Quadriceps activation in closed and in open kinetic chain exercise

PURPOSE: For treatment of various knee disorders, muscles are trained in open or closed kinetic chain tasks. Coordination between the heads of the quadriceps muscle is important for stability and optimal joint loading for both the tibiofemoral and the patellofemoral joint. The aim of this study was to examine whether the quadriceps femoris muscles are activated differently in open versus closed kinetic chain tasks. METHODS: Ten healthy men and women (mean age 28.5 +/- 0.7) extended the knees isometrically in open and closed kinetic chain tasks in a reaction time paradigm using moderate force. Surface electromyography (EMG) recordings were made from four different parts of the quadriceps muscle. The onset and amplitude of EMG and force data were measured. RESULTS: In closed chain knee extension, the onset of EMG activity of the four different muscle portions of the quadriceps was more simultaneous than in the open chain. In open chain, rectus femoris (RF) had the earliest EMG onset while vastus medialis obliquus was activated last (7 +/- 13 ms after RF EMG onset) and with smaller amplitude (40 +/- 30% of maximal voluntary contraction (MVC)) than in closed chain (46 +/- 43% MVC). CONCLUSIONS: Exercise in closed kinetic chain promotes more balanced initial quadriceps activation than does exercise in open kinetic chain. This may be of importance in designing training programs aimed toward control of the patellofemoral joint.     

Strain on the anterior cruciate ligament during closed kinetic chain exercises

PURPOSE: The purpose of this investigation was to characterize the ACL strains produced during four commonly prescribed CKC exercises; the step-up, the step-down, the lunge, and the one-legged sit to stand. We hypothesized that the ACL strains produced during the lunge and one-legged sit to stand exercises (the exercises that challenge the leg musculature to a greater extent and utilize greater hip flexion) would be less than those produced during the step-up and step-down exercises. METHODS: The strains in the anteromedial bundle of the ACL were measured while nine subjects, who had normal ligaments, performed the four exercises. Peak ACL strain values and the ACL strain patterns as a function of knee flexion angle were compared between exercises. RESULTS: No significant differences were found between the peak ACL strain values (mean +/- SEM) between exercises (step-up: 2.5 +/- 0.36; step-down: 2.6 +/- 0.34; lunge 1.9 +/- 0.50; one-legged sit to stand: 2.8 +/- 0.27). The mean ACL strain values as a function of knee flexion angle were not significantly different. On average, there was a significant increase in ACL strain as the knee was extended for each exercise. CONCLUSIONS: The ACL strain responses produced during these CKC exercises were equal and similar to those produced during other rehabilitation exercises (i.e., squatting, active extension of the knee) previously tested.     

Validity of lower extremity strength and power utilizing a new closed chain dynamometer

PURPOSE: The purpose of this study was to compare selected variables measured on a traditional isokinetic dynamometer (Cybex II) with a new lower extremity, closed chain dynamometer (Omnikinetic, OmK). METHODS: Twelve subjects (6 male, 6 female, age = 28+/-5 yr, mean +/- SD) performed Cybex II knee flexion and extension at 1.05, 3.14, and 5.23 rad x s(-1). A maximal effort of 10 repetitions of lower extremity concentric extension and eccentric flexion at 36% of subject's 1-RM was performed on the OmK. Crank power and joint (ankle, knee, and hip) kinetics were recorded as a mean of 10 repetitions. RESULTS: t-Tests revealed right versus left leg differences (P < 0.05) for Cybex II peak torque flexion at 5.23 rad x s(-1), and OmK knee and hip peak power and hip root mean square power (RMS) power. Cybex peak knee torques were related (Pearson r values 0.78-0.92, P < 0.01) to OmK peak knee torques. Cybex average power was related to OmK knee power (Pearson r values 0.71-0.96, P < 0.01) and OmK crank power (r = 0.62-0.94, P < .01). Correlations tended to be stronger comparing the OmK with the fastest (5.23 rad x s(-1)) Cybex II speed. CONCLUSIONS: These results suggest that the OmK knee and crank kinetic data are comparable to Cybex It isokinetic dynamometry. The ability to evaluate lower extremity joint exercise at a subject's maximal movement speed, in addition to the use of a closed-chain, multi-joint motion, may allow for the OmK to provide a more global evaluation of lower extremity kinetics during seated concentric-extension, eccentric-flexion exercise.     

The effects of downhill slope on kinematics and kinetics of the lower extremity joints during running

BackgroundThe purpose of this study was to investigate how lower extremity kinematics and kinetics change when running downhill.MethodsFifteen male recreational runners ran on an instrumented treadmill with three different slope conditions [level (0°), moderate (−6°), and steep (−9°)] at a controlled speed of 3.2 m/s. Ten consecutive steps were selected for analysis for each of the slope conditions and the order of slope conditions was randomized. Synchonized motion analysis and force plate were used to determine joint kinematics and kinetics.ResultsCompared to level running, participants demonstrated significantly larger knee flexion but smaller ankle plantar-flexion and hip flexion during downhill running (Ps < 0.05). Significantly smaller peak propulsive ground reaction forces and posterior impulses were found during downhill running (Ps < 0.05). Furthermore, participants experienced significantly larger extension moment and negative joint power at the knee (Ps < 0.05) but smaller plantar-flexion moment and negative joint power at the ankle during downhill running (Ps < 0.05). Negative net joint work increased for all joints with increased declinations and the knee joint showed the greatest increase in negative net joint work amongst the three joints (Ps < 0.05).SignificanceThese findings indicate that runners modify their running mechanics resulting in greater kinetic demand on the knee during downhill running. Differences in lower extremity injury mechanisms with different running slopes may be linked to the changes in loading at the knee but further investigation using clinical trials is needed to support the potential relationship.     

The effects of visual cognitive tasks on landing stability and lower extremity injury risk in high-level soccer players

BackgroundVisual cognition plays a pivotal role in sports. It is widely recognized that there is an intriguing coupling that they could affect each other through interaction between visual cognition and motor control, but few studies linked the effects of visual cognitive tasks on landing stability to postural control and injury risk.Research questionWhether visual cognitive tasks affect the landing stability and lower limb injury risk of professional soccer players?MethodsThe current study used a three-dimensional Multiple Object Tracking (MOT) task to simulate visual cognitive difficulties experienced in soccer matches. Fifteen male high-level soccer athletes (height: 181.43 ± 7.36 cm, weight: 75.37 ± 10.67 kg, training years: 10.07 ± 2.98 yr) from our school team were recruited and completed a landing action from a high platform with and without MOT tasks. Vicon infrared high-speed motion capture system and three-dimensional force measuring platform were used to collect various outcomes simultaneously.ResultsThe Time to Stabilization (TTS) during landing was significantly prolonged, while the Medial-Lateral Stability Index (MLSI), Anterior-Posterior Stability (APSI), Dynamic Postural Index Stability Index (DPSI), the trajectory lengths, and envelope area of COP during landing were also increased during MOT dual-task.DiscussionThe decline of these indicators reflected the deterioration in postural stability and greater requirements for maintaining balance which could increase the risk of injury in soccer athletes. We advocate that adequate visual attention and visual information processing might play critical roles in maintaining dynamic balance through the supraspinal neural network.     

Prevention of ACL injury, part II: effects of ACL injury prevention programs on neuromuscular risk factors and injury rate

Prevention strategies have been developed based on existing knowledge in an attempt to alter neuromuscular control and lower extremity biomechanics in order to reduce anterior cruciate ligament (ACL) injury rates. These strategies have included different training programs ranging from injury education to multicomponent training. Many training programs have been demonstrated as resulting in altered lower extremity movement patterns. The effects of current training programs on ACL injury rate, however, are inconsistent. This review was focused on the effects of current ACL injury training programs on neuromuscular risk factors and ACL injury rate. Recommendations were made based on the available evidence for clinicians and coaches to implement ACL injury prevention programs.     

Patellofemoral stresses during open and closed kinetic chain exercises. An analysis using computer simulation

Rehabilitation of the symptomatic patellofemoral joint aims to strengthen the quadriceps muscles while limiting stresses on the articular cartilage. Some investigators have advocated closed kinetic chain exercises, such as squats, because open kinetic chain exercises, such as leg extensions, have been suspected of placing supraphysiologic stresses on patellofemoral cartilage. We performed computer simulations on geometric data from five cadaveric knees to compare three types of open kinetic chain leg extension exercises (no external load on the ankle, 25-N ankle load, and 100-N ankle load) with closed kinetic chain knee-bend exercises in the range of 20 degrees to 90 degrees of flexion. The exercises were compared in terms of the quadriceps muscle forces, patellofemoral joint contact forces and stresses, and "benefit indices" (the ratio of the quadriceps muscle force to the contact stress). The study revealed that, throughout the entire flexion range, the open kinetic chain stresses were not supraphysiologic nor significantly higher than the closed kinetic chain exercise stresses. These findings are important for patients who have undergone an operation and may feel too unstable on their feet to do closed chain kinetic chain exercises. Open kinetic chain exercises at low flexion angles are also recommended for patients whose proximal patellar lesions preclude loading the patellofemoral joint in deeper flexion.     

右美托咪定对止血带诱发下肢缺血再灌注损伤的影响

 目的 观察右美托咪定对止血带诱发下肢缺血再灌注期间体内炎性反应因子水平和氧化应激反应的影响。方法 选择临床上应用止血带行关节镜下单侧前交叉韧带重建术的患者40例,随机分成对照组和右美托咪定组,每组各20例。右美托咪定组给予右美托咪定1 μg/kg的负荷量静脉泵注10 min,随后以1 μg/(kg·h)的速率持续泵入至手术结束。对照组以同样速率泵入0.9%生理盐水。各组于硬膜外麻醉前(T0),止血带充气1 h(T1),止血带释放后20 min(T2)、1 h(T3)、6 h(T4),分别抽取患侧股静脉血3 ml,检测各个时间点血清中超氧化物歧化酶(SOD)的活性、丙二醛(MDA)的浓度、肿瘤坏死因子-α(TNF-α)和白介素-6(IL-6)的浓度。结果 (1)SOD:与T0比较,对照组T3、T4时间和右美托咪定组T4时间点明显降低(P<0.05);但右美托咪定组在T3、T4时间点高于对照组(P<0.05)。MDA: 与T0比较,对照组T1~T4各个时间点和右美托咪定组T3、T4时间点均明显升高(P<0.05);但右美托咪定组T3、T4时间点低于对照组(P<0.05)。(2)TNF-α:与T0比较,对照组T1~T4各个时间点和右美托咪定组T3、T4时间点均明显升高(P<0.05);与对照组比较,右美托咪定组于T1~T4各时间点均低于对照组(P<0.05)。(3)IL-6:与T0时间点比较,对照组和右美托咪定组T1~T3时间点均无明显变化、T4时间点显著升高(P<0.05); 但右美托咪定组T4时间点显著降低(P<0.05)。结论 右美托咪定以1 μg/(kg·h)的负荷量及1 μg/(kg·h)维持量持续静脉泵注,可有效降低止血带引起的下肢I/R后血清中炎性反应因子水平,减轻氧自由基所致的下肢I/RI。     

下肢损伤保肢治疗的评估及方法

下肢损伤的保肢治疗需要综合多方面的病情评估,如骨折缺损程度、肌肉的活性、血管及神经损伤、肢体缺血时间及当地医疗水平等。根据对病情评估的结果,结合现在医疗技术水平,才能更好地实施相应治疗。本文就下肢损伤保肢治疗的评估及方法作一简要综述。     

Evaluation of lower extremity overuse injury potential in runners

INTRODUCTION: The purpose of this study was to identify biomechanical and anthropometric variables that contribute to overuse injuries in runners. METHODS: Comparisons were made between a group of runners who had sustained at least one overuse running injury and a group of runners who had been injury free throughout their running careers. Groups were well matched in important training variables. Synchronized kinetic and rearfoot kinematic variables of both feet were collected by filming subjects running over a force platform at a speed of 4 m x s(-1). RESULTS: The injury-free group demonstrated significantly greater posterior thigh (hamstring) flexibility, as measured by a standard sit and reach test. This was the only anthropometric variable in which the groups differed. Within each group, there were no significant differences between left and right foot landing for any biomechanical variable. Biomechanical variables that demonstrated significantly lower values for the injury free group were the vertical force impact peak and the maximal vertical loading rate, with the maximal rate of rearfoot pronation and the touchdown supination angle showing a trend toward being greater in the injury free group. CONCLUSION: These results suggest that runners who have developed stride patterns that incorporate relatively low levels of impact forces, and a moderately rapid rate of pronation are at a reduced risk of incurring overuse running injuries.     

The effect of a single treatment of the Protonics system on lower extremity kinematics during gait and the lateral step up exercise

INTRODUCTION: Patellofemoral pain (PFP) is often attributed to abnormal patellar tracking. The Protonics knee orthosis was developed to reduce femoral internal rotation by altering pelvic alignment via hamstring activation. The purpose of this research was to determine if a single treatment with the orthosis improved lower extremity alignment during gait and the lateral step up exercise. We hypothesized that anterior pelvic tilt, hip internal rotation and adduction, and external rotation of the tibia with respect to the femur would decrease after use of the brace. METHODS: Nineteen females (23.4+/-3.1 year, 1.66+/-0.05 m, 65.3+/-20.4 kg) with chronic PFP participated. Three-dimensional kinematic data were collected for each subject at 60 Hz during pre-treatment (PRE), after a placebo condition with the orthosis set at zero resistance (PLAC), and post-treatment (POST). Treatment consisted of having the subject perform the rehabilitation exercises recommended by the Protonics manufacturer. A repeated measures ANOVA was performed on each dependent variable (alpha=0.05). RESULTS: This investigation did not verify the changes in alignment proposed by the manufacturer as a result of acute application of the Protonics system. However, after the use of the brace, pelvic rotation and hip hike were decreased during the lateral step up exercise. CONCLUSION: Based on the results of this study, it was concluded that a single application of the Protonics system did not alter anterior pelvic tilt, hip internal rotation and adduction, or tibial external rotation during the lateral step up and gait.     

The effects of graded resistance exercise on platelet aggregation and activation

PURPOSE: The purpose of this study was to examine the effects of resistance exercise with varying intensity but with similar volume on platelet aggregation and activation. METHODS: Thirteen healthy male subjects randomly completed three resistance exercise test trials at an intensity corresponding to 40%, 60%, and 80% of one repetition maximum (1-RM) in which the subjects performed six exercises including upper- and lower-body parts. Venous blood samples were obtained before and immediately after each exercise trial and analyzed for platelet count (PLT), plateletcrit (PCT), mean platelet volume (MPV), platelet aggregation, and beta-thromboglobulin (B-TG). Plasma volume changes were estimated from hemoglobin and hematocrit readings before and after each exercise trial. RESULTS: Although all exercise trials were followed by a significant (P < 0.05) increase in PLT (thrombocytosis), PCT, and MPV, this rise was not related to the exercise intensity (P > 0.05). Exercise was also followed by a significant increase (P < 0.05) in platelet aggregation, but this only occurred with the high but not with the low concentrations of adenosine diphosphate (ADP). Although ANOVA showed a significant overall increase (P < 0.05) in the concentration of B-TG after exercise, this rise only reached the assigned level of significance (P < 0.05) after 80% exercise trial. CONCLUSION: It was concluded therefore that resistance exercise is followed by an increase in PLT, PCT, and MPV, and this occurred in parallel with an in vivo activation of platelet as manifested by an increase in platelet aggregation and a rise in B-TG.     

The effects of plyometric versus dynamic stabilization and balance training on lower extremity biomechanics

BACKGROUND: Neuromuscular training that includes both plyometric and dynamic stabilization/balance exercises alters movement biomechanics and reduces ACL injury risk in female athletes. The biomechanical effects of plyometric and balance training utilized separately are unknown. HYPOTHESIS: A protocol that includes balance training without plyometric training will decrease coronal plane hip, knee, and ankle motions during landing, and plyometric training will not affect coronal plane measures. The corollary hypothesis was that plyometric and balance training effects on knee flexion are dependent on the movement task tested. STUDY DESIGN: Controlled laboratory study. METHODS: Eighteen high school female athletes participated in 18 training sessions during a 7-week period. The plyometric group (n = 8) performed maximum-effort jumping and cutting exercises, and the balance group (n = 10) used dynamic stabilization/ balance exercises during training. Lower extremity kinematics were measured during the drop vertical jump and the medial drop landing before and after training using 3D motion analysis techniques. RESULTS: During the drop vertical jump, both plyometric and balance training reduced initial contact (P = .002), maximum hip adduction angle (P = .015), and maximum ankle eversion angle (P = .020). During the medial drop landing, both groups decreased initial contact (P = .002) and maximum knee abduction angle (P = .038). Plyometric training increased initial contact knee flexion (P = .047) and maximum knee flexion (P = .031) during the drop vertical jump, whereas the balance training increased maximum knee flexion (P = .005) during the medial drop landing. CONCLUSION: Both plyometric and balance training can reduce lower extremity valgus measures. Plyometric training affects sagittal plane kinematics primarily during a drop vertical jump, whereas balance training affects sagittal plane kinematics during single-legged drop landing. CLINICAL RELEVANCE: Both plyometric and dynamic stabilization/balance exercises should be included in injury-prevention protocols.