Inter-subject variability in muscle synergies during squatting movements

This study investigated muscle synergies during squats, focusing on the individual variability in motor control strategies. Sixteen healthy young adults performed 20 squats at a consistent speed. Muscle synergies were extracted using non-negative matrix factorization, followed by k-means clustering and discriminant analysis to categorize similar muscle synergies. The analysis revealed an average of 3.3 ± 0.4 muscle synergies per squat. Further clustering analysis identified six distinct types of muscle synergies across subjects. Among them, one synergy involving trunk, hip, and knee extensors was universal across all subjects, representing a fundamental motor strategy for successful squat execution. In contrast, the remaining synergies varied across subjects, exhibiting mutual exclusivity, where individuals systematically select one synergy type or another during the same squatting phase. These findings demonstrate inter-subject variability in muscle synergies during the squat and underscore the coexistence of universal and individualized muscle synergies in human motor control, providing practical insights for designing personalized squat training and rehabilitation strategies guided by neuromechanical principles.

Effects of Step Length and Stride Variation During Forward Lunges on Lower-Extremity Muscle Activity

BACKGROUND

The forward lunge is a closed-chain weight-bearing multi-joint exercise simulating the activities of daily living, such as walking or stair climbing, which mainly activates hip, knee, and ankle musculature and is also used by athletes and other individuals to train lower-extremity musculature.

OBJECTIVES

The purpose of this study is to compare lower-extremity muscle recruitment patterns between stride and step length variations in forward lunges.

METHODS

Twenty participants had a mean (±SD) age, mass, and height of 26 ± 6 y, 79 ± 8 kg, and 176 ± 7 cm, respectively, for males, and 27 ± 4 y, 62 ± 6 kg, and 161 ± 7 cm, respectively, for females. All participants used their 12-repetition maximum weight while performing a short step and long step forward lunge with a stride (striding forward and pushing back to the starting position) and without a stride (lunging up and down with feet stationary). During each lunge variation, surface electromyography (EMG) data were collected from the quadriceps, hamstrings, gastrocnemius, hip adductors, gluteus maximus, and gluteus medius muscles, and then normalized as a percent of each muscle's maximum voluntary isometric contraction. A repeated measures two-way analysis of variance was employed (p < 0.01), with step length and stride comprising the two factors.

RESULTS

The following had no significant interactions: (1) quadriceps, hamstrings, gastrocnemius, hip adductor, and gluteus maximus EMG activities were significantly greater in lunges with a long step compared to lunges with a short step; and (2) gluteus maximus and gluteus medius EMG activities were significantly greater in lunges with a stride compared to lunges without a stride. The following had significant interactions: (1) gluteus medius EMG activities were significantly greater in lunges with a long step with and without a stride compared to lunges with a short step with and without a stride; (2) quadriceps EMG activities were generally significantly greater in lunges with long and short steps with a stride compared to lunges with long and short steps without a stride, in lunges with a long step with a stride compared to lunges with a short step with a stride, and in lunges with a short step without a stride compared to lunges with a long step without a stride; (3) hamstring and hip adductor EMG activities were significantly greater in lunges with a long step with a stride compared to lunges with a long step without a stride, and in lunges with a long step with and without a stride compared to lunges with a short step with and without a stride; and (4) gastrocnemius EMG activities were significantly greater in lunges with a long step with and without a stride compared to lunges with a short step with and without a stride.

CONCLUSIONS

Lower-extremity muscle activity is generally greater in forward lunges with a long step compared to a short step, and greater in lunges with a stride compared to without a stride. During the externally loaded forward lunge, high to very high muscle activity occurs in the quadriceps, gluteus maximus, and gluteus medius, thus enhancing muscle hypertrophy and strength in these muscles, while moderate muscle activity occurs in the hamstrings, gastrocnemius, and adductor longus.

Is it truly impossible to strengthen the vastus medialis in isolation from the entire quadriceps muscle group?

Background

To date, no specific exercises have been designed to selectively strengthen the vastus medialis muscle. Therefore, the purpose of this research is to provide a clear answer to the question: Is it truly impossible to strengthen the vastus medialis independently of the entire quadriceps muscle group? Methods: Thirty-three females with lateral patellar compression syndrome were randomly divided into 2 groups: one focused on selective strengthening of the vastus medialis (n = 16) and the other on general strengthening of the quadriceps (n = 17). The intervention lasted 8 weeks. Muscles cross-sectional area and electrical activity were assessed using ultrasound and electromyography, respectively. Data analysis was done using independent and dependent t-tests.

Results

In the selective strengthening group, significant increases were observed in the activity and cross-sectional area of the vastus medialis, as well as in the ratios of vastus medialis/vastus lateralis activity and cross-section from pre-to post-intervention (P < 0.01). In the general strengthening group, significant increases were noted in the cross-sectional area of the vastus lateralis and the activity of both muscles, with a greater increase in the vastus lateralis (P < 0.01).

Conclusions

Contrary to previous evidence, our findings demonstrate that preferential activation and selective strengthening of the vastus medialis muscle, independent of the other quadriceps components, is achievable through the training protocol employed in this study.

Evaluating the Association Between Vastus Medialis Oblique Characteristics and Patellar Instability: A Comprehensive Case-Control Study

BACKGROUND

The contribution of vastus medialis oblique muscle (VMO) weakness or dysfunction to patellofemoral pain syndrome is well recognized, yet its role in lateral patellar instability and recurrent patellar dislocations remains unclear. This study investigates the association between VMO characteristics and patellar instability.

HYPOTHESIS

Altered VMO structure, characterized by differences in muscle elevation and cross-sectional area (CSA), is associated with patellar instability.

STUDY DESIGN

A case-control study.

LEVEL OF EVIDENCE

Level 3.

METHODS

The study included 204 participants, matched on a 1:1 ratio by age and sex, from a local hospital registry from 2005 to 2020. VMO measurements were taken via magnetic resonance imaging, and included muscle elevation, CSA, fiber angulation, and CSA-to-thigh circumference ratio. Univariate analysis, and multivariable regression model with adjustment for potential confounders were constructed. In addition, a secondary analysis was performed to evaluate the variations in VMO characteristics and mass across primary and recurrent patellar instability groups.

RESULTS

Patients with patellar instability demonstrated significant differences in VMO characteristics compared with controls, including increased muscle elevation (13 mm vs 5.9 mm; P < 0.01), increased muscle fiber angulation (42.5° vs 35.3°; P < 0.01), reduced CSA (716 mm2 vs 902 mm2; P < 0.01), and a lower CSA-to-thigh circumference ratio (0.05 vs 0.07; P < 0.01). These findings remained significant in the multivariable adjusted model. Moreover, the secondary analysis revealed that both primary and recurrent instability patients had similar VMO characteristics alterations compared with controls, with slightly more pronounced reductions in VMO CSA in those sustaining recurrent instability episodes.

CONCLUSION

This study confirms a statistically significant association between altered VMO characteristics and patellar instability, emphasizing the importance of considering VMO characteristics in the evaluation and management of patients with patellar instability.

Hip and knee muscles co-activation ratio during hip-focused exercises: a multichannel surface electromyography study

This study aimed to evaluate the muscle activation ratio of hip and knee during hip-focused exercises. Eleven active university students performed 13 hip-focused exercises frequently used in the treatment of knee disorders. The average sEMG amplitude of tensor fasciae latae (TFL), gluteus medius (GMed), gluteus maximus (GMax), adductor longus (AL), vastus medialis (VM), vastus lateralis (VL), and GMed/AL, GMax/AL, and VL/VM ratios were determined. Repeated-measures analyses of variance were performed to determine if there were differences in muscle activation while performing each of the 13 exercises. Sidelying clam-shell had the highest GMax/AL ratio of all the exercises examined. The hip hike exercise (5.36) had the highest GMed/AL ratio. The VL/VM ratio ranged from 0.77 to 1.16. Based on these results, sidelying clam-shell had the highest GMax/AL ratio. The hip hike exercise had a higher GMed/AL ratio compared to other hip-focused exercises. Additionally, forward lunge, squat, and single-leg squat with resistance band around the knee had the highest activity VL/VM ratio among exercises.

Evaluation of the results of closed kinetic chain exercises applied in the conservative treatment of patellofemoral pain syndrome by means of shear wave elastography: A randomized controlled trial

PURPOSE

Non-selective closed kinetic chain exercises (NSKCE) and or selective closed kinetic chain exercises (SCKCE) has been shown to increase Vastus medialis obliquus (VMO) muscle power in patellofemoral pain syndrome (PFPS). However, the superiority of the exercises to each other has not been shown. This study aimed to evaluating the effects of different exercises on the stiffness of the VMO and vastus lateralis (VL) muscles, pain management, functional scores, and thigh circumferences.

METHODS

One hundred 60 knees of 80 patients followed up in our outpatient clinic between December 2016 and February 2018 were included in the study. Patients were divided into two groups as 40 patients with single-sided PFPS (20 male and 20 female patients) and 40 healthy controls (20 male and 20 female patients). The patients in each group were divided into subgroups according to NSCKCE or SCKCE. VMO and VL muscles were measured by shear wave elastography (SWE) before and after a 6-weeks therapy.

RESULTS

There was a significant decrease in Visual Analog Scale (VAS) score while a significant increase was found in Lysholm Knee Scale (LKS), however, no statistically difference was found between the two exercise groups in PFPS patients. The effect of both exercises on pain and functional improvement was similar.

CONCLUSION

Decrease in VAS scores, increase in LKS scores, increase in thigh circumference measurements, and increase in the stiffness of VMO and VL muscles were observed in both groups who received SCKCE and NSCKCE on PFPS patients.

TRIAL REGISTRATION

Study registered at ClinicalTrials.gov (registration number: NCT05427357).

DESIGN

Randomized controlled trial.

Neuromuscular control strategies of the lower limb during a typical Tai Chi brush knee and twist step in practitioners with and without knee pain: a pilot study

As a complex movement, Tai Chi (TC) could be challenging for knee control, and the compensatory changes in TC biomechanics of knee pain patients are unknown. The Brush Knee and Twist Step (BKTS) is a typical TC movement that involves basic leg motion repeated in the whole TC. This pilot study examined electromyography and retro-reflective marker trajectory data to investigate neuromuscular control strategies of the lower extremity during BKTS in TC practitioners with and without knee pain. Twelve experienced TC practitioners with (n = 6) and without knee pain (n = 6) participated. Our results revealed that knee pain practitioners presented muscle imbalance in the vastus medialis-vastus lateralis and vastus lateralis-biceps femoris, and poor alignment of the knee with the toes in TC lunge. Additionally, they adaptively developed rigid coordination strategies, showing higher levels of lower limb muscle co-contraction and activity compared to controls. Training programs for TC practitioners with knee pain should be designed to modify both abnormal muscle synergy patterns and incorrect lunge during TC, which may improve exercise safety.

Effects of differences in femoral anteversion and hip flexion angle on hip abductor muscles activity during clam exercise in females

This study aimed to determine differences in the hip abductor muscle activity during clam exercise at different hip flexion and femoral anteversion angles. Thirty healthy females were divided into two groups based on the femoral anteversion angle: the excessive femoral anteversion group and the normal group. Clam exercise was performed at three different hip flexion angles (60°, 45°, and 30°). Tensor fascia latae, gluteus medius, and superior portion of gluteus maximus activities were measured during the exercise, and the results were normalized to the activity during maximum voluntary isometric contraction to calculate the gluteal-to-tensor fascia latae muscle activation index. The superior portion of gluteus maximus activities at a hip flexion of 60° and 45° were greater than that at 30°. The excessive femoral anteversion group had a lower gluteal-to-tensor fascia latae muscle activation index than the normal group; the gluteal-to-tensor fascia latae muscle activation index for hip flexion at 60° was higher than that at 45°, and the gluteal-to-tensor fascia latae muscle activation index for hip flexion at 60° and 45° were higher than that at 30°. Therefore, the femoral anteversion angle and hip joint position were related to the activity of the hip abductor muscles during clam exercise. These findings may provide a rationale for instructing exercises to maximize the activity of the hip abductor muscles in individuals with an excessive femoral anteversion angle.

Female Lower Body Muscle Forces: A Musculoskeletal Modeling Comparison of Back Squats, Split Squats and Good Mornings

The aim of this study was to analyze lower leg muscle forces during strength exercises such as back squats, good mornings and split squats, with a particular emphasis on females. By focusing on females, who are more vulnerable to anterior cruciate ligament injuries, we aimed to better understand muscle engagement and its role in injury prevention. Eight participants were monitored during exercises with a barbell load of 25% of body weight and, during the back squat, an additional 50% load. The analysis was conducted using personalized musculoskeletal models, electromyography (EMG) and Vicon motion capture systems to assess various muscle groups, including the m. gluteus maximus and m. gluteus medius, as well as the hamstring and quadriceps muscles. The back squat produced the highest forces for the quadriceps muscles, particularly the rectus femoris (>25 N/kg), as well as in the back leg during the split squat (>15 N/kg). The gluteal muscles were most active during good mornings and in the front leg of the split squat, especially the m. gluteus maximus medial part (>20 N/kg). The hamstrings generated the highest muscle forces in the front leg of the split squat, with the greatest forces observed in the m. semimembranosus. Our research highlights how musculoskeletal modeling helps us to understand the relationship among muscles, joint angles and anterior cruciate ligament injury risks, especially in strength training females. The results emphasize the need for personalized exercise guidance and customized models to make strength training safer and more effective.

Effects of step lengths on biomechanical characteristics of lower extremity during split squat movement

Objective: To quantify the effects of increasing the step length of the split squat on changes in kinematics, kinetics, and muscle activation of the lower extremity. Methods: Twenty male college students participated in the test (age: 23.9 ± 3.7, height: 175.1 ± 4.9). Data on kinematics, kinetics, and EMG were collected during split squat exercise at four different step lengths in a non-systematic manner. One-way repeated measurements ANOVA were used to compare characteristic variables of peak angle, moment, and RMS among the four step length conditions. Results: The step length significantly changes the peak angles of the hip (p = 0.011), knee (p = 0.001), ankle (p < 0.001) joint, and the peak extension moment of the hip (p < 0.001), knee (p = 0.002) joint, but does not affect the ankle peak extension moment (p = 0.357) during a split squat. Moreover, a significant difference was observed in the EMG of gluteus maximus (p < 0.001), vastus medialis (p = 0.013), vastus lateralis (p = 0.020), biceps femoris (p = 0.003), Semitendinosus (p < 0.001), medialis gastrocnemius (p = 0.035) and lateralis gastrocnemius (p = 0.005) during four step lengths, but no difference in rectus femoris (p = 0.16). Conclusion: Increases in step length of split squat had a greater activation on the hip extensor muscles while having a limited impact on the knee extensor muscles. The ROM, joint moment, and muscle activation of the lead limb in the split squat all should be considered in cases of individual preventative or rehabilitative prescription of the exercise. Moreover, the optimal step length for strength training in healthy adults appears to be more suitable when it is equal to the length of the individual lower extremity.

Minimally invasive small incision surgical technique for unicompartmental knee arthroplasty

PURPOSE

It is always a challenge for orthopaedic surgeons to minimise surgical incisions while ensuring excellent surgical results. We propose the minimally invasive small incision (MISI) technique and an extramedullary positioning technique in the unicompartmental knee arthroplasty (UKA) surgery. This study aimed to clarify the early postoperative clinical outcomes and component alignment between MISI and conventional minimally invasive surgical (MIS) techniques.

METHODS

We prospectively enrolled 60 patients who underwent MISI-UKA and 60 patients who underwent MIS-UKA as controls. Clinical parameters include the time of straight leg raising, postoperative walking time with walker assistance, hospital stay, Numerical Rating Scale (NRS) pain score and Knee Society Score (KSS). The postoperative components and lower extremity alignment were compared between the two groups with radiographic image measurement.

RESULTS

The MISI group obtained a smaller incision during knee extension (P < 0.001) but a longer tourniquet usage time than the MIS group. The MISI group lost less blood (P < 0.001). The MISI group achieved straight leg raising and walking with aid earlier after surgery, with a shorter hospital stay than the MIS group (P < 0.001). Range of motion (ROM), NRS and KSS scores revealed no significant difference between the two groups in six months postoperative follow-up (P > 0.05). Radiographic measurement results between the two groups revealed no statistical difference (P > 0.05) CONCLUSION: The MISI-UKA could achieve faster earlier recovery after surgery and shorter hospital stays without compromising the principles of proper prosthesis position and limb alignment compared with the conventional MIS-UKA.

Biomechanical effects of exercise fatigue on the lower limbs of men during the forward lunge

Background: During competition and training, exercises involving the lungs may occur throughout the sport, and fatigue is a major injury risk factor in sport, before and after fatigue studies of changes in the lungs are relatively sparse. This study is to investigate into how fatigue affects the lower limb's biomechanics during a forward lunge. Methods: 15 healthy young men participate in this study before and after to exposed to a fatigue protocol then we tested the forward lunge to obtain kinematic, kinetic changing during the task, and to estimate the corresponding muscles' strength changes in the hip, knee, and ankle joints. The measurement data before and after the fatigue protocol were compared with paired samples t-test. Results: In the sagittal and horizontal planes of the hip and knee joints, in both, the peak angles and joint range of motion (ROM) increased, whereas the moments in the sagittal plane of the knee joint smaller. The ankle joint's maximum angle smaller after fatigue. Peak vertical ground reaction force (vGRF) and peak contact both significantly smaller after completing the fatigue protocol and the quadriceps mean and maximum muscular strength significantly increased. Conclusion: After completing a fatigue protocol during lunge the hip, knee, and ankle joints become less stable in both sagittal and horizontal planes, hip and knee range of motion becomes greater. The quadriceps muscles are more susceptible to fatigue and reduced muscle force. Trainers should focus more on the thigh muscle groups.

Effect of Adding Kinesio Taping to Exercise Therapy in the Treatment of Patellofemoral Pain Syndrome

Background and objectives: Patellar taping has been widely used for the primary or adjunctive treatment of patellofemoral pain syndrome (PFPS); however, there are limited data in terms of functional outcomes. This study aimed to investigate whether there is any beneficial effect of adding Kinesio Taping^® (KT) to exercise therapy in the treatment of PFPS. Materials and Methods: Twenty patients (27.5 ± 5.4 years) with PFPS who applied KT and 19 patients (27.3 ± 7.4 years) who did not were included in this study. Quadriceps muscle strength and acceleration time (AT) were assessed using an isokinetic device. Patient-reported outcomes were evaluated using the Kujala anterior knee pain scale (AKPS). Both groups underwent one-month exercise therapy. Results: There was no significant difference in quadriceps strength, AT, and AKPS at baseline and at 1 month between the taping and non-taping groups (p > 0.05). However, for quadriceps muscle strength, the effect of time*group interaction was statistically significant (F(1.37) = 4.543, p < 0.05, partial eta squared 0.109), showing that improvement in the quadriceps strength was higher in the non-taping group than that in the taping group. Conclusions: Adding KT to exercise therapy did not elicit extra benefits in quadriceps muscle strength and AT, and AKPS among PFPS with abnormal patellar tracking at one month.

Change of the cross-sectional area of vastus medialis oblique in patients with recurrent patellar dislocation treated by tibial tubercle transfer combined with medial patellofemoral ligament reconstruction on axial CT

PURPOSE

To investigate the change of the cross-sectional area (CSA) of vastus medialis oblique (VMO) in patients with recurrent patellar dislocation (RPD) treated by tibial tubercle transfer combined with medial patellofemoral ligament (MPFL) reconstruction by imaging methods, and to guide clinical treatment and rehabilitation.

METHODS

From October 2015 to March 2022, 23 patients with RPD who underwent tibial tubercle transfer combined with MPFL reconstruction were retrospectively enrolled. All patients were assessed by CT in the supine position with the knee fully extended and the quadriceps relaxed. The CSA of VMO and the ratio of CSA of VMO to body weight (CSA/BW) were measured at the upper pole of the patella, 5 mm above the upper pole of the patella and 5 mm below the upper pole of patella. The differences of measured parameters were compared before surgery and at follow-up, including CSA of VMO and CSA/BW. Test level α = 0.05.

RESULTS

The tibial tubercle-trochlear groove (TT-TG) distance was significantly reduced at follow-up compared with that before surgery (27.91 ± 1.95 mm vs 12.33 ± 1.07 mm, P < 0.001). The CSA of VMO was significantly increased at follow-up compared with that before surgery at 5 mm below the upper pole of the patella (473.06 ± 106.32 mm² vs 562.97 ± 157.90 mm², P < 0.001), at the upper pole of the patella (641.23 ± 188.45 mm² vs 700.23 ± 177.55 mm², P = 0.029), and at 5 mm above the upper pole of the patella (788.25 ± 238.62 mm² vs 849.79 ± 180.84 mm², P = 0.018). The CSA/BW was significantly increased at follow-up compared with that before surgery at 5 mm below the upper pole of the patella (7.83 ± 2.52 mm²/kg vs 9.22 ± 3.54 mm²/kg, P < 0.001), at the upper pole of the patella (10.48 ± 3.62 mm²/kg vs 11.42 ± 4.14 mm²/kg, P = 0.020), and at 5 mm above the upper pole of the patella (12.86 ± 4.65 mm²/kg vs 13.68 ± 3.86 mm²/kg, P = 0.017).

CONCLUSION

After tibial tubercle transfer combined with MPFL reconstruction, CSA of VMO increased in patients with RPD, which will help to enhance patellar stability and reduce recurrence.

In vivo kinematic comparison of medial pivot total knee arthroplasty in weight-bearing and non-weight-bearing deep knee bending

BACKGROUND

This study aimed to determine the kinematics of medial pivot total knee arthroplasty by comparing weight-bearing and non-weight-bearing deep knee bending and to evaluate the effect of the weight-bearing state on the kinematics.

METHODS

The kinematics of 19 knees were investigated under fluoroscopy during squatting (weight-bearing) and active-assisted knee bending (non-weight-bearing) using two- to three-dimensional registration technique. Accordingly, range of motion, anteroposterior translation for the medial and lateral low contact points, axial rotation of the femoral component relative to the tibial component and kinematic pathway were evaluated.

FINDINGS

There was no difference in range of motion between the two states. The medial anteroposterior translation showed no significant movement with no anterior translation in both the weight-bearing and non-weight-bearing from 0° to 90° of flexion. Regarding the lateral anteroposterior translation, a posterior translation was observed during weight-bearing, whereas a slight anterior translation from 0° to 30° of flexion and subsequent posterior translation were found in the non-weight-bearing. Femoral external rotation was observed in the weight-bearing, whereas femoral internal rotation was seen from 0° to 30° of flexion and subsequent femoral external rotation was observed in the non-weight-bearing. The kinematic pathway showed medial pivot motion and subsequent bicondylar rollback in the weight-bearing, whereas only medial pivot motion was observed in the non-weight-bearing.

INTERPRETATION

The medial anteroposterior translation of the femur during deep knee bending showed no anterior motion in the two states. The lateral anteroposterior translation and femoral rotation were different in the mid-flexion range between the two states.

Differences in the muscle activities of the quadriceps femoris and hamstrings while performing various squat exercises

Background

Knee injuries in the lower limbs frequently occur, and lower limb muscles need to be strengthened to reduce injuries. Activating muscles can help strengthen muscles.. This study aimed to determine the squat exercises [general squat (GS), wall squat (WS), and Spanish squat (SS)] that effectively increased muscle activity using electromyography (EMG).

Methods

In this cross-sectional study, 22 participants performed three different squat exercises with EMG attached to the rectus femoris (RF), vastus lateralis (VL), vastus medialis, biceps femoris, semitendinosus, and semimembranosus. The Kruskal–Wallis H test was used to compare thigh muscle activities among the various squat exercises.

Results

During SS, RF showed greater muscle activation compared to WS and GS (RF: χ2 = 21.523, p = 0.000, η² = 0.333). VL also showed greater muscle activation during SS compared to WS (VL: χ2 = 7.101, p = 0.029, η² = 0.109).

Conclusions

The results from this study indicate that SS shows more activation in the RF and VL muscles compared to GS and WS. These findings suggest that SS can provide more muscle activation for the RF and VL muscles and will greatly help those who lack muscle activation in these muscles.

Electromyographic examination of knee training using a hybrid assistive limb after anterior cruciate ligament reconstruction: A case report

Muscle co-contraction can result in higher joint contact forces, compromising knee joint mobility for stability, thus leading to impaired lower extremity neuromuscular control, delayed return to sports, and increased incidence of secondary anterior cruciate ligament (ACL) injury post-ACL reconstruction. Hybrid assistive limb (HAL) training has the potential to correct impairment of antagonistic or synergistic muscle movement of the knee joint through bioelectric signal feedback from muscle signals with computer processing. We considered that HAL training would contribute to improve peak muscle torque through coordinating or decreasing higher levels of muscle co-contractions and reducing differences between hamstring and quadriceps muscle activity on electromyography (EMG). While playing handball, a 20-year-old female injured her ACL upon landing on one leg. Two months post-injury, she underwent arthroscopic, anatomic single-bundle ACL reconstruction with a semitendinosus tendon autograft. At a 4-month follow-up, she underwent knee HAL training, which was performed once a week for three sessions. EMG data were collected during the evaluations of pre- and post-HAL training. The average muscle amplitude was used to calculate the difference between vastus lateralis (VL) and semitendinosus (ST) muscles, and the muscle co-contraction index (CCI). The CCI reflects the simultaneous activation of antagonistic muscles, which is determined for knee extensor-flexor muscle pairs. Post-knee HAL training, the CCI of the lateral hamstring and quadriceps muscles during extension was lower than that during pre-HAL training in all sessions. However, no differences were found in the CCI for the medial hamstring and quadriceps muscles during extension and flexion pre- and post-knee HAL training. For post-knee HAL training, the difference between VL and ST EMG data during a closed-chain squat was lower than that during pre-HAL training in all sessions. Knee HAL training contributed to improved peak muscle torque through coordinating or decreasing higher levels of muscle co-contractions, and it reduced differences between hamstring and quadriceps muscle activity in the ACL reconstructed leg as depicted by EMG.

Active heel-slide exercise therapy facilitates the functional and proprioceptive enhancement following total knee arthroplasty compared to continuous passive motion

PURPOSE

The aim was to compare active heel-slide exercise (AHSE) + standard physiotherapy (PT) to continuous passive motion (CPM) + standard PT during inpatient rehabilitation of total knee arthroplasty (TKA) patients in terms of postoperative outcomes.

METHODS

Patients were randomly assigned into AHSE or CPM groups. Both groups received standard PT (range of motion and strengthening exercises, and ambulation) during hospital stay. Patients were evaluated regarding functional outcomes, knee proprioception, pain intensity, active range of motion, knee circumference, length of hospital stay, time for achieving straight leg raise actively, time for achieving 70° knee flexion.

RESULTS

Groups were similar at baseline (n.s.). At discharge, AHSE group was better in terms of pain intensity (p < 0.001), Hospital for Special Surgery knee score (p = 0.001), rise from sitting (p = 0.015), ascend/descend stairs (p = 0.038), and timed up and go test (p = 0.028) compared to CPM group. AHSE group was able to perform the straight leg raise earlier than CPM group during inpatient period (p = 0.001) and demonstrated improved proprioception at discharge and at 3-month follow-up (p < 0.05). No statistical differences were detected between groups in other evaluation parameters (n.s.).

CONCLUSION

Our findings support AHSE therapy offers a more functional rehabilitation and leads beneficial results for patients following TKA. Therefore, active exercise approach encouraging patients to participate in their rehabilitation should be first choice in acute postoperative rehabilitation following TKA rather than CPM.

LEVEL OF EVIDENCE

II.

Effect of Whole-Body Vibration Training on Muscle Activation for Individuals with Knee Osteoarthritis

Whole-body vibration (WBV) training may improve the strength of lower extremity muscles in patients with knee osteoarthritis (KOA), but the inconsistency in vibration parameters leads to differences in findings. This cross-sectional study is aimed at observing the effects of different vibration frequencies and knee flexion angles on the activation of lower extremity muscles in patients with KOA. Enrolled participants received WBV training at 0, 30, and 60° knee flexion angles with vibration frequencies of 0, 5, 10, and 20 Hz. Activation rates for vastus medialis, vastus lateralis, rectus femoris, biceps femoris, and semitendinosus in different combinations were collected through surface electromyography. The effects of frequency and angle on muscle activation rate were quantified by repeated measures ANOVA. Individual and synergistic effects of frequency and angle were also analysed. Twenty-six participants with KOA were included. Muscle activation increased with the vibration frequency in 0–20 Hz range and with knee flexion angle in 0–60° range. WBV training at 20 Hz was the most effective for knee muscle activation, and static squatting at 60° was the most suitable for WBV training. Therefore, WBV training can increase the activation rate of knee flexor and extensor muscles in patients with KOA, and the most efficient combination was 20 Hz vibration frequency and 60° knee flexion. When applying WBV to patients with KOA, individual differences and rehabilitation purposes should be considered in selecting vibration parameters and knee angle to effectively increase neuromuscular activity.

In vivo kinematics of a newly updated posterior-stabilised mobile-bearing total knee arthroplasty in weight-bearing and non-weight-bearing high-flexion activities

BACKGROUND

The purpose of this study was to clarify the in vivo kinematics of a newly updated posterior-stabilised (PS) mobile-bearing total knee arthroplasty during high-flexion activities in weight-bearing (WB) and non-weight-bearing (NWB) conditions. The hypothesis was that the kinematics would differ between the WB and NWB conditions, and the kinematics would be affected by the WB condition.

METHODS

The kinematics of 19 knees were investigated under fluoroscopy during squatting (WB) and active-assisted knee flexion (NWB) with two- and three-dimensional registration technique. Accordingly, the range of motion, anteroposterior (AP) translation of the medial and lateral contact points, axial rotation of the femoral component relative to the tibial component, and kinematic pathway were evaluated.

RESULTS

There was no difference in the knee's range of motion between the WB and NWB conditions. The medial AP translation of the femur did not differ in each flexion angle between WB and NWB conditions except for flexions of 70°. There was no difference in the lateral AP translation of the femur at all tested flexion angles between the WB and NWB conditions. The external femoral rotation and the medial pivot motion were observed throughout all flexion angles in WB conditions. The clinical relevance is that this implant could produce ideal medial AP stability and medial pivot motion.

CONCLUSION

The medial AP translation of the femur was stable for AP direction when it was in both WB and NWB conditions. In WB conditions, the medial pivot motion was observed throughout all flexion angles.

LEVEL OF EVIDENCE

III.

Lower Extremities Strength Differences in Female Volleyball Players With Stage 1 Patellar Tendinopathy

Kabacinski, J, Murawa, M, Fryzowicz, A, Gorwa, J, and Dworak, LB. Lower extremities strength differences in female volleyball players with stage 1 patellar tendinopathy. J Strength Cond Res XX(X): 000-000, 2020-The main purpose of the study was to compare the muscle strength between the involved knee (IK) and uninvolved knee (UK) in 12 female volleyball players with stage 1 chronic patellar tendinopathy. Evaluation included the isometric maximal strength to body mass (MS/BM) of the lower extremities extensors for unilateral and bilateral conditions, concentric isokinetic peak torque to body mass (PT/BM) of the hamstrings and quadriceps at 60°·s and 180°·s, IK to UK extensors maximal strength ratio (SR), IK to UK hamstrings (or quadriceps) peak torque ratio (TR), and hamstrings to quadriceps peak TR (H/Q). The results indicated a significantly lower unilateral and bilateral MS/BM of lower extremities extensors for IK than UK (p < 0.001). However, there were no significant differences in SR variable between the unilateral condition and bilateral condition (p = 0.448). Only at the 60°·s velocity, significantly lower quadriceps PT/BM for IK compared with the UK (p < 0.001) and the control group (p < 0.001) were observed. Torque ratio related to the quadriceps group was significantly lower at 60°·s than 180°·s (p = 0.004). Furthermore, significantly higher H/Q for IK compared with UK (p < 0.001) and control group (p = 0.008) only at 60°·s was found. These findings show a significant isometric strength asymmetry for both unilateral and bilateral conditions and a significant concentric strength asymmetry at the low velocity. This study suggests strengthening the weaker quadriceps group and balancing the strength between hamstrings and quadriceps within the knee with patellar tendinopathy.

Acute Effects of Open Kinetic Chain Exercise Versus Those of Closed Kinetic Chain Exercise on Quadriceps Muscle Thickness in Healthy Adults

This study aimed to compare immediate changes in the thickness of the rectus femoris (RF), vastus intermedius (VI), vastus lateralis (VL), vastus medialis (VM), and vastus medialis oblique (VMO) muscles after open kinetic chain exercise (OKCE) and closed kinetic chain exercise (CKCE) and identify the effect of both exercise types on each quadricep muscle for early rehabilitation to prevent knee joint injury. Twenty-six healthy participants (13 males and 13 females) were randomly divided into the OKCE (n = 13) and CKCE (n = 13) groups. The thickness of their quadriceps muscles was measured using a portable ultrasonic imaging device before and after exercise in the sequence RF, VI, VL, VM, and VMO. A two-way repeated measures analysis of variance was used to compare the thickness of each component of the quadriceps muscles between the two groups. The thickness of the RF, VL, VM, and VMO muscles increased after OKCE, and the thickness of the VI muscle showed the greatest increase with a medium–large effect size (F = 8.52, p = 0.01, and d = 0.53). The thickness of the VI, VL, VM, and VMO muscles increased after CKCE, and the VMO muscle had the largest effect size (F = 11.71, p = 0.00, and d = 1.02). These results indicate that the thickness of the quadriceps muscles can be selectively improved depending on the type of exercise.

Myoelectric Responses of Lower-Body Muscles Performing Squat and Lunge Exercise Variations Adopting Visual Feedback With a Laser Sensor

STUDY DESIGN

Cross-over study.

CONTEXT

The squat, single-leg squat, forward lunge, and reverse lunge are fundamental movements often performed in activities of daily living, sports competitions, and sport-specific training.

OBJECTIVE

The purpose of this study was to investigate the effect of visual feedback with a laser sensor (VFLS) versus a control condition on the myoelectric activity (surface electromyography [sEMG]) of the vastus medialis oblique (VMO), vastus lateralis, gluteus medius (Gmed), and erector spinae muscles during the performance of several squat variations with bodyweight.

METHODS

Nineteen female college students (20 [2.5] y, 165.3 [10.2] cm, 66.4 [4.1] kg, 2 [1.2] y of resistance training experience) with a background in strength or sports training volunteered to participate in this study. Over 4 separate visits, subjects performed 2 sets of 10 repetitions of a squat variation exercise in random order (ie, squat, single-leg squat, forward lunge, and reverse lunge). The first set of a given squat variation condition was considered a control set, and then after 3-minute rest, a second set was performed with VFLS.

RESULTS

Significant decreases in VMO and Gmed myoelectric activity were observed during the VFLS set versus the control set for the forward lunge exercise (P = .03). No differences were observed between the control set and VFLS set in the sEMG normalized signal for all muscles analyzed for the squat and single-leg squat, respectively. However, the sample entropy of the sEMG signal for the erector spinae became more irregular during the VFLS set versus the control set for the squat exercise (P = .01), whereas the Gmed presented a more irregular sEMG signal during the VFLS set versus the control set for the single-leg squat (P = .08).

CONCLUSION

Laser sensor biofeedback may induce significant decreases in VMO and Gmed activation performing forward lunge exercise. Therefore, laser sensor biofeedback may induce a reduction in muscle activity of neutralizers muscles during a few squat bodyweight variations (bilateral, single-leg, forward, and reverse lunge).

Muscle activity of the vastus medialis obliquus during squat motion after static stretching of the tensor fasciae latae

[Purpose] The purpose of this study was to investigate the changes of muscle activity during squat motion after stretching the tensor fasciae latae muscle. [Participants and Methods] The participants comprised 19 healthy males. The test muscles were the vastus medialis obliquus and vastus lateralis. The participants performed the squat motion before and after stretching the tensor fasciae latae. We measured the muscle activities and the onset timing of the vastus medialis obliquus relative to that of the vastus lateralis during squat motions. [Results] The onset timing of the vastus medialis obliquus relative to that of the vastus lateralis was decreased, and the vastus medialis obliquus activity and vastus medialis obliquus/vastus lateralis activity ratio were increased after stretching the tensor fasciae latae. [Conclusion] This study revealed that stretching of the tensor fasciae latae increases the relative vastus medialis obliquus muscle activity.

Motor unit discharge rate and the estimated synaptic input to the vasti muscles is higher in open compared with closed kinetic chain exercise

Conflicting results have been reported on whether closed kinetic chain exercises (such as a leg press) may induce more balanced activation of vastus medialis (VM) and lateralis (VL) muscles compared with open kinetic chain exercise (such as pure knee extension). This study aimed to 1) compare between-vasti motor unit activity and 2) analyze the combined motor unit behavior from both muscles between open and closed kinetic chain exercises. Thirteen participants (four women, mean ± SD age: 27 ± 5 yr) performed isometric knee extension and leg press at 10, 30, 50, 70% of the maximum voluntary torque. High density surface EMG signals were recorded from the VM and VL and motor unit firings were automatically identified by convolutive blind source separation. We estimated the total synaptic input received by the two muscles by analyzing the difference in discharge rate from recruitment to target torque for motor units matched by recruitment threshold. When controlling for recruitment threshold and discharge rate at recruitment, the motor unit discharge rates were higher for knee extension compared with the leg press exercise at 50% [estimate = 1.2 pulses per second (pps), standard error (SE) = 0.3 pps, P = 0.0138] and 70% (estimate = 2.0 pps, SE = 0.3 pps, P = 0.0001) of maximal torque. However, no difference between the vasti muscles were detected in both exercises. The estimates of synaptic input to the muscles confirmed these results. In conclusion, the estimated synaptic input received by VM and VL was similar within and across exercises. However, both muscles had higher firing rates and estimated synaptic input at the highest torque levels during knee extension. Taken together, the results show that knee-extension is more suitable than leg-press exercise at increasing the concurrent activation of the vasti muscles.

NEW & NOTEWORTHY There is a significant debate on whether open kinetic chain, single-joint knee extension exercise can influence the individual and combined activity of the vasti muscles compared with closed kinetic chain, multijoint leg press exercise. Here we show that attempting to change the contribution of either the vastus medialis or vastus lateralis via different forms of exercise does not seem to be a viable strategy. However, the adoption of open kinetic chain knee extension induces greater discharge rate and estimated synaptic input to both vasti muscles compared with the leg press.

Squatting versus squatting with hip adduction in management of patellofemoral osteoarthritis: A randomized controlled trial

BACKGROUND

Patellofemoral osteoarthritis is a common presentation in the outpatients' physical therapy clinics. The muscle imbalance between the vastus medialis oblique and vastus lateralis muscles is one of the main factors that lead to the development of this condition.

OBJECTIVE

To compare the effect of a squatting versus squatting with hip adduction in management of patellofemoral osteoarthritis.

METHODS

Patients in group A received a traditional physical therapy program in addition to squatting exercise and those in group B received a traditional physical therapy program in addition to squatting with hip adduction exercise for four weeks. The primary outcome measures were pain on the numerical rating scale (NRS) and performance of functional activities by Kujala scale, while the secondary outcomes were vastus medialis oblique (VMO) and vastus lateralis (VL) amplitudes as well as the VMO:VL ratio by surface electromyography were considered before and after intervention.

RESULTS

Thirty patients (group A n= 15; group B n= 15) were randomized and analyzed. Comparing both groups post-program revealed that there was no significant difference between both groups regarding the vastus medialis oblique activity, VMO:VL ratio, pain intensity and performance of functional activities.

CONCLUSION

Both a traditional physical therapy program in addition to squatting exercise and a traditional physical therapy program in addition to squatting exercise with hip adduction are effective in reduction of pain intensity increases performance of functional activities, and vastus medialis oblique amplitude. However, there is no superiority of one program over the other.

The effect of different hip rotation angles on electromyography activity of the quadriceps muscle during closed kinetic chain tasks in healthy females

[Purpose] The purpose of this study was to investigate electromyographic activity of the quadriceps muscle in different positions of hip rotation (while standing on the toes) in healthy females. [Participants and Methods] The study was conducted on 35 healthy females. Electromyographic activity of the rectus femoris, vastus medialis oblique, and vastus lateralis muscles were recorded with the hip in a neutral position as well as different angles of internal and external rotation (15, 30, and 45 degrees (°)) while the participants were standing on their toes. [Results] There was a significant difference of 15° in external rotation, a neutral position, 15° of internal rotation, and at the end of an internal rotation position. Paired comparison between muscle activity using Bonferroni showed that vastus lateralis activity in 15° of external rotation, a neutral position, 15° of internal rotation, and at the end of a position of internal rotation was more than that of rectus femoris muscle. [Conclusion] The present study showed that average vastus lateralis activity was the highest in all positions. However, the positions studied in the current study did not lead to an increase in muscle activity of the vastus medialis oblique as a medial dynamic stabilizer compared to vastus lateralis.

Electromyographic analysis of hip and knee muscles during specific exercise movements in females with patellofemoral pain syndrome: An observational study

Hip muscle strengthening and knee extensor strengthening are common training exercises for patellofemoral pain syndrome (PFPS). PFPS engendered by insufficient hip abductor and external rotator muscle strength has been of interest, but these exercise movements may increase the lateral vector force of the patella warrants clarification. So, the purpose of this study was to assess muscular activations of vastus lateralis (VL), vastus medialis oblique (VMO), and gluteus medius muscles in electromyographic analysis during hip abduction and external rotator movements and open and closed kinetic chain knee extension movements.The gluteus medius, VMO, and VL muscles, in addition to the ratio of the VL and VMO muscles, were assessed through surface electromyography in 4 movements. Each muscle's amplitude expressed as a percent of maximum voluntary contraction (MVC). The differences on MVC at the terminal joint angle and during the movements were compared.Thirty female patients with PFPS were recruited. During hip abduction and external rotation movements, the MVC of the gluteus medius muscle increased, and those of the VMO and VL muscles increased in the open and closed kinetic chain knee extension movements. The MVCs of VL in the hip abduction and external rotation movements were significantly higher than those of the VMO muscle (P < .05). The ratios of the VL and VMO muscles in the open and closed kinetic chain knee extension movements approached 1, and they were significantly higher than those in the hip abduction and external rotation movements (P < .05). The highest MVC of the VMO muscle was observed at the terminal joint angle in the closed kinetic chain knee extension movement.Selective gluteus medius muscle activation was induced during the hip abduction and external rotation movements, accompanied by an increase in VL muscle activation. In open and closed kinetic chain knee movements, the ratios of the VL and VMO muscles approached 1. More selective VMO muscle activation was induced during the closed kinetic chain knee movements.

Hip position and sex differences in motor unit firing patterns of the vastus medialis and vastus medialis oblique in healthy individuals

Weakness of the vastus medialis oblique (VMO) has been proposed to explain the high prevalence of knee pain in female subjects. Clinicians commonly use exercises in an attempt to preferentially activate the VMO. Recently, our group found evidence to support clinical theory that the VMO is neurologically distinct from the vastus medialis (VM). However, the ability to voluntarily activate these muscle subsections is still disputed. The aim of this study was to determine if VM and VMO activation varies between sexes and if control of the two muscles is different between rehabilitation exercises. Thirteen men and 13 women performed isometric straight leg raises in two hip positions, neutral hip rotation and 30 degrees lateral hip rotation. Bipolar intramuscular fine-wire electrodes were inserted into the VM and VMO to obtain motor unit recruitment thresholds and initial firing rates at recruitment. Linear mixed models and Tukey post hoc tests were used to assess significant differences in 654 motor units. Women demonstrated faster motor unit firing rate at recruitment, 1.18 ± 0.56 Hz higher than men. Motor units fired 0.47 ± 0.19 Hz faster during neutral hip rotation compared with lateral hip rotation. The VMO motor units were recruited 2.92 ± 1.28% earlier than the VM. All motor units were recruited 3.74 ± 1.27% earlier during neutral hip rotation than lateral hip rotation. Thus the VM and the VMO can be activated differentially, and their motor unit recruitment properties are affected by sex and hip position.

NEW & NOTEWORTHY This is the first study to reveal differential activation of the vastus medialis oblique from the vastus medialis in clinical exercise protocols. Our research group used fine-wire electrodes to examine EMG signals of the vastus medialis oblique and vastus medialis to avoid possible cross talk. We also consider the effect of sex on motor unit firing patterns because of higher prevalence of knee pain in women, and yet few studies evaluating the sex differences in neuromuscular control.

Patellar malalignment treated with modified knee extension training: An electromyography study

BACKGROUND

Patellar malalignment (PM) in most patients is ascribed to an imbalance of peripatellar soft tissue tension.

RESEARCH QUESTION

Conservative treatment of PM initially with enforced training of the vastus medialis obliquus (VMO) has been widely applied. Non-operative techniques for treatment of PM require continuing development.

METHODS

Thirty healthy young adults participated in the study. Two surface electromyography (EMG) electrodes were placed on the skin of the dominant lower thigh in each subject: one on the center of the muscle belly of the VMO and the other on the symmetric location of the vastus lateralis (VL). Maximum of knee extension action (from various angles of knee flexion to full extension) was initiated. Tests were conducted with knee flexion decreasing by 10° at each step. Each action was repeated three times, and the average value was calculated. The root mean square value of excited muscles in the EMG was recorded. The ratio of the VMO to the VL (VMO/VL) was used to indicate the effectiveness of the treatment. The knee position varied from 90° flexion initially, decreasing by 10° at each step.

RESULTS

Nine sets of values were obtained. All extension actions were effective (VMO/VL >1; range, 1.23-1.35). The maximal value was observed at 60° flexion (VMO/VL = 1.35). Differences were not significant among the nine groups (p = 0.08, ANOVA).

SIGNIFICANCE

Using the described knee extension training for conservative treatment of PM may be an effective alternative. The technique is simple, and the results of our experimental tests are encouraging. This method may become another popular and effective technique for treating PM.

The effects of unilateral and bilateral eccentric overload training on hypertrophy, muscle power and COD performance, and its determinants, in team sport players

The study aimed to compare the chronic eccentric-overload training effects of unilateral (lateral lunge) vs bilateral (half-squat) using an inertial device, on hypertrophy and physical performance. Twenty-seven young team sports male players performed a 4 sets of 7 repetitions of inertial eccentric overload training, biweekly for 6 weeks, distributed in unilateral lunge group (UG: age: 22.8 ± 2.9 years; body mass: 75.3 ± 8.8 kg; height: 177.3 ± 3.7 cm) and bilateral squat group (BG: age: 22.6 ± 2.7 years; body mass: 79.5 ± 12.8 kg; height: 164.2 ± 7 cm). Lower limb muscle volume, counter movement jump (CMJ), power with both (POWER), dominant (POWERd) and no-dominant leg (POWERnd), change of direction turn of 90° with dominant (COD90d) and no-dominant leg (COD90nd) and 180° (COD180d and COD180nd), and 10m sprint time (T-10m) were measured pre and post-intervention. The UG obtained an increase of adductor major (+11.1%) and vastus medialis (+12.6%) higher than BG. The BG obtained an increase of vastus lateralis (+9.9%) and lateral gastrocnemius (+9.1%) higher than UG. Both groups improved CMJ, POWER, POWERd, POWERnd, COD90 and DEC-COD90, without changes in T-10m. The UG decrease DEC-COD90nd (-21.1%) and BG increase POWER (+38.6%) substantially more than the other group. Six-weeks of unilateral / bilateral EO training induce substantial improvements in lower limbs muscle volume and functional performance, although unilateral training seems to be more effective in improving COD90 performance.

Changes in lower limb muscle activity based on angle of ankle abduction during lunge exercise

[Purpose] This study compared the activity of the quadriceps femoris muscle according to the angle of ankle abduction during a lunge exercise. [Subjects and Methods] Fifteen male healthy volunteers participated in the study. All participants performed the lunge exercise with different angles of ankle abduction (0°, 20°, 40°, 60°). The activity of the rectus femoris (RF), vastus lateralis (VL) and vastus medialis oblique (VMO) muscles were recorded for the four angles by using a surface electromyography system. [Results] There were significant differences between the rectus femoris (RF), vastus lateralis (VL) and vastus medialis oblique (VMO) with every angle of the ankle joint. The most significantly increased muscle activity was evident in the vastus medialis oblique (VMO) when the ankle abduction was 60°. [Conclusion] These findings suggest that as the ankle abduction angle increases during the lunge exercise, the muscle activity of the quadriceps femoris muscle increases and this could be helpful in the selective muscle strengthening of the vastus medialis oblique muscle (VMO) with the ankle in the 60° abduction position.

Towards evidence based strength training: a comparison of muscle forces during deadlifts, goodmornings and split squats

BACKGROUND

To ensure an efficient and targeted adaptation with low injury risk during strength exercises, knowledge of the participant specific internal loading conditions is essential. The goal of this study was to calculate the lower limb muscles forces during the strength exercises deadlifts, goodmornings and splits squats by means of musculoskeletal simulation.

METHODS

11 participants were assessed performing 10 different variations of split squats by varying the step length as well as the maximal frontal tibia angle, and 13 participants were measured performing deadlift and goodmorning exercises. Using individualised musculoskeletal models, forces of the Quadriceps (four parts), Hamstrings (four parts) and m. gluteus maximus (three parts) were computed.

RESULTS

Deadlifts resulted highest loading for the Quadriceps, especially for the vasti (18-34 N/kg), but not for the rectus femoris (8-10 N/kg), which exhibited its greatest loading during split squats (13-27 N/kg) in the rear limb. Hamstrings were loaded isometrically during goodmornings but dynamically during deadlifts. For the m. gluteus maximus, the highest loading was observed during split squats in the front limb (up to 25 N/kg), while deadlifts produced increasingly, large loading over large ranges of motion in hip and knee.

CONCLUSIONS

Acting muscle forces vary between exercises, execution form and joint angle. For all examined muscles, deadlifts produced considerable loading over large ranges of motion, while split squats seem to be highly dependent upon exercise variation. This study provides key information to design strength-training programs with respect to loading conditions and ranges of motion of lower extremity muscles.

Quantifying knee mechanics during balance training exercises

Patellofemoral pain (PFP) is common among runners and those recovering from anterior cruciate ligament reconstruction. Training programs designed to prevent or treat injuries often include balance training, although balance interventions have been reported to coincide with more knee injuries. Knowledge of the effect of balance exercises on knee mechanics may be useful when designing training programs. High knee abduction moment has been implicated in the development of PFP, and imbalance between vastus lateralis (VL) and vastus medialis oblique (VMO) may contribute to patellofemoral stress. The purpose was to quantify knee abduction moment and vasti muscle activity during balance exercises. Muscle activity of VMO and VL, three-dimensional lower-extremity kinematics, and ground reaction forces of healthy recreational athletes (12M, 13F) were recorded during five exercises. Peak knee abduction moment, ratio of VMO:VL activity, and delay in onset of VMO relative to VL were quantified for each exercise. The influence of sex and exercise on each variable was determined using a mixed-model ANOVA. All analyses indicated a significant main effect of exercise, p<0.05. Follow-up comparisons showed low peak knee abduction moment and high VMO:VL ratio for the task with anterior-posterior motion. Delay of VMO relative to VL was similar among balance board tasks.

The Effect of Increasing Volume of Exercise on Activation Pattern of Vastus Medialis and Lateralis and its Correlation With Anterior Knee Pain in Karate Elites

Background

The effects of exercise volume on the pattern of muscle activity is one of the most important factors in training management and injury risk reduction. In the lower limb, the quadriceps muscle which plays a determining role in performing the stance and other karate techniques could be injured in intensive exercise and may induce anterior knee pain in athletes.

Objectives

The aim of this study was to determine the relationship between training volume and muscle activity of vastus medialis and vastus lateralis and its association with anterior knee pain in karate elites.

Patients and Methods

Male and female athletes from national junior and cadet karate team (14 to 18 years) were invited to participate in the study at the beginning and the end of the training camps. Studies involved measurement of electromyographic muscle activity of vastus medialis and vastus lateralis in both lower extremities with surface electromyography device and assessment of movement by electrogoniometery. Muscle activity was recorded in three tests of dachi, walking up and walking down stairs. Simultaneously, anterior knee pain was evaluated using visual analogue scale and anterior knee pain scale questionnaire.

Results

Eight athletes of a total number of 23 reported increased ratings of pain in their right knees. No differences in muscle activity were observed in tests of Dachi and stairs between the groups with and without pain. Comparing Dachi task pattern at the beginning and end of training camps, there was no significant difference in pattern of biomechanical movement; however, reducing the amount of muscle activity in early and late phases of tasks was observed in electromyographic assessment.

Conclusions

The results showed that performing the same task after a six-week training period, less muscle activity was required in all phases in two groups of tasks, including karate-specific movement (dachi) and activities of daily living (up or down stairs).

Does the Dumbbell-Carrying Position Change the Muscle Activity in Split Squats and Walking Lunges?

Stastny, P, Lehnert, M, Zaatar, AMZ, Svoboda, Z, and Xaverova, Z. Does the dumbbell-carrying position change the muscle activity in split squats and walking lunges? J Strength Cond Res 29(11): 3177–3187, 2015—The forward walking lunge (WL) and split squat (SSq) are similar exercises that have differences in the eccentric phase, and both can be performed in the ipsilateral or contralateral carrying conditions. This study aimed to determine the effects of dumbbell-carrying position on the kinematics and electromyographic (EMG) amplitudes of the gluteus medius (Gmed), vastus medialis (VM), vastus lateralis (VL), and biceps femoris during WLs and SSqs. The resistance-trained (RT) and the non–resistance-trained (NT) groups (both n = 14) performed ipsilateral WLs, contralateral WLs, ipsilateral SSqs, and contralateral SSqs in a randomized order in a simulated training session. The EMG amplitude, expressed as a percentage of the maximal voluntary isometric contraction (%MVIC), and the kinematics, expressed as the range of motion (ROM) of the hip and knee, were measured during 5 repetition maximum for both legs. The repeated measure analyses of variance showed significant differences between the RT and NT groups. The NT group showed a smaller knee flexion ROM (p < 0.001, η² = 0.36) during both types of WLs, whereas the RT group showed a higher eccentric Gmed amplitude (p < 0.001, η² = 0.46) during all exercises and a higher eccentric VL amplitude (p < 0.001, η² = 0.63) during contralateral WLs. Further differences were found between contralateral and ipsilateral WLs in both the RT (p < 0.001, η² = 0.69) and NT groups (p < 0.001, η² = 0.80), and contralateral WLs resulted in higher eccentric Gmed amplitudes. Contralateral WLs highly activated the Gmed (90% MVIC); therefore, this exercise can increase the Gmed maximal strength. The ipsilateral loading condition did not increase the Gmed or VM activity in the RT or NT group.

KINESIO TAPING NÃO ALTERA A RELAÇÃO EMG ENTRE VASTO LATERAL E VASTO MEDIAL DURANTE MEIO-AGACHAMENTO

RESUMO Introdução: Kinesio Taping é uma técnica realizada com aplicação de fitas elásticas sobre a pele, que se propõe a produzir determinados efeitos com fins de prevenção e tratamento das lesões musculoesqueléticas. No entanto, os meios pelos quais tais efeitos ocorrem continuam sendo investigados e discutidos, principalmente no que diz respeito à utilização no campo da reabilitação e do esporte. Objetivo: Analisar a relação da atividade eletromiográfica encontrada nos músculos vasto lateral (VL) e vasto medial (VM) em duas condições: sem aplicação de Kinesio Taping (GnKT) e com aplicação de Kinesio Taping (GKT) em uma população saudável, com experiência em treinamento de força. Métodos: Dezoito sujeitos do sexo masculino (idade: 28,1 ± 6,9 anos; massa corporal: 85,5 ± 8,3 kg; estatura: 179,5 ± 6,9 cm; comprimento de membro inferior: 97,0 ± 4,2 cm) realizaram o exercício de meio-agachamento livre, com velocidade controlada, sem e com aplicação de Kinesio Taping. A relação foi verificada pela proporção de magnitude de ativação (VM/VL), utilizando-se os valores de root mean square (RMS). A sequência para realização dos exercícios nas condições mencionadas foi randomizada e balanceada. Resultados: Os valores encontrados para a razão VM/VL na situação GnKT foram de 83,96 ± 5,79% para VM e 84,13 ± 7,16% para VL. Já na situação GKT, 84,55 ± 16,97% para VM e 80,53 ± 9,20% para VL. Não foram observadas diferenças significativas nos valores de RMS para a relação VM/VL submetidos a aplicação de Kinesio Taping. Conclusão: A aplicação de Kinesio Taping não demonstrou influenciar a relação da atividade eletromiográfica entre os músculos vasto lateral e vasto medial durante a execução do exercício de meio-agachamento.

The effect of exercise on vastus medialis oblique muscle architecture: An ultrasound investigation

The vastus medialis oblique (VMO) is thought to be implicated in patellofemoral pain (PFP), and weakness in this portion of the vastus medialis muscle may lead to PFP. Management includes physiotherapy to strengthen the VMO. Although this intervention has been shown to be effective, the effects on the architecture of the muscle have not been investigated. This study aims to determine the changes in VMO architecture following a program of strengthening exercises. Twenty-one male participants underwent an initial ultrasound scan to measure the fiber angle and the insertion level of the VMO on the patella. Each subject then undertook a 6-week quadriceps femoris strengthening program; the scan and measurements were then repeated. A significant increase in VMO fiber angle and insertion length was observed. Average fiber angle increased by 5.24°; average insertion length increased by 2.7 mm. There was found to be a significant negative correlation between the initial values and the degree of change. Pearson's coefficient of correlation for measurements of patella length taken before and after exercise was 0.921, indicating a high degree of reliability. There was a significant positive correlation between fiber angle change and declared level of compliance (R(2)  = 0.796). The results reported here indicate that physiotherapy leads to a significant change in VMO morphology. Given the inverse correlation noted between initial architectural parameters and the degree of change, we suggest that patients who would benefit most from physiotherapy can be identified in clinic using a simple ultrasound technique. Clin. Anat. 29:752-758, 2016. © 2016 Wiley Periodicals, Inc.

Regional Surface Electromyography of the Vastus Lateralis During Strength and Power Exercises

Neuromuscular activation during and chronic adaptation from exercise are innately linked and both can vary along a muscle's length. During high-force and high-speed exercise, intramuscular hypertrophy follows set patterns that provide the greatest biomechanical advantages. However, it is unknown if muscle activity as recorded by surface electromyography (sEMG) will follow these patterns. The purpose of the present study was to compare vastus lateralis intramuscular sEMG during the heavy squat (HS) and unloaded jump squat (JS) exercises. Ten subjects performed HS with 80% of maximum load and unloaded JS to parallel-depth, while intramuscular peak sEMG and mean sEMG were measured at 33% (proximal), 50% (middle), and 67% (distal) thigh length. Muscle activity was compared between regions and exercises using a 3 × 2 repeated measures ANOVA with Bonferoni post hoc corrections. Peak sEMG was greater proximally in JS than HS (p = 0.033), but similar in the middle and distal regions (p = 0.521, 0.594, respectively), whereas mean sEMG was similar between all regions (p = 0.150-0.979). In addition, a main effect was found in which peak and mean sEMG were greater proximally than the middle and distal regions (p = 0.001, 0.006). Muscle activity measured using sEMG displayed dissimilar patterns to previously observed regional hypertrophy. Specifically, although previous research found greater proximal hypertrophy in JS than HS, in the present study peak sEMG was greater in HS than JS. Furthermore, distally where HS elicited greater hypertrophy than JS, no differences in sEMG were present. Thus, regional sEMG appears not to be a viable tool for predicting differences in regional hypertrophy, most likely due to technological constraints and intramuscular differences in muscle structure.

Is there a role of pulsed electromagnetic fields in management of patellofemoral pain syndrome? Randomized controlled study at one year follow-up

Patellofemoral pain syndrome (PFPS) is a common cause of recurrent or chronic knee pain in young adults, generally located in the retropatellar region. Etiology is controversial and includes several factors, such as anatomical defects, muscular imbalance, or joint overuse. Good results have been reported with exercise therapy, including home exercise program (HEP). Joint inflammation with increase of pro-inflammatory cytokines levels in the synovial fluid might be seen especially when chondromalacia becomes evident. Biophysical stimulation with pulsed electromagnetic fields (PEMFs) has shown anti-inflammatory effects and anabolic chondrocyte activity. The purpose of this randomized controlled study was to evaluate if the combination of HEP with PEMFs was more effective than HEP alone in PFPS treatment. Thirty-one PFPS patients were enrolled in this study. All patients were instructed to train with HEP. Patients in the PEMFs group associated HEP with PEMFs. Function and pain were assessed with Victorian Institute of Sport Assessment score (VISA), Visual Analog Scale (VAS), and Feller's Patella Score at baseline at 2, 6, and 12 months of follow-up. Drug assumption was also recorded. Increase in VISA score was significantly higher in PEMFs group compared to controls at 6 and 12 months, as well as the increase in the Feller's Patella Score at 12 months. VAS score became significantly lower in the PEMFs group with respect to control group since 6 month follow-up. Pain reduction obtained with PEMFs enhanced practicing therapeutic exercises leading to a better recovery process; this is extremely important in addressing the expectations of young patients, who wish to return to sporting activities.

Muscle Activation of Vastus Medialis Oblique and Vastus Lateralis in Sling-Based Exercises in Patients with Patellofemoral Pain Syndrome: A Cross-Over Study

Objectives. To examine what changes are caused in the activity of the vastus medialis oblique (VMO) and vastus lateralis (VL) at the time of sling-based exercises in patients with patellofemoral pain syndrome (PFPS) and compare the muscular activations in patients with PFPS among the sling-based exercises. Methods. This was a cross-over study. Sling-based open and closed kinetic knee extension and hip adduction exercises were designed for PFPS, and electromyography was applied to record maximal voluntary contraction during the exercises. The VMO and VL activations and VMO : VL ratios for the three exercises were analyzed and compared. Results. Thirty male (age = 21.19 ± 0.68 y) and 30 female (age = 21.12 ± 0.74 y) patients with PFPS were recruited. VMO activations during the sling-based open and closed kinetic knee extension exercises were significantly higher (P = 0.04 and P = 0.001) than those during hip adduction exercises and VMO : VL ratio for the sling-based closed kinetic knee extension and hip adduction exercises approximated to 1. Conclusions. The sling-based closed kinetic knee extension exercise produced the highest VMO activation. It also had an appropriate VMO : VL ratio similar to sling-based hip adduction exercise and had beneficial effects on PFPS.

Vastus medialis oblique and vastus lateralis activity during a double-leg semisquat with or without hip adduction in patients with patellofemoral pain syndrome

Background

The purpose was to investigate the effect of double-leg semisquat with hip adduction on the activation of vastus medialis oblique (VMO) and vastus lateralis (VL) in patients with patellofemoral pain syndrome (PFPS).

Methods

Thirty patients with PFPS were designated to the study group, while 30 healthy matched subjects were enrolled in the control group. The activation of VL and VMO was recorded with surface electromyography (EMG) during double-leg semisquat (DS) and double-leg semisquat with hip adduction (DS-HA). The time domain and frequency domain indexes of the electromyography data were collected for analysis.

Results

In the study group, the time domain indexes (RMS, IEMG) and frequency domain index (MPF) of VL were significant higher than VMO in the test of DS (P < 0.05); and the time domain of VMO was significantly higher in the test of DS-HA when compared to DS (P < 0.05) while there was no difference in the activation of VL.

Conclusions

In the study group, an increase in activity of the VMO was observed through the surface EMG signal in the double-leg semisquat exercise with hip adduction compared to the exercise without hip adduction. This finding indicates that VMO activation can be more selectively obtained through the exercise with hip adduction which can help balance the VL and VMO.

Effects of the slow speed-targeting squat exercise on the vastus medialis oblique/vastus lateralis muscle ratio

[Purpose] This study investigated the effects of the slow speed-targeting squat exercise on the vastus medialis oblique/vastus lateralis ratio. [Subjects] Ten asymptomatic men were recruited. [Methods] The EMG activities of the vastus medialis oblique and vastus lateralis muscles were recorded using surface electrodes. The subject performed the squat exercise under 3 different conditions. [Results] The vastus medialis oblique/vastus lateralis ratio in condition 2 (1.5 ± 0.7) was significantly higher than that in conditions 1 and 3 (1.0 ± 0.5, 1.1 ± 0.8, respectively) [Conclusion] Therefore, an effectively slow movement speed is recommended for selective strengthening of vastus medialis oblique using a slow speed-targeting device that provides biofeedback.