Biomedical subjects

Karim Chamari

Publications and source records attributed to Karim Chamari.

9 recordsLinked to original sources

PubMed2006

Higher plantar pressure on the medial side in four soccer-related movements.

OBJECTIVE: To measure the plantar pressure in four soccer-related movements in 15 male soccer players (mean (SD) age 20.9 (1.3) years, height 173 (4) cm, weight 61.7 (3.6) kg). DESIGN: To record plantar pressure distribution, the players wore soccer boots with 12 circular studs and with an insole pressure recorder device equipped with 99 sensors. Plantar pressure was recorded in five successful trials in each of the four soccer-related movements: running, sideward cutting, 45 degrees cutting and landing from a vertical jump. Each footprint was divided into 10 recorded areas for analysis. RESULTS: Compared with running at 3.3 m/s, maximal speed sideward cutting and 45 degrees cutting induced higher peak pressure (p<0.05) under the second toe, medial forefoot, medial arch and medial heel. The peak pressure of the maximal jump landing was lower under the medial forefoot and lateral forefoot as compared with running (p<0.05). The pressure-time integral showed that sideward cutting and 45 degrees cutting induced higher pressures (p<0.05) than running for all recorded areas, except for the lateral forefoot and the lateral arch. In all the four soccer-related movements, a higher pressure was found on the medial side of the plantar surface as compared with the lateral side. CONCLUSIONS: These data suggest that the medial side of the plantar surface may be more prone to injuries, and that foot orthosis adoption, improved soccer boot design and specific muscle training could be considered to reduce pressure and the subsequent risk of injury.

Adult↗

PubMed2006

Difference in plantar pressure between the preferred and non-preferred feet in four soccer-related movements.

OBJECTIVE AND PARTICIPANTS: The present study measured the difference in plantar pressure between the preferred and non-preferred foot in four soccer-related movements in 15 male university soccer players (mean (SD) age 20.9 (1.3) years, mean (SD) height 173 (4) cm and mean (SD) weight 61.7 (3.6) kg). DESIGN: To record plantar pressure distribution, players randomly wore three types of soccer shoes (classical 6-stud and 12-stud, and specially designed 12-stud) embedded with an insole pressure recorder device with 99 sensors, divided into 10 areas for analysis. Plantar pressure was recorded in five successful trials in each of the four soccer-related movements: running (at 3.3 m/s), sideward cutting, 45 degrees cutting and landing from a vertical jump. RESULTS: Plantar pressures of the preferred and non-preferred foot were different in 115 of 120 comparisons. The overall plantar pressure of the preferred foot was higher than that of the non-preferred foot. Specifically, in each of the four movements, higher pressure was found in the preferred foot during the take-off phase, whereas this was found in the non-preferred foot during the landing phase. This would suggest a tendency of the preferred foot for higher motion force and of the non-preferred foot for a greater role in body stabilisation. CONCLUSIONS: The data indicate that the preferred and non-preferred foot should be treated independently with regard to strength/power training to avoid unnecessary injuries. Different shoes/insoles and different muscular strengthening programmes are thus suggested for each of the soccer player's feet.

Adult↗

PubMed2006

The use of an eccentric chainring during an outdoor 1 km all-out cycling test.

This study assessed whether an eccentric chainring that increases crank arm length at the downstroke and decreases it during the upstroke improves performance in a track cycling event: the 1000m time trial. It also determined whether selected physical and physiological variables and the velocity profile are associated with eccentric chainring performance. Twelve cyclists performed an outdoor 1000m time trial on a 333m banked, cement-surfaced track using two different chainrings, round and eccentric, in randomised order. The important findings of this study were that (1) performance did not significantly differ between chainrings; (2) neither the physiological variables (lactate and heart rate) nor the velocity profile (lap times) were affected by use of the eccentric design; (3) when time was saved with the eccentric chainring, it was significantly correlated with estimated lower limb muscle volume (r=-0.605), circumference (r=-0.739), estimated calf muscle volume (r=-0.772) and cross-sectional area (r=-0.745). Moreover, estimated lower limb muscle volume (r=-0.703), estimated calf muscle volume (r=-0.772) and cross-sectional area (r=-0.871) significantly predicted performance with the eccentric chainring. The physical variables associated with eccentric chainring performance were muscle anthropometric parameters. We have interpreted our results cautiously and suggest that the subjects who had greater lower limb muscle volume and greater calf muscle volume, seem to have had a significant advantage in performing with the eccentric chainring. Further testing with track specialists performing at national or international level would be helpful to define the maximal possibilities of this chainring.

Adolescent↗

PubMed2006

The effects of exercise intensity or drafting during swimming on subsequent cycling performance in triathletes.

The purpose of this study was to compare the affects of drafting or a reduction of exercise intensity during swimming on the power output sustained (P(mean)) during a subsequent cycle time trial (TT). In addition the relationship between peak power output (PPO) and P(mean) generated during the cycle TT after swimming was examined. Nine well-trained triathletes performed an incremental cycling test to exhaustion for determination of PPO. In addition, each subject performed three swim-cycle (SC) trials consisting of 20 min cycle TT preceded by a 400 m swimming trial completed as (1) "all out" and in a non-drafting situation (SC(100%)); (2) at 90% of SC(100%) in a non-drafting situation (SC(90%)); (3) in a drafting position at the same controlled velocity as SC(100%) (SC(drafting)). Swimming velocity (ms(-1)) was significantly (p<0.01) lower at each time point during the 400 m swimming trial in SC(90%) compared with SC(100%) and SC(drafting). There was no significant difference in velocity between SC(100%) and SC(drafting). Blood lactate (BLA) concentration was also significantly (p<0.01) lower after swimming in SC(90%) compared to SC(100%) and SC(drafting) (3.8+/-0.9 versus 7.3+/-2.4 and 7.9+/-2.4mM). The Pmean was also significantly (p<0.05) lower in SC(100%) relative to the SC(90%) and SC(drafting) (226+/-15 versus 253+/-33 and 249+/-36W). There was no significant correlation between PPO (W) and P(mean) for SC(100%) (r=-0.32), SC(90%) (r=0.65; p=0.058) or SC(drafting) (r=0.54). This study indicates that drafting or swimming at a lower velocity did not induce any conflicting affects on power output during a subsequent cycle TT. However, this study confirms that P(mean) during a cycle TT is reduced when prior swimming is performed. Furthermore the positive relationship typically observed between PPO and P(mean) is disrupted by swimming activity performed before a cycling TT. This factor should be considered in terms of physiological analysis of triathletes.

Adult↗

PubMed2006

Cardiorespiratory responses to Yo-yo Intermittent Endurance Test in nonelite youth soccer players.

This study examined the validity of the Yo-yo Intermittent Endurance Test (Level 1; YYIET) as indicator of aerobic power in youth soccer players. Cardiorespiratory responses were determined in 18 moderately trained nonelite youth soccer players (age, 16.6 +/- 0.8 years; height, 178.7 +/- 6.2 cm; body mass, 69.8 +/- 6.0 kg; VO2peak, 52.8 +/- 7.4 ml x kg(-1) x min(-1)) while performing the YYIET and an incremental treadmill test. Maximal heart rate (HRmax), respiratory exchange ratio (RER), O2 pulse, VO2peak, and maximal ventilation (VEmax) were measured. Group YYIET VO2peak, HRmax, RER, and O2 pulse were not significantly different from treadmill responses (p > 0.05). VEmax was significantly lower (p < 0.05) during the YYIET compared to the treadmill condition. No significant correlation was found between treadmill VO2peak and YYIET performance (p > 0.05). This study showed that the YYIET elicits peak VO2 and HR responses. However, YYIET performance results were not related to VO2peak measured in laboratory. Furthermore, the individual VO2peak reached during the TM did not reflect the VO2peak obtained during the YYIET, as shown by the large limits of agreement. As a consequence, compared to other shuttle run field tests, YYIET seems to be a weak indicator of aerobic power in youth moderately trained youth soccer player.

Adolescent↗

PubMed2006

Aerobic fitness and yo-yo continuous and intermittent tests performances in soccer players: a correlation study.

Yo-yo tests are very popular in soccer; however, no study has addressed details of their relation to canonical aspects of aerobic fitness. Furthermore, no information is available on the effect of the individual levels of lower limbs' explosive strength on yo-yo tests in soccer players. The purpose of this study was to examine the physiological determinants of Yo-yo Endurance Test Level 2 (YYETL2) and Yo-yo Intermittent Recovery Test Level 1 (YYIRTL1) in soccer players. Twenty-four soccer players (body mass, 74.6 +/- 8.5 kg; height, 178.1 +/- 4.5 cm; age, 25.6 +/- 5.1 years) were tested for VO2max and ventilatory threshold (VT) on a motorized treadmill. Lower-limb explosive strength was assessed using vertical countermovement jumps (CMJ) performed on a force platform. Results showed that YYETL2 and YYIRTL1 performances (m) were significantly related (r = 0.75, p = 0.00002). YYETL2 results were significantly related to VO2max, VTVO2, and speed at VT (r = 0.75, 0.76, and 0.83, respectively; p < 0.00002). Peak treadmill speed results were significantly related to YYETL2 and YYIRTL1 (r = 0.87 and 0.71, respectively; p < 0.0003). YYIRTL1 was related to CMJ peak power (r = 0.57; p = 0.003). These findings show that YYETL2 and YYIRTL1, although adopting similar starting and progression speeds, are influenced by different physiological variables. From these results, YYETL2 can be considered an aerobic fitness-related field test, whereas YYIRTL1 can be regarded as an aerobic-anaerobic, soccer-specific field test.

Adult↗

PubMed2005

Physiology of soccer: an update.

Soccer is the most popular sport in the world and is performed by men and women, children and adults with different levels of expertise. Soccer performance depends upon a myriad of factors such as technical/biomechanical, tactical, mental and physiological areas. One of the reasons that soccer is so popular worldwide is that players may not need to have an extraordinary capacity within any of these performance areas, but possess a reasonable level within all areas. However, there are trends towards more systematic training and selection influencing the anthropometric profiles of players who compete at the highest level. As with other activities, soccer is not a science, but science may help improve performance. Efforts to improve soccer performance often focus on technique and tactics at the expense of physical fitness. During a 90-minute game, elite-level players run about 10 km at an average intensity close to the anaerobic threshold (80-90% of maximal heart rate). Within this endurance context, numerous explosive bursts of activity are required, including jumping, kicking, tackling, turning, sprinting, changing pace, and sustaining forceful contractions to maintain balance and control of the ball against defensive pressure. The best teams continue to increase their physical capacities, whilst the less well ranked have similar values as reported 30 years ago. Whether this is a result of fewer assessments and training resources, selling the best players, and/or knowledge of how to perform effective exercise training regimens in less well ranked teams, is not known. As there do exist teams from lower divisions with as high aerobic capacity as professional teams, the latter factor probably plays an important role. This article provides an update on the physiology of soccer players and referees, and relevant physiological tests. It also gives examples of effective strength- and endurance-training programmes to improve on-field performance. The cited literature has been accumulated by computer searching of relevant databases and a review of the authors' extensive files. From a total of 9893 papers covering topics discussed in this article, 843 were selected for closer scrutiny, excluding studies where information was redundant, insufficient or the experimental design was inadequate. In this article, 181 were selected and discussed. The information may have important implications for the safety and success of soccer players and hopefully it should be understood and acted upon by coaches and individual soccer players.

Europe↗

PubMed2003

Correlation between heart rate and performance during Olympic windsurfing competition.

The aim of this study was to examine the heart rate (HR) response to Olympic windsurfing competition and to check if there was any correlation between racing HR, performance, and the variables measured during laboratory maximal exercise. Ten elite windsurfers [age: 20.93 (3.46) years; height: 178.10 (6.34) cm; body mass: 66.79 (5.90) kg] performed a laboratory maximal oxygen consumption (.VO(2max)) trial and national windsurf competitions wearing a HR monitor. One hundred and forty-three individual races were examined. Racing HR was expressed as a percentage of (1) HR(max) (maximal treadmill HR) and (2) HR(reserve) (HR(max)-HR(rest)). The performance (racing classification: RC, which is inversely proportional to performance) was significantly correlated to the racing HR response in both light wind (LW): LW-RC=-0.12(%HR(reserve))+13.03; r=-0.71, r(2)=0.50, p<0.001, and medium wind (MW): MW-RC=-0.11(%HR(reserve))+10.99; r=-0.66, r(2)=0.43, p<0.001. The results showed similar correlations between performance and %HR(max). Post racing lactate concentration was higher in LW compared to MW [7.14 (0.21) and 5.18 (2.02) mmol.l(-1), respectively]. There was a negative correlation between the highest racing HR (%HR(reserve)) of each athlete and the second ventilatory threshold expressed as a percentage of .VO(2max) ( r=-0.71, p<0.05). To summarize, this study showed that light and medium wind Olympic windsurfing performances are highly dependent on the capacity of the athlete to maintain a high HR for long periods of time. Furthermore, windsurfing is highly dependent on the athlete's physical fitness level as shown by the correlations between racing HRs and laboratory physiological variables.

Adult↗

PubMed2002

Effects of an enhanced heart rate reserve on aerobic performance in patients with a heart transplant.

OBJECTIVE: The aim of this study was to investigate whether a high-intensity warm-up at the start of a graded, symptom-limited exercise test would enhance heart rate reserve and thus improve the aerobic performance of orthotopic heart transplant patients. DESIGN: Adrenal and cardiorespiratory responses were compared in 10 orthotopic heart transplant patients who performed two graded, symptom-limited exercise tests on an ergocycle. RESULTS: At the start of the graded, symptom-limited exercise test, high intensity increased the norepinephrine level more than usual intensity between rest and the third minute of exercise. This higher norepinephrine level was followed by a higher heart rate response from the fourth minute of exercise. Heart rate reserve was enhanced during high-intensity exercise, without any significant change in peak oxygen uptake. CONCLUSIONS: This specific warm-up enhanced heart rate reserve during a graded, symptom-limited exercise test on an ergocycle. Mechanisms more important than limited heart rate reserve are involved in the limitation of exercise tolerance in orthotopic heart transplant patients.

Adrenergic alpha-Agonists↗