Abdominal Activity Research Articles

Electrophysiological properties of abdominal muscle‐projecting expiratory motoneurons of rats

Expiration is considered a passive process during resting breathing condition. There is a lack of information about the intrinsic electrophysiological properties of expiratory motoneurons and their possible changes in conditions in which the expiration becomes an active process, such as hypoxia. Considering that abdominal expiratory muscle activity depends on excitability of these motoneurons, here we aimed to characterize the electrophysiological properties of abdominal muscle‐projecting expiratory motoneurons combining retrograde tracer, immunofluorescence and whole cell patch clamp, in thoraco‐lumbar spinal cord slices from juvenile Wistar rats. Three different types of cholinergic expiratory motoneurons with similar capacitance were recorded: neurons with spontaneous action potentials whose resting potential hyperpolarizes (−65 ± 5 mV vs −69.7 ± 4 mV, n=9) and firing frequency decreases (8.5 ± 2 Hz vs 1.7 ± 1.3 Hz, n=9) after synaptic blockade. The passive properties of these motoneurons, such as input resistance and excitability, did not change after synaptic blockade (Ri = 0.16 ± 0.03 GΩ vs 0.13 ± 0.03 GΩ; Excitability = 40 ± 10 Hz vs 32 ± 11 Hz, n=9). The second group of motoneurons also exhibited spontaneous action potentials, but showed spike frequency adaptation, slowing or ceasing firing frequency during a maintained stimulus. Their membrane potential also hyperpolarized (−60 ± 1 mV vs −66 ± 1 mV, n=4) and firing frequency was abolished by synaptic blockade. On the other hand, no differences in the input resistance was observed (0.13 ± 0.01 GΩ vs 0.11 ± 0.01 GΩ, n=4). The third group did not show spontaneous action potential and synaptic blockade did not change membrane potential (−72.2 ± 2 mV vs −76 ± 3 mV, n=6) or input resistance (0.1 ± 0.04 GΩ vs 0.06 ± 0.02 GΩ, n=6). However, synaptic blockade decreased their intrinsic excitability. Overall, our data show that there are three different populations of abdominal muscle‐projecting expiratory motoneurons in rats, which may contribute to recruitment of expiratory muscles in different physiological and pathophysiological conditions.Support or Funding InformationFAPESP, CAPES, CNPQ

Long-term facilitation of expiratory and sympathetic activities following acute intermittent hypoxia in rats.

Acute intermittent hypoxia (AIH) promotes persistent increases in ventilation and sympathetic activity, referred as long-term facilitation (LTF). Augmented inspiratory activity is suggested as a major component of respiratory LTF. In this study, we hypothesized that AIH also elicits a sustained increase in expiratory motor activity. We also investigated whether the expiratory LTF contributes to the development of sympathetic LTF after AIH. Rats were exposed to AIH (10×6-7% O2 for 45s, every 5min), and the cardiorespiratory parameters were evaluated during 60min using invivo and insitu approaches. In unanesthetized conditions (n=9), AIH elicited a modest but sustained increase in baseline mean arterial pressure (MAP, 104±2 vs. 111±3mmHg, P<0.05) associated with enhanced sympathetic and respiratory-related variabilities. In the insitu preparations (n=9), AIH evoked LTF in phrenic (33±12%), thoracic sympathetic (75±25%) and abdominal nerve activities (69±14%). The sympathetic overactivity after AIH was phase-locked with the emergence of bursts in abdominal activity during the late-expiratory phase. In anesthetized vagus-intact animals, AIH increased baseline MAP (113±3 vs. 122±2mmHg, P<0.05) and abdominal muscle activity (535±94%), which were eliminated after pharmacological inhibition of the retrotrapezoid nucleus/parafacial respiratory group (RTN/pFRG). These findings indicate that increased expiratory activity is also an important component of AIH-elicited respiratory LTF. Moreover, the development of sympathetic LTF after AIH is linked to the emergence of active expiratory pattern and depends on the integrity of the neurones of the RTN/pFRG.

Abdominal SEMG Feedback for Diaphragmatic Breathing: A Methodological Note

Diaphragmatic breathing from a developmental perspective is a whole-body process. During exhalation, the abdominal wall contracts, and during inhalation, the abdominal wall relaxes. This pattern is often absent in many clients who tend to lift their chest when they inhale and do not expand their abdomen. Even if their breathing includes some abdominal movement, in many cases only the upper abdomen above the belly button moves while the lower abdomen shows limited or no movement. This article describes factors that contribute to the lack of abdominal movement during breathing, as well as a methodology to record the surface electromyography (SEMG) activity from the lower abdominal muscles (external/internal abdominal oblique and transverse abdominis). Strategies are presented to teach clients how to engage the lower abdominal muscles to facilitate effortless breathing. For example, when the person exhales, the lower abdominal muscles contract to flatten the abdomen and push the diaphragm upward, and these muscle relax during inhalation to allow the diaphragm to descend. Lower abdominal SEMG recording can also be used as a surrogate indicator for SEMG activity from the pelvic floor. To enhance activation of the lower abdominal muscles during a breathing cycle, specific exercises are described. In summary, lower abdominal SEMG feedback is a useful strategy to facilitate complete abdominal involvement during breathing.

The acute effects of targeted abdominal muscle activation training on spine stability and neuromuscular control.

BackgroundTargeted activation of the transversus abdominis (TrA) muscle through the abdominal drawing-in maneuver (ADIM) is a frequently prescribed exercise for the prevention and rehabilitation of low back pain. However, there is still debate over the role the ADIM plays in maintaining a stable spine during movement. Thus, a single cohort pre/post-intervention protocol was used to examine whether 5 min of ADIM training prior to a dynamic movement task alters dynamic spine stability and control.MethodsThirteen healthy participants performed a repetitive spine flexion task twice, once before and once after they received biofeedback training on how to correctly perform the ADIM in standing. Abdominal and back muscle activation (indwelling and surface electromyography, EMG) and 3D kinematic data were recorded during all trials. EMG activation (percent maximum) and local dynamic stability of spine movement [maximum finite-time Lyapunov exponent (λmax)] were compared before and after the training using Friedman’s rank test and repeated-measures ANOVA, respectively. To assess the moderating effects of absolute changes in EMG (∆EMG) of each muscle after training on changes in stability, the ∆EMG (peak and mean) were added to the ANOVA as separate covariates (ANCOVA).ResultsFollowing ADIM training, there were greater peak and mean levels of activation in all tested abdominal muscles, including TrA, (p < 0.05), but not in the back muscles. The ANOVA showed no significant change in λmax following training (p = 0.633). However, after considering the moderating effects of the ∆EMG seen in each muscle with training, it was found that only changes in TrA EMG significantly influenced stability. The ANCOVA revealed a significant main effect of training on stability as well as a significant interaction effect between training and ∆EMG recorded from TrA (p < 0.05); those with larger increases in TrA activation demonstrated larger improvements in stability.ConclusionAs a group, 5 min of ADIM training did not change spine stability during dynamic movement. However, those who were most successful in improving TrA activation with a 5-min ADIM training session showed the greatest improvements in local dynamic spine stability after training. As such, dynamic spine stability in some individuals may benefit from ADIM training.Electronic supplementary materialThe online version of this article (doi:10.1186/s12984-016-0126-9) contains supplementary material, which is available to authorized users.

Influence of chronic low back pain and fear of movement on the activation of the transversely oriented abdominal muscles during forward bending

Introduction: Chronic low back pain (CLBP) and fear of movement (kinesiophobia) are associated with an overactivation of paravertebral muscles during forward bending. This impairs spine motor control and contributes to pain perpetuation. However, the abdominal muscles activation is engaged too in spine stabilization but its modulation with kinesiophobia remains unknown. Our study tested whether CLBP and kinesiophobia affected the activation pattern of abdominal muscles during trunk flexion/extension. Methods: Surface electromyographical recordings of the internal oblique/transversus abdominis (IO/TrA) and external oblique (EO) muscles were analyzed in 12 people with CLBP and 13 pain-free subjects during low-velocity forward bending back and forth from erected posture. Tampa Scale of Kinesiophobia was also administrated. Results: IO/TrA activation, but not EO, was modulated across the phases of movement in both groups, i.e. maximal at onset of flexion and end of extension, and minimal at full flexion. In CLBP group only, IO/TrA activation was increased near to full trunk flexion and in correlation with kinesiophobia. Conclusions: The phase-dependence of IO/TrA activation during trunk flexion/extension in standing may have a role in spine motor control. The influence of kinesiophobia in CLBP should be further investigated as an important target in CLBP management.

Bioenergetic status and oxidative stress during escape response until exhaustion in whiteleg shrimp Litopenaeus vannamei

The escape response in some decapod crustaceans through tail-flipping represents an excellent model of short-term, exhausting muscular activity to understand the role of energy depletion and oxidative stress in muscle fatigue. In this study indicators of oxidative stress and changes in energy metabolism were measured during escape response until fatigue in whiteleg shrimp Litopenaeus vannamei. The escape response of individual shrimp was elicited in a tank by prodding the shrimp with a stick until exhaustion (no further response). A control group consisted of undisturbed shrimp, and a third group was allowed to recover. Arginine phosphate (ArgP) and adenylic energy charge (AEC) were measured by reverse phase HPLC, while fuels, reserves, antioxidant enzyme activities (superoxide dismutase, catalase, glutathione peroxidase-GPx), thiobarbituric acid reactive substances, and protein carbonyl content were analyzed by spectrophotometric methods. Shrimp reached fatigue after 31 tail-flips, which decreased abdominal muscle ArgP by 75% and AEC by 18%. Hemolymph lactate levels increased 5 times and muscle GPx activity by 2.7 times. After 1h of recovery, ArgP and AEC base levels were re-established, while hemolymph lactate concentration and GPx activity were still increased, and glucose hemolymph content increased 1.8 times. The drastic decrease in ArgP levels prevents a drop of AEC to a critical level, in accordance with a situation of non-lethal stress. Although no significant changes were observed in muscle glycogen or lactate concentrations, the increase in hemolymph lactate levels indicates an important contribution of muscle glycolysis to prevent a more pronounced decrease in ATP and AEC. The increase in GPx activity in abdominal muscle suggests an increase in reactive oxygen species production during intensive muscular activity, which was adequately neutralized, for no signs of oxidative damage occurred, as indicated by the lack of lipid and protein oxidation. These responses suggest adequate energy efficiency and prevention of oxidative damage during the escape response, in accordance with the adaptative value of such behavior to avoid instantaneous danger, with a capacity of rapid recovery.

The effects of neuromuscular electrical stimulation at different frequencies on the activations of deep abdominal stabilizing muscles.

Low back pain is associated with transversus abdominis (TrA) dysfunction. Recently, it was proposed that Neuromuscular Electrical Stimulation (NMES) could be used to stimulate deep abdominal muscle contractions and improve lumbopelvic stability. The purpose of this study was to determine the optimal stimulation frequency required during NMES for the activation of deep abdominal muscles. Twenty healthy volunteers between the ages of 24 and 32 were included. The portable research-stimulator was applied using a 10 second contraction time, and a 10 second resting time at 20 Hz, 50 Hz, and 80 Hz. Changes in muscle thicknesses were determined for the TrA, obliquus internus (OI), and obliquus externus (OE) by real time ultrasound imaging. Significant thickness increases in the TrA, OI, and OE were observed during NMES versus the resting state (p < 0.05). Of the frequencies examined, 50 Hz NMES produced the greatest increase in TrA thickness (1.33 fold as compared with 1.22 fold at 20 Hz and 1.21 fold at 80 Hz) (p < 0.05). Our results indicate that NMES can preferentially stimulate contractions in deep abdominal stabilizing muscles. Most importantly, 50 Hz NMES produced greater muscle thickness increases than 20 or 80 Hz.

Ultrasound measurement of deep and superficial abdominal muscles thickness during standing postural tasks in participants with and without chronic low back pain

BackgroundActivity of deep abdominal muscles increases the lumbar stability. Majority of previous studies indicated abdominal muscle activity dysfunction during static activity in patients with low back pain (LBP). However, the number of studies that evaluated deep abdominal muscle activity in dynamic standing activities in patients is limited, while this assessment provides better understanding of pain behavior during these activities. ObjectiveInvestigation of superficial and deep abdominal muscles activity in participants with chronic LBP as compared to healthy individuals during standing tasks. DesignCase control study. MethodsUltrasound imaging was used to measure the thickness of transverse abdominis (TrA), internal oblique (IO) and external oblique (EO) muscles in female participants with (N = 45) and without chronic LBP (CLBP) (N = 45) during tests. The Biodex Balance System was used to provide standing tasks. The thickness of each muscle in a standing task was normalized to actual thickness at rest in the supine lying position to estimate its activity. ResultsThe results indicate increases in thickness of all muscles in both groups during dynamic as compared to static standing tasks (P < 0.05, ES > 0.5). Lower percentages of thickness change for TrA muscle and higher for EO muscle were found in the patients as compared to healthy individuals during all tests (P < 0.05, ES > 1.28). ConclusionsHigher activity of superficial than deep abdominal muscles in patients as compared to healthy individuals during standing tasks indicates motor control dysfunction in patients with CLBP. Standing tasks can discriminate the individuals with and without LBP and can be progressively used in training.

Abdominal Muscle Activity during Mechanical Ventilation Increases Lung Injury in Severe Acute Respiratory Distress Syndrome.

ObjectiveIt has proved that muscle paralysis was more protective for injured lung in severe acute respiratory distress syndrome (ARDS), but the precise mechanism is not clear. The purpose of this study was to test the hypothesis that abdominal muscle activity during mechanically ventilation increases lung injury in severe ARDS.MethodsEighteen male Beagles were studied under mechanical ventilation with anesthesia. Severe ARDS was induced by repetitive oleic acid infusion. After lung injury, Beagles were randomly assigned into spontaneous breathing group (BIPAPSB) and abdominal muscle paralysis group (BIPAPAP). All groups were ventilated with BIPAP model for 8h, and the high pressure titrated to reached a tidal volume of 6ml/kg, the low pressure was set at 10 cmH2O, with I:E ratio 1:1, and respiratory rate adjusted to a PaCO2 of 35–60 mmHg. Six Beagles without ventilator support comprised the control group. Respiratory variables, end-expiratory volume (EELV) and gas exchange were assessed during mechanical ventilation. The levels of Interleukin (IL)-6, IL-8 in lung tissue and plasma were measured by qRT-PCR and ELISA respectively. Lung injury scores were determined at end of the experiment.ResultsFor the comparable ventilator setting, as compared with BIPAPSB group, the BIPAPAP group presented higher EELV (427±47 vs. 366±38 ml) and oxygenation index (293±36 vs. 226±31 mmHg), lower levels of IL-6(216.6±48.0 vs. 297.5±71.2 pg/ml) and IL-8(246.8±78.2 vs. 357.5±69.3 pg/ml) in plasma, and lower express levels of IL-6 mRNA (15.0±3.8 vs. 21.2±3.7) and IL-8 mRNA (18.9±6.8 vs. 29.5±7.9) in lung tissues. In addition, less lung histopathology injury were revealed in the BIPAPAP group (22.5±2.0 vs. 25.2±2.1).ConclusionAbdominal muscle activity during mechanically ventilation is one of the injurious factors in severe ARDS, so abdominal muscle paralysis might be an effective strategy to minimize ventilator-induce lung injury.

Effect of craniocervical posture on abdominal muscle activities.

[Purpose] The aim of this study was to investigate the influence of the craniocervical posture on abdominal muscle activities in hook-lying position. [Subjects] This study recruited 12 healthy young adults. [Methods] Each subject was asked to adopt a supine position with the hip and knee flexed at 60°. Surface electromyographic signals of transversus abdominis/internal oblique, rectus abdominis, and external oblique in different craniocervical postures (extension, neutral, and flexion) were compared. [Results] The transversus abdominis and rectus abdominis showed increased muscle activities in craniocervical flexion compared to craniocervical extension and neutral position. Greater muscle activities of the external oblique were seen in craniocervical flexion than in craniocervical extension. [Conclusion] Craniocervical flexion was found to be effective to increase the abdominal muscle activities. Consideration of craniocervical posture is recommended when performing trunk stabilization exercises.

Differences in abdominal muscle activation during coughing between smokers and nonsmokers.

[Purpose] The purpose of this study was to compare the activity of the abdominal muscles during coughing between smokers and nonsmokers. [Subjects] A total of 30 healthy adults (15 smokers, 15 nonsmokers) participated. [Methods] The percentage maximal voluntary isometric contraction values (%MVIC) of the rectus abdominis (RA), external abdominal oblique (EO), and internal abdominal oblique (IO) and transversus abdominis (TrA) were measured using surface electromyography. [Results] The %MVIC of the IO and TrA statistically significantly differed and the %MVIC of IO and TrA was found to be higher during coughing in nonsmokers compared with during coughing in smokers. [Conclusion] The activity of the deep abdominal muscles in nonsmokers was also higher than that of smokers during coughing.

The comparison of abdominal muscle activation on unstable surface according to the different trunk stability exercises

[Purpose] This study aimed to determine the effect of abdominal muscle activities and the activation ratio related to trunk stabilization to compare the effects between the abdominal drawing-in maneuver and lumbar stabilization exercises on an unstable base of support. [Subjects and Methods] Study subjects were 20 male and 10 female adults in their 20s without lumbar pain, who were equally and randomly assigned to either the abdominal drawing-in maneuver group and the lumbar stabilization exercise group. Abdominal muscle activation and ratio was measured using a wireless TeleMyo DTS during right leg raise exercises while sitting on a Swiss ball. [Results] Differences in rectus abdominis, external oblique abdominis, and internal oblique abdominis muscle activation were observed before and after treatment. Significant differences were observed between the groups in the muscle activation of the external oblique abdominis and internal oblique abdominis, and the muscle activation ratio of external oblique abdominis/rectus abdominis and internal oblique abdominis/rectus abdominis. [Conclusion] Consequently trunk stability exercise enhances internal oblique abdominis activity and increases trunk stabilization. In addition, the abdominal drawing-in maneuver facilitates the deep muscle more than LSE in abdominal muscle. Therefore, abdominal drawing-in maneuver is more effective than lumbar stabilization exercises in facilitating trunk stabilization.

Effect of neck flexion restriction on sternocleidomastoid and abdominal muscle activity during curl-up exercises.

[Purpose] The purpose of this study was to investigate the effect of neck flexion restriction on sternocleidomastoid (SCM), rectus abdominis (RA), and external oblique (EO) muscle activity during a traditional curl-up exercise and a curl-up with neck flexion restriction. [Subjects] In total, 13 healthy male subjects volunteered for this study. [Methods] All subjects performed a traditional curl-up exercise and a curl-up exercise in which neck flexion was restricted by the subject’s hand. Surface electromyography (EMG) signals were recorded from the SCM, RA, and EO during the curl-up. [Results] There was significantly lower EMG activity of the SCM during the curl-up exercise with neck flexion restriction compared to the traditional curl-up exercise. Conversely, the activity of the RA and EO muscles was significantly higher in the curl-up exercise with neck flexion restriction than in the traditional curl-up exercise. [Conclusion] Neck flexion restriction is recommended to prevent excessive activation of superficial cervical flexors during the curl-up exercise.

Abdominal muscle activity according to knee joint angle during sit-to-stand

[Purpose] This study assessed the activity of the abdominal muscles according to the angle of the knee joints during sit-to-stand. [Subjects and Methods] Thirty healthy adult males participated in this study. Subjects initiated sit-to-stand at knee joint angles of 60°, 90°, or 120°. An electromyography system was used to measure the maximum voluntary isometric contraction of the rectus abdominis, external oblique, and internal oblique and transverse abdominis muscles. [Results] Percent contraction differed significantly among the three knee joint angles, most notably for the internal oblique and transverse abdominis muscles. [Conclusion] Wider knee joint angles more effectively activate the abdominal muscles, especially those in the deep abdomen, than do narrower angles.

Changes in the activity of trunk and hip extensor muscles during bridge exercises with variations in unilateral knee joint angle.

[Purpose] This study compared abdominal and hip extensor muscle activity during a bridge exercise with various knee joint angles. [Subjects and Methods] Twenty-two healthy male subjects performed a bridge exercise in which the knee joint angle was altered. While subjects performed the bridge exercise, external oblique, internal oblique, gluteus maximus, and semitendinosus muscle activity was measured using electromyography. [Results] The bilateral external and internal oblique muscle activity was significantly higher at 0° knee flexion compared to 120°, 90°, and 60°. The bilateral gluteus maximus muscle activity was significantly different at 0° of knee flexion compared to 120°, 90°, and 60°. The ipsilateral semitendinosus muscle activity was significantly increased at 90° and 60° of knee flexion compared to 120°, and significantly decreased at 0° knee flexion compared with 120°, 90°, and 60°. The contralateral semitendinosus muscle activity was significantly higher at 60° of knee flexion than at 120°, and significantly higher at 0° of knee flexion than at 120°, 90°, and 60°. [Conclusion] Bridge exercises performed with knee flexion less than 90° may be used to train the ipsilateral semitendinosus. Furthermore, bridge exercise performed with one leg may be used to train abdominal and hip extensor muscles.

The abdominal drawing-in manoeuvre for detecting activity in the deep abdominal muscles: is this clinical tool reliable and valid?

ObjectiveThe abdominal drawing-in manoeuvre (ADIM) is a common clinical tool for manually assessing whether a preferential activation of the deep abdominal muscles in patients with low back pain (LBP) is...

Stumbling reactions during perturbed walking: Neuromuscular reflex activity and 3-D kinematics of the trunk – A pilot study

Reflex activity of the lower leg muscles involved when compensating for falls has already been thoroughly investigated. However, the trunk׳s role in this compensation strategy remains unclear. The purpose of this study, therefore, was to analyze the kinematics and muscle activity of the trunk during perturbed walking. Ten subjects (29±3yr;79±11cm;74±14kg) walked (1m/s) on a split-belt treadmill, while 5 randomly timed, right-sided perturbations (treadmill belt deceleration: 40m/s2) were applied. Trunk muscle activity was assessed with a 12-lead-EMG. Trunk kinematics were measured with a 3D-motion analysis system (12 markers framing 3 segments: upper thoracic area (UTA), lower thoracic area (LTA), lumbar area (LA)). The EMG–RMS [%] (0–200ms after perturbation) was analyzed and then normalized to the RMS of normal walking. The total range of motion (ROM;[°]) for the extension/flexion, lateral flexion and rotation of each segment were calculated. Individual kinematic differences between walking and stumbling [%; ROM] were also computed. Data analysis was conducted descriptively, followed by one- and two-way ANOVAs (α=0.05).Stumbling led to an increase in ROM, compared to unperturbed gait, in all segments and planes. These increases ranged between 107±26% (UTA/rotation) and 262±132% (UTS/lateral flexion), significant only in lateral flexion. EMG activity of the trunk was increased during stumbling (abdominal: 665±283%; back: 501±215%), without significant differences between muscles.Provoked stumbling leads to a measurable effect on the trunk, quantifiable by an increase in ROM and EMG activity, compared to normal walking. Greater abdominal muscle activity and ROM of lateral flexion may indicate a specific compensation pattern occurring during stumbling.

Correlation Between Abdominal Muscle Thickness and Maximal Expiratory Pressure.

The activity of abdominal muscles mainly produces high expiratory pressure. These include the rectus abdominis, external oblique, internal oblique, and transverse abdominis muscles. The purpose of this study was to determine whether maximal expiratory pressure is associated with each abdominal muscle thickness at rest. Thirty-nine healthy male volunteers (mean age ± SD, 20.7 ± 2.7 years) participated in the study. The thickness of the right rectus abdominis, external oblique, internal oblique, and transverse abdominis muscles was measured by B-mode sonography in the supine position. The maximal expiratory pressure was obtained with a spirometer in the sitting position. The correlations between each abdominal muscle thickness and maximal expiratory pressure were determined by the Pearson correlation coefficient. The correlation coefficient between the rectus abdominis muscle and maximal expiratory pressure was 0.571 (P< .001). Correlation coefficients between the external oblique, internal oblique, and transverse abdominis muscles and maximal expiratory pressure were 0.297 (P = .066), 0.267 (P = .100), and 0.022 (P = .894), respectively. Our results indicate that the rectus abdominis muscle thickness might be more highly correlated with expiratory pressure production than the external oblique, internal oblique, and transverse abdominis muscle thickness.

Balance recovery is compromised and trunk muscle activity is increased in chronic obstructive pulmonary disease

Increased respiration in chronic obstructive pulmonary disease (COPD) requires greater abdominal muscle activation, which may impact on contribution of the trunk to postural control. This study aimed to determine whether recovery of balance from postural perturbations and trunk muscle activity differs in people with and without COPD before and/or after exercise. Electromyography (EMG) of the obliquus internus (OI) and externus (OE) abdominis, rectus abdominis (RA), erector spinae (ES) and deltoid muscles was recorded with surface electrodes during rapid shoulder flexion and extension. Time taken to regain baseline centre of pressure velocity (vCOP) and the number of postural adjustments following arm movement was calculated from force plate data. Time to recover balance in the direction of postural disturbance (anteroposterior vCOP) was longer in COPD, particularly more severe COPD, than controls. Mediolateral vCOP (perpendicular to the perturbation) and the number of postural adjustments did not differ between groups, but people with more severe COPD were less successful at returning their mediolateral vCOP to baseline. Abdominal muscle EMG was similar between groups, but controls had greater ES EMG during arm movements. Individuals with more severe COPD had greater OE and RA EMG both before and during arm movement compared to those with less severe COPD and controls. Following exercise, OE and ES EMG increased in people with less severe COPD. This study shows that severe COPD is associated with impaired ability to recover balance and greater trunk muscle activity during postural challenges. Augmented trunk muscle activity may limit the contribution of trunk movements to balance recovery and could contribute to increased falls risk.

Expiratory activation of abdominal muscle is associated with improved respiratory stability and an increase in minute ventilation in REM epochs of adult rats.

Breathing is more vulnerable to apneas and irregular breathing patterns during rapid eye movement (REM) sleep in both humans and rodents. We previously reported that robust and recurrent recruitment of expiratory abdominal (ABD) muscle activity is present in rats during REM epochs despite ongoing REM-induced muscle atonia in skeletal musculature. To develop a further understanding of the characteristics of ABD recruitment during REM epochs and their relationship with breathing patterns and irregularities, we sought to compare REM epochs that displayed ABD muscle recruitment with those that did not, within the same rats. Specifically, we investigated respiratory characteristics that preceded and followed recruitment. We hypothesized that ABD muscle recruitment would be likely to occur following respiratory irregularities and would subsequently contribute to respiratory stability and the maintenance of good ventilation following recruitment. Our data demonstrate that epochs of REM sleep containing ABD recruitments (REM(ABD+)) were characterized by increased respiratory rate variability and increased presence of spontaneous brief central apneas. Within these epochs, respiratory events that displayed ABD muscle activation were preceded by periods of increased respiratory rate variability. Onset of ABD muscle activity increased tidal volume, amplitude of diaphragmatic contractions, and minute ventilation compared with the periods preceding ABD muscle activation. These results show that expiratory muscle activity is more likely recruited when respiration is irregular and its recruitment is subsequently associated with an increase in minute ventilation and a more regular respiratory rhythm.