Immediate effects of co-contraction training on motor control of the trunk muscles in people with recurrent low back pain

Although deficits in the activation of abdominal muscles are present in people with low back pain (LBP), this can be modified with motor training. Training of deep abdominal muscles in isolation from the other trunk muscles, as an initial phase of training, has been shown to improve the timing of activation of the trained muscles, and reduce symptoms and recurrence of LBP. The aim of this study was to determine if training of the trunk muscles in a non-isolated manner can restore motor control of these muscles in people with LBP. Ten subjects with non-specific LBP performed a single session of training that involved three tasks: “abdominal curl up”, “side bridge” and “birdog”. Electromyographic activity (EMG) of trunk and deltoid muscles was recorded with fine-wire and surface electrodes during rapid arm movements and walking, before and immediately following the intervention. Onset of trunk muscle EMG relative to that of the prime mover (deltoid) during arm movements and the mean, standard deviation (SD) and coefficient of variation of abdominal muscle EMG during walking were calculated. There was no significant change in the times of onset of trunk muscle EMG during arm movements nor was there any change in the variability of EMG of the abdominal muscles during walking. However, the mean amplitude and SD of abdominal EMG was reduced during walking after training. The results of this study suggest that unlike isolated voluntary training, co-contraction training of the trunk muscles does not restore the motor control of the deep abdominal muscles in people with LBP after a single session of training.     

Comparison of Trunk Activity during Gait Initiation and Walking in Humans

To understand the role of trunk muscles in maintenance of dynamic postural equilibrium we investigate trunk movements during gait initiation and walking, performing trunk kinematics analysis, Erector spinae muscle (ES) recordings and dynamic analysis. ES muscle expressed a metachronal descending pattern of activity during walking and gait initiation. In the frontal and horizontal planes, lateroflexion and rotation occur before in the upper trunk and after in the lower trunk. Comparison of ES muscle EMGs and trunk kinematics showed that trunk muscle activity precedes corresponding kinematics activity, indicating that the ES drive trunk movement during locomotion and thereby allowing a better pelvis mobilization. EMG data showed that ES activity anticipates propulsive phases in walking with a repetitive pattern, suggesting a programmed control by a central pattern generator. Our findings also suggest that the programs for gait initiation and walking overlap with the latter beginning before the first has ended.     

Electromyography of back muscles during quadrupedal and bipedal walking in primates

Despite the extensive electromyographic research that has addressed limb muscle function during primate quadrupedalism, the role of the back muscles in this locomotor behavior has remained undocumented. We report here the results of an electromyographic (EMG) analysis of three intrinsic back muscles (multifidus, longissimus, and iliocostalis) in the baboon (Papio anubis), chimpanzee (Pan troglodytes), and orangutan (Pongo pygmaeus) during quadrupedal walking. The recruitment patterns of these three back muscles are compared to those reported for the same muscles during nonprimate quadrupedalism. In addition, the function of the back muscles during quadrupedalism and bipedalism in the two hominoids is compared. Results indicate that the back muscles restrict trunk movements during quadrupedalism by contracting with the touchdown of one or both feet, with more consistent activity associated with touchdown of the contralateral foot. Moreover, despite reported differences in their gait preferences and forelimb muscle EMG patterns, primates and nonprimate mammals recruit their back muscles in an essentially similar fashion during quadrupedal walking. These quadrupedal EMG patterns also resemble those reported for chimpanzees, gibbons and humans (but not orangutans) walking bipedally. The fundamental similarity in back muscle function across species and locomotor behaviors is consistent with other data pointing to conservatism in the evolution of the neural control of tetrapod limb movement, but does not preclude the suggestion (based on forelimb muscle EMG and spinal lesion studies) that some aspects of primate neural circuitry are unique. © 1994 Wiley-Liss, Inc.     

Agreement of measured and calculated muscle activity during highly dynamic movements modelled with a spherical knee joint

The inclusion of muscle forces into the analysis of joint contact forces has improved their accuracy. But it has not been validated if such force and activity calculations are valid during highly dynamic multidirectional movements. The purpose of this study was to validate calculated muscle activation of a lower extremity model with a spherical knee joint for running, sprinting and 90°-cutting. Kinematics, kinetics and lower limb muscle activation of ten participants were investigated in a 3D motion capture setup including EMG. A lower extremity rigid body model was used to calculate the activation of these muscles with an inverse dynamics approach and a cubic cost function. Correlation coefficients were calculated to compare measured and calculated activation. The results showed good correlation of the modelled and calculated data with a few exceptions. The highest average correlations were found during walking (r = 0.81) and the lowest during cutting (r = 0.57). Tibialis anterior had the lowest average correlation (r = 0.33) over all movements while gastrocnemius medius had the highest correlation (r = 0.9). The implementation of a spherical knee joint increased the agreement between measured and modelled activation compared to studies using a hinge joint knee. Although some stabilizing muscles showed low correlations during dynamic movements, the investigated model calculates muscle activity sufficiently.     

Electromyographic and kinematic studies of tail movements in dogs during treadmill locomotion

Electromyographic (EMG) activities of three tail muscles, the extensor caudae lateralis (ECL), abductor caudae externus (ACE), and flexor caudae longus (FCL), were recorded bilaterally in seven adult dogs during walking, trotting, and galloping on a treadmill. Each dog's movements were recorded with a 16 mm high-speed camera system, and angular movements of the tail were analyzed. During walking and trotting, reciprocal EMG bursts were observed between right and left tail muscles and corresponded with lateral movements of the tail. The tonic discharges that were observed in ECL and FCL seemed to maintain the position of the tail. During galloping, synchronized EMG activity of all tail muscles produced reactive torques to counter those generated by cyclic limb movements and kept the tail in a stable position. These results suggest that tail movements are important in maintaining body balance during locomotion in the dog. © 1993 Wiley-Liss, Inc.     

Between-day repeatability of lower limb EMG measurement during running and walking

There are minimal data describing the between-day repeatability of EMG measurements during running. Furthermore, there are no data characterising the repeatability of surface EMG measurement from the adductor muscles, during running or walking. The purpose of this study was to report on the consistency of EMG measurement for both running and walking across a comprehensive set of lower limb muscles, including adductor magnus, longus and gracilis. Data were collected from 12 lower limb muscles during overground running and walking on two separate days. The coefficient of multiple correlation (CMC) was used to quantify waveform similarity across the two sessions for signals normalised to either maximal voluntary isometric contraction (MVIC) or mean/peak signal magnitude. For running, the data showed good or excellent repeatability (CMC = 0.87–0.96) for all muscles apart from gracilis and biceps femoris using the MVIC method. Similar levels of repeatability were observed for walking. Importantly, using the peak/mean method as an alternative to the MVIC method, resulted in only marginal improvements in repeatability. The proposed protocol facilitated the collection of repeatable EMG data during running and walking and therefore could be used in future studies investigating muscle patterns during gait.     

Kinematic and EMG analysis of horizontal bimanual climbing in humans

Climbing is an increasingly popular recreational and competitive behavior, engaged in a variety of environments and styles. However, injury rates are high in climbing populations, especially in the upper extremity and shoulder. Despite likely arising from an arboreal, climbing ancestor and being closely related to primates that are highly proficient climbers, the modern human shoulder has devolved a capacity for climbing. Limited biomechanical research exists on manual climbing performance. This study assessed kinematic and muscular demands during a bimanual climbing task that mimicked previous work on climbing primates. Thirty participants were recruited – 15 experienced and 15 inexperienced climbers. Motion capture and electromyography (EMG) measured elbow, thoracohumeral and trunk angles, and activity of twelve shoulder muscles, respectively, of the right-side while participants traversed across a horizontal climbing apparatus. Statistical parametric mapping was used to detect differences between groups in kinematics and muscle activity. Experienced climbers presented different joint motions that more closely mimicked the kinematics of climbing primates, including more elbow flexion (p = 0.0045) and internal rotation (p = 0.021), and less thoracohumeral elevation (p = 0.046). Similarly, like climbing primates, experienced climbers generally activated the shoulder musculature at a lower percentage of maximum, particularly during the exchange from support to swing and swing to support phase. However, high muscle activity was recorded in all muscles in both participant groups. Climbing experience coincided with a positive training effect, but not enough to overcome the high muscular workload of bimanual climbing. Owing to the evolved primary usage of the upper extremity for low-force, below shoulder-height tasks, bimanual climbing may induce high risk of fatigue-related musculoskeletal disorders.     

Anticipatory postural adjustments to arm movement reveal complex control of paraspinal muscles in the thorax

Anatomical and empirical data suggest that deep and superficial muscles may have different functions for thoracic spine control. This study investigated thoracic paraspinal muscle activity during anticipatory postural adjustments associated with arm movement. Electromyographic (EMG) recordings were made from the right deep (multifidus/rotatores) and superficial (longissimus) muscles at T5, T8, and T11 levels using fine-wire electrodes. Ten healthy participants performed fast unilateral and bilateral flexion and extension arm movements in response to a light. EMG amplitude was measured during 25 ms epochs for 150 ms before and 400 ms after deltoid EMG onset. During arm flexion movements, multifidus and longissimus had two bursts of activity, one burst prior to deltoid and a late burst. With arm extension both muscles were active in a single burst after deltoid onset. There was differential activity with respect to direction of trunk rotation induced by arm movement. Right longissimus was most active with left arm movements and right multifidus was most active with right arm movements. All levels of the thorax responded similarly. We suggest that although thoracic multifidus and longissimus function similarly to control sagittal plane perturbations, these muscles are differentially active with rotational forces on the trunk.     

Muscle blood flow and fiber activity in partially curarized rats during exercise

We previously reported that low doses of d-tubocurarine attenuated glycogen loss in red muscles of rats during treadmill walking but that the initial hyperemia in the muscles was normal. The present studies were performed to 1) determine with electromyography (EMG) whether red muscle fiber activity is reduced in walking, curarized rats and 2) study muscle blood flow and glycogen loss during running with different doses of curare (dose response). At 0.5 min of treadmill walking (15 m/min), integrated EMG in vastus intermedius (VI) muscle was reduced by an average of 18% in curarized (60 micrograms/kg) rats, although blood flow (measured with microspheres) was the same as in saline control rats. Comparison of blood flows and glycogen loss in quadriceps muscles at 1 min of treadmill running (30 m/min) with different curare doses (20-60 micrograms/kg) demonstrated that red muscle glycogen loss was inversely related to curare dose but that blood flows in the same muscles were unaffected by curare. These findings provide support for our previous conclusion that at the initiation of low to moderate treadmill exercise, red muscle blood flow is not proportional to the activity or metabolism of the muscle fibers.     

Critical illness VR rehabilitation device (X-VR-D): Evaluation of the potential use for early clinical rehabilitation

We present a new critical illness VR rehabilitation device (X-VR-D) that enables diversified self-training and is applicable early in the rehabilitation of severely injured or ill patients. The X-VR-D consists of a VR program delivering a virtual scene on a flat screen and simultaneously processing commands to a moving chair mounted on a motion system. Sitting in the moving chair and exposed to a virtual reality environment the device evokes anticipatory and reactive muscle contractions in trunk and extremities for postural control. In this study we tested the device in 10 healthy subjects to evaluate whether the enforced perturbations indeed evoke sufficient and reproducible EMG muscle activations.

We found that particular fast roll and pitch movements evoke adequate trunk and leg muscle activity. Higher angular velocities and higher angles of inclination elicited broader EMG bursts and larger amplitudes. The muscle activation pattern was highly consistent between different subjects and although we found some habituation of EMG responses in consecutive training sessions, the general pattern was maintained and was predictable for specific movements. The habituation was characterized by more efficient muscle contractions and better muscle relaxation during the rest positions of the device. Furthermore we found that the addition of a virtual environment to the training session evoked more preparatory and anticipatory muscle activation than sessions without a virtual environment.

We conclude that the X-VR-D is safe and effective to elicit consistent and reproducible muscle activity in trunk and leg muscles in healthy subjects and thus can be used as a training method.     

Control of climbing behavior in the cockroach, Blaberus discoidalis. II. Motor activities associated with joint movement

Deathhead cockroaches employ characteristic postural strategies for surmounting barriers. These include rotation of middle legs to re-direct leg extension and drive the animal upward. However, during climbing the excursions of the joints that play major roles in leg extension are not significantly altered from those seen during running movements. To determine if the motor activity associated with these actions is also unchanged, we examined the electromyogram activity produced by the slow trochanteral extensor and slow tibial extensor motor neurons as deathhead cockroaches climbed over obstacles of two different heights. As they climbed, activity in the slow trochanteral extensor produced a lower extension velocity of the coxal-trochanteral joint than the same frequency of slow trochanteral extensor activity produces during horizontal running. Moreover, the pattern of activity within specific leg cycles was altered. During running, the slow trochanteral extensor generates a high-frequency burst prior to foot set-down. This activity declines through the remainder of the stance phase. During climbing, motor neuron frequency no longer decreased after foot set-down, suggesting that reflex adjustments were made. This conclusion was further supported by the observation that front leg amputees generated even stronger slow trochanteral extensor activity in the middle leg during climbing movements.     

The effect of speed and influence of individual muscles on hamstring mechanics during the swing phase of sprinting

The purpose of this study was to characterize the effect of speed and influence of individual muscles on hamstring stretch, loading, and work during the swing phase of sprinting. We measured three-dimensional kinematics and electromyography (EMG) activities of 19 athletes sprinting on a treadmill at speeds ranging from 80% to 100% of maximum speed. We then generated muscle-actuated forward dynamic simulations of swing and double float phases of the sprinting gait cycle. Simulated lower extremity joint angles and model predicted excitations were similar to measured quantities. Swing phase simulations were used to characterize the effects of speed on the peak stretch, maximum force, and negative work of the biceps femoris long head (BF), the most often injured hamstring muscle. Perturbations of the double float simulations were used to assess the influence of individual muscles on BF stretch.

Peak hamstring musculotendon stretch occurred at 90% of the gait cycle (late swing) and was independent of speed. Peak hamstring force and negative musculotendon work increased significantly with speed (p<0.05). Muscles in the lumbo-pelvic region had greater influence on hamstring stretch than muscles acting about the knee and ankle. In particular, the hip flexors were found to induce substantial hamstring stretch in the opposite limb, with that influence increasing with running speed. We conclude that hamstring strain injury during sprinting may be related to the performance of large amounts of negative work over repeated strides and/or resulting from a perturbation in pelvic muscle coordination that induces excessive hamstring stretch in a single stride.     

Persistence of improvements in postural strategies following motor control training in people with recurrent low back pain.

This study investigated long-term effects of training on postural control using the model of deficits in activation of transversus abdominis (TrA) in people with recurrent low back pain (LBP). Nine volunteers with LBP attended four sessions for assessment and/or training (initial, two weeks, four weeks and six months). Training of repeated isolated voluntary TrA contractions were performed at the initial and two-week session with feedback from real-time ultrasound imaging. Home program involved training twice daily for four weeks. Electromyographic activity (EMG) of trunk and deltoid muscles was recorded with surface and fine-wire electrodes. Rapid arm movement and walking were performed at each session, and immediately after training on the first two sessions. Onset of trunk muscle activation relative to prime mover deltoid during arm movements, and the coefficient of variation (CV) of EMG during averaged gait cycle were calculated. Over four weeks of training, onset of TrA EMG was earlier during arm movements and CV of TrA EMG was reduced (consistent with more sustained EMG activity). Changes were retained at six months follow-up (p<0.05). These results show persistence of motor control changes following training and demonstrate that this training approach leads to motor learning of automatic postural control strategies.     

Trunk Muscle Activity Is Modified in Osteoporotic Vertebral Fracture and Thoracic Kyphosis with Potential Consequences for Vertebral Health

This study explored inter-relationships between vertebral fracture, thoracic kyphosis and trunk muscle control in elderly people with osteoporosis. Osteoporotic vertebral fractures are associated with increased risk of further vertebral fractures; but underlying mechanisms remain unclear. Several factors may explain this association, including changes in postural alignment (thoracic kyphosis) and altered trunk muscle contraction patterns. Both factors may increase risk of further fracture because of increased vertebral loading and impaired balance, which may increase falls risk. This study compared postural adjustments in 24 individuals with osteoporosis with and without vertebral fracture and with varying degrees of thoracic kyphosis. Trunk muscle electromyographic activity (EMG) associated with voluntary arm movements was recorded and compared between individuals with and without vertebral fracture, and between those with low and high thoracic kyphosis. Overall, elderly participants in the study demonstrated co-contraction of the trunk flexor and extensor muscles during forwards arm movements, but those with vertebral fractures demonstrated a more pronounced co-contraction than those without fracture. Individuals with high thoracic kyphosis demonstrated more pronounced alternating flexor and extensor EMG bursts than those with less kyphosis. Co-contraction of trunk flexor and extensor muscles in older individuals contrasts the alternating bursts of antagonist muscle activity in previous studies of young individuals. This may have several consequences, including altered balance efficacy and the potential for increased compressive loads through the spine. Both of these outcomes may have consequences in a population with fragile vertebrae who are susceptible to fracture.     

Differences in muscle function during walking and running at the same speed

Individual muscle contributions to body segment mechanical energetics and the functional tasks of body support and forward propulsion in walking and running at the same speed were quantified using forward dynamical simulations to elucidate differences in muscle function between the two different gait modes. Simulations that emulated experimentally measured kinesiological data of young adults walking and running at the preferred walk-to-run transition speed revealed that muscles use similar biomechanical mechanisms to provide support and forward propulsion during the two tasks. The primary exception was a decreased contribution of the soleus to forward propulsion in running, which was previously found to be significant in walking. In addition, the soleus distributed its mechanical power differently to individual body segments between the two gait modes from mid- to late stance. In walking, the soleus transferred mechanical energy from the leg to the trunk to provide support, but in running it delivered energy to both the leg and trunk. In running, earlier soleus excitation resulted in it working in synergy with the hip and knee extensors near mid-stance to provide the vertical acceleration for the subsequent flight phase in running. In addition, greater power output was produced by the soleus and hip and knee extensors in running. All other muscle groups distributed mechanical power among the body segments and provided support and forward propulsion in a qualitatively similar manner in both walking and running.     

Hamstring muscle kinematics and activation during overground sprinting

Hamstring muscle strain injury is one of the most commonly seen injuries in sports such as track and field, soccer, football, and rugby. The purpose of this study was to advance our understanding of the mechanisms of hamstring muscle strain injuries during over ground sprinting by investigating hamstring muscle-tendon kinematics and muscle activation. Three-dimensional videographic and electromyographic (EMG) data were collected for 20 male runners, soccer or lacrosse players performing overground sprinting at their maximum effort. Hamstring muscle-tendon lengths, elongation velocities, and linear envelop EMG data were analyzed for a running gait cycle of the dominant leg. Hamstring muscles exhibited eccentric contractions during the late stance phase as well as during the late swing phase of overground sprinting. The peak eccentric contraction speeds of the hamstring muscles were significantly greater during the late swing phase than during the late stance phase (p=0.001) while the hamstring muscle-tendon lengths at the peak eccentric contraction speeds were significantly greater during the late stance phase than during the late swing phase (p=0.001). No significant differences existed in the maximum hamstring muscle-tendon lengths between the two eccentric contractions. The potential for hamstring muscle strain injury exists during the late stance phase as well as during the late swing phases of overground sprinting.     

Adaptation to sudden unexpected loading of the low back--the effects of repeated trials

The purpose of this study was to investigate short-term changes in reactions to sudden unexpected loading of the low back. The study utilized a set-up where a horizontal force of 58 N pointing forward suddenly was applied to the upper part of the subject's trunk. EMG activity from the erector spinae muscles and trunk movement data were recorded during 10 trials for 19 subjects. The analysis included EMG reaction time, mean rectified EMG amplitude during the period 50-250 ms after the sudden loading, and time elapsed until stopping of the forward movement of the trunk (stopping time). Reaction time means ranged from 66 to 97 ms (79+/-9 ms), and no difference was found between the trials. Conversely, the mean stopping time for the first trial (468 ms) was significantly higher than for trials 3-10 (359- 371 ms), and the average EMG amplitude during the period 50-250 ms after the sudden loading was lower for the first trial. This study showed that some subjects adapted to sudden unexpected loadings of the low back through a reduction in stopping time and a progression in EMG response during the first few trials. This possible adaptation to repeated trials have been overlooked in previous studies.     

Electromyography of selected lower-limb muscles fatigued by exercise at the intensity of soccer match-play.

Surface electromyography has been useful in comparing muscular activity among different sports movements and it is a valuable technique for evaluating muscle activation, co-ordination and fatigue. Since these important variables have not been investigated during the full game in soccer, the present study aimed to investigate the activity of major muscles of the lower extremity during a soccer-simulation fatiguing protocol. Ten amateur soccer players (age 21.40+/-3.13 years; height 1.77+/-0.06 m; mass 74.55+/-8.5 kg) were tested. The exercise protocol, performed on a programmable motorised treadmill, consisted of the different intensities observed during soccer match-play (walking, jogging, running, sprinting). Electromyographic activity was recorded from the rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA) and gastrocnemius (GC) muscles before exercise, at half-time and immediately after the 90-min exercise protocol. The EMG data were analysed using custom-written software to compute the root mean square (RMS) value over ten gait cycles. With regard to RF, BF and TA, a significant main effect (P< 0.05) was found for condition (pre-game, half-time and post-game), speed (6, 12, 15 and 21 km h(-1)) (P<0.05) and interaction between condition and speed (P< 0.05). For GC, a significant effect was not found for condition or interaction between condition and speed, but a significant main effect (P< 0.001) was found for speed, with the RMS value increasing continually with increasing speed from 6 to 2 1km h(-1). The results indicated that after a simulation of the exercise intensity of soccer-play the EMG activity in major lower-limb muscles was less than before. This decrease indicated that prolonged intermittent exercise had an effect on muscle activity even when work-rate was sustained.     

Influence of shoes increasing dorsiflexion and decreasing metatarsus flexion on lower limb muscular activity during fitness exercises, walking, and running

The aim of the present study was to compare electromyographic activity during fitness exercises, walking, and running among 3 different dorsiflexion shoes (+2 degrees , +4 degrees , and +10 degrees ) and standard shoes (-4 degrees ). The 3 different dorsiflexion shoes tested in this study have a curvature placed in the middle of the sole. This design was specially projected to decrease the metatarsus flexion. Electromyographic activity of 9 lower limb muscles was measured on 12 healthy female subjects during 5 fitness exercises (unload squat, side and front step, submaximal ballistic plantar flexion, and lunge exercise), and during running (10 km x h(-1)) and walking (4.5 km x h(-1)) on a treadmill. EMG signal was analyzed with the root mean square (RMS) and integrated EMG. All RMS data measured during these exercises were expressed as percentages of maximum voluntary isometric contraction. The results show that dorsiflexion affects muscle recruitment and reorganizes the motor pattern. The general tendency was that the tibialis anterior activity increased with dorsiflexion. However, an optimal dorsiflexion existed for various exercises. It is concluded that shoes with moderate dorsiflexion can activate lower limb muscles differently compared with both standard shoes and shoes with large dorsiflexion during submaximal exercises and locomotion.     

Oblique abdominal muscle activity in response to external perturbations when pushing a cart

Cyclic activation of the external and internal oblique muscles contributes to twisting moments during normal gait. During pushing while walking, it is not well understood how these muscles respond to presence of predictable (cyclic push-off forces) and unpredictable (external) perturbations that occur in pushing tasks. We hypothesized that the predictable perturbations due to the cyclic push-off forces would be associated with cyclic muscle activity, while external perturbations would be counteracted by cocontraction of the oblique abdominal muscles. Eight healthy male subjects pushed at two target forces and two handle heights in a static condition and while walking without and with external perturbations. For all pushing tasks, the median, the static (10th percentile) and the peak levels (90th percentile) of the electromyographic amplitudes were determined. Linear models with oblique abdominal EMGs and trunk angles as input were fit to the twisting moments, to estimate trunk stiffness. There was no significant difference between the static EMG levels in pushing while walking compared to the peak levels in pushing while standing. When pushing while walking, the additional dynamic activity was associated with the twisting moments, which were actively modulated by the pairs of oblique muscles as in normal gait. The median and static levels of trunk muscle activity and estimated trunk stiffness were significantly higher when perturbations occurred than without perturbations. The increase baseline of muscle activity indicated cocontraction of the antagonistic muscle pairs. Furthermore, this cocontraction resulted in an increased trunk stiffness around the longitudinal axis.