Exploring the effect of repeated-day familiarization on the ability to generate reliable maximum voluntary muscle activation

Maximum voluntary isometric contractions (MVCs) are commonly used to normalize electromyography (EMG) data and must be reliable even if the individual has no prior experience performing MVCs. This study explored the effect of familiarization over three testing sessions on MVC performance and reliability by comparing muscle activation during standardized maximal and sub-maximal muscle contractions. Participants were recruited into two groups: (1) individuals who regularly engaged in upper body resistance training; (2) individuals with little or no prior experience in upper body resistance training. EMG was collected from two pairs of muscles; biceps brachii and triceps brachii from the arm, and erector spinae and external oblique from the trunk. The trunk muscles were chosen as muscles that are less frequently activated in isolation in day-to-day life. It was found that there were no significant improvements in MVC performance or within-day reliability over the three testing sessions for both resistance trained and non-resistance trained groups. Resistance-trained individuals showed a trend to be more reliable within-day than non-resistance trained participants. Day-to-day MVC reliability, particularly of the erector spinae muscle, was limited in some participants. This suggests that further efforts are needed to improve our capability of reliably eliciting muscle activation MVCs for EMG normalization, especially for muscles that are less frequently activated in isolation.     

Effect of the upper limbs muscles activity on the mechanical energy gain in pole vaulting

The shoulder muscles are highly solicited in pole vaulting and may afford energy gain. The objective of this study was to determine the bilateral muscle activity of the upper-limbs to explain the actions performed by the vaulter to bend the pole and store elastic energy. Seven experienced athletes performed 5-10 vaults which were recorded using two video cameras (50Hz). The mechanical energy of the centre of gravity (CG) was computed, while surface electromyographic (EMG) profiles were recorded from 5 muscles bilateral: deltoideus, infraspinatus, biceps brachii, triceps, and latissimus dorsi muscles. The level of intensity from EMG profile was retained in four sub phases between take-off (TO1) and complete pole straightening (PS). The athletes had a mean mechanical energy gain of 22% throughout the pole vault, while the intensities of deltoideus, biceps brachii, and latissimus dorsi muscles were sub phases-dependent (p<0.05). Stabilizing the glenohumeral joint (increase of deltoideus and biceps brachii activity) and applying a pole bending torque (increase of latissimus dorsi activity) required specific muscle activation. The gain in mechanical energy of the vaulter could be linked to an increase in muscle activation, especially from latissimusdorsi muscles.     

Characteristics of Surface Electromyography of Forehand Smash of Badminton Players

To understand the characteristics of the forehand smash of badminton player and improve their performance, this study took eight badminton players as the subject, obtained the kinematics data through the Qualisys infrared high-speed camera, obtained the electromyography (EMG) data through the ME-6000 surface EMG test system, and compared and analyzed their forehand smash action. The results showed that the greater the angle and speed of different joints in the forehand smash was, the greater the speed and strength of hitting the ball was; the discharge amount of biceps brachii (BB) was the smallest, followed by triceps brachii (TB), flexor carpi ulnaris (FCU), anterior deltoid (AD), posterior deltoid (FD), and pectoralis major (PM), and the activation order was PM → AD → FD → BB → TB → FCU; deltoid muscle and pectoralis major muscle were the main muscle groups in the exercise, which showed the characteristic that trunk muscles drove arm muscles.     

Differences in muscle activation between submaximal and maximal 6-minute rowing tests

This study aimed to establish the differences in muscle activation between a 6-minute simulated race (all-out test) and a submaximal (blood lactate [LA] concentration 4 mmol·L(-1)) 6-minute effort (submax test) on a rowing ergometer. Eleven healthy, well-trained subjects performed the submax test followed after 1-hour rest by the all-out test. Surface electromyographic (sEMG) signal of muscles gastrocnemius medialis (GC), rectus femoris (RF), vastus lateralis (VL), biceps femoris, gluteus maximus (GM), erector spinae (ES), lower latissimus dorsi (LD_lo), upper latissimus dorsi (LD_up), brachioradialis (BR) and biceps brachii (BB), and other biomechanical, biochemical, and respiratory parameters were monitored during rowing. During the all-out test, the subjects covered a longer distance with larger average power output, higher stroke frequency, LA concentration, and oxygen consumption compared to the submax test (p < 0.05). During the submax test, the average rectified values (ARVs) of sEMG signal increased significantly only in the RF and LD_lo muscles. During the all-out test, the ARVs of the RF, VL, and GM muscles increased (p < 0.05), whereas the MDFs of the RF, ES, and LD_lo muscles decreased (p < 0.05). Compared to the submax test, the ARVs of the GC, RF, VL, LD_lo, LD_up, and BB muscles were significantly higher during the all-out test. However, only for the RF muscle, the all-out test resulted in a significantly lower MDF value compared to the submax test. The most involved muscles that would need special attention in training seem to be the leg and shoulder girdle extensors and arm flexors but not the trunk and hip extensors.     

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.     

Electromyography variables during the golf swing: A literature review

The aim of the study was to review systematically the literature available on electromyographic (EMG) variables of the golf swing. From the 19 studies found, a high variety of EMG methodologies were reported. With respect to EMG intensity, the right erector spinae seems to be highly activated, especially during the acceleration phase, whereas the oblique abdominal muscles showed moderate to low levels of activation. The pectoralis major, subscapularis and latissimus dorsi muscles of both sides showed their peak activity during the acceleration phase. High muscle activity was found in the forearm muscles, especially in the wrist flexor muscles demonstrating activity levels above the maximal voluntary contraction. In the lower limb higher muscle activity of the trail side was found. There is no consensus on the influence of the golf club used on the neuromuscular patterns described. Furthermore, there is a lack of studies on average golf players, since most studies were executed on professional or low handicap golfers.Further EMG studies are needed, especially on lower limb muscles, to describe golf swing muscle activation patterns and to evaluate timing parameters to characterize neuromuscular patterns responsible for an efficient movement with lowest risk for injury.     

The long head of the triceps brachii as a free functioning muscle transfer

This anatomic study investigates the possibility of using the long head of the triceps brachii muscle as a free functioning muscle transfer for the upper limb. It has been reported that the long head is not difficult to harvest and that its loss does not create significant donor-site morbidity. The muscle was studied in 23 fresh frozen upper limbs. The long head in all 23 specimens had a constant and proximal vascular pedicle from the profunda brachii artery and vein. The mean pedicle was long (4 cm) and had large-caliber vessels (diameter, 3-mm artery and 4-mm vein). Angiograms were carried out in five specimens and dye perfusion studies in six specimens. A single branch from the radial nerve of at least 7 cm in length innervated the muscle. Muscle architecture was studied in 12 specimens and revealed that the long head of the triceps is better suited for forearm reconstruction than either the gracilis or the latissimus dorsi muscles. The mean physiologic cross-sectional area (8.36 cm(2)) and fiber length (10.8 cm on the superficial surface and 8.2 cm on the deep surface) of the long head match more closely those of the flexor digitorum profundus and the extensor digitorum communis, the muscles most commonly replaced.     

MVC techniques to normalize trunk muscle EMG in healthy women

Normalization of the surface electromyogram (EMG) addresses some of the inherent inter-subject and inter-muscular variability of this signal to enable comparison between muscles and people. The aim of this study was to evaluate the effectiveness of several maximal voluntary isometric contraction (MVC) strategies, and identify maximum electromyographic reference values used for normalizing trunk muscle activity. Eight healthy women performed 11 MVC techniques, including trials in which thorax motion was resisted, trials in which pelvis motion was resisted, shoulder rotation and adduction, and un-resisted MVC maneuvers (maximal abdominal hollowing and maximal abdominal bracing). EMG signals were bilaterally collected from upper and lower rectus abdominis, lateral and medial aspects of external oblique, internal oblique, latissimus dorsi, and erector spinae at T9 and L5. A 0.5 s moving average window was used to calculate the maximum EMG amplitude of each muscle for each MVC technique. A great inter-subject variability between participants was observed as to which MVC strategy elicited the greatest muscular activity, especially for the oblique abdominals and latissimus dorsi. Since no single test was superior for obtaining maximum electrical activity, it appears that several upper and lower trunk MVC techniques should be performed for EMG normalization in healthy women.     

Influence of fatigue on upper limb muscle activity and performance in tennis

The study examined the fatigue effect on tennis performance and upper limb muscle activity. Ten players were tested before and after a strenuous tennis exercise. Velocity and accuracy of serve and forehand drives, as well as corresponding surface electromyographic (EMG) activity of eight upper limb muscles were measured. EMG and force were also evaluated during isometric maximal voluntary contractions (IMVC). Significant decreases were observed after exercise in serve accuracy (−11.7%) and velocity (−4.5%), forehand accuracy (−25.6%) and consistency (−15.6%), as well as pectoralis major (PM) and flexor carpi radialis (FCR) IMVC strength (−13.0% and −8.2%, respectively). EMG amplitude decreased for PM and FCR in serve, forehand and IMVC, and for extensor carpi radialis in forehand. No modification was observed in EMG activation timing during strokes or in EMG frequency content during IMVC. Several hypotheses can be put forward to explain these results. First, muscle fatigue may induce a reduction in activation level of PM and forearm muscles, which could decrease performance. Second, conscious or subconscious strategies could lead to a redistribution of muscle activity to non-fatigued muscles in order to protect the organism and/or limit performance losses. Otherwise, the modifications of EMG activity could also illustrate the strategies adopted to manage the speed-accuracy trade-off in such a complex task.     

Variations in muscle activation levels during traditional latissimus dorsi weight training exercises: An experimental study.

BACKGROUND: Exercise beliefs abound regarding variations in strength training techniques on muscle activation levels yet little research has validated these ideas. The purpose of the study is to determine muscle activation level, expressed as a percent of a normalization contraction, of the latissimus dorsi, biceps brachii and middle trapezius/rhomboids muscle groups during a series of different exercise tasks. METHODS: The average muscle activity during four tasks; wide grip pulldown, reverse grip pull down [RGP], seated row with retracted scapula, and seated rows with non-retracted scapulae was quantified during two 10 second isometric portions of the four exercises. A repeated measures ANOVA with post-hoc Tukey test was used to determine the influence of exercise type on muscle activity for each muscle. RESULTS & DISCUSSION: No exercise type influenced biceps brachii activity. The highest latissimus dorsi to biceps ratio of activation occurred during the wide grip pulldown and the seated row. Highest levels of myoelectric activity in the middle trapezius/rhomboid muscle group occurred during the seated row. Actively retracting the scapula did not influence middle trapezius/rhomboid activity. CONCLUSION: Variations in latissimus dorsi exercises are capable of producing small changes in the myoelectric activity of the primary movers.     

Effect of balance taping on trunk stabilizer muscles for back extensor muscle endurance: A randomized controlled study

Objective:The purpose of this study was to investigate the difference in back extensor muscle endurance before and after kinesiology tape application to all back stabilizer muscles and to the erector spinae alone.Methods:We assessed 32 adults (16 men and 16 women), randomly divided into two groups. In the erector spinae taping (EST) group, kinesiology tape was applied only to the erector spinae, and in the total muscle taping (TMT) group, kinesiology tape was applied to the erector spinae, latissimus dorsi, lower trapezius, internal oblique abdominis, and external oblique abdominis.Results:Both groups showed significant difference in terms of back extensor muscle endurance after kinesiology tape application (p<0.05). Between-group comparison revealed that the TMT group had more back extensor muscle endurance than the EST group (p<0.05) after kinesiology tape application.Conclusions:These findings indicate that, to improve back extensor muscle endurance, kinesiology tape should be applied to all back stabilizer muscles, rather than to the erector spinae muscles alone.     

An empirical approach to characterizing trunk muscle coactivation using simulation input modeling techniques

Accurately describing trunk muscle coactivation is fundamental to quantifying the spine reaction forces that occur during lifting tasks and has been the focus of a great deal of research in the spine biomechanics literature. One limitation of previous approaches has been a lack of consideration given to the variability in these coactivation strategies. The research presented in this paper is an empirical approach to quantifying and modeling trunk muscle coactivation using simulation input modeling techniques. Electromyographic (EMG) data were collected from 28 human subjects as they performed controlled trunk extension exertions. These exertions included isokinetic (10 and 45°/s) and constant acceleration (50°/s/s) trunk extensions in symmetric and asymmetric (30°) postures at two levels of trunk extension moment (30 and 80 Nm). The EMG data were collected from the right and left pairs of the erector spinae, latissimus dorsi, rectus abdominis, external obliques and internal obliques. Each subject performed nine repetitions of each combination of independent variables. The data collected during these trials were used to develop marginal distributions of trunk muscle activity as well as a 10×10 correlation matrix that described how the muscles cooperated to produce these extension torques. These elements were then combined to generate multivariate distributions describing the coactivation of the trunk musculature. An analysis of these distributions revealed that increases in extension moment, extension velocity and sagittal flexion angle created increases in both the mean and the variance of the distributions of the muscular response, while increases in the rate of trunk extension acceleration decreased both the mean and variance of the distributions of activity across all muscles considered. Increases in trunk asymmetry created a decrease in mean of the ipsi–lateral erector spinae and an increase in the mean of all other muscles considered, but there was little change in the variance of these distributions as a function of asymmetry.     

Sex-specific myoelectric manifestations of localized fatigue during a multi-joint repetitive task

We have previously demonstrated that fatigue at different locations impacts joint angles, angular variability, and coordination variability differently. However, the neuromuscular control aspects underlying these kinematic changes have never been demonstrated. Seventeen young adults (8 males) were recruited. Electromyographic electrodes were placed on: upper trapezius, pectoralis major, anterior and middle deltoid, biceps and triceps brachii, and left and right erector spinae. Subjects performed the repetitive pointing task (RPT) at 1 Hz for 30 s before and after localized fatigue tasks, which consisted of one shoulder, one elbow and one lower back isometric fatiguing protocols until exhaustion in randomized order. Electromyographic amplitude (RMS), variability (SD) and mean power frequency (MnPF) were calculated for each of the pre-fatigue and post-fatigue RPT trials. There were sex × fatigue location interaction effects on upper trapezius RMS (p = 0.038) with males’ values increasing the most after shoulder fatigue. Females’ triceps brachii RMS was greater compared to males after shoulder, elbow, and trunk fatigue (p = 0.003, p = 0.001 and p = 0.007 respectively). There were sex × fatigue location effects on left erector spinae MnPF (p = 0.011) with males and females’ values decreasing the most after trunk fatigue, but more so in males. Results demonstrate that males and females compensate differently during a repetitive pointing task when their elbows, shoulders and trunks are locally fatigued, which could have implications on sex-specific workplace injury risks. See Table 1 for acronyms.     

Lumbopelvic flexibility modulates neuromuscular responses during trunk flexion–extension

Various stimuli such as the flexibility of lumbopelvic structures influence the neuromuscular responses of the trunk musculature, leading to different load sharing strategies and reflex muscle responses from the afferents of lumbopelvic mechanoreceptors. This link between flexibility and neuromuscular response has been poorly studied.The aim of this study was to investigate the relationship between lumbopelvic flexibility and neuromuscular responses of the erector spinae, hamstring and abdominal muscles during trunk flexion–extension. Lumbopelvic movement patterns were measured in 29 healthy women, who were separated into two groups according to their flexibility during trunk flexion–extension. The electromyographic responses of erector spinae, rectus abdominis and biceps femoris were also recorded.Subjects with greater lumbar flexibility had significantly less pelvic flexibility and vice versa. Subjects with greater pelvic flexibility had a higher rate of relaxation and lower levels of hamstring activation during maximal trunk flexion.The neuromuscular response patterns of the hamstrings seem partially modulated by pelvic flexibility. Not so with the lumbar erector spinae and lumbar flexibility, despite the assertions of some previous studies. The results of this study improve our knowledge of the relationships between trunk joint flexibility and neuromuscular responses, a relationship which may play a role in low back pain.     

Trunk and upper limb muscle activation during flat and topspin forehand drives in young tennis players

This study compared EMG activity of young tennis players' muscles during forehand drives in two groups, GD-those able to raise by more than 150% the vertical velocity of racket-face at impact from flat to topspin forehand drives, and GND, those not able to increase their vertical velocity to the same extent. Upper limb joint angles, racket-face velocities, and average EMGrms values, were studied. At similar joint angles, a fall in horizontal velocity and a rise in racket-face vertical velocity from flat to topspin forehand drives were observed. Shoulder muscle activity rose from flat to topspin forehand drives in GND, but not for drives in GD. Forearm muscle activity reduced from flat to topspin forehand drives in GD, but muscle activation was similar in GND. The results show that radial deviation increased racket-face vertical velocity more at impact from the flat to topspin forehand drives than shoulder abduction.     

PLAD (personal lift assistive device) stiffness affects the lumbar flexion/extension moment and the posterior chain EMG during symmetrical lifting tasks

The PLAD (personal lift assistive device) was designed to reduce the lumbar moment during lifting and bending tasks via elastic elements. This investigation examined the effects of modulating the elastic stiffness. Thirteen men completed 90 lifts (15 kg) using 6 different PLAD stiffnesses in stoop, squat and freestyle lifting postures. The activity of 8 muscles were recorded (latissimus dorsi, thoracic and lumbar erector spinae, rectus abdominis, external oblique, gluteus maximus, biceps femoris and rectus femoris), 3D electromagnetic sensors tracked the motion of each segment and strain gauges measured the elastic tension. EMG data were rectified, filtered, normalized and integrated as a percentage of the lifting task. The highest PLAD tension elicited the greatest reduction in erector spinae activity (mean of thoracic and lumbar) in comparison to the no-PLAD condition for the stoop (37%), squat (38%), and freestyle (37%) lifts, while prompting comparable reductions in gluteus maximums and biceps femoris activity. The highest PLAD stiffness also elicited the greatest reduction in the integrated L4/L5 flexion moment for the stoop (19.0%), squat (18.4%) and freestyle (17.4%) lifts without changing peak lumbar flexion. Each increase in PLAD stiffness further reduced the muscle activity of the posterior chain and the dynamic lumbar moment.     

Electromyography of trunk muscles in isometric graded axial rotation.

This study was conducted to determine the pattern, magnitude, and phasic inter-relationship of the trunk muscles in maximal isometric and graded isometric axial rotational contractions and compare them with those previously observed from the same subjects in the same experimental session in dynamic conditions. In 50 normal young healthy subjects (27 male and 23 female), after a suitable skin preparation, bipolar silver-silver chloride recessed pregelled surface electrodes were placed on external oblique, internal oblique, rectus abdominis, pectoralis major, latissimus dorsi, erector spinae at T(10) and L(3) levels bilaterally with 2 cm interelectrode distance. EMG signals from grounded subjects were suitably preamplified and amplified by a fully isolated system. These subjects were stabilized in an upright-seated posture in the Axial Rotation Tester (AROT), which was placed in isometric mode for force and rotation output from the AROT. The 14 channels of EMG, the force and the rotation were sampled at 1 kHz. The subjects initially registered their isometric maximal voluntary contraction (MVC) on both sides which was used for reference and then performed their 25%, 50% and 75% of MVC bilaterally in an isometric mode in a random order. The EMG magnitude, the slope of the rise of the EMG, and the phasic interrelationship of muscles were analyzed. The results showed that female sample generated only 65% of torque of their male counterparts. There were no significant differences between the male and the female samples in the EMG variables. Exertions to the left and to the right were not significantly different from each other for the measured variables. However, the magnitude contribution of the muscles and the slope of rise of EMG were significantly different in two directions (p<0.001). The phasic interrelationship of the external obliques, the latissimus dorsi and the erector spinae were different from other muscles (p<0.01). With the increasing grades of contraction the latissimus dorsi and the external obliques increased their magnitude significantly whereas that of the erectores spinae underwent a decrease in proportionate terms (but not in absolute magnitude) suggesting their role as stabilizers but not as rotators.     

Surface electromyography as a tool to assess the responses of car passengers to lateral accelerations. Part II: Objective comparison of vehicles

The purpose of this study was to objectively assess the response of car passengers to lateral accelerations. Surface EMG signals were collected bilaterally from the cervical erector spinae (CES), latissimus dorsi (LD), erector spinae (ES), external oblique (EO), and vastus lateralis (VL) muscles of 10 subjects. Lateral acceleration was also recorded. Three chassis-seat configurations AA, BA and BB were tested, with the first letter denoting the chassis and the second the seat. SEMG signals were often contaminated by noise, and were, therefore, denoised using the methods explained in part I. Reciprocal phasic activity was observed for all muscles except for the EO, and the reaction of passengers to lateral accelerations was interpreted as a bust torsion. The RMS of EMG segments was used as an indication of muscle activity. Muscle activation of VL and ES were significantly affected by the configuration tested (p < 0.05), with greater activation levels observed for the chassis A than for the chassis B. Such a finding implies that greater roll requires greater muscle activity, thus resulting in less comfortable vehicles. Therefore, SEMG can be used to provide an objective measure of discomfort in passengers subjected to lateral accelerations in a car seat.     

Relative growth rates of limb muscles in the diprotodont marsupial, Setonix brachyurus

The fore- and hindlimb muscles of 12 Setonix brachyurus joeys, aged 5 to 175 days postpartum, and four adults were dissected out and weighed. Individual muscles and muscle groups were analysed for absolute and relative growth changes. From comprising almost 59% of the total limb musculature at birth the forelimb muscles finally constitute just over 9% in the adult; the hindlimb muscles start at just over 41% and end at almost 91%. In both limbs, the extensor actions predominate in the proximal limb segment because of their propulsive functions, whereas in the distal segment the flexor muscles tend to be the larger because of their shock-absorbing and spring functions. During growth of the fore-limb there is a relative increase in the size of latissimus dorsi and triceps brachii and a decrease in the distal segment muscles; in the hindlimb the gluteal and hamstring muscles increase at the expense of the distal segment muscles. Specializations for speed include long distal hindlimb segments and proximally located muscle bellies. The above findings reflect the adaptations and changing locomotor patterns from birth to adult in the Quokka.     

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.