Biomarkers for rapid H-reflex operant conditioning among females.

Operant conditioning of a spinal monosynaptic pathway using the Hoffman reflex (H-reflex) is well established in animal and human studies. There is a subset within the human population (∼20% nonresponders) who are unable to up train this pathway suggesting some distinct or unique identifying characteristics. Importantly, females, who have a nine times higher rate of injury during human performance activities than men, have been understudied in areas of CNS neuroplasticity. Our long-term goal is to understand if innate ability to rapidly up train the H-reflex is predictive of future performance-based injury among females. In this study, we primarily determined whether healthy, young females could rapidly increase the H-reflex within a single session of operant conditioning and secondarily determined if electro-physiological, humoral, cognitive, anthropometric, or anxiety biomarkers distinguished the responders from nonresponders. Eighteen females (mean age: 24) participated in the study. Overall, females showed a group main effect for up training the H-reflex (P < 0.05). Of the cohort, 10 of 18 females met the criteria for up training the H-reflex (responders). The responders showed lower levels of estradiol (P < 0.05). A multivariate stepwise regression model supported that extracellular to intracellular water ratio (ECW/ICW) and H-max/M-max ratio explained 60% of the variation in up training among females. These findings support that females can acutely upregulate the H-reflex with training and that electro-physiological and hormonal factors may be associated with the up training.NEW & NOTEWORTHY Young females who acutely increase their H-reflexes with operant conditioning had lower levels of estradiol. However, the best predictors of those who could up-train the H-reflex were baseline H-reflex excitability (H-max/M-max) and extracellular to intracellular water ratio (ECW/ICW). Future studies are warranted to understand the complex relationship between operant conditioning, human performance, and injury among active young females.

Healthcare educational debt in the united states: unequal economic impact within interprofessional team members.

BACKGROUND: Advancing healthcare access and quality for underserved populations requires a diverse, culturally competent interprofessional workforce. However, high educational debt may influence career choice of healthcare professionals. In the United States, health professions lack insight into the maximum educational debt that can be supported by current entry-level salaries. The purpose of this interprofessional economic analysis was to examine whether average educational debt for US healthcare graduates is supportable by entry-level salaries. Additionally, the study explored whether trainees from minoritized backgrounds graduate with more educational debt than their peers in physical therapy. METHODS: The study modeled maximum educational debt service ratios for 12 healthcare professions and 6 physician specialties, incorporating profession-specific estimates of entry-level salary, salary growth, national average debt, and 4 loan repayment scenarios offered by the US Department of Education Office of Student Financial Aid. Net present value (NPV) provided an estimate for lifetime "economic power" for the modeled careers. The study used a unique data source available from a single profession (physical therapy, N = 4,954) to examine whether educational debt thresholds based on the repayment model varied between minoritized groups and non-minoritized peers. RESULTS: High salary physician specialties (e.g. obstetrics/gynecology, surgery) and professions without graduate debt (e.g. registered nurse) met debt ratio targets under any repayment plan. Professions with strong salary growth and moderate debt (e.g. physician assistant) required extended repayment plans but had high career NPV. Careers with low salary growth and high debt relative to salary (e.g. physical therapy) had career NPV at the lowest range of modeled professions. 29% of physical therapy students graduated with more debt than could be supported by entry-level salaries. Physical therapy students from minoritized groups graduated with 10-30% more debt than their non-minoritized peers. CONCLUSIONS: Graduates from most healthcare professions required extended repayment plans (higher interest) to meet debt ratio benchmarks. For several healthcare professions, low debt relative to salary protected career NPV. Students from minoritized groups incurred higher debt than their peers in physical therapy.

Neuromuscular and gene signaling responses to passive whole-body heat stress in young adults.

This study aimed to investigate whether acute passive heat stress 1) decreases muscle Maximal Voluntary Contraction (MVC); 2) increases peripheral muscle fatigue; 3) increases spinal cord excitability, and 4) increases key skeletal muscle gene signaling pathways in skeletal muscle. Examining the biological and physiological markers underlying passive heat stress will assist us in understanding the potential therapeutic benefits. MVCs, muscle fatigue, spinal cord excitability, and gene signaling were examined after control or whole body heat stress in an environmental chamber (heat; 82 °C, 10% humidity for 30 min). Heart Rate (HR), an indicator of stress response, was correlated to muscle fatigue in the heat group (R = 0.59; p < 0.05) but was not correlated to MVC, twitch potentiation, and H reflex suppression. Sixty-one genes were differentially expressed after heat (41 genes >1.5-fold induced; 20 < 0.667 fold repressed). A strong correlation emerged between the session type (control or heat) and principal components (PC1) (R = 0.82; p < 0.005). Cell Signal Transduction, Metabolism, Gene Expression and Transcription, Immune System, DNA Repair, and Metabolism of Proteins were pathway domains with the largest number of genes regulated after acute whole body heat stress. Acute whole-body heat stress may offer a physiological stimulus for people with a limited capacity to exercise.

Corticospinal modulation of vibration-induced H-reflex depression.

The purpose of this study was to examine corticospinal modulation of spinal reflex excitability, by determining the effect of transcranial magnetic stimulation (TMS) on soleus H-reflexes while they were almost completely suppressed by lower extremity vibration. In 15 healthy adults, a novel method of single-limb vibration (0.6 g, 30 Hz, 0.33 mm displacement) was applied to the non-dominant leg. Soleus muscle responses were examined in six stimulation conditions: (1) H-reflex elicited by tibial nerve stimulation, (2) tibial nerve stimulation during vibration, (3) subthreshold TMS, (4) subthreshold TMS during vibration, (5) tibial nerve stimulation 10 ms after a subthreshold TMS pulse, and (6) tibial nerve stimulation 10 ms after a subthreshold TMS pulse, during vibration. With or without vibration, subthreshold TMS produced no motor evoked potentials and had no effect on soleus electromyography (p > 0.05). In the absence of vibration, H-reflex amplitudes were not affected by subthreshold TMS conditioning (median (md) 35, interquartile range (IQ) 18-56 vs. md 46, IQ 22-59% of the maximal M wave (Mmax), p > 0.05). During vibration, however, unconditioned H-reflexes were nearly abolished, and a TMS conditioning pulse increased the H-reflex more than fourfold (md 0.3, IQ 0.1-0.7 vs. md 2, IQ 0.9-5.0% of Mmax, p < 0.008). Limb vibration alone had no significant effect on corticospinal excitability. In the absence of vibration, a subthreshold TMS pulse did not influence the soleus H-reflex. During limb vibration, however, while the H-reflex was almost completely suppressed, a subthreshold TMS pulse partially restored the H-reflex. This disinhibition of the H-reflex by a corticospinal signal may represent a mechanism involved in the control of voluntary movement. Corticospinal signals that carry the descending motor command may also reduce presynaptic inhibition, temporarily increasing the impact of sensory inputs on motoneuron activation.

Quantitative muscle MRI as a sensitive marker of early muscle pathology in myotonic dystrophy type 1.

BACKGROUND: Quantitative muscle MRI as a sensitive marker of early muscle pathology and disease progression in adult-onset myotonic dystrophy type 1. The utility of muscle MRI as a marker of muscle pathology and disease progression in adult-onset myotonic dystrophy type 1 (DM1) was evaluated. METHODS: This prospective, longitudinal study included 67 observations from 36 DM1 patients (50% female), and 92 observations from 49 healthy adults (49% female). Lower-leg 3T magnetic resonance imaging (MRI) scans were acquired. Volume and fat fraction (FF) were estimated using a three-point Dixon method, and T2-relaxometry was determined using a multi-echo spin-echo sequence. Muscles were segmented automatically. Mixed linear models were conducted to determine group differences across muscles and image modality, accounting for age, sex, and repeated observations. Differences in rate of change in volume, T2-relaxometry, and FF were also determined with mixed linear regression that included a group by elapsed time interaction. RESULTS: Compared with healthy adults, DM1 patients exhibited reduced volume of the tibialis anterior, soleus, and gastrocnemius (GAS) (all, P < .05). T2-relaxometry and FF were increased across all calf muscles in DM1 compared to controls. (all, P < .01). Signs of muscle pathology, including reduced volume, and increased T2-relaxometry and FF were already noted in DM1 patients who did not exhibit clinical motor symptoms of DM1. As a group, DM1 patients exhibited a more rapid change than did controls in tibialis posterior volume (P = .05) and GAS T2-relaxometry (P = .03) and FF (P = .06). CONCLUSIONS: Muscle MRI renders sensitive, early markers of muscle pathology and disease progression in DM1. T2 relaxometry may be particularly sensitive to early muscle changes related to DM1.

Simultaneous Recording of Motor Evoked Potentials in Hand, Wrist and Arm Muscles to Assess Corticospinal Divergence.

The purpose of this study was to further develop methods to assess corticospinal divergence and muscle coupling using transcranial magnetic stimulation (TMS). Ten healthy right-handed adults participated (7 females, age 34.0 ± 12.9 years). Monophasic single pulses were delivered to 14 sites over the right primary motor cortex at 40, 60, 80 and 100% of maximum stimulator output (MSO), using MRI-based neuronavigation. Motor evoked potentials (MEPs) were recorded simultaneously from 9 muscles of the contralateral hand, wrist and arm. For each intensity, corticospinal divergence was quantified by the average number of muscles that responded to TMS per cortical site, coactivation across muscle pairs as reflected by overlap of cortical representations, and correlation of MEP amplitudes across muscle pairs. TMS to each muscle's most responsive site elicited submaximal MEPs in most other muscles. The number of responsive muscles per cortical site and the extent of coactivation increased with increasing intensity (ANOVA, p < 0.001). In contrast, correlations of MEP amplitudes did not differ across the 60, 80 and 100% MSO intensities (ANOVA, p = 0.34), but did differ across muscle pairs (ANOVA, p < 0.001). Post hoc analysis identified 4 sets of muscle pairs (Tukey homogenous subsets, p < 0.05). Correlations were highest for pairs involving two hand muscles and lowest for pairs that included an upper arm muscle. Correlation of MEP amplitudes may quantify varying levels of muscle coupling. In future studies, this approach may be a biomarker to reveal altered coupling induced by neural injury, neural repair and/or motor learning.

Impact of short- and long-term electrically induced muscle exercise on gene signaling pathways, gene expression, and PGC1a methylation in men with spinal cord injury.

Exercise attenuates the development of chronic noncommunicable diseases (NCDs). Gene signaling pathway analysis offers an opportunity to discover if electrically induced muscle exercise regulates key pathways among people living with spinal cord injury (SCI). We examined short-term and long-term durations of electrically induced skeletal muscle exercise on complex gene signaling pathways, specific gene regulation, and epigenetic tagging of PGC1a, a major transcription factor in skeletal muscle of men with SCI. After short- or long-term electrically induced exercise training, participants underwent biopsies of the trained and untrained muscles. RNA was hybridized to an exon microarray and analyzed by a gene set enrichment analysis. We discovered that long-term exercise training regulated the Reactome gene sets for metabolism (38 gene sets), cell cycle (36 gene sets), disease (27 gene sets), gene expression and transcription (22 gene sets), organelle biogenesis (4 gene sets), cellular response to stimuli (8 gene sets), immune system (8 gene sets), vesicle-mediated transport (4 gene sets), and transport of small molecules (3 gene sets). Specific gene expression included: oxidative catabolism of glucose including PDHB (P < 0.001), PDHX (P < 0.001), MPC1 (P < 0.009), and MPC2 (P < 0.007); Oxidative phosphorylation genes including SDHA (P < 0.006), SDHB (P < 0.001), NDUFB1 (P < 0.002), NDUFA2 (P < 0.001); transcription genes including PGC1α (P < 0.030) and PRKAB2 (P < 0.011); hypertrophy gene MSTN (P < 0.001); and the myokine generating FNDC5 gene (P < 0.008). Long-term electrically induced exercise demethylated the major transcription factor PGC1a. Taken together, these findings support that long-term electrically induced muscle activity regulates key pathways associated with muscle health and systemic metabolism.

Myotonic dystrophy type 1 alters muscle twitch properties, spinal reflexes, and perturbation-induced trans-cortical reflexes.

BACKGROUND: Neurophysiologic biomarkers are needed for clinical trials of therapies for myotonic dystrophy (DM1). We characterized muscle properties, spinal reflexes (H-reflexes), and trans-cortical long-latency reflexes (LLRs) in a cohort with mild/moderate DM1. METHODS: Twenty-four people with DM1 and 25 matched controls underwent assessment of tibial nerve H-reflexes and soleus muscle twitch properties. Quadriceps LLRs were elicited by delivering an unexpected perturbation during a single-limb squat (SLS) visuomotor tracking task. RESULTS: DM1 was associated with decreased H-reflex depression. The efficacy of doublet stimulation was enhanced, yielding an elevated double-single twitch ratio. DM1 participants demonstrated greater error during the SLS task. DM1 individuals with the least-robust LLR responses showed the greatest loss of spinal H-reflex depression. CONCLUSIONS: DM1 is associated with abnormalities of muscle twitch properties. Co-occurring alterations of spinal and trans-cortical reflex properties underscore the central nervous system manifestations of this disorder and may assist in gauging efficacy during clinical trials.

Sustained submaximal contraction yields biphasic modulation of soleus Post-activation depression in healthy humans.

The amplitude of the H-reflex during the development and progression of fatigue reflects a complex interplay between central and peripheral factors. The purpose of this study is to characterize H-reflex homosynaptic post-activation depression (PAD) in an online fashion during a sustained submaximal fatigue task. The task required a high motor output in order to increase the likelihood of creating partial muscle ischemia with accumulation of fatigue metabolites, an important potential inhibitory influence upon the H-reflex during the progression of fatigue. Eleven subjects without neurologic impairment maintained volitional, isometric plantar flexion at 60% of maximal voluntary contraction until exhaustion. A paired-pulse stimulus (2 Hz) was delivered to the tibial nerve to elicit paired H-reflexes before, during, and after the fatigue protocol. The normalized amplitude of the second H-reflex (depression ratio) served as an estimate of PAD. Depression ratio increased during the first half of the fatigue protocol (P < 0.001), indicating a diminution of PAD, and then returned as exhaustion approached. The biphasic behavior of homosynaptic H-reflex depression during fatigue to exhaustion suggests a role for metabolic mediators of post-activation depression during fatigue.

Whole body heat exposure modulates acute glucose metabolism.

AIM: Exercise modulates glucose tolerance and homeostasis in both healthy and diabetic individuals. Heat stress is a fundamental element of exercise. The acute glycemic response and alterations in glucose clearance following whole body passive heat stress in the absence of muscle activity has yet to be examined in humans. Knowledge of this relationship may prove useful, particularly in populations with compromised glucoregulation from reduced activity. PURPOSE: To determine insulin/glucose levels before and after an acute bout of heat stress in healthy, lean individuals and examine the effects of whole body heat stress (WBHS) and exercise on acute glucose tolerance in an expanded cohort. METHODS: Ten subjects (24.1 ± 0.7 years) participated in a randomized control/WBHS session (up to 30 minutes at 73 °C) with fasting glucose (FG) and insulin drawn at baseline, immediately after and 30 minutes post heat stress. In the follow-up experiment, 20 anthropometrically diverse subjects (24.6 ± 2.1 years) underwent an oral glucose tolerance test (OGTT) under the conditions above. RESULTS: FG levels rose 10% immediately following heat stress (8.6 (±5.6) mg/dl, p < .01) and returned to near baseline levels 30 minutes following WBHS. Insulin release showed its greatest increase at 30 minutes post WBHS (2.7 ± 3.5) uU/ml p < .05). WBHS resulted in a decrease in glucose uptake [AUC increased 8.2% (1430.6 ± 1957.03) mg/dl (p = .005)], particularly in nonlean individuals. CONCLUSION: WBHS modulates physiologic markers of metabolism. An acute bout of WBHS increases glucose and insulin levels in healthy individual and decreases glucose uptake in response to a glucose challenge, particularly those who are non-lean.

Fatigability, oxygen uptake kinetics and muscle deoxygenation in incomplete spinal cord injury during treadmill walking.

PURPOSE: The purpose of the present study was to characterize hypothesized relationships among fatigability and cardiorespiratory fitness in individuals with chronic motor-incomplete SCI (iSCI) during treadmill walking. The theoretical framework was that exacerbated fatigability would occur concomitantly with diminished cardiorespiratory fitness in people with iSCI. METHODS: Subjects with iSCI (n = 8) and an able-bodied reference group (REF) (n = 8) completed a 6-min walking bout followed by a walking bout of 30-min or until volitional exhaustion, both at a self-selected walking speed. Fatigability was assessed using both perceived fatigability and performance fatigability measures. Pulmonary oxygen uptake kinetics (VO2 on-kinetics) was measured breath-by-breath and changes in deoxygenated hemoglobin/myoglobin concentration (∆[HHb]) of the lateral gastrocnemius was measured by near-infrared spectroscopy. Adjustment of VO2 and ∆[HHb] on-kinetics were modeled using a mono-exponential equation. RESULTS: Perceived fatigability and performance fatigability were 52% and 44% greater in the iSCI group compared to the REF group (p = 0.003 and p = 0.004). Phase II time constant (τp) of VO2 on-kinetics and ∆[HHb] ½ time during resting arterial occlusion were 55.4% and 16.3% slower in iSCI vs REF (p < 0.01 and p = 0.047, respectively). CONCLUSIONS: The results of the present study may suggest that compromised O2 delivery and/or utilization may have contributed to the severity of fatigability in these individuals with iSCI. The understanding of the extent to which fatigability and VO2 and Δ[HHb] on-kinetics impacts locomotion after iSCI will assist in the future development of targeted interventions to enhance function.

Influence of the Menstrual Cycle and Training on the Performance of a Perturbed Single-Leg Squatting Task in Female Collegiate Athletes.

Background: Anterior cruciate ligament (ACL) injuries often occur when an athlete experiences an unexpected disruption, or perturbation, during sports. ACL injury rates may also be influenced by the menstrual cycle. Purpose: To determine whether training adaptations to knee control and muscle activity during a perturbed single-leg squatting (SLS) task depend on menstrual cycle phase in female athletes. Study Design: Controlled laboratory study. Methods: A total of 21 healthy female collegiate athletes (current or former [<3 years]) who competed in 9 different sports performed an SLS task in which they attempted to match their knee position (user signal) to a target signal. The protocol consisted of a 9-condition pretest, 5 sets of 3 training trials, and a 9-condition posttest. One perturbation was delivered in each condition by altering the resistance of the device. Sagittal knee control (absolute error between the target signal and user signal) was assessed using a potentiometer. Muscle activity during perturbed squat cycles was normalized to maximal activation and to corresponding muscle activity during unperturbed squat cycles (%unperturbed) within the same test condition. Athletes performed the protocol during a distinct menstrual cycle phase (early follicular [EF], late follicular [LF], midluteal [ML]). Two-way mixed analysis of variance was used to determine the effects of the menstrual cycle and training on knee control and muscle activity during task performance. Venous blood was collected for hormonal analysis, and a series of health questionnaires and anthropometric measures were also assessed to determine differences among the menstrual cycle groups. Results: After training, athletes demonstrated better knee control during the perturbed squat cycles (lower absolute error, P < .001) and greater soleus feedback responses to the perturbation (%unperturbed, P = .035). Better knee control was demonstrated in the ML phase versus the EF phase during unperturbed and perturbed squat cycles (P < .039 for both). Quadriceps activation was greater in the ML phase compared with the EF and LF phases, both immediately before and after the perturbation (P < .001 for all). Conclusion: Athletes learned to improve knee control during the perturbed performance regardless of menstrual cycle phase. The best knee control and greatest quadriceps activation during the perturbed squatting task was found in the ML phase. Clinical Relevance: These findings may correspond to a lower incidence of ACL injury in the luteal phase and alterations in exercise performance across the menstrual cycle.

Psychometric Analysis of an Integrated Clinical Education Tool for Physical Therapists.

INTRODUCTION: Integrated clinical education (ICE) courses require opportunities for practice, assessment of performance, and specific feedback. The purposes of this study were to 1) analyze the internal consistency of a tool for evaluating students during ICE courses, 2) examine the responsiveness of the tool between midterm and final assessments, and 3) develop a model to predict the final score from midterm assessments and explore relationships among the 6 domains. REVIEW OF LITERATURE: Several clinical education assessment tools have been developed for terminal clinical experiences, but few have focused on the needs of learners during the ICE. SUBJECTS: Eighty-five student assessments were collected from 2 consecutive cohorts of physical therapist students in a first full-time ICE course. METHODS: The tool contained 29 items within 6 domains. Items were rated on a 5-point scale from dependent to indirect supervision. Cronbach's alpha was used to analyze the internal consistency of the tool, whereas responsiveness was examined with paired t-test and Cohen's d. A best subsets regression model was used to determine the best combination of midterm variables that predicted the final total scores. Coefficients of determination (R2) were calculated to explore the relationships among domains. RESULTS: The tool was found to have high internal consistency at midterm and final assessment (α = 0.97 and 0.98, respectively). Mean scores increased over time for each domain score and for the total score (P < .001; d = 1.5). Scores in 3 midterm domains predicted more than 57% of the variance in the final total score. DISCUSSION AND CONCLUSION: Results support the use of this tool to measure student performance and growth in a first full-time ICE course. Targeted measurement of students' abilities in ICE courses assists with differentiating formative and summative learning needed to achieve academic success.

National Benchmarks to Understand how Doctor of Physical Therapy Learners from Minoritized Race and Ethnicity Groups Perceive their Physical Therapist Education Program.

OBJECTIVE: The demographic homogeneity of the physical therapist workforce and its educational pathway may undermine the profession's potential to improve the health of society. Building academic environments that support the development of all learners is fundamental to building a workforce to meet societal health care needs. The Benchmarking in Physical Therapy Education study uses the Physical Therapy Graduation Questionnaire to comprehensively assess learner perceptions of the physical therapist academic environment. The present report examined whether racial and ethnic minoritized (REM) physical therapist learners perceive their Doctor of Physical Therapy (DPT) education differently from their non-REM peers. METHODS: Five thousand and eighty graduating DPT learners in 89 institutions provided demographic data and perceptions of a range of learning environment domains. Analyses included REM versus non-REM comparisons as well as comparisons among individual race and ethnicity groups. RESULTS: Compared to their non-minoritized peers, REM respondents expressed less satisfaction with their education and lower confidence in their preparedness for entry-level practice. REM respondents observed more faculty professionalism disconnects and demonstrated less agreement that their program had fostered their overall psychological well-being. REM respondents experienced higher rates of mistreatment than their peers and reported higher rates of exhaustion and disengagement, the 2 axes of academic burnout. Black/African American and Hispanic/Latino/a/x (Hispanic, Latino, Latina, and/or Latinx) respondents incurred significantly more educational debt than Asian and White respondents. REM respondents reported greater empathy and greater interest in working in underserved communities. CONCLUSION: REM respondents perceived the physical therapist learning environment more negatively than their non-minoritized peers but expressed strong interest in serving people from underserved communities. These national benchmarks offer academic institutions the opportunity to self-assess their own environment and to work to improve the quality of the educational experience for all learners. IMPACT: In a nationwide benchmarking study, learners from minoritized race and ethnicity backgrounds reported more negative experiences and outcomes during physical therapist education than their non-minoritized peers. These same learners demonstrated high empathy and interest in serving people from underserved (under-resourced) communities. Learning environments that permit all individuals to thrive may be an essential avenue to improve the health of a rapidly diversifying society.

Tolerance for Ambiguity: Correlations With Medical and Physical Therapy Student Traits and Experiences Within the Learning Environment.

PURPOSE: Health care professions trainees and clinicians who perceive ambiguous situations as sources of threat (low tolerance for ambiguity [TFA]) experience greater risk for mental health disorders and professional burnout. Physical therapists likely encounter substantial ambiguity because of the biopsychosocial nature of their main therapeutic strategies. The purpose of this study was to identify student traits and experiences within the learning environment that differentiate students with high and low TFA for medicine and physical therapy (PT), and to identify areas of interprofessional overlap and distinction. METHOD: Graduation Questionnaire survey data from graduating PT (n = 2,727) and medical students (n = 33,159) from the 2019-2020 and 2020-2021 academic years were sorted according to student TFA score, and respondents in the highest and lowest TFA quartiles were retained for analysis. Difference-in-differences analysis was used to reduce the number of potential explanatory factors to a parimonious subset that was put into linear regression models. Inferential statistics were applied to all significant factors identified from the linear regression models. RESULTS: For both professions, higher TFA was generally associated with more positive ratings of the learning environment (student-faculty interactions, faculty professionalism, satisfaction with career choice), lower experiences of exhaustion and disengagement (the 2 axes of academic burnout), and higher scores for the empathy domain of perspective taking. Uniquely for medical students, low TFA was associated with lower empathy scores and a lower degree of interest in working with underserved individuals. CONCLUSIONS: Findings suggest that for both professions, high TFA corresponded with better ratings of the educational experience and with traits that are advantageous for patient-centered practice and occupational resilience. Interventions to cultivate TFA among health care trainees may be an important way to meet the growing demand for humanistic health care professionals who are prepared to meet society's complex needs.

Low-frequency electrically induced exercise after spinal cord injury: Physiologic challenge to skeletal muscle and feasibility for long-term use.

CONTEXT: Skeletal muscle has traditionally been considered a "force generator": necessary for purposes of locomotion, but expendable for non-ambulators who use wheelchairs, such as people with a spinal cord injury (SCI). Active skeletal muscle plays an indispensable role in regulating systemic metabolic functions, even in people with paralysis, but because of severe osteoporosis, high tetanic muscle forces induced with high frequency electrical stimulation may be risky for some individuals. The purpose of this study was to compare the physiologic muscle properties incurred by two low force/low frequency repetitive stimulation protocols (1 and 3 Hz); and, to assess the acceptability of each protocol among people with SCI. METHODS: Ten individuals with chronic SCI (12.9 years) and 11 individuals without SCI (NonSCI) participated in the study. Participants received either 1 or 3 Hz stimulation to the quadriceps muscle on Day 1, then the converse on Day 2. Each session consisted of 1000 stimulus pulses. RESULTS: The initial and maximum forces were similar for the 1 and 3 Hz frequencies. The fatigue index (FI) for SCI and NonSCI groups were lower (P < 0.007) for 3 Hz than for 1 Hz (0.34 ± 0.17 versus 0.65 ± 0.16 and 0.72 ± 0.14 versus 0.87 ± 0.07, respectively). CONCLUSION: The 3 Hz stimulation offered the greatest physiological challenge and was perceived as more acceptable for long term use among people with SCI.

Active-resisted stance modulates regional bone mineral density in humans with spinal cord injury.

OBJECTIVE: In people with spinal cord injury (SCI), active-resisted stance using electrical stimulation of the quadriceps delivered a therapeutic stress to the femur (∼150% of body weight) and attenuated bone mineral density (BMD) decline. In standard densitometry protocols, BMD is averaged over the entire bone cross-section. An asymmetric adaptation to mechanical load may be masked by non-responding regions. The purpose of this study was to test a novel method to assess regional BMD of the femur in individuals with SCI. We hypothesize that there will be regional bone-sparing changes as a result of active-resisted stance. DESIGN: Mixed cross-sectional and longitudinal. SETTING: Research laboratory. PARTICIPANTS: Twelve individuals with SCI and twelve non-SCI controls. INTERVENTION: Individuals with SCI experienced active-resisted stance or passive stance for up to 3 years. OUTCOME MEASURES: Peripheral quantitative computed tomography images from were partitioned so that femur anatomic quadrants could be separately analyzed. RESULTS: Over 1.5 years, the slope of BMD decline over time was slower at all quadrants for the active-resisted stance limbs. At >2 years of training, BMD was significantly higher for the active-resisted stance group than for the passive stance group (P = 0.007). BMD was preferentially spared in the posterior quadrants of the femur with active-resisted stance. CONCLUSIONS: A regional measurement technique revealed asymmetric femur BMD changes between passive stance and active-resisted stance. Future studies are now underway to better understand other regional changes in BMD after SCI.

Exercise Prescription Principles among Physicians and Physical Therapists for Patients with Impaired Glucose Control: A Cross-Sectional Study.

Exercise confers a multitude of benefits with limited adverse side effects, making it a powerful "medication" for a plethora of diseases. In people living with uncontrolled glucose levels, exercise can be an effective "medication" to assist in the management of hyperglycemia. We sought to survey healthcare providers (physicians and physical therapists) to determine the current state of exercise recommendation for people with glucose control issues. Healthcare providers were surveyed from six academic medical centers in the Midwest to determine the recommended exercise parameters (type, frequency, duration, intensity, and timing) for patients with glucose control issues. Data from 209 practitioners who completed the survey were used for analysis. Chi-square tests were used to determine differences in exercise recommendations between physical therapists (PTs) and physicians (MD/DOs). PTs and MD/DOs recommended similar exercise parameters. Of all respondents, 78.9% recommended exercise to patients with glucose control issues. Respondents who considered themselves to be active exercisers were more likely to recommend exercise than those who were not exercisers. Only 6.1% of all respondents recommended post-meal exercise. Healthcare providers overwhelmingly recommended exercise for people with glucose control issues, but the "timing" is not congruent with best practice recommendations.

Impaired Glucose Tolerance and Visceral Adipose Tissue Thickness among Lean and Non-Lean People with and without Spinal Cord Injury.

After spinal cord injury (SCI), multiple adaptations occur that influence metabolic health and life quality. Prolonged sitting and inactivity predispose people with SCI to body composition changes, such as increased visceral adipose tissue (VAT) thickness, which is often associated with impaired glucose tolerance. Our goal is to understand whether VAT is an index of leanness, and, secondarily, whether mobility methods influence glucose tolerance for people living with SCI. A total of 15 people with SCI and 20 people without SCI had fasting oral glucose tolerance tests (OGTT) and VAT thickness (leanness) measured during a single session. Glucose was 51% and 67% greater for individuals with SCI relative to those without SCI after 60 and 120 min of an OGTT (p < 0.001). Glucose area under the curve (AUC) was 28%, 34%, and 60% higher for non-lean people with SCI than lean people with SCI and non-lean and lean people without SCI, respectively (p = 0.05, p = 0.009, p < 0.001). VAT was associated with glucose AUC (R2 = 0.23, p = 0.004). Taken together, these findings suggest that leanness, as estimated from VAT, may be an important consideration when developing rehabilitation programs to influence metabolism among people with SCI.

Multifractal Nonlinearity Moderates Feedforward and Feedback Responses to Suprapostural Perturbations.

An adaptive response to unexpected perturbations requires near-term and long-term adjustments over time. We used multifractal analysis to test how nonlinear interactions across timescales might support an adaptive response following an unpredictable perturbation. We reanalyzed torque data from 44 young and 24 older adults who performed a single-leg squat task challenged by an unexpected mechanical perturbation and a secondary visual-cognitive task. We report three findings: (a) multifractal nonlinearity interacted with pre-perturbation torque production and task error to presage greater pre-voluntary feedforward increases and greater voluntary reductions, respectively, in post-perturbation task error; (b) multifractal nonlinearity presaged relatively smaller task error than standard deviations of both pre-perturbation torques and pre-perturbation task error; and (c) increased task demand (e.g., age-related changes in dexterity and dual-task settings) led to multifractal nonlinearity presaging reduced task error. All these results were consistent with our expectations, except that a pre-perturbation knee torque-dependent increase in post-perturbation task error appeared later for older than for younger participants. This correlational multifractal modeling offered theoretical clarity on the possible roles of nonlinear interactions across timescales, moderating both feedforward and feedback processes, and presaging greater stability when the standard deviation is relatively large and task demands are strong. Thus, multifractal nonlinearity usefully describes movement variability even when paired with classical descriptors like the standard deviation. We discuss potential insights from these findings for understanding suprapostural dexterity and developing rehabilitative interventions.