Dynamic stretching is not detrimental to neuromechanical and sensorimotor performance of ankle plantarflexors

The acute effects of two dynamic stretching (DS) protocols on changes in the ankle range of motion (RoM), neuromechanical, and sensorimotor properties of the plantarflexor muscle group were examined. Eighteen participants received slow (SDS) or fast dynamic stretching (FDS) on two separate days. Outcome measures were assessed pre‐ and 2 minutes post‐interventions, and included maximum dorsiflexion angle, maximum isometric torque at neutral ankle position, maximum concentric and eccentric torques, force matching capacity, joint position sense and medial gastrocnemius muscle and tendon strain. Possibly and likely small increases in dorsiflexion RoM were observed after SDS (mean ± 90% confidence intervals; 1.8 ± 1.2°) and FDS (2.1 ± 1.2°), respectively. Very likely moderate decreases in muscle strain after SDS (?38.0 ± 20.6%) and possibly small decrease after FDS (?13.6 ± 21.2%) were observed. SDS resulted in a likely beneficial small increase in tendon strain (25.3 ± 29.7%) and a likely beneficial moderate increase after FDS (41.4 ± 44.9%). Effects on strength were inconsistent. Possibly small effect on positional error after SDS (?27.1 ± 37.5%), but no clear effect after FDS was observed. Both DS protocols increased RoM, and this was more due to an increase in tendon elongation rather than the muscle. However, SDS showed greater improvement than FDS in both neuromechanical and sensorimotor performance, and hence, SDS can be recommended as part of warm‐up in sporting contexts.     

Acute effects of static stretching on peak torque and the hamstrings‐to‐quadriceps conventional and functional ratios

Recent evidence has shown acute static stretching may decrease hamstring‐to‐quadriceps (H:Q) ratios. However, the effects of static stretching on the functional H:Q ratio, which uses eccentric hamstrings muscle actions, have not been investigated. This study examined the acute effects of hamstrings and quadriceps static stretching on leg extensor and flexor concentric peak torque (PT), leg flexor eccentric PT, and the conventional and functional H:Q ratios. Twenty‐two women (mean ± SD age=20.6 ± 1.9 years; body mass=64.6 ± 9.1 kg; height=164.5 ± 6.4 cm) performed three maximal voluntary unilateral isokinetic leg extension, flexion, and eccentric hamstring muscle actions at the angular velocities of 60 and 180°/s before and after a bout of hamstrings, quadriceps, and combined hamstrings and quadriceps static stretching, and a control condition. Two‐way repeated measures ANOVAs (time × condition) were used to analyze the leg extension, flexion, and eccentric PT as well as the conventional and functional H:Q ratios. Results indicated that when collapsed across velocity, hamstrings‐only stretching decreased the conventional ratios (P<0.05). Quadriceps‐only and hamstrings and quadriceps stretching decreased the functional ratios (P<0.05). These findings suggested that stretching may adversely affect the conventional and functional H:Q ratios.     

Determinants of musculoskeletal flexibility: viscoelastic properties, cross-sectional area, EMG and stretch tolerance

Cross-sectional area, stiffness, viscoelastic stress relaxation, stretch tolerance and EMG activity of the human hamstring muscle group were examined in endurance-trained athletes with varying flexibility. Subjects were defined as tight (n=10) or normal (n=8) based on a clinical toe-touch test. Cross-sectional area was computed from magnetic resonance imagining (MRI) images. Torque (Nm) offered by the hamstring muscle group, electromyographic (EMG) activity, knee joint angle and velocity were continuously monitored during two standardized stretch protocols. Protocol 1 consisted of a slow stretch at 0.087 rad/s (dynamic phase) to a pre-determined final angle followed by a 90-s static phase. In the dynamic phase final angle and stiffness was lower in tight (28.0±2.9 Nm/rad) than normal subjects (54.9±6.5 Nm/rad), P<0.01. In the static phase tight subjects had lower peak (15.4±1.8 Nm) and final torque (10.8±1.6 Nm) than normal subjects (31.6±4.1 Nm, 24.1±3.7 Nm, respectively)(P<0.01), but torque decline was similar. Protocol 2 consisted of a slow stretch to the point of pain and here tight subjects reached a lower maximal angle, torque, stiffness and energy than normal subjects (P<0.01). On the other hand, stiffness was greater in tight subjects in the common range (P<0.01). Cross-sectional area of the hamstring muscles and EMG activity during the stretch did not differ between the groups. However, lateral hamstring cross-sectional area was positively related to mid-range stiffness (P<0.05), but inversely related to final stiffness, peak torque and the toe-touch test (P<0.01). Final angle and peak torque in protocol 1 combined to improve the predictability of the toe-touch test (R²=0.77, P<0.001). These data show that the toe-touch test (R²=0.77, P<0.001). These data show that the toe-touch test is largely a measure of hamstring flexibility. Further, subjects with a restricted joint range of movement on a clinical toe-touch test have stiffer hamstring muscles and a lower stretch tolerance.     

Effects of contract‐relax vs static stretching on stretch‐induced strength loss and length–tension relationship

The purpose of this study was to determine the acute effects of contract‐relax stretching (CRS) vs static stretching (SS) on strength loss and the length‐tension relationship. We hypothesized that there would be a greater muscle length‐specific effect of CRS vs SS. Isometric hamstring strength was measured in 20 healthy people at four knee joint angles (90°, 70°, 50°, 30°) before and after stretching. One leg received SS, the contralateral received CRS. Both stretching techniques resulted in significant strength loss, which was most apparent at short muscle lengths [SS: P = 0.025; stretching × angle P < 0.001; 11.7% at 90° P < 0.01; 5.6% at 70° nonsignificant (ns); 1.3% at 50° ns; ?3.7% at 30° ns. CRS: P < 0.001; stretching × angle P < 0.001; 17.7% at 90°, 13.4% at 70°, 11.4% at 50°, all P < 0.01, 4.3% at 30° ns]. The overall stretch‐induced strength loss was greater (P = 0.015) after CRS (11.7%) vs SS (3.7%). The muscle length effect on strength loss was not different between CRS and SS (stretching × angle × stretching technique P = 0.43). Contrary to the hypothesis, CRS did not result in a greater shift in the length–tension relationship, and in fact, resulted in greater overall strength loss compared with SS. These results support the use of SS for stretching the hamstrings.     

Warm-up and stretching in the prevention of muscular injury

Muscular injury is one of the major problems facing today's athletes, both recreational and professional. Injuries to skeletal muscle represent >30% of the injuries seen in sports medicine clinics. As a result, it is imperative to utilise the most effective means to aid in deterring these injuries. However, there are conflicting opinions regarding methods of reducing muscular injury through warm-up and stretching techniques.Therefore, the purpose of this article is to examine the potential of a warm-up and/or stretching routine in deterring muscular injury during physical activity. The article examines a variety of studies regarding warm-up, stretching and muscular injury. The article also provides a definition of warm-up and stretching to provide clarity on this topic. Many of the differences within previous research were due to conflicting definitions. We also address this issue by examining research on muscular injury and physical adaptations to muscular injury and training.This article provides contradictory evidence to conclusions that have been drawn in previous review articles, which determined that warm-up and/or stretching protocols did not deter injury. The research included here conveys that certain techniques and protocols have shown a positive outcome on deterring injuries. As a result, a warm-up and stretching protocol should be implemented prior to physical activity. The routine should allow the stretching protocol to occur within the 15 minutes immediately prior to the activity in order to receive the most benefit. In addition, current information regarding improvements in flexibility is reviewed.     

Assessment of player performance following return to sport after hamstring muscle strain injury

OBJECTIVE: To determine if there is any decrease in playing performance of athletes following return to sport after recovery from hamstring muscle strain injury. DESIGN: Prospective cohort study. PARTICIPANTS: One professional Australian football team over two playing seasons. METHODS: For every game, the team coach rated player performance proportional to time spent on the ground playing (an integer score out of a maximum of 10). Player performance ratings were compared pre- and post-hamstring muscle strain injury to assess player performance upon return to sport. RESULTS: Thirteen athletes had hamstring injuries and the required player ratings were available. The mean player performance rating for the entire playing season in which the player was injured was 6.9. The mean player performance rating for the two games prior to injury was 6.8 as opposed to 5.4 for the two games after return to sport. Athletes had a significantly lower player performance rating immediately upon return to sport when compared to ratings for the entire season (p<0.001) and when compared to ratings from the two games prior to injury (p<0.001). CONCLUSIONS: Following return to sport from hamstring injury, player performance as assessed by the team coach is reduced. This suggests that some athletes may return to sport prior to complete resolution of the injury.     

Acute decrease in the stiffness of resting muscle belly due to static stretching

The purpose of the study was to examine the acute effect of static stretching exercise on the resting stiffness of gastrocnemius muscle belly. Ten healthy young adults performed standing wall stretching in dorsiflexion for 1 min at a time and repeated five times. Before and after stretching, the shear modulus was measured in medial and lateral heads of the resting gastrocnemius muscle with ultrasound shear‐wave elastography. After the stretching, dorsiflexion range of motion (ROM) of the ankle joint increased (P < 0.01) by 3.9° and returned in 20 min. Immediately after stretching, shear modulus decreased (P < 0.01) by 14%, compared with before stretching across muscle heads. The decrease in shear modulus returned in 20 min after stretching. In the comparison group of 10 additional subjects, the standing intervention without stretching had no influence on these measures. There was a negative correlation between dorsiflexion ROM and shear modulus in either head before and after stretching. The results demonstrate the transient decreases in the stiffness of the resting gastrocnemius muscle belly and indicate that joint flexibility is greater in individuals with lower resting stiffness of the muscle belly.     

Effects of muscle activation on shear between human soleus and gastrocnemius muscles

Lateral connections between muscles provide pathways for myofascial force transmission. To elucidate whether these pathways have functional roles in vivo, we examined whether activation could alter the shear between the soleus (SOL) and lateral gastrocnemius (LG) muscles. We hypothesized that selective activation of LG would decrease the stretch‐induced shear between LG and SOL. Eleven volunteers underwent a series of knee joint manipulations where plantar flexion force, LG, and SOL muscle fascicle lengths and relative displacement of aponeuroses between the muscles were obtained. Data during a passive full range of motion were recorded, followed by 20° knee extension stretches in both passive conditions and with selective electrical stimulation of LG. During active stretch, plantar flexion force was 22% greater (P < 0.05) and relative displacement of aponeuroses was smaller than during passive stretch (P < 0.05). Soleus fascicle length changes did not differ between passive and active stretches but LG fascicles stretched less in the active than passive condition when the stretch began at angles of 70° and 90° of knee flexion (P < 0.05). The activity‐induced decrease in the relative displacement of SOL and LG suggests stronger (stiffer) connectivity between the two muscles, at least at flexed knee joint angles, which may serve to facilitate myofascial force transmission.     

The repeated bout effect can occur without mechanical and neuromuscular changes after a bout of eccentric exercise

Changes in muscle fascicle mechanics have been postulated to underpin the repeated bout effect (RBE ) observed following exercise‐induced muscle damage (EIMD ). However, in the medial gastrocnemius (MG ), mixed evidence exists on whether fascicle stretch amplitude influences the level of EIMD , thus questioning whether changes in fascicle mechanics underpin the RBE . An alternative hypothesis is that neural adaptations contribute to the RBE in this muscle. The aim of this study was to investigate the neuromechanical adaptations during and after repeated bouts of a highly controlled muscle lengthening exercise that aimed to maximize EIMD in MG . In all, 20 subjects performed two bouts of 500 active lengthening contractions (70% of maximal activation) of the triceps surae, separated by 7 days. Ultrasound constructed fascicle length‐torque (L‐T) curves of MG , surface electromyography (EMG ), maximum torque production, and muscle soreness were assessed before, 2 hours and 2 days after each exercise bout. The drop in maximum torque (4%) and the increase in muscle soreness (24%) following the repeated bout were significantly less than following the initial bout (8% and 59%, respectively), indicating a RBE . However, neither shift in the L‐T curve nor changes in EMG parameters were present. Furthermore, muscle properties during the exercise were not related to the EIMD or RBE . Our results show that there are no global changes in gastrocnemius mechanical behavior or neural activation that could explain the observed RBE in this muscle. We suggest that adaptations in the non‐contractile elements of the muscle are likely to explain the RBE in the triceps surae.     

体外原代培养肝细胞牵张损伤模型的建立及细胞骨架、 粘弹性变化的实验研究

目的 建立培养肝细胞牵张损伤模型,探讨肝细胞损伤、细胞骨架和粘弹性的改变及其发生机制。方法：用BioFlex培养皿培养原代肝细胞贴壁生长后,通过小型生物撞击机分别以驱动压力150kPa、250kPa牵张损伤细胞。然后对正常肝细胞及牵张损伤后肝细胞骨架Factin微丝排列及分布变化在激光共聚焦显微镜下进行形态学观察,同时测定肝细胞的粘弹性。结果 牵张损伤后肝细胞微丝大部分断裂,网状结构消失,收缩呈絮状,或遗留粗大的微丝束,粘弹性显著降低。结论 肝细胞粘弹性显著降低与细胞骨架的损伤断裂,可能是细胞损伤力学特性变化的分子生物学机制。     

Impact of stretching on the performance and injury risk of long-distance runners

Stretching, either prior to exercise or at the end, or both, is typically carried out by all individuals undertaking sporting activity whether they be elite or recreational athletes. The many forms of stretching available to the athlete, either passive or active, have long been thought to improve performance, decrease injury and generally be advantageous to the athlete. This review examines the current state of the literature and evaluates what athletes can and should do with respect to this controversial topic.     

Hip and knee muscle torque is not impaired in the first three months of a first-time lateral ankle sprain

ObjectivesThe primary objective was to compare hip and knee isometric muscle strength between individuals with a first-time acute lateral ankle sprain and controls. A secondary objective was to investigate hip and knee isometric muscle strength three months post-injury.DesignCross-sectional and prospective follow-up components.SettingLaboratory environment.ParticipantsForty-two participants (21 acute lateral ankle sprain and 21 controls) matched for age, sex, physical activity and leg dominance participated.Main outcome measuresHip and knee isometric muscle torque was assessed using a rigidly fixated hand-held dynamometer. Testing in acute lateral ankle sprain participants was performed within four weeks of injury and three months post-injury. Controls were tested at one timepoint.ResultsThere were no differences in hip or knee isometric muscle torque between acute lateral ankle sprain and control participants (mean differences <0.08). Hip and knee isometric muscle torque in acute ankle sprain participants did not differ between baseline and three months post-injury testing (mean difference <0.06).ConclusionsProximal lower limb isometric strength is not impaired within the first three months of sustaining a first-time lateral ankle sprain injury. This implies that hip and knee isometric strength deficits in individuals with CAI may occur at some later stage.     

Performance aspects of an injury prevention program: a ten-week intervention in adolescent female football players

The injury rate in football is high, and effective injury prevention methods are needed. An exercise program, the "11," has been designed to prevent the most common injury types in football. However, the effect of such a program on performance is not known. The aim of this randomized-controlled trial was to investigate the effect of the "11" on performance after a 10-week training period. Thirty-four adolescent female football players were randomly assigned to either an intervention (n=18) or a control group (n=16). The "11" is a 15-min program consisting of ten exercises for core stability, lower extremity strength, balance and agility. Performance tests included isokinetic and isometric strength protocols for the quadriceps and hamstrings, isometric hip adduction and abduction strength, vertical jump tests, sprint running and soccer skill tests. There was no difference between the intervention and control groups in the change in performance from the pre- to post-test for any of the tests used. In conclusion, no effect was observed on a series of performance tests in a group of adolescent female football players using the "11" as a structured warm-up program.     

Rehabilitation of muscle after injury – the role of anti‐inflammatory drugs

Non‐steroidal anti‐inflammatory drugs (NSAIDs) are widely consumed among athletes worldwide in relation to muscle injury and soreness. This review aims to provide an overview of studies investigating their effects on skeletal muscle, in particular the repair processes in injured muscle. Muscle injury occurs in diverse situations and the nature of muscle injuries varies significantly, complicating extrapolations between experimental models and “real life.” Classical muscle strain injuries occur at the interphase between the muscle fibers and connective tissue, most often in the myotendinuous junction, whereas contusion or overload injury can damage both myofibers and intramuscular connective tissue. The role of NSAIDs in muscle repair is complicated by differences in injury models used, variables evaluated, and time point(s) selected for evaluations. While the temporal pattern of the influence of NSAIDs on muscle repair is difficult to settle on, it appears that a potential beneficial effect of NSAIDs in the early phase after injury is not maintained in the long term, or is even negated by a long‐term repair deficit. At the cellular level, evidence exists for a negative influence of NSAIDs on the muscle stem cell population (satellite cells). At a structural level, it is known that muscle connective tissue undergoes significant remodeling during muscle regeneration, but the potential of NSAID exposure to alter this response in humans needs investigation.     

原发性骨质疏松或骨量低下患者下肢肌力与平衡功能相关性研究

目的:研究原发性骨质疏松和骨量低下患者下肢肌肉力量与平衡功能的相关性。方法:入组患者为57名通过GE Express超声波跟骨骨密度仪检测诊断为原发性骨质疏松或骨量低下的绝经期女性患者;采用美国Biodex Medical Systems公司生产的Biodex System 4多关节等速测试系统测试下肢肌力;采用单腿站立平衡检测(single leg balance test,SLBT)结果反映患者平衡功能,所得数据应用spss15.0软件进行Pearson线性相关分析,得出线性回归方程。结果:原发性骨质疏松患者优势腿单腿站立时间与慢速屈肌群相对峰力矩的相关系数r=0.540(P=0.000),与中速屈肌群相对峰力矩的相关系数r=0.523(P=0.000),与慢速伸肌群相对峰力矩相关系数r=0.378(P=0.004),与中速伸肌群相对峰力矩的相关系数r=0.282(P=0.034)。结论:原发性骨质疏松患者优势腿伸肌肌力和屈肌肌力与平衡功能均呈正相关,其中屈肌肌力对平衡功能的影响大于伸肌肌力。     

The effect of whole body vibration on the H‐reflex,the stretch reflex,and the short‐latency response during hopping

The effect of whole body vibration (WBV) on reflex responses is controversially discussed in the literature. In this study, three different modalities of reflex activation with increased motor complexity have been selected to clarify the effects of acute WBV on reflex activation: (1) the electrically evoked H‐reflex, (2) the mechanically elicited stretch reflex, and (3) the short‐latency response (SLR) during hopping. WBV‐induced changes of the H‐reflex, the stretch reflex, and the SLR during hopping were recorded in the soleus and gastrocnemius muscles and were analyzed before, during (only the H‐reflex), immediately after, 5 min and 10 min after WBV. The main findings were that (1) the H‐reflexes were significantly reduced during and at least up to 5 min after WBV, (2) the stretch reflex amplitudes were also significantly reduced immediately after WBV but recovered to their initial amplitudes within 5 min, and (3) the SLR during hopping showed no vibration‐induced modulation. With regard to the modalities with low motor complexities, the decreased H‐ and stretch reflex responses are assumed to point toward a reduced Ia afferent transmission during and after WBV. However, it is assumed that during hopping, the suppression of reflex sensitivity is compensated by facilitatory mechanisms in this complex motor task.     

训练性下腰痛躯干肌功能变化特点及防治干预

为探讨训练性下腰痛患者躯干肌功能变化 ,分别应用CYBEX 6 0 0 0型等速测试训练系统、彩超、肌电图、立位腰椎侧位X线片测试腰痛组(n=4 0 )和正常组 (n =4 0 )的躯干肌力指标、骶棘肌横截面积、腰背肌肌电指标及腰椎曲度。结果显示 ,在腰痛组与正常组 ,除躯干屈肌PT/BW、ER及骶棘肌横截面积差异无统计学意义 (P >0 0 5 )外 ,其他指标相比差异均有统计学意义(P <0 0 5 )。提示由于缺乏有效的腰背肌锻炼 ,训练性下腰痛患者存在明显的躯干肌肌力失衡 ,其主要由腰背肌肌力下降引起 ;同时腰背肌肌爆发力以及腰背肌静态耐力也明显下降 ,腰椎生理曲度变小 ,但不伴随有明显的椎旁肌萎缩 ;耐力比ER(动态耐力)与下腰痛关系并不密切。同时在此基础上设计了预防训练性下腰痛的现场干预实验 ,结果显示训练性下腰痛发生率明显降低 (锻炼组 8 93% ,对照组 17 0 1% ,P <0 0 1)。提示腰背肌锻炼可降低训练性下腰痛的发生率。