Energy conversion strategies during 100 m sprinting

The aims of this study were to examine energy conversion strategies during 100 m sprinting and to determine whether there are opportunities for performance enhancement beyond the usual 'maximum effort throughout' strategy. The roles of aerodynamic drag and kinetic energy recovery on the overall whole-body energy balance are discussed. A mathematical model based on sprinting with maximum effort, converting chemical energy as rapidly as possible to mechanical energy, is used to calculate a reference performance. Subsequent calculations show the effect of inserting a period of constant-speed running on overall running time. The paper explores how the timing of entry into the second phase affects the overall running time. Overall, the calculations show that no benefits result from adopting a running strategy involving the insertion of a constant-speed phase; the analysis confirms that the strategy of running with maximum effort is the optimum. For a certain range of conditions, the insertion of a short period of constant-speed running has been shown to have a negligible effect on overall running time. For elite male athletes, the constant-speed phase may be entered between 55 and 60 m from the start line, while for elite female athletes the corresponding values are between 46 and 53 m from the start.     

Energy conversion strategies during 100 m sprinting

The aims of this study were to examine energy conversion strategies during 100 m sprinting and to determine whether there are opportunities for performance enhancement beyond the usual ‘maximum effort throughout’ strategy. The roles of aerodynamic drag and kinetic energy recovery on the overall whole-body energy balance are discussed. A mathematical model based on sprinting with maximum effort, converting chemical energy as rapidly as possible to mechanical energy, is used to calculate a reference performance. Subsequent calculations show the effect of inserting a period of constant-speed running on overall running time. The paper explores how the timing of entry into the second phase affects the overall running time. Overall, the calculations show that no benefits result from adopting a running strategy involving the insertion of a constant-speed phase; the analysis confirms that the strategy of running with maximum effort is the optimum. For a certain range of conditions, the insertion of a short period of constant-speed running has been shown to have a negligible effect on overall running time. For elite male athletes, the constant-speed phase may be entered between 55 and 60 m from the start line, while for elite female athletes the corresponding values are between 46 and 53 m from the start.     

瘦素与运动

瘦素是由脂肪组织分泌的具有增加能量消耗、减少食物摄取、减少体脂、控制体重和调节能量平衡的一种激素,与体脂含量密切相关,其分泌受多种因素影响。急性运动对血中瘦素的影响有不变和下降的不同结果;长期运动训练可降低血瘦素的含量,这是由于体脂量的下降所致。运动对血瘦素的效应存在着延时性。     

Effects of weighted vests and sled towing on sprint kinematics

In this study, we compared sprint kinematics of sled towing and vest sprinting with the same relative loads. Twenty athletes performed 30-m sprints in three different conditions: (a) un-resisted, (b) sled towing, and (c) vest sprinting. During sled towing and vest sprinting, external loads of 15% and 20% of body mass were used. Sprint times were recorded over 10 and 30 m. Sagittal-plane high-speed video data were recorded at 5, 15, and 25 m from the start. Relative to the un-resisted condition, sprint time increased (7.5 to 19.8%) in both resisted conditions, resulting mainly from decreased step length (-5.2 to -16.5%) with small decreases in step frequency (-2.7 to -6.1%). Sled towing increased stance phase duration (14.7 to 26.0%), trunk angle (12.5 to 71.5%), and knee angle (10.3 to 22.7%), and decreased swing phase duration (-4.8 to -15.2%) relative to the un-resisted condition. Vest sprinting increased stance phase duration (12.8 to 24.5%) and decreased swing phase duration (-8.4 to -14.4%) and trunk angle (-1.7 to -13.0%). There were significant differences between the two resisted conditions in trunk, thigh, and knee angles. We conclude that sled towing and vest sprinting have different effects on some kinematics and hence change the overload experienced by muscle groups.     

Effects of weighted vests and sled towing on sprint kinematics

In this study, we compared sprint kinematics of sled towing and vest sprinting with the same relative loads. Twenty athletes performed 30-m sprints in three different conditions: (a) un-resisted, (b) sled towing, and (c) vest sprinting. During sled towing and vest sprinting, external loads of 15% and 20% of body mass were used. Sprint times were recorded over 10 and 30 m. Sagittal-plane high-speed video data were recorded at 5, 15, and 25 m from the start. Relative to the un-resisted condition, sprint time increased (7.5 to 19.8%) in both resisted conditions, resulting mainly from decreased step length ( ? 5.2 to ? 16.5%) with small decreases in step frequency ( ? 2.7 to ? 6.1%). Sled towing increased stance phase duration (14.7 to 26.0%), trunk angle (12.5 to 71.5%), and knee angle (10.3 to 22.7%), and decreased swing phase duration ( ? 4.8 to ? 15.2%) relative to the un-resisted condition. Vest sprinting increased stance phase duration (12.8 to 24.5%) and decreased swing phase duration ( ? 8.4 to ? 14.4%) and trunk angle ( ? 1.7 to ? 13.0%). There were significant differences between the two resisted conditions in trunk, thigh, and knee angles. We conclude that sled towing and vest sprinting have different effects on some kinematics and hence change the overload experienced by muscle groups.     

运动竞技能力与补糖

糖是体内最主要最能快速动员的供能物质,赛前（运动前）和赛中（运动中）及时补充糖类对保持运动能力具有重要意义。一般使用糖原负荷的方法提高糖原储备的长期补糖。赛前补糖的目的主要是优化肌肉和肝脏糖原储备,维持运动时血糖稳定,保障60 min内快速运动能力和长时间末期的冲刺力;赛中补糖可显著改善糖代谢环境,提高机体运动能力,运动时间长于1 h的运动项目应在补充的液体中加人适量的糖和电解质。对于冰球等高强度、间歇性运动项目进行赛前和赛中补糖有利于运动员提高赛场竞技能力,对于一次性大强度或一次性的力量性运动以及高强度以无氧代谢占优势的一些专项（大于80% Vo2max的有氧代谢为主）一般不主张在比赛前专门补充糖,补糖不当反而有损其运动能力。     

短跑技术专门练习的创新与教学训练效果的实验比较研究

为了革新传统的短跑技术专门练习，将48名大学体育系学生分组进行教学训练实验研究。研究采用了高速摄影及影片解析、数理统计等方法，实验结果表明：在提高专项成绩方面实验组成绩的提高幅度明显高于对照组；实验组摆动腿伸髋速度和两腿煎绞速度明显高于对照组；实验组摆动腿着地速度显著高于对照组。实验结果提示：实验组所采用的创新短跑专门练习比传统短跑专门练习更有利于提高100m跑专项成绩及掌握专项技术。     

Leg amputation side determines performance in curve sprinting: a case study on a Paralympic medalist

The lower limb kinetics of curve sprinting in amputees are not well described in the literature, particularly with respect to the effect of the side of amputation. This is an issue due to the importance of the knowledge for prosthetic design and classification of athletes. Thus, the aim of this study was to investigate the influence of side of amputation on curve sprinting performance in athletes with a unilateral leg amputation. A three-dimensional motion analysis system (Vicon), four force plates (Kistler) and a modified mathematical human model (ALASKA) were used to compare clockwise and counter clockwise curve sprinting lower limb kinematics and kinetics of a Paralympic medalist with a left-sided knee exarticular amputation. Results reveal that vertical ground reaction force application and total vertical impulse were lower when the affected limb was at the inside of the curve. The unaffected limb showed joint mechanics different to those established for non-amputee athletes and might contribute better to propulsion when being the inside limb. Curve sprinting biomechanics and the ability to attain high radial velocities are directly dependent on the side of amputation relative to the curve direction in a unilateral amputee athlete of highest performance level.     

析短跑运动的肌肉放松机制

从现代短跑运动技术结构特征、运动生理学和运动心理学角度 ,分析影响短跑肌肉放松及如何尽可能地保持短跑最高速度的机制 ,并就提高短跑运动肌肉放松能力 ,对短跑教学与训练提出一些参考意见。     

Influence of force-vector and force application plyometric training in young elite basketball players

Plyometric training composed by unilateral exercises with horizontal jumping direction seems to be an effective way to improve physical performance in athletes. The present study aimed to compare the influence of a combined jumping direction and force application (horizontal-unilateral vs. vertical-bilateral) plyometric training on linear sprinting, jumping, change of direction (COD) and dynamic balance in young elite basketball players. Twenty young (U-13 to U-14) male basketball players (age: 13.2?±?0.7 years, body mass: 59.5?±?12.7?kg, height: 172.9?±?7.9?cm) were randomly assigned either to a unilateral-horizontal (UH, n?=?10) or bilateral-vertical (BV, n?=?10) plyometric group, twice a week for 6-wk. Both groups performed between 60 and 100 jumps/session. UH executed all jumps unilaterally with horizontal direction, while jumps in the BV were bilaterally with vertical direction. Performance was assessed by a linear sprinting test, vertical and horizontal jumping tests, COD tests (V-cut and 5+5?m with a 180°COD test), an ankle dorsiflexion test and dynamic balance tests (anterior and postero-lateral directions). Within-group differences showed substantial improvements (Effect size (ES):0.31–1.01) in unilateral vertical and horizontal jumping, V-cut test and postero-lateral direction with right leg after both training interventions. Furthermore, UH group also substantially improved (ES:0.33–0.78) all sprinting times and postero-lateral direction with left leg, while BV enhanced anterior direction with left leg (ES:0.25). Between-group analyses showed substantially greater improvements (ES:0.33) in 10-m and V-cut test in UH than in BV. The likely beneficial effect (small ES) achieved in sprinting abilities suggests the combination of unilateral-horizontal jumps to improve such abilities.     

瘦素(Leptin)与体力活动的研究综述

L eptin是 ob基因表达的脂肪组织源激素 ,其主要作用是减少体脂、控制体重和调节机体能量平衡。它的产生和代谢受到遗传和体内外环境因素的调控和影响。运动训练可减低 ob m RNA的表达和血 leptin浓度 ,训练所致的体脂量下降是产生这种作用的重要决定因素。单次运动对 lepin表达和其血中浓度的效应 ,有减低与无影响的研究结果。运动的这些效应可能依赖于运动负荷量和热能消耗量 ,也与一些激素和代谢物有关。     

The influence of biological maturity on motor performance among habitually barefoot versus habitually shod adolescents

Biological maturation is associated with physiological changes which in turn affect motor performance. No study has assessed the association between growing up habitually shod versus habitually barefoot and motor performance in the context of maturation, so this approach is unique. The purpose of this study was to examine the influence of biological maturity on motor performance dependent on the participants’ footwear habits. Sixty-five German habitually shod (mean age 13.28?±?0.83 years) and fifty-five South African habitually barefoot (mean age 13.38?±?0.87 years) participants were included. Dynamic postural control was determined via backward balancing, explosive strength by standing long jump and sprinting performance based on a 20-m sprinting test. All tests were performed barefoot and shod. Biological maturation was calculated by using the maturity offset value. Linear mixed models were used to analyse interactions between the maturity offset value, footwear habits and motor performance. Throughout maturation, there was a significant difference between habitually barefoot and habitually shod balance performance (P?=?0.001). Maturation led to balance improvements in habitually barefoot adolescents, but not in habitually shod adolescents. No such differences could be observed for standing long jump and 20-m sprint performance. Maturity offset was a significant predictor for jumping and sprinting performances (P?相似文献   

Measurement procedures affect the interpretation of metatarsophalangeal joint function during accelerated sprinting

Abstract

The metatarsophalangeal joint (MPJ) is a significant absorber of energy in sprinting. This study examined the influence of MPJ axis choice and filter cut-off frequency on kinetic variables describing MPJ function during accelerated sprinting. Eight trained sprinters performed maximal sprints along a runway. Three-dimensional high-speed (1000 Hz) kinematic and kinetic data were collected at the 20 m point. Three axis definitions for the five MPJs were compared. MPJ moments, powers and energies were calculated using different filter cut-off frequencies. The more anatomically appropriate dual axis resulted in less energy absorbed at the MPJ compared to the oblique axis which also absorbed less energy compared to the perpendicular axis. Furthermore, a low cut-off frequency (8 Hz) substantially underestimated MPJ kinematics, kinetics and the energy absorbed at the joint and lowered the estimate of energy production during push-off. It is concluded that a better understanding of MPJ function during sprinting would be obtained by using an oblique or anatomically appropriate representation of the joint together with appropriate kinematic data sampling and filtering so that high frequency movement characteristics are retained.     

瘦素(Leptin)的生理作用机制及长期运动对其水平的影响

采用文献资料法,分析瘦素(Leptin)的生理作用机制及长期运动对其水平的影响。结果显示:ob基因编码的Leptin具有降低脂肪含量,维持能量平衡,调节代谢、生殖、激素分泌,提高免疫机能等多方面的功能。长期运动对Leptin的影响较为复杂,除了体脂变化、能量平衡变化和激素水平变化等因素外,可能还有未知因素,需要更多的实验探究长期运动对Leptin调节的作用机制。     

Collegiate baseball players with more optimal functional movement patterns demonstrate better athletic performance in speed and agility

Sports injuries are common among baseball players and may result in abnormal movement patterns, increased risks of future injury, and unsatisfactory performance. The Functional Movement Screen (FMS?) has been developed to detect abnormal functional movement patterns and can be used for predicting risks of sports injury. However, whether FMS? scores are associated with athletic performance remains unclear. The goal of this study was to determine the association between functional movements and athletic performance in elite baseball players. Core stability, muscular strength and flexibility of the lower extremities, and FMS?, as well as athletic performance in sprinting, agility, and balance tests were assessed in 52 male collegiate Division I baseball players placed into two groups based on FMS? scores. The high-scoring group demonstrated better athletic performance than the low-scoring group, with a shorter duration of the agility test. No group differences were found in core stability, muscular strength, or muscle flexibility, except for rectus femoris flexibility. Thus, the FMS? score is associated with sprinting and agility performance in elite baseball players. These findings indicate that the FMS? may have a role in predicting athletic performance and thereby help determine the goals of training regimens or return-to-play strategies.     

The three-dimensional kinetic behaviour of the pelvic rotation in maximal sprint running

The purpose of this study was to investigate the effect of lumbosacral kinetics on sprinting. Twelve male sprinters performed 50 m sprints at maximal effort. Kinematic and ground reaction force data were recorded at approximately 40 m from sprint commencement. A whole-body inverse dynamics approach was applied to calculate joint forces and torques at the hip and lumbosacral joints. The contribution of the hips and lumbosacral joint torques to pelvic rotation was subsequently calculated, with joint force powers indicating the rate of mechanical energy transfer between segments across joint centres calculated for both hip joints. The kinetic analysis indicated that the lumbosacral torsional torque contributed significantly to pelvic rotation. Additionally, the pelvic rotation exerted anterior–posterior joint forces on the hips, contributing to the large positive joint force power at the hip of the stance leg. These hip joint force powers assisted in motion recovery during sprinting. In conclusion, the lumbosacral torsional torque might contribute to the recovery motion in sprinting through application of the anterior–posterior joint forces at the hip joints via pelvic rotation.     

短跑支撑阶段重心水平速度的运动生物力学分析

对10名一级左右男子短跑运动员途中跑支撑阶段重心水平速度进行运动生物力学分析,结果显示：（1）支撑阶段支撑腿膝关节最小角出现在垂直支撑以后;重心水平速度在着地后逐渐下降,在垂直阶段之前达到最小,而后逐渐增大;（2）髋关节的运动学指标在很大程度上反映运动员的短跑水平,髋关节的力量与柔韧性很大程度上决定运动员的竞技能力;（3）支撑腿支撑阶段踝关节的运动学参数应成为评定运动员短跑技术好坏的一项重要指标,过分追求小腿的回摆速度是不对的。     

Muscle activity in sprinting: a review

The use of electromyography (EMG) is widely recognised as a valuable tool for enhancing the understanding of performance drivers and potential injury risk in sprinting. The timings of muscle activations relative to running gait cycle phases and the technology used to obtain muscle activation data during sprinting are of particular interest to scientists and coaches. This review examined the main muscles being analysed by surface EMG (sEMG), their activations and timing, and the technologies used to gather sEMG during sprinting. Electronic databases were searched using ‘Electromyography’ OR ‘EMG’ AND ‘running’ OR ‘sprinting’. Based on inclusion criteria, 18 articles were selected for review. While sEMG is widely used in biomechanics, relatively few studies have used sEMG in sprinting due to system constraints. The results demonstrated a focus on the leg muscles, with over 70% of the muscles analysed in the upper leg. This is consistent with the use of tethered and data logging EMG systems and many sprints being performed on treadmills. Through the recent advances in wireless EMG technology, an increase in the studies on high velocity movements such as sprinting is expected and this should allow practitioners to perform the analysis in an ecologically valid environment.     

刚体方位广义坐标“布里恩角”在描述下肢环节定点运动中的应用

目前已有专家学者用欧拉角来描述髋关节的运动 ,然而 ,欧拉角的运用会出现数学计算上的困难 ,且所涉及的转轴与人体基本运动轴不一致。笔者介绍与人体运动轴较为相符 ,又可避免数学计算困难的一种人体下肢环节空间运动简化的方法 ,即用布里恩角描述下肢环节的定点运动。     

Energy conversion rates during sprinting with an emphasis on the performance of female athletes

Computed results from a mathematical model of the bioenergetics of sprinting, which incorporates a three-equation representation of anaerobic metabolism, were compared with measured distance-time data for female athletes from the finals of the 100-m event at the World Championships of 1987. The computed results closely model the performance of the competitors over the course of the entire race. The three main contributions to anaerobic metabolism were investigated and comparisons were made between male and female sprinters. Whereas the time constants for adenosine triphosphate (ATP) and phosphocreatine utilization for the two sexes were found to be similar, for oxygen-independent glycolysis the time constants of the female athletes were found to be higher. The maximum powers generated by female athletes during ATP conversion and glycolysis were only slightly lower than the figures found for male athletes, but the value for phosphocreatine utilization was substantially lower. The lower value for phosphocreatine utilization might explain the more pronounced fall-off in running speed over the latter stages of a race that female athletes experience in comparison with men. Although anaerobic sources dominate energy provision for both male and female sprinters, the calculations show that the latter make greater use of aerobic energy supplies.