Muscle glycogen and diet in elite soccer players

Summary The top players in an elite soccer team volunteered as subjects in a study to determine intramuscular glycogen concentrations after a regular season match, and whether optimal glycogen levels could be re-attained prior to the team's next match. Fifteen players were biopsied in the M. vastus lateralis following a regular season game (Day I). Of these, eight were biopsied 24 h later in the evening of a free day during which no training session was held (Day II), and again 24 h later after a very light training session (Day III). Muscle glycogen concentrations for the eight players averaged (± SD) 45.9±7.9, 68.9±2.7, and 72.8±8.3 mmol glucose units ×kg^–1 wet muscle weight on Day I, Day II, and Day III respectively. Dietary records were analysed during a week of peak season competition and training. The average daily total energy consumption and total quantity of carbohydrates consumed were less than what is normally consumed by athletes in similar sports. The inability of the players to maintain even normal, resting levels of muscle glycogen is probably related to their dietary practices.Supported in part by grants from the JÄrnhardtska Fund and the Swedish Football Association     

Strength training effects on physical performance and serum hormones in young soccer players

To determine the effects of simultaneous explosive strength and soccer training in young men, 8 experimental (S) and 11 control (C) players, aged 17.2 (0.6) years, were tested before and after an 11-week training period with respect to the load-vertical jumping curve [loads of 0–70 kg (counter-movement jump CMJ0–70)], 5- and 15-m sprint performances, submaximal running endurance and basal serum concentrations of testosterone, free testosterone and cortisol. In the S group, the 11-week training resulted in significant increases in the low-force portion of the load-vertical jumping curve (5–14% in CMJ0–30, P<0.01) and in resting serum total testosterone concentrations (7.5%, P<0.05), whereas no changes were observed in sprint running performance, blood lactate during submaximal running, resting serum cortisol and resting serum free testosterone concentrations. In the C group, no changes were observed during the experimental period. In the S group, the changes in CMJ0 correlated (P<0.05–0.01) with the changes in the 5-m (r=0.86) and 15-m (r=0.92) sprints, whereas the changes in CMJ40 correlated negatively with the changes in the testosterone:cortisol ratio (r=–0.84, –0.92, respectively, P<0.05). These data indicate that young trained soccer players with low initial strength levels can increase explosive strength by adding low-frequency, low-intensity explosive-type strength training. The inverse correlations observed between changes in CMJ40 and changes in the testosterone:cortisol ratio suggest that a transient drop in this ratio below 45% cannot always be interpreted as a sign of overstrain or neuroendocrine dysfunction.An erratum to this article can be found at     

Anterior cruciate ligament ruptures in German elite soccer players: Epidemiology,mechanisms, and return to play

Background

Anterior cruciate ligament ruptures (ACLRs) are severe sports-related injuries with significant consequences for affected players and teams. This study aims to identify the epidemiology and injury-related lay-off after ACLR in professional male soccer players from the first-division German Bundesliga.

The effect of the Ramadan fast on physical performance and dietary habits in adolescent soccer players

The purpose of this study was to examine the effect of the Ramadan fast on performance capacities, dietary habits, and the daily behavioral patterns in adolescent (14–16-year-old) soccer players. Nineteen male players performed a series of fitness tests before and at the end of Ramadan fast. Caloric intake, physical activity pattern and sleep habits were evaluated during the week before the Ramadan fast and during the last week of the Ramadan fast. The fast resulted in a significant reduction in aerobic capacity [3,000 m run time (mean ± SD): 812.8 ± 73.3 s vs. 819.9 ± 73.4 s, P < 0.001], speed endurance (Sum 6 × 40 m run time: 46.36 ± 1.36 s vs. 46.73 ± 1.31 s, P < 0.001, and performance decrement: 9.0 ± 1.5% vs. 9.5 ± 1.7%, P < 0.05), and jumping performance (44.8 ± 4.5 cm vs. 44.0 ± 4.5 cm, P < 0.05), but had no significant effect on sprint performance (7.38 ± 0.25 s vs. 7.40 ± 0.26 s, P = 0.20) or agility (4 × 10 m shuttle run time: 9.53 ± 0.35 s vs. 9.55 ± 0.37 s, P = 0.26). Daily intense physical activity was significantly reduced during Ramadan (6.4 ± 0.2 h/week vs. 4.5 ± 0.1 h/week, P < 0.005). There were no significant differences in total caloric intake (3012 ± 412 kcal/day vs. 3240 ± 348 kcal/day, P = 0.39) or total daily sleeping hours (8.6 ± 0.7 h/day vs. 8.6 ± 0.5 h/day, P = 0.80) between Ramadan and a regular month. The results indicate that Ramadan fasting can lead to a significant decrease in athletic performance capacities. The decrease in performance does not necessarily relate to changes in caloric intake and sleeping hours during the fast.     

The slope of the oxygen pulse curve does not depend on the maximal heart rate in elite soccer players

INTRODUCTION:

It is unknown whether an extremely high heart rate can affect oxygen pulse profile during progressive maximal exercise in healthy subjects.

OBJECTIVE:

Our aim was to compare relative oxygen pulse (adjusted for body weight) curves in athletes at their maximal heart rate during treadmill cardiopulmonary exercise testing.

METHODS:

A total of 180 elite soccer players were categorized in quartiles according to their maximum heart rate values (n  =  45). Oxygen consumption, maximum heart rate and relative oxygen pulse curves in the extreme quartiles, Q1 and Q4, were compared at intervals corresponding to 10% of the total duration of a cardiopulmonary exercise testing.

RESULTS:

Oxygen consumption was similar among all subjects during cardiopulmonary exercise testing; however subjects in Q1 started to exhibit lower maximum heart rate values when 20% of the test was complete. Conversely, the relative oxygen pulse was higher in this group when cardiopulmonary exercise testing was 40% complete (p<.01). Although the slopes of the lines were similar (p = .25), the regression intercepts differed (p<.01) between Q1 and Q4. During the last two minutes of testing, a flat or decreasing oxygen pulse was identified in 20% of the soccer players, and this trend was similar between subjects in Q1 and Q4.

CONCLUSION:

Relative oxygen pulse curve slopes, which serve as an indirect and non-invasive surrogate for stroke volume, suggest that the stroke volume is similar in young and aerobically fit subjects regardless of the maximum heart rate reached.     

Pain and affective distress before and after ACL surgery: a comparison of amateur and professional male soccer players in the early postoperative period

Pain thresholds and levels of distress before and in the early postoperative period after anterior cruciate ligament surgery were measured in professional and amateur male soccer players and compared. Between June 2005 and March 2007, 30 soccer players (10 amateur, 20 professional) with acute or chronic tears of the anterior cruciate ligament who were scheduled for a bone-tendon-bone ACL reconstruction procedure were enrolled in the study. Measures of pain intensity, depression and anxiety were assessed 1 day pre-operation and 1 week and 3 weeks post-operation (T1 T2 and T3). Pain was assessed using a visual analog scale (VAS), depression with the Beck Depression Inventory (BDI), and anxiety with both the state and trait forms of the State-Trait Anxiety Inventory (STAI). Scores on the VAS, BDI, and STAI in both groups were analyzed. The mean VAS scores at T1 and T2 in professional players were not significantly higher than those in amateur players (P>0.05). Professionals had significantly higher BDI scores at T1 and T2 (P<0.05), but this difference was not significant at T3 (P=0.12). High depression scores did not correlate with high pain scores. Pain scores between professional and amateur soccer players with ACL injuries were not significantly different pre-op or in the early post-op period. Depression was more common in professionals before and after their ACL surgery, but anxiety levels were not significantly different between the two groups.     

Salivary cortisol in top-level professional soccer players

We have tested the hypothesis that salivary cortisol increases after a competitive training match in top-level male professional soccer players divided in team A (n = 11) versus team B (n = 11). Saliva samples collected before and after the match were analyzed. Salivary cortisol concentrations were measured by enzyme-linked immunosorbent assay. The results from a two-way ANOVA with repeated measures showed no significant changes in salivary cortisol between either teams or time points (P > 0.05). Further investigation regarding competitive matches in a competition environment is warranted. In summary, the influence of intensive competitive training match alone appears to be minimal on salivary cortisol changes in top-level soccer adapted to this type of stress. From a practical application, the variability of the responses among the players leads us to suggest that there is a need to individually analyse the results with team sports.     

Validity of heart rate as an indicator of aerobic demand during soccer activities in amateur soccer players

In order to validate the use of heart rate (HR) in describing and monitoring physiological demands during soccer activities, the HR versus oxygen uptake (O₂) relationship determined on the field during soccer-specific exercises was compared to that found in the laboratory during treadmill exercise. Seven male amateur soccer players [mean (SE), age 25.3 (1.2) years, body mass 72.9 (2.1) kg, stature 1.76 (0.03) m] performed three trials on the field (two laps of a purpose-made circuit including a variety of soccer activities) at different intensities (moderate, high and very high, according to their rate of perceived exertion) and an incremental test on a treadmill in the laboratory. HR increased linearly with O₂ during both field and laboratory tests according to exercise intensity (P<0.01). The mean correlation coefficients of the HR–O₂ relationships obtained in the laboratory and on the field were 0.984 (0.012) and 0.991 (0.005) (P<0.001), respectively. The mean value of the HR–O₂ regression equation slope and intercept obtained in laboratory [0.030 (0.002) and 79.6 (4.6), respectively] were not significantly different compared to those found on the field [0.032 (0.003) and 76.7 (9.7)]. The present study seems to confirm that HR measured during soccer exercises effectively reflects the metabolic expenditure of this activity. Thus, with the aid of laboratory reference tests, the physiological demands of soccer activities can be correctly estimated from HR measured on the field in amateur soccer players.     

Protein requirements in male adolescent soccer players

Few investigations have studied protein metabolism in children and adolescent athletes which makes difficult the assessment of daily recommended dietary protein allowances in this population. The problematic in paediatric competitors is the determination of additional protein needs resulting from intensive physical training. The aim of this investigation was to determine protein requirement in 14-year-old male adolescent soccer players. Healthy male adolescent soccer players (N = 11, 13.8 +/- 0.1 year) participated in a short term repeated nitrogen balance study. Diets were designed to provide proteins at three levels: 1.4, 1.2 and 1.0 g protein per kg body weight (BW). Nutrient and energy intakes were assessed from 4 day food records corresponding to 4 day training periods during 3 weeks. Urine was collected during four consecutive days and analysed for nitrogen. The nitrogen balances were calculated from mean daily protein intake, mean urinary nitrogen excretion and estimated faecal and integumental nitrogen losses. Nitrogen balance increased with both protein intake and energy balance. At energy equilibrium, the daily protein intake needed to balance nitrogen losses was 1.04 g kg(-1) day(-1). This corresponds to an estimated average requirement (EAR) for protein of 1.20 g kg(-1) day(-1) and a recommended daily allowance (RDA) of 1.40 g kg(-1) day(-1) assuming a daily nitrogen deposition of 11 mg kg(-1). The results of the present study suggest that the protein requirements of 14-year-old male athletes are above the RDA for non-active male adolescents.     

Isometric and isokinetic muscle strength,anthropometry and physical activity in 8 and 13 year old Swedish children

Summary Isometric muscle strength of the handgrip and of trunk flexion and extension, and isokinetic torque of elbow and knee flexion and knee extension were assessed in a random sample of 8 and 13 year old Swedish children. The results were compared with respect to sex and age in absolute terms and relative to weight, height² and estimates of lean body mass and cross-sectional muscle area. Daily physical activity was also estimated. The muscle strength variables were in general found to be very similar in the 8 year old boys and girls. In the 13 year old group the boys were generally stronger than the girls, in both absolute and relative terms, except for similar torque values during knee extension. The absolute and relative muscle strength and torque values were higher in the older than in the younger children, with the exception of trunk strength per unit of body weight and of lean body mass, which were similar in boys of both ages and significantly lower in the older than in the younger girls. No significant correlation was found between the estimates of physical activity and isometric and isokinetic muscle strength and torque.     

TW3 and Fels skeletal ages in elite youth soccer players

Background: Skeletal age (SA) tends to be advanced for chronological age (CA) in adolescent male soccer players.

Aim: The study compared SA assessments with the TW3 and Fels methods in a sample of male, elite youth soccer players.

Methods: SAs were assessed with the Tanner–Whitehouse 3 (TW3) radius–ulna–short bone (RUS) and Fels methods in a sample of 40 elite youth soccer players 12.5–16.1 years of age. Players were classified as late, on time or early on the basis of relative SA, the difference between SA and CA. Players who reached skeletal maturity were labeled mature.

Results: SA was in advance of CA. Among 14 players >15.0 years, two are skeletally mature with the Fels method (CA 15.7 and 15.9 years), while 11 are skeletally mature with the TW3 method (CA 15.0–16.1 years).

Conclusion: The TW3 and Fels methods yield different SAs in elite youth soccer players. Significantly more 15-year-old boys are classified as skeletally mature with the TW3 method than with the Fels method. These observations have implications for international age group competitions as well as for medico-legal circumstances that require CA verification. SA is not a valid measure of CA and should not be used as such.     

The effects of one-half of a soccer match on the postural stability and functional capacity of the lower limbs in young soccer players

OBJECTIVE:

Most injuries occur during the final 15 minutes of each half of a soccer match, suggesting that physical exertion may influence changes in neuromuscular control and the body''s ability to stabilize the joints of the lower extremities. The aim of this study was to analyze the effects of one-half of a soccer match on the functional capacity and stability of the lower limbs in young soccer players.

METHODS:

We analyzed 27 soccer players by evaluating the functional capacity of their lower limbs using the hop test protocol and their level of postural stability using the Biodex Stability System. The evaluations were performed before and after 45 minutes of game time.

RESULTS:

After the match, there was a decrease in the overall stability index (OSI) (F_(1,23) = 5.64, p = 0.026) and the anterior-posterior stability index (APSI) (F_(1,23) = 5.24,p = 0.032). In the single and triple hop tests, there was a higher functional capacity in the dominant limb compared to the non-dominant limb in the pre- and post-game comparisons.

CONCLUSION:

The results of this study show that there is a decrease in the stability of the lower limbs in young soccer players after a 45 minutes soccer match, but the same result was not found for the functional capacity.     

TW3 and Fels skeletal ages in elite youth soccer players

BACKGROUND: Skeletal age (SA) tends to be advanced for chronological age (CA) in adolescent male soccer players. AIM: The study compared SA assessments with the TW3 and Fels methods in a sample of male, elite youth soccer players. METHODS: SAs were assessed with the Tanner-Whitehouse 3 (TW3) radius-ulna-short bone (RUS) and Fels methods in a sample of 40 elite youth soccer players 12.5-16.1 years of age. Players were classified as late, on time or early on the basis of relative SA, the difference between SA and CA. Players who reached skeletal maturity were labeled mature. RESULTS: SA was in advance of CA. Among 14 players >15.0 years, two are skeletally mature with the Fels method (CA 15.7 and 15.9 years), while 11 are skeletally mature with the TW3 method (CA 15.0-16.1 years). CONCLUSION: The TW3 and Fels methods yield different SAs in elite youth soccer players. Significantly more 15-year-old boys are classified as skeletally mature with the TW3 method than with the Fels method. These observations have implications for international age group competitions as well as for medico-legal circumstances that require CA verification. SA is not a valid measure of CA and should not be used as such.     

Early osteoarthritis and reduced quality of life after retirement in former professional soccer players

OBJECTIVES:

This study aims to compare the prevalence of osteoarthritis in two groups: one comprising former professional soccer players and the other comprising non-professional-athlete participants.

METHODS:

Twenty-seven male former professional soccer players and 30 male volunteers from different non-sports professional areas participated in the study. All participants underwent bilateral knee radiography and magnetic resonance imaging. In addition, the quality of life, knee pain and joint function were evaluated and compared using questionnaires given to all participants in both groups. Specific knee evaluations, with regard to osteoarthritis and quality of life, were performed in both groups using the Knee Injury and Osteoarthritis Outcome Score subjective questionnaires and the Short-form 36. The chi-squared test, Fisher''s exact test, the Mann-Whitney U test and Student''s t-test were used for group comparisons.

RESULTS:

The between-groups comparison revealed significant differences in the following: pain, symptoms and quality of life related to the knee in the Knee Injury and Osteoarthritis Outcome Score subscales; the physical aspects subscale of the SF-36; total whole-organ magnetic resonance imaging scores with regard to the dominant and non-dominant knees. Former soccer players had worse scores than the controls in all comparisons.

CONCLUSIONS:

Both the clinical and magnetic resonance evaluations and the group comparisons performed in this study revealed that former soccer players have a worse quality of life than that of a control group with regard to physical aspects related to the knee; these aspects include greater pain, increased symptoms and substantial changes in radiographic and magnetic resonance images of the knee.     

The relationships among peak torque, mean power output, mechanomyography, and electromyography in men and women during maximal, eccentric isokinetic muscle actions

The purpose of the present investigation was to examine the velocity-related patterns of peak torque (PT), mean power output (MP), mechanomyographic (MMG) amplitude, and electromyographic (EMG) amplitude of the vastus lateralis (VL) muscle in men and women during maximal, eccentric isokinetic muscle actions of the leg extensors. Eight women [mean (SD)] [aged 23 (3) years] and seven men [aged 23 (2) years] volunteered for this investigation. Their PT was measured on a calibrated dynamometer at randomly ordered velocities of 30, 90, and 150°·s^–1. A piezoelectric MMG recording sensor was placed between bipolar surface EMG electrodes (Ag-AgCl) over the VL muscle. Their MP was determined using the dynamometer software. The results indicated no sex-related differences (P>0.05) for the patterns of PT, MP, MMG amplitude, or EMG amplitude across velocity. The normalized values for MP and MMG amplitude increased (P<0.05) from 30 to 150°·s^–1 (30°·s^–1<90°·s^–1<150°·s^–1), while PT and EMG amplitudes remained unchanged across velocity. The results indicated close associations between the velocity-related patterns of MP and MMG amplitudes as well as PT and EMG amplitudes. Thus, MMG amplitude reflected the velocity-related changes in muscle power output, but not torque production, while EMG amplitude reflected torque production, but not muscle power output. During maximal, eccentric isokinetic muscle actions, EMG and MMG signals provided unique information regarding the electrical and mechanical aspects of muscle strength and power. Electronic Publication     

Health-related physical fitness of adolescents and young adults with myelomeningocele

To assess components of health-related physical fitness in adolescents and young adults with myelomeningocele (MMC), and to study relations between aerobic capacity and other health-related physical fitness components. This cross-sectional study included 50 adolescents and young adults with MMC, aged 16–30 years (25 males). Aerobic capacity was quantified by measuring peak oxygen uptake (peakVO₂) during a maximal exercise test on a cycle or arm ergometer depending on the main mode of ambulation. Muscle strength of upper and lower extremity muscles was assessed using a hand-held dynamometer. Regarding flexibility, we assessed mobility of hip, knee and ankle joints. Body composition was assessed by measuring thickness of four skin-folds. Relations were studied using linear regression analyses. Average peakVO₂ was 1.48 ± 0.52 l/min, 61% of the participants had subnormal muscle strength, 61% had mobility restrictions in at least one joint and average sum of four skin-folds was 74.8 ± 38.8 mm. PeakVO₂ was significantly related to gender, ambulatory status and muscle strength, explaining 55% of its variance. Adolescents and young adults with MMC have poor health-related physical fitness. Gender and ambulatory status are important determinants of peakVO₂. In addition, we found a small, but significant relationship between peakVO₂ and muscle strength.     

Energy expenditure and physical fitness of ice-hockey players

Summary We examined the energy expenditure in ice-hockey players under conditions of a model training match. The results were obtained in a group of 13 players of the national representative team (age 24.4 years), and in 1 goaler. In the players we also followed the physical fitness by means of a loading experiment on bicycle ergometer in the middle of the racing season, and before the opening of the World Championship 1971.The principial results are as follows: the energy expenditure during the play is 0.48 kcal/min·kg (3137% BMR), the oxygen debt 6.3 1. The anaerobic part of the metabolism is approximately two thirds of the total energy expenditure. The average heart rate during the activity on ice was 152 beats per minute, the pulmonary ventilation 92 1, the oxygen uptake 32 ml/min·kg. During one turn (1.17 min) the players covered the distance 285 m.The comparison of maximum values of the indices obtained by ergometrical examination in two examinations did not show any substancial differences. We can assume that the decrease observed in several indices may have been caused by a low motivation at loading up to the maximum (the lactic acid, pulmonary ventilation, oxygen uptake). Other findings (the fat percentage increment) can be explained by a less intensive training, unbalance between performance and nutrition. A relatively independent index is the W 170 which has shown the unchanged level of cardiorespiratory functions. From the results various conclusions can be drawn for the work of trainers. The ice-hockey proves to be an activity with mostly submaximal metabolic rate, where appears a great part of anaerobic metabolism simultaneously with high requirements for the aerobic metabolism. For the training practice the requirements follow to intensify the interval training, to increase the play intensity in the training, to use the necessary number of play exercises requiring the typical anaerobic power, and to load the players, in the preparatory period, more often by endurance activities for the aerobic endurance be developed.     

Neuroplus biofeedback improves attention,resilience, and injury prevention in elite soccer players

Performance and injury prevention in elite soccer players are typically investigated from physical‐tactical, biomechanical, and metabolic perspectives. However, executive functions, visuospatial abilities, and psychophysiological adaptability or resilience are also fundamental for efficiency and well‐being in sports. Based on previous research associating autonomic flexibility with prefrontal cortical control, we designed a novel integrated autonomic biofeedback training method called Neuroplus to improve resilience, visual attention, and injury prevention. Herein, we introduce the method and provide an evaluation of 20 elite soccer players from the Italian Soccer High Division (Serie‐A): 10 players trained with Neuroplus and 10 trained with a control treatment. The assessments included psychophysiological stress profiles, a visual search task, and indexes of injury prevention, which were measured pre‐ and posttreatment. The analysis showed a significant enhancement of physiological adaptability, recovery following stress, visual selective attention, and injury prevention that were specific to the Neuroplus group. Enhancing the interplay between autonomic and cognitive functions through biofeedback may become a key principle for obtaining excellence and well‐being in sports. To our knowledge, this is the first evidence that shows improvement in visual selective attention following intense autonomic biofeedback.     

Muscle morphology and performance in master athletes: A systematic review and meta-analyses

IntroductionThe extent to which chronic exercise training preserves age-related decrements in physical function, muscle strength, mass and morphology is unclear. Our aim was to conduct a systematic review of the literature to determine to what extent chronically trained master athletes (strength/power and endurance) preserve levels of physical function, muscle strength, muscle mass and morphology in older age, compared with older and younger controls and young trained individuals.MethodsThe systematic data search included Medline, EMBASE, SPORTDiscus, CINAHL and Web of Science databases.Inclusion criteriai) master athletes mean exercise training duration ≥20 years ii) master athletes mean age of cohort >59 years) iii) at least one measurement of muscle mass/volume/fibre-type morphology and/or strength/physical function.ResultsFifty-five eligible studies were identified. Meta-analyses were carried out on maximal aerobic capacity, maximal voluntary contraction and body composition. Master endurance athletes (42.0 ± 6.6 ml kg⁻¹ min⁻1) exhibited VO_2max values comparable with young healthy controls (43.1 ± 6.8 ml kg⁻¹ min⁻¹, P = .84), greater than older controls (27.1 ± 4.3 ml kg⁻¹ min⁻¹, P < 0.01) and master strength/power athletes (26.5 ± 2.3 mlkg⁻¹ min⁻¹, P < 0.01), and lower than young endurance trained individuals (60.0 ± 5.4 ml kg⁻¹ min⁻¹, P < 0.01). Master strength/power athletes (0.60 (0.28–0.93) P < 0.01) and young controls (0.71 (0.06–1.36) P < 0.05) were significantly stronger compared with the other groups. Body fat% was greater in master endurance athletes than young endurance trained (−4.44% (−8.44 to −0.43) P < 0.05) but lower compared with older controls (7.11% (5.70–8.52) P < 0.01).ConclusionDespite advancing age, this review suggests that chronic exercise training preserves physical function, muscular strength and body fat levels similar to that of young, healthy individuals in an exercise mode-specific manner.