Rectus Femoris Activity Research Articles

Characterising lower limb muscle activity and test-retest repeatability of EMG measures in healthy adults during upright pedalling

Background: Upright pedalling (UP) has similarities to walking in terms of both muscle activation and biomechanical activity. Therefore, UP is a potential rehabilitation therapy for enhancing walking recovery. The development of UP as a rehabilitation intervention requires understanding of muscle activity patterns elicited during pedalling in a range of participants, including young healthy adults. The aims of this study were: to characterise muscle activation patterns during UP in young healthy adults, and to investigate the test-retest repeatability of EMG-derived measures used to characterise activity patterns. Methods: Participants (total n=8, females: n=7) performed two UP sessions, separated by a 1-hour rest period. During UP, muscle activity of rectus femoris (RF) and biceps femoris (BF) was recorded using surface EMG. Lower limb muscle activity was characterised by average, integrated activity (iEMG) for each muscle group according to four 90° phases of the 360° wheel turn. This procedure provided a measure of muscle activity throughout the pedalling cycle. Testretest repeatability of mean iEMG values for each pedal revolution was calculated using an intraclass correlation coefficient (ICC) with 95% confidence intervals (CI). Results: Characterisation of activity: muscle activity for all participants during UP demonstrated reciprocal muscle activation of BF and RF. More specifically, RF exhibited double bursts of activity at 0–135° and 270–360°, whereas BF demonstrated a single burst at 135–270°. Test-retest repeatability: appeared high for RF when considering the point estimate (ICC=0.837), but the associated wide CIs (-0.224–1.39) mean that this finding is imprecise. A lack of repeatability observed for BF (ICC=0.02) was also inconclusive due to wide CI's (-0.258–0.737). Conclusions: UP elicited a reciprocal muscle activation pattern in RF and BF in a small sample of young healthy volunteers. Definitive test-retest repeatability of recorded measures was not established. Implications: This study has contributed normative data on muscle activation patterns during walking-like activity, and data to inform sample size for definitively testing intra-participant variance.

Breakpoints in ventilation, cerebral and muscle oxygenation, and muscle activity during an incremental cycling exercise.

The aim of this study was to locate the breakpoints of cerebral and muscle oxygenation and muscle electrical activity during a ramp exercise in reference to the first and second ventilatory thresholds. Twenty-five cyclists completed a maximal ramp test on an electromagnetically braked cycle-ergometer with a rate of increment of 25 W/min. Expired gazes (breath-by-breath), prefrontal cortex and vastus lateralis (VL) oxygenation [Near-infrared spectroscopy (NIRS)] together with electromyographic (EMG) Root Mean Square (RMS) activity for the VL, rectus femoris (RF), and biceps femoris (BF) muscles were continuously assessed. There was a non-linear increase in both cerebral deoxyhemoglobin (at 56 ± 13% of the exercise) and oxyhemoglobin (56 ± 8% of exercise) concomitantly to the first ventilatory threshold (57 ± 6% of exercise, p > 0.86, Cohen's d < 0.1). Cerebral deoxyhemoglobin further increased (87 ± 10% of exercise) while oxyhemoglobin reached a plateau/decreased (86 ± 8% of exercise) after the second ventilatory threshold (81 ± 6% of exercise, p < 0.05, d > 0.8). We identified one threshold only for muscle parameters with a non-linear decrease in muscle oxyhemoglobin (78 ± 9% of exercise), attenuation in muscle deoxyhemoglobin (80 ± 8% of exercise), and increase in EMG activity of VL (89 ± 5% of exercise), RF (82 ± 14% of exercise), and BF (85 ± 9% of exercise). The thresholds in BF and VL EMG activity occurred after the second ventilatory threshold (p < 0.05, d > 0.6). Our results suggest that the metabolic and ventilatory events characterizing this latter cardiopulmonary threshold may affect both cerebral and muscle oxygenation levels, and in turn, muscle recruitment responses.

고관절 각도에 따른 대퇴사두근의 Q-setting 운동 시 근활성도에 미치는 영향

Purpose : The aim of this study was to find out differences between muscle activity of quadriceps according to hip angle. Method : 40 healthy adults produced maximum isometric muscle contraction of quadriceps femoris and each part of the quadriceps femoris were measured with a surface EMG in hip joint angle of <TEX>$90^{\circ}$</TEX>, <TEX>$135^{\circ}$</TEX>, <TEX>$180^{\circ}$</TEX>. Result : There was no significant difference between muscle activity of vastus medialis and lateralis according to hip angle. But there was significant difference in muscle activity of rectus femoris and the muscle activity was maximum at 135 degrees of hip angle. Conclusion : In conclusion, maximum muscle activation of rectus femoris is affected by hip angle, and the findings from this study may be helpful for physical therapists in selecting hip position when instructing patients to do Q-setting exercise. So, we suggest that patients perform Q-setting exercise at 135 degrees of hip angle for the best result.

The functional effect of a distal rectus femoris tenotomy in adults with cerebral palsy

The purpose of this study was to determine the effect of a distal rectus femoris tenotomy on function and gait in adults with cerebral palsy who had diminished knee flexion during swing. A stiff knee gait pattern is commonly seen in individuals with cerebral palsy and frequently leads to tripping and falling. Five subjects, 25–51 years, (34.6±10.3 years) participated in the study; each individual had the surgery after the age of 18. Four of the five subjects underwent bilateral distal rectus femoris tenotomies for a total of nine limbs being studied. Four of the five subjects had a single procedure of a distal rectus femoris tenotomy and one subject also had bilateral adductor tenotomies. All individuals underwent a pre-operative and post-operative, (3.28±1.6 years) three-dimensional gait analysis. Pre-operative gait revealed diminished peak knee flexion and out of phase rectus femoris activity with a quiet vastus lateralis during swing in all subjects. Significant findings after a distal rectus femoris tenotomy included: improved peak swing knee flexion, improved peak stance hip extension, and increased total knee excursion without loss in knee extension strength. During swing, knee flexion angle improved on average 11° which correlated with subjective report of less shoe wear, tripping, and falling due to improved clearance. In conclusion, a distal rectus femoris tenotomy should be considered a surgical option for adults with cerebral palsy and a stiff knee gait pattern to improve mobility, function, and quality of life.

THE CHANGE IN LOWER LIMB KINEMATIC AND EMG ACTIVITY OF SPRINTING AFTER SOCCER-SPECIFIC FATIGUE AMONG FEMALE SOCCER PLAYERS

BackgroundHamstring strain during sprinting is one of the dominant injuries among soccer players, which constitutes 12–16% of all injury. Fatigue is claimed to alter the lower limb mechanism during sprinting,...

A comparison of electromyography and stroke kinematics during ergometer and on-water rowing

This study assessed muscle recruitment patterns and stroke kinematics during ergometer and on-water rowing to validate the accuracy of rowing ergometry. Male rowers (n = 10; age 21 ± 2 years, height 1.90 ± 0.05 m and body mass 83.3 ± 4.8 kg) performed 3 × 3 min exercise bouts, at heart and stroke rates equivalent to 75, 85 and 95% V̇O2peak, on both dynamic and stationary rowing ergometers, and on water. During exercise, synchronised data for surface electromyography (EMG) and 2D kinematics were recorded. Overall muscle activity was quantified by the integration of rmsEMG and averaged for each 10% interval of the stroke cycle. Muscle activity significantly increased in rectus femoris (RF) and vastus medialis (VM) (P <0.01), as exercise intensity increased. Comparing EMG data across conditions revealed significantly (P <0.05) greater RF and VM activity during on-water rowing at discrete 10% intervals of stroke cycle. In addition, the drive/recovery ratio was significantly lower during dynamic ergometry compared to on-water (40 ± 1 vs. 44 ± 1% at 95%, P <0.01). Results suggest that significant differences exist while comparing recruitment and kinematic patterns between on-water and ergometer rowing. These differences may be due to altered acceleration and deceleration of moving masses on-ergometer not perfectly simulating the on-water scenario.

Effectiveness of roundhouse kick in elite Taekwondo athletes

The roundhouse kick is a powerful attack in Taekwondo. Most athletes intently perform this kick for scoring in competition. Therefore, kinematic and kinetic analyzes of this kick were the topics of interest; however, they were separately investigated and rarely recorded for impact force. Our objectives were to investigate knee and ankle joint kinematics and electromyographic (EMG) activity of leg muscle and compare them between high-impact (HI) and low-impact (LO) kicks. Sixteen male black-belt Taekwondo athletes performed five roundhouse kicks at their maximal effort. Electrogoniometer sensors measured angular motions of ankle and knee joints. Surface EMG activities were recorded for tibialis anterior, gastrocnemius medialis, rectus femoris, and biceps femoris muscles. Based on maximal impact forces, the athletes were classified into HI and LO groups. All athletes in both groups showed greater activation of rectus femoris than other muscles. The HI group only showed significantly less plantarflexion angles than the LO group during preimpact and impact phases (P<0.05). During the impact phase, the HI group demonstrated significantly greater biceps femoris activation than the LO group (P<0.05). In conclusion, rectus femoris activation could predominantly contribute to the powerful roundhouse kicks. Moreover, high biceps femoris co-activation and optimal angle of ankle plantarflexion of about 35° could help achieve the high impact force.

Stiff-knee gait in cerebral palsy: How do patients adapt to uneven ground?

Patients with cerebral palsy frequently experience foot dragging and tripping during walking due to reduced toe clearance mostly caused by a lack of adequate knee flexion in swing (stiff-knee gait). The aim of this study was to investigate adaptive mechanism to an uneven surface in stiff-knee walkers with cerebral palsy. Sixteen patients with bilateral cerebral palsy, GMFCS I–II and stiff-knee gait, mean age 14.1 (SD=6.2) years, were compared to 13 healthy controls with mean age 13.5 (SD=4.8) years. Gait analysis including EMG was performed under even and uneven surface conditions. Similar strategies to improve leg clearance were found in patients as well as in controls. Both adapted with significantly reduced speed and cadence, increased outward foot rotation, knee and hip flexion as well as anterior pelvic tilt. Therefore cerebral palsy and stiff-knee gait did not affect the adaptation capacity on the uneven surface.On the uneven surface an average increase in knee flexion of 7° (SD=3°) and 12° (SD=5°) was observed in controls and patients with cerebral palsy, respectively. Although rectus femoris activity was increased in patients with cerebral palsy, they were able to increase their knee flexion during swing. The results of this study suggest that walking on uneven surface has the potential to improve knee flexion in stiff-knee walkers. Therefore training on uneven surface could be used as a conservative treatment regime alone, in combination with Botulinum neurotoxin or in the rehabilitation of surgery.

Isometric contraction of an upper extremity and its effects on the contralateral lower extremity.

[Purpose] The aim of this study was to examine effects of the isometric contraction of an upper limb in a supine position on the muscle activity of a healthy adult in the contralateral lower limb. [Subjects] The subjects were 40 healthy adults (35 males and 5 females). [Methods] The muscle activity of the rectus femoris (RF), biceps femoris, anterior tibialis, and medial gastrocnemius (MG) of the contralateral lower limb was measured using electromyography while the subjects flexed, extended, abducted, and adducted the shoulder joint of an upper limb. [Results] The muscle activity of the RF of the contralateral lower limb was significantly high when the subject flexed the shoulder joint of an upper limb, and the muscle activity of the MG of the contralateral lower limb was significantly high when the subject adducted the shoulder joint of an upper limb. [Conclusion] The isometric contraction that results from flexion and adduction of the shoulder joint of an upper limb in a supine position is considered to selectively affect the RF and MG activity of the contralateral lower limb.

The Effects of Eccentric Training on Electromyographic Activity and Performance in Soccer Players

The purpose of the present study was to investigate the effects of eccentric training using a multi-joint dynamometer, on the electromyographic activity of rectus femoris, biceps femoris and medial gastrocnemius during counter movement jumps, drop jumps as well as during maximal eccentric actions. Sixteen amateur soccer players was divided into equal sized groups, the control group who participated in their regular training and the training group who performed 16 sessions (in 8 weeks) of eccentric exercise using a multi joint isokinetic dynamometer. The performance of counter movement and drop jumps were evaluated on a force plate. Additionally, maximal isometric, concentric and eccentric force were assessed on the isokinetic dynamometer. After the eccentric training, the electromyographic activity during the concentric phase of counter movement jumps was found to be increased in rectus femoris (p<0.05) and reduced in biceps femoris (p<0.05). During drop jumps, electromyographic activity of the experimental group found to be increased in the pre-activation phase of gastrocnemius (p<0.05). Additionally, during the takeoff phase of the drop jumps smaller angles for hip and ankle joints were observed (p<0.05). Finally, the electromyographic activity during eccentric strength evaluation were found to be elevated in rectus femoris (p<0.05) and decreased in gastrocnemius (p<0.05). The eccentric training which can cause neural adaptations, faster recruitment of motor units as well as changes in the architecture in muscle tendon system may also cause the alterations in electromyographic activity of leg muscles as observed in the present investigation.

Effects of the Indoor Horseback Riding Exercise on Electromyographic Activity and Balance in One-leg Standing.

[Purpose] This study investigated the influence of the indoor horseback riding exercise on the electromyographic activity of the lower extremity and balance during one-leg standing. [Subjects] Twenty normal adults were divided into an indoor horseback riding exercise group (IHREG, n=10), which performed the indoor horseback riding exercise using equipment 3 times a week for 3 weeks, and a control group (CG, n=10), which performed no exercise. [Methods] For comparitive analysis, an electromyographic test was performed to measure the electromyographic activities of the rectus femoris (RF), adductor longus (AL), and gluteus medius and the Biodex Balance System was used to measure the anteroposterior stability index (APSI), mediolateral stability index, and overall stability index (OSI). [Results] The electromyographic activities of RF and AL significantly increased and the balance abilities of APSI and OSI decreased significantly in the IHREG compared to the CG. [Conclusion] We consider indoor horseback riding exercise is an effective intervention for increasing electromyographic activities of the RF and AL, and the balance abilities of APSI and OSI of normal adults.

Relationship between neuromuscular fatigue and spasticity in chronic stroke patients: A pilot study

IntroductionThe aim of this study was to assess the effects of neuromuscular fatigue on stretch reflex-related torque and electromyographic activity of spastic knee extensor muscles in hemiplegic patients. The second aim was to characterize the time course of quadriceps muscle fatigue during repetitive concentric contractions. MethodsEighteen patients performed passive, isometric and concentric isokinetic evaluations before and after a fatigue protocol using an isokinetic dynamometer. Voluntary strength and spasticity were evaluated following the simultaneous recording of torque and electromyographic activity of rectus femoris (RF), vastus lateralis (VL) and biceps femoris (BF). ResultsIsometric knee extension torque and the root mean square (RMS) value of VL decreased in the fatigued state. During the fatigue protocol, the normalized peak torque decreased whereas the RMS of RF and BF increased between the first five and last five contractions. There was a linear decrease in the neuromuscular efficiency-repetitions relationships for RF and VL. The peak resistive torque and the normalized RMS of RF and VL during passive stretching movements were not modified by the fatigue protocol for any stretch velocity. DiscussionThis study showed that localized quadriceps muscle fatigue caused a decrease in voluntary strength which did not modify spasticity intensity. Changes in the distribution of muscle fiber type, with a greater number of slow fibers on the paretic side, may explain why the stretch reflex was not affected by fatigue.

Static vs. Dynamic Acute Stretching Effect on Quadriceps Muscle Activity during Soccer Instep Kicking

The purpose of this study was to compare the effects of static and dynamic stretching on quadriceps muscle activation during maximal soccer instep kicking. The kicking motion of twelve male college soccer players (body height: 174.66 ± 5.01 cm; body mass: 72.83 ± 4.83 kg; age: 18.83 ± 0.75 years) was captured using six synchronized high-speed infra-red cameras whilst electromyography (EMG) signals from vastus medialis (VM), lateralis (VL) and rectus femoris (RF) were recorded before and after static or dynamic stretching. Analysis of variance designs showed a higher increase in knee extension angular velocity (9.65% vs. −1.45%, p < 0.001), RF (37.5% vs. −8.33%, p < 0.001), VM (12% vs. −12%, p < 0.018), and VL EMG activity (20% vs. −6.67%, p < 0.001) after dynamic stretching exercises. Based on these results, it could be suggested that dynamic stretching is probably more effective in increasing quadriceps muscle activity and knee extension angular velocity during the final swing phase of a maximal soccer instep kick than static stretching.

Timing of Muscle Response to a Sudden Leg Perturbation: Comparison between Adolescents and Adults with Down Syndrome

Movement disturbances associated with Down syndrome reduce mechanical stability, worsening the execution of important tasks such as walking and upright standing. To compensate these deficits, persons with Down syndrome increase joint stability modulating the level of activation of single muscles or producing an agonist-antagonist co-activation. Such activations are also observed when a relaxed, extended leg is suddenly released and left to oscillate passively under the influence of gravity (Wartenberg test). In this case, the Rectus femoris of adults with Down syndrome displayed peaks of activation after the onset of the first leg flexion. With the aim to verify if these muscular reactions were acquired during the development time and to find evidences useful to give them a functional explanation, we used the Wartenberg test to compare the knee joint kinematics and the surface electromyography of the Rectus femoris and Biceps femoris caput longus between adolescents and adults with Down syndrome. During the first leg flexion, adolescents and adults showed single Rectus femoris activations while, a restricted number of participants exhibited agonist-antagonist co-activations. However, regardless the pattern of activation, adults initiated the muscle activity significantly later than adolescents. Although most of the mechanical parameters and the total movement variability were similar in the two groups, the onset of the Rectus femoris activation was well correlated with the time of the minimum acceleration variability. Thus, in adolescents the maximum mechanical stability occurred short after the onset of the leg fall, while adults reached their best joint stability late during the first flexion. These results suggest that between the adolescence and adulthood, persons with Down syndrome explore a temporal window to select an appropriate timing of muscle activation to overcome their inherent mechanical instability.

Gait impairment in cervical spondylotic myelopathy: analysis of muscle activation timing

Introduction:Gait impairment is aprimary symptomof cervical spondylotic myelopathy (CSM). Analysis of the timing of muscle activation during gait, using surface electromyography (SEMG), can improve the understanding of a gait deficit. The aim of this study was to comparemuscle activation timing during gait in peoplewith untreated CSM and in ageand gendermatched healthy controls. Patients/Materials and Methods: Ethical approval was obtained from a hospital Ethics Committee. Sixteen people with untreated CSM were recruited consecutively from a neurosurgery clinic, and matched to healthy controls of the same age (±5 years) and gender. Participants from both groups completed at least ten walking trials at comfortable gait speed along a 10-metrewalkway. Healthy controls then completed a second set of ten walking trials at the same speed as the CSM participants to whom they were matched. SEMG signals were recorded during gait from rectus femoris, biceps femoris, tibialis anterior andmedial gastrocnemius using standard electrode recording and placement procedures. Signals were processed using MATLAB® and the timing of activation was extracted using a previously validated reliable method [1]. The duration of activation for each muscle was expressed as a percentage of gait cycle time. Data for CSM participants and healthy controls were compared using paired t-tests. Results: The mean comfortable walking speed of CSM participants was 1.12m/s, while healthy controls walked at a mean of 1.49m/s. Comparing both groups at comfortable walking speed, CSM participants demonstrated significantly prolonged activation of rectus femoris (33% gait cycle duration compared to 22% in healthy controls, p=0.04), biceps femoris (32% vs 22%, p=0.001) and tibialis anterior (42% vs 30%, p=0.007), but not medial gastrocnemius (32% vs 29%, p=0.4). Co-activation of rectus and biceps femoris was also prolonged in CSM (14% vs 9%, p=0.04). No differences were found in the co-activation time of tibialis anterior and medial gastrocnemius (7% vs 4%, p=0.17). The results of the matchedspeedanalysismirrored thefindingsat comfortable speed, with the samemuscles showing statistically significant differences between CSM participants and controls. Discussion and conclusions: This study was the first to identify andquantify abnormallyprolongeddurationof activationof the lower limb muscles as a feature of gait in CSM. The persistence of thesefindings atmatchedgait speed confirmed that thesewere features of abnormal neuromuscular control, andnot a consequence of slower gait speed. Prolonged duration of activation may be a strategy to compensate for lack of stability or weakness of lower limb muscles during gait. Reference

The effects of closed and open kinetic chain exercises on lower limb muscle activity and balance in stroke survivors

The major contributors to physical disability after stroke are the negative impairments related to loss of functional ability and muscle strength. The aim of this study was to examine the effects of close kinetic chain (CKC) exercise and open kinetic chain (OKC) exercise on muscle activation of the paretic lower limb and balance in chronic stroke subjects. Thirty-three patients with chronic stroke of over 6 months were enrolled. They were randomly allocated to three groups: CKC exercise group (n = 11), OKC exercise group (n = 11), and control group (n = 11). CKC and OKC exercise groups were trained 5 times per week for 6 weeks. The control group maintained routine activities and did not participate in any regular exercise program. All subjects were measured on muscle activation of the paretic lower limb and balance. Muscle activation of rectus femoris (RF) and biceps femoris (BF) was significantly increased in both CKC exercise and OKC exercise groups, compared to the control group. However, muscle activation of gastrocnemius (GC) and tibialis anterior (TA) was significantly increased in only the CKC exercise group. Antero-posterior (A-P) andmedio-lateral (M-L) sway velocities (both with EO and EC) were decreased with the application of CKC exercise. These findings indicate that the CKC exercise can improve lower limb muscle strength, and balance in chronic stroke, and it may carry over into an improvement in functional performance.

Influence of wearing an unstable shoe construction on compensatory control of posture

This study investigated the influence of wearing unstable shoe construction (WUS) on compensatory postural adjustments (CPA) associated with external perturbations. Thirty-two subjects stood on a force platform resisting an anterior-posterior horizontal force applied to a pelvic belt via a cable, which was suddenly released. They stood under two conditions: barefoot and WUS. The electromyographic (EMG) activity of gastrocnemius medialis, tibialis anterior, rectus femoris, biceps femoris, rectus abdominis, and erector spinae muscles and the center of pressure (CoP) displacement were acquired to study CPA. The EMG signal was used to assess individual muscle activity and latency, antagonist co-activation and reciprocal activation at joint and muscle group levels. Compared to barefoot, WUS led to: (1) increased gastrocnemius medialis activity, (2) increased total agonist activity, (3) decreased antagonist co-activation at the ankle joint and muscle group levels, (4) increased reciprocal activation at the ankle joint and muscle group levels, and (5) decrease in all muscle latencies. No differences were observed in CoP displacement between conditions. These findings demonstrate that WUS led to a reorganization of the postural control system associated to improved performance of some components of postural control responses.

The Effect of Squat Depth on Multiarticular Muscle Activation in Collegiate Cross-Country Runners

The squat is a closed-chain lower body exercise commonly performed by many athletes. Muscle activity has been examined during partial and parallel squats in male weightlifters, but not in male and female runners. Therefore, this study measured muscle activity with surface electromyography (EMG) during partial and parallel squats in 20 Division I collegiate cross-country runners (10 males and 10 females) in a randomized crossover design. We hypothesized the parallel squat would increase extensor muscle activitation (i.e. hamstrings and erector spinae). Furthermore, we sought to determine if changes in muscle activity were different between males and females. Participants performed 6 repetitions using their 10 repetition maximum loads for each condition during EMG testing. EMG was performed on the right rectus femoris, biceps femoris, lumbar erector spinae, and lateral head of the gastrocnemius. Rectus femoris activity (0.18 ± 0.01 vs. 0.14 ± 0.01 mV) and erector spinae activity (0.16 ± 0.01 vs. 0.13 ± 0.01 mV) were significantly higher (p < 0.05) during the parallel squat than during the partial squat condition. This increase in muscle activity may be attributed to greater ranges of motion at the hip and knee joints. Biceps femoris and gastrocnemius activity were similar between conditions. No significant differences existed between males and females (squat condition × gender; p > 0.05). During preliminary isokinetic testing, both male and female runners demonstrated deficient hamstrings-to-quadriceps ratios, which would not likely improve by performing parallel squats based on our EMG findings. Despite the reduced load of the parallel squat, rectus femoris and erector spinae activity were elevated. Thus, parallel squats may help runners to train muscles vital for uphill running and correct posture, while preventing injury by using lighter weights through a larger range of motion.

Transmission of Whole-Body Vibration and Its Effect on Muscle Activation

The aim of current study was to measure the transmission of whole-body vibration through the entire body and to relate this to body posture and induced muscular activation. Eight clinically healthy subjects performed 3 static body postures-high squat (135°), deep squat (110°), and erect stance, whereas vibration transmission was assessed over a wide range of accelerations (from 0.33 to 7.98 g) and frequencies (from 30 to 50 Hz). To assess the vibration transmission, 9 triaxial accelerometers were attached from the ankle up to the head and the root mean square of acceleration signal of each site-specific body point was calculated. Additionally, muscle activity from 7 lower limb muscles was recorded. The results showed a significant attenuation of the platform accelerations transmitted from the feet to the head. Compared with erect stance, knee bent posture significantly diminished vibration transmission at the hip, spine, and the head (p < 0.05). Vibration transmission to the spine was significantly lower in deep vs. high squat (p < 0.05), suggesting that further knee bending may reduce the risk of overloading the spine. Vibration increased the muscle activity in most leg and hip muscles during both squat postures, although, on average, no clear dose-response relationship between the acceleration and/or frequency and muscle response was found. The muscular activation of vastus medialis and rectus femoris showed clear negative correlation to the vibration transmission at the sternum. The specific vibration parameters used in the present study can be considered as safe and suitable for a training program. Moreover, the present results contribute to optimize the most advantageous whole-body vibration protocol and to determine the beneficial effects on muscle and bone.

Changes in electromyographic activity after botulinum toxin injection of the rectus femoris in patients with hemiparesis walking with a stiff-knee gait

PurposeThis study was designed to evaluate the effects of botulinum toxin type-A (BoNTA) injection of the rectus femoris (RF) muscle on the electromyographic activity of the knee flexor and extensor and on knee and hip kinematics during gait in patients with hemiparesis exhibiting a stiff-knee gait. MethodTwo gait analyses were performed on fourteen patients: before and four weeks after BoNTA injection. Spatiotemporal, kinematic and electromyographic parameters were quantified for the paretic limb. ResultsBoNTA treatment improved gait velocity, stride length and cadence with an increase of knee angular velocity at toe-off and maximal knee flexion in the swing phase. Amplitude and activation time of the RF and co-activation duration between the RF and biceps femoris were significantly decreased. The instantaneous mean frequency of RF was predominantly lower in the pre-swing phase. ConclusionsThe results clearly show that BoNTA modified the EMG amplitude and frequency of the injected muscle (RF) but not of the synergist and antagonist muscles. The reduction in RF activation frequency could be related to increased activity of slow fibers. The frequency analysis of EMG signals during gait appears to be a relevant method for the evaluation of the effects of BoNTA in the injected muscle.