Electromyographic Activity of the Lumbar and Hip Extensors During Dynamic Trunk Extension Exercise

Archives of Physical Medicine and Rehabilitation. Nov, 2002  |  Pubmed ID: 12422323

To evaluate the effects of exercise intensity and multiple sets on muscle activation patterns during trunk extension exercise.

Derecruitment of the Lumbar Musculature with Fatiguing Trunk Extension Exercise

Spine. Feb, 2003  |  Pubmed ID: 12567032

This was a descriptive study involving 20 healthy individuals.

Gender Differences in Skeletal Muscle Fatigability Are Related to Contraction Type and EMG Spectral Compression

Journal of Applied Physiology (Bethesda, Md. : 1985). Jun, 2003  |  Pubmed ID: 12576411

The purposes of this study were 1) to evaluate gender differences in back extensor endurance capacity during isometric and isotonic muscular contractions, 2) to determine the relation between absolute load and endurance time, and 3) to compare men [n = 10, age 22.4 +/- 0.69 (SE) yr] and women (n = 10, age 21.7 +/- 1.07 yr) in terms of neuromuscular activation patterns and median frequency (MF) shifts in the electromyogram (EMG) power spectrum of the lumbar and hip extensor muscles during fatiguing submaximal isometric trunk extension exercise. Subjects performed isotonic and isometric trunk extension exercise to muscular failure at 50% of maximum voluntary contraction force. Women exhibited a longer endurance time than men during the isometric task (146.0 +/- 10.9 vs. 105.4 +/- 7.9 s), but there was no difference in endurance performance during the isotonic exercise (24.3 +/- 3.4 vs. 24.0 +/- 2.8 repetitions). Absolute load was significantly related to isometric endurance time in the pooled sample (R(2) = 0.34) but not when men and women were analyzed separately (R(2) = 0.05 and 0.04, respectively). EMG data showed no differences in neuromuscular activation patterns; however, gender differences in MF shifts were observed. Women demonstrated a similar fatigability in the biceps femoris and lumbar extensors, whereas in men, the fatigability was more pronounced in the lumbar musculature than in the biceps femoris. Additionally, the MF of the lumbar extensors demonstrated a greater association with endurance time in men than in women (R(2) = 0.45 vs. 0.19). These findings suggest that gender differences in muscle fatigue are influenced by muscle contraction type and frequency shifts in the EMG signal but not by alterations in the synergistic activation patterns.

Leg Muscle Activity During Walking with Assistive Devices at Varying Levels of Weight Bearing

Archives of Physical Medicine and Rehabilitation. Sep, 2004  |  Pubmed ID: 15375835

To evaluate the muscle activation patterns at varying levels of weight-bearing forces during assisted walking with an axillary crutch and a recently designed device that allows weight transfer through the pelvic girdle (ED Walker).

Sex Differences in Muscle Fatigability and Activation Patterns of the Human Quadriceps Femoris

European Journal of Applied Physiology. May, 2005  |  Pubmed ID: 15791418

The purposes of this study were to determine if the fatigability of the quadriceps femoris varies by biological sex under conditions of normal muscle blood flow and ischemia, and if differences in neuromuscular activation patterns exist. Young men and women (n = 11/group; age 20-39 years) performed a sustained knee extension contraction at 25% of maximal force under conditions of occluded (OCC) and normal muscle blood flow (NON-OCC). Electromyographic (EMG) activity was recorded from the vastus lateralis (VL), rectus femoris (RF), vastus medialis (VM) and biceps femoris (BF) muscles, and analyzed for fatigue-induced changes in the amplitude and burst rate and duration (transient changes in motor unit recruitment) of the signal. Additionally, force fluctuations during the sustained contraction were quantified. Women had a longer time to task failure during the NON-OCC task [214.9 +/- 20.5 vs. 169.1 +/- 20.5 (SE) s] (P = 0.02), but not during the OCC task (179.6 + 19.6 vs. 165.2 +/- 19.6 s). EMG data demonstrated sex differences in the neuromuscular activation pattern of the RF muscle and the collectively averaged QF muscles. During the NON-OCC and OCC tasks women achieved a higher relative activation of the RF at task failure than men (NON-OCC: 40.68 +/- 4.57 vs. 24.49 +/- 4.19%; OCC: 36.80 +/- 5.45 vs. 24.41 +/- 2.12%) (P = 0.02 and 0.05, respectively). Also, during both tasks, they demonstrated a greater relative activation at task failure than men when an average of the VL, VM and RF was considered. Additionally, women exhibited a greater coefficient of variation in force fluctuations during the last-third of the fatiguing NON-OCC task (6.21 +/- 0.567 vs. 4.56 +/- 0.56%) (P = 0.001). No sex differences in EMG burst rate or duration were observed, although there was a trend towards greater EMG burst rate of the RF in association with muscle fatigue in the women (P = 0.09). Interestingly, the only neuromuscular activation variable that displayed a significant relationship with the time to task failure was the average relative EMG of the QF at task failure, and this relationship was observed under both experimental blood flow conditions (NON-OCC: r = 0.47, P = 0.03; OCC: r = 0.44, P = 0.04). These results indicate that sex differences in muscle blood flow and/or muscle metabolism are in part responsible for the female advantage in fatigue-resistance. Additionally, these findings suggest that men synergistically recruit the RF compartment to a lesser extent than women in association with muscle fatigue, and that women achieve an overall greater relative activation of the QF at task failure than men. However, the implications of these sex differences in neuromuscular activation patterns during fatiguing muscular contractions on the ability to withstand muscle fatigue (prolonged time to task failure) does not appear to be causally related.

Resistance and Functional Training Reduces Knee Extensor Position Fluctuations in Functionally Limited Older Adults

European Journal of Applied Physiology. Dec, 2005  |  Pubmed ID: 16193338

The purpose of this study was to determine the effect of task-specificity on knee extensor steadiness adaptations in functionally limited older adults. Twenty-four functionally limited older adults (74.6+/-7.6 years: 22 women, 2 men) completed a 10-week control period followed by 10 weeks (2 days/week) of resistance (RT), functional (FT) (practicing everyday tasks, i.e., chair rises) or functional + resistance (FRT) training, which featured both shortening and lengthening movements. During testing, subjects performed a steady isometric [10, 25, 50% of maximal voluntary contraction (MVC)] and shortening/lengthening (5, 30, 65% of MVC) knee extensor contractions. There were no steadiness (isometric, shortening or lengthening contractions) changes in the control period and no adaptations in isometric steadiness due to training. RT induced a 37% reduction in shortening fluctuations at 5% of MVC and 35% reduction in lengthening fluctuations at both 30% and 65% of MVC. FRT induced a 60% reduction in shortening fluctuations at 30% of MVC. No adaptations in dynamic steadiness were observed in the FT group. Further analysis indicated that those who were the least steady at baseline showed the greatest training effects during isometric (RT: R (2)=0.25, FRT: R (2)=0.49, FT: R (2)=0.38), shortening (RT: R (2)=0.36, FRT: R (2)=0.36, FT: R (2)=0.35) and lengthening (RT: r (2)=0.29, FRT: r (2)=0.44) contractions. In conclusion, steadiness improvements in groups performing resistance exercise, without a concomitant improvement in the FT group, supports a role for task-specificity in explaining steadiness adaptations, particularly for unsteady older adults.

The Use of Magnetic Resonance Imaging to Evaluate Lumbar Muscle Activity During Trunk Extension Exercise at Varying Intensities

Spine. Nov, 2005  |  Pubmed ID: 16284595

Descriptive, repeated measures analysis of exercise-induced changes in lumbar muscle transverse relaxation time (T2).

Adaptations in Human Neuromuscular Function Following Prolonged Unweighting: II. Neurological Properties and Motor Imagery Efficacy

Journal of Applied Physiology (Bethesda, Md. : 1985). Jul, 2006  |  Pubmed ID: 16514003

Strength loss following disuse may result from alterations in muscle and/or neurological properties. In this paper, we report our findings on human plantar flexor neurological properties following 4 wk of limb suspension [unilateral lower limb suspension (ULLS)], along with the effect of motor imagery (MI) training on these properties. In the companion paper (Part I), we report our findings on the changes in skeletal muscle properties. Additionally, in the present paper, we analyze our findings to determine the relative contribution of neural and muscular factors in strength loss. Measurements of central activation, the H-reflex, and nerve conduction were made before and after 4 wk of ULLS (n = 18; 19-28 yr). A subset of the subjects (n = 6) performed PF MI training 4 days/wk. Following ULLS, we observed a significant increase in the soleus H-reflex (45.4 +/- 4.0 to 51.9 +/- 3.7% expressed relative to the maximal muscle action potential). Additionally, there were longer intervals between the delivery of an electrical stimulus to the tibial nerve and the corresponding muscle action potential (M-wave latency; mean prolongation 0.49 ms) and H-reflex wave (H-wave latency; mean prolongation 0.46 ms). The efficacy of MI on strength was ambiguous, with no significant effect detected (although a modest effect size was observed; eta2 = 0.18). These findings suggest that unweighting induces plastic changes in neural function that appear to be spatially distributed throughout the nervous system. In terms of the relative contribution of neural and muscular factors regulating strength loss, we observed that neural factors (primarily deficits in central activation) explained 48% of the variability in strength loss, whereas muscular factors (primarily sarcolemma function) explained 39% of the variability.

Adaptations in Human Neuromuscular Function Following Prolonged Unweighting: I. Skeletal Muscle Contractile Properties and Applied Ischemia Efficacy

Journal of Applied Physiology (Bethesda, Md. : 1985). Jul, 2006  |  Pubmed ID: 16514004

Strength loss following disuse may result from alterations in muscle and/or neurological properties. In this paper, we report our findings on human plantar flexor muscle properties following 4 wk of limb suspension (unilateral lower limb suspension), along with the effect of applied ischemia (Isc) on these properties. In the companion paper (Part II), we report our findings on the changes in neurological properties. Measurements of voluntary and evoked forces, the compound muscle fiber action potential (CMAP), and muscle cross-sectional area (CSA) were collected before and after 4 wk of unilateral lower limb suspension in adults (n = 18; 19-28 yr). A subset of subjects (n = 6) received applications of Isc 3 days/wk (3 sets; 5-min duration). In the subjects not receiving Isc, the loss in CSA and strength was as expected ( approximately 9 and 14%). We observed a 30% slowing in the duration of the CMAP, a 10% decrease in evoked doublet force, a 12% increase in the twitch-to-doublet force ratio, and an altered postactivation potentiation response (11% increase in the postactivation potentiation-to-doublet ratio). We also detected a 10% slowing in the ability of the plantar flexor to develop force during the initial phase of an evoked contraction, along with a 6% reduction in in vivo specific doublet force. In the Isc subjects, no preservation was observed in strength or the evoked muscle properties. However, the Isc group did maintain CSA of the lateral gastrocnemius, as the control subjects' lateral gastrocnemius atrophied 10.2%, whereas the subjects receiving Isc atrophied 4.7%. Additionally, Isc abolished the unweighting-induced slowing in the CMAP. These findings suggest that unweighting alters the contractile properties involved in the excitation-contraction coupling processes and that Isc impacts the sarcolemma.

Growth Hormone and Muscle Function Responses to Skeletal Muscle Ischemia

Journal of Applied Physiology (Bethesda, Md. : 1985). Dec, 2006  |  Pubmed ID: 16888046

We examined the effects of ischemia (ISC) alone and with low-intensity exercise (ISC+EX) on growth hormone (GH) and muscle function responses. Nine men (22 +/- 0.7 yr) completed 3 study days: an ISC day (thigh cuff inflated five times, 5 min on, 3 min off), an ISC+EX day [knee extension at 20% maximal voluntary contraction (MVC) with ISC], and a control day. MVCs and submaximal contraction tasks (15 and 30% MVC) were performed before and following the perturbations. Surface electromyogram signals were collected from thigh muscles and analyzed for median frequency and root mean square alterations. Blood samples were collected every 10 min (190 min total) and analyzed for GH concentrations. Peak GH concentrations and GH area under the curve were highest (P < 0.01) on the ISC+EX day (7.5 microg/l and 432 microg.l(-1).min(-1), respectively) compared with the ISC (0.9 microg/l and 76.4 microg.l(-1).min(-1)), and CON (1.1 microg/l and 83.8 microg.l(-1).min(-1)) days. A greater GH pulse amplitude, mass/pulse, and production rate were also observed on the ISC+EX day (P < 0.05). Following the intervention, force production decreased on the ISC and ISC+EX days by 16.1 and 55.8%, respectively, and did not return to baseline values within 5 min of recovery. During the submaximal contractions, median frequency shifted to lower frequencies for most of the muscles examined, and root mean square electromyogram was consistently elevated for ISC+EX day. In conclusion, ISC coupled with resistance exercise acutely increases GH levels and reduces MVC, whereas ISC alone decreases force capacity, without alterations in GH levels.

Accelerometry As a Measure of Subject Compliance in Unilateral Lower Limb Suspension

Aviation, Space, and Environmental Medicine. Sep, 2006  |  Pubmed ID: 16964746

Human unilateral lower limb suspension (ULLS) is a commonly used model to study the effects of disuse and unweighting of human skeletal muscle. ULLS requires subjects to ambulate on crutches with an elevated shoe on the weight-bearing limb or a strap on the unloaded limb for prolonged periods of time (i.e., 4-5 wk). Ensuring compliance during ULLS participation is critical to the integrity of the study.

Evaluation of Spastic Muscle in Stroke Survivors Using Magnetic Resonance Imaging and Resistance to Passive Motion

Archives of Physical Medicine and Rehabilitation. Dec, 2006  |  Pubmed ID: 17141645

To assess the feasibility of using magnetic resonance imaging (MRI) and resistance to passive movement to evaluate spastic muscle.

Reduced Physical Activity Increases Intermuscular Adipose Tissue in Healthy Young Adults

The American Journal of Clinical Nutrition. Feb, 2007  |  Pubmed ID: 17284732

Recent findings suggest that higher levels of intermuscular adipose tissue (IMAT) are associated with glucose dysregulation, lower levels of muscle strength, and a heightened risk of disability. Although several studies have described adaptations in muscle after reduced physical activity, the change in IMAT in healthy young adults is unknown.

Effect of Prolonged Unweighting of Human Skeletal Muscle on Neuromotor Force Control

European Journal of Applied Physiology. May, 2007  |  Pubmed ID: 17287986

The purpose of this study was to determine the effect of 4 weeks of unilateral lower limb suspension (ULLS) on the fluctuations in motor output and the associated physiological changes. Subjects (n = 17) performed steady isometric plantarflexion (PF) and knee extension (KE) tasks, and KE shortening and lengthening contractions (intensity = 25% maximum). Spinal excitability of the soleus muscle was assessed via the H-reflex, muscle cross-sectional area (CSA) via MRI, along with EMG activity during the PF tasks. Following ULLS, isometric force fluctuations increased approximately 12% for the PF, and 22% for the KE (P < 0.05), with no difference in the pattern of PF muscle activation (P = 0.46). The unsteadiness of lengthening KE contractions increased 25% following ULLS (P = 0.03), while KE steadiness during shortening contractions was not altered (P = 0.98). Significant correlations were observed between the percent changes in PF isometric force fluctuations and H-reflex (r = 0.49, P = 0.04), and between the PF isometric force fluctuations and PF CSA (r = -0.61, P < 0.01). These findings suggest the effects of unweighting on neuromotor performance are muscle group and contraction type dependent, and that the disuse-paradigm altering muscle CSA and spinal excitability may serve to mediate the associated loss of steadiness.

Fatigue-induced Changes in Phasic Muscle Activation Patterns During Dynamic Trunk Extension Exercise

American Journal of Physical Medicine & Rehabilitation / Association of Academic Physiatrists. May, 2007  |  Pubmed ID: 17303959

To investigate the influence of fatigue on phasic muscle-activation patterns during dynamic trunk extension exercise.

Effects of Exercise Load and Blood-flow Restriction on Skeletal Muscle Function

Medicine and Science in Sports and Exercise. Oct, 2007  |  Pubmed ID: 17909396

Resistance training at low loads with blood flow restriction (BFR) (also known as Kaatsu) has been shown to stimulate increases in muscle size and strength. It is unclear how occlusion pressure, exercise intensity, and occlusion duration interact, or which combination of these factors results in the most potent muscle stimulus.

Reliability of Techniques to Assess Human Neuromuscular Function in Vivo

Journal of Electromyography and Kinesiology : Official Journal of the International Society of Electrophysiological Kinesiology. Feb, 2007  |  Pubmed ID: 16427317

The purpose of this study was to comprehensively evaluate the reliability of a large number of commonly utilized experimental tests of in vivo human neuromuscular function separated by 4-weeks. Numerous electrophysiological parameters (i.e., voluntary and evoked electromyogram [EMG] signals), contractile properties (i.e., evoked forces and rates of force development and relaxation), muscle morphology (i.e., MRI-derived cross-sectional area [CSA]) and performance tasks (i.e., steadiness and time to task failure) were assessed from the plantarflexor muscle group in 17 subjects before and following 4-weeks where they maintained their normal lifestyle. The reliability of the measured variables had wide-ranging levels of consistency, with coefficient of variations (CV) ranging from approximately 2% to 20%, and intraclass correlation coefficients (ICC) between 0.53 and 0.99. Overall, we observed moderate to high-levels of reliability in the vast majority of the variables we assessed (24 out of the 29 had ICC>0.70 and CV<15%). The variables demonstrating the highest reliability were: CSA (ICC=0.93-0.98), strength (ICC=0.97), an index of nerve conduction velocity (ICC=0.95), and H-reflex amplitude (ICC=0.93). Conversely, the variables demonstrating the lowest reliability were: the amplitude of voluntary EMG signal (ICC=0.53-0.88), and the time to task failure of a sustained submaximal contraction (ICC=0.64). Additionally, relatively little systematic bias (calculated through the limits of agreement) was observed in these measures over the repeat sessions. In conclusion, while the reliability differed between the various measures, in general it was rather high even when the testing sessions are separated by a relatively long duration of time.

Kinesthetic Motor Imagery and Spinal Excitability: the Effect of Contraction Intensity and Spatial Localization

Clinical Neurophysiology : Official Journal of the International Federation of Clinical Neurophysiology. Aug, 2008  |  Pubmed ID: 18486544

Data on whether motor imagery (MI) modulates spinal excitability are equivocal. The purpose of this study was to determine if imagined muscle contractions of the left plantar flexor (PF) alter spinal excitability, and if so, to determine whether this alteration is intensity dependent and/or localized to the target muscles. Our research questions required two experiments.

Quantification of the Corticospinal Silent Period Evoked Via Transcranial Magnetic Stimulation

Journal of Neuroscience Methods. Aug, 2008  |  Pubmed ID: 18588914

A magnetic pulse to the cortex during a muscle contraction produces a motor evoked potential (MEP) followed by electrical quiescence before activity resumes that is indicative of corticospinal inhibition and commonly referred to as the corticospinal slient period (SP). The purpose of the present study was to determine the effect of stimulus intensity and quantification method on the between-visit variability of the SP in healthy individuals. On two occasions we recorded the SP from 9 humans at 3 stimulus intensities (10, 20 and 30% above active motor threshold [AMT]) and quantified the SP based on 8 common criteria. We evaluated the effect of stimulus intensity on reliability by using the limits of agreement, and this analysis revealed that the lower stimulus intensities (10 and 20% AMT) exhibited heteroscedasticity, which indicates the amount of random error increases as the silent period increases. The 30% AMT intensity was homoscedastic. We used both visual and mathematical approaches to quantify the SP, and observed that the between-visit coefficient of variation (CV) was less for the visual methods, and that the CV was reduced when the SP onset was earliest in the temporal occurrence of events (i.e. MEP onset to EMG return CV=12%). Inter-rater reliability for the visual analyses were high (r=0.91-0.99). These results suggest that SPs evoked with a stimulus intensity >or=30% AMT and quantified visually by defining the start of the SP at stimulus delivery or the start of the MEP be utilized to decrease the between visit variability.

Neuromuscular Plasticity During and Following 3 Wk of Human Forearm Cast Immobilization

Journal of Applied Physiology (Bethesda, Md. : 1985). Sep, 2008  |  Pubmed ID: 18635877

Prolonged reductions in muscle activity results in alterations in neuromuscular properties; however, the time course of adaptations is not fully understood, and many of the specific adaptations have not been identified. This study evaluated the temporal evolution of adaptations in neuromuscular properties during and following 3 wk of immobilization. We utilized a combination of techniques involving nerve stimulation and transcranial magnetic stimulation to assess changes in central activation of muscle, along with spinal (H reflex) and corticospinal excitability [i.e., motor-evoked potential (MEP) amplitude, silent period (SP)] and contractile properties in 10 healthy humans undergoing 3 wk of forearm immobilization and 9 control subjects. Immobilization induced deficits in central activation (85 +/- 3 to 67 +/- 7% ) that returned to baseline levels 1 wk after cast removal. The flexor carpii radialis MEP amplitude increased greater than twofold after the first week of immobilization and remained elevated throughout immobilization and 1 wk after cast removal. Additionally, we observed a prolongation of the SP 1 wk after cast removal compared with baseline (78.5 +/- 7.1 to 98.2 +/- 8.7 ms). The contractile properties were also altered, since the rate of evoked force relaxation was slower following immobilization (-14.5 +/- 1.4 to -11.3 +/- 1.0% peak force/ms), and remained depressed 1 wk after cast removal (-10.5 +/- 0.8% peak force/ms). These observations detail the time course of adaptations in corticospinal and contractile properties associated with disuse and illustrate the profound effect of immobilization on the human neuromuscular system as evidenced by the alterations in corticospinal excitability persisting 1 wk following cast removal.

Sarcopenia =/= Dynapenia

The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences. Aug, 2008  |  Pubmed ID: 18772470

Maximal voluntary force (strength) production declines with age and contributes to physical dependence and mortality. Consequently, a great deal of research has focused on identifying strategies to maintain muscle mass during the aging process and elucidating key molecular pathways of atrophy, with the rationale that the loss of strength is primarily a direct result of the age-associated declines in mass (sarcopenia). However, recent evidence questions this relationship and in this Green Banana article we argue the role of sarcopenia in mediating the age-associated loss of strength (which we will coin as dynapenia) does not deserve the attention it has attracted in both the scientific literature and popular press. Rather, we propose that alternative mechanisms underlie dynapenia (i.e., alterations in contractile properties or neurologic function), and urge that greater attention be paid to these variables in determining their role in dynapenia.

Immobilization-induced Increase in Fatigue Resistance is Not Explained by Changes in the Muscle Metaboreflex

Muscle & Nerve. Nov, 2008  |  Pubmed ID: 18932206

Immobilization has been reported to enhance fatigability, which is paradoxical in light of the metabolic and molecular alterations that occur in atrophied muscles. We examined whether the immobilization-induced enhancement in fatigability was associated with attenuation in the muscle metaboreflex response. Ten subjects were examined after 3 weeks of hand-forearm immobilization. The time to task failure of a handgrip contraction (20% intensity) was determined along with heart rate (HR) and mean arterial pressure (MAP) at rest, during the task and during a 2-min postexercise muscle ischemia (PEMI) test that continues to stimulate the metaboreflex. Immobilization decreased strength by 25% (P<0.01) and increased the time to task failure by 21% (P=0.03). However, no changes were observed for the HR and MAP responses to the exercise task or during PEMI (P>0.05). These findings indicate that the augmentation of time to task failure with immobilization is not associated with changes in the pressor or metaboreflex responses.

Restoration of Voluntary Muscle Strength After 3 Weeks of Cast Immobilization is Suppressed in Women Compared with Men

Archives of Physical Medicine and Rehabilitation. Jan, 2009  |  Pubmed ID: 19154845

To investigate sex-related differences in the loss and recovery of voluntary muscle strength after immobilization.

Comments on Point:Counterpoint: Estrogen and Sex Do/do Not Influence Post-exercise Indexes of Muscle Damage, Inflammation, and Repair

Journal of Applied Physiology (Bethesda, Md. : 1985). Mar, 2009  |  Pubmed ID: 19244554

Blood Flow Restricted Exercise and Skeletal Muscle Health

Exercise and Sport Sciences Reviews. Apr, 2009  |  Pubmed ID: 19305199

For nearly half a century, high mechanical loading and mechanotransduction pathways have guided exercise recommendations for inducing muscle hypertrophy. However, emerging research on low-intensity exercise with blood flow restriction challenges this paradigm. This article will describe the BFR exercise model and discuss its efficacy, potential mechanisms, and clinical viability.

Muscle Functional Magnetic Resonance Imaging and Acute Low Back Pain: a Pilot Study to Characterize Lumbar Muscle Activity Asymmetries and Examine the Effects of Osteopathic Manipulative Treatment

Osteopathic Medicine and Primary Care. 2009  |  Pubmed ID: 19712459

Muscle functional magnetic resonance imaging (mfMRI) measures transverse relaxation time (T2), and allows for determination of the spatial pattern of muscle activation. The purposes of this pilot study were to examine whether MRI-derived T2 or side-to-side differences in T2 (asymmetries) differ in low back muscles between subjects with acute low back pain (LBP) compared to asymptomatic controls, and to determine if a single osteopathic manipulative treatment (OMT) session alters these T2 properties immediately and 48-hours after treatment.

In Vivo Alterations in Skeletal Muscle Form and Function After Disuse Atrophy

Medicine and Science in Sports and Exercise. Oct, 2009  |  Pubmed ID: 19727027

Prolonged reductions in muscle activity and mechanical loading (e.g., bed rest, cast immobilization) result in alterations in skeletal muscle form and function. The purpose of this review article was to synthesize recent findings from several studies on the dramatic effects of disuse on skeletal muscle morphology and muscle performance in humans. Specifically, the following are discussed: 1) how the antigravity muscles are most susceptible to atrophy and how the degree of atrophy varies between muscle groups; 2) how disuse alters muscle composition by increasing intermuscular adipose tissue; 3) the influence of different disuse models on regulating the loss of muscle mass and strength, with immobilization causing greater reductions than bed rest and limb suspension do; 4) the observation that disuse decreases strength to a greater extent than muscle mass and the role of adaptations in both neural and contractile properties that influences this excessive loss of strength; 5) the equivocal findings on the effect of disuse on muscle fatigue resistance; and 6) the reduction in motor control after prolonged disuse. Lastly, emerging data warranting further inquiry into the modulating role of biological sex on disuse-induced adaptations are also discussed.

Delayed-onset Muscle Soreness Induced by Low-load Blood Flow-restricted Exercise

European Journal of Applied Physiology. Dec, 2009  |  Pubmed ID: 19727801

We performed two experiments to describe the magnitude of delayed-onset muscle soreness (DOMS) associated with blood flow restriction (BFR) exercise and to determine the contribution of the concentric (CON) versus eccentric (ECC) actions of BFR exercise on DOMS. In experiment 1, nine subjects performed three sets of unilateral knee extension BFR exercise at 35% of maximal voluntary contraction (MVC) to failure with a thigh cuff inflated 30% above brachial systolic pressure. Subjects repeated the protocol with the contralateral limb without flow restriction. Resting soreness (0-10 scale) and algometry (pain-pressure threshold; PPT) were assessed before and 24, 48 and 96 h post-exercise. Additionally, MVC and vastus lateralis cross-sectional area (CSA) were measured as indices of exercise-induced muscle damage. At 24-h post-exercise, BFR exercise resulted in more soreness than exercise without BFR (2.8 +/- 0.3 vs 1.7 +/- 0.5) and greater reductions in PPT (15.2 +/- 1.7 vs. 20 +/- 2.3 N) and MVC (14.1 +/- 2.5% decrease vs. 1.5 +/- 4.5% decrease) (p

Effect of Encapsulating Arginine Containing Molecules on PLGA: a Solid-state NMR Study

Journal of Pharmaceutical Sciences. Jun, 2010  |  Pubmed ID: 20014285

Design of polymer-drug composites based on the lactide/glycolic acid often rely on the chemical complementarity between the polymer and functional groups in a pharmaceutical guest. We previously characterised decapeptide (AZD)/poly(D,L-lactide-co-glycolide) (PLGA) film formulations aiming at localising the interacting groups responsible for the changes in the bulk properties of the polymer matrix and understanding the mechanism of stabilisation of the drug into the polymer matrix. The results suggested interactions to occur between the arginine residue in the peptide and the carbonyl end group of the polymer chains. In order to clarify the role of arginine in directing the drug-polymer interactions, arginine and hexapeptide containing arginine were encapsulated in a PLGA 50/50 polymer. Variable temperature T1 rh H measurements and WISE experiments indicated significant changes in the local dynamics of the polymer chains. These effects were enhanced near and above T(g) suggesting the presence of guests promote the appearance of backbone motion of the polymer chains. The localisation of the interactions on the carbonyl groups of the polymer was further confirmed by the WISE experiments.

Men and Women Exhibit a Similar Time to Task Failure for a Sustained, Submaximal Elbow Extensor Contraction

European Journal of Applied Physiology. Apr, 2010  |  Pubmed ID: 20024575

Sex differences in muscle fatigue-resistance have been observed in a variety of muscles and under several conditions. This study compared the time to task failure (TTF) of a sustained isometric elbow extensor (intensity 15% of maximal strength) contraction in young men (n = 12) and women (n = 11), and examined if their neurophysiologic adjustments to fatigue differed. Motor-evoked potential amplitude (MEP), silent period duration, interference electromyogram (EMG) amplitude, maximal muscle action potential (M (max)), heart rate, and mean arterial pressure were measured at baseline, during the task, and during a 2-min ischemia period. Men and women did not differ in TTF (478.2 +/- 31.9 vs. 500.4 +/- 41.3 s; P = 0.67). We also performed an exploratory post hoc cluster analysis, and classified subjects as low (n = 15) or high endurance (n = 8) based on TTF (415.3 +/- 16.0 vs. 626.7 +/- 25.8 s, respectively). The high-endurance group exhibited a lower MEP and EMG at baseline (MEP 16.3 +/- 4.1 vs. 37.2 +/- 3.0% M (max), P < 0.01; EMG 0.98 +/- 0.18 vs. 1.85 +/- 0.26% M (max), P = 0.03). These findings suggest no sex differences in elbow extensor fatigability, in contrast to observations from other muscle groups. The cluster analyses results indicated that high- and low-endurance groups displayed neurophysiologic differences at baseline (before performing the fatigue task), but that they did not differ in fatigue-induced changes in their neurophysiologic adjustments to the task.

Effect of Encapsulating a Pseudo-decapeptide Containing Arginine on PLGA: a Solid-state NMR Study

Journal of Pharmaceutical Sciences. Jun, 2010  |  Pubmed ID: 20112432

The effects of incorporating an amorphous decapeptide in PLGA on the cooperative and local motions of the polymer chains have been evaluated. Whereas assessment of the bulk properties is used traditionally for studies of host-guest interactions, there are only rare examples where molecular-level understanding of such amorphous host-guest systems has been sought. Moreover, addressing the mechanism of interactions and stabilisation of a drug in a polymeric network is a key factor for the achievement of reproducibility of the formulations and ultimately the preparation of composites able to deliver drugs with consistency. We present a methodology combining the study of the dynamics by solid-state NMR and the characterisation of the bulk properties to address and localise the presence of interactions in PLGA/guest composites. The results (estimation of relaxation times, 2D wideline separation and T(g) measurements) suggested (1) the existence of a drug-polymer solid solution and (2) significant changes in the local dynamics of both the drug and the polymer in their composites depending on the loading level. The changes in the local dynamics as well as in the cooperative motions of the polymer chains in the composites were attributed to the formation of guest-polymer interactions. Differentiation of the affinity of glycolide or lactide units for interactions was also apparent.

Functional Consequences of Sarcopenia and Dynapenia in the Elderly

Current Opinion in Clinical Nutrition and Metabolic Care. May, 2010  |  Pubmed ID: 20154609

The economic burden due to the sequela of sarcopenia (muscle wasting in the elderly) are staggering and rank similarly to the costs associated with osteoporotic fractures. In this article, we discuss the societal burden and determinants of the loss of physical function with advancing age, the physiologic mechanisms underlying dynapenia (muscle weakness in the elderly), and provide perspectives on related critical issues to be addressed.

Older Adults Exhibit More Intracortical Inhibition and Less Intracortical Facilitation Than Young Adults

Experimental Gerontology. Sep, 2010  |  Pubmed ID: 20417265

Aging results in decreased neuromuscular function, which is likely associated with neurologic alterations. At present little is known regarding age-related changes in intracortical properties.

Cast Immobilization Increases Long-interval Intracortical Inhibition

Muscle & Nerve. Sep, 2010  |  Pubmed ID: 20544941

Immobilization reduces muscle performance, and despite these performance losses being associated with neural impairments little is known regarding adaptations in cortical properties. We utilized transcranial magnetic stimulation to assess changes in flexor carpi radialis (FCR) intracortical facilitation (ICF), and short- and long-interval intracortical inhibition (SICI and LICI) in healthy humans undergoing 3 weeks of immobilization. Measurements were obtained at rest and during contraction (15% intensity). Central activation and the Hoffman reflex (H-reflex) were also assessed. Strength decreased 43.2% +/- 6.1% following immobilization, and central activation also decreased (97.5% +/- 2.4% to 73.2% +/- 8.3%). No changes in ICF, SICI, or LICI were observed at rest; however, LICI was increased during contraction (67.5% +/- 6.9% to 53.1% +/- 6.7% of unconditioned response). The increase in LICI correlated with the loss of strength (r = -0.63). The H-reflex increased following immobilization. These findings suggest that immobilization increases intracortical inhibition during contraction, and this increase is primarily mediated by GABA(B) receptors.

Novel Methods for Quantifying Neurophysiologic Properties of the Human Lumbar Paraspinal Muscles

Journal of Neuroscience Methods. Jan, 2011  |  Pubmed ID: 20969893

Our understanding the neurophysiologic characteristics of the human paraspinal muscles has historically been hindered by the lack of experimental techniques to examine these muscles function in vivo. In this article we describe a paired-pulse transcranial magnetic stimulation (TMS) protocol to quantify intracortical facilitation (ICF) and short-interval intracortical inhibition (SICI) of the lumbar paraspinal muscles, and an electromechanical tapping protocol to measure the amplitude of the short-latency stretch reflex. Test-retest reliability of these protocols was examined across two sessions separated by 30-min in healthy adults. We assessed relative reliability by calculating the intraclass correlation coefficient (ICC), and absolute reliability was assessed via coefficient of variation (CV). ICF and SICI in the lumbar paraspinal muscles exhibited the classical facilitatory and inhibitory responses observed in appendicular skeletal muscles (∼30% facilitation and inhibition, respectively). The motor evoked potential amplitude (MEP), ICF, SICI, and stretch reflex amplitude measurements did not significantly differ between the two testing sessions (p>0.05). The MEP amplitude, ICF and stretch reflex amplitude exhibited the highest relative and absolute reliability (ICC=0.89-0.91, CV=10.6-11.1%); whereas the SICI measure exhibited somewhat lower reliability (ICC=0.75, CV=20.1%). The stretch reflex protocol performed in the first testing session did not influence the TMS outcome measures in the second testing session (p>0.05). These innovative methods may be useful in studying basic physiology, the pathology of low back pain, as well as the mechanisms of action of treatment interventions.

Exploring the Pathophysiology of Mal De Debarquement

Journal of Neurology. Jun, 2011  |  Pubmed ID: 21170723

Time to Task Failure of Trunk Extensor Muscles Differs with Load Type

Journal of Motor Behavior. 2011  |  Pubmed ID: 21186461

Time to task failure of trunk extensor muscles during seated submaximal isometric exertions was assessed in 18 healthy participants using 2 different load types. One required supporting an inertial load (position-matching task) whereas the 2nd required maintaining an equivalent torque against a rigid restraint (force-matching task). Time to task failure was significantly longer for position-matching tasks compared to the force-matching tasks. This finding is opposite to that reported for the appendicular muscles. A subset of 4 individuals completed a 2nd experiment to test the time to task failure of the elbow flexors in the position- and force-matching tasks. Time to task failure of the elbow flexors was significantly longer for the force-matching tasks compared to position matching. Thus, the same population shows that the effects of load type on time to task failure are opposite for the appendicular and axial muscles. This could be an important issue in understanding the mechanisms of task failure, and the endurance capacity of the trunk extensor muscles.

Age-Related Changes in Motor Cortical Properties and Voluntary Activation of Skeletal Muscle

Current Aging Science. Apr, 2011  |  Pubmed ID: 21529329

Aging is associated with dramatic reductions in muscle strength and motor control, and many of these age related changes in muscle function result from adaptations in the central nervous system. Aging is associated with widespread qualitative and quantitative changes of the motor cortex. For example, advancing age has been suggested to result in cortical atrophy, reduced cortical excitability, reduced cortical plasticity, as well as neurochemical abnormalities. The associated functional effects of these changes likely influence numerous aspects of muscle performance such as muscle strength and motor control. For example, there is evidence to suggest that the muscle weakness associated with aging is partially due to impairments in the nervous system's ability to fully activate motor neurons- particularly in the larger proximal muscle groups. In this review article we discuss age-related changes in the motor cortex, as well as the ability or lack thereof- of older adults to voluntarily activate skeletal muscle. We also provide perspectives on scientific and clinical questions that need to be addressed in the near future.

Neurophysiologic Effects of Spinal Manipulation in Patients with Chronic Low Back Pain

BMC Musculoskeletal Disorders. 2011  |  Pubmed ID: 21781310

While there is growing evidence for the efficacy of SM to treat LBP, little is known on the mechanisms and physiologic effects of these treatments. Accordingly, the purpose of this study was to determine whether SM alters the amplitude of the motor evoked potential (MEP) or the short-latency stretch reflex of the erector spinae muscles, and whether these physiologic responses depend on whether SM causes an audible joint sound.

A Preliminary Study of Symptomatic Fatigue in Rural Older Adults

Aging Clinical and Experimental Research. Oct, 2011  |  Pubmed ID: 22027409

Background & Aims: The purpose of this study was to evaluate the prevalence of symptomatic fatigue and its relation to physical function and self-perceived health in a sample of older, rural community-dwelling adults with commonly-used clinical fatigue scales. Methods: This is an exploratory, descriptive study of 30 subjects from 4 rural counties. All subjects were 70+ years of age and had no recent history of hospitalization. Subjects were assessed in their homes and completed a standard test of physical function, twelve functional assessment instruments, and two commonly-used clinical fatigue scales: the Fatigue Severity Scale (FSS) and the FACIT Fatigue Scale. Results: Depending on the fatigue instrument and criteria used, 23-47% of subjects exhibited symptomatic fatigue. Regardless of the scale, fatigue was associated with several negative consequences: decreased physical function performance, lower morale, and reduced physical composite scores on the SF-36 quality of life questionnaire. Of note, these differences remained significant even after accounting for depression scale scores. In addition, fatigue was associated with a greater incidence of risk for malnutrition. Conclusions: Together, these findings suggest that symptomatic fatigue may be quite prevalent in older individuals in rural settings, and warrants further consideration when presented in the clinical setting, as it may be associated with several negative health outcomes.

Social, Societal, and Economic Burden of Mal De Debarquement Syndrome

Journal of Neurology. Jan, 2012  |  Pubmed ID: 22231864

Mal de debarquement syndrome (MdDS) is a disorder of phantom perception of self-motion of unknown cause. The purpose of this work was to describe the quality of life (QOL) of patients with MdDS and to estimate the economic costs associated with this disorder. A modified version of a QOL survey used for another neurological disease (multiple sclerosis; MSQOL-54) was used to assess the impact of MdDS on QOL in 101 patients. The estimated economic costs were based on self-reported direct and indirect costs of individuals living in the United States using Medicare reimbursement payment rates for 2011 in 79 patients. Patients with MdDS reported a poor overall QOL as indicated by a mean composite QOL score of 59.26 ± 1.89 (out of 100). The subcategories having the lowest QOL rating were role limitations due to physical problems (18.32 ± 3.20), energy (34.24 ± 1.47), and emotional problems (36.30 ± 4.00). The overall physical health composite score including balance was 49.40 ± 1.69, and the overall mental health composite score was 52.40 ± 1.83. The cost to obtain a diagnosis was $2,997 ± 337, which included requiring an average of 19 physician visits per patient. The direct cost of MdDS medical care was $826 ± 140 per patient per year, which mainly included diagnostic imaging and physician visits. The indirect costs (i.e., lost wages) were $9,781 ± 2,347 per patient per year. Among 65 patients who were gainfully employed when they acquired MdDS, the indirect costs were $11,888 ± 2,786 per patient per year. Thus, the total annual cost of the disorder ranged from $11,493 ± 2,341 to $13,561 ± 2,778 per patient per year depending on employment status prior to developing MdDS. MdDS negatively and dramatically impacts QOL, and also imposes a substantial economic burden on MdDS patients. These findings underscore the need for further basic and clinical research on MdDS.

Non-thrust Manual Therapy Reduces Erector Spinae Short-latency Stretch Reflex Asymmetries in Patients with Chronic Low Back Pain

Journal of Electromyography and Kinesiology : Official Journal of the International Society of Electrophysiological Kinesiology. Jan, 2012  |  Pubmed ID: 22285058

The purpose of this study was to determine if non-thrust manual therapy (MT) attenuated side-to-side differences (asymmetry) of the erector spinae (ES) stretch reflex amplitude in nine patients with chronic LBP. We used electromechanical tapping to elicit short-latency stretch reflexes (SR) from the ES muscles before and after non-thrust MT. A large asymmetry in the SR was observed at baseline, with the higher of the paraspinal sides exhibiting a 100.2±28.2% greater value than the lower side. Following the intervention, this SR asymmetry was reduced (100.2±28.2% to 36.6±23.1%; p=0.03). This change was largely due to reduced amplitude on the side that was higher at baseline (35% reduction following treatment; p=0.05), whereas no change over time was observed in the low side (p=0.23). Additionally, there was no difference between the respective sides following the intervention (p=0.38), indicating that the asymmetry was normalized following treatment. These findings provide insight into the mechanism(s) of action of non-thrust MT, and suggest that it acts to down regulate the gain of the muscle spindles and/or the various sites of the Ia reflex pathway. Ultimately, developing a better understanding of the physiologic effects of manual therapies will assist in optimizing treatment strategies for patients with LBP.

The Influence of Heel Height on Lower Extremity Kinematics and Leg Muscle Activity During Gait in Young and Middle-aged Women

Gait & Posture. Jan, 2012  |  Pubmed ID: 22300729

The aim of this study was to evaluate the changes in electromyographic (EMG) activity of the lower limb muscles, and hip, knee and ankle kinematics during gait while wearing low- (4-cm) and high-heeled (10-cm) shoes in 31 young and 15 middle-aged adult women. We observed an increase in knee flexion and decrease in ankle eversion associated with elevated heel heights suggesting that compensatory mechanisms attenuating ground reaction forces may be compromised during gait with higher-heeled shoes. Additionally, we observed increased muscle activity during high-heeled gait that may exacerbate muscle fatigue. Collectively, these findings suggest that permanent wearing of heeled footwear could contribute to muscle overuse and repetitive strain injuries.

The Effect of Walking in High- and Low-Heeled Shoes on Erector Spinae Activity and Pelvis Kinematics During Gait

American Journal of Physical Medicine & Rehabilitation / Association of Academic Physiatrists. Feb, 2012  |  Pubmed ID: 22311060

OBJECTIVE: Wearing high-heeled shoes may produce deleterious effects on the musculoskeletal system. The purpose of this study was to evaluate the changes in electromyographic (EMG) activity of the erector spinae muscles and pelvis kinematics during gait while wearing low- and high-heeled shoes in both young and middle-aged adult women. DESIGN: In 31 young women (20-25 yrs) and 15 middle-aged women (45-55 yrs) without back pain, the EMG activity of the erector spinae muscle and pelvis kinematics in the sagittal, frontal, and transverse planes were assessed during gait on flat surface at natural speeds in three conditions: without shoes and in low- (4 cm) and high- (10 cm) heeled shoes. RESULTS: In younger women, significant differences in lumbar erector spinae EMG activity were observed during gait at initial ground contact as well as in toe off between the three conditions, with an increasing amount of EMG activity being observed in association with increased heel height. In middle-aged women, significantly higher lumbar erector spinae EMG activity was noted during gait with high-heeled shoes compared with gait without shoes. Interestingly, younger women exhibited an increase in pelvic range of motion in the sagittal plane during high-heeled gait compared with low-heeled gait and walking without shows; however, this compensatory response was not observed in middle-aged women. CONCLUSIONS: From a clinical perspective, increased lumbar erector spinae muscle activity associated with wearing high-heeled shoes could exacerbate muscle overuse and lead to low back problems. The lower pelvic range of motion associated with wearing high heels in middle-aged women may indicate that tissues in the lumbopelvic region become more rigid with age and that the harmful effect of high-heeled shoes on posture and spinal tissues may be more pronounced with advancing age.

Dynapenia and Aging: an Update

The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences. Jan, 2012  |  Pubmed ID: 21444359

In 2008, we published an article arguing that the age-related loss of muscle strength is only partially explained by the reduction in muscle mass and that other physiologic factors explain muscle weakness in older adults (Clark BC, Manini TM. Sarcopenia =/= dynapenia. J Gerontol A Biol Sci Med Sci. 2008;63:829-834). Accordingly, we proposed that these events (strength and mass loss) be defined independently, leaving the term "sarcopenia" to be used in its original context to describe the age-related loss of muscle mass. We subsequently coined the term "dynapenia" to describe the age-related loss of muscle strength and power. This article will give an update on both the biological and clinical literature on dynapenia-serving to best synthesize this translational topic. Additionally, we propose a working decision algorithm for defining dynapenia. This algorithm is specific to screening for and defining dynapenia using age, presence or absence of risk factors, a grip strength screening, and if warranted a test for knee extension strength. A definition for a single risk factor such as dynapenia will provide information in building a risk profile for the complex etiology of physical disability. As such, this approach mimics the development of risk profiles for cardiovascular disease that include such factors as hypercholesterolemia, hypertension, hyperglycemia, etc. Because of a lack of data, the working decision algorithm remains to be fully developed and evaluated. However, these efforts are expected to provide a specific understanding of the role that dynapenia plays in the loss of physical function and increased risk for disability among older adults.