Once thought to be a waste product of oxygen limited(anaerobic)metabolism,lactate is now known to form continuously under fully oxygenated(aerobic)conditions.Lactate shuttling between producer(driver)and consumer cell...Once thought to be a waste product of oxygen limited(anaerobic)metabolism,lactate is now known to form continuously under fully oxygenated(aerobic)conditions.Lactate shuttling between producer(driver)and consumer cells fulfills at least 3 purposes;lactate is:(1)a major energy source,(2)the major gluconeogenic precursor,and(3)a signaling molecule.The Lactate Shuttle theory is applicable to diverse fields such as sports nutrition and hydration,resuscitation from acidosis and Dengue,treatment of traumatic brain injury,maintenance of glycemia,reduction of inflammation,cardiac support in heart failure and following a myocardial infarction,and to improve cognition.Yet,dysregulated lactate shuttling disrupts metabolic flexibility,and worse,supports oncogenesis.Lactate production in cancer(the Warburg effect)is involved in all main sequela for carcinogenesis:angiogenesis,immune escape,cell migration,metastasis,and self-sufficient metabolism.The history of the tortuous path of discovery in lactate metabolism and shuttling was discussed in the 2019 American College of Sports Medicine Joseph B.Wolffe Lecture in Orlando,FL.展开更多
Background: Epidemiologic research to learn the incidence, type, location, and severity of female soccer injuries and the risk factors for sustaining a sport injury is the first step in developing preventive policies....Background: Epidemiologic research to learn the incidence, type, location, and severity of female soccer injuries and the risk factors for sustaining a sport injury is the first step in developing preventive policies. The aim of this study was to analyze the incidence of injuries in the population of female soccer players in Spain.Methods: The injuries incurred by 25,397 female soccer players were registered by the medical staff of the Spanish Football Federation during 1 season. A standardized medical questionnaire was used to classify the injury according to type, severity, location, and injury mechanism. A total of 2108 injuries was reported with an incidence of 0.083 injuries per player per season. Most injuries were in the lower limbs(74.0%), mainly affecting knee(30.4%) and ankle joints(17.9%).Results: The proportion of injuries derived from contact with another player was higher during matches(33.7%) than during training(11.4%;p < 0.001). Noncontact injuries were classified as severe more frequently than were contact injuries(51.0% vs. 42.6%; p < 0.001). A higher incidence of injury was found in adult soccer players(≥18 years) vs. their counterparts younger than 18 years(0.094 vs. 0.072 injuries per player per year, respectively; p < 0.001). There were no differences between age groups in any other injury variable(e.g., type, mechanism, location, or severity; p > 0.05).Conclusion: Most female soccer injuries were located at the knee and ankle; the injury mechanism determined the playing time lost; and the player's age did not affect injury characteristics.展开更多
Background: Pacing, defined as percentage changes of speed between successive splits, has been extensively studied in running and cycling endurance sports; however, less information about the trends in change of speed...Background: Pacing, defined as percentage changes of speed between successive splits, has been extensively studied in running and cycling endurance sports; however, less information about the trends in change of speed during cross-country(XC) ski racing is available. Therefore, the aim of the present study was to examine the effect of performance(quartiles of race time(Q), with Q1 the fastest and Q4 the slowest) level on pacing in the Vasaloppet ski race, the largest XC skiing race in the world.Methods: For this purpose, we analyzed female(n = 19,465) and male(n = 164,454) finishers in the Vasaloppet ski race from 2004 to 2017 using a one-way(2 sexes) analysis of variance with repeated measures to examine percentage changes of speed between 2 successive splits. Overall,the race consisted of 8 splits.Results: The race speeds of Q1, Q2, Q3, and Q4 were 13.6 § 1.8, 10.6 § 0.5, 9.2 § 0.3, and 8.1 § 0.4 km/h, respectively, among females and16.7 § 1.7, 13.1 § 0.7, 10.9 § 0.6, and 8.9 § 0.7 km/h, respectively, among males. The overall pacing strategy of finishers was variable. A small sex ￡ split interaction on speed was observed(h2= 0.016, p < 0.001), with speed difference between sexes ranging from 14.9%(Split 7) to27.0%(Split 1) and larger changes in speed between 2 successive splits being shown for females(p < 0.001, h2= 0.004). A large performance ￡ split interaction on speed, with Q1 presenting the smallest changes of speed between splits, was shown for females(h2= 0.149, p <0.001) and males(h2= 0.169, p < 0.001).Conclusion: Male and fast XC skiers are more even pacers. Coaches and athletes should develop tailored sex-and performance-level pacing strategies; for instance, they should advise fast XC skiers to start fast and maintain their speed, rather than starting slowly and trying to make up time by going faster at times during the race.展开更多
Background:Determining the prevalence of doping in sport might be useful for anti-doping authorities to gauge the effectiveness of anti-doping policies implemented to prevent positive attitudes toward doping.Using que...Background:Determining the prevalence of doping in sport might be useful for anti-doping authorities to gauge the effectiveness of anti-doping policies implemented to prevent positive attitudes toward doping.Using questionnaires and personal interviews,previous investigations have found that the prevalence of doping might be different among different sports disciplines;however,there is no sport-specific information about the proportion of adverse and atypical findings(AAF) in samples used for doping control.The aim of the present investigation was to assess the differences in the frequency of adverse analytical and atypical findings among sports using the data made available by the World Anti-Doping Agency.Methods:The data included in this investigation were gathered from the Testing Figures Reports made available annually from 2003 to 2015 by the World Anti-Doping Agency.These Testing Figures Reports include information about the number of samples analyzed,the number of AAFs reported,and the most commonly found drugs in the urine and blood samples analyzed.A total of 1,347,213 samples were analyzed from the individual sports selected for this investigation,and 698,371 samples were analyzed for disciplines catalogued as team sports.Results:In individual sports,the highest proportions of AAF were 3.3%±1.0% in cycling,3.0%±0.6% in weightlifting,and 2.9%±0.6% in boxing.In team sports,the highest proportions of AAF were 2.2%±0.5% in ice hockey,2.0%±0.5% in rugby,and 2.0%±0.5% in basketball.Gymnastics and skating had the lowest proportions at(≤1.0%) for individual sports,and field hockey,volleyball and football had the lowest proportions for team sports(≤1.4%).Conclusion:As suggested by the analysis,the incidence of AAF was not uniform across all sports disciplines,with the different proportions pointing to an uneven use of banned substances depending on the sport.This information might be useful for increasing the strength and efficacy of anti-doping policies in those sports with the highest prevalence in the use of banned substances.展开更多
Background: The primary purpose of this investigation was to determine the differences in resting heart rate variability and heart rate recovery between norm-referenced aerobic fitness groupings, independent of body c...Background: The primary purpose of this investigation was to determine the differences in resting heart rate variability and heart rate recovery between norm-referenced aerobic fitness groupings, independent of body composition, in Black men. Additionally, we sought to clarify the independent relationships that heart rate variability and heart rate recovery displayed with maximal aerobic fitness and selected body composition measures. Methods: Body mass index, waist circumference, and the sum of skinfold thickness were determined in forty Black men (23 ± 3 years). Each subject assumed a supine position while heart rate variability was analyzed for 5-minute and recorded as normalized high-frequency power and normalized low-frequency power to normalized high frequency ratio. A graded exercise treadmill protocol was performed to attain maximal aerobic fitness. Heart rate recovery was recorded at 1- and 2-minute of a cool-down period. Heart rate variability and heart rate recovery were compared across two groups whose maximal aerobic fitness was either below or above the normative mean value for the age group of men. Results: The results indicated that heart rate variability was higher in the group whose maximal aerobic fitness was above the normative mean value compared with the lower fit group (p < 0.05), but the differences disappeared when adjusting for body composition (p > 0.05). Regression analysis revealed that the sum of skinfolds accounted for the variation in normalized high frequency power (R2 = 0.20, p < 0.05) and normalized low-frequency power to normalized high frequency ratio (R2 = 0.30, p < 0.05), while waist circumference accounted for the variation in heart rate recovery at 2-minute (R2 = 0.20, p Conclusion: The results suggest that heart rate variability and heart rate recovery hold independent relationships to body composition but not aerobic fitness in young-adult, Black men.展开更多
High intensity interval training(HIIT)causes oxidative stress and haematological alteration.Present study was aimed to evaluate the effect of 8 weeks’supplementation of vitamin C and E on HIIT induced changes in lipi...High intensity interval training(HIIT)causes oxidative stress and haematological alteration.Present study was aimed to evaluate the effect of 8 weeks’supplementation of vitamin C and E on HIIT induced changes in lipid profile parameters and haematological variables.Hundred six male adolescent players were randomly assigned into five age-matched groups,i.e.,Control(no exercise+placebo),HIIT(placebo),HIIT+vitamin-C(1000mg/day),HIIT+vitamin-E 400 IU/day)and combined HIIT+vitamin C and E.Morning and evening sessions(90min)of HIIT included 4 phases(15min each)with 3 sets(4min each).Each 4min HIIT set consisted of 2min intense sprint workout(90%–95%of heart rate maximum[HRmax])followed by 1min active recovery(60%–70%HRmax)followed by 1min of complete rest(1:1 work-rest ratio).Lipid profile parameters,haematological variables,endurance capacity and vertical jump were evaluated by standard protocols.Significant decrease in body weight,fat%,total cholesterol,triglyceride,Total Cholesterol/High Density Lipoprotein-Cholesterol and significant increase in High Density Lipoprotein-Cholesterol,maximal oxygen consumption,vertical jump were observed for all four intervention groups.White blood cell count,red blood cell count,haemoglobin percentage and haematocrit values were significantly decreased while platelet count and platelet-to-leukocyte ratio(PLR)ratio were increased significantly only for HIIT group.Blood level of tocopherol and ascorbic acid was significantly increased(values were within the normal range)in all the respective vitamin supplemented groups.Supplementation of vitamin C and E secures health protection with suppressed haemolysis and improved inflammatory blood variables with enhanced explosive leg strength and lipid profile parameters without any concomitant change in endurance capacity.展开更多
Purpose The purpose of the present study was to examine the day-to-day consistency and inter-subject variability of com-posite and individual,neuromuscular and torque patterns of responses as a result of a fatiguing b...Purpose The purpose of the present study was to examine the day-to-day consistency and inter-subject variability of com-posite and individual,neuromuscular and torque patterns of responses as a result of a fatiguing bout of maximal,bilateral,isokinetic leg extension muscle actions.Methods Ten men (Mean ± SD =21.6 ± 2.5 years) completed two testing visits consisting of pretest and posttest maximal voluntary isometric contractions (MVIC) as well as 25 maximal,bilateral,isokinetic (180°/s),leg extension muscle actions.Electromyographic (EMG) and mechanomyographic (MMG) signals were collected from the vastus lateralis and normalized to the MVIC.Performance fatigability was defined as the percent decline in torque between the average of repetitions 1,2,and 3 and repetitions 23,24,and 25.Polynomial regression was used to examine the individual and composite relation-ships between EMG amplitude (AMP),EMG mean power frequency (MPF),MMG AMP,MMG MPF,and torque versus repetitions.Results There was no significant difference (d =0.80;P =0.17) in the performance fatigability between Day 1 (19.3% ± 7.1%)and Day 2 (26.9% ± 11.3%).Polynomial regression indicated substantial inter-subject variability,but high day-to-day consistency.Conclusion The composite EMG AMP,MMG AMP,and MMG MPF patterns of responses demonstrated consistency across days.The composite EMG MPF patterns of responses,however,were not consistent between Day 1 and Day 2.In addition,based on the high inter-subject variability,future studies should present both composite patterns of neuromuscular responses and the patterns of responses on a subject-by-subject basis to make inferences regarding fatigue-induced changes in motor unit activation strategies.展开更多
Purpose To examine and compare the effects of three days of dynamic constant external resistance(DCER)and isokinetic(ISOK)training and subsequent detraining on thigh muscle cross-sectional area(TMCSA)and thigh lean ma...Purpose To examine and compare the effects of three days of dynamic constant external resistance(DCER)and isokinetic(ISOK)training and subsequent detraining on thigh muscle cross-sectional area(TMCSA)and thigh lean mass(TLM),ISOK peak torque(PT),DCER strength,isometric force,muscle activation,and percent voluntary activation(%VA).Methods Thirty-one apparently-healthy untrained men(mean±SD age=22.2±4.2 years;body mass=77.9±12.9 kg;height=173.9±5.4 cm)were randomly assigned to a DCER training group(n=11),ISOK training group(n=10)or control(CONT)group(n=10).Subjects visited the laboratory eight times.The first visit was a familiarization session,the second visit was a pre-training assessment,the subsequent three visits were for unilateral training of the quadriceps(if assigned to a training group),and the last three visits were the post-training assessments conducted at three days,one week,and two weeks after training ended.Results DCER strength increased from pre-to post-training assessment 1 in both limbs for the DCER group only,and remained elevated during post-training assessments 2 and 3(P<0.05).In addition,surface EMG for the biceps femoris was higher at post-training assessment 3 than at the pre-training assessment,and post-training assessments 1 and 2(P<0.05).No other training-related changes were found.Conclusion The primary finding of this study was that DCER strength of the trained and untrained limbs can be increased with three days of training.This has important implications for injury rehabilitation,where in the initial period post-injury strength gains on an injured limb can possibly be obtained with short-term contralateral resistance training.展开更多
Powerlifting regularly exposes athletes to extreme stimuli such as chronic heavy resistance training(HRT),and many powerlifters choose to augment their performance with anabolic-androgenic steroids(AAS).However,little...Powerlifting regularly exposes athletes to extreme stimuli such as chronic heavy resistance training(HRT),and many powerlifters choose to augment their performance with anabolic-androgenic steroids(AAS).However,little is known about the myocellular adaptations that occur from long-term HRT and AAS use,especially into middle age.We were presented with the unique opportunity to study muscle cells from an elite-level powerlifter(EPL;age 40 years)with≥30 years of HRT experience and≥15 years of AAS use.The purpose of this case study was to identify myocellular characteristics[myosin heavy chain(MHC)fiber type,fiber size,and myonuclear content]in EPL,as well as compare these data to existing litera-ture.The participant underwent a resting vastus lateralis muscle biopsy and single fibers were analyzed for MHC content via SDS-PAGE.A subset of fibers underwent MHC-specific imaging analysis via confocal microscopy to identify cell size(cross-sectional area,CSA)and myonuclear domain(MND)size.MHC fiber type distribution was 9% I,12% I/IIa,79% IIa,and 0% other isoforms.This pure MHC IIa(fast-twitch)fiber content was amongst the highest reported in the literature.Imaging analysis of MHC IIa fibers revealed a mean CSA of 4218±933μm^(2) and MND of 12,548±3181μm^(3).While the fast-twitch fiber CSA was comparable to values in previous literature,mean MND was smaller than has been reported in untrained men,implying greater capacity for growth and repair.These findings showcase the unique muscle cell structure of an elite powerlifter,extending the known physiological limits of human muscle size and strength.展开更多
Purpose The aims of this study were to propose an alternative method to assess an optimal performance improvement rate(PIR)that would be used as a tool for coaches and elite athletes willing to reach their personal be...Purpose The aims of this study were to propose an alternative method to assess an optimal performance improvement rate(PIR)that would be used as a tool for coaches and elite athletes willing to reach their personal best,mainly those seeking for national,continental or even world record(WR)in middle-distance events.We further compared the improvement rate of women vs.men of the top-10 ranked athletes in the IAAF running these middle-distance events Method The top 10 athletes in the IAAF ranking of 800 m,1500 m,and 3000 m events for each sex were assessed for their history of race times before achieving their personal record(PR).The difference between PR(‘actual’season)and the best race time in the last season was defined as the 1st season improvement rate(1-SIR),whereas the average improvement rate in the last and preceding seasons was the multi-season improvement rate(M-SIR).1-SIR and M-SIR were calculated for each athlete.Result There were sex differences in the 1500 m with a large effect size(d=−0.746)in 1-SIR(P=0.001)and very large(d=−2.249)in M-SIR(P=0.001).Women improved more than men before the PR/WR achievements in the 800 m and 1500 m events(P=0.001)and had similar improvement rates before performing PR/WR in 3000 m events(P=0.533).Conclusion Women improve more before PR/WR achievement in 800 m and 1500 m races.However,in the 3000 m men and women have similar improvement rates in previous seasons before the PR/WR achievement.展开更多
Emerging viral diseases represent a serious issue to public and global healthcare systems and have a high potential for disease dissemination in sport/physical activity and exercise facilities.The Coronavirus disease ...Emerging viral diseases represent a serious issue to public and global healthcare systems and have a high potential for disease dissemination in sport/physical activity and exercise facilities.The Coronavirus disease 2019(COVID-19)pandemic has frightened the sports and physical activity community and enthusiasts for potential trans-mission,dissemination,and lethality in vulnerable populations;those with chronic diseases,co-morbidities,the elderly people,and in young and healthy people.This pandemic has caused a chain reaction with cancellations of sports competitions and gymnasiums closing around the world.Currently,some sporting events are gradually resuming in certain regions of the world and also the return of competitions and training.In general,without fans and public,the sports media can only report the infection of athletes and coaching staff members.However,this situation is dynamic-the world is currently experiencing the second wave of the disease;with the safety and containment measures for the disease is changing daily.The purpose of this article is to present information concerning the COVID-19 pandemic,to clarify health issues for professionals and people connected to sport and physical activity venues,presenting information to assist in educations and the health promotion and prevention.The time is now for making changes,reviewing the actions and conducts necessary for prevention,and most importantly not letting our guard down,even as vaccines become available for all people in the world.Remembering that even after getting vaccinated,it is necessary to continue with safety measures,for example,the use of facial masks and social distance and hygiene,that is,washing your hands frequently and/or sanitizing with 70%alcohol.We can't let our guard down for COVID-19.展开更多
文摘Once thought to be a waste product of oxygen limited(anaerobic)metabolism,lactate is now known to form continuously under fully oxygenated(aerobic)conditions.Lactate shuttling between producer(driver)and consumer cells fulfills at least 3 purposes;lactate is:(1)a major energy source,(2)the major gluconeogenic precursor,and(3)a signaling molecule.The Lactate Shuttle theory is applicable to diverse fields such as sports nutrition and hydration,resuscitation from acidosis and Dengue,treatment of traumatic brain injury,maintenance of glycemia,reduction of inflammation,cardiac support in heart failure and following a myocardial infarction,and to improve cognition.Yet,dysregulated lactate shuttling disrupts metabolic flexibility,and worse,supports oncogenesis.Lactate production in cancer(the Warburg effect)is involved in all main sequela for carcinogenesis:angiogenesis,immune escape,cell migration,metastasis,and self-sufficient metabolism.The history of the tortuous path of discovery in lactate metabolism and shuttling was discussed in the 2019 American College of Sports Medicine Joseph B.Wolffe Lecture in Orlando,FL.
文摘Background: Epidemiologic research to learn the incidence, type, location, and severity of female soccer injuries and the risk factors for sustaining a sport injury is the first step in developing preventive policies. The aim of this study was to analyze the incidence of injuries in the population of female soccer players in Spain.Methods: The injuries incurred by 25,397 female soccer players were registered by the medical staff of the Spanish Football Federation during 1 season. A standardized medical questionnaire was used to classify the injury according to type, severity, location, and injury mechanism. A total of 2108 injuries was reported with an incidence of 0.083 injuries per player per season. Most injuries were in the lower limbs(74.0%), mainly affecting knee(30.4%) and ankle joints(17.9%).Results: The proportion of injuries derived from contact with another player was higher during matches(33.7%) than during training(11.4%;p < 0.001). Noncontact injuries were classified as severe more frequently than were contact injuries(51.0% vs. 42.6%; p < 0.001). A higher incidence of injury was found in adult soccer players(≥18 years) vs. their counterparts younger than 18 years(0.094 vs. 0.072 injuries per player per year, respectively; p < 0.001). There were no differences between age groups in any other injury variable(e.g., type, mechanism, location, or severity; p > 0.05).Conclusion: Most female soccer injuries were located at the knee and ankle; the injury mechanism determined the playing time lost; and the player's age did not affect injury characteristics.
文摘Background: Pacing, defined as percentage changes of speed between successive splits, has been extensively studied in running and cycling endurance sports; however, less information about the trends in change of speed during cross-country(XC) ski racing is available. Therefore, the aim of the present study was to examine the effect of performance(quartiles of race time(Q), with Q1 the fastest and Q4 the slowest) level on pacing in the Vasaloppet ski race, the largest XC skiing race in the world.Methods: For this purpose, we analyzed female(n = 19,465) and male(n = 164,454) finishers in the Vasaloppet ski race from 2004 to 2017 using a one-way(2 sexes) analysis of variance with repeated measures to examine percentage changes of speed between 2 successive splits. Overall,the race consisted of 8 splits.Results: The race speeds of Q1, Q2, Q3, and Q4 were 13.6 § 1.8, 10.6 § 0.5, 9.2 § 0.3, and 8.1 § 0.4 km/h, respectively, among females and16.7 § 1.7, 13.1 § 0.7, 10.9 § 0.6, and 8.9 § 0.7 km/h, respectively, among males. The overall pacing strategy of finishers was variable. A small sex ￡ split interaction on speed was observed(h2= 0.016, p < 0.001), with speed difference between sexes ranging from 14.9%(Split 7) to27.0%(Split 1) and larger changes in speed between 2 successive splits being shown for females(p < 0.001, h2= 0.004). A large performance ￡ split interaction on speed, with Q1 presenting the smallest changes of speed between splits, was shown for females(h2= 0.149, p <0.001) and males(h2= 0.169, p < 0.001).Conclusion: Male and fast XC skiers are more even pacers. Coaches and athletes should develop tailored sex-and performance-level pacing strategies; for instance, they should advise fast XC skiers to start fast and maintain their speed, rather than starting slowly and trying to make up time by going faster at times during the race.
文摘Background:Determining the prevalence of doping in sport might be useful for anti-doping authorities to gauge the effectiveness of anti-doping policies implemented to prevent positive attitudes toward doping.Using questionnaires and personal interviews,previous investigations have found that the prevalence of doping might be different among different sports disciplines;however,there is no sport-specific information about the proportion of adverse and atypical findings(AAF) in samples used for doping control.The aim of the present investigation was to assess the differences in the frequency of adverse analytical and atypical findings among sports using the data made available by the World Anti-Doping Agency.Methods:The data included in this investigation were gathered from the Testing Figures Reports made available annually from 2003 to 2015 by the World Anti-Doping Agency.These Testing Figures Reports include information about the number of samples analyzed,the number of AAFs reported,and the most commonly found drugs in the urine and blood samples analyzed.A total of 1,347,213 samples were analyzed from the individual sports selected for this investigation,and 698,371 samples were analyzed for disciplines catalogued as team sports.Results:In individual sports,the highest proportions of AAF were 3.3%±1.0% in cycling,3.0%±0.6% in weightlifting,and 2.9%±0.6% in boxing.In team sports,the highest proportions of AAF were 2.2%±0.5% in ice hockey,2.0%±0.5% in rugby,and 2.0%±0.5% in basketball.Gymnastics and skating had the lowest proportions at(≤1.0%) for individual sports,and field hockey,volleyball and football had the lowest proportions for team sports(≤1.4%).Conclusion:As suggested by the analysis,the incidence of AAF was not uniform across all sports disciplines,with the different proportions pointing to an uneven use of banned substances depending on the sport.This information might be useful for increasing the strength and efficacy of anti-doping policies in those sports with the highest prevalence in the use of banned substances.
文摘Background: The primary purpose of this investigation was to determine the differences in resting heart rate variability and heart rate recovery between norm-referenced aerobic fitness groupings, independent of body composition, in Black men. Additionally, we sought to clarify the independent relationships that heart rate variability and heart rate recovery displayed with maximal aerobic fitness and selected body composition measures. Methods: Body mass index, waist circumference, and the sum of skinfold thickness were determined in forty Black men (23 ± 3 years). Each subject assumed a supine position while heart rate variability was analyzed for 5-minute and recorded as normalized high-frequency power and normalized low-frequency power to normalized high frequency ratio. A graded exercise treadmill protocol was performed to attain maximal aerobic fitness. Heart rate recovery was recorded at 1- and 2-minute of a cool-down period. Heart rate variability and heart rate recovery were compared across two groups whose maximal aerobic fitness was either below or above the normative mean value for the age group of men. Results: The results indicated that heart rate variability was higher in the group whose maximal aerobic fitness was above the normative mean value compared with the lower fit group (p < 0.05), but the differences disappeared when adjusting for body composition (p > 0.05). Regression analysis revealed that the sum of skinfolds accounted for the variation in normalized high frequency power (R2 = 0.20, p < 0.05) and normalized low-frequency power to normalized high frequency ratio (R2 = 0.30, p < 0.05), while waist circumference accounted for the variation in heart rate recovery at 2-minute (R2 = 0.20, p Conclusion: The results suggest that heart rate variability and heart rate recovery hold independent relationships to body composition but not aerobic fitness in young-adult, Black men.
文摘High intensity interval training(HIIT)causes oxidative stress and haematological alteration.Present study was aimed to evaluate the effect of 8 weeks’supplementation of vitamin C and E on HIIT induced changes in lipid profile parameters and haematological variables.Hundred six male adolescent players were randomly assigned into five age-matched groups,i.e.,Control(no exercise+placebo),HIIT(placebo),HIIT+vitamin-C(1000mg/day),HIIT+vitamin-E 400 IU/day)and combined HIIT+vitamin C and E.Morning and evening sessions(90min)of HIIT included 4 phases(15min each)with 3 sets(4min each).Each 4min HIIT set consisted of 2min intense sprint workout(90%–95%of heart rate maximum[HRmax])followed by 1min active recovery(60%–70%HRmax)followed by 1min of complete rest(1:1 work-rest ratio).Lipid profile parameters,haematological variables,endurance capacity and vertical jump were evaluated by standard protocols.Significant decrease in body weight,fat%,total cholesterol,triglyceride,Total Cholesterol/High Density Lipoprotein-Cholesterol and significant increase in High Density Lipoprotein-Cholesterol,maximal oxygen consumption,vertical jump were observed for all four intervention groups.White blood cell count,red blood cell count,haemoglobin percentage and haematocrit values were significantly decreased while platelet count and platelet-to-leukocyte ratio(PLR)ratio were increased significantly only for HIIT group.Blood level of tocopherol and ascorbic acid was significantly increased(values were within the normal range)in all the respective vitamin supplemented groups.Supplementation of vitamin C and E secures health protection with suppressed haemolysis and improved inflammatory blood variables with enhanced explosive leg strength and lipid profile parameters without any concomitant change in endurance capacity.
文摘Purpose The purpose of the present study was to examine the day-to-day consistency and inter-subject variability of com-posite and individual,neuromuscular and torque patterns of responses as a result of a fatiguing bout of maximal,bilateral,isokinetic leg extension muscle actions.Methods Ten men (Mean ± SD =21.6 ± 2.5 years) completed two testing visits consisting of pretest and posttest maximal voluntary isometric contractions (MVIC) as well as 25 maximal,bilateral,isokinetic (180°/s),leg extension muscle actions.Electromyographic (EMG) and mechanomyographic (MMG) signals were collected from the vastus lateralis and normalized to the MVIC.Performance fatigability was defined as the percent decline in torque between the average of repetitions 1,2,and 3 and repetitions 23,24,and 25.Polynomial regression was used to examine the individual and composite relation-ships between EMG amplitude (AMP),EMG mean power frequency (MPF),MMG AMP,MMG MPF,and torque versus repetitions.Results There was no significant difference (d =0.80;P =0.17) in the performance fatigability between Day 1 (19.3% ± 7.1%)and Day 2 (26.9% ± 11.3%).Polynomial regression indicated substantial inter-subject variability,but high day-to-day consistency.Conclusion The composite EMG AMP,MMG AMP,and MMG MPF patterns of responses demonstrated consistency across days.The composite EMG MPF patterns of responses,however,were not consistent between Day 1 and Day 2.In addition,based on the high inter-subject variability,future studies should present both composite patterns of neuromuscular responses and the patterns of responses on a subject-by-subject basis to make inferences regarding fatigue-induced changes in motor unit activation strategies.
文摘Purpose To examine and compare the effects of three days of dynamic constant external resistance(DCER)and isokinetic(ISOK)training and subsequent detraining on thigh muscle cross-sectional area(TMCSA)and thigh lean mass(TLM),ISOK peak torque(PT),DCER strength,isometric force,muscle activation,and percent voluntary activation(%VA).Methods Thirty-one apparently-healthy untrained men(mean±SD age=22.2±4.2 years;body mass=77.9±12.9 kg;height=173.9±5.4 cm)were randomly assigned to a DCER training group(n=11),ISOK training group(n=10)or control(CONT)group(n=10).Subjects visited the laboratory eight times.The first visit was a familiarization session,the second visit was a pre-training assessment,the subsequent three visits were for unilateral training of the quadriceps(if assigned to a training group),and the last three visits were the post-training assessments conducted at three days,one week,and two weeks after training ended.Results DCER strength increased from pre-to post-training assessment 1 in both limbs for the DCER group only,and remained elevated during post-training assessments 2 and 3(P<0.05).In addition,surface EMG for the biceps femoris was higher at post-training assessment 3 than at the pre-training assessment,and post-training assessments 1 and 2(P<0.05).No other training-related changes were found.Conclusion The primary finding of this study was that DCER strength of the trained and untrained limbs can be increased with three days of training.This has important implications for injury rehabilitation,where in the initial period post-injury strength gains on an injured limb can possibly be obtained with short-term contralateral resistance training.
文摘Powerlifting regularly exposes athletes to extreme stimuli such as chronic heavy resistance training(HRT),and many powerlifters choose to augment their performance with anabolic-androgenic steroids(AAS).However,little is known about the myocellular adaptations that occur from long-term HRT and AAS use,especially into middle age.We were presented with the unique opportunity to study muscle cells from an elite-level powerlifter(EPL;age 40 years)with≥30 years of HRT experience and≥15 years of AAS use.The purpose of this case study was to identify myocellular characteristics[myosin heavy chain(MHC)fiber type,fiber size,and myonuclear content]in EPL,as well as compare these data to existing litera-ture.The participant underwent a resting vastus lateralis muscle biopsy and single fibers were analyzed for MHC content via SDS-PAGE.A subset of fibers underwent MHC-specific imaging analysis via confocal microscopy to identify cell size(cross-sectional area,CSA)and myonuclear domain(MND)size.MHC fiber type distribution was 9% I,12% I/IIa,79% IIa,and 0% other isoforms.This pure MHC IIa(fast-twitch)fiber content was amongst the highest reported in the literature.Imaging analysis of MHC IIa fibers revealed a mean CSA of 4218±933μm^(2) and MND of 12,548±3181μm^(3).While the fast-twitch fiber CSA was comparable to values in previous literature,mean MND was smaller than has been reported in untrained men,implying greater capacity for growth and repair.These findings showcase the unique muscle cell structure of an elite powerlifter,extending the known physiological limits of human muscle size and strength.
文摘Purpose The aims of this study were to propose an alternative method to assess an optimal performance improvement rate(PIR)that would be used as a tool for coaches and elite athletes willing to reach their personal best,mainly those seeking for national,continental or even world record(WR)in middle-distance events.We further compared the improvement rate of women vs.men of the top-10 ranked athletes in the IAAF running these middle-distance events Method The top 10 athletes in the IAAF ranking of 800 m,1500 m,and 3000 m events for each sex were assessed for their history of race times before achieving their personal record(PR).The difference between PR(‘actual’season)and the best race time in the last season was defined as the 1st season improvement rate(1-SIR),whereas the average improvement rate in the last and preceding seasons was the multi-season improvement rate(M-SIR).1-SIR and M-SIR were calculated for each athlete.Result There were sex differences in the 1500 m with a large effect size(d=−0.746)in 1-SIR(P=0.001)and very large(d=−2.249)in M-SIR(P=0.001).Women improved more than men before the PR/WR achievements in the 800 m and 1500 m events(P=0.001)and had similar improvement rates before performing PR/WR in 3000 m events(P=0.533).Conclusion Women improve more before PR/WR achievement in 800 m and 1500 m races.However,in the 3000 m men and women have similar improvement rates in previous seasons before the PR/WR achievement.
文摘Emerging viral diseases represent a serious issue to public and global healthcare systems and have a high potential for disease dissemination in sport/physical activity and exercise facilities.The Coronavirus disease 2019(COVID-19)pandemic has frightened the sports and physical activity community and enthusiasts for potential trans-mission,dissemination,and lethality in vulnerable populations;those with chronic diseases,co-morbidities,the elderly people,and in young and healthy people.This pandemic has caused a chain reaction with cancellations of sports competitions and gymnasiums closing around the world.Currently,some sporting events are gradually resuming in certain regions of the world and also the return of competitions and training.In general,without fans and public,the sports media can only report the infection of athletes and coaching staff members.However,this situation is dynamic-the world is currently experiencing the second wave of the disease;with the safety and containment measures for the disease is changing daily.The purpose of this article is to present information concerning the COVID-19 pandemic,to clarify health issues for professionals and people connected to sport and physical activity venues,presenting information to assist in educations and the health promotion and prevention.The time is now for making changes,reviewing the actions and conducts necessary for prevention,and most importantly not letting our guard down,even as vaccines become available for all people in the world.Remembering that even after getting vaccinated,it is necessary to continue with safety measures,for example,the use of facial masks and social distance and hygiene,that is,washing your hands frequently and/or sanitizing with 70%alcohol.We can't let our guard down for COVID-19.
