Effect of isometric horizontal abduction on pectoralis major and serratus anterior EMG activity during three exercises in subjects with scapular winging

The aim of this study was to determine the effect of isometric horizontal abduction using Thera-Band during three exercises (forward flexion, scaption, and wall push-up plus) in subjects with scapular winging by investigating the electromyographic (EMG) amplitude of the pectoralis major, serratus anterior and the pectoralis major/serratus anterior activity ratio. Twenty-four males with scapular winging participated in this study. The subjects performed the forward flexion, scaption, and wall push-up plus with and without isometric horizontal abduction using Thera-Band. Surface EMG was used to collect the EMG data of the pectoralis major and serratus anterior during the three exercises. Two-way repeated analyses of variance with two within-subject factors (isometric horizontal abduction condition and exercise type) were used to determine the statistical significance of pectoralis major and serratus anterior EMG activity and the pectoralis major/serratus anterior EMG activity ratio. Pectoralis major EMG activity was significantly lower during forward flexion and wall push-up plus with isometric horizontal abduction, and serratus anterior EMG activity was significantly greater with isometric horizontal abduction. Additionally, the pectoralis major/serratus anterior activity ratio was significantly lower during the forward flexion and wall push-up plus with isometric horizontal abduction. The results of this study suggest that isometric horizontal abduction using Thera-Band can be used as an effective method to facilitate the serratus anterior activity and to reduce excessive pectoralis major activity during exercises for activating serratus anterior.     

Electromyographic normalization procedures for determining exercise intensity of closed chain exercises for strengthening the quadriceps femoris muscles

The purpose of this study was to compare the electromyographic (EMG) amplitudes of the quadriceps femoris (QF) muscles during a maximum voluntary isometric contraction (MVIC) to submaximal and maximal dynamic concentric contractions during active exercises. A secondary purpose was to provide information about the type of contraction that may be most appropriate for normalization of EMG data if one wants to determine if a lower extremity closed chain exercise is of sufficient intensity to produce a strengthening response for the QF muscles. Sixty-eight young healthy volunteers (39 female, 29 male) with no lower extremity pain or injury participated in the study. Surface electrodes recorded EMG amplitudes from the vastus medialis obliquus (VMO), rectus femoris (RF), and vastus lateralis (VL) muscles during 5 different isometric and dynamic concentric exercises. The last 27 subjects performed an additional 4 exercises from which a second data set could be analyzed. Maximum isokinetic knee extension and moderate to maximum closed chain exercises activated the QF significantly more than a MVIC. A 40-cm. lateral step-up exercise produced EMG amplitudes of the QF muscles of similar magnitude as the maximum isokinetic knee extension exercises and would be an exercise that could be considered for strengthening the QF muscles. Most published EMG studies of exercises for the QF have been performed by comparing EMG amplitudes during dynamic exercises to a MVIC. This procedure can lead one to overestimate the value of a dynamic exercise for strengthening the QF muscles. We suggest that when studying the efficacy of a dynamic closed chain exercise for strengthening the QF muscles, the exercise be normalized to a dynamic maximum muscle contraction such as that obtained with knee extension during isokinetic testing.     

Effects of physioball and conventional floor exercises on early phase adaptations in back and abdominal core stability and balance in women

The purpose of this study was to compare the effects of 5 weeks of physioball core stability and balance exercises with conventional floor exercises in women. The experimental group (n = 15) performed curl-ups and back extensions on the physioball while the control group (n = 15) performed the same exercises on the floor. Baseline and post-training tests included electromyography (EMG) recordings of the rectus abdominus and erector spinae muscles; abdominal, back, and knee strength measurements with the Cybex Norm System; and 2 unilateral stance balance tests. The physioball group was found to have significantly greater mean change in EMG flexion and extension activity (p = 0.04 and p = 0.01, respectively) and greater balance scores (p < 0.01) than the floor exercise group. No significant changes (p > 0.05) were observed for heart rate or Cybex strength measurements. Early adaptations in a short-term core exercise program using the physioball resulted in greater gains in torso balance and EMG neuronal activity in previously untrained women when compared to performing exercises on the floor.     

Reliability of electromyographic normalization methods for evaluating the hip musculature.

The purpose of this study was to determine the reliability of three normalization methods for analyzing hip abductor activation during rehabilitation exercises. Thirteen healthy subjects performed three open kinetic chain and three closed kinetic chain hip abductor exercises. Surface EMG activity for the gluteus medius was collected during each exercise and normalized based on a maximum voluntary isometric contraction (MVIC), mean dynamic (m-DYN), and peak dynamic activity (pk-DYN). Intraclass coefficient correlations (ICCs), intersubject coefficients of variation (CVs), and intrasubject CVs were then calculated for each normalization method. MVIC ICCs exceeded 0.93 for all exercises. M-DYN and pk-DYN ICCs exceeded 0.85 for all exercises except for the sidelying abduction exercise. Intersubject CVs ranged from 55% to 77% and 19% to 61% for the MVIC and dynamic methods, respectively. Intrasubject CVs ranged from 11% to 22% for all exercises under all normalization methods. The MVIC method provided the highest measurement reliability for determining differences in activation amplitudes between hip abductor exercises in healthy subjects. Future research should determine if these same results would apply to a symptomatic patient population.     

Comparison of muscle activation levels during arm abduction in the plane of the scapula vs. proprioceptive neuromuscular facilitation upper extremity patterns

This study quantified activation of 8 muscles of the shoulder, trunk, and back during standing performance of (a) arm abduction in the plane of the scapula (scaption), (b) proprioceptive neuromuscular facilitation (PNF) diagonal 1 flexion (D1F), and (c) PNF diagonal 2 flexion (D2F) while lifting a dumbbell with the dominant hand. Twelve men (26.1 ± 4.4 years) and 13 women (24.5 ± 1.9 years) volunteered to participate. Electromyographic signals were collected with DE-3.1 double-differential surface electrodes at a sampling frequency of 1,000 Hz. Electromyographic signals were normalized to peak activity in the maximum voluntary isometric contraction (MVIC) trial and expressed as a percentage. One-way repeated-measures analysis of variance with Bonferroni corrections (α = 0.05) examined muscle activation patterns across the 3 conditions. For the middle trapezius, average activation was greater (p < 0.001) for D2F (70.5 ± 23.4% MVIC) than D1F (46.4 ± 19.6% MVIC). Lower trapezius average activation was greater (p < 0.001) for D2F (55.3 ± 23.8% MVIC) than D1F (40.1 ± 16% MVIC). The anterior deltoid showed greater activation (p = 0.009) for scaption (92.4 ± 26% MVIC) than D1F (74.4 ± 21.4% MVIC). The erector spinae showed greater activation for D2F (34.2 ± 12% MVIC; p < 0.001) and D1F (41.7 ± 21.4% MVIC; p < 0.001) than scaption (14.5 ± 12.3% MVIC). During D2F and scaption, all 6 muscles of the shoulder complex demonstrated very high activation levels (>60% MVIC) with the exception of the lower trapezius (55% MVIC). In contrast, erector spinae and external oblique muscles exhibited moderate activation (21-40% MVIC) during arm elevation. The 6 muscles of the shoulder complex displayed high to very high muscle activation at a level appropriate for strength training during all 3 exercise conditions.     

The effect of increasing resistance on trunk muscle activity during extension and flexion exercises on training devices

Although progressive resistance training of trunk muscles on devices is very common, today, the effects of increasing resistance on trunk muscle activity during dynamic extension and flexion movements on training devices have not been reported yet. Thirty healthy subjects participated in maximal isometric and submaximal dynamic (at 30%, 50% and 70% of maximum mean torque (MMT)) extension and flexion exercises on Tergumed lumbar training devices. The normalized (as a percentage of maximal voluntary isometric contractions (MVIC)) electromyographic activity of 16 abdominal and back muscles was investigated. The results of the present study indicated that in general, with increasing resistance from 30% MMT to 50% MMT and 70% MMT, the activity of all back muscles during the extension exercises and the activity of all abdominal muscles during the flexion exercises increased significantly. To train strength (>60% of MVIC), low intensities (30% and 50% MMT) appeared sufficient to affect the back muscles, but for the abdominals higher resistance (70% MMT) was required. In contrast to the other back muscles, the lumbar multifidus demonstrated high activity levels during both the extension and the flexion exercises. As the lumbar multifidus is demonstrated to be an important muscle in segmental stabilization of the lumbar spine, this finding may help in understanding the efficacy of rehabilitation programs using specific training devices.     

Influence of the intensity of a conditioning contraction on the subsequent twitch torque and maximal voluntary concentric torque

This study aimed to clarify the influence of the intensity of a conditioning contraction on subsequent isometric twitch and maximal voluntary concentric torques. Subjects (n=12men) performed voluntary isometric plantar flexion for six seconds as a conditioning contraction, at intensities of 40%, 60%, 80% and 100% of a maximal voluntary isometric contraction (MVIC). Before and immediately after the conditioning contraction, isometric twitch and maximal voluntary concentric (180°/s) plantar flexion torques were determined. Surface electromyograms were recorded from the triceps surae muscles and M-wave amplitudes and root-mean-square values of the electromyographic signals (RMS(EMG)) were calculated. The isometric twitch torque increased significantly after conditioning contraction at all intensities (P<0.05), whereas maximal voluntary concentric torque increased significantly only at 80% and 100% MVIC conditions (P<0.05). It is concluded that during a six second conditioning contraction, the effect of the intensity of a conditioning contraction on subsequent torque development is different between an isometric twitch and maximal voluntary concentric contractions, with the latter being less affected.     

Surface electromyographic activation patterns and elbow joint motion during a pull-up, chin-up, or perfect-pullup™ rotational exercise

This study compared a conventional pull-up and chin-up with a rotational exercise using Perfect·Pullup? twisting handles. Twenty-one men (24.9 ± 2.4 years) and 4 women (23.5 ± 1 years) volunteered to participate. Electromyographic (EMG) signals were collected with DE-3.1 double-differential surface electrodes at a sampling frequency of 1,000 Hz. The EMG signals were normalized to peak activity in the maximum voluntary isometric contraction (MVIC) trial and expressed as a percentage. Motion analysis data of the elbow were obtained using Vicon Nexus software. One-factor repeated measures analysis of variance examined the muscle activation patterns and kinematic differences between the 3 pull-up exercises. Average EMG muscle activation values (%MVIC) were as follows: latissimus dorsi (117-130%), biceps brachii (78-96%), infraspinatus (71-79%), lower trapezius (45-56%), pectoralis major (44-57%), erector spinae (39-41%), and external oblique (31-35%). The pectoralis major and biceps brachii had significantly higher EMG activation during the chin-up than during the pull-up, whereas the lower trapezius was significantly more active during the pull-up. No differences were detected between the Perfect·Pullup? with twisting handles and the conventional pull-up and chin-up exercises. The mean absolute elbow joint range of motion was 93.4 ± 14.6°, 100.6 ± 14.5°, and 99.8 ± 11.7° for the pull-up, chin-up, and rotational exercise using the Perfect·Pullup? twisting handles, respectively. For each exercise condition, the timing of peak muscle activation was expressed as a percentage of the complete pull-up cycle. A general pattern of sequential activation occurred suggesting that pull-ups and chin-ups were initiated by the lower trapezius and pectoralis major and completed with biceps brachii and latissimus dorsi recruitment. The Perfect·Pullup? rotational device does not appear to enhance muscular recruitment when compared to the conventional pull-up or chin-up.     

An electromyographic study of elbow motion during postexercise muscle soreness

Postexercise muscle soreness was induced in the elbow flexors of human volunteer subjects through the use of a regimen of eccentric contractions. Physical examination before and 48 h after the exercise included measurements of range of elbow motion at the elbow and of arm diameter. Electromyographic (EMG) observations, utilizing fine wire electrodes introduced into each of the elbow flexors, were carried out before and 48 h after the exercise. These observations included resting EMG levels, EMG activity under various isometric loads, and activity during active and passive extensions. The soreness induced was accompanied by a reduction in resting elbow angle while the subjects stood with arms relaxed at their sides, decreased range of both flexion and extension of the elbow, and swelling of the arm. EMG measurements showed no increase in EMG activity as the sore arms were extended passively at the elbow, indicating that the extra resistance to extension associated with the soreness was not a result of stretch receptor-induced activity in the flexors. The results rule out the possibility that neuromuscular activity is responsible for the restriction of motion and are consistent with the idea that edematous changes within the perimuscular connective tissue alter the elastic behavior of the muscles and cause restriction of motion.     

Superimposing hip extension on knee flexion evokes higher activation in biceps femoris than knee flexion alone

Hamstring muscle function during knee flexion has been linked to hamstring injury and performance. However, it is unclear whether knee flexion alone (KF) requires similar hamstring electromyography (EMG) activity pattern to simultaneous hip extension and knee flexion (HE-KF), a combination that occurs in the late swing phase of sprinting. This study examined whether HE-KF maximal voluntary isometric contraction (MVIC) evokes higher (EMG) activity in biceps femoris long head (BFlh) and semitendinosus (ST) than KF alone. Effects of shank rotation angles were also tested. Twenty-one males performed the above-mentioned MVICs while EMG activity was measured along ST and BFlh. Conditions were compared using a one-way mixed functional ANOVA model under a fully Bayesian framework. Higher EMG activity was found in HE-KF in all shank rotation positions than in KF in the middle region of BFlh (highest in the 9th channel, by 0.022 mV [95%CrI 0.014 to 0.030] in neutral shank position). For ST, this was only observed in the neutral shank position and in the most proximal channel (by 0.013 mV [95%CrI 0.001 to 0.025]). We observed muscle- and region-specific responses to HE-KF. Future studies should examine whether hamstring activation in this task is related to injury risk and sprint performance.     

Posture-dependent trunk extensor EMG activity during maximum isometrics exertions in normal male and female subjects.

Posture-dependent trunk function data are important for appropriate normalization of submaximal trunk exertions, and is also necessary to define a more precise and specific use for strength testing in the prevention and diagnosis of spinal disorders. The aim of the current study was to quantify maximal effort trunk muscle extensor activity and trunk isometric extension torque over a functional range of sagittal standing postures. Twenty healthy, young adult male and female subjects performed isometric extension tasks over a sagittal posture range of -20 degrees extension to +50 degrees flexion, in 10 degrees increments. Erector spinae muscle activity was recorded bilaterally at the level of L3 using surface EMG electrodes. Isometric trunk extension torque was measured using a trunk dynamometer. EMG and trunk torque differed significantly between genders, but there were no differences between male and female subjects when the data were normalized with respect to the upright posture. For the combined male and female population, upright posture normalized L3 EMG activity (EMGn) and trunk extension torque (Tn) increased 1.7-fold and 3.5-fold, respectively, over the 70 degrees range of sagittal postures examined. The ratio (Tn/EMGn) increased two-fold (0.83 to 1.67) from -20 degrees extension to +50 degrees flexion, indicating that the neuromuscular efficiency increases with flexion. Trunk extension torque normalized with respect to the upright posture was linearly and positively correlated (r = 0.59, P < 0.001) to similarly normalized L3 EMG activity. This relatively weak correlation suggests that trunk muscle synergism and/or intrinsic muscle length-tension relationships are also modulated by posture. This study provides data that can be used to estimate trunk extensor muscle function over a broad range of sagittal postures. Our findings indicate that appropriate postural normalization of trunk extensor EMG activity is necessary for studies where submaximal trunk exertions are performed over a range of upright postures.     

Technical report: Reliability and validity of the iSAM 9000 isokinetic dynamometer

This study assessed the mechanical reliability and validity of the INRTEK iSAM 9000 isokinetic dynamometer, and compared the obtained torque values of the prototype device with those from a traditional device. Sixty volunteers (40 men and 20 women) were tested at 60 degrees per second for shoulder, knee, and trunk flexion, and extension on both the Cybex 6000 and a new isokinetic dynamometer (iSAM 9000). Intraclass correlation coefficients (ICC) and standard errors of measurement (SEM) revealed a high level of reproducibility and precision in the device's torque measurements (ICC range = 0.94-0.98; SEM range = 5.2-29.7). Pearson r values revealed very high relationships between the two instruments (set 1: r = 0.84-0.93; set 2: r = 0.87-0.93; P < 0.05). Significantly higher peak torque for both sets of left and right knee flexion and extension, right shoulder extension and trunk extension was found for the iSAM 9000 compared to the Cybex 6000 (P < 0.05). The strong ICCs and small SEMs support the device's mechanical reliability and validity. The high correlation coefficients between the prototype dynamometer and the Cybex 6000 support the new device's validity in the measurement of isokinetic torque. The findings of this study will be used to refine the next generation of the INRTEK isokinetic device with respect to test protocols and the reliability of measuring human muscle performance.     

Comparison of erector spinae and hamstring muscle activities and lumbar motion during standing knee flexion in subjects with and without lumbar extension rotation syndrome

The aim of this study was to compare the activity of the erector spinae (ES) and hamstring muscles and the amount and onset of lumbar motion during standing knee flexion between individuals with and without lumbar extension rotation syndrome. Sixteen subjects with lumbar extension rotation syndrome (10 males, 6 females) and 14 healthy subjects (8 males, 6 females) participated in this study. During the standing knee flexion, surface electromyography (EMG) was used to measure muscle activity, and surface EMG electrodes were attached to both the ES and hamstring (medial and lateral) muscles. A three-dimensional motion analysis system was used to measure kinematic data of the lumbar spine. An independent-t test was conducted for the statistical analysis. The group suffering from lumbar extension rotation syndrome exhibited asymmetric muscle activation of the ES and decreased hamstring activity. Additionally, the group with lumbar extension rotation syndrome showed greater and earlier lumbar extension and rotation during standing knee flexion compared to the control group. These data suggest that asymmetric ES muscle activation and a greater amount of and earlier lumbar motion in the sagittal and transverse plane during standing knee flexion may be an important factor contributing to low back pain.     

Jogging gait kinetics following fatiguing lumbar paraspinal exercise

A relationship exists between lumbar paraspinal muscle fatigue and quadriceps muscle activation. The objective of this study was to determine whether hip and knee joint moments during jogging changed following paraspinal fatiguing exercise. Fifty total subjects (25 with self-reported history of low back pain) performed fatiguing, isometric lumbar extension exercise until a shift in EMG median frequency corresponding to a mild level of muscle fatigue was observed. We compared 3-dimensional external joint moments of the hip and knee during jogging before and after lumbar paraspinal fatigue using a 10-camera motion analysis system. Reduced external knee flexion, knee adduction, knee internal rotation and hip external rotation moments and increased external knee extension moments resulted from repetitive lumbar paraspinal fatiguing exercise. Persons with a self-reported history of LBP had larger knee flexion moments than controls during jogging. Neuromuscular changes in the lower extremity occur while resisting knee and hip joint moments following isolated lumbar paraspinal exercise. Persons with a history of LBP seem to rely more heavily on quadriceps activity while jogging.     

EMG activity of low back extensor muscles during cyclic flexion/extension

Cyclic trunk flexion/extension is known to be a risk factor for low back pain or disorders. Changes in the in vivo low back musculature associated with cyclic flexion/extension have not been adequately examined. The purpose of this study was to investigate the effects of cyclic flexion/extension on muscle activity of the low back extensors by quantifying changes in activation timing and mean amplitude of electromyography (EMG). Trunk flexion angle and EMG were recorded during 30 cyclic flexion/extension movements over a 5 min period, and during isometric extension performed before and after the 5 min period. Mean EMG in isometric extension increased (30% increase in average) significantly after cyclic flexion/extension, confirming a transfer of extension moment from viscoelastic passive tissues to the extensor muscles in isometric extension. However, in the extension phase of cyclic flexion/extension, a significant delay in the re-activation and a decrease in the mean amplitude of EMG were observed. The results of this study, together with findings in previous research, suggest that the biomechanical effects and potential risk associated with cyclic flexion/extension may be sensitive to the task demands. Further research is needed to investigate how different moment generating components function together to compensate for the loss of tissue stiffness under varying task conditions.     

Are the maximum shortening velocity and the shape parameter in a Hill-type model of whole muscle related to activation?

Mathematical models of the inter-relationship of muscle force, velocity, and activation are useful in forward dynamic simulations of human movement tasks. The objective of this work was to determine whether the parameters (maximum shortening velocity V(max) and shape parameter k) of a Hill-type muscle model, interrelating muscle force, velocity, and activation, are themselves dependent on the activation. To fulfill this objective, surface EMG signals from four muscles, as well as the kinematics and kinetics of the arm, were recorded from 14 subjects who performed rapid-release elbow extension tasks at 25%, 50%, 75%, and 100% activation (MVC). The experimental elbow flexion angle was tracked by a forward dynamic simulation of the task in which V(max) and k of the triceps brachii were varied at each activation level to minimize the difference between the simulated and experimental elbow flexion angle. Because a preliminary analysis demonstrated no dependency of k on activation, additional simulations were performed with constant k values of 0.15, 0.20, and 0.25. The optimized values of V(max) normalized to the average value within a subject were then regressed onto the activation. Normalized V(max) depended significantly on the activation (p<0.001) for all values of k. Furthermore, the estimated V(max) values were not sensitive to the selected k value. The results support the use of Hill-type models in which V(max) depends on activation in forward dynamic simulations modeling muscles with mixed fiber-type composition recruited in the range of 25-100% activation. The use of more accurate models will lend greater confidence to the results of forward dynamic simulations.     

EMG of upper trapezius − Electrode sites and association with clavicular kinematics

The upper trapezius (UT) has been widely studied and related to alterations in clavicular kinematics in subject with shoulder disorders. However, the most common electrode site used to capture UT EMG is between C7 and the acromion, placing the electrodes over the acromial fibers rather than clavicular ones. Therefore, this study aimed to investigate the relationship between clavicular movements (elevation and retraction) and UT EMG recorded from three electrode sites (traditional electrode positioning and two different sites proposed for clavicular fibers evaluation). Furthermore, the position associated with the highest EMG during maximal isometric voluntary contractions (MVIC), for each electrode site, was determined for normalization purposes. EMG was simultaneously captured in the three electrode sites of 20 healthy subjects, during MVIC at five different positions and during shoulder elevation and abduction in scapular plane. Clavicular kinematics was recorded using an electromagnetic tracking system during the dynamic contractions. Shoulder abduction with head rotation and lateral flexion elicited the highest EMG amplitude on the three electrode sites and was used to normalize the signals. A cross-correlation analysis showed high correlations between all electrode sites and clavicular movements. However, the traditional electrode site seems to record more informative signals in healthy subjects.     

Feasibility of using EMG driven neuromusculoskeletal model for prediction of dynamic movement of the elbow.

Neuromusculoskeletal (NMS) modeling is a valuable tool in orthopaedic biomechanics and motor control research. To evaluate the feasibility of using electromyographic (EMG) signals with NMS modeling to estimate individual muscle force during dynamic movement, an EMG driven NMS model of the elbow was developed. The model incorporates dynamical equation of motion of the forearm, musculoskeletal geometry and musculotendon modeling of four prime elbow flexors and three prime elbow extensors. It was first calibrated to two normal subjects by determining the subject-specific musculotendon parameters using computational optimization to minimize the root mean square difference between the predicted and measured maximum isometric flexion and extension torque at nine elbow positions (0-120 degrees of flexion with an increment of 15 degrees ). Once calibrated, the model was used to predict the elbow joint trajectories for three flexion/extension tasks by processing the EMG signals picked up by both surface and fine electrodes using two different EMG-to-activation processing schemes reported in the literature without involving any trajectory fitting procedures. It appeared that both schemes interpreted the EMG somewhat consistently but their prediction accuracy varied among testing protocols. In general, the model succeeded in predicting the elbow flexion trajectory in the moderate loading condition but over-drove the flexion trajectory under unloaded condition. The predicted trajectories of the elbow extension were noted to be continuous but the general shape did not fit very well with the measured one. Estimation of muscle activation based on EMG was believed to be the major source of uncertainty within the EMG driven model. It was especially so apparently when fine wire EMG signal is involved primarily. In spite of such limitation, we demonstrated the potential of using EMG driven neuromusculoskeletal modeling for non-invasive prediction of individual muscle forces during dynamic movement under certain conditions.     

Neuromuscular Activation of the Vastus Intermedius Muscle during Isometric Hip Flexion

Although activity of the rectus femoris (RF) differs from that of the other synergists in quadriceps femoris muscle group during physical activities in humans, it has been suggested that the activation pattern of the vastus intermedius (VI) is similar to that of the RF. The purpose of present study was to examine activation of the VI during isometric hip flexion. Ten healthy men performed isometric hip flexion contractions at 25%, 50%, 75%, and 100% of maximal voluntary contraction at hip joint angles of 90°, 110° and 130°. Surface electromyography (EMG) was used to record activity of the four quadriceps femoris muscles and EMG signals were root mean square processed and normalized to EMG amplitude during an isometric knee extension with maximal voluntary contraction. The normalized EMG was significantly higher for the VI than for the vastus medialis during hip flexion at 100% of maximal voluntary contraction at hip joint angles of 110° and 130° (P < 0.05). The onset of VI activation was 230–240 ms later than the onset of RF activation during hip flexion at each hip joint angle, which was significantly later than during knee extension at 100% of maximal voluntary contraction (P < 0.05). These results suggest that the VI is activated later than the RF during hip flexion. Activity of the VI during hip flexion might contribute to stabilize the knee joint as an antagonist and might help to smooth knee joint motion, such as in the transition from hip flexion to knee extension during walking, running and pedaling.     

Effects of hand and knee positions on muscular activity during trunk extension exercise with the Roman chair

This experimental study was performed to investigate the effects of hand and knee positions on muscular activity during back extension exercises with the Roman chair. Eighteen asymptomatic male amateur athletes performed four prone back extension exercises with two hand positions (crossed-arms and behind-the-head), and two knee positions (extended knee and 90° flexed knee). Surface electromyography (sEMG) was performed to collect data from the lower trapezius (LT), latissimus dorsi (LD), erector spinae in the T12 paraspinal region (ES-T12), erector spinae at the L3 level (ES-L3), gluteus maximus (GM), and biceps femoris (BF). Two-way repeated analysis of variance with two within-subject factors (two hand positions and two knee positions) was used to determine the significance of differences between the exercise conditions, and which hand and knee positions resulted in greater activation with exercise variation. The root mean square sEMG values were normalized using the maximum voluntary isometric contraction (MVIC) and represented as the % of the maximum EMG (%mEMG). There was no significant interaction between knee and hand positions in the %mEMG data. The results showed that the hand position affected the normalized activation of LT; the behind-the-head position resulted in significantly greater muscle activation than the crossed-arms hand position (P < 0.05). The activations of the LD, ES-T10, ES-L4, and GM were greater in the 90° flexed-knee position compared to the extended-knee position (P < 0.05). Although back extension exercise using the Roman chair has been shown to effectively activate the extensor musculature, our results indicated that changing the knee and hand positions could activate specific muscles differently. To achieve greater activation of trunk extensor muscle during extension exercise with the Roman chair, the flexed-knee position is a useful means of increasing resistance.