Isometric and isokinetic torque curves at the knee joint

Isometric and isokinetic torques of bilateral quadriceps and hamstrings were measured with Isokinetic Rehabilitation and Testing System (Model No. Cybex 340) on 40 normal untrained subjects, 20 males and 20 females, ranging between the ages of 23 and 35 years. The mean peak isometric and isokinetic torque values of both muscle groups showed no significant differences between dominant (right) and nondominant (left) limbs in both sexes; however there were significant differences between the male and the female. As the angular velocity increased, the peak torque significantly decreased, and the point of peak torque output occurred significantly later in the range of motion for quadriceps and hamstrings (p less than 0.01). There were no significant changes in the hamstrings to quadriceps (H/Q) ratios as the angular velocity increased. However, there were significant differences of mean H/Q ratio between male and female (p less than 0.01). Height had significant positive correlation with peak isometric and isokinetic torques for both quadriceps and hamstrings (p less than 0.01). Weight was found to correlate significantly with peak isometric and isokinetic torques (p less than 0.01). The mean isometric torques were significantly higher than the mean isokinetic torques for any joint angles in both sexes (p less than .01).     

Neuromuscular Changes in Female Collegiate Athletes Resulting From a Plyometric Jump-Training Program

OBJECTIVE: To assess performance changes induced by a 6- week plyometric jump-training program. DESIGN AND SETTING: We used a quasiexperimental design to compare groups formed on the basis of team membership. Testing was conducted in an athletic training research laboratory, both before and after a 6-week period of preseason basketball conditioning. SUBJECTS: Nineteen female collegiate basketball players from a National Collegiate Athletic Association Division I program (8 subjects) and a National Association of Intercollegiate Athletics Division II program (11 subjects) who had no history of anterior cruciate ligament injury and who had no history of any lower extremity injury during the preceding 6 months. MEASUREMENTS: The variables of primary interest were hamstrings and quadriceps isokinetic peak torque. Of secondary interest were 5 variables derived from step-down and lunging maneuvers performed on a computerized forceplate system and 4 variables derived from tracking the position of the body core during performance of a T-pattern agility drill with a computerized infrared tracking system. RESULTS: A significant group x trial interaction was found for hamstrings peak torque at 60 degrees.s(-1) (F(1,17) = 9.16, P =.008.), and the proportion of total variance attributable to the treatment effect produced by the jump-training program was relatively large (eta(2) =.35, omega(2) =.30). None of the other variables demonstrated statistically significant changes. CONCLUSIONS: Our primary results support plyometric jump training as a strategy for improving neuromuscular attributes that are believed to reduce the risk of anterior cruciate ligament injury in female college basketball players. They also provide the basis for reasonable isokinetic strength goals.     

南阳地区回族青少年Heath-Carter体型特征

目的 探讨南阳地区回族青少年体型发育特征及其规律。 方法 应用Heath-Carter体型法对1357名南阳地区回族学生体型进行评价。 结果 7～18岁青少年身高、体质量随年龄的增加而增长;体脂肪率除8岁组外,其他各年龄组女生>男生。南阳地区回族男生的平均体型为偏中胚层的内胚层型（5.3~4.0~3.4）,女生为偏外胚层的内胚层型（5.0~2.5~3.3）;男生和女生的体型均以内胚层系体型为主（男40.0%、女29.0%）;内因子值除17岁组外,其他各年龄组男生>女生;中因子值各年龄组男生>女生;外因子值7～13岁各组女生>男生,14～18岁各组男生>女生。 结论 南阳地区回族女生较男生瘦削,皮下脂肪量较少。回族男生较女生身体的线形程度高,充实度增加。南阳地区回族青少年体脂较多,可能与其不合理饮食和生活习惯有关。     

Cross-sectional reference values for height, weight and body mass index of school children living in Tehran, Iran

AIM: The aim of the study was to create reference values for weight, height and body mass index (BMI) of school children living in Tehran. METHOD AND SAMPLES: The study subjects consisted of 1,420 girls between 6 and 17 years of age and 1,515 boys between 6 and 15 years of age. Samples were collected by a multistage sampling method from schools in different areas of Tehran. All participants were established to be healthy and their height, weight and BMI evaluated. Reference standard values estimated by the LMS method using LMS Light software and 3rd, 5th, 10th, 25th, 50th, 75th, 90th, 97th and 85th (only for BMI) centiles were constructed and the results compared with US reference values. RESULTS: The centiles provided a good fit to the data. In boys, there were some significant differences of mean standard deviation scores (SDS) of height and BMI from zero, but there were no significant differences in weight. In girls, the mean SDS of height, weight and BMI were significantly lower than zero, especially for 7-9 years of age. Among 12-13-year-old girls, the mean SDS of height, weight and BMI came closer to zero, and the differences were not significant. Thereafter, although girls seemed to be shorter than US reference measures, their weight and BMI did not differ from reference values significantly. CONCLUSION: Our results for boys between 6 and 15 years are comparable with US reference values; however, the US reference values, especially for height, are not applicable for Iranian girls between 6 and 17 years.     

儿童青少年血清IGF-1及IGFBP-3的 正常参考值研究

目的 探讨儿童青少年血清胰岛素生长因子-1（IGF-1）及胰岛素因子结合蛋白-3（IGFBP-3）的正常参考值。方法 选取2018年1月~2019年1月在我院体检的312例健康的儿童、青少年为研究对象,分别测定其IGF-1、IGFBP-3水平,并分析IGF-1、IGFBP-3与年龄、性别、发育阶段的关系。结果 男孩血清IGF-1峰值为13岁,女孩为11岁;男孩血清IGFBP-3峰值为14岁,女孩为11岁;高峰值出现后,IGF-1、IGFBP-3水平随年龄增长缓慢下降或维持高峰值;同年龄比较男孩血清IGF-1水平高于女孩、IGFBP-3水平低于女孩,差异有统计学意义（P＜0.05）;年龄、发育阶段与血清IGF-1值呈正相关（r=0.241,P＜0.01）,IGFBP-3与年龄呈正相关（r=0.323,P＜0.01）。结论 建立儿童青少年IGF-1、IGFBP-3水平正常参考值,可与监测其生长、临床症状以及生长激素治疗后随访具有重要的参考价值。     

A cross-sectional survey of upper and lower limb strength in boys and girls during childhood and adolescence

Changes in height and weight during childhood and adolescence are well documented, yet there is comparatively little comprehensive information about muscular development during this time. In a cross-sectional survey standing height, body weight and isometric strength of the elbow flexor and quadriceps muscles have been measured in 267 boys and 284 girls aged from 5 to 17 years. All the children were from private London schools. The mean heights and weights for each age group were between the 50th and 75th centiles for British children. The strength of both muscle groups in the boys and girls rose steadily in each age group from 8 to 12 years, after which there was a rapid increase in strength of both the quadriceps and elbow flexors in boys which continued even when growth in height and body weight had virtually ceased. In the pre-adolescent phase of growth, muscle strength of the elbow flexors and quadriceps increased as a function of height squared and cubed respectively, suggesting that stretch as a result of elongation of the long bones, and for the quadriceps, loading, may be the primary stimuli during this phase. In the postpubertal phase some other stimulus, such as a direct action of hormones on the muscle, must be responsible for the continued increase in strength in the boys.     

儿童关于特质的性别差异信念的发展

目的:考察3~8岁儿童关于特质的性别差异信念及其发展特点。方法:采用个别测查法对379名儿童进行测查。结果:①从总体上看,各年龄组儿童倾向于将男性化特质归于男孩,将女性化特质归于女孩;②男孩比女孩更倾向于将男性化特质与男孩相联系,而女孩比男孩则更倾向于将女性化特质与女孩相联系;③从总体上看,学前阶段儿童将男性化特质与男孩相联系、将女性化特质与女孩相联系的倾向逐渐增强,6岁之后二者均处于稳定水平。结论:我国儿童从3岁起就持有关于特质的性别差异信念,他们对同性特质的性别差异信念强于对异性特质的性别差异信念,并且这些信念在学前期间不断增强,6岁左右趋于稳定。     

Stabilization of asthma prevalence among adolescents and increase among schoolchildren (ISAAC phases I and III) in Spain

BACKGROUND: Most studies show a steep increase in asthma prevalence in the last decades, although few studies had applied the same methodology. Recent reports point out the possibility that the epidemic has come to an end. We have studied the prevalence of asthma in a very large sample of children, repeating the study eight years apart. METHODS: Repeated cross-sectional studies using the International Study of Asthma and Allergies in Childhood (ISAAC) protocol in a sample of Spanish schoolchildren 6-7 (parent-reported) and 13-14 (self-reported) years old in 1994-95 (phase I) and 2002-2003 (phase III). The number of participants was 42 417 in phase I and 42 813 in phase III. The participation rate was over 87% (13-14 years) and 70% (6-7 years). RESULTS: The prevalence of wheezing in the previous year in children aged 13-14 years was 9.0 and 9.3% for boys and 9.6 and 9.2% for girls for phases I and III, respectively. Children 6-7 years of age showed a substantial increase in wheezing in the previous year (7.0 and 10.7% for boys and 5.3 and 8.2% for girls). Other symptoms and severity indexes followed the same patterns. CONCLUSIONS: In the last 8 years, the prevalence of asthma has not changed in 13-14-year-old Spanish children but has increased substantially in 6-7-year olds.     

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.     

Longitudinal models of long bone growth during adolescence.

Data from the Child Research Council (Denver, CO) were utilized to model longitudinal adolescent growth of the humerus, radius, femur, and tibia for 36 girls (10-16 years) and 33 boys (10-17 years). Multilevel modeling procedures were used to estimate variation, covariation, and the polynomial parameters necessary for generating growth curves. At age 10, long bone lengths for girls and boys are similar; by age 16, each of the boys' arm bones is about 20 mm longer and each of their leg bones is about 30 mm longer. Due to the earlier maturation of girls, the models show the length of each of their long bones exceeding that of boys to some degree during some period of adolescence. Peak velocities for leg bones are attained earlier than those for arm bones; in both sexes, age at humeral peak velocity coincides with age at peak height velocity (PHV). At age 13, correlations among lengths and among velocities of bones are strong to moderate, and girls consistently display higher variation than do boys for both long bone length and growth velocity. Considered relative to the average velocity of each bone's growth, the tibia is the most variable of the four long bones at age 13 years.     

中国7岁以下儿童重量指数的生长规律及参照标准建立

目的分析中国7岁以下正常儿童重量指数（PI）随年龄增长的变化规律,制定0～2岁儿童PI的参照标准及生长曲线。方法体重和身高测量值来自2005年＂中国九市7岁以下儿童体格发育调查＂,根据体重和身高测量值计算PI值[体重（kg）.身长-3（m-3）],并建立7岁以下正常儿童PI数据库。分析PI在各主要百分位（P3、P50及P97）上的变化规律,比较PI在性别和城郊群体水平上的差异。以3岁以下儿童为参照人群,采用LMS方法建立PI参照值及标准化曲线,模型构建使用LMSPro软件。选择＂转换年龄＂模式,具体参数：男性自由度L-M-S=3-11-6,POWER=0.05及OFSET=0.10;女性自由度L-M-S=3-11-4,POWER=0.05及OFSET=0.15。结果 0～7岁儿童总样本量为138775名,其中城区69760名（男34901名,女34859名）,郊区69015名（男34650名,女34365名）,男女及城郊样本量各半,各年龄组1496～1666名。0～2岁儿童曲线拟合的数据：男23703名,女23625名,每年龄组1512～1622名。①PI随年龄增长先攀升,2～3月龄达峰值,然后急速下降,2岁以后趋缓,并随年龄增长持续缓慢下降。男女间、城郊间差异均不明显;但在1月龄至3岁,男性略高于女性,1～6月龄及2～3岁时郊区略高于城区。②采用百分位和标准差单位两种表达形式给出0～2岁儿童数值及标准化生长曲线图。结论本研究分析了中国7岁以下正常儿童PI的生长规律,建立了0～2岁儿童PI的参照标准及生长曲线,为进一步研究和应用PI奠定基础。     

GnRH agonist stimulation of the pituitary-gonadal axis in children: age and sex differences in circulating inhibin-B and activin-A

BACKGROUND: Inhibin-B decreases and activin increases FSH secretion in adults. We investigated whether an FSH-inhibin/activin feedback loop exists before or during puberty. METHODS: FSH secretion was stimulated with 10 microg/kg leuprolide acetate (GnRH agonist) in 18 girls, ages 1.0-13.2 years, and 11 boys, ages 8.9-15.2 years, with variations in pubertal development, and in five normal 9- to 10-year-old girls. Blood, obtained at 0, 0.5, 1, 2, 4, 8, 12, 16, 20 and 24 h after GnRH agonist, was analysed for LH, FSH, activin-A, inhibin-A, inhibin-B, follistatin 288 and estradiol/testosterone. RESULTS: FSH increased within 30 min of GnRH agonist administration with a peak greater in girls than boys (P=0.0006). Baseline inhibin-B was greater in boys than girls (P=0.01), while baseline activin-A concentrations were greater in girls. GnRH agonist-stimulated FSH increased inhibin-B in girls by 8 h and in boys by 20 h (P<0.05), but did not affect activin-A. Inhibin-B increases were seen only in girls older than 5 years. CONCLUSIONS: An inhibin-B-FSH feedback loop exists prior to the onset of puberty in girls older than 5 years. Sex differences in activin-A and inhibin-B concentrations may be responsible for sex differences in serum FSH concentrations.     

躯干运动控制对落地过程中膝关节生物力学指标的影响

目的 明确躯干运动控制对单腿落地过程中膝关节生物力学的影响。方法 招募20名健康男性篮球运动员，采用 Vicon 运动捕捉系统、Kistler 三维测力台、Noraxon表面肌电测试系统测量在躯干控制条件下单腿落地过程中膝关节运动学、动力学和表面肌电的参数。结果 深吸气落地和带杆落地与自然落地比较在触地时刻膝关节屈曲角、峰值屈曲角、峰值屈曲力矩有统计学差异,触地时刻膝关节屈曲角、峰值屈曲角显著增大，峰值屈曲力矩显著减小；深吸气落地和带杆落地膝关节峰值外翻角、峰值外翻力矩及膝关节腘绳肌、股四头肌肌肌电活动量差异无统计学意义。结论 深吸气或带杆落地降低了篮球运动员落地运动中前交叉韧带（anterior cruciate ligament，ACL）损伤的风险，研究结果 为篮球运动员落地运动中ACL损伤预防提供理论基础。     

湖南侗族青少年身高、体重及体表面积研究

目的了解湖南侗族青少年学生身高、体重及体表面积的发育情况。方法调查了982例(男486例,女496例)7～17岁的侗族青少年学生的身高、体重,计算出每位学生的体表面积和体重指数,并与全国青少年平均值进行比较。结果侗族青少年学生的身高、体重、体重指数及体表面积随年龄增长而增长,男生11～15岁为快速增长期,女生10～14岁为快速增长期。体重指数在14岁后出现明显的性别差异;9岁开始女生体表面积值超过男生,14岁开始男生体表面积值又超过女生,15岁以后,男女生体表面积之差逐渐加大。结论湖南侗族青少年的身高、体重及其体重指数和体表面积的发育水平均不及全国青少年的平均水平。     

Assessment of linear growth of affluent urban Pakistani adolescents according to CDC 2000 references

BACKGROUND: The appropriateness of using international reference data for assessing growth of children and adolescents from developing countries has been debated. If the growth performance in at least those sections of the society that may be considered affluent has reached the levels represented by the international reference, the case for adoption of the NCHS reference would be strong. Findings from studies in younger children indicate appropriateness of these standards but data from older children are lacking. AIM: The study aimed to compare the linear growth of affluent Pakistani adolescents living in Karachi with the NCHS reference so as to assess the appropriateness of using these standards for assessing the growth status of Pakistani adolescents. SUBJECTS AND METHODS: Data were collected from 876 girls and 819 boys aged 10-15 years studying in well known and established affluent urban public schools in Karachi. A portable stadiometer (Minimeter by CMS, London) was used for measuring heights. Heights were compared using the United States Center for Disease Control (CDC 2000) reference values to assess growth status. RESULTS: The mean ages of boys and girls were 12.82 and 12.63, respectively. Mean Height for Age Z score (HAZ) (-0.02) was very close to CDC 2000 reference values but the growth pattern was not similar. Younger children were relatively taller and the older children were shorter than CDC standards. Mean HAZ scores for 10, 11, 12, 13, 14 and 15-year-old boys and girls were 1.12 and 1.03, 0.54 and 0.55, 0.47 and 0.26, 0.29 and -0.21, -0.08 and -0.64, -0.19 and -0.53, respectively. The mean HAZ for boys (0.12) was slightly higher and that for girls slightly lower (HAZ = -0.14) than the reference population. Even among the relatively affluent group of children studied HAZ scores increased with relative socio-economic status. CONCLUSIONS: Although in terms of averages for 10-15-year-old boys and girls the height status was not very different from CDC standards, the growth curves of Pakistani children was slightly different from CDC 2000 standards. Further studies are needed to assess the appropriateness of using international growth standards for assessing height status of Pakistani adolescents.     

优秀青少年男子篮球运动员腰腹屈伸肌群生物力学特征

背景：目前,等速测试系统在评定各专项运动员肌肉功能的应用越来越受到重视,但运用等速肌力测试技术研究优秀青少年男子篮球运动员腰腹肌力特征的报道较少。 目的：研究优秀青少年男子篮球运动员腰腹屈伸肌群生物力学特征,为篮球项目的腰腹力量训练、科学选材和预防腰腹损伤提供依据。 方法：采用Cybex-Norm等速肌力测试系统,对广州男子篮球队运动员18人测定腰腹屈伸肌群在慢速60(°)/s和快速180(°)/s的肌力和做功情况。 结果与结论：受试者腰腹屈伸肌群的峰力矩和相对峰力矩在同一测试速度下,伸肌群大于屈肌群(P < 0.01);腰腹屈伸肌群的峰力矩、相对峰力矩、总功均随着测试速度的增加呈减小趋势(P < 0.05),伸肌群的峰力矩和相对峰力矩减少更显著(P < 0.01);腰腹屈伸肌群的相对功率随着测试速度的增加而呈上升趋势(P < 0.01);外线球员腰腹屈伸肌群各测试指标成绩优于内线球员;在等速向心收缩时,随测试速度加快,腰腹屈伸肌群的峰力矩屈伸比呈递减趋势,躯干稳定性减弱。结果提示,优秀青少年男子篮球运动员腰腹伸肌群肌力大于屈肌群;外线球员腰腹屈伸肌群的肌力优于内线球员;等速快速运动时,腰腹屈伸肌群力量减小,腰腹关节屈伸肌力平衡性减弱,应加强青少年男子篮球运动员腰腹核心肌群快速力量训练。   中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

Stability of somatotypes: A longitudinal study of Belgian children age 6 to 17 years

The purpose of this study was to investigate the stability of somatotypes in Belgian children and adolescents, 52 boys and 30 girls, followed longitudinally from 6 to 17 years of age. The anthropometric Heath-Carter somatotypes, with a stature correction for endomorphy, were estimated at 1-year intervals. Mean somatotypes were most different between the earliest and oldest ages in both boys and girls. For boys, the means from 9 to 13 years and from 14 to 17 years did not differ. Means were 2-4-2½, 2½-4-4, and 2-4-4 at 6, 12, and 17 years, respectively. The scatter of somatotypes about their means was smallest at 6–8 years and greatest at 11–13 years in both boys and girls (P <0.05). For girls, the mean somatotypes from 8 or 9 years through adolescence were not different, although they tended to become more meso-endomorphic. Means were 2-4½-2½, 3-4-3½, and 3½-3½-3 at 6, 12, and 17 years, respectively. The average migratory distance for boys was 6.4 (range = 3.7–12.9) and 7.8 (3.9–21.8) for girls. Many subjects had changes that were three to four times greater than others. Boys were lower in ectomorphy at 6–8 years than at older ages, while girls were higher in mesomorphy at 6 than at 12–17 years (P <.05). Interage partial correlations for each component were highest (r² ? .49) between adjacent years, but were poor to moderate as time intervals increased. The findings of this longitudinal study confirm and further define the instability of somatotypes previously observed in cross-sectional studies of Belgian children and adolescents. © 1995 Wiley-Liss, Inc.     

Secular change in height, sitting height and leg length in rural Oaxaca, southern Mexico: 1968-2000

OBJECTIVE: To evaluate secular changes in height, sitting height and estimated leg length between 1968 and 2000 in residents in a rural Zapotec-speaking community in Oaxaca, southern Mexico. MATERIALS AND METHODS: Height and sitting height were measured in school children 6-13 years (1968; 1978, 2000), in adolescents 13-17 years (1978, 2002) and adults 19-29 years (1978, 2000). Leg length was estimated as height minus sitting height. The sitting height/ height ratio was calculated. Subjects were grouped by sex into four age categories: 6-9, 10-13, 13-17 and 19-29 years for analysis. The Preece-Baines Model I growth curve was fitted to cross-sectional means for 1978 and 2000. RESULTS: There were no differences between children 6-9 and 10-13 years in 1968 and 1978 with the exception of the sitting height ratio in girls 6-9 years. Children of both sexes 6-13 years and adolescent boys 13-17 years were significantly larger in the three dimensions in 2000 compared to 1978; adolescent girls differed only in height and sitting height. Adult males in 2000 were significantly taller with longer legs than those in 1978, but the samples did not differ in sitting height and the ratio. Adult females in 1978 and 2000 did not differ significantly in the three dimensions. Rates of secular change in height and sitting height between 1978 and 2000 were reasonably similar in the three age groups of male children and adolescents, but the rate for estimated leg length was highest in 10-13-year-old boys. Secular gains were smaller in adult males, but were proportionally greater in estimated leg length. Girls 6-9 and 10-13 years experienced greater secular gains in height, sitting height and estimated leg length than adolescent and young adult females, while secular gains and rates decreased from adolescent girls to young adult women. Ages of peak velocity for height, sitting height and estimated leg length declined in boys, while only ages of peak velocity for height and estimated leg length declined in girls. CONCLUSIONS: There are major secular increases in height, sitting height and estimated leg length of children and adolescents of both sexes since 1978. Secular gains in height are of similar magnitude in boys and girls 6-13 years, but are greater in adolescent and young adult males than females. The secular increase in height of young adults of both sexes is smaller than that among adolescents. Estimated leg length accounts for about 60% of the secular increase in height in children of both sexes. Estimated leg length and sitting height contribute equally to the secular increase in height in adolescent boys, whereas estimated leg length accounts for about 70% of the secular increase in height in young adult males. Sitting height contributes about two-thirds of the secular increase in height in adolescent and young adult females.     

The development of balance control in children: comparisons of EMG and kinetic variables and chronological and developmental groupings

This cross-sectional study examined electromyographic (EMG) and kinetic variables during reactive balance responses in children grouped according to developmental level as compared with chronological age. Purposes were to explore relationships between the two types of variables and the effectiveness of the two grouping methods. Forty-four children between 9 months and 10 years old were tested for reactive balance control on a moveable platform. Surface electrodes measured EMG activity in the gastrocnemius (GA), hamstrings (HA), paraspinals (PS), tibialis anterior (TA), quadriceps (QA), and abdominal (AB) muscles. Timing and distance of center-of-pressure (COP) movements and peak muscle torques at the ankle, knee, and hip were also examined. Significant relationships and group differences were found between postural muscle activity and both the torque generated in the lower limbs and the timing and distance of COP adjustments employed to restabilize balance. As postural muscle activity increased and became more coordinated in timing, peak torque at the ankle and hip also increased, while the distance of and time to complete COP readjustments decreased. Children in younger/developmentally lower groups had smaller-magnitude and less-synergic muscle activity, lower peak torques, longer times to restabilize the COP, and greater COP paths than older/higher developmental groupings. Grouping by developmental level produced more statistical differences than did grouping by age. The correspondence of GA, HA, and PS muscle activity with COP measures and joint peak torques confirms that these muscles are key contributors to the balance synergy correcting for induced forward sway. Additionally, developmental level appears to be a much better predictor of balance improvement than chronological age.     

Muscle strength and function before and after anterior cruciate ligament reconstruction using semitendonosus and gracilis.

This study assessed the quadriceps and hamstring strength before and 6 months after anterior cruciate ligament (ACL) reconstructive surgery using the hamstrings and related the findings to functional performance. Six months after surgery is a critical time for assessment as this is when players are returning to sport. Maximum isokinetic strength of 31 patients with complete unilateral ACL ruptures was measured at speeds of 60 degrees and 120 degrees per second. Functional assessment included the single hop, the triple hop, the shuttle run, side-step and carioca tests. All patients underwent a controlled quadriceps emphasized home-based physiotherapy program both before and after surgery. Results show that before surgery there was a 7.3% quadriceps strength deficit at 60 degrees per second compared to the uninjured leg but no hamstring strength deficit. After surgery there was a statistically significant but relatively small loss of muscle strength. The quadriceps strength deficit had increased to 12% and there was a 10% hamstring deficit. Post-operatively there was an 11% and 6.3% improvement in the hop tests, a 9% (P < 0.01) improvement in the shuttle run, a 15% (P < 0.001) improvement in the side step and a 24% (P < 0.001) improvement in the carioca tests (P < 0.001) despite the loss of muscle strength.