Phase Knee Flexion Research Articles

Preparatory knee flexion movement facilitates faster sideways jumping execution in male collegiate soccer goalkeepers

ABSTRACT Preparatory lower-limb loading conditions may affect the jump-to-reach performance of soccer goalkeepers. This study investigated the effect of pre-jump lower-limb loading/unloading during bilateral knee flexion–extension movements on sideways jump-to-reach performance in 18 male collegiate soccer goalkeepers. Participants performed the two-choice (high and low targets) reaction-time single-leg jump-to-reach task under two conditions: without preparatory movements (no-prep) and with continuous alternating knee extension and flexion movements (prep). The ‘go’ cue was provided with different preparatory loading conditions during the pre-jump knee extension and flexion phases. Performance was assessed using three-dimensional kinematic data and ground reaction forces. A significant main effect of the preparatory condition was observed for the jump take-off time. Pairwise comparisons revealed that the jump take-off time was 3.4–4.4% faster when initiated during the knee flexion phase than the no-prep condition and the extension phase (p ≤ .028). Increasing lower-limb loading and downward body movement with knee flexion appeared to facilitate effective loading to take-off to reach the high target and faster downward-directed take-off to reach the low target, respectively. Pre-jump knee flexion movement could be utilised by soccer goalkeepers to facilitate faster take-off to maximise their chances of saving shots within the reach of single-leg side-jumping.

A Biomechanical Study on Failed Snatch Based on the Human and Bar Combination Barycenter.

Objective The purpose of this research was to use a new method the human and bar combination barycenter to exposit the differences between successful and failed characteristics of snatch attempts in competition. Try to establish an effective biomechanical method that can uncover the main factors for the failed snatch. The obtained results will provide valuable information for weightlifters to improve the success rate in snatch by altering their technical issues accordingly. Methods A 3-D video analysis method was used to compare the characteristics of the heaviest successful and failed attempts of ten elite weightlifters in the men's 73 kg category. The video was captured under competitive conditions at the 2019 World Weightlifting Championships, the 2019 Asian Weightlifting Championships, and the 2020 China Olympic Trial. The video data were digitized using the SIMI°Motion7.50 3-D system (Germany). Results Significant difference (P > 0.05) was not found between the successful and failed attempts in the parameters, such as the maximal vertical rising velocity, the maximal vertical height, and the vertical displacement of the barbell. The maximal descending acceleration of the human body, the time duration, the angles of the hip, and knee joints were no significant difference. However, significant differences were found in the variation of the human and bar combination barycenter on the X-axis in the inertial ascent stage and the squat support stage (t = 2.862, P < 0.05; t = 3.376, P < 0.05). Conclusions A probable cause of the failed snatch is that the displacement of human and bar combination barycenter on the X-axis is not enough to reach the position for supporting barbell during the inertial ascent stage and the squat support stage. The reason is that the strength of reclining of torso at the end of the force phase is insufficient. Insufficient knee flexion in the knee flexion phase (M2), which leads to a lower maximum vertical velocity of barbell, may be an indirect factor leading to the failed snatch. The cumulative variation of human and bar combination barycenter on the X-axis can effectively determine the technical characteristics between the success and failure in snatch.

Differences in the flexion and extension phases during kneeling investigated by kinematic and contact point analyses: a cross-sectional study

BackgroundKneeling is necessary for certain religious and ceremonial occasions, crouching work, and gardening, which many people take part in worldwide. However, there have been few reports about kneeling activities. The purpose of this study was to clarify the kinematics of kneeling.MethodsThe subjects were 15 healthy young males. Kneeling activity was analysed within a knee flexion angle from 100° to maximum flexion (maxflex, mean ± SD = 161.3 ± 3.2°). The kinematic and contact point (CP) analyses were performed using a 2D/3D registration method, in which a 3D bone model created from computed tomography images was matched to knee lateral fluoroscopic images and analysed on a personal computer.ResultsIn the kinematic analysis, the femur translated 37.5 mm posteriorly and rotated 19.8° externally relative to the tibia during the knee flexion phase. During the knee extension phase, the femur translated 36.4 mm anteriorly, which was almost the same amount as in the knee flexion phase. However, the femur rotated only 7.4° internally during the knee extension phase. In the CP analysis, the amount of anterior translation of the CP in the knee extension phase was greater in the medial CP and smaller in the lateral CP than that of posterior translation in the knee flexion phase.ConclusionsIn kneeling, there was a difference in the rotational kinematics between the flexion phase and the extension phase. The kinematic difference between the flexion and extension phases may have some effect on the meniscus and articular cartilage.

Preparatory Knee Flexion-Extension Movements Enhance Rapid Sidestepping Performance in Collegiate Basketball Players.

Lower-limb weight-bearing load distribution in stationary standing influences the timing of rapid first step initiation of importance for functional movement activities and agility performance in sports. This study investigated the effect of pre-step lower-limb loading and unloading with preparatory knee flexion-extension movements on sidestepping performance in fifteen male collegiate basketball players. Participants performed two-choice (step limb) reaction time sidestepping under two conditions: without preparatory movements before the go cue (no-prep–NP) and with continuous alternating knee extension and flexion movements (prep–P). The reaction signal was provided at the beginning of knee extension and flexion and during these movements which corresponded with the largest and smallest loading instants and the transition states between those instants. Sidestepping performance was assessed with three-dimensional kinematic data and ground reaction forces. Step initiation onset time was significantly faster by 13–15% than the NP condition when initiated in the knee flexion phase (p ≤ 0.028, r ≥ 0.70), whereas step-limb unloading interval from step initiation to step lift-off was significantly faster by 12–15% in the knee extension phase (p ≤ 0.01, r ≥ 0.74). The preparatory movements significantly shortened step lift-off by 10–12% (p ≤ 0.013, r ≥ 0.73) and step duration by 17–21% (p < 0.001, r ≥ 0.85) with 19–22% faster step velocity (p < 0.001, r ≥ 0.84), which resulted in 14–15% shorter overall time to step landing (p < 0.001, r ≥ 0.84), irrespective of the loading phases. These results indicated that lower-limb loading with pre-step knee flexion facilitated faster step initiation, while lower-limb unloading with knee extension facilitated faster step-limb unloading, both resulting in faster step lift-off. Bilateral knee flexion-extension movements as a preparatory action could be utilized by invasion sports players to facilitate reactive stepping performance for more effective movement initiation.

Effect of a simple core muscle training program on trunk muscle strength and neuromuscular control among pediatric soccer players

PurposeThe purpose of this study was to examine the effect of simple core muscle training (CMT) program on trunk muscle strength and neuromuscular control among pediatric athletes.MethodsForty-nine male soccer players (mean age, 10.8 years) participated. The CMT program had three components (bench, side bench, and Nordic hamstrings) and was performed at least three times weekly for a year. Trunk flexion/extension muscle strength and the K/H ratio (determined by dividing knee separation distance by hip separation distance during drop-jump test and used as an index of lower limb valgus alignment) were measured, and the Y balance test (YBT) was performed before and after intervention. This study did not include the pure control group among the same team. To consider the effect of CMT on trunk muscle strength due to physical growth, we used the data of trunk muscle strength from the local cohort study previously conducted in our institution. One hundred participants who matched the age, height, body weight, and body mass index of the training group was designated as a control group.ResultsIn the training group, the trunk flexion/extension strength significantly increased at 6 months (p < 0.001, p < 0.001, respectively) and 12 months (p < 0.001, p < 0.001, respectively) compared to initial value. The K/H ratio at initial contact and maximum knee flexion phase significantly increased at 6 months (p < 0.001 and p < 0.001, respectively); however, it did not increase at 12 months (p = 0.384 and p = 0.070, respectively) compared to the initial value. In the YBT, the maximized reach distance in each direction significantly increased after intervention on both the dominant and non-dominant sides, except in the posteromedial direction on the non-dominant foot. Compared to the control group, although there was no significant difference in trunk flexion/extension strength at baseline (p = 0.141 and p = 0.390, respectively), the training group showed significantly higher trunk flexion/extension muscle strength at 12 months (p < 0.001 and p < 0.001, respectively).ConclusionThe CMT program increased trunk muscle strength and improved dynamic balance among pediatric male athletes.Level of evidenceLevel II

Monitoring Muscle Fatigue Progression during Dynamic Exercise.

To develop and validate a novel model for assessment of peripheral fatigue progression during dynamic exercise. Seven males and four females (24 ± 3 yr) completed one-legged knee-extensor exercise at 40% of peak power output (PPO) for 12 min (40% PPO). Additionally, an exhaustive bout lasting approximately 6 min (84% ± 2% PPO; 59 ± 10 W) was contrasted to two bouts completed at ±5% of the target workload. Trials were completed in randomized order. Percutaneous electrical stimulation of m. vastus lateralis during the passive knee-flexion phase allowed quantification of maximal twitch force every 30 s in parallel with RPE. Elicited twitch force remained unchanged during the 40% PPO trial. During the three exhaustive bouts, exercise differed in duration (561 ± 154 s, 366 ± 64 s, 245 ± 61 s; P < 0.001) and amplitude of elicited twitch force showed a curvilinear decline across time. Elicited twitch force at exhaustion was approximately 60% reduced and similar between the exhaustive trials (intraclass correlation coefficient, 0.76; 95% confidence interval, 0.48-0.92). The increase in RPE during exercise was strongly correlated to the gradually reduced evoked twitch force (repeated-measures correlation, 0.89; 95% confidence interval, 0.62-0.97). The developed model permits quantification of muscle fatigue progression during continuous dynamic one-legged knee-extension and a biphasic fatigue pattern is demonstrated during intense exercise. The model is sensitive to small changes in intensity, and it provides a novel approach for studying muscular mechanisms and their temporal relation to fatigue progression in vivo.

Biomechanic and Energetic Effects of a Quasi-Passive Artificial Gastrocnemius on Transtibial Amputee Gait

State-of-the-art transtibial prostheses provide only ankle joint actuation and thus do not provide the biarticular function of the amputated gastrocnemius muscle. We develop a prosthesis that actuates both knee and ankle joints and then evaluate the incremental effects of this prosthesis as compared to ankle actuation alone. The prosthesis employs a quasi-passive clutched-spring knee orthosis, approximating the largely isometric behavior of the biological gastrocnemius, and utilizes a commercial powered ankle-foot prosthesis for ankle joint functionality. Two participants with unilateral transtibial amputation walk with this prosthesis on an instrumented treadmill, while motion, force, and metabolic data are collected. Data are analyzed to determine differences between the biarticular condition with the activation of the knee orthosis and the monoarticular condition with the orthosis behaving as a free-joint. As hypothesized, the biarticular system is shown to reduce both affected-side knee and hip moment impulse and positive mechanical work in both participants during the late stance knee flexion phase of walking, compared to the monoarticular condition. The metabolic cost of walking is also reduced for both participants. These very preliminary results suggest that biarticular functionality may provide benefits beyond even those of the most advanced monoarticular prostheses.

Activity of Lower Limb Muscles During Squat With and Without Abdominal Drawing-in and Pilates Breathing.

Barbosa, AC, Martins, FM, Silva, AF, Coelho, AC, Intelangelo, L, and Vieira, ER. Activity of lower limb muscles during squat with and without abdominal drawing-in and Pilates breathing. J Strength Cond Res 31(11): 3018-3023, 2017-The purpose of this study was to assess the effects of abdominal drawing-in and Pilates breathing on the activity of lower limb muscles during squats. Adults (n = 13, 22 ± 3 years old) with some Pilates experience performed three 60° squats under each of the following conditions in a random order: (I) normal breathing, (II) drawing-in maneuver with normal breathing, and (III) drawing-in maneuver with Pilates breathing. Peak-normalized surface electromyography of the rectus femoris, biceps femoris, gastrocnemius medialis, and tibialis anterior during the knee flexion and extension phases of squat exercises was analyzed. There were significant differences among the conditions during the knee flexion phase for the rectus femoris (p = 0.001), biceps femoris (p = 0.038), and tibialis anterior (p = 0.001), with increasing activation from conditions I to III. For the gastrocnemius medialis, there were significant differences among the conditions during the knee extension phase (p = 0.023), with increased activity under condition I. The rectus and biceps femoris activity was higher during the extension vs. flexion phase under conditions I and II. The tibialis anterior activity was higher during the flexion compared with the extension phase under all conditions, and the medial gastrocnemius activity was higher during the extension phase under condition I. Doing squats with abdominal drawing-in and Pilates breathing resulted in increased rectus, biceps femoris, and tibialis anterior activity during the flexion phase, increasing movement stability during squat exercises.

Effects of Shoes and a Prefabricated Medial Arch Support on Medial Gastrocnemius and Tibialis Anterior Activity while doing Leg Press Exercise in Normal Feet Athletes

Background: Nowadays, different types of exercise machines are being used in the field of athletic training, recreation, post-injury and post-operation rehabilitation. Leg press is a commonly-used one that retrains muscles and simulates natural functional activities. In this activity, feet are in contact with a footrest to exert muscular forces. In addition, the footrest inserts reactive forces to feet and from the feet load would transfer to structures that are more proximal. Any misalignment in foot structure may interfere its function. Objective: The aim of this study was to assess the effect of shoes and using a prefabricated medial arch support on the activity of Tibialis anterior and medial gastrocnemius muscles while doing leg press exercise in normal feet subjects. Method: 14 men with normal Medial Longitudinal Arch and normal Body Mass Index aged between 18-35 years old, with at least 6 months experience of doing leg press volunteered to participate in this study. Medial gastrocnemius and Tibialis anterior activity were measured by surface electromyography while doing leg press with 70% of subjects 1 Repetition Maximum. To increase accuracy, motion was divided into knee flexion and knee extension phases. Peak Amplitude, Time to Peak Amplitude and Root Mean Square variables were used for analysis. Wilcoxon nonparametric test was used to compare the results. Results: No statistically significant difference was found in the electromyographic parameters of Medial gastrocnemius nor Tibialis anterior in any phases of motion, except for an increase in Tibialis anterior time to peak amplitude in shod condition compared with barefoot in knee extension phase of motion (p-value=0.008) and Tibialis anterior RMS in knee flexion phase in orthotic condition compared to shod (p-value=0.03). Conclusion: It seems that in high loads shoes or medial arch supports cannot change electromyographic parameters in Medial gastrocnemius nor Tibialis anterior in any phase of motion while working with leg press device.

Bihemispheric Transcranial Direct Current Stimulation Acutely Improves Strength And Force Steadiness In Post-stroke Hemiparetic Patients

Transcranial direct current stimulation (tDCS) has been applied within rehabilitation programs in post-stroke patients. Two approaches have been used to minimize inter-hemispheric unbalance: cathodal tDCS upon the contralesional hemisphere to reduce inhibition of the ipsilesional hemisphere, and anodal tDCS upon the ipsilesional hemisphere to increase its excitability. PURPOSE: The purpose of present study was to investigate whether bihemisferic tDCS in both ipsilesional and contralesional motor cortex modulate the maximal strength and force steadiness of lower limbs in chronic stroke patients. METHODS: In a double blind, crossover, randomized sham-controlled experimental design, 10 chronic stroke patients performed bilateral knee extension and flexion isokinetic tests at submaximal and maximal workloads [2 sets of 10 repetitions at 50% peak torque and 1 set of 3 reps at 100% peak torque, respectively] with and without bihemispheric tDCS. RESULTS: After tDCS the peak torque increased only for the knee extension in the non-paretic limb (P = 0.008), while no difference was found in the paretic limb (P > 0.05). The force steadiness reflected by the coefficient of variation during the extension phase of the knee extension decreased in tDCS vs. sham condition in both paretic (P = 0.01) and non-paretic limbs (P = 0.04). However, in the knee flexion phase, the coefficient of variation after tDCS decreased only in paretic limb (P = 0.05). CONCLUSION: A single session of bihemispheric tDCS might enhance the maximal strength and force steadiness in chronic stroke patients. These findings warrant additional research to ratify the potential role of bihemispheric tDCS to improve motor performance in stroke patients. Supported by Supported by the Brazilian Council for the Technological and Research Development (CNPq) and Carlos Chagas Foundation for the Research Development in the State of Rio de Janeiro (FAPERJ)

정규 저크(Normalized Jerk)를 이용한 태권도 돌려차기 동작 분석

The purpose of this study was to evaluate the round-house kick of Teakwondo and to compare between elite and novice Teakwondo players using the normalized jerk method. MATLAB v6.5(Mathworks Inc., USA) was employed to analyze the normalized jerk. Fourteen male subjects who had no musculo-skeletal diseases were participated and were classified into two groups(7 elite and 7 non-elite Teakwondo players). While all subjects performed the round-house kick, the height of target set up based on the center of trunk position, respectively. In this study, independent t-test (elite and non-elite) was applied to obtain the differences of normalized jerk value between the two groups. Significance level was set as p=.05. The forward backward and upward downward normalized jerk values of the kicking foot COM(center of mass) were found to be significantly different between elite and non-elite groups in the maximum knee flexion phase. Significant difference was seen in the upward downward normalized jerk value of the kicking foot COM from maximum knee flexion to impact between elite and non-elite groups(p.05). The forward backward and upward downward normalized jerk values of the kicking foot COM were found to be significantly different between elite and non-elite groups during overall round-house kicking phase(p.05). The left-side right-side and upward downward normalized jerk values of the whole body COM(center of mass) were found to be significantly different between elite and nonelite groups in the maximum knee flexion phase(p.05). Significant difference was seen in the left-side right-side normalized jerk value of the kicking whole body COM from maximum knee flexion to impact between elite and non-elite groups(p.05). The normalized jerk values of upward downward were found to be significantly different between elite and non-elite groups during overall round-house kicking phase(p.05).

The influence of soccer-specific activity on the kinematics of an agility sprint

The aim of this study was to investigate the influence of soccer-specific fatigue on the kinematics of an agility sprint. Ten male professional soccer players (age 24.7±4.4 years, body mass 77.1±8.3 kg) completed an intermittent treadmill protocol replicating the activity profile of match-play, comprising two 45-min halves separated by a 15-min passive half-time interval. Pre-exercise and at 15-min intervals each player completed an agility sprint that consisted of a 180° cutting manoeuvre. Knee joint kinematics in the frontal and sagittal planes were determined for both the support and turning leg using a nine-camera automated motion analysis system operating at 200 Hz. During the penultimate foot contact, knee kinematics were characterized by joint flexion and increased varus alignment. Knee flexion at touchdown decreased significantly (P<0.05) as a function of exercise duration from 57.4±15.5° before exercise to 37.0±5.9° at the end of the second half. The range of joint movement during the knee flexion phase increased significantly during the first half (T 45=66.6±18.2°) and remained elevated during the second half (T 75=66.4±18.1°; T 90=65.7±20.4°; T 105=70.2±19.4°) relative to pre-exercise values (51.8±18.8°). During the final foot contact, knee kinematics were also characterized by flexion and increased varus alignment. Knee flexion at touchdown decreased during each half, with the knee angle at the end of the first half (30.6±7.0°) significantly (P=0.02) straighter than before exercise (39.5±6.3°), and significantly straighter at the end of the second half (30.2±2.9°) than after the half-time interval (37.7±7.8°) or before exercise. The range of knee flexion during ground contact increased significantly during each half. The range of knee varus during flexion changed from a varus displacement during the first 15 min to a valgus displacement thereafter. Peak valgus observed at the end of each half (T 45=4.7±7.9°; T 105=6.9±7.4°) was significantly (P<0.05) greater than before exercise. The range of valgus movement during knee extension was greatest following the passive half-time interval (T 60=6.2±7.3°), and tended to increase throughout the second half. Prolonged exposure to soccer-specific intermittent exercise therefore induced changes in knee kinematics that may have implications for injury incidence. The increased varus alignment and time-dependent decrease in knee flexion at touchdown represent two potential mechanisms for increased injury risk.

Effect of Varying Hamstring Tension on Anterior Cruciate Ligament Strain During in Vitro Impulsive Knee Flexion and Compression Loading

The hamstring muscles are well positioned to limit both anterior tibial translation and anterior cruciate ligament strain during the knee flexion phase of a jump landing. We hypothesized that systematically increasing or decreasing hamstring tension during the knee flexion phase of a simulated jump landing would significantly affect peak relative strain in the anterior cruciate ligament. Ten cadaveric knees from four male and six female donors (mean age [and standard deviation] at the time of death, 60.3 +/- 23.6 years) were mounted in a custom fixture to initially position the specimen in 25 degrees of knee flexion and simulate axial impulsive loading averaging 1700 N to cause an increase in knee flexion. Quadriceps, hamstring, and gastrocnemius muscle forces were simulated with use of pretensioned linear springs, with the tension in the hamstrings arranged to be increased, held constant, decreased, at "baseline," or absent during knee flexion. Impulsive loading applied along the tibia and femur was monitored with use of triaxial load transducers, while uniaxial load cells monitored quadriceps and medial and lateral hamstring forces. Relative strain in the anterior cruciate ligament was measured with use of a differential variable reluctance transducer, and tibiofemoral kinematics were measured optoelectronically. For each specimen, anterior cruciate ligament strains were recorded over eighty impact trials: ten preconditioning trials, ten "baseline" trials involving decreasing hamstring tension performed before and after three sets of ten trials conducted with increasing hamstring tension, constant hamstring tension, or no hamstring tension. Peak relative strains in the anterior cruciate ligament were normalized for comparison across specimens. Increasing hamstring force during the knee flexion landing phase decreased the peak relative strain in the anterior cruciate ligament by >70% compared with the baseline condition (p = 0.005). Neither a constant hamstring muscle force nor the absence of a hamstring force significantly changed the peak strain in the anterior cruciate ligament relative to the baseline condition. Increasing hamstring muscle force during the knee flexion phase of a simulated jump landing significantly reduces the peak relative strain in the anterior cruciate ligament in vitro.

Influence of a Horizontal Approach on the Mechanical Output During Drop Jumps

This study investigated the influence of a horizontal approach to mechanical output during drop jumps. Participants performed drop jumps from heights of 15, 30, 45, and 60 cm with zero, one, two, and three approach steps. The peak summed power during the push-off phase changed quadratically across heights (6.2 ± 0.3, 6.7 ± 0.4, 6.4 ± 0.4, and 6.0 ± 0.4 kW, respectively) driven by the ankle joint response. Summed peak power was 10% greater with an approach attributed to the knee joint response. Downward phase dorsiflexion (31%), knee flexion (35%), and peak vertical force (32%) increased with drop heights. Vertical approach force (22%) increased, while knee flexion (11%) and downward duration (17%) decreased. An approach may improve drop jump training for explosive tasks.

Minimization of the knee shear joint load in leg-extension equipment

We developed an analytical biomechanical model for leg-extension equipment and the associated knee-extension/flexion exercises. The shear component, ϕ t , of the tibiofemoral joint load was calculated taking into account all the fundamental elements of the equipment mechanics (resistance pad placement, cam/pulley system geometry, selected weight stack, etc.) and the instantaneous values of the relevant kinematical parameters (knee-flexion angle ( θ f), angular velocity, and angular acceleration). The optimal distance ( a R ) OPT between the knee-flexion/extension axis and the resistance pad placement point was derived by minimizing ϕ t . ( a R ) OPT is nearly independent of joint angular velocity and, for appreciably high resistance torques, becomes nearly independent of resistance level and cam/pulley geometry: for θ f > 40°, ϕ t is minimized by placing the resistance pad distally along the lower leg; for θ f ≤ 40°, ϕ t can be completely eliminated by continuously moving the resistance pad proximally during knee-extension phase and distally during knee-flexion phase (0.17 m ≤ ( a R ) OPT ≤ 0.4 m). In the presence of knee angular accelerations and hamstrings co-contractions, not predictable in advance, the value of ( a R ) OPT obtained neglecting these effects still represents a good compromise for joint protection. This work establishes the rational basis for the design and clinical use of a leg-extension equipment that minimizes ϕ t .

INFLUENCE OF AGE ON NEUROMUSCULAR CONTROL OF THE KNEE.

Purpose/Hypothesis: An increased incidence of injury has made neuro-muscular control of the knee joint a focus of attention in motor control research. The central nervous system (CNS) controls the knee against unpredictable perturbations that occur during movement. Age associated changes in the musculoskeletal, neuromuscular and sensory systems compromise the ability of the elderly to respond effectively to a perturbation, thereby placing the older population at a higher risk of injury. Weight bearing exercises have been primarily used to re-educate neuromuscular control of the knee following pathology. Limited information is available on the strategies used by the elderly to control the knee during dynamic activities. This study examined the effect of age on the neuromuscular control of the knee by examining accuracy of performance, muscle synergies and long latency reflexes (LLR) during a functional weight bearing exercise. We hypothesized that the elderly would show greater impairment in neuro-muscular control than the young. Number of Subjects: Ten young and ten elderly subjects performed a single leg squat exercise (SLS) while tracking a sinusoidal target with knee motion at different levels of resistances (4%, 8% and 12% body weight). Materials/Methods: Subjects first performed a set of learning trials to gain proficiency with the task. Later, they performed the SLSs with random perturbations (drop in resistance level to 0% BW) during the knee flexion phase. A split plot repeated measures ANOVA was used to assess between and within group differences in movement accuracy, synergistic activation patterns (EMG), and long latency reflexes. Results: The elderly group 1) had a 50% greater absolute error in tracking the target angle when compared to the younger group (p < 0.05); 2) showed a 60% greater activation of the quadriceps and hamstrings at all levels of resistances as compared to the younger group (p < 0.05); and showed 15% greater LLR for the quadriceps and biceps femoris when compared to the younger group (p < 0.05). Conclusions: These results indicate that the elderly recruit higher percentages of MVC and have greater error when performing the SLS weight bearing exercise. Clinical Relevance: Age associated changes of the sensorimotor system necessitates greater muscle activity to help stabilize the knee in the elderly. These findings provide important clinical implications when developing rehabilitation programs for the young and elderly.

Differences in the movement pattern of a forward lunge in two types of anterior cruciate ligament deficient patients: copers and non-copers

Objective. To determine whether differences in the knee joint movement pattern of a forward lunge could be quantified in healthy subjects and in anterior cruciate ligament deficient subjects who were able to return to the same activity level as before their injury ( copers) and in those who were not ( non-copers). Design. The movement patterns of the injured leg of the coper and non-coper anterior cruciate ligament deficient subjects and the right leg of the control subjects were compared statistically. Background. The forward lunge seems to be a less stressful test than the commonly used one-legged hop test, which makes it a possible tool for evaluating and comparing the functional performance of non-copers and copers. Methods. The movement pattern of a forward lunge was analysed by using a two-dimensional inverse dynamics method. The electromyographic activity of the quadriceps and hamstring muscles were recorded. Results. The non-copers moved more slowly and loaded the knee joint less than the copers and controls. The copers moved more slowly during the knee flexion phase but as fast as the controls during the knee extension. The EMG results suggest that the copers stabilized their knee joint by increasing the co-contraction of the hamstrings during the extension phase. Conclusions. Differences between the three groups’ movement patterns could be quantified. The forward lunge test seems appropriate to discriminate between the knee function in coper and non-coper anterior cruciate ligament deficient subjects. Relevance Information about the performance of movements, which significantly load the knee joint in coper and non-coper anterior cruciate ligament deficient patients may contribute to a better understanding of dynamic knee joint stabilization, which is relevant in relation to the development of rehabilitation strategies.

KNEE STIFFNESS MEASUREMENT DURING HOPPING AT DIFFERENT FREQUENCIES

1506 The purpose of this study was to develop and verify a theoretical model concerning the measurement of human knee stiffness during the hopping stance phase. The knee joint during the hopping stance phase is modeled as a rotational spring. This model predicted that there were three different stiffness values during the hopping stance phase. These stiffnesses were separated by two different equilibrium points. These equilibrium points were defined as the knee angles at maximum knee flexion and extension angular velocity during weight acceptance and propulsion phase respectively. The three stiffness values include two for the knee flexion phase (before and after the first equilibrium point) and one for the knee extension phase (before the second equilibrium point). Knee joint stiffness values were defined as the slopes of the knee joint angle squared vs. angular velocity squared graph of each phase. Kinematic data of hip, knee and ankle joint markers were captured with high-speed video cameras (120 Hz) while subjects hopped at three different frequencies: preferred, 120% and 80% of the preferred hopping frequency. Five consecutive hopping cycles were collected. Video images were digitized and 2D kinematics (knee joint angle and angular velocity) were calculated. The first (third) knee joint stiffness value decreased (increased) significantly with different hopping frequencies. No significant change was observed for the knee stiffness of the second phase. Compared to previous literature, this model provides more detailed information regarding knee joint function during the hopping stance phase.

EMG Comparison of Lateral Step-Up and Stepping Machine Exercise

The availability and use of stairstepping machines in both the rehabilitation and fitness industries have seen a significant increase in the last several years. The primary purpose of this study was to evaluate the electromyographic (EMG) activity levels of the rectus femoris (R), vastus medialis (V), biceps femoris (B), gastrocnemius (G), and semimembranosus/semitendonosus (S) muscles during exercise on a stepping machine and during performance of an 8-in lateral step-up. Eighteen subjects, without prior knee pathology, participated in the study. The root mean square EMG activity was obtained using surface electromyography and normalized to percent of maximum voluntary isometric contraction. Each exercise was broken down into knee flexion and knee extension phases for descriptive purposes. Analysis of variance (p < .05) was used for between exercise comparisons. Mean R and V activity were significantly greater during the lateral step-up exercise. Mean G activity was significantly greater for stepping machine exercise. Both B and S showed no significant mean differences between exercises. The stepping machine, in general, showed decreased activity during the knee extension phase and very little activity during the knee flexion phase when compared to the lateral step-up. The results indicate that exercise on the stepping machine would result in a more conservative rehabilitation approach for strengthening the quadriceps and hamstrings. J Orthop Sports Phys Ther 1992;16(3):108-113.