Publications

BACKGROUND: Recent studies suggest that wearing high-heel shoes increases the risk of developing certain musculoskeletal pain conditions. In this study we sought to examine whether heel height alters lumbar and hip extensor muscle timing characteristics during a standardized trunk flexion task. METHODS: Thirty-one young, healthy women (22-27 years; 168.6 +/- 5.1 cm; 57.1 +/- 11.8 kg) participated in this study. Lumbar erector spinae (ES), gluteus maximus (GM), and biceps femoris (BF) electromyographic (EMG) signals were recorded during a trunk flexion task where subjects were instructed to flex their trunk in the sagittal plane and then return to a neutral posture. The task was repeated under three footwear conditions: while wearing no footwear, while wearing shoes with 4-cm heels, and while wearing shoes with 10-cm heels. EMG onset and offset times, as well as EMG duration, were calculated for each muscle and compared across conditions. RESULTS: We observed a significantly earlier onset of the ES EMG activity (1.36 +/- 0.61 vs. 1.56 +/- 0.67 s), and significantly delayed onset of the GM EMG activity (1.72 +/- 0.66 vs. 1.28 +/- 0.58 s) during the flexion phase of movement in the 10-cm heeled compared to the no footwear condition. The GM muscle also exhibited an earlier offset time in the 10-cm heel condition compared to the no footwear condition during the flexion movement (2.57 +/- 0.67 vs. 3.30 +/- 0.61 s) as well as during the return from flexion movement phase (10.87 +/- 0.58 vs. 11.69 +/- 0.65 s). These alterations in timing characteristic resulted in an overall decrease in the EMG duration for the GM muscle during the flexion movement. CONCLUSION: The results of this study suggest that high-heels alter trunk and hip extensor muscle coordination patterns. These findings, when considered in combination with other recent findings on the biomechanical effects of wearing high-heels, raise concern about whether wearing high heels results in abnormal spine loading patterns and increases the risk for developing musculoskeletal injuries.

PURPOSE OF REVIEW: Age-related muscle weakness causes a staggering economic, public, and personal burden. Most research has focused on internal muscular mechanisms as the root cause to strength loss. Here, we briefly discuss age-related impairments in the brain and peripheral nerve structures that may theoretically lead to muscle weakness in old age. RECENT FINDINGS: Neuronal atrophy in the brain is accompanied by electrical noise tied to declines in dopaminergic neurotransmission that degrades communication between neurons. Additionally, sensorimotor feedback loops that help regulate corticospinal excitability are impaired. In the periphery, there is evidence for motor unit loss, axonal atrophy, demyelination caused by oxidative damage to proteins and lipids, and modified transmission of the electrical signal through the neuromuscular junction. SUMMARY: Recent evidence clearly indicates that muscle weakness associated with aging is not entirely explained by classically postulated atrophy of muscle. In this issue, which focuses on 'Ageing: Biology and Nutrition' we will highlight new findings on how nervous system changes contribute to the aging muscle phenotype. These findings indicate that the ability to communicate neural activity to skeletal muscle is impaired with advancing age, which raises the question of whether many of these age-related neurological changes are mechanistically linked to impaired performance of human skeletal muscle. Collectively, this work suggests that future research should explore the direct link of these 'upstream' neurological adaptions and onset of muscle weakness in elders. In the long term, this new focus might lead to novel strategies to attenuate the age-related loss of muscle strength.

The purpose of this study was to determine whether anodal transcranial direct current stimulation (tDCS) delivered while performing a sustained submaximal contraction would increase time to task failure (TTF) compared to sham stimulation. Healthy volunteers (n = 18) performed two fatiguing contractions at 20% of maximum strength with the elbow flexors on separate occasions. During fatigue task performance, either anodal or sham stimulation was delivered to the motor cortex for up to 20 minutes. Transcranial magnetic stimulation (TMS) was used to assess changes in cortical excitability during stimulation. There was no systematic effect of the anodal tDCS stimulation on TTF for the entire subject set (n = 18; p = 0.64). Accordingly, a posteriori subjects were divided into two tDCS-time groups: Full-Time (n = 8), where TTF occurred prior to the termination of tDCS, and Part-Time (n = 10), where TTF extended after tDCS terminated. The TTF for the Full-Time group was 31% longer with anodal tDCS compared to sham (p = 0.04), whereas TTF for the Part-Time group did not differ (p = 0.81). Therefore, the remainder of our analysis addressed the Full-Time group. With anodal tDCS, the amount of muscle fatigue was 6% greater at task failure (p = 0.05) and the amount of time the Full-Time group performed the task at an RPE between 8-10 ("very hard") increased by 38% (p = 0.04) compared to sham. There was no difference in measures of cortical excitability between stimulation conditions (p = 0.90). That the targeted delivery of anodal tDCS during task performance both increased TTF and the amount of muscle fatigue in a subset of subjects suggests that augmenting cortical excitability with tDCS enhanced descending drive to the spinal motorpool to recruit more motor units. The results also suggest that the application of tDCS during performance of fatiguing activity has the potential to bolster the capacity to exercise under conditions required to derive benefits due to overload.

Enhancement of cardiovascular and muscular fitness through exercise and lifestyle interventions is critical to in alleviating mobility impairment in older adults. In this review article, we discuss the current knowledge-base surrounding mobility improvements in seniors following behavioral interventions that use lifestyle modifications involving physical activity and dietary interventions.

The interrelationship between muscle strength, motor unit (MU) number, and age is poorly understood, and in this study we sought to determine whether age-related differences in muscle strength are moderated by estimates of functioning MU number and size. Eighteen older adults (OA; 67 +/- 1.20 years) and 24 young adults (YA; 22 +/- 0.74 years) participated in this study. Maximum voluntary pinch-grip strength of the nondominant hand was determined and estimates of MU number were obtained from the abductor pollicis brevis muscle using the noninvasive motor unit number index (MUNIX) technique. The MUNIX technique was also utilized to derive a motor unit size index (MUSIX). An analysis of covariance (Age Group x MUNIX or MUSIX) was used to test heterogeneity of regression slopes, with body mass and gender serving as covariates. We observed that the slope of pinch-grip strength on the estimated number of MUs between YA and OA differed, indicated by an Age Group x MUNIX interaction (p = 0.04). Specifically, after controlling for the effect of body mass and gender, the slope in OA was significantly positive (0.14 +/- 0.06 N/MUs, p = 0.03), whereas no such relationship was found in YA (-0.08 +/- 0.09 N/MUs, p = 0.35). A significant Age Group x MUSIX interaction was also observed for strength (p 0.01). In contrast to MUNIX, the slope in younger adults was significantly positive (0.48 +/- 0.11 N/muV, p 0.01), whereas no such relationship was found in older adults (-0.30 +/- 0.22 N/muV, p = 0.18). These findings indicate that there is an interrelationship between muscle strength, MU numbers, and aging, which suggests that a portion of muscle weakness in seniors may be attributable to the loss of functioning motor units.

Mal de debarquement syndrome (MdDS) is a poorly characterized and understood disorder of perceived motion. We sought to characterize postural control and the psychological impact of MdDS. Additionally, we explored whether patients with MdDS exhibit altered corticospinal and intracortical excitability. In a case-control study we compared patients with MdDS to age- and sex-matched controls (n=8/group). Postural stability (sigmar) was quantified from plane phase plots based on center or pressure, and psychological indices of depression, fatigue and kinesiophobia were obtained. Transcranial magnetic stimulation (TMS) was used to assess corticospinal excitability by quantifying the motor evoked potential (MEP) amplitude of the flexor carpi radialis, and intracortical excitability was assessed by quantifying indices of intracortical facilitation (ICF), and short-interval and long-interval intracortical inhibition using a paired-pulse TMS paradigm. The patients with MdDS exhibited greater mean (+/-standard error of the mean) sigmar during semi-tandem stance (10.9 +/- 1.5 compared to 7.1 +/- 0.7, p=0.04), higher levels of kinesiophobia (41.6 +/- 2.8 compared to 27.3 +/- 2.2), and higher levels of fatigue (27.0 +/- 4.1 compared to 48.4 +/- 1.0). Patients with MdDS exhibited a higher mean motor threshold (MT) (58.1 +/- 2.5 compared to 47.4 +/- 2.7% of stimulator output), and larger MEP (13.1 +/- 3.1 compared to 5.1 +/- 1.2% of maximal compound muscle action potential) but there was no difference in measures of intracortical excitability. These findings suggest that patients with MdDS exhibit impaired postural stability, and high levels of kinesiophobia and fatigue. Additionally, we observed that patients with MdDS exhibit higher MT and large MEP amplitudes, but do not exhibit differences in measures of intracortical excitability, compared to controls. These findings help characterize MdDS, and provide insight into the physiology of MdDS.

BACKGROUND AND 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 and the Functional Assessment of Chronic Illness Therapy-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 Short Form-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.

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.

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.