Effects of photobiomodulation therapy on muscle function in individuals with multiple sclerosis.

BACKGROUND: In people with multiple sclerosis (pwMS), muscle fatigue and weakness are common issues that can interfere with daily activities. Photobiomodulation therapy (PBMT), comprising light in a 600-1100 nm bandwidth, is a low-level laser therapy thought to improve muscle performance in non-disease populations, in part, by improving mitochondrial function and thus, might be beneficial in pwMS. Given this potential, we aimed to investigate the effects of PBMT on muscle performance in pwMS, both in the short-term and over an extended period. METHODS: This study consisted of two parts with a randomized double-blind crossover design. In study I, muscle function was assessed in four sessions before and after PBMT in ambulatory pwMS (N = 17, F = 14) as follows: maximal voluntary contraction (MVC) and muscle fatigue of the right tibialis anterior (TA) muscle was compared at baseline and following a two-min submaximal fatiguing contraction. Then, PBMT was administered to the belly of TA muscle at different doses of energy of an active device (40 J, 80 J, 120 J) or placebo. The muscle function assessment was then repeated. OUTCOME VARIABLES: muscle force recovery (%), muscle fatigue (%). Statistical tests included McNemar's exact test, Wilcoxon signed-rank test, and the Friedman test. In study II, a subgroup from study I (N = 12, F = 11) received individualized doses (i.e., best dose-effect observed in study I) of active, or placebo PBMT, which was administered on the TA muscle for two weeks. Muscle function assessments were performed pre- and post-PBMT in four sessions similar to study I. OUTCOME VARIABLES: Baseline strength (N), endurance time (s), and muscle fatigue (%). The Wilcoxon signed-rank test was used for statistical analysis. Values are reported as mean (SD). RESULTS: In study I, participants who received a high dose of PBMT showed significant improvement in force recovery (101.89 % (13.55 %)) compared to the placebo group (96.3 % (18.48 %); p = 0.03). Muscle fatigue did not significantly improve with either active PBMT or placebo. In study II, active PBMT resulted in a significant improvement in muscle strength compared to both the baseline (pre-PBMT = 162.70 N (37.52 N); post-PBMT = 185.56 N (33.95 N); p = 0.01) and the placebo group (active PBMT: mean-change = 22.87 N (23.67 N); placebo: mean-change = -4.12 N (31.95 N); p = 0.02). Endurance time and muscle fatigue did not show significant improvement with either active PBMT or placebo. CONCLUSION: Our findings suggest that an individualized dose of PBMT might improve muscle performance, including force recovery and strength in individuals with mild-moderate MS. Therefore, PBMT might be a novel therapeutic modality, either as a standalone treatment or in combination with other interventions, to improve muscle performance in pwMS.

Innovations in Multiple Sclerosis Care: The Impact of Artificial Intelligence via Machine Learning on Clinical Research and Decision-Making.

Artificial intelligence (AI) and its specialized subcomponent machine learning are becoming increasingly popular analytic techniques. With this growth, clinicians and health care professionals should soon expect to see an increase in diagnostic, therapeutic, and rehabilitative technologies and processes that use elements of AI. The purpose of this review is twofold. First, we provide foundational knowledge that will help health care professionals understand these modern algorithmic techniques and their implementation for classification and clustering tasks. The phrases artificial intelligence and machine learning are defined and distinguished, as are the metrics by which they are assessed and delineated. Subsequently, 7 broad categories of algorithms are discussed, and their uses explained. Second, this review highlights several key studies that exemplify advances in diagnosis, treatment, and rehabilitation for individuals with multiple sclerosis using a variety of data sources-from wearable sensors to questionnaires and serology-and elements of AI. This review will help health care professionals and clinicians better understand AI-dependent diagnostic, therapeutic, and rehabilitative techniques, thereby facilitating a greater quality of care.

Forearm muscle mitochondrial capacity and resting oxygen uptake: Relationship to symptomatic fatigue in persons with multiple sclerosis.

BACKGROUND: Mitochondrial dysfunction has been implicated in the pathogenesis of multiple sclerosis (MS). Whether mitochondrial alterations are a function of ambulatory dysfunction or are of a non-ambulatory systemic nature is unclear. OBJECTIVE: To compare oxidative capacity, and rest muscle oxygen consumption (mVO2) in the upper limb of persons with multiple sclerosis (PwMS) to a control group (CON), whereby an upper limb would be comparatively independent of ambulation or deconditioning. METHODS: Near infra-red spectroscopy was used to measure oxidative capacity of the wrist flexors in PwMS (n = 16) and CON (n = 13). Oxidative capacity was indicated by the time constant (TC) of mVO2 recovery following brief wrist flexion contractions. Measurements included well-being, depression, symptomatic fatigue, disability, handgrip strength, cognition, and functional endurance. Analysis was by T-tests and Pearson correlations with p ≤ 0.05. Data are mean (SD). RESULTS: TC of mVO2 recovery was slower in PwMS (MS = 47(14) sec, CON = 36(11) sec; p = 0.03). No significant correlations were found between oxidative capacity and any other measures. Rest mVO2 was not different between groups, but correlated with symptomatic fatigue (r = 0.694, p = 0.003) and strength (0.585, p = 0.017) in PwMS. CONCLUSION: Oxidative capacity was lower in the wrist flexors of PwMS, possibly indicating a systemic component of the disease. Within PwMS, rest mVO2 was associated with symptomatic fatigue.

Navigator Role for Promoting Adaptive Sports and Recreation Participation in Individuals With Disabilities.

OBJECTIVE: The aims of the study were to gain a better understanding of the resources, barriers, and facilitators of participation in adaptive sport and recreational activities as a means of achieving physical activity recommendations in individuals with disability and to understand preferences for a patient navigator service to help mitigate the barriers. DESIGN: Clinical, academic, and community stakeholders applied a community-engaged research approach to develop online surveys and focus group questions for adults with a disability or parents of a child with a disability to meet study objectives. RESULTS: One hundred ninety-eight adults and 146 parents completed the online surveys. Sixteen adults and 18 parents took part in focus groups. Many participants lacked knowledge of available adaptive sport and recreational resources; other barriers were expense, limited number of trained volunteers, and need for instruction. Conversely, persons were facilitated by community, socialization, and words of encouragement/motivation. Participants strongly preferred a patient navigator to be a person active in adaptive sport and recreational or an informative resource-filled website. CONCLUSIONS: Our findings suggest that physical activity programs including adaptive sport and recreational should be designed to offer people with disabilities opportunities to build social networks and strengthen social support. A patient navigator service could help increase participation in adaptive sport and recreational and physical activity within a community context.

Team triathlon effects on physiological, psychological, and immunological measures in women breast cancer survivors.

PURPOSE: Exercise after breast cancer diagnosis and treatment improves cancer-related outcomes, although the mechanisms involved are not clear. This study evaluated the impact of exercise on body composition, strength, endurance, quality of life (QOL), fatigue, and endocrine and inflammatory biomarkers in breast cancer survivors participating in a highly monitored, clinically supervised, moderate-intensity exercise program. The association of hormonal and inflammatory biomarkers with the observed physiological changes was assessed. METHODS: Female breast cancer survivors (BCS; n = 46) who engaged in a goal-oriented 14-week triathlon exercise training program were compared to an untrained control group of female BCS (n = 16). Psychosocial metrics, QOL, cancer-related fatigue, and exercise self-efficacy were evaluated via pre- and post-exercise intervention questionnaires. Serum estradiol and inflammatory biomarkers (C-reactive protein (CRP), sTNFR1a, estradiol, leptin, and adiponectin) were measured prior to the exercise training program start and after the completion of the goal triathlon. RESULTS: After exercise training, the exercise group had lower BMI and arm circumferences. Greater positive change was noted in the trained group for QOL, fatigue, and self-efficacy questionnaires. Functional endurance improved in the trained but not the control group. Knee and elbow strength were not different between the groups, except that knee flexion at 180 degrees∙sec-1 was higher in trained. The only significantly different biomarker was adiponectin, which decreased in the trained group. CONCLUSIONS: Group triathlon exercise training may be beneficial to BCS by significantly improving their psychosocial measures, functional endurance, and BMI.

Exercise and lifestyle physical activity recommendations for people with multiple sclerosis throughout the disease course.

OBJECTIVES: To provide clinicians who treat multiple sclerosis (MS) patients with evidence-based or expert opinion-based recommendations for promoting exercise and lifestyle physical activity across disability levels. METHODS: The National MS Society ("Society") convened clinical and research experts in the fields of MS, exercise, rehabilitation, and physical activity to (1) reach consensus on optimal exercise and lifestyle physical activity recommendations for individuals with MS at disability levels 0-9.0 on the Expanded Disability Status Scale (EDSS) and (2) identify and address barriers/facilitators for participation. RECOMMENDATIONS: Based on current evidence and expert opinion, the Society makes the following recommendations, endorsed by the Consortium of Multiple Sclerosis Centers:Healthcare providers should endorse and promote the benefits/safety of exercise and lifestyle physical activity for every person with MS.Early evaluation by a physical or occupational therapist or exercise or sport scientist, experienced in MS (hereafter referred to as "specialists"), is recommended to establish an individualized exercise and/or lifestyle physical activity plan.Taking into account comorbidities and symptom fluctuations, healthcare providers should encourage ⩾150 min/week of exercise and/or ⩾150 min/week of lifestyle physical activity.Progress toward these targets should be gradual, based on the person's abilities, preferences, and safety.If disability increases and exercise/physical activity becomes more challenging, referrals to specialists are essential to ensure safe and appropriate prescriptions.When physical mobility is very limited, exercise should be facilitated by a trained assistant.

Promoting Team-Based Exercise Among African American Breast Cancer Survivors.

Physical activity benefits the health and well-being of breast cancer survivors (BCS). Yet, many African American survivors do not routinely exercise and have increased risk of poor outcomes. The purpose of this mixed-method study was to identify motivational factors compelling African American BCS to participate in a 14-week team walking program and to intend to continue exercise after the intervention concluded. Focus groups were held with participants ( n = 12) before and after training. Content analysis discovered themes before the intervention: Not wanting to go at it alone, exercise not a life or treatment priority, cancer treatment affected activity, advocates to exercise, and can exercise really help? Four themes postintervention themes included: In the same boat, changed mind-set, improved weight and activity, and overcoming barriers. Physical data verified improvements. Results suggest that a team-based exercise training program may assist in overcoming a sedentary behavior tendency and subsequently improve health among survivors.

Physical activity and annual medical outlay in U.S. colorectal, breast and prostate cancer survivors.

Multiple chronic conditions in cancer survivors are highly prevalent and may increase health care costs for both patients and the health care system. Studies of cancer survivors reveal positive effects of physical activity (PA) on reducing risk of cancer recurrence, other chronic conditions, and secondary cancer. Few nationally representative studies have examined how physical activity levels have affected survivors' annual economic burden in the United States. Leisure-time physical activity data from the National Health Interview Survey was linked to health care expenditure data from the Medical Expenditure Panel Survey data (2008-2012). We calculated per-person annual total medical expenditures for identified colorectal, breast, and prostate cancer survivors. We conducted multivariable analyses controlled for survival years and other sociodemographic variables. Generalized linear models were performed to measure correlation between medical expenditure and PA level using STATA 14. All analyses considered the complex survey design and were conducted in 2017. Of 1015 cancer survivors sampled, 30% (n = 305) adhered to physical activity recommendation, while the other 70% (n = 710) did not. Multivariable-adjusted expenditure in adherence group was $9108.8 (95% CI 7410.9-10,806.7) versus 12,899.1 (95% CI 11,450.2-14,348) in non-adherence group. Stratified analyses revealed cancer survivors who adhered to their PA recommendation saved $4686.1 (1-5 years' survival time) and $2874.5 (11 or more years' survival time) on average for total health care expenditure, respectively. Analyses of the national representative sample revealed that the economic burden of survivors from the three most prevalent cancers is substantial. Increasing survivor's PA to guidelines may reduce U.S. health care expenditure.

Wellness and multiple sclerosis: The National MS Society establishes a Wellness Research Working Group and research priorities.

BACKGROUND: People with multiple sclerosis (MS) have identified "wellness" and associated behaviors as a high priority based on "social media listening" undertaken by the National MS Society (i.e. the Society). OBJECTIVE: The Society recently convened a group that consisted of researchers with experience in MS and wellness-related research, Society staff members, and an individual with MS for developing recommendations regarding a wellness research agenda. METHOD: The members of the group engaged in focal reviews and discussions involving the state of science within three approaches for promoting wellness in MS, namely diet, exercise, and emotional wellness. RESULTS: That process informed a group-mediated activity for developing and prioritizing research goals for wellness in MS. This served as a background for articulating the mission and objectives of the Society's Wellness Research Working Group. CONCLUSION: The primary mission of the Wellness Research Working Group is the provision of scientific evidence supporting the application of lifestyle, behavioral, and psychosocial approaches for promoting optimal health of mind, body, and spirit (i.e. wellness) in people with MS as well as managing the disease and its consequences.

Cardio-protection afforded by ß-blockade is maintained during resistance exercise.

OBJECTIVES: Whether or not the cardio-protective effect of ß-adrenergic blockade is retained during resistance exercise has not been systematically evaluated. Therefore the purpose of this study was to measure selected cardiorespiratory responses to isometric exercise involving hand-gripping, single-leg extension, or double-leg dead-lift, under placebo (control), ß1-selective (atenolol), and non-selective (propranolol) adrenergic blockade conditions. DESIGN: Eleven young male adults were evaluated in a randomized, double-blinded, repeated measures study design and performed all three exercise modalities at 30% of maximal voluntary contraction under placebo, atenolol and propranolol conditions. METHODS: Heart rate, systolic and diastolic blood pressure, rate-pressure product, oxygen uptake, cardiac output, stroke volume and total peripheral resistance were directly measured or calculated at rest and during the third minute of each of the three exercise modes. RESULTS: Irrespective of drug condition, a graded pressor response was observed going from rest to exercise so that rest

Triathlon training for women breast cancer survivors: feasibility and initial efficacy.

ᅟ: Exercise can improve quality of life (QOL) in breast cancer survivors. In contrast to many group or home-based exercise programs, little is known about the effectiveness of goal-oriented recreational activities. PURPOSE: The purpose of this study was to evaluate a clinically overseen team triathlon training program on improving physiological and psychosocial health-related measures in female breast cancer survivors. METHODS: Twenty-three participants (age = 48 (8), BMI = 25 (1), mean (SE)) were recruited from a 14-week sprint triathlon (800-m swim, 20-km bike, 5-km run) team training program for women breast cancer survivors (4 (3) years post-surgery, chemo-, or radiation-therapy). Training included two supervised group and three home-based individual sessions per week. Pre- and post-training outcomes included isokinetic knee extensor strength (60, 180, and 300° s-1), 6-min walk test (6MWT), maximal oxygen uptake (VO2 max), QOL (Functional Assessment of Cancer Therapy -Breast (FACT-B)), and barriers to exercise. Outcomes were also obtained 6 months post except for VO2 max. Significance was set at p < 0.05. RESULTS: Data are mean (SD) from 21 complete data sets. Knee extensor peak torque significantly improved only at 300° s-1 (pre 40.3(8.5) ftlb; post 45.2(8.4); p = 0.001). 6MWT significantly improved (pre 632.8(62.1) m; post 657.4(53.2); p = 0.014) as did VO2 max (pre 31.3(5.8) ml kg-1 min-1; post 35.9(5.8); p < 0.001). FACT-B also improved (pre 114(12); post 122(13); p = 0.004), including the FACT-G total score, social well-being, and breast cancer subscales while barriers to exercise decreased (pre 54(12); post 36(9); p < 0.001). Strength, 6MWT, and barriers to exercise remained improved after 6 months. CONCLUSIONS: Team triathlon training in breast cancer survivors can increase aerobic capacity and improve QOL which may contribute to healthier lifestyles in breast cancer survivors.

Reliability and Validity of Ratings of Perceived Exertion in Persons With Multiple Sclerosis.

OBJECTIVE: To test the reliability and validity of using the Borg rating of perceived exertion (RPE) scale (ratings 6-20) in persons with multiple sclerosis (PwMS). DESIGN: Nonrandomized repeated measures. SETTING: Research laboratory. PARTICIPANTS: Volunteer sample (N=27) comprised of 16 PwMS (10 women) and 11 age-matched persons without multiple sclerosis (MS) (6 women). Clinical measures included symptomatic fatigue, depression, and MS functional capacity. INTERVENTIONS: A submaximal cycling test was performed to estimate maximal capacity. Participants then pedaled for 2 minutes at 50% and 60% of predicted maximal oxygen consumption per unit time (V˙o2), and physiological measures and RPE were obtained (week 1: response protocol). One week later, participants replicated the prescribed V˙o2 using the RPE range from week 1 (week 2: reproduction protocol). V˙o2, heart rate, and respiratory quotient were measured continuously; RPE and workload were measured every minute; and blood lactate and mean arterial pressure were measured after exercise. MAIN OUTCOME MEASURES: RPE, workload, V˙o2, and heart rate from week 1 to week 2. RESULTS: PwMS had greater fatigue (P<.01) and disability (P<.001). Baseline measures were similar between groups and weeks. During exercise, RPE, workload, V˙o2, and heart rate were similar between groups. Both groups had an intraclass correlation coefficient >.86 for RPE, workload, and V˙o2. The intraclass correlation coefficient was comparatively lower for heart rate for both groups (MS group: .72, non-MS group: .83). RPE was highly correlated with V˙o2 (r=.691, P<.001) and workload (r=.700, P<.001) for the MS group. CONCLUSIONS: Results suggest that RPE can be reliably reproduced, is valid, and may be used in exercise prescription in mildly to moderately impaired PwMS during cycling exercise.

Survivors speak: a qualitative analysis of motivational factors influencing breast cancer survivors' participation in a sprint distance triathlon.

AIMS AND OBJECTIVES: To examine motivational factors influencing breast cancer survivors to participate in triathlon training, complete a triathlon and maintain an exercise thereafter. BACKGROUND: Routine exercise has been shown to improve quality of life and reduce recurrence for breast cancer survivors. Yet physical and psychological factors present barriers for initiating and maintaining an exercise routine. Research is limited in exploring factors of exercise motivation from the survivor's perspective. DESIGN: Qualitative design using focus groups and individual follow-up phone interviews to explore motivation for exercise initiation and maintenance. METHODS: One to two weeks after completing a triathlon, 11 breast cancer survivors who trained together participated in one of three focus groups to discuss their experience. Five months post triathlon 6 of the 11 participants were successfully contacted and phone interviews were conducted to explore exercise maintenance. Focus groups and interviews were analysed using content and thematic analysis. RESULTS: Five themes emerged (1) Champion for Exercise, (2) Part of a Team, (3) Everyone Had a Story, (4) Not Really Exercise and (5) What Do We Do Now? Overall, survivors recognised their need for lifestyle change (e.g. moving from a sedentary lifestyle to a more active one). More importantly, they identified the team approach to exercise initiation was crucial in their success in sustaining a behavioural change. CONCLUSIONS: Emphasis needed on developing team exercise training programmes for survivors. Nurses can play a critical role in discussing with survivors, the benefits of exercise initiation and maintenance. RELEVANCE TO CLINICAL PRACTICE: Breast cancer survivors are hesitant to initiate routine exercise. Training with women who share a common lived experience increases the likelihood of success. Nurses are in a position to encourage breast cancer survivors to participate in group exercise programmes as a way to improve quality of life.

Movement strategies for maintaining standing balance during arm tracking in people with multiple sclerosis.

The purpose of this study was to quantify hip and ankle movement strategies during a standing arm tracking task in people with multiple sclerosis (MS). Full-body kinematics and kinetics were assessed with motion analysis cameras and force plates in nine MS and nine age-matched control subjects. While standing, participants used their dominant hand to track a target moving around a large horizontal or vertical figure eight on a screen in front of them. The target moved at constant speed, or linearly increasing speeds, with a frequency between 0.05 Hz and 0.35 Hz. Hip and ankle moments and angles during tracking were calculated from kinematic and kinetic measurements. Ratios of peak-to-peak (PP) hip/ankle moments (kinetics) and angles (kinematics) were calculated to determine the strategies of the hips and ankles used to maintain balance during arm movements. Center of mass (CoM) root mean square (RMS) acceleration was calculated as a measure of overall balance performance. The MS group produced larger PP hip/ankle moments at all speeds compared with the control group (P < 0.05). The CoM RMS acceleration increased with tracking speed for both groups but was not significantly different between groups. Additionally, the ratios of hip to ankle moments were highly correlated with the Berg Balance Scale during horizontal steady-speed tracking in MS. These results suggest that people with MS increase the use of the hip during standing arm tracking compared with age-matched control subjects. This adapted strategy might allow people with MS to achieve balance performance similar to control subjects, possibly increasing the importance of the hip in maintaining balance during voluntary movements.

Relative changes in ankle and hip control during bilateral joint movements in persons with multiple sclerosis.

OBJECTIVE: The purpose of this study was to quantify hip and ankle impairments contributing to movement dysfunction in multiple sclerosis (MS). METHODS: Volitional phasing of bilateral hip and ankle torques was assessed using a load-cell-instrumented servomotor drive system in ten participants with MS and 10 age-matched healthy participants. The hips and ankles were separately bilaterally oscillated 180° out of phase (40° range of motion) at a frequency of 0.75 Hz while the other joints were held stationary. Participants were instructed to assist in the same direction as the robot-imposed movement. The hip and ankle torques were measured and work was calculated for each movement. RESULTS: Total negative work at the ankle was significantly different between groups (p=0.040). The participants with MS produced larger negative work during hip flexion (p=0.042) and ankle flexion (p=0.037). Negative work at the hip was significantly correlated with the Berg Balance Scores and Timed 25 Feet Walk Test, and trends demonstrated increasing negative work with increasing clinical impairment in MS. CONCLUSIONS: These results suggest an increased importance of the hip in functional balance and gait in MS. SIGNIFICANCE: Rehabilitation strategies targeting ankle recovery or compensation using the hip might improve movement function in MS.

Muscle endurance, cancer-related fatigue, and radiotherapy in prostate cancer survivors.

INTRODUCTION: In this study we investigated muscle and cancer-related fatigue (CRF) in prostate cancer survivors (CS) undergoing radiotherapy (RT). METHODS: In 13 CS and 12 controls, CRF was assessed by the Piper Fatigue Scale (PFS), Epworth Sleepiness Scale--Depression subscale (CES-D), physical activity (accelerometer), and hemoglobin levels (Hb). Muscle measures included strength, activation, contractile properties, and endurance during intermittent dorsiflexion. Testing occurred before and after 6 weeks of RT in CS. RESULTS: After RT, the PFS score increased from initial levels in CS only without changes in sleepiness, depression, or physical activity. Hb decreased in CS only [mean (SD): pre, 15 (1.1); post, 14.5 (1.1) g/dl; P = 0.04]. Endurance decreased in CS [mean (SD): pre, 519 (340) s; post, 388 (203) s; P = 0.04] and increased in controls [mean (SD: pre, 616 (387) s; post, 753 (553) s; P = 0.03]. Only endurance was associated with PFS in CS (r = -0.55, P = 0.05). DISCUSSION: Muscle endurance is impaired after RT and may contribute to CRF in CS.

Ratings of perceived exertion during aerobic exercise in multiple sclerosis.

OBJECTIVE: To compare ratings of perceived exertion (RPEs) during aerobic exercise in people with multiple sclerosis (MS) and control participants. DESIGN: Prospective experimental study. SETTING: An exercise testing laboratory. PARTICIPANTS: Sedentary adults (n=12) with mild MS (Expanded Disability Status Scale score < or = 3) aged 30 to 45 years and sedentary age-matched and sex-matched controls (n=12). INTERVENTIONS: All participants underwent a graded aerobic exercise test on a cycle ergometer with breath-by-breath gas measurements and continuous heart rate monitoring. MAIN OUTCOME MEASURES: After completing the Modified Fatigue Impact Scale, participants rated their effort sense every 30 seconds during exercise using the modified Borg 10-point scale. RESULTS: The 2 study groups showed similar baseline characteristics except for higher fatigue scores in the MS group. There were no significant differences for any fitness measure, including oxygen cost slope (in VO(2) x min(-1) x W(-1)), VO(2), or work rate during exercise. Neither heart rate nor RPE--measured at 25%, 50%, 75%, and 100% of VO(2)peak--differed between groups. CONCLUSIONS: Despite greater reported fatigue levels, participants with MS showed similar RPE and physiologic responses to submaximal and maximal exercise compared with controls. In MS, the Borg 10-point scale may help improve evidence-based exercise prescriptions, which otherwise may be limited by fatigue, motor impairment, heat sensitivity, or autonomic dysfunction.

Time to task failure and muscle activation vary with load type for a submaximal fatiguing contraction with the lower leg.

The purpose was to compare the time to failure and muscle activation patterns for a sustained isometric submaximal contraction with the dorsiflexor muscles when the foot was restrained to a force transducer (force task) compared with supporting an equivalent inertial load and unrestrained (position task). Fifteen men and women (mean+/-SD; 21.1+/-1.4 yr) performed the force and position tasks at 20% maximal voluntary contraction force until task failure. Maximal voluntary contraction force performed before the force and position tasks was similar (333+/-71 vs. 334+/-65 N), but the time to task failure was briefer for the position task (10.0+/-6.2 vs. 21.3+/-17.8 min, P<0.05). The rate of increase in agonist root-mean-square electromyogram (EMG), EMG bursting activity, rating of perceived exertion, fluctuations in motor output, mean arterial pressure, and heart rate during the fatiguing contraction was greater for the position task. EMG activity of the vastus lateralis (lower leg stabilizer) and medial gastrocnemius (antagonist) increased more rapidly during the position task, but coactivation ratios (agonist vs. antagonist) were similar during the two tasks. Thus the difference in time to failure for the two tasks with the dorsiflexor muscles involved a greater level of neural activity and rate of motor unit recruitment during the position task, but did not involve a difference in coactivation. These findings have implications for rehabilitation and ergonomics in minimizing fatigue during prolonged activation of the dorsiflexor muscles.

Leg sympathetic response to noxious skin stimuli is similar in high and low level human spinal cord injury.

OBJECTIVE: To determine if sympathetically mediated vasoconstriction in the lower extremities is injury level dependent. Although sympathetic responses have been measured in the limbs of people with high and low level SCI using blood flow measurements, including Doppler ultrasound and venous plethysmography, a direct comparison between injury levels has not been made. METHODS: Volunteers with chronic SCI were grouped according to injury level. Above T6: high level (HL, n=7), and T6 and below: low level (LL, n=6). All subjects had complete motor and sensory loss. Leg arterial flows were recorded by venous occlusion plethysmography, and continuous heart rate and mean arterial pressure (MAP) were measured. The conditioning stimulus consisted of transcutaneous stimulation to the arch of the contralateral foot. RESULTS: HL and LL subjects demonstrated a significant decrease in arterial conductance during stimulation with no significant difference found between groups. As expected, only group HL demonstrated a significant increase in MAP. CONCLUSIONS: These results support our hypothesis that local (leg) sympathetic responses are similar for both high and low level SCI. SIGNIFICANCE: While low level SCI does not typically present with autonomic dysreflexia, bouts of increased reflex sympathetic activity could have ramifications for metabolism as well as renal and motor system function.