Upper-limb surface electro-myography at maximum supination and pronation torques: the effect of elbow and forearm angle.

Forearm pronation and supination, and increased muscular activity in the wrist extensors have been both linked separately to work-related injuries of the upper limb, especially humeral epicondylitis. However, there is a lack of information on forearm torque strength at ranges of elbow and forearm angles typical of industrial tasks. There is a need for strength data on forearm torques at different upper limb angles to be investigated. Such a study should also include the measurement of muscular activity for the prime torque muscles and also other muscles at possible risk of injury due to high exertion levels during tasks requiring forearm torques.Twenty-four male subjects participated in the study that involved maximum forearm torque exertions for the right arm, in the pronation and supination directions, and at four elbow and three forearm rotation angles. Surface EMG (SEMG) was used to evaluate the muscular activity of the pronator teres (PT), pronator quadratus (PQ), biceps brachi (BB), brachioradialis (BR), mid deltoid (DT) and the extensor carpi radialis brevis (ECRB) during maximum torque exertions. Repeated measures ANOVA indicated that both direction and forearm angle had a significant effect on the maximum torques (p<0.05) while elbow angle and the interactions were highly significant (p<0.001). The results revealed that supination torques were stronger overall with a mean maximum value of 16.2 Nm recorded for the forearm 75% prone. Mean maximum pronation torque was recorded as 13.1 Nm for a neutral forearm with the elbow flexed at 45 degrees. The data also indicated that forearm angle had a greater effect on supination torque than pronation torque. Supination torques were stronger for the mid-range of elbow flexion, but pronation torques increased with increasing elbow extension. The strength profiles for the maximum torque exertions were reflected in the EMG changes in the prime supinators and pronators. In addition, the EMG data expressed as the percentage of Maximum Voluntary Electrical activity (MVE), revealed high muscular activity in the ECRB for both supination (26-43% MVE) and pronation torques (17-55% MVE). The results suggest that the ECRB acts as a stabiliser to the forearm flexors for gripping during pronation torques depending on forearm angle, but acts as a prime mover in wrist extension for supination torques with little effect of elbow and forearm angle. This indicates a direct link between forearm rotations against resistance and high muscular activity in the wrist extensors, thereby increasing stress on the forearm musculo-skeletal system, especially the lateral epicondyle.     

Strength and fatigability of selected muscles in upper limb: assessing muscle imbalance relevant to tennis elbow.

PURPOSE: The aetiology of tennis elbow has remained uncertain for more than a century. To examine muscle imbalance as a possible pathophysiological factor requires a reliable method of assessment. This paper describes the development of such a method and its performance in healthy subjects. We propose a combination of surface and fine-wire EMG of shoulder and forearm muscles and wrist strength measurements as a reliable tool for assessing muscle imbalance relevant to the pathophysiology of tennis elbow. METHODS: Six healthy volunteers participated. EMG data were acquired at 50% maximal voluntary isometric contraction from five forearm muscles during grip and three shoulder muscles during external rotation and abduction, and analysed using normalized median frequency slope as a fatigue index. Wrist extension/flexion strength was measured using a purpose-built dynamometer. RESULTS: Significant negative slope of median frequency was found for all muscles, with good reproducibility, and no significant difference in slope between the different muscles of the shoulder and the wrist. (Amplitude slope showed high variability and was therefore unsuitable for this purpose.) Wrist flexion was 27+/-8% stronger than extension (mean+/-SEM, p=0.006). CONCLUSION: This is a reliable method for measuring muscle fatigue in forearm and shoulder. EMG and wrist strength studies together can be used for assessing and identifying the muscle balance in the wrist-forearm-shoulder chain.     

Wrist splint effects on muscle activity and force during a handgrip task

Wrist splints are commonly prescribed to limit wrist motion and provide support at night and during inactive periods but are often used in the workplace. In theory, splinting the wrist should reduce wrist extensor muscle activity by stabilizing the joint and reducing the need for co-contraction to maintain posture. Ten healthy volunteers underwent a series of 24 10-s gripping trials with surface electromyography on 6 forearm muscles. Trials were randomized between splinted and nonsplinted conditions with three wrist postures (30 degrees flexion, neutral, and 30 degrees extension) and four grip efforts. Custom-made Plexiglas splints were taped to the dorsum of the hand and wrist. It was found that when simply holding the dynamometer, use of a splint led to a small (<1% MVE) but significant reduction in activity for all flexor muscles and extensor carpi radialis (all activity <4% maximum). At maximal grip, extensor muscle activity was significantly increased with the splints by 7.9-23.9% MVE. These data indicate that splinting at low-to-moderate grip forces may act to support the wrist against external loading, but appears counterproductive when exerting maximal forces. Wrist bracing should be limited to periods of no to light activity and avoided during tasks that require heavy efforts.     

Individual muscle force parameters and fiber operating ranges for elbow flexion-extension and forearm pronation-supination

We have quantified individual muscle force and moment contributions to net joint moments and estimated the operating ranges of the individual muscle fibers over the full range of motion for elbow flexion/extension and forearm pronation/supination. A three dimensional computer graphics model was developed in order to estimate individual muscle contributions in each degree of freedom over the full range of motion generated by 17 muscles crossing the elbow and forearm. Optimal fiber length, tendon slack length, and muscle specific tension values were adjusted within the literature range from cadaver studies such that the net isometric joint moments of the model approximated experimental joint moments within one standard deviation. Analysis of the model revealed that the muscles operate on varying portions of the ascending limb, plateau region, and descending limb of the force-length curve. This model can be used to further understand isometric force and moment contributions of individual muscles to net joint moments of the arm and forearm and can serve as a comprehensive reference for the forces and moments generated by 17 major muscles crossing the elbow and wrist.     

Effect of upper and lower extremity control strategies on predicted injury risk during simulated forward falls: a study in healthy young adults

Fall-related wrist fractures are common at any age. We used a seven-link, sagittally symmetric, biomechanical model to test the hypothesis that systematically alterations in the configuration of the body during a forward fall from standing height can significantly influence the impact force on the wrists. Movement of each joint was accomplished by a pair of agonist and antagonist joint muscle torque actuators with assigned torque-angle, torque-velocity, and neuromuscular latency properties. Proportional-derivative joint controllers were used to achieve desired target body segment configurations in the pre- andor postground contact phases of the fall. Outcome measures included wrist impact forces and whole-body kinetic energy at impact in the best, and worst, case impact injury risk scenarios. The results showed that peak wrist impact force ranged from less than 1 kN to more than 2.5 kN, reflecting a fourfold difference in whole-body kinetic energy at impact (from less than 40 J to more than 160 J) over the range of precontact hip and knee joint angles used at impact. A reduction in the whole-body kinetic energy at impact was primarily associated with increasing negative work associated with hip flexion. Altering upper extremity configuration prior to impact significantly reduced the peak wrist impact force by up to 58% (from 919 N to 2212 N). Increased peak wrist impact forces associated greater shoulder flexion and less elbow flexion. Increasing postcontact arm retraction can reduce the peak wrist impact force by 28% (from 1491 N to 1078 N), but postcontact hip and knee rotations had a relatively small effect on the peak wrist impact force (8% reduction; from 1411 N to 1303 N). In summary, the choice of the joint control strategy during a forward fall can significantly affect the risk of wrist injury. The most effective strategy was to increase the negative work during hip flexion in order to dissipate kinetic energy thereby reducing the loss in potential energy prior to first impact. Extended hip or elbow configurations should be avoided in order to reduce forearm impact forces.     

Kinetic chain of overarm throwing in terms of joint rotations revealed by induced acceleration analysis

This study investigated how baseball players generate large angular velocity at each joint by coordinating the joint torque and velocity-dependent torque during overarm throwing. Using a four-segment model (i.e., trunk, upper arm, forearm, and hand) that has 13 degrees of freedom, we conducted the induced acceleration analysis to determine the accelerations induced by these torques by multiplying the inverse of the system inertia matrix to the torque vectors. We found that the proximal joint motions (i.e., trunk forward motion, trunk leftward rotation, and shoulder internal rotation) were mainly accelerated by the joint torques at their own joints, whereas the distal joint motions (i.e., elbow extension and wrist flexion) were mainly accelerated by the velocity-dependent torques. We further examined which segment motion is the source of the velocity-dependent torque acting on the elbow and wrist accelerations. The results showed that the angular velocities of the trunk and upper arm produced the velocity-dependent torque for initial elbow extension acceleration. As a result, the elbow joint angular velocity increased, and concurrently, the forearm angular velocity relative to the ground also increased. The forearm angular velocity subsequently accelerated the elbow extension and wrist flexion. It also accelerated the shoulder internal rotation during the short period around the ball-release time. These results indicate that baseball players accelerate the distal elbow and wrist joint rotations by utilizing the velocity-dependent torque that is originally produced by the proximal trunk and shoulder joint torques in the early phase.     

Effects of posture,movement and hand load on shoulder muscle activity

The influence of external factors such as arm posture, hand loading and dynamic exertion on shoulder muscle activity is needed to provide insight into the relationship between internal and external loading of the shoulder joint. Surface electromyography was collected from 8 upper extremity muscles on 16 participants who performed isometric and dynamic shoulder exertions in three shoulder planes (flexion, mid-abduction and abduction) covering four shoulder elevation angles (30°, 60°, 90° and 120°). Shoulder exertions were performed under three hand load conditions: no load, holding a 0.5 kg load and 30% grip. It was found that adding a 0.5 kg load to the hand increased shoulder muscle activity by 4% maximum voluntary excitation (MVE), across all postures and velocities. Performing a simultaneous shoulder exertion and hand grip led to posture specific redistribution of shoulder muscle activity that was consistent for both isometric and dynamic exertions. When gripping, anterior and middle deltoid activity decreased by 2% MVE, while posterior deltoid, infraspinatus and trapezius activity increased by 2% MVE and biceps brachii activity increased by 6% MVE. Increased biceps brachii activity with gripping may be an initiating factor for the changes in shoulder muscle activity. The finding that hand gripping altered muscle activation, and thus the internal loading, of the shoulder may play an important role in shoulder injury development and rehabilitation.     

Effects of postural muscle fatigue on the relation between segmental posture and movement.

The purpose of this study was to examine whether fatigue of postural muscles might influence the coordination between segmental posture and movement. Seven healthy adults performed series of fifteen fast wrist flexions and extensions while being instructed to keep a dominant upper limb posture as constant as possible. These series of voluntary movements were performed before and after a fatiguing submaximal isometric elbow flexion, and also with or without the help of an elbow support. Surface EMG from muscles Delto?deus anterior, Biceps brachii, Triceps brachii, Flexor carpi ulnaris, Extensor carpi radialis were recorded simultaneously with wrist, elbow and shoulder accelerations and wrist and elbow displacements. Fatigue was evidenced by a shift of the elbow and shoulder muscles EMG spectra towards low frequencies. Kinematics of wrist movements and corresponding activations of wrist prime-movers, as well as the background of postural muscle activation before wrist movement were not modified. There were only slight changes in timing of postural muscle activations. These data indicate that postural fatigue induced by a low-level isometric contraction has no effect on voluntary movement and requires no dramatic adaptation in postural control.     

Muscle moment arm and normalized moment contributions as reference data for musculoskeletal elbow and wrist joint models

A geometric musculoskeletal model of the elbow and wrist joints was developed to calculate muscle moment arms throughout elbow flexion/extension, forearm pronation/supination, wrist flexion/extension and radial/ulnar deviation. Model moment arms were verified with data from cadaver specimen studies and geometric models available in the literature. Coefficients of polynomial equations were calculated for all moment arms as functions of joint angle, with special consideration to coupled muscles as a function of two joint angles. Additionally, a “normalized potential moment (NPM)” contribution index for each muscle across the elbow and wrist joints in four degrees-of-freedom was determined using each muscle's normalized physiological cross-sectional area (PCSA) and peak moment arm (MA). We hypothesize that (a) a geometric model of the elbow and wrist joints can represent the major attributes of MA versus joint angle from many literature sources of cadaver and model data and (b) an index can represent each muscle's normalized moment contribution to each degree-of-freedom at the elbow and wrist. We believe these data serve as a simple, yet comprehensive, reference for how the primary 16 muscles across the elbow and wrist contribute to joint moment and overall joint performance.     

Moment-generating capacity of upper limb muscles in healthy adults

Muscle strength and volume vary greatly among individuals. Maximum isometric joint moment, a standard measurement of strength, has typically been assessed in young, healthy subjects, whereas muscle volumes have generally been measured in cadavers. This has made it difficult to characterize the relationship between isometric strength and muscle size in humans. We measured maximum isometric moments about the shoulder, elbow, and wrist in 10 young, healthy subjects, ranging in size from a 20th percentile female to a 97th percentile male. The volumes of 32 upper limb muscles were determined from magnetic resonance images of these same subjects, and grouped according to their primary function. The maximum moments produced using the shoulder adductors (67.9+/-28.4 Nm) were largest, and were approximately 6.5(+/-1.2) times greater than those produced using the wrist extensors (10.2+/-4.6 Nm), which were smallest. While there were substantial differences in moment-generating capacity among these 10 subjects, moment significantly covaried with muscle volume of the appropriate functional group, explaining between 95% (p<0.0001; shoulder adductors) and 68% (p=0.004; wrist flexors) of the variation in the maximum isometric joint moments among subjects. While other factors, such as muscle moment arms or neural activation and coordination, can contribute to variation in strength among subjects, they either were relatively constant across these subjects compared to large differences in muscle volumes or they covaried with muscle volume. We conclude that differences in strength among healthy young adults are primarily a consequence of variation in muscle volume, as opposed to other factors.     

Impaired neuromuscular function during isometric, shortening, and lengthening contractions after exercise-induced damage to elbow flexor muscles

The purpose of this study was to examine the effect of exercise-induced damage of the elbow flexor muscles on steady motor performance during isometric, shortening, and lengthening contractions. Ten healthy individuals (age 22+/-4 yr) performed four tasks with the elbow flexor muscles: a maximum voluntary contraction, a one repetition maximum (1 RM), an isometric task at three joint angles (short, intermediate, and long muscle lengths), and a constant-load task during slow (approximately 7 degrees/s) shortening and lengthening contractions. Task performance was quantified as the fluctuations in wrist acceleration (steadiness), and electromyography was obtained from the biceps and triceps brachii muscles at loads of 10, 20, and 40% of 1 RM. Tasks were performed before, immediately after, and 24 h after eccentric exercise that resulted in indicators of muscle damage. Maximum voluntary contraction force and 1-RM load declined by approximately 45% immediately after exercise and remained lower at 24 h ( approximately 30% decrease). Eccentric exercise resulted in reduced steadiness and increased biceps and triceps brachii electromyography for all tasks. For the isometric task, steadiness was impaired at the short compared with the long muscle length immediately after exercise (P<0.01). Furthermore, despite no differences before exercise, there was reduced steadiness for the shortening compared with the lengthening contractions after exercise (P=0.01), and steadiness remained impaired for shortening contractions 24 h later (P=0.01). These findings suggest that there are profound effects for the performance of these types of fine motor tasks when recovering from a bout of eccentric exercise.     

Power produced by maximal velocity elbow flexion

An analysis of horizontal elbow flexion at maximal velocity was made to determine how different loads affected power output. Twenty male subjects operated a specially constructed dynamometer initially performing a maximal effort isometric trial with the elbow fully extended and then three dynamic trials at each of three loads equal to 75, 50, and 25 per cent of the maximal isometric strength. Angular acceleration was used to calculate forearm torque, and power was obtained by taking the product of torque and angular velocity. Power was found to be a cubic function of time and a fourth-order polynomial function of angular displacement reaching a peak early in the movement. The 50 per cent load resulted in a higher peak level of power than either the 25 or 75 per cent loads.     

Fall arrest strategy affects peak hand impact force in a forward fall

We measured the peak hand impact force involved in bimanually arresting a forward fall to the ground from a 1-m shoulder height in five healthy young males. The effects of three different subject instruction sets: "arrest the fall naturally"; "keep the head as far from the ground as possible"; and "minimize the peak hand forces" were studied by measuring body segment kinematics, ground reaction forces, and upper-extremity myoelectric activity. The hypotheses were tested that the (a) arrest strategy did not influence peak impact force, (b) arm configuration, impact velocity and upper-extremity electromyography (EMG) levels correlate to the peak impact force (c) and impacting the ground with one hand leading the other does not increase the impact force over that obtained with simultaneous hand use. The results show that these subjects were able to volitionally decrease the peak impact force at the wrist by an average of 27% compared with a "natural landing" (p=0.014) and 40% compared with a "stiff-arm landing" (p<0.0005). The magnitude of the peak unilateral wrist force varied from 0.65 to 1.7 body weight for these moderate falls onto a padded surface. Peak force correlated with the elbow angle at impact, wrist velocity at impact and with pre-EMG triceps activity. The force was not significantly higher for non-simultaneous hand impacts. We conclude that fall arrest strategy can substantially alter the peak impact forces applied to the distal forearm during a fall arrest. Therefore, the fall arrest strategy likely influences wrist injury risk independent of bone strength.     

Neuromechanical control of the forearm muscles during gripping with sudden flexion and extension wrist perturbations

The purpose of this study was to investigate how gripping modulates forearm muscle co-contraction prior to and during sudden wrist perturbations. Ten males performed a sub-maximal gripping task (no grip, 5% and 10% of maximum) while a perturbation forced wrist flexion or extension. Wrist joint angles and activity from 11 muscles were used to determine forearm co-contraction and muscle contributions to wrist joint stiffness. Co-contraction increased in all pairs as grip force increased (from no grip to 10% grip), corresponding to a 36% increase in overall wrist joint stiffness. Inclusion of individual muscle contributions to wrist joint stiffness enhanced the understanding of forearm co-contraction. The extensor carpi radialis longus (ECRL) and brevis had the largest stiffness contributions (34.5 ± 1.3% and 20.5 ± 2.3%, respectively), yet muscle pairs including ECRL produced the lowest co-contraction. The muscles contributing most to wrist stiffness were consistent across conditions (ECRL for extensors; Flexor Digitorum Superficialis for flexors), suggesting enhanced contributions rather than muscular redistribution. This work provides investigation of the neuromuscular response to wrist perturbations and gripping demands by considering both co-contraction and muscle contributions to joint stiffness. Individual muscle stiffness contributions can be used to enhance the understanding of forearm muscle control during complex tasks.     

Fatigue and muscle activation during submaximal elbow flexion in children with cerebral palsy

The purpose of this study was to investigate whether children with cerebral palsy (CP), like typically developing peers, would compensate for muscle fatigue by recruiting additional motor units during a sustained low force contraction until task failure.Twelve children with CP and 17 typically developing peers performed one submaximal isometric elbow flexion contraction until the task could no longer be sustained at on average 25% (range 10–35%) of their maximal voluntary torque. Meanwhile surface electromyography (EMG) was measured from the biceps brachii and triceps brachii, and acceleration variations of the forearm were detected by an accelerometer. Slopes of the change in EMG amplitude and median frequency and accelerometer variation during time normalised to their initial values were calculated.Strength and time to task failure were similar in both groups. Children with CP exhibited a lower increase in EMG amplitude of the biceps brachii and triceps brachii during the course of the sustained elbow flexion task, while there were no significant group differences in median frequency decrease or acceleration variation increase. This indicates that children with CP do not compensate muscle fatigue with recruitment of additional motor units during sustained low force contractions.     

A new technique for the selective recording of extensor carpi radialis longus and brevis EMG.

Tennis Elbow or Lateral Epicondylalgia is manifested by pain over the region of the lateral epicondyle of the humerus, related to use of the wrist extensor muscles. Extensor carpi radialis longus (ECRL) and brevis (ECRB) have been implicated in the dysfunction associated with Lateral Epicondylalgia. For muscles in the human forearm, particularly those in close proximity, selective recordings are nearly impossible without the use of fine wire, indwelling electrodes. These can be inserted in precise locations and have small recording areas. Standard electromyography texts indicate, however, that the activity of ECRL and ECRB cannot be distinguished, even with intramuscular electrodes. We present a new technique for determining the most appropriate sites at which to insert intramuscular electrodes for selective recordings of ECRB and ECRL. The location of ECRB and ECRL was measured on 10 cadaver specimens, 5 right arms and 5 left arms. The distance from the muscle origin to (1) insertion, (2) largest portion of the muscle belly, (3) most proximal fibres and (4) most distal fibres were measured and expressed relative to forearm length. The mean distance and 95% confidence interval was calculated for each of the four measures. These data indicated a significant separation of the belly of each muscle along the length of the forearm. These relative distances were used to mark electrode insertion points on three volunteers. Fine wire electrodes were used to record the electromyogram in three participants. Each participant was required to perform isometric contractions to produce (1) wrist extension torque, (2) radial deviation torque, (3) elbow flexion torque and (4) finger extension. The electromyographic recordings show clear differentiation of ECRB and ECRL with the relative activation patterns reflecting the underlying anatomical organisation of the two muscles. This technique provides an important objective method that can be used in conjunction with manual muscle testing to provide a means of ensuring accurate intramuscular electromyographic recording from these two muscles.     

The effect of leg muscle activation state and localized muscle fatigue on tibial response during impact

The purpose of this research was to examine the effects of voluntarily manipulating muscle activation and localized muscle fatigue on tibial response parameters, including peak tibial acceleration, time to peak tibial acceleration, and the acceleration slope, measured at the knee during unshod heel impacts. A human pendulum delivered consistent impacts to 15 female and 15 male subjects. The tibialis anterior and lateral gastrocnemius were examined using electromyography, thus allowing voluntary contraction to various activation states (baseline, 15%, 30%, 45%, and 60% of the maximum activation state) and assessing localized muscle fatigue. A skin-mounted uniaxial accelerometer, preloaded medial to the tibial tuberosity, allowed tibial response parameter determination. There were significant decreases in peak acceleration during tibialis anterior fatigue, compared to baseline and all other activation states. In females, increased time to peak acceleration and decreased acceleration slope occurred during fatigue compared to 30% and 45%, and compared to 15% through 60% of the maximum activation state, respectively. Slight peak acceleration and acceleration slope increases, and decreased time to peak acceleration as activation state increased during tibialis anterior testing, were noted. When examining the lateral gastrocnemius, the time to peak acceleration was significantly higher across gender in the middle activation states than at the baseline and fatigue states. The acceleration slope decreased at all activation states above baseline in females, and decreased at 60% of the maximum activation state in males compared to the baseline and fatigue states. Findings agree with localized muscle fatigue literature, suggesting that with fatigue there is decreased impact transmission, which may protect the leg. The relative effects of leg stiffness and ankle angle on tibial response need to be verified.     

Reduced elbow extension torque during vibrations

Impact sports and vibration platforms trigger vibrations within soft tissues and the skeleton. Although the long-term effects of vibrations on the body have been studied extensively, the acute effects of vibrations are little understood. This study determined the influence of acute vibrations at different frequencies and elbow angles on maximal isometric elbow extension torque and muscle activity. Vibrations were generated by a pneumatic vibrator attached to the lever of a dynamometer, and were applied on the forearm of 15 healthy female subjects. The subjects were instructed to push maximally against the lever at three different elbow angles, while extension torque and muscle activity were quantified and compared between vibration and non-vibration (control) conditions. A change in vibration frequency had no significant effects on torque and muscle activity although vibrations in general decreased the maximal extension torque relative to the control by 1.8% (±5.7%, p>0.05), 7.4% (±7.9%, p<0.01), and 5.0% (±8.2%, p<0.01) at elbow angles of 60°, 90°, and 120°, respectively. Electromyographic activity increased significantly between ～30% and 40% in both triceps and biceps with vibrations. It is speculated that a similar increase in muscle activity between agonist and antagonist, in combination with an unequal increase in muscle moment arms about the elbow joint, limit the maximal extension torque during exposure to vibrations. This study showed that maximal extension torque decreased during vibration exposure while muscle activity increased and suggests that vibrations may be counterproductive during activities requiring maximal strength but potentially beneficial for strength training.     

Trainability of Muscular Activity Level during Maximal Voluntary Co-Contraction: Comparison between Bodybuilders and Nonathletes

Antagonistic muscle pairs cannot be fully activated simultaneously, even with maximal effort, under conditions of voluntary co-contraction, and their muscular activity levels are always below those during agonist contraction with maximal voluntary effort (MVE). Whether the muscular activity level during the task has trainability remains unclear. The present study examined this issue by comparing the muscular activity level during maximal voluntary co-contraction for highly experienced bodybuilders, who frequently perform voluntary co-contraction in their training programs, with that for untrained individuals (nonathletes). The electromyograms (EMGs) of biceps brachii and triceps brachii muscles during maximal voluntary co-contraction of elbow flexors and extensors were recorded in 11 male bodybuilders and 10 nonathletes, and normalized to the values obtained during the MVE of agonist contraction for each of the corresponding muscles (% EMG_MVE). The involuntary coactivation level in antagonist muscle during the MVE of agonist contraction was also calculated. In both muscles, % EMG_MVE values during the co-contraction task for bodybuilders were significantly higher (P<0.01) than those for nonathletes (biceps brachii: 66±14% in bodybuilders vs. 46±13% in nonathletes, triceps brachii: 74±16% vs. 57±9%). There was a significant positive correlation between a length of bodybuilding experience and muscular activity level during the co-contraction task (r = 0.653, P = 0.03). Involuntary antagonist coactivation level during MVE of agonist contraction was not different between the two groups. The current result indicates that long-term participation in voluntary co-contraction training progressively enhances muscular activity during maximal voluntary co-contraction.     

Assessment of functional recovery in tennis elbow

Objectives: (a) To investigate changes in muscular strength, fatigue and activity in recovered tennis elbow (RTE); (b) to assess the appropriateness of EMG and strength measurements in monitoring functional recovery in tennis elbow (TE).Methods: Study included three age-matched female groups of Control (C) (n = 8, no history of musculoskeletal problems), TE (n = 7, local tenderness at the lateral epicondyle and pain with resisted wrist and middle finger extension) and RTE (n = 6, asymptomatic for at least 6 months, no lateral epicondyle tenderness). Measurements included metacarpophalangeal (MCP), wrist, shoulder and grip isometric strength and EMG measures of muscle fatigue and activity for five forearm muscles (wrist extensors and flexors).Results: Strength was greater (p < 0.05) for all measurements in C compared to RTE and TE except for MCP extension. Only MCP extension was stronger in RTE than TE. EMG revealed increased activity of extensor carpi radialis (ECR) in RTE, decreased in TE.Conclusions: Despite attenuation of pain, global upper limb weakness in RTE indicated incomplete functional recovery. Increased strength of MCP extension may protect weakened wrist extensors from further injury. Monitoring the ECR activity as well as strength measurements may provide a useful assessment of functional recovery in TE.