Rectus Femoris Activity Research Articles

The effects of enhanced abdominal activation on quadriceps muscle activity levels during selected unilateral lower extremity exercises.

The purpose of this study was to investigate the effect of Abdominal Enhancement (AE) on the muscle activation of vastus medialis obliquus (VMO), vastus lateralis (VL) and rectus femoris (RF) muscle activation levels during eccentric, isometric and concentric phases of single leg raise (SLR), single leg wall squat (SLWS) and forward lunge (FL) exercises. Sixteen healthy individuals (Age: 24.6±1.7years) were included in the study. Internal Obliques/Transversus Abdominis (IO/TA), VMO, RF and VL muscle activation levels were measured by surface EMG during the exercises in two conditions: with and without AE. The abdominal drawing-in technique was used for AE. Repeated-measures analysis of variance was performed for statistical analysis. With AE, the average of IO/TA muscle activation level was 28.9%. VMO and VL muscle activation levels were significantly greater with AE during SLR (p=.02), SLWS (p<.001) and FL (VMO, p=.008, VL, p=.04) exercises. The effect of AE on VMO muscle activation level ranged from 2.5% to 5% (Effect size range: 0.54 to 0.91) and VL muscle activation level ranged from 2.1% to 5.5% (Effect size range: 0.35-1.24). RF muscle activation level did not change with AE (p>.05). The results of this study showed that AE increased VMO and VL muscle activities during SLR, SLWS and FL exercises but the corresponding changes were small. Even if this is not enough for muscle strengthening, exercises with AE may be used to enhance knee joint stability while controlling lumbopelvic stability.

The effects of fatigue on synergy of selected lower limb muscles during running

The purpose of this study was to investigate the effect of fatigue on selected lower extremity muscles synergy during running using non-negative matrix factorization algorithm method. Sixteen male recreational runners participated in this study. The surface electromyographic activity of rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF), semitendinosus, gastrocnemius medialis (GM), soleus (SO) and tibialis anterior (TA) were recorded on treadmill at 3.3 m s−1 before and after the fatigue protocol. Synergy pattern and relative muscle weight were calculated by non-negative matrix factorization (NNMF) algorithm method. The results showed that using the VAF method, five muscle synergies were extracted from the emg data during running. After the fatigue, the number of muscular synergies did not show a change, but relative weight of the muscles changed. Fatigue did not have any effect on the structure of muscular synergy, but changed the relative weight of muscles. These changes could be the strategy of the central nervous system to maintain optimal function of the motor system.

Comparison of the electromyographic activity of the abdominal and rectus femoris muscles during traditional crunch and Rock Gym® device

Abdominal exercises are performed with the purpose of preventing or rehabilitating low back pain, improving sports performance, and increasing strength and endurance during activities of daily living, and for aesthetic reasons. The objective of this study is to analyze and compare the electromyographic activity of the rectus abdominis (RA), external oblique abdominis (EO), and rectus femoris (RF) muscles during traditional crunch and exercise with Rock Gym® device. A convenience sample of 15 healthy men (mean ± standard deviation, age 22.47 ± 2.26 years, body fat percentage 13.44 ± 4.37%) was selected. All men regularly participated in physical activity. Electromyographic recordings were performed using simple differential surface electrodes during five repetitions of each abdominal exercise (traditional and Rock Gym® at levels RG1, RG2, RG3, and RG4) in a randomized and counterbalanced manner. Electromyographic signals were quantified by root mean square and normalized using the maximum voluntary isometric contraction. Data were analyzed using repeated measures analysis of variance (p < 0.05). Electromyographic activity of the abdominal muscles RA and EO in the crunch exercise was significantly higher (RA) or similar (EO) compared with the Rock Gym® device; however, the activity of the RF muscle in the device was significantly greater in relation to the traditional exercise. Traditional crunch produced greater or similar EMG activity in the abdominal muscles and minimized RF activity compared with the Rock Gym® device; hence, traditional crunch is preferred for training, especially for people with weak abdominal musculature and/or problems in the lower back.

Long-term effects of shoe mileage on ground reaction forces and lower limb muscle activities during walking in individuals with genu varus

BackgroundShoe mileage is an important factor that may influence the risk of sustaining injuries during walking. The aims of this study were to examine the effects of shoe mileage on ground reaction forces and activity of lower limb muscles during walking in genu varus individuals compared with controls. MethodsFifteen healthy and 15 genu varus females received a new pair of running shoes. They were asked to wear these shoes over 6 months. Pre and post intervention, mechanical shoe testing was conducted and ground reaction forces and muscle activities of the right leg were recorded during walking at preferred gait speed. FindingsSignificant group-by-time interactions were found for shoe stiffness, antero-posterior and vertical impact peak. We observed higher shoe stiffness and lower impact peaks after intervention in both groups with larger effect sizes in genu varus. Significant group-by-time interactions were identified for vastus medialis (loading phase) and rectus femoris (loading and push-off). For vastus medialis, significant decreases were found from pre-to-post during the loading phase in the control group. Rectus femoris activity was higher post intervention during the loading and push-off phases in both groups with larger effect sizes in genu varus. InterpretationOur findings indicate that the observed changes in ground reaction forces are more prominent in genu varus individuals. Together with our findings on shoe stiffness, it seems appropriate to change running shoes after an intense wearing time of 6 months, particularly in genu varus individuals.

Effects of Whole Body Electromyostimulation on Muscle Activity and Muscle Thickness of Rectus Femoris, and Muscle Thickness of Abdominis Muscle in Healthy Adults

Background: Whole body-electromyostimulation (WB-EMS) is widely used for the rehabilitation and recovery of patients with various neuromusculoskeletal disorders.Objects: To objectively measure changes in lower extremity and abdominal muscles after sit-to-stand dynamic movement training using WB-EMS.Methods: A total of 46 healthy adults (23 experimental and 23 control subjects) performed sit-to-stand exercise; the experimental group with WB-EMS, and the control group without WB-EMS. The muscle activity of the lower extremity, and the muscle thickness of the lower extremity and abdominal muscles were measured before and after the intervention.Results: In terms of electromyographic activity, there was a significant interaction effect for the rectus femoris (RF) muscle (F=30.212, p=.000). With regards to ultrasonographic imaging, the muscle thickness of the RF muscle had a significant interaction effect at the muscle contraction ratio (F=8.071, p=.007). The deep abdominal muscles, such as the transverse abdominal (TrA) and internal oblique (IO) muscles, also showed significant interaction effects at the muscle contraction ratio (F=5.474, p=.024, F=24.151, p=.000, respectively)Conclusion: These findings suggest that WB-EMS may help to improve the muscular activity of the RF muscle, and the muscle thickness of the RF muscle and deep muscles such as the TrA and IO muscles.

Investigation the EMG Activities of Lower Limb Muscles When Doing Squatting Exercise in Water and on Land.

(1) Background: Squatting is one of the common closed-kinetic chain (CKC) exercises for knee rehabilitation. Some patients cannot perform squatting exercises on land occasionally due to knee pain. Several studies had suggested that lower limb muscle activities are lower in water than on land while performing CKC exercises. The purpose of this study is to investigate the surface electromyography (sEMG) activities of Rectus femoris (RF) and Biceps femoris (BF) muscles when doing a squatting exercise in water and on land. (2) Methods: This was a cross-sectional experimental study. A total of 20 healthy participants (10 males, 10 females) were recruited by convenience sampling. The sEMG of RF and BF muscles in water and on land were collected and the knee motions were videotaped. Participants were instructed to perform closed kinetic-chain back squatting exercises at a specific speed (30 beats per minute) in water and on land at angular speed of 45°/s. Eight repetitions of the squatting exercise (0–90° knee flexion) were performed. The mean percentage maximal voluntary contraction (%MVC) between two muscles was compared in two conditions. The %MVC of RF and BF muscles at different specific knee flexion angles (30°, 60° and 90° knee flexion) was also identified. (3) Result: Muscle activities of RF (p = 0.01) and BF (p < 0.01) muscles were significantly lower in water than on land. The %MVC of RF and BF muscles was found to be 15.01% and 10.68% lower in water than on land respectively. For different knee angle phases, the differences in %MVC between land and water had significant difference for both RF muscles and BF muscles. (4) Conclusion: This study found a difference of mean percentage MVC of RF and BF muscles between land and water in different phases of squatting. The water medium reduced the two muscles’ activities to a similar extent. The result showed that the aquatic environment allows an individual to perform squatting with less muscle activation which may serve as an alternative knee exercise option for patients who encounter difficulty in land squatting due to lower limb muscle weakness or a high level of knee pain.

Effects of Ankle Joint Motion on Pelvis-Hip Biomechanics and Muscle Activity Patterns of Healthy Individuals in Knee Immobilization Gait.

The purpose of the study was to investigate the pelvis-hip biomechanics and trunk and lower limb muscle activity patterns between healthy people walking in two gaits and evaluate the effects of ankle joint motion on these two gaits. The two gaits included walking with combined knee and ankle immobilization and with individual knee immobilization. Ten healthy participants were recruited and asked to walk along a 10 m walk away at their comfortable speeds in the two gaits. Kinematic data, ground reaction force, and electromyography waveforms of trunk and lower limb muscles on the right side were collected synchronously. Compared to individual knee immobilization gait, people walking in the combined knee and ankle immobilization gait increased the range and average angle of the anterior pelvic tilt during the first double support and the single support phase, respectively. The combined knee and ankle immobilization gait also increased the range of hip abduction during the second double support phase. These kinematic alternations caused changes in trunk and lower limb muscle activity patterns. The ankle immobilization increased the range of gluteus maximus activation in the first double support phase, the range of rectus abdominis activation, the average amplitude of rectus femoris activation in the single support phase, and the range of rectus femoris activation in swing phase and decreased the range of and tibialis anterior activation in the first double support phase. The ankle immobilization also increased the average values of proximodistal component in AKI gait during the single support phase. This study revealed significant differences in pelvis-hip biomechanics and trunk and lower limb muscle activity patterns between the two gaits.

The effects of vibration foam roller applied to hamstring on the quadriceps electromyography activity and hamstring flexibility.

This study investigates the effect of vibration foam roller (VFR) applied to the hamstring, on the quadriceps electromyography (EMG) activity and hamstring flexibility. A total of 16 subjects were randomly assigned to either the VFR group (n=8) or the nonvibration foam roller group (NVFR, n=8). The two groups applied the foam roller or the VFR to the dominant hamstring, at a rate of 40 times per min, for a total of 200 times in 5 min. The primary outcome was to measure hamstring extensibility using the sit and reach test. The EMG activity of the dominant rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM) was measured as the secondary outcome. Results indicate a significant increase in the sit and reach distance after the intervention in both groups, as compared to preintervention. The sit and reach difference between VFR and NVFR show no significant difference after the intervention. Significant increases were observed after intervention in the %maximum voluntary isometric contraction (%MVIC) of VL, VM, and RF in the VFR group, and RF in the NVFR group, as compared to the preintervention values. Furthermore, %MVIC values of VL and RF, but not the VM muscle, were significantly different between the two groups. These findings suggest that regardless of vibration, the application of foam roller to hamstring may exert a positive effect on hamstring flexibility. Furthermore, these results indicate that the application of foam roller with vibrations causes more EMG activation in the antagonists.

Impact of instrumental analysis of stiff knee gait on treatment appropriateness and associated costs in stroke patients

BackgroundStiff Knee Gait (SKG) in stroke patients is typically treated by the inhibition of the rectus femoris (RF) with botulinum toxin (BoNT) after clinical evaluation, obtaining an average pooled recovery in knee flexion (KF) of 7 degrees. PurposeOur hypothesis is that this limited recovery after BoNT could depend on the inadequacy in the selection of patients to be treated. The aim of this study was to assess the percentage of inappropriate treatments (PIT) that can be avoided when instrumental gait analysis (GA) is used, and to estimate the associated cost savings. MethodsWe retrospectively analyzed GA data from chronic stroke patients with SKG and clinically assessed knee extensors spasticity referred to our laboratory over a five-year period. Gait kinematics and dynamic electromyography data were used. Patients were considered unsuitable for RF inhibition when: their SKG was determined by inadequate ankle push-off (APO) rather than by a brake from knee extensors, based on a previously published algorithm using gait kinematics (PITKIN); when RF was not active during KF (PITEMG); and when a proximal braking mechanism was found, if this was not due to RF activity (PITGA). Results160 patients, age 20–87 years, gait speed 9–77%height/s, KF peak -4–44 degrees, were included. Of these, in 119 cases poor APO was the main cause of SKG, thus leading to PITKIN = 74%. In 48 out of 107 non-obese subjects, RF spasticity was not involved in SKG, resulting in PITEMG = 45%. Finally, patients with a braking activity as the main cause and concurrent RF activity were 20/107 = 19%, resulting in PITGA = 81% SignificanceWhen treating SKG, proper use of GA can reduce the percentage of inappropriate treatments by BoNT at the RF up to 81%. Savings are in the order of €100k/year when considering centers treating 100 or more patients/year.

The Effect Of Knee Joint Angle Difference On The Compartment Neuromuscular Activation In Rectus Femoris

Bi-articular muscles play an important role to smooth movement in human. However, the biomechanics and physiological function of those muscles is unclear. Thus, this study investigates the function of rectus femoris as a famous bi-articular muscle in lower limbs. PURPOSE:The purpose of this study is to unravel the compartment neuromuscular activation of rectus femoris during isometric knee extension and hip flexion in different knee angles. METHODS:Subjects were eight healthy men. Knee extension with hip flexion were performed in isometric contraction. Knee angle was set up at 90, 60, 30, and 0 degree. Also, there were three contractions as follow: Maximum voluntary contraction (MVC), 80%MVC and 60%MVC. Muscle activation of rectus femoris was measured by using multi-channel surface electromyography, and calculated the average rectified value (ARV). We evaluated the ARV of rectus femoris divided into proximal, medium and distal compartment. We evaluated the ARV of rectus femoris divided into proximal, medium and distal compartment. RESULTS:In the proximal region at 30 degrees knee angle, averaged ARV value in the MVC (0.113 mV) was significantly higher than those of other two contraction groups (80%MVC: 0.071 mV, p<0.05 vs MVC; 60%MVC: 0.047 mV, p<0.01 vs MVC). There was no significant differences in ARVs both in medium and distal compartments. CONCLUSIONS:Proximal region of rectus femoris has the role of knee extension and hip flexion in slightly flexed knee joint position. We conclude that the difference of knee angle affects the compartment neuromuscular activation in rectus femoris.

Effect Of Knee Joint Angle On Neuromuscular Activation Of The Quadriceps Femoris During Fatiguing Contractions

In muscle fatigue studies, repetitive muscle contractions at a submaximal force level (e.g., 50% of maximum voluntary contraction [MVC]) are frequently used as a fatiguing task such as isometric knee extensions. Contrary to submaximal fatiguing contractions, when MVC is used to induce muscle fatigue, muscle force will decrease despite maximal effort and amplitude and/or frequency of electromyographyic (EMG) signals will also change with the development of muscle fatigue. However, it is unclear the effect angle of knee joint on the neuromuscular activation of individual muscles of quadriceps femoris during repetitive knee extension tasks. PURPOSE: We sought of this study was to assess the effect of knee joint angle on the neuromuscular activation pattern of the four individual muscles in the quadriceps femoris during repetitive fatiguing MVCs. METHODS: Fifteen healthy men and women (age, 25 ± 3 years; height, 165 ± 11 cm; weight, 57 ± 10 kg) performed two fatiguing tasks consisting of 40 MVCs at knee joint angles of 80° (flexed) and 140° (extended). Neuromuscular activation of the vastus intermedius (VI), vastus lateralis, (VL), vastus medialis (VM) and rectus femoris (RF) was recorded using surface electrodes, and median frequency (MF) and root mean square (RMS) of EMG signals (normalized by pre-test MVCs) were calculated. RESULTS: MVCs significantly decreased from the 10th to the 40th repetition at both knee joint angles. The MFs of VI and VM in the flexed knee joint angle and that of RF at the flexed and extended knee joint angles were significantly decreased after the 10th repetition. There were no significant changes in normalized EMG amplitude in any muscles specific to knee angle. Stepwise regression analysis revealed predictive synergetic action may take place in RF, VM, and VI in the flexed joint angle and between RF and VM at the extended joint angle. CONCLUSION: These results suggest that neuromuscular activation of RF and VM is independent, but activation of VI and VL is dependent, upon knee joint angle, which may, in part, explain joint angle-specific muscle fatigue.

The effect of altered stride length on iliocapsularis and pericapsular muscles of the anterior hip: An electromyography investigation during asymptomatic gait

BackgroundAnterior pericapsular muscles potentially contribute to active hip joint stability in walking by controlling anterior femoral translation in peak extension. Alternatively, these muscles could flex the hip and tension the anterior capsule to aid initiation of swing. Although never investigated, the location of Iliocapsularis and its extensive anterior hip capsule attachment imply a potential role in these functions. We hypothesised if these muscles contribute to control of femoral head translation (rather than hip flexion), their activation would decrease when peak hip extension is reduced during shorter stride walking. Research questionsTo provide the first description of iliocapsularis activity during walking and challenge the hypothesised roles of the anterior pericapsular hip muscles in gait by walking with shortened strides. MethodsFifteen healthy volunteers walked with self-selected and shortened stride lengths. Electromyographic recordings were made from iliocapsularis, iliacus and anterior gluteus minimus with intramuscular electrodes, and rectus femoris with surface electrodes. Stride characteristics were measured using force sensors and 3D motion capture. Ensembles of burst activity profiles for each stride length were compared. ResultsIliocapsularis displayed a consistent EMG burst around toe-off (terminal hip extension) that peaked during early swing phase with self-selected strides. In shortened strides, iliocapsularis EMG increased during mid to late stance (p = 0.03), with no difference in other muscles. Iliocapsularis, iliacus and rectus femoris activity decreased during early stance (p < 0.01) in short strides, whereas gluteus minimus EMG increased (p = 0.03). SignificanceIliocapsularis displayed an EMG burst around toe-off during walking, and greater EMG during mid-late stance in short stride walking, which was not seen in other pericapsular muscles. Shortened strides increase the demand for active tensioning of the hip joint capsule in initial swing, and suggests a role for iliocapsularis during active hip flexion in pain free young individuals.

Performance of stair negotiation in patients with cerebral palsy and stiff knee gait

BackgroundDue to the limited knee range of motion, achieving adequate foot clearance while walking on level ground constitutes a major problem for patients with cerebral palsy and stiff knee gait. Stair negotiation as an activity of daily life requires a considerably higher knee range of motion than level ground walking, but little is known yet as to whether such patients are able to walk stairs.Research question: The aim of this study was to investigate how patients with a limited knee range of motion negotiate stairs. Do they increase their peak knee flexion and use the same pattern as in walking on level ground? How do the muscles act during stair negotiation? MethodsIn this explorative study, 17 adults with bilateral, spastic cerebral palsy and stiff knee gait and 25 healthy subjects were examined. 3D motion analysis, including electromyography, was performed while walking on level ground, upstairs, and downstairs. A linear mixed model was used for between- and within-group comparisons. ResultsWalking upstairs and downstairs, patients increased their peak knee flexion by around 30° compared to level walking. Thus, increased knee flexion may be seen as the main mechanism for maintaining foot clearance on stairs. An increased pelvic obliquity (elevation) and hip flexion were also found and involved subjects showed a slight increase in rectus femoris activity when walking on stairs compared to level walking within the phases of high knee flexion. SignificanceThis study showed that patients with cerebral palsy and stiff knee gait are able to flex their knees more than would be required for level walking. Hence, the patients are able to adapt their rectus activity to stair walking to some extent. Therefore, further investigations might help to open up new therapeutic options to facilitate level walking and stair negotiation in patients with stiff knee gait.

Whole-body vibration impedes the deterioration of postural control in patients with multiple sclerosis

ObjectiveThe current study aimed to investigate if whole-body vibration (WBV) might attenuate the processing functional and neuromuscular degeneration of postural control in patients with MS. DesignPerformance in postural control was assessed before and after 6 weeks of a control (CON) and a WBV intervention period. SettingLaboratory at the University of Freiburg & home-based training ParticipantsOut of 29 interested participants, 15 subjects with severe MS fit inclusion criteria. Main outcome measuresCentre of pressure displacement (COP), muscle activity and co-contraction indices of m. soleus (SOL), gastrocnemius medialis (GM), tibialis anterior (TA), biceps (BF) and rectus femoris (RF) as well as SOL H/M-ratios. ResultsAfter CON, COP was significantly enhanced with reduced muscle activity in RF and diminished shank muscle co-contraction. After WBV, no changes were observed in COP and neuromuscular control. However, over time, TA activity was reduced, but with no changes in muscle activation of SOL, GM and BF or H/M-ratios. ConclusionsAfter CON, MS patients experienced substantial deteriorations in postural control which have previously been associated with greater postural instability. No further disease-associated deteriorations were observed following the intervention. Thus, WBV might alleviate neurodegeneration of postural control in people with MS.

Neuromusculoskeletal Simulation Reveals Abnormal Rectus Femoris-Gluteus Medius Coupling in Post-stroke Gait.

Post-stroke gait is often accompanied by muscle impairments that result in adaptations such as hip circumduction to compensate for lack of knee flexion. Our previous work robotically enhanced knee flexion in individuals post-stroke with Stiff-Knee Gait (SKG), however, this resulted in greater circumduction, suggesting the existence of abnormal coordination in SKG. The purpose of this work is to investigate two possible mechanisms of the abnormal coordination: (1) a reflex coupling between stretched quadriceps and abductors, and (2) a coupling between volitionally activated knee flexors and abductors. We used previously collected kinematic, kinetic and EMG measures from nine participants with chronic stroke and five healthy controls during walking with and without the applied knee flexion torque perturbations in the pre-swing phase of gait in the neuromusculoskeletal simulation. The measured muscle activity was supplemented by simulated muscle activations to estimate the muscle states of the quadriceps, hamstrings and hip abductors. We used linear mixed models to investigate two hypotheses: (H1) association between quadriceps and abductor activation during an involuntary period (reflex latency) following the perturbation and (H2) association between hamstrings and abductor activation after the perturbation was removed. We observed significantly higher rectus femoris (RF) activation in stroke participants compared to healthy controls within the involuntary response period following the perturbation based on both measured (H1, p < 0.001) and simulated (H1, p = 0.022) activity. Simulated RF and gluteus medius (GMed) activations were correlated only in those with SKG, which was significantly higher compared to healthy controls (H1, p = 0.030). There was no evidence of synergistic coupling between any combination of hamstrings and hip abductors (H2, p > 0.05) when the perturbation was removed. The RF-GMed coupling suggests an underlying abnormal coordination pattern in post-stroke SKG, likely reflexive in origin. These results challenge earlier assumptions that hip circumduction in stroke is simply a kinematic adaptation due to reduced toe clearance. Instead, abnormal coordination may underlie circumduction, illustrating the deleterious role of abnormal coordination in post-stroke gait.

Effect of Different Types of Shoes on Lower Limb Muscular Activation during Walking in Women

Purpose: The present study intended to compare the effects on the female body of high-heeled shoe types, including regular high heels, wedge heels, and platform heels, with those of sneakers during level walking by examining muscular activity in the lower limbs. Materials and Methods: Participants were 20 women in their 20s or 30s who regularly wear different types of size 8 (US size). The heel height tested was 7 cm, and electromyographic muscular activation (% maximal voluntary isometric contraction) was measured in the rectus femoris, tibialis anterior, and semitendinosus muscles of participants’ dominant legs during walking 15 m at a self–selected walking velocity step speed. Results: Rectus femoris revealed significant electromyographic differences among shoe types in terms of muscular activation (p = .013). Multiple comparisons among shoe types and activation of various muscles were carried out. These showed significant (p &lt; .05) differences in rectus femoris muscular activation among shoe types, most notably between sneakers and platform heels (average -15.69 (SD = 4.22) (p = .002)) and between sneakers and high heels (average 13.83 (SD = 4.22) (p = .010)). Conclusion: Results obtained revealed significant variation in muscular activation of rectus femoris among shoe types. Multiple pairwise comparisons of the differences in muscular activation of rectus femoris revealed significant differences between sneakers and high heeled shoes and between sneakers and platform heels. Therefore, the results of the present study are expected to be beneficial for ordinary individuals in selecting appropriate types of shoes that reduce the level of the muscle activation.

Effect of acceleration on the rate of power development and neural activity of the leg extensors across the adult life span.

The rate of power development (RPD) represents the capacity to rapidly generate power during a dynamic muscle contraction. As RPD is highly susceptible to aging, its decline can have important functional consequences. However, the effect of age on RPD in response to rapid changes in movement velocity (cfr. fall incidence) is not yet clear. Therefore, the present study aimed to examine the effect of age on RPD and neural drive in response to different accelerations. Three maximal isokinetic leg extensor tests at 540°/s with different initial acceleration phases at 3200, 5700 and 7200°/s2 were performed. RPD, which is the slope of the power-time curve during the acceleration phase, was calculated for 83 subjects aged between 20 and 69years. Mean electromyography signal amplitude was determined for rectus femoris (RF), vastus lateralis (VL) and biceps femoris muscles. The average annual age-related decline rate of RPD at highest acceleration was - 2.93% and was - 1.52% and - 1.82% higher compared to lower acceleration rates (p < 0.001). This deficit can probably be explained by an age-related impairment in neural drive during the first 75ms of the acceleration phase, as evidenced by a reduced RF and VL neuromuscular activity of - 0.30% and - 0.36% at highest versus lowest acceleration (p < 0.05). These findings highlight the inability of aged individuals to quickly respond to abrupt changes in movement velocity, which requires more focus in training and prevention programs.

Acute Effects of Different Stretching Techniques on Lower Limb Kinematics, Kinetics and Muscle Activities during Vertical Jump

The purpose of this study was to examine the acute effects of different stretching techniques on performance and lower limb kinematics, kinetics and muscle activities during vertical jump in female aerobics athletes. 10 female college aerobics athletes participated in this study. Three-dimensional kinematic and kinetic data, as well as electromyography of rectus femoris, biceps femoris and gastrocnemius medialis were collected using Vicon motion analysis system, Kistler force plate and Wireless surface electromyographic system respectively during the test. No significant differences in jump height had been determined among these 3 warm-up methods. Hip peak flexion and internal rotation angles decreased significantly after BSM and peak adduction angle decreased significantly after SSM and BSM during landing. Knee peak flexion and internal rotation angles increased significantly after SSM and BSM during take-off. Also, BSM showed significantly greater peak flexion compared with SSM. Ankle peak plantarflexion angle increased significantly after BSM. In addition, BSM showed significantly greater improvement in the variation range than SSM except for the ankle int-external rotation. Existence of no significant differences in the peak value of vertical ground reaction force during take-off and landing phase had been determined among these 3 warm-up methods, and muscle activities of rectus femoris, biceps femoris and gastrocnemius medialis were likewise not significantly different. The results of this study suggest that it would be suitable for female aerobics athletes to perform ballistic stretching in warm-up in order to improve flexibility without decreasing the following vertical jumping event and may also reduce the risk of ankle sprain injury.

Single-Leg Squat Delicacies-The Position of the Nonstance Limb is an Important Consideration.

Context: The single-leg squat task is often used as a rehabilitative exercise or as a screening tool for the functional movement of the lower limb. Objective: To establish the effect of 3 different positions of the nonstance leg on 3-dimensional kinematics, muscle activity, and center of mass displacement during a single-leg squat. Design: Within-subjects, repeated-measures design. Setting: Movement analysis laboratory. Participants: A total of 10 participants, aged 28.2 (4.42) years performed 3 squats to 60° of knee flexion with the nonstance (1)hip at 90° flexion and knee at 90° flexion, (2)hip at 30° flexion with the knee fully extended, or (3)hip in neutral/0° and the knee flexed to 90°. Main Outcome Measures: Trunk, hip, knee and ankle joint angles, and center of mass displacement were recorded with inertial sensors while muscle activity was captured through wireless electromyography. Results: Most trunk flexion (21.38° [18.43°]) occurred with the nonstance hip at 90° and most flexion of the stance hip (23.10° [6.60°]) occurred with the nonstance hip at 0°. Biceps femoris activity in the 90° squat was 40% more than in the 0° squat, whereas rectus femoris activity in the 0° squat was 29% more than in the 90° squat. Conclusion: The position of the nonstance limb should be standardized when the single-leg squat is used for assessment and be adapted to the aim when used in rehabilitation.

Could scooting be a useful option for aerobic exercise in chronic obstructive pulmonary disease?

BackgroundMany patients with COPD are ventilatory limited and unable to tolerate effective levels of aerobic training. A scooter could be an enticing training modality if muscle activity is partitioned and distal leg muscle activity is emphasized. The aim of this study was to determine whether scooting might emphasize leg heaviness (desired muscle burden), relative to the breathing heaviness, when compared with walking. MethodsParticipants completed two endurance tests, walking and scooting. The intensity for each targeted similar tolerable exercise times (tlimit) simulating comparable training session exposure. Participants scored (Borg0-10) leg and breathing heaviness throughout each test and the slope calculated. Electromyography was used to quantify leg muscle activity. Results15 participants with COPD (mean[SD]: age = 64[11]y; FEV1 = 52[17]%predicted; FEV1/FVC = 50[10]%) completed the study. Successful matching of intensity between modalities was demonstrated by similar tlimit (difference [95%CI] = -0.3[-2.8 to 2.1]min). Scooting resulted in more (60[24 to 95]%) activity of the gastrocnemius in the propulsion and less (−82[-91 to −72]%) in the support leg. Rectus femoris activity was reduced (−68[-95 to −41]%) and increased (117[49 to 184]%) in the propulsion and support leg, respectively. There was no significant difference (0.1[-0.1 to 0.2]) in the relationship between breathing and leg heaviness when scooting was compared to walking. ConclusionsScooting is associated with increased activity of the distal muscles of propulsion of the scooting leg. However, this is offset by the increased activity of the support leg as it resists the rotational force of propulsion, such that the relationship between breathing and leg heaviness is not altered.