The aim of this study was to investigate variations in cognitive performance and difficulty perception in 9–10-year-old boys. Fifteen healthy boys (Age = 9.8 ± 0.4 years; Height = 146 ± 5.2 cm; Body mass = 34.2 ± 2.9 kg) performed three cognitive tasks, the reaction time (RT), the trail-making test, TMT (to evaluate flexibility), and the barrage tests (to evaluate selective attention [SA]). The tests were performed at 07:00 and 17:00 h. The results demonstrated that oral temperature, RT, and flexibility were significantly higher at 17:00 h than at 07:00 h. A significant main effect of diurnal variation was found for RT (t = 3.075, p = 0.008), SA (t = 2.43, p = 0.029), and executive function (TMT, Parts A and B) (t = 5.86, p < 0.001; t = 4.85, p < 0.001, respectively). However, these rhythms of cognitive performance were not correlated with the rhythm of core temperature at 07:00 h. In conclusion perceived difficulty was correlated with executive function in situations with higher level of difficulties.