Vastus Medialis Activity Research Articles

Differences of Surface Electromyography during Incremental Cycling Exercise in Hypoxia and Normoxia Using Wavelet Transform Analysis

Previous studies indicated that there was a difference between hypoxia and normoxia for amplitude parameters of surface electromyography (EMG). However, there are few reports on frequency parameters of EMG because of limitations of traditional analytical methods. PURPOSE: The purpose of this study was to investigate the differences of surface electromyography during incremental cycling exercise in hypoxia and normoxia using wavelet transform analysis. METHODS: Subjects were fourteen active and healthy men. (mean±SD; age: 21.08 ± 1.50 years; height: 1.69 ± 0.06 m; weight: 60.16 ± 7.77 kg; maximal oxygen consumption: 51.11. ±9.54 ml / min / kg). The subjects performed incremental cycling exercise test to exhaustion in hypoxia (FIO2: 13.4%) and normoxia conditions (FIO2: 20.9%). EMG activities of vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF) and biceps femoris (BF) were recorded during cycling exercise test at a sampling rate of 2000 Hz. Integrated electromyogram (iEMG) and mean power frequency (MPF) for each exercise intensity were calculated from the EMG data. Contentious wavelet analysis was used to calculate MPF, and mother wavelet was set at morlet wavelet. The differences between exercise intensities and FIO2 conditions were compared using a two-way analysis of variance. The significance level was set at p< 0.05. RESULTS: iEMG of each muscle significantly increased with increasing exercise intensities (all: p < 0.01). However, there were no significant differences between FIO2 conditions for each muscle (VL: p = 0.37; VM: p = 0.49; RF: p = 0.37; BF: p = 0.64). MPF of VL significantly decreased with increasing exercise intensities (p < 0.01), and MPF in hypoxia was higher than that in normoxia (p < 0.01). MPF of VM significantly decreased with increasing exercise intensities (p<0.01), but there were no significant differences between FIO2 conditions (p = 0.37). In addition, there were no significant differences between exercise intensities (RF: p = 0.49; BF: p = 0.57) and FIO2 conditions (RF: p = 0.49; BF: p = 0.19) for RF and BF. CONCLUSION: The current results demonstrated that the change in MPF was different for each muscle, and MPF of VL in hypoxia was only higher than that in normoxia, and suggested hypoxia exposure affects neuromuscular activity agonist muscle during exercise.

Joint angle and movement velocity effects on muscle activity of elderly with knee osteoarthritis – Categorized and probabilistic analysis

The aim of the study was to determine the effects of joint angle position and angular velocity on concentric and eccentric knee muscles activity of elderly with osteoarthritis (OA) in a deterministic and probabilistic approach compared to matched controls. Concentric and eccentric muscle activation of vastus medialis (VM) and semitendinous (ST) muscles were recorded of eleven elderly women with knee OA (median (Md (25–75%)) age of 62 years (60–72) and Md of body mass index (BMI) of 26 kg/m2 (24.5–27.2)) and ten controls (Md 65 years (62–69) and Md of BMI 24.5 kg/m2 (23.6–28.9), during twenty-five knee extension-flexion movements. Activation type, angular velocities (90° s−1 and 240° s−1) and joint angle intervals were categorized into groups. The cumulative frequency distributions of the normalized sEMG envelope were computed and the probability to be out of specific norm-reference limits (controls) was calculated. No statistical differences between groups were found. Higher probabilities were found for VM and ST (concentric) and ST (eccentric) activation to be out of norm (55%, 53% and 84%, respectively) at 240 s−1 in different joint angles. During dynamic contractions, concentric and eccentric activity of medial knee muscles of elderly with OA were affected in a different way by joint angles and angular velocity compared to matched controls. The probabilistic analysis provided an additional understanding of the muscle activation between elderly with knee OA and healthy older people.

Electromyographic and biomechanical analysis of step negotiation in Charcot Marie Tooth subjects whose level walk is not impaired

BackgroundCharcot-Marie-Tooth (CMT) is a slowly progressive disease characterized by muscular weakness and wasting with a length-dependent pattern. Mildly affected CMT subjects showed slight alteration of walking compared to healthy subjects (HS). Research questionTo investigate the biomechanics of step negotiation, a task that requires greater muscle strength and balance control compared to level walking, in CMT subjects without primary locomotor deficits (foot drop and push off deficit) during walking. MethodsWe collected data (kinematic, kinetic, and surface electromyographic) during walking on level ground and step negotiation, from 98 CMT subjects with mild-to-moderate impairment. Twenty-one CMT subjects (CMT-NLW, normal-like-walkers) were selected for analysis, as they showed values of normalized ROM during swing and produced work at push-off at ankle joint comparable to those of 31 HS. Step negotiation tasks consisted in climbing and descending a two-step stair. Only the first step provided the ground reaction force data. To assess muscle activity, each EMG profile was integrated over 100% of task duration and the activation percentage was computed in four phases that constitute the step negotiation tasks. ResultsIn both tasks, CMT-NLW showed distal muscle hypoactivation. In addition, during step-ascending CMT-NLW subjects had relevant lower activities of vastus medialis and rectus femoris than HS in weight-acceptance, and, on the opposite, a greater activation as compared to HS in forward-continuance. During step-descending, CMT-NLW showed a reduced activity of tibialis anterior during controlled-lowering phase. SignificanceStep negotiation revealed adaptive motor strategies related to muscle weakness due to disease in CMT subjects without any clinically apparent locomotor deficit during level walking. In addition, this study provided results useful for tailored rehabilitation of CMT patients.

Effect of various foot wedge conditions on the electromyographic activity of lower extremity muscles during load lifting

AbstractThe level of muscle activity can be decreased with optimized foot wedge condition. The aim of this study was to evaluate the effect of different foot wedge conditions on the activity of selected lower extremity muscles during load lifting. Nine able‐bodied male subjects participated in this study. Electromyography activity of the vastus medialis (VM), vastus lateralis (VL), medialis gastrocnemius (MG), and soleus (SOL) muscles was recorded during dynamic load lifting using the squat technique in 5 conditions: i) non‐wedge (NW), ii) 1 cm heel height increasing (PW1), iii) 3 cm heel height increasing (PW3), iv) 1 cm in front of the feet (AW1), and v) 1 cm inside the feet (MW1). The results showed that the VM activity decreases in the MW1 compared to other conditions and significantly compared to the PW1 and PW3 conditions (p &lt; .05). Decreases in the VL activity in the AW1 as well as in descending and ascending phases of MW1 were observed (p &lt; .05). Also in the descending phase, the SOL activity in AW1 decreased significantly compared to NW condition (p &lt; .05). However, there was no significant difference in MG activity between different conditions (p &gt; .05). It seems that placing wedges in the anterior and medial area of the feet may decrease quadriceps muscles activity and probably can delay reaching time to fatigue during load lifting. These findings may be helpful in designing special shoes for ergonomics fields and work environments.

Visual feedback during pedaling allows individuals poststroke to alter inappropriately prolonged paretic vastus medialis activity.

Individuals who have experienced a stroke often demonstrate inappropriate muscle activity phasing in the paretic leg during locomotion. Past research has demonstrated that inappropriate paretic phasing varies between behavioral contexts and is reduced during unilateral pedaling with the nonparetic leg inactive. We investigated whether individuals could voluntarily alter activity in a target muscle of the paretic limb in a consistent behavioral context and whether this voluntary change differed between bilateral and unilateral pedaling. During a fixed-speed motorized pedaling task, participants were asked to use visual feedback to deactivate the vastus medialis (VM) before a 90° target region of the pedaling cycle, as measured by surface electromyography and by change in fraction of total cycle amplitude in the target region. We based the start of this target region on the earliest observed deactivation for this muscle (found in fast pedaling), which allowed us to challenge both the paretic and nonparetic VM. During visual feedback, participants significantly reduced the fraction of activity found in the target region, with no significant difference in degree of reduction between paretic and nonparetic legs or between bilateral and unilateral pedaling. Surprisingly, in bilateral pedaling, individuals with greater clinical impairment demonstrated greater paretic limb response to feedback. Our results demonstrated that during this tightly constrained task, the paretic VM showed a surprisingly similar flexibility of muscle activity to the nonparetic VM. Our findings show that participants were able to use provided visual feedback to modulate the degree of an observed poststroke muscle-phasing impairment. NEW & NOTEWORTHY This study demonstrates that by using visual feedback during a constrained task with minimized kinematic control requirements, participants with poststroke hemiplegia can voluntarily change muscle activity phase in the vastus medialis. Surprisingly, we did not observe a significant difference in ability to alter phasing between paretic and nonparetic legs or between bilateral and unilateral pedaling. In this visual feedback task, participants appear to modify muscle activity well in both the paretic and nonparetic legs.

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.

The effect of whole-body vibration training on the lower extremity muscles' electromyographic activities in patients with knee osteoarthritis.

Background: Whole-Body Vibration Training (WBVT) is a novel neuromuscular training method that has been recently developed as a rehabilitation tool. The purpose of this study was to determine whether WBVT is effective on electromyographic activity of the muscles of the lower limbs in patients with knee osteoarthritis. Methods: The study was designed as a single blinded randomized clinical trial (IRCT201601171637N5), 45 patients with knee osteoarthritis were randomly assigned to three groups; WBVT (n = 15) receiving 12 sessions vibration therapy, control group (n =15) doing two exercise in the home and placebo (n =15) doing exercise like WBVT group on-off vibration system. Electromyographic activities of vastus lateralis and vastus medialis, semitendinosus, gastrocnemius and soleus were evaluated pre and post intervention. The pairedsamples t-test and ANOVA were applied respectively to determine the differences in each group and among the groups (P≤0.05). Results: The RMS value of vastus medialis in semi squat position in placebo group (p=0.024), vastus lateralis in SLR position in WBVT group (p=0.037), soleus in knee flexion in WBVT group (p=0.018), semitendinosus in knee flexion in WBVT group (p=0.007) and RMS response of Semitendinosus in ankle plantar flexion in control group (p=0.047) were revealed significant differences between the pre- and post- intervention. The ANOVA test confirmed the significant differences between the studied groups according to the EMG activity of vastus medialis in semi squat position (p=0.045), semitendinosus in semi squat position (p=0.046) and in plantar flexion position (p=0.015) and also soleus in plantar flexion position (p=0.003). Conclusions: The findings of this study showed the beneficial effects of WBVT in the improvement of the muscles RMS values in the patients with knee OA especially muscles' progression rates in a four-week period.

The effects of a simulated occupational kneeling exposure on squat mechanics and knee joint load during gait

Occupational kneeling is associated with an increased risk for tibiofemoral knee osteoarthritis. Forces on the knee in the kneeling posture, as well as the greater incidence of meniscus tears among workers, likely contribute to the increased risk. We hypothesise that an additional mechanism may contribute – altered neuromuscular control due to prolonged high knee flexion. Forty participants (20 male, 20 female) completed an evaluation of gait and squatting before, immediately following, and 30 min following a 30 min simulated occupational kneeling exposure. An increase in the peak external knee adduction moment and a delay in vastus medialis activation onset during walking were observed post-kneeling, as well as increased frontal plane knee motion during squatting. This was the first investigation to find changes in high flexion transitions as a result of kneeling. Greater frontal plane knee motion may increase the risk for meniscal tears, and subsequently, knee osteoarthritis.Practitioner Summary: A 30 min simulated occupational kneeling exposure resulted in small but significant gait changes. The greatest effect was on frontal plane knee movement during squatting, which is especially relevant to occupations requiring frequent kneeling/squatting. This increased motion may indicate an increased risk of injury, which supports a link to knee osteoarthritis.

A Novel Electromyographic Approach to Estimate Fatigue Threshold in Maximum Incremental Strength Tests.

Evaluation of muscular fatigue thresholds in athletes performing short-duration and explosive exercises is difficult because classic parameters do not suffer large variations. Therefore, the aim of this study was to develop a new method to estimate the fatigue threshold in single muscles. Our approach is based on electromyographic data recorded during a maximum incremental strength test until the one repetition maximum is reached. Ten men and 10 women performed a half-squat strength test consisting of five incremental intensities of one repetition maximum. Neither heart rate nor blood lactate concentrations showed significant differences at the various intensities tested. Surface electromyographic activities of vastus lateralis, vastus medialis, and rectus femoris were recorded, finding a break point corresponding to the fatigue threshold occurring in men at 70.74%, 71.48%, and 72.52% of one repetition maximum, respectively. In women, break-point values were 76.66% for vastus lateralis, 76.27% for vastus medialis, and 72.10% for rectus femoris. In conclusion, surface electromyography could be a useful, rapid, and noninvasive tool to determine the fatigue threshold of independent muscles during a maximal half-squat strength test.

A comparison of lower limb muscle activation pattern using voluntary response index between pronated and normal foot structures during forward jump landing

BackgroundPronated of the foot is one of the important factors contributing to musculoskeletal problems affecting the lower extremities. It is known that in a pronated foot, excessive mechanical load is applied to the lower limb structures which may result in altered biomechanics and muscle activation patterns. The aim of this study was to determine changes in the muscle activation pattern of the lower extremities in individuals with pronated, compared to normal, feet, using the voluntary response index (VRI). MethodsIn this cross sectional study, 15 asymptomatic pronated foot individuals (mean age 23.27 ± 3.28 years) and 15 normal subjects (mean age 23.40 ± 3.11 years) were recruited by simple non-random sampling. Electrical activities of gluteus medius (GM), vastus lateralis (VL), vastus medialis (VM), biceps femoris, semitendinosus (ST), and medial gastrocnemius (MG) muscles were recorded during a forward jump landing task. Voluntary response index (VRI) variables, included similarity index (SI) and magnitude (Mag) were also evaluated. ResultsMuscle activity of VM (p < 0.001) and ST (p = 0.010) were significantly higher but VL (p = 0.039) and MG (p = 0.001) were significantly lower in pronated foot, compared to normal subjects. Similarity index was found to be different (p < 0.001) between pronated foot and healthy individuals. No significant difference was found in terms of Mag between the two groups (p = 0.576). ConclusionThe altered pattern of lower limb muscle activation identified in the pronated foot during landing may be attributed to the different activation involving VL, VM, MG and ST muscles. Adaptations to the biomechanical effects, due to the pronated foot causing altered activation of VL, VM, MG, and ST muscles, results in an altered pattern of muscle activation. This change in activation pattern may harm the effectiveness of movement control processes; and might also predispose individuals with pronated feet, to injuries. It seems that an altered motor strategy with the aim of minimizing biomechanical changes, predisposes individuals to injuries. However, further large scale studies are needed to support the findings of the present study.

저항운동의 속도 차이가 중년여성의 근력 불균형에 미치는 영향

This study tested the hypothesis that strength imbalance would improve at after slow-speed resistance training but would not alter at after normal-speed resistance training. Twelve middle aged women were randomly divided into slow-speed resistance training group (SSG, n=6) and normal-speed resistance training group (NSG, n=6). SSG was performed for 15 repetition × 3 sets and total 7-s per repetition (concentric: 3-s, isometric: 1-s, eccentric: 3-s), and NSG was also performed the for 35 repetition × 3 sets and total 3-s per repetition (concentric: 1-s, isometric: 1-s, eccentric: 1-s). Both groups performed the low intensity resistance training at 30% of 1-RM for 105-s per set, rest for 1 min between sets, rest for 3 min between exercises, and 2~3 times per week, for 4 weeks. All subjects were measured for body composition (weight, BMI, and %fat), muscle activity and muscle fatigue of biceps brachii, vastus medialis and vastus lateralis in dominant (DL) and non-dominant (NDL). At SSG, LSI (%) = (1-NDL/DL) × 100 of muscle activity was significantly decreased in biceps brachii, vastus medialis, and vastus lateralis after 4-week resistance training compared with before (P.05). However, LSI of muscle activity did not show statistically significant differences in NSG after 4-week resistance training compared with before. LSI of muscle fatigue did not show statistically significant differences in both groups after 4-week resistance training compared with before. Our results suggest that strength imbalance improve at after slow-speed resistance training.

Patellar bracing affects sEMG activity of leg and thigh muscles during stance phase in patellofemoral pain syndrome

BackgroundDecreases in patellofemoral pain symptoms with bracing treatment have been established; but, the mechanisms remain unclear. The purpose of this study was to determine the immediate and long-term effects of the patellar bracing on electromyography (EMG) activity of the Vastus Medialis (VM) and Lateralis (VL), Rectus Femoris, lateral Gastrocnemius, Biceps Femoris and Semitendinosus (ST) muscles during level walking. Methods12 eligible women aged 20–30 years with diagnosis of patellofemoral pain participated in the before and after study. Intervention consisted of 8 weeks of patellar bracing. First, patients were tested without brace, then with a brace, and finally eight weeks later without a brace. Surface EMG activation of the selected muscles during level walking was recorded. ResultsAfter eight weeks of patellar bracing, EMG activity of VM muscle was significantly higher when compared to first session without brace (p=0.011) at mid-stance sub-phase. Additionally, EMG activity of ST muscle during first session with brace was significantly lower when compared to first session without brace at mid-stance sub-phase (without brace) (p=0.012). EMG activity of VM muscle after eight weeks of patellar bracing was significantly higher than the first session without brace at late stance and preswing sub-phase (p=0.013). ConclusionLong-term wearing of patellar bracing increases EMG activity of VM during mid-stance and late stance and preswing sub-phases of gait and immediate effect of patellar brace is decrease of EMG activity of ST muscle during mid-stance.

Vastus medialis and lateralis activity during voluntary and stimulated contractions

The purpose of this study was to investigate the relative activation of vastus medialis (VM) and vastus lateralis (VL) muscles during voluntary and stimulated isometric contractions at different joint angles. Sixteen healthy men (mean age: 26 years) completed maximal voluntary and stimulated contractions of the knee extensor muscles at 30°, 65°, and 100° of knee flexion. VM/VL ratios were calculated from voluntary electromyographic (EMG) and evoked torque recordings. Both EMG and VM/VL torque ratios were significantly lower at 30° than at 100° of knee flexion (P < 0.05). These results can be explained by the relatively small contribution of the VM muscle to knee extension torque at short muscle length. Such disadvantage of the VM muscle at extended knee positions does not seem to be compensated by an increased neural drive. Muscle Nerve 56: 968-974, 2017.

Slower but not faster unilateral fatiguing knee extensions alter contralateral limb performance without impairment of maximal torque output.

The purpose of the present study was to examine the effects of unilateral fatigue of the knee extensors at different movement velocities on neuromuscular performance in the fatigued and non-fatigued leg. Unilateral fatigue of the knee extensors was induced in 11 healthy young men (23.7 ± 3.8 years) at slower (60°/s; FAT60) and faster movement velocities (240°/s; FAT240) using an isokinetic dynamometer. A resting control (CON) condition was included. The fatigue protocols consisted of five sets of 15 maximal concentric knee extensions using the dominant leg. Before and after fatigue, peak isokinetic torque (PIT) and time to PIT (TTP) of the knee extensors as well as electromyographic (EMG) activity of vastus medialis, vastus lateralis, and biceps femoris muscles were assessed at 60 and 240°/s movement velocities in the fatigued and non-fatigued leg. In the fatigued leg, significantly greater PIT decrements were observed following FAT60 and FAT240 (11-19%) compared to CON (3-4%, p = .002, d = 2.3). Further, EMG activity increased in vastus lateralis and biceps femoris muscle following FAT240 only (8-28%, 0.018 ≤ p ≤ .024, d = 1.8). In the non-fatigued leg, shorter TTP values were found after the FAT60 protocol (11-15%, p = .023, d = 2.4). No significant changes were found for EMG data in the non-fatigued leg. The present study revealed that both slower and faster velocity fatiguing contractions failed to show any evidence of cross-over fatigue on PIT. However, unilateral knee extensor fatigue protocols conducted at slower movement velocities (i.e., 60°/s) appear to modulate torque production on the non-fatigued side (evident in shorter TTP values).

EMG Asymetricity of Selected Knee Extensor Muscles in Sustained Squat Posture (A Yogic Posture) of Athletes in Relation to their Gender and Performance

Squat is a popular yogic exercise or posture, most frequently used for quadriceps strengthening and rehabilitation. It is used for evaluation process or test by physiotherapists/clinicians/others associated with rehabilitation of athletes to strengthen their lower-body muscles and connective tissues after joint-related injury. It has been used extensively for therapeutic treatment of ligament lesions, patellofemoral dysfunctions, patellar subluxation and patellar dislocation etc. The purpose of this study was to compare the effect of sustained squat posture (a yogic posture) of athletes among male (n1=32) and female (n2=18) with high and low performance (based upon median split method) on EMG activity of Vastus Medialis (VM) and Vastus Lateralis (VL) muscles for 120 seconds. Squatting was performed at an angle of 135o-150o because strength of knee extensor (muscles) varies between these angles and is an important consideration for the performance of numerous physical daily routine activities such as walking, running, cycling, stepping and driving including development of fundamental skills for different sports across all ages and sex. VM and VL from the Quadriceps muscle group were chosen for recording the physiological signal simultaneously from right and left leg of the subjects, as these muscles determines stress on the patellofemoral joint and stabilizes the patellar bone during squatting. Frequency and time domain variables were selected to extract meaningful information from the EMG signal using the algorithm developed in MATLAB. The selected variables were Median Frequency (MDF), Mean Frequency (MNF), Root Mean Square (RMS) and Integrated EMG (IEMG). Statistical analysis showed significant differences among gender and performance level along with significant bilateral asymmetry in these athletes. Understanding from the findings is pivotal for achieving optimal muscular strength, for the development of strength endurance and reducing the prospect of training-related injuries

Comparison of Muscle Activation Levels Between Healthy Individuals and Persons Who Have Undergone Anterior Cruciate Ligament Reconstruction During Different Phases of Weight-Bearing Exercises.

Study Design Cross-sectional, controlled laboratory study. Background Quantification of muscular activation during different phases of functional activities is important to understand activation deficits in individuals who have undergone anterior cruciate ligament reconstruction (ACLR). Objectives To compare activation levels of the vastus medialis (VM), medial hamstrings (MH), and gluteus medius (GMed) muscles during the different phases of weight-bearing tasks between individuals who had undergone ACLR and healthy controls. Methods Surface electromyography was used to measure the activation levels of the VM, MH, and GMed muscles in 16 participants who had undergone ACLR (average time since surgery, 4 years) and 15 healthy participants during the reach and return phases of the Star Excursion Balance Test (SEBT) and the ascending and descending phases of a step-down task (SDT). Repeated-measures analyses of variance were performed to determine whether muscle activation levels differed between groups during different phases of the tasks. Results There were significant group-by-phase interactions for the GMed during both the SEBT and SDT. Gluteus medius activation was lower for the ACLR group during the return phase of the posteromedial direction of the SEBT compared to the control group (P = .03). During the SDT, GMed activation was higher for the ACLR group during the ascending phase than during the descending phase (P<.001), while the control group showed no difference between phases (P = .71). Conclusion Individuals who had undergone ACLR have similar VM and MH activation compared to healthy individuals during different phases of the SDT and SEBT. However, phase differences for GMed activity and decreased GMed activity relative to healthy individuals were observed among ACLR participants. J Orthop Sports Phys Ther 2016;46(11):984-992. Epub 11 Oct 2016. doi:10.2519/jospt.2016.5896.

Activation level of vastus medialis muscle in different rehabilitation exercises

Excessive lateralization, which often occurs by the weakening of Vastus Medialis (VM) muscle of the patella, is one of the causes of Patellofemoral Pain Syndrome (PFPS) For prevention and rehabilitation of PFPS, the VM strength is essential. Objective: The aim of the study was to compare the VM activation level in four different exercises used in the prevention and rehabilitation of PFPS that are isometric knee extension at 30° and 60° and isometric squat at 60° with or without hip adduction. Methods: A sample of 14 sedentary healthy subjects, aged between 20 and 40 years was included. The EMG signal of VM muscle was collected during Maximal Voluntary Isometric Contraction with duration of five seconds for each exercise. From the captured EMG signal, a period of three seconds was cut and thereafter the Root Mean Square value for each exercise was obtained. Results: The results showed that there was significantly greater activation in VM extension exercises compared to squat exercises. However, there was no significant difference between the two extension exercises, as well as between squat exercises. Conclusion: It can be concluded that the best exercises to maximize the activation of the VM are the isometric knee extension, regardless of the rated angle, since they have greater VM activation level, essential for the prevention and rehabilitation of PFPS

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.

BackgroundThe 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.ObjectivesThe 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 MethodsMale 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.ResultsEight 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.ConclusionsThe 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).

Comparison Of Muscle Activation Using A Nitrogen Piston-based Resistance Device With Free Weights

Resistance training is especially important for populations at risk of sarcopenia and osteopenia such as older adults or astronauts working in microgravity. A limitation of common forms of resistance training is that they are gravity-based and lack efficacy in microgravity. Therefore, to maintain muscle and bone mass in microgravity, an alternative solution must be sought. One alternative is the use of a gas-filled piston-based resistance training system. PURPOSE: The goal of the current study is to assess the effectiveness of a Nitrogen-filled piston-based resistance training system (NitroForce) compared to isotonic resistance training. METHODS: Thirty recreational athletes performed five repetitions of squat and toe-raise exercises, in two experimental conditions: NitroForce and Isotonic. The NitroForce condition was characterized by resistance of approximately 70% of the participant’s one repetition maximum (1RM) while resistance was supplied using the NitroForce system. Isotonic condition was characterized by participants performing each exercise with resistance equal to 70% of 1RM provided by free weights. Surface electromyography (sEMG, 1928 Hz, Delsys) was recorded from the vastus medialis (VM), vastus lateralis (VL), and the lateral (LG) and medial heads of the gastrocnemius (MG). Mean sEMG amplitude was quantified using the RMS (20 ms smoothing window) and normalized to MVC for each muscle in each condition. Paired samples t-tests were used to compare mean sEMG values. Significance was set at p < 0.05. RESULTS: In the squat exercise, VM activation was significantly greater in the NitroForce compared to isotonic condition (p = 0.039), but no differences were observed in the VL (p = 0.367). No significant differences were observed between the NitroForce and isotonic conditions for the LG (p = 0.400) or MG (p = 0.442) in the toe-raise exercise. CONCLUSIONS: These data demonstrate that muscle activation intensity as measured by sEMG is not significantly different in the NitroForce compared to isotonic conditions. Therefore, the NitroForce provides a similar level of resistance and overload to standard isotonic resistance training loads. However, due to the non-gravity-based nature of the NitroForce, it may provide a better resistance training solution in microgravity environments.

Regional Activation within the Vastus Medialis in Dynamic Contractions

PURPOSE: Regions within the vastus medialis (VM) are known to preferentially produce knee extension force and patellar stabilization. In dynamic tasks, the central nervous system may recruit different VM regions preferentially to cope with changes in mechanical demand resulting from knee movement. The purpose of this study was to determine the effect of knee angle during the concentric and eccentric phases of dynamic movement on the regional activation within the VM. METHODS: Ten healthy women performed two tasks: A) 10 knee flexion-extension open-kinetic chain (OKC) movements between 90 and 10 degrees of knee flexion against an isotonic resistance (10% isometric maximal voluntary contraction); B) 5 closed-kinetic chain (CKC) single-leg squats. Each of the concentric and the eccentric phases of both tasks were performed in 3s. A high-density surface electromyography grid (13x5 electrodes spaced 8 mm apart) was placed across the VM. For each task, the knee angle excursion was segmented in intervals of 10 degrees, and an amplitude distribution was calculated using the average rectified value (ARV) for each channel of the grid. The location of the most active region within the VM was calculated as the barycenter of the three electrodes with the largest ARV. Two-way ANOVAs with repeated measures were used to test the effect of knee angle and phase of the movement on the location of the barycenter, separately for the two tasks. RESULTS: In the OKC task, the barycenter was more distal at more flexed knee positions (P < 0.05; total shift: 7±17 mm) and more so in the eccentric than the concentric phase (P < 0.05; 9±17 mm). Similarly, the barycenter was more distal at more flexed knee positions in the CKC task (P < 0.01; total shift: 21±18 mm) and in the eccentric phase but only between 30 and 10 degrees (P < 0.01; 13±16 mm). CONCLUSIONS: This study reveals differences in regional activation within the VM during dynamic contractions. Although large variability was observed across participants, preferential activation of the proximal VM was observed in both tasks at more extended knee positions and in the concentric phase. As regional activation may result in a different contribution of the VM as a patellar stabilizer, these findings may have implications for therapeutic exercise and for the study of mechanisms of patellofemoral pain syndrome.