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.     

Comparison of muscle activation using various hand positions during the push-up exercise

Popular fitness literature suggests that varied hand placements during push-ups may isolate different muscles. Scientific literature, however, offers scant evidence that varied hand placements elicit different muscle responses. This study examined whether different levels of electromyographic (EMG) activity in the pectoralis major and triceps brachii muscles are required to perform push-ups from each of 3 different hand positions: shoulder width base, wide base, and narrow base hand placements. Forty subjects, 11 men and 29 women, performed 1 repetition of each push-up. The EMG activity for subjects' dominant arm pectoralis major and triceps brachii was recorded using surface electrodes. The EMG activity was greater in both muscle groups during push-ups performed from the narrow base hand position compared with the wide base position (p < 0.05). This study suggests that, if a goal is to induce greater muscle activation during exercise, then push-ups should be performed with hands in a narrow base position compared with a wide base position.     

A comparative electromyographical investigation of muscle utilization patterns using various hand positions during the lat pull-down

This study aimed at investigating the effects of different hand positions on the electromyographic (EMG) activity of shoulder muscles during the performance of the lat pull-down exercise. Ten healthy men performed 3 repetitions of the lat pull-down exercise using their experimentally determined 10RM (repetition maximum) weight. Four different common variations of the lat pull-down were used: close grip (CG), supinated grip (SG), wide grip anterior (WGA), and wide grip posterior (WGP). Normalized root mean square of the EMG (NrmsEMG) activity for the right posterior deltoid (PD), latissimus dorsi (LD), pectoralis major (PM), teres major (TM), and long head of the triceps (TLH) were recorded using surface electrodes and normalized using maximum voluntary contractions. Repeated measures analysis of variance for each muscle detected statistical differences (p < 0.05) in myoelectric activity among hand positions during both the concentric and eccentric phases of the exercise. During the concentric phase, NrmsEMG results for the LD included WGA > WGP, SG, CG. For the TLH: WGA > WGP, SG, CG and WGP > CG, SG. For the PD: CG, WGA, SG > WGP. For the PM: CG, WGA, SG > WGP. During the eccentric phase, the LD produced the following patterns: WGA > WGP, SG, CG and WGP > CG. The TLH pattern showed WGA > SG and CG. For the PD: CG > WGA, WGP. The results indicate that changes in handgrip position affect the activities of specific muscles during the lat pull-down movement. Also, performance of the lat pull-down exercise using the WGA hand position produces greater muscle activity in the LD than any other hand position during both the concentric or eccentric phases of the movement.     

The effect of handgrip position on upper extremity neuromuscular responses to arm cranking exercise.

The purpose of this study was to determine if handgrip position during arm cranking exercise influences the neuromuscular activity of muscles biceps brachii (BB), lateral head of triceps brachii (TB), middle deltoid (DT), infraspinatus (IS) and brachioradialis (BR). Fifteen participants cranked an arm ergometer using three different handgrip positions (supinated, pronated, and neutral). Electromyographic (EMG) data were recorded from the aforementioned muscles, and relative duration of EMG activation and amplitude were quantified for the first and second 180 degrees of crank angle. EMG measures were analyzed with MANOVA and follow-up univariate procedures; alpha was set at 0.01. The relative durations of EMG activation did not differ between handgrip positions. Muscle IS exhibited 36% less amplitude in the supinated versus neutral handgrip position (second half-cycle), and muscle BR displayed 63% greater amplitude across cycles in the neutral versus supinated and pronated handgrip positions. The greater BR activity displayed in the neutral handgrip position may reflect its anatomical advantage as an elbow flexor when the forearm is in neutral position. Muscle IS exhibited less activity in the supinated position and may be clinically relevant if it allows arm cranking to occur without subsequent shoulder pain, which is often the aim of shoulder rehabilitation.     

Strength training's chronic effects on muscle architecture parameters of different arm sites

Strength training generates alterations in muscle geometry, which can be monitored by imaging techniques as, for example, the ultrasound (US) technique. There is no consensus about the homogeneity of hypertrophy in different muscle sites. Therefore, the purpose of this study was to compare the muscle thickness (MT) and pennation angle (PA) in 3 different sites (50, 60, and 70% of arm length) of the biceps brachii and triceps brachii after 12 weeks of strength training. Forty-nine healthy untrained men were divided into 2 groups: Training Group ([TG, n = 40] 29.90 ± 1.72 years; 79.53 ± 11.84 kg; 173 ± 0.6 cm) and Control Group (n = 9 25.89 ± 3.59 years; 73.96 ± 9.86 kg; 171 ± 6 cm). The TG underwent a strength training program during 12 weeks, which included exercises such as a free-weight bench press, machine lat pull-down, triceps extension in lat pull-down, and standing free-weight biceps curl with a straight bar. A US apparatus was used to measure the PA and MT at the 3 sites. The maximal voluntary isometric contraction (MVC) test was conducted for each muscle group. After 12 weeks of training, a significant difference was observed between MT in biceps brachii, with an improvement of 12% in the proximal site, whereas the distal site increased by only 4.7% (p < 0.05). For the long head of the triceps brachii, the MT and PA at the 3 sites presented significant increases, but no significant variation was observed among them, probably because of the pennated-fiber arrangement. The MVC increased significantly for both muscle groups. The results indicated that the strength training program was efficient in promoting hypertrophy in both muscles, but with dissimilar responses of the pennated and fusiform muscle architecture at different arm sites.     

Shoulder and elbow muscle activity during fully supported trajectory tracking in neurologically intact older people

An inability to perform tasks involving reaching is a common problem for stroke patients. Knowledge of normal muscle activation patterns during these tasks is essential to the identification of abnormal patterns in post-stroke hemiplegia. Findings will provide insight into changes in muscle activation patterns associated with recovery of upper limb function.In this study with neurologically intact participants the co-ordination of shoulder and elbow muscle activity during two dimensional reaching tasks is explored. Eight participants undertook nine tracking tasks in which trajectory (orientation and length), duration, speed and resistance to movement were varied. The participants’ forearm was supported using a hinged arm-holder, which constrained their hand to move in a two dimensional plane. EMG signals were recorded from triceps, biceps, anterior deltoid, upper, middle and lower trapezius and pectoralis major.A wide variation in muscle activation patterns, in terms of timing and amplitude, was observed between participants performing the same task. EMG amplitude increased significantly with length, duration and resistance of the task for all muscles except anterior deltoid. Co-activation between biceps and triceps was significantly dependent on both task and trajectory orientation. Activation pattern of pectoralis major was dependent on trajectory. Neither trajectory orientation nor task condition affected the activation pattern of anterior deltoid. Normal ranges of timing of muscle activity during the tasks were identified.     

Muscle activity during maximal isometric forearm rotation using a power grip

This study aimed to provide quantitative activation data for muscles of the forearm during pronation and supination while using a power grip. Electromyographic data was collected from 15 forearm muscles in 11 subjects while they performed maximal isometric pronating and supinating efforts in nine positions of forearm rotation. Biceps brachii was the only muscle with substantial activation in only one effort direction. It was significantly more active when supinating (µ = 52.1%, SD = 17.5%) than pronating (µ = 5.1%, SD = 4.8%, p < .001). All other muscles showed considerable muscle activity during both pronation and supination. Brachioradialis, flexor carpi radialis, palmaris longus, pronator quadratus and pronator teres were significantly more active when pronating the forearm. Abductor pollicis longus and biceps brachii were significantly more active when supinating. This data highlights the importance of including muscles additional to the primary forearm rotators in a biomechanical analysis of forearm rotation. Doing so will further our understanding of forearm function and lead to the improved treatment of forearm fractures, trauma-induced muscle dysfunction and joint replacements.     

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.     

Effect of muscle length on surface EMG wave forms in isometric contractions

To elucidate the influence of muscle length on surface EMG wave form, comparisons were made of surface EMGs of the biceps and triceps brachii muscles during isometric contractions at different muscle lengths. Muscle lengths were altered by setting the elbow joint angle at several intervals between the limits of extension and flexion. The intensity of the isometric contractions was 25% of maximum voluntary contraction at the individual joint angles. Slowing was obvious in the EMG wave forms of biceps as muscle length increased. The so-called 'Piper rhythm' appeared when the muscle was more than moderately lengthened. The slowing trend with muscle lengthening, though less marked, was also seen in triceps. Zero-cross analysis revealed quasi-linear relationships between muscle length and slowing. Frequency analysis confirmed the development of 'Piper rhythm'. An attempt was made to interpret the slowing associated with muscle lengthening in terms of the propagation of myoelectric signals in muscle fibers. given the effect of muscle length on EMG wave forms, a careful control of joint angle may be required in assessing local making fatigue when using EMG spectral indices.     

Effect of post-tetanic potentiation of pectoralis and triceps brachii muscles on bench press performance

The effect of post-tetanic potentiation (PTP) induced in the pectoralis and triceps brachii muscles by high-frequency submaximal percutaneous electrical stimulation (PES) on average and maximal power attained in bench press throwing was measured in 12 healthy men. Three PES regimens were used: (a) a 7-second and (b) a 10-second trial at 100 Hz, and (c) an intermittent trial with 8 1-second tetanic trains at 100 Hz with rest periods of 20 seconds. Only nonsignificant (p > 0.05) increase was observed in average power at 8 minutes and in maximal power at 5, 8, and 11 minutes after tetanus after 7-second trial, and in maximal power at 5 and 8 minutes after tetanus after an intermittent trial. These data indicate that PES application was a noneffective stimulus for increased bench press performance. A great interindividual variability response was observed and, therefore, PTP induction for improving upper-body muscle performance needs further experiments.     

Effect of verbal instruction on muscle activity during the bench press exercise

Recent research suggests that humans have some ability to selectively activate or relax some muscles during isometric or dynamic muscle actions without changing posture or position. This study sought to reveal whether trained athletes could isolate either the pectoral or triceps muscles, respectively, at different intensities when given verbal technique instruction. Eleven male Division III football players performed 3 sets of bench press at 50% 1-repetition max (1RM) and 80% 1RM while electromyographic (EMG) activity was recorded from the pectoralis major (PM), anterior deltoid (AD), and triceps brachii (TB). In the first set, the subjects performed the exercise without instruction. In the second set, the subjects were given verbal instructions to use only chest muscles. In the third set, the subjects were instructed to use only triceps muscles. Mean normalized root mean square EMG activity was calculated during 3 repetitions in each condition. Repeated-measures analysis of variance was used to detect differences from the preinstruction condition, with significance set to p ≤ 0.017 as indicated by a Bonferroni correction for multiple comparisons. During the 50% max lift with verbal instructions to focus on chest muscles, PM EMG activity increased by 22% over preinstruction activity (p = 0.005), whereas AD and TB activities were statistically unchanged. When the subjects were instructed to focus on only the triceps muscles, PM returned to baseline activity, whereas TB activity was increased by 26% (p = 0.005). When the lift was increased to 80% max, PM and AD activities were both increased with verbal instructions to use only chest muscles. The TB activity was unchanged during the 80% lifts, regardless of instructions. In conclusion, it is found that verbal technique instruction is effective in shifting muscle activity during a basic lift, but it may be less effective at higher intensities.     

Gliding flight in the American Kestrel (Falco sparverius): An electromyographic study

Electromyographic (EMG) activity was studied in American Kestrels (Falco sparverius) gliding in a windtunnel tilted to 8 degrees below the horizontal. Muscle activity was observed in Mm. biceps brachii, triceps humeralis, supracoracoideus, and pectoralis, and was absent in M. deltoideus major and M. thoracobrachialis (region of M. pectoralis). These active muscles are believed to function in holding the wing protracted and extended during gliding flight. Quantification of the EMG signals showed a lower level of activity during gliding than during flapping flight, supporting the idea that gliding is a metabolically less expensive form of locomotion than flapping flight. Comparison with the pectoralis musculature of specialized gliding and soaring birds suggests that the deep layer of the pectoralis is indeed used during gliding flight and that the slow tonic fibers found in soaring birds such as vultures represents a specialization for endurant gliding. It is hypothesized that these slow fibers should be present in the wing muscles that these birds use for wing protraction and extension, in addition to the deep layer of the pectoralis. © 1993 Wiley-Liss, Inc.     

The influence of task and angle on torque production and muscle activity at the elbow

This study investigated the effect of changing internal mechanical variables and task demands on muscle activity and torque production during high effort isometric contractions of the elbow flexors. The effect of adding a 50% maximal voluntary contraction (MVC) of supination to an MVC of elbow flexion was studied over a range of angles from 30° to 110° of elbow flexion. Surface EMGs were recorded from the biceps brachii (BIC), brachioradialis (BRAD) and triceps brachii (TRI) of 10 healthy subjects. BIC was the only muscle to show a consistent trend of increasing root mean square (rms) EMG with increasing elbow flexion angle. BIC activity also remained constant or increased with the addition of the supination task at all angles. In contrast, BRAD showed decreased activity when supination was added at several angular positions. Maximal flexion torque was reduced when the second task of submaximal supination was added. This torque reduction was statistically significant at all angles except 70° and appeared related to the decreased contribution from BRAD. In a small subset of subjects, however, BRAD activity did not decrease when the second degrees of freedom (df) task was added. These subjects exhibited higher flexion torques averaged over task than the majority, at all angles except 30°. These data support the view that internal mechanical considerations influence the manner in which the central nervous system (CNS) distributes activity to muscular synergists in response to altered task demands. Further, subject-specific patterns exist which must be recognized if these findings are to be incorporated in training or rehabilitation programmes.     

Facilitation of triceps brachii muscle contraction by tendon vibration after chronic cervical spinal cord injury.

One way to improve the weak triceps brachii voluntary forces of people with chronic cervical spinal cord injury may be to excite the paralyzed or submaximally activated fraction of muscle. Here we examined whether elbow extensor force was enhanced by vibration (80 Hz) of the triceps or biceps brachii tendons at rest and during maximum isometric voluntary contractions (MVCs) of the elbow extensors performed by spinal cord-injured subjects. The mean +/- SE elbow extensor MVC force was 22 +/- 17.5 N (range: 0-23% control force, n = 11 muscles). Supramaximal radial nerve stimuli delivered during elbow extensor MVCs evoked force in six muscles that could be stimulated selectively, suggesting potential for force improvement. Biceps vibration at rest always evoked a tonic vibration reflex in biceps, but extension force did not improve with biceps vibration during triceps MVCs. Triceps vibration induced a tonic vibration reflex at rest in one-half of the triceps muscles tested. Elbow extensor MVC force (when >1% of control force) was enhanced by vibration of the triceps tendon in one-half of the muscles. Thus triceps, but not biceps, brachii tendon vibration increases the contraction strength of some partially paralyzed triceps brachii muscles.     

Neuromuscular fatigue during maximal concurrent hand grip and elbow flexion or extension.

The objective was to investigate muscle fatigue measuring changes in force output and force tremor and electromyographic activity (EMG) during two sustained maximal isometric contractions for 60s: (1) concurrent hand grip and elbow flexion (HG and EF); or (2) hand grip and elbow extension (HG and EE). Each force tremor amplitude was decomposed into four frequency bands (1-3, 4-10, 11-20, and 21-50Hz). Surface EMGs were recorded from the flexor digitorum superficialis (FDS), extensor digitorum (ED), biceps brachii (BB) and lateral head of triceps brachii (TB). The HG and EF forces for the HG and EF and the HG force for the HG and EE declined rapidly, whereas the EE force remained almost constant near to the initial value for the first 40s and then declined. The decrease in EMG amplitude was observed not for the FDS muscle but for the ED muscle. The HG tremor amplitude for each frequency band showed similar decreasing rate, whereas the decreases in EF and EE tremor amplitudes for the lower band (below 10Hz) were slower than those for the higher band (above 11Hz). The neuromuscular mechanisms underlying muscle fatigue during sustained maximal concurrent contractions of hand grip and elbow flexion or extension are discussed.     

Direction-specific recruitment of rotator cuff muscles during bench press and row

Recent studies indicate that rotator cuff (RC) muscles are recruited in a reciprocal, direction-specific pattern during shoulder flexion and extension exercises. The main purpose of this study was to determine if similar reciprocal RC recruitment occurs during bench press (flexion-like) and row (extension-like) exercises. In addition, shoulder muscle activity was comprehensively compared between bench press and flexion; row and extension; and bench press and row exercises. Electromyographic (EMG) activity was recorded from 9 shoulder muscles sites in 15 normal volunteers. All exercises were performed at 20, 50 and 70% of subjects’ maximal load. EMG data were normalized to standard maximal voluntary contractions. Infraspinatus activity was significantly higher than subscapularis during bench press, with the converse pattern during the row exercise. Significant differences in activity levels were found in pectoralis major, deltoid and trapezius between the bench press and flexion exercises and in lower trapezius between the row and extension exercises. During bench press and row exercises, the recruitment pattern in each active muscle did not vary with load. During bench press and row exercises, RC muscles contract in a reciprocal direction-specific manner in their role as shoulder joint dynamic stabilizers to counterbalance antero-posterior translation forces.     

EMG and MMG of agonist and antagonist muscles as a function of age and joint angle.

The aim of this study was to determine the effect of elbow joint position on electromyographic (EMG) and mechanomyographic (MMG) activities of agonist and antagonist muscles in young and old women. Surface EMG and MMG were recorded from the triceps and biceps brachii, and brachioradialis muscles during isometric elbow extensions in young and old women. The measurements were carried out at an optimal joint angle (A(o)), as well as at smaller (A(s) = A(o) - 30 degrees ) and larger (A(l) = A(o) + 30 degrees ) angles. The normalized to force EMG amplitude (RMS-EMG/F) was smaller in old women compared to young in all muscles. The RMS-EMG/F of the triceps brachii muscle was not affected by muscle length while that of the biceps brachii and brachioradialis muscles increased at shortest muscle length in both groups. The normalized to force MMG amplitude (RMS-MMG/F) was smaller in old than in young in the triceps brachii muscle only. There was an increase in RMS-MMG/F with triceps brachii and biceps brachii muscle shortening in both groups, and in the brachioradialis muscle -- in young only. Compared to young, older women exhibited a bigger force fluctuation during maximum voluntary contraction, but these did not contribute significantly to the RMS-MMG. Skinfold thickness accounted for the RMS-EMG/F and RMS-MMG/F differences seen between old and young women in the biceps brachii muscle only. It is concluded that, the EMG and MMG response to muscles length change in agonist and antagonist muscles is generally similar in old and young women but the optimal angle shifts toward a bigger value in older women.     

EMG and MMG activities of agonist and antagonist muscles in Parkinson’s disease patients during absolute submaximal load holding

The purpose of the study was (1) to assess changes in electromyographical (EMG) and mechanomyographical (MMG) signals of the biceps and triceps brachii muscles during absolute submaximal load holding in Parkinson’s disease patients tested during their medication “ON-phase” and in age-matched controls, and (2) to check whether mechanomyography can be useful in evaluation of neuromuscular system activity in Parkinson’s disease patients.The data analysis was performed on nine females with Parkinson’s disease and six healthy, age-matched females. The EMG and MMG signals were recorded from the short head of the biceps brachii (BB) and the lateral head of the triceps brachii (TB) muscles.It was concluded that compared to the controls, the Parkinson’s disease patients exhibited higher amplitude in the biceps brachii muscle and lower median frequency of the MMG signal in the both tested muscles. However, no differences in the EMG amplitude and an increase of the EMG median frequency in the triceps brachii muscle of the Parkinson’s disease group were observed. The MMG was not affected by physiological postural tremor and can depict differences between parkinsonians and controls, which may suggest that it is valuable tool for neuromuscular assessment for this condition.     

Contribution of the biceps brachii and pronator teres muscles to the efforts of pronation or supination. I. Statistical work (author's transl)

The electrical activity of the biceps brachii and pronator teres muscles is studied through the prono-supination of the forearm in some isometrical conditions (static work) with different loads and joint positions. If the pronator teres is always being active in pronation, this activity is a function of the load and of the wrist and elbow positions. The same phenomena can be observed for the biceps brachii but when in supination. From the curvilinear relationships between the integrated electrical activity and the load--observed on both muscles--some torque-angle relationships can be established for the biceps brachii which show that a bifunctional muscle seems to be characterized by a very and unique force-length relationship.     

Relationship between muscle coordination and forehand drive velocity in tennis

This study aimed at investigating the relationship between trunk and upper limb muscle coordination and stroke velocity during tennis forehand drive. The electromyographic (EMG) activity of ten trunk and dominant upper limb muscles was recorded in 21 male tennis players while performing five series of ten crosscourt forehand drives. The forehand drive velocity ranged from 60% to 100% of individual maximal velocity. The onset, offset and activation level were calculated for each muscle and each player. The analysis of muscle activation order showed no modification in the recruitment pattern regardless of the velocity. However, the increased velocity resulted in earlier activation of the erector spinae, latissimus dorsi and triceps brachii muscles, as well as later deactivation of the erector spinae, biceps brachii and flexor carpi radialis muscles. Finally, a higher level of activation was observed with the velocity increase in the external oblique, latissimus dorsi, middle deltoid, biceps brachii and triceps brachii. These results might bring new knowledge for strength and tennis coaches to improve resistance training protocols in a performance and prophylactic perspective.