Blood redistribution during exercise in subjects with spinal cord injury and controls

Effect of spinal cord injury on the skin temperature of different regions of interest during a graded exercise test in a moderate temperature environment

The gradient between core and skin temperature is a relevant factor in heat exchange between the human body and the environment, but people with spinal cord injury (SCI), due to their autonomic dysfunction, have impaired mechanisms that condition skin temperature response. This study aimed to determine how SCI affects skin temperature response in different ROIs during a graded exercise test in a moderate temperature environment. 32 participants were included in the study [SCI (N = 16); Non-SCI (N = 16)]. A graded exercise test was conducted on an arm crank ergometer, with a staged duration of 3 min separated by 1 min of rest. Skin temperature was measured using infrared thermography at rest, after each interval and during recovery. Individuals with SCI exhibited lower skin temperature in the anterior leg during exercise than Non-SCI (p < 0.001). During recovery, SCI athletes experienced a lower skin temperature restoration in the anterior arm, posterior arm and anterior leg (p < 0.05). The anterior leg is an interesting region to measure during exercise in people with SCI for assessing the physiological effect of the injury, probably for the autonomic dysfunction in skin temperature regulation, but the effect observed during recovery in the arms suggests the presence of different mechanisms involved in skin temperature regulation.

Cardiac biomarker responses following high-intensity interval and continuous exercise: the influence of ACE-I/D gene polymorphism and training status in men

This study aimed to investigate the relationship between pre- and postexercise cardiac biomarker release according to athletic status (trained vs. untrained) and to establish whether the I/D polymorphism in the angiotensin-converting enzyme (ACE) gene had an influence on cardiac biomarkers release with specific regard on the influence of the training state. We determined cardiac troponin I (cTnI) and N-terminal pro-brain natriuretic peptide (NT-proBNP) in 29 trained and 27 untrained male soccer players before and after moderate-intensity continuous exercise (MICE) and high-intensity interval exercise (HIIE) running tests. Trained soccer players had higher pre (trained: 0.014 ± 0.007 ng/mL; untrained: 0.010 ± 0.005 ng/mL) and post HIIE (trained: 0.031 ± 0.008 ng/mL; untrained: 0.0179 ± 0.007) and MICE (trained: 0.030 ± 0.007 ng/mL; untrained: 0.018 ± 0.007) cTnI values than untrained subjects, but the change with exercise (ΔcTnI) was similar between groups. There was no significant difference in baseline and postexercise NT-proBNP between groups. NT-proBNP levels were elevated after both HIIE and MICE. Considering three ACE genotypes, the mean pre exercise cTnI values of the trained group (DD: 0.015 ± 0.008 ng/mL, ID: 0.015 ± 0.007 ng/mL, and II: 0.014 ± 0.008 ng/mL) and their untrained counterparts (DD: 0.010 ± 0.004 ng/mL, ID: 0.011 ± 0.004 ng/mL, and II: 0.010 ± 0.006 ng/mL) did not show any significant difference. To sum up, noticeable difference in baseline cTnI was observed, which was related to athletic status but not ACE genotypes. Neither athletic status nor ACE genotypes seemed to affect the changes in cardiac biomarkers in response to HIIE and MICE, indicating that the ACE gene does not play a significant role in the release of exercise-induced cardiac biomarkers indicative of cardiac damage in Iranian soccer players.NEW & NOTEWORTHY Our study investigated the impact of athletic status and angiotensin-converting enzyme (ACE) gene I/D polymorphism on cardiac biomarkers in soccer players. Trained players showed higher baseline cardiac troponin I (cTnI) levels, whereas postexercise ΔcTnI remained consistent across groups. N-terminal pro-brain natriuretic peptide increased after exercise in both groups, staying within normal limits. ACE genotypes did not significantly affect pre-exercise cTnI. Overall, athletic status influences baseline cTnI, but neither it nor ACE genotypes significantly impact exercise-induced cardiac biomarker responses in this population.

Accidental boosting in an individual with tetraplegia - considerations for the interpretation of cardiopulmonary exercise testing

CONTEXT

Autonomic dysreflexia (AD), characterized by a transient increase in systolic blood pressure (BP), is experienced by individuals with spinal cord injury (SCI) and can be purposefully induced ('boosting') to counteract autonomic dysfunction that impairs cardiovascular responses to exercise. Herein, we demonstrate the impact of unintentional boosting observed during cardiopulmonary exercise testing (CPET) in an inactive male with SCI (C5, motor-complete).

FINDINGS

On two separate occasions the individual performed a standard arm-crank CPET (1-min stages, 7W increase in resistance) following by a longer CPET (4-min stages, 12W increase in resistance), both to volitional exhaustion. The second CPET was performed to confirm the accuracy of exercise intensity prescription and verify peak exercise parameters. Immediately following the second CPET on the initial visit, the individual reported symptoms of AD, verified as a 58mmHg increase in systolic BP from baseline. Relative to the first CPET, performed only 35 min earlier, there were pronounced differences in peak exercise responses. In comparison to the longer CPET performed on the second visit without a concomitant episode of AD (thereby controlling for the type of CPET protocol administered), peak exercise outcomes were considerably elevated: power output (Δ19W), oxygen uptake (Δ3.61 ml·kg·^-1min^-1), ventilation (Δ11.4 L ·min^-1) and heart rate (Δ9 b·min^-1).

CONCLUSION/CLINICAL RELEVANCE

This case raises important considerations around the nuances of CPET in this population. In individuals susceptible to BP instability, the physiologically boosted state may explain a significant proportion of the variance in peak aerobic capacity and should be closely monitored before and after clinical CPET.

Influence of respiratory loading on left-ventricular function in cervical spinal cord injury

KEY POINTS

Cervical spinal cord injury (C-SCI) alters both the cardiac and respiratory systems, however little is known as to how these systems interact following injury. Here, we manipulated inspiratory or expiratory intrathoracic pressure (ITP) to mechanistically test the role of the respiratory pump on circulatory function in highly-trained individuals with C-SCI and an able-bodied reference group. In individuals with C-SCI, greater ITP during expiratory loading caused dynamic hyperinflation that was associated with impaired left-ventricular filling. More negative ITP during inspiratory loading did not significantly alter left-ventricular volumes in either group. Interventions that prevent dynamic hyperinflation and/or enhance the ability to generate expiratory pressures may help preserve left-ventricular filling in individuals with C-SCI.

ABSTRACT

Cervical spinal cord injury (C-SCI) negatively impacts cardiac and respiratory function. As the heart and lungs are linked via the pulmonary circuit these systems are interdependent. Here, we utilized inspiratory and expiratory loading to assess whether augmenting the respiratory pump improves left-ventricular (LV) filling and output in individuals with motor-complete C-SCI. We hypothesized LV end-diastolic volume (LVEDV) would increase and decrease with inspiratory and expiratory loading, respectively. Participants (C-SCI: 7M/1F, 35±7 years; able-bodied: 7M/1F, 32±6 years) were assessed under five conditions during 45° head-up tilt; unloaded, inspiratory loading with -10 and -20cmH₂ O esophageal pressure (Pes) on inspiration, and expiratory loading with +10 and +20cmH₂ O Pes on expiration. An esophageal balloon catheter monitored Pes and LV structure and function were assessed by echocardiography. In C-SCI only, (1) +20cmH₂ O reduced LVEDV vs. unloaded (81±15 vs. 88±11 mL, p = 0.006); (2) heart rate was higher during +20cmH₂ O compared to unloaded (p = 0.001) and +10cmH₂ O (p = 0.002); (3) cardiac output was higher during +20cmH₂ O than unloaded (p = 0.002); and (4) end-expiratory lung volume was higher during +20cmH₂ O vs. unloaded (63±10 vs. 55±13% total lung capacity, p = 0.003) but was unaffected by inspiratory loading. In both groups, -10 and -20cmH₂ O had no significant effect on LVEDV. These findings suggest greater expiratory positive pressure acutely impairs LV filling in C-SCI, potentially via impaired venous return, mediastinal constraint and/or direct ventricular interaction subsequent to dynamic hyperinflation. Inspiratory loading did not significantly improve LV function in C-SCI and neither inspiratory nor expiratory loading affected cardiac function or lung volumes in able-bodied participants. Abstract figure legend Background: Cervical spinal cord injury (C-SCI) alters both the cardiac and respiratory systems. However, expiratory function is compromised to a greater extent than inspiratory function. Experimental set up: To examine how the cardiac and respiratory systems interact following C-SCI we manipulated inspiratory or expiratory intrathoracic pressure (ITP) to mechanistically test how changes in ITP and lung volumes influence cardiac function in highly-trained individuals with C-SCI and an able-bodied reference group. Participants were assessed under five conditions during 45° head-up tilt; unloaded, two inspiratory loading, and two expiratory loading conditions.

KEY FINDINGS

Following C-SCI, greater ITP during expiratory loading increased lung volumes and was associated with impaired left-ventricular filling. Interventions that prevent increases in lung volumes and/or enhance the ability to generate expiratory pressures may help preserve left-ventricular filling in individuals with C-SCI. A portion of this figure was created with biorender.com This article is protected by copyright. All rights reserved.

Preparing for snow-sport events at the Paralympic Games in Beijing in 2022: recommendations and remaining questions

During the 2022 Winter Paralympic Games in Beijing, the Para snow-sport events will be held at high altitudes and in possibly cold conditions while also requiring adjustment to several time zones. Furthermore, the ongoing COVID-19 pandemic may lead to suboptimal preparations. Another concern is the high rate of injuries that have been reported in the Para alpine and snowboard events. In addition to these challenges, Para athletes various impairments may affect both sports-specific demands and athlete health. However, the group of Para snow-sport athletes is an understudied population. Accordingly, this perspective paper summarises current knowledge to consider when preparing for the Paralympic Games in Beijing and point out important unanswered questions. We here focus specifically on how sport-specific demands and impairment-related considerations are influenced by altitude acclimatisation, cold conditions, travel fatigue and jetlag, complications due to the COVID-19 pandemic, and injury prevention and sports safety considerations. As Para athletes with spinal cord injury, limb deficiency, cerebral palsy and visual impairment account for the majority of the Para snow-sport athletes, the focus is mainly on these impairment groups. In brief, we highlight the extra caution required to ensure athlete health, performance and sports safety among Para athletes participating in the snow-sport events in the 2022 Beijing Paralympic Games. Although there is an urgent need for more high-quality research focusing on Para winter athletes, we hope these non-consensus recommendations will help prepare for the 2022 Beijing Paralympic Winter Games.

High altitude exposures and intestinal barrier dysfunction

Gastrointestinal complaints are often reported during ascents to high altitude (> 2500 m), though their etiology is not known. One potential explanation is injury to the intestinal barrier which has been implicated in the pathophysiology of several diseases. High altitude exposures can reduce splanchnic perfusion and blood oxygen levels causing hypoxic and oxidative stress. These stressors might injure the intestinal barrier leading to consequences such as bacterial translocation and local/systemic inflammatory responses. The purpose of this mini review is to 1) discuss the impact of high-altitude exposures on intestinal barrier dysfunction, and 2) present medications and dietary supplements which may have relevant impacts on the intestinal barrier during high-altitude exposures. There is a small but growing body of evidence which shows that acute exposures to high altitudes can damage the intestinal barrier. Initial data also suggests that prolonged hypoxic exposures can compromise the intestinal barrier through alterations in immunological function, microbiota, or mucosal layers. Exertion may worsen high-altitude related intestinal injury via additional reductions in splanchnic circulation and greater hypoxemia. Collectively these responses can result in increased intestinal permeability and bacterial translocation causing local and systemic inflammation. More research is needed to determine the impact of various medications and dietary supplements on the intestinal barrier during high-altitude exposures.

Effects of arm cranking exercise on muscle oxygenation between active and inactive muscles in people with spinal cord injury

Objective: We investigated the effects of the incremental arm-cranking exercise (ACE) on tissue oxygen saturation (StO₂) between active and inactive muscles, and the relationship between peak oxygen uptake (VO_2peak) and changes in the StO₂ in inactive muscles.Design: Observational study.Setting: Community-based supervised intervention.Participants: The participants were individuals with motor and sensory complete spinal cord injury (complete SCI; n = 8) and motor complete but sensory incomplete SCI (incomplete SCI; n = 8), and able-bodied (AB) individuals (n = 8) matched for age, height, and body mass index.Intervention: The ACE was performed at a rate increasing by 10 watts min^-1 until exhaustion.Outcome Measures: VO_2peak, heart rate (HR), and StO₂.Results: While VO_2peak was similar among the groups, peak HR was significantly higher in both SCI groups than in the AB (P < 0.05). In active muscles (biceps brachii), no differences in the StO₂ were observed among the groups (P > 0.05). In inactive muscles (vastus lateralis), the StO₂ in the AB and the incomplete SCI began to decrease at approximately 40% of the peak work rate; however, they remained unchanged in the complete SCI. The reductions in StO₂ in the AB were significantly greater than in the incomplete SCI.Conclusions: These results suggest that sympathetic vasoconstriction occurred in the incomplete SCI and AB, although it did not occur in the complete SCI, probably due to a reduction in sympathetic nerve activity. Sympathetic vasoconstriction in inactive muscles may not contribute to an individual's VO_2peak regardless of their group.

Experimental high thoracic spinal cord injury impairs the cardiac and cerebrovascular response to orthostatic challenge in rats

Spinal cord injury (SCI) impairs the cardiovascular responses to postural challenge, leading to the development of orthostatic hypotension (OH). Here, we apply lower body negative pressure (LBNP) to rodents with high-level SCI to demonstrate the usefulness of LBNP as a model for experimental OH studies, and to explore the effect of simulated OH on cardiovascular and cerebrovascular function following SCI. Male Wistar rats (n = 34) were subjected to a sham or T3-SCI surgery and survived into the chronic period postinjury (i.e., 8 wk). Cardiac function was tracked via ultrasound pre- to post-SCI to demonstrate the clinical utility of our model. At study termination, we conducted left-ventricular (LV) catheterization and insonated the middle cerebral artery to investigate the hemodynamic, cardiac, and cerebrovascular response to a mild dose of LBNP that is sufficient to mimic clinically defined OH in rats with T3-SCI but not sham animals. In response to mimicked OH, there was a greater decline in stroke volume, cardiac output, maximal LV pressure, and blood pressure in SCI compared with sham (P < 0.034), whereas heart rate was increased in sham but decreased in SCI (P < 0.029). SCI animals also had an exaggerated reduction in peak, minimum and mean middle cerebral artery flow, for a given change in blood pressure, in response to LBNP (P < 0.033), implying impaired dynamic cerebral autoregulation. Using a preclinical SCI model of OH, we demonstrate that complete high thoracic SCI impairs the cardiac response to OH and disrupts dynamic cerebral autoregulation.NEW & NOTEWORTHY This is the first use of LBNP to interrogate the cardiac and cerebrovascular responses to simulated OH in a preclinical study of SCI. Here, we demonstrate the utility of our simulated OH model and use it to demonstrate that SCI impairs the cardiac response to simulated OH and disrupts dynamic cerebrovascular autoregulation.

The impact of body position and exercise on the measurement of liver Young's modulus by real-time shear wave elastography

BACKGROUND

In the past ten years, liver biopsies have been used as a method to accurately diagnose the stage of fibrosis.

OBJECTIVE

This study aimed to evaluate whether body position and exercise affect the measurement of liver Young's modulus of healthy volunteers by real-time shear wave elastography (RT-SWE).

METHODS

RT-SWE was used to measure liver Young's modulus in the supine and left lateral positions of 70 healthy volunteers at rest and measure the liver Young's modulus in the lying position before exercise, and at zero, five, and ten minutes of rest after exercise.

RESULTS

The liver Young's modulus in the left lateral position was significantly higher than in the supine position (P< 0.05), and the measured value in the supine position was more stable than the left lateral position. The liver Young's modulus measured at zero minutes after exercise was significantly higher than that measured before exercise (P< 0.05). The liver Young's modulus measured at five minutes after exercise was significantly higher than that measured at zero minutes after exercise (P<0.05) and was not statistically different from the measured value before exercise (P> 0.05). The liver Young's modulus measured at ten minutes after exercise was significantly higher from that measured at zero minutes after exercise (P< 0.05) and was not statistically different from the measured value at five minutes after exercise (P> 0.05).

CONCLUSION

Body position and exercise have a significant impact on the measurement of liver Young's modulus. It is recommended that the examinees take a supine position during the measurement, and measurement should be conducted at least ten minutes after exercise.

Exercise Improves Cardiorespiratory Fitness, but Not Arterial Health, after Spinal Cord Injury: The CHOICES Trial

Arterial stiffness, as measured by carotid-femoral pulse wave velocity (cfPWV), is elevated after spinal cord injury (SCI). In the uninjured population, exercise training has been shown to reduce arterial stiffness. In a randomized, multi-center clinical trial, we evaluated the impact of two exercise interventions on cardiovascular disease risk factors in persons with chronic SCI. A total of 46 adults with motor-complete SCI with neurological levels of injury between the fourth cervical and sixth thoracic spinal cord segments (C4-T6) were randomly assigned to either body-weight-supported treadmill training (BWSTT) or arm-cycle ergometer training (ACET). Participants trained 3 days per week for 24 weeks. Exercise session duration progressed gradually to reach 30 and 60 min for ACET and BWSTT, respectively. The primary outcome was arterial stiffness, assessed by cfPWV, and was measured at baseline, 12 weeks of training, and at 24 weeks. Secondary outcomes included cardiorespiratory fitness (CRF) and cardiometabolic health measures and were measured before and after completion of training. Fourteen participants per intervention arm completed the exercise intervention. Our results show no effect of either exercise intervention on arterial stiffness (p = 0.07) and cardiometabolic health measures (p > 0.36). However, peak oxygen uptake increased with ACET compared with BWSTT (p = 0.04). The findings of this trial demonstrate that although 24 weeks of upper-body exercise improved CRF in persons with motor-complete SCI ≥T6, neither intervention resulted in improvements in arterial stiffness or cardiometabolic health measures. ClinicalTrials.gov identifier: NCT01718977.

Assessment of Exercise Stroke Volume and Its Prediction From Oxygen Pulse in Paralympic Athletes With Locomotor Impairments: Cardiac Long-Term Adaptations Are Possible

The determinants of cardiac output (CO) during exercise, i.e., stroke volume (SV) and heart rate (HR), could differ in Paralympic athletes (PAthl) with spinal cord injury (SCI) with respect to PAthl with locomotor impairments caused by different health conditions (HCs). The purposes of the present study were the comparisons of two groups of PAthl, one with SCI and the other with either amputation (AMP) or post poliomyelitis syndrome (PM), assessing the (1) peak cardiorespiratory responses and determinants (SV and HR) of CO during maximal and submaximal arm cranking exercise (ACE), respectively; (2) correlations between peak oxygen uptake (VO_2peak) and the highest SV obtained during submaximal exercise; and (3) correlations between oxygen pulse (O₂ pulse, ratio between VO₂ and HR) and both SV and O₂ arterio-venous difference [(a-v)O₂diff]. Each athlete (19 PAthl with SCI, 9 with AMP, and 5 with PM) completed a continuous incremental cardiopulmonary ACE test to volitional fatigue to assess peak responses. In a different session, CO was indirectly measured through carbon dioxide (CO₂) rebreathing method at sub-maximal exercise intensities approximating 30, 50, and 70% of the VO_2peak. There were no significant differences between the PAthl groups in age, anthropometry, and VO_2peak. However, peak HR was significantly lower, and peak O₂ pulse was significantly higher in PAthl with AMP/PM compared to those with SCI. During sub-maximal exercise, PAthl with AMP/PM displayed significantly higher SV values (154.8 ± 17.60 ml) than PAthl with SCI (117.1 ± 24.66 ml). SV correlated significantly with VO_2peak in both PAthl with SCI (R ² = 0.796) and AMP/PM (R ² = 0.824). O₂ pulse correlated significantly with SV in both PAthl with SCI (R ² = 0.888) and AMP/PM (R ² = 0.932) and in the overall sample (R ² = 0.896). No significant correlations were observed between O₂ pulse and (a-v)O₂diff. It was concluded that in PAthl with different HCs: (1) significant differences, as a consequence of the different HC, exist in the determinants of CO at maximal and submaximal ACE; (2) SV is a significant determinant of VO_2peak, suggesting cardiac adaptations possible also in PAthl with SCI; and (3) SV can be predicted from O₂ pulse measurements during submaximal exercise in both groups of PAthl.

Comparison of Different Blood Lactate Threshold Concepts for Constant Load Performance Prediction in Spinal Cord Injured Handcyclists

Background

Endurance capacity is one of the main performance determinants in handcycling. There are two exercise test procedures primarily applied to determine endurance capacity, to verify training adaptations and predict race performance. This study aims to evaluate the agreement of these applied concepts in handcycling.

Methods

In a repeated measures cross-over design, 11 highly trained male spinal cord injured (Th12 to L1) handcyclists (age: 40 ± 9 years, height: 183 ± 8 cm, body mass: 73.2 ± 8.5 kg) performed a graded exercise test (GXT) and a lactate minimum test (LMT) to determine lactate threshold at 4 mmol L^–1 (LT_{4 mmol L}−1) and lactate minimum (LM)_, respectively. The agreement of both lactate thresholds concepts for constant load performance prediction (change of ≤ 1 mmol L^–1 during the last 20 min) was evaluated within constant load tests (CLT; 30 min) at a power output (PO) corresponding to LT_{4 mmol L–1} and LM. Oxygen uptake (V.⁢O2), respiratory exchange ratio (RER), heart rate (HR) and blood lactate (La) were measured during all tests.

Results

Power output at the corresponding thresholds (LT_{4 mmol L}−₁: 149 ± 34 W vs. LM: 137 ± 18 W) revealed no significant difference (p = 0.06). During the CLT at LT_{4 mmol⋅L}−₁ and LM, V.⁢O2, and RPE were not significantly different. However, LA, RER, and HR were significantly higher (p ≤ 0.02) during CLT at LT_{4 mmol L}−¹. Bland–Altman plots indicate a wide range of dispersion for all parameters between both lactate threshold concepts. Evaluations of LT_{4 mmol L}−₁ and LM did not meet the criteria for constant load performance within the CLT for 33 and 17% of the athletes, respectively.

Discussion

Both exercise tests and the corresponding lactate threshold concept revealed appropriate estimates to predict a steady state performance for the majority of participants. However, as PO determination at LT_{4 mmol L}−₁ and LM exceeds the criteria for constant load performance (increase of ≥ 1 mmol L^–1) for 33 and 17% respectively the current results indicate the common criteria for constant load performance (change of ± 1 mmol L^–1) might not be sufficiently precise for elite athletes in handcycling. Consequently, exercise test results of elite athletes should be analyzed individually and verified by means of several CLT.

Exercise-Induced Alterations in Sympathetic-Somatomotor Coupling in Incomplete Spinal Cord Injury

The aim of this study was to understand how high- and low-intensity locomotor training (LT) affects sympathetic-somatomotor (SS) coupling in people with incomplete spinal cord injury (SCI). Proper coupling between sympathetic and somatomotor systems allows controlled regulation of cardiovascular responses to exercise. In people with SCI, altered connectivity between descending pathways and spinal segments impairs sympathetic and somatomotor coordination, which may have deleterious effects during exercise and limit rehabilitation outcomes. We postulated that high-intensity LT, which repeatedly engages SS systems, would alter SS coupling. Thirteen individuals (50 ± 7.2 years) with motor incomplete spinal cord injuries (American Spinal Injury Association Impairment Scale C or D; injury level >T6) participated in a locomotor treadmill training program. Patients were randomized into either a high-intensity (high-LT; 70-85% of maximum predicted heart rate; n = 6) group or a low-intensity (low-LT; 50-65% of maximum predicted heart rate; n = 7) group and completed up to 20 LT training sessions over 4-6 weeks, 3-5 days/week. Before and after taining, we tested SS coupling by eliciting reflexive sympathetic activity through a cold stimulation, noxious stimulation, and a mental math task while we measured tendon reflexes, blood pressure, and heart rate. Participants who completed high- versus low-LT exhibited significant decreases in reflex torques during triggered sympathetic activity (cold: -83 vs. 13%, p < 0.01; pain: -65 vs. 54%, p < 0.05; mental math: -43 vs. 41%; p < 0.05). Mean arterial pressure responses to sympathetic stimuli were slightly higher following high- versus low-LT (cold: 30 vs. -1.5%; pain: 6 vs. -12%; mental math: 5 vs. 7%), although differences were not statistically significant. These results suggest that high-LT may be advantageous to low-LT to improve SS coupling in people with incomplete SCI.

A new conceptual framework for the integrated neural control of locomotor and sympathetic function: implications for exercise after spinal cord injury

All mammals, including humans, are designed to produce sustained locomotor movements. Many higher centres are involved in movement, but ultimately these centres act upon a core "rhythm-generating" network within the brainstem-spinal cord. In addition, endurance-based locomotor exercise requires sympathetic neural support to maintain homeostasis and to provide needed metabolic resources. This review focuses on the roles and integration of these 2 neural systems. Part I reviews the cardiovascular, thermoregulatory, and metabolic functions under spinal sympathetic control as revealed by spinal cord injury at different levels. Part II examines the integration between brainstem-spinal sympathetic pathways and the neural circuitry producing motor rhythms. In particular, the rostroventral medulla (RVM) contains the neural circuitry that (i) integrates heart rate, contractility, and blood flow in response to postural changes; (ii) initiates and maintains cardiovascular adaptations for exercise; (iii) provides direct descending innervation to preganglionic neurons innervating the adrenal glands, white adipose tissue, and tissues responsible for cooling the body; (iv) integrates descending sympathetic drive for energy substrate mobilization (lipolysis); and (v) is the relay for descending locomotor commands arising from higher brain centres. A unifying conceptual framework is presented, in which the RVM serves as the final descending supraspinal "exercise integration centre" linking the descending locomotor command signal with the metabolic and homeostatic support needed to produce prolonged rhythmic activities. The role and rationale for an ascending sympathetic and locomotor drive from the lower to upper limbs within this framework is presented. Examples of new research directions based on this unifying framework are discussed.

Hemodynamic and cardiorespiratory responses to various arm cycling regimens in men with spinal cord injury

Study design

Repeated measures within-subjects crossover study.

Objectives

High intensity interval exercise (HIIE) elicits higher oxygen consumption (VO₂) and heart rate (HR) versus moderate intensity continuous exercise (MICE) in men with spinal cord injury (SCI). No study has compared hemodynamic responses to HIIE versus MICE in SCI. In this study, we determined hemodynamic and cardiorespiratory responses to different bouts of arm cycling in men with SCI.

Setting

Human Performance Laboratory, San Diego, CA.

Methods

Five men (age and injury duration = 42.6 ± 16.1 yr and 9.9 ± 7.6 yr) with SCI participated in the study. VO₂peak and peak power output were initially assessed. Subsequent visits included MICE, HIIE, sprint interval exercise (SIE), and a no-exercise control (CON). Energy expenditure was matched across modes and equal to 100 ± 10 kcal. During the bouts, cardiac output (CO), stroke volume (SV), HR, and VO₂ were measured.

Results

Heart rate, SV, and CO increased in response to all exercise bouts and were higher during exercise versus CON. During HIIE and SIE, heart rate approached 90% of maximum, and stroke volume increased by 40% which was higher (p < 0.05) versus MICE and CON. In addition, exercise led to a two (MICE) to threefold increase in CO (HIIE and SIE) although it was not different from CON. VO₂ during SIE and HIIE was higher (p < 0.05) versus MICE.

Conclusions

Similar to results in non-disabled populations, HIIE and SIE elicit near-maximal values of SV and CO.

Effects of exercise interventions on cardiovascular health in individuals with chronic, motor complete spinal cord injury: protocol for a randomised controlled trial [Cardiovascular Health/Outcomes: Improvements Created by Exercise and education in SCI (CHOICES) Study]

INTRODUCTION

Recent studies demonstrate that cardiovascular diseases and associated complications are the leading cause of morbidity and mortality in individuals with spinal cord injury (SCI). Abnormal arterial stiffness, defined by a carotid-to-femoral pulse wave velocity (cfPWV) ≥10 m/s, is a recognised risk factor for heart disease in individuals with SCI. There is a paucity of studies assessing the efficacy of conventional training modalities on arterial stiffness and other cardiovascular outcomes in this population. Therefore, this study aims to compare the efficacy of arm cycle ergometry training (ACET) and body weight-supported treadmill training (BWSTT) on reducing arterial stiffness in individuals with chronic motor complete, high-level (above the sixth thoracic segment) SCI.

METHODS AND ANALYSIS

This is a multicentre, randomised, controlled, clinical trial. Eligible participants will be randomly assigned (1:1) into either ACET or BWSTT groups. Sixty participants with chronic (>1 year) SCI will be recruited from three sites in Canada (Vancouver, Toronto and Hamilton). Participants in each group will exercise three times per week up to 30 min and 60 min for ACET and BWSTT, respectively, over the period of 6 months. The primary outcome measure will be change in arterial stiffness (cfPWV) from baseline. Secondary outcome measures will include comprehensive assessments of: (1) cardiovascular parameters, (2) autonomic function, (3) body composition, (4) blood haematological and metabolic profiles, (5) cardiorespiratory fitness and (6) quality of life (QOL) and physical activity outcomes. Outcome measures will be assessed at baseline, 3 months, 6 months and 12 months (only QOL and physical activity outcomes). Statistical analyses will apply linear-mixed modelling to determine the training (time), group (ACET vs BWSTT) and interaction (time × group) effects on all outcomes.

ETHICS AND DISSEMINATION

Ethical approval was obtained from all three participating sites. Primary and secondary outcome data will be submitted for publication in peer-reviewed journals and widely disseminated.

TRIAL REGISTRATION NUMBER

NCT01718977; Pre-results.

TRIAL STATUS

Recruitment for this study began on January 2013 and the first participant was randomized on April 2013. Recruitment stopped on October 2018.

Characteristics of cardiovascular responses to an orthostatic challenge in trained spinal cord-injured individuals

Background

We investigated cardiovascular responses to an orthostatic challenge in trained spinal cord-injured (SCI) individuals compared to able-bodied (AB) individuals.

Methods

A total of 23 subjects participated, divided into three groups: seven were trained as spinal cord-injured (Tr-SCI) individuals, seven were able-bodied individuals trained as runners (Tr-AB), and nine were untrained able-bodied individuals (UnTr-AB). We measured the cardiovascular autonomic responses in all three groups during each 5-min head-up tilt (HUT) of 0°, 40°, and 80°. Stroke volume (SV), heart rate (HR), and cardiac output (Qc) as cardiovascular responses were measured by impedance cardiography. Changes in deoxyhemoglobin (∆[HHb]) and total hemoglobin (∆[Hb_tot]) concentrations of the right medial gastrocnemius muscle were measured using near-infrared spectroscopy (NIRS).

Results

As the HUT increased from 0° to 80°, Tr-SCI group showed less change in SV at all HUT levels even if HR increased significantly. Mean arterial pressure (MAP) also did not significantly increase as tilting increased from 0° to 80°. Regarding peripheral vascular responses, the alterations of ∆[Hb_tot] from 0° to 80° were less in Tr-SCI group compared to AB individuals.

Conclusion

There is a specific mechanism whereby blood pressure is maintained during a HUT in Tr-SCI group with the elicitation of peripheral vasoconstriction and the atrophy of the vascular vessels in paraplegic lower limbs, which would be associated with less change in SV in response to an orthostatic challenge.

Effect of Unintentional Boosting on Exercise Performance in a Tetraplegic Athlete

Boosting is the induction of autonomic dysreflexia (AD) to reflexively activate otherwise dormant thoracolumbar sympathetic circuitry to "boost" the capacity of the cardiovascular system and enhance exercise performance. AD is a life-threatening condition unique to individuals with spinal cord injury (SCI) characterized by a sudden increase in sympathetic activity below the level of the SCI. Here we report on the temporal HR response to an episode of unintentional boosting during a validated field-based exercise performance test in an athlete with tetraplegia.An athlete with SCI (C6 motor-complete, sensory-incomplete) completed a 20 ×20 m repeated sprint field test on two consecutive days. During the 13th sprint on day 2, the athlete unintentionally boosted via bladder overdistension. Average HR when boosted (i.e., sprints 14-20) was considerably higher than before boosting (141 ± 4 vs 116 ± 7 bpm) and compared with corresponding sprints on day 1 (141 ± 4 bpm vs 120 ± 1 bpm). Average time to complete 20 m sprints when boosted was also faster than the corresponding sprints on day 1 (6.70 ± 0.05 s vs 6.87 ± 0.05 s).This case report highlights the immediate effect of boosting on HR and field-based exercise performance and supports the suggestion that exercise performance in athletes with SCI is limited by cardiovascular capacity.

Comparison of peak oxygen uptake and exercise efficiency between upper-body poling and arm crank ergometry in trained paraplegic and able-bodied participants

Purpose

To compare peak oxygen uptake (VO_2peak) and exercise efficiency between upper-body poling (UBP) and arm crank ergometry (ACE) in able-bodied (AB) and paraplegic participants (PARA).

Methods

Seven PARA and eleven AB upper-body trained participants performed four 5-min submaximal stages, and an incremental test to exhaustion in UBP and ACE. VO_2peak was the highest 30-s average during the incremental test. Metabolic rate (joule/second = watt) at fixed power outputs of 40, 60, and 80 W was estimated using linear regression analysis on the original power-output-metabolic-rate data and used to compare exercise efficiency between exercise modes and groups.

Results

VO_2peak did not significantly differ between UBP and ACE (p = 0.101), although peak power output was 19% lower in UBP (p < 0.001). Metabolic rate at fixed power outputs was 24% higher in UBP compared to ACE (p < 0.001), i.e., exercise efficiency was lower in UBP. PARA had 24% lower VO_2peak compared to AB (p = 0.010), although there were no significant differences in peak power output between PARA and AB (p = 0.209).

Conclusions

In upper-body-trained PARA and AB participants, VO_2peak did not differ between UBP and ACE, indicating that these two test modes tax the cardiovascular system similarly when the upper body is restricted. As such, the 19% lower peak power output in UBP compared to ACE may be explained by the coinciding lower efficiency.

Electronic supplementary material

The online version of this article (10.1007/s00421-018-3912-1) contains supplementary material, which is available to authorized users.

Autonomic Nervous System in Paralympic Athletes with Spinal Cord Injury

Individuals sustaining a spinal cord injury (SCI) frequently suffer from sensorimotor and autonomic impairment. Damage to the autonomic nervous system results in cardiovascular, respiratory, bladder, bowel, and sexual dysfunctions, as well as temperature dysregulation. These complications not only impede quality of life, but also affect athletic performance of individuals with SCI. This article summarizes existing evidence on how damage to the spinal cord affects the autonomic nervous system and impacts the performance in athletes with SCI. Also discussed are frequently used performance-enhancing strategies, with a special focus on their legal aspect and implication on the athletes' health.

Peak oxygen uptake in Paralympic sitting sports: A systematic literature review, meta- and pooled-data analysis

Background

Peak oxygen uptake (VO_2peak) in Paralympic sitting sports athletes represents their maximal ability to deliver energy aerobically in an upper-body mode, with values being influenced by sex, disability-related physiological limitations, sport-specific demands, training status and how they are tested.

Objectives

To identify VO_2peak values in Paralympic sitting sports, examine between-sports differences and within-sports variations in VO_2peak and determine the influence of sex, age, body-mass, disability and test-mode on VO_2peak.

Design

Systematic literature review and meta-analysis.

Data sources

PubMed, CINAHL, SPORTDiscus^TM and EMBASE were systematically searched in October 2016 using relevant medical subject headings, keywords and a Boolean.

Eligibility criteria

Studies that assessed VO_2peak values in sitting sports athletes with a disability in a laboratory setting were included.

Data synthesis

Data was extracted and pooled in the different sports disciplines, weighted by the Dersimonian and Laird random effects approach. Quality of the included studies was assessed with a modified version of the Downs and Black checklist by two independent reviewers. Meta-regression and pooled-data multiple regression analyses were performed to assess the influence of sex, age, body-mass, disability, test mode and study quality on VO_2peak.

Results

Of 6542 retrieved articles, 57 studies reporting VO_2peak values in 14 different sitting sports were included in this review. VO_2peak values from 771 athletes were used in the data analysis, of which 30% participated in wheelchair basketball, 27% in wheelchair racing, 15% in wheelchair rugby and the remaining 28% in the 11 other disciplines. Fifty-six percent of the athletes had a spinal cord injury and 87% were men. Sports-discipline-averaged VO_2peak values ranged from 2.9 L∙min^-1 and 45.6 mL∙kg^-1∙min^-1 in Nordic sit skiing to 1.4 L∙min^-1 and 17.3 mL∙kg^-1∙min^-1 in shooting and 1.3 L∙min^-1 and 18.9 mL∙kg^-1∙min^-1 in wheelchair rugby. Large within-sports variation was found in sports with few included studies and corresponding low sample sizes. The meta-regression and pooled-data multiple regression analyses showed that being a man, having an amputation, not being tetraplegic, testing in a wheelchair ergometer and treadmill mode, were found to be favorable for high absolute and body-mass normalized VO_2peak values. Furthermore, high body mass was favourable for high absolute VO_2peak values and low body mass for high body-mass normalized VO_2peak values.

Conclusion

The highest VO_2peak values were found in Nordic sit skiing, an endurance sport with continuously high physical efforts, and the lowest values in shooting, a sport with low levels of displacement, and in wheelchair rugby where mainly athletes with tetraplegia compete. However, VO_2peak values need to be interpreted carefully in sports-disciplines with few included studies and large within-sports variation. Future studies should include detailed information on training status, sex, age, test mode, as well as the type and extent of disability in order to more precisely evaluate the effect of these factors on VO_2peak.

Chronic, complete cervical6-7 cord transection: distinct autonomic and cardiac deficits

Spinal cord injury (SCI) resulting in tetraplegia is a devastating, life-changing insult causing paralysis and sensory impairment as well as distinct autonomic dysfunction that triggers compromised cardiovascular, bowel, bladder, and sexual activity. Life becomes a battle for independence as even routine bodily functions and the smallest activity of daily living become major challenges. Accordingly, there is a critical need for a chronic preclinical model of tetraplegia. This report addresses this critical need by comparing, for the first time, resting-, reflex-, and stress-induced cardiovascular, autonomic, and hormonal responses each week for 4 wk in 12 sham-operated intact rats and 12 rats with chronic, complete C_6-7 spinal cord transection. Loss of supraspinal control to all sympathetic preganglionic neurons projecting to the heart and vasculature resulted in a profound bradycardia and hypotension, reduced cardiac sympathetic and parasympathetic tonus, reduced reflex- and stress-induced sympathetic responses, and reduced sympathetic support of blood pressure as well as enhanced reliance on angiotensin to maintain arterial blood pressure. Histological examination of the nucleus ambiguus and stellate ganglia supports the profound and distinct autonomic and cardiac deficits and reliance on angiotensin to maintain cardiovascular stability following chronic, complete cervical_6-7 cord transection. NEW & NOTEWORTHY For the first time, resting-, reflex-, and stress-induced cardiovascular, autonomic, and hormonal responses were studied in rats with chronic, complete C_6-7 cord transection. Loss of supraspinal control of all sympathetic preganglionic neurons reduced cardiac sympathetic and parasympathetic tonus, reflex and stress-induced sympathetic responses, and sympathetic support of blood pressure as well as enhanced reliance on angiotensin to maintain arterial blood pressure. Histological examination supports the distinct deficits associated with cervical cord injury.

Running Out of Options: Rhabdomyolysis Associated with Cannabis Hyperemesis Syndrome

Cannabis hyperemesis syndrome (CHS) is a condition in which some patients with long-term, frequent use of cannabis paradoxically develop recurrent episodes of nausea and vomiting. The pathophysiology underlying this condition is poorly understood, as is the explanation for its common association with patients' discovery that hot-water bathing alleviates symptoms. We describe the case of a 24-year-old male with daily marijuana use and a history of CHS who was found to have rhabdomyolysis induced by a period of 15 h of continuous jogging after he discovered that this activity helped to alleviate his symptoms. To our knowledge, this is the first reported case of exercise-alleviated CHS symptoms, and we propose that this case provides support to the theory of redistribution of enteric blood flow as the mechanism behind the learned hot-water bathing behavior seen so commonly in CHS.

Arm Cycling Combined with Passive Leg Cycling Enhances VO2peak in Persons with Spinal Cord Injury Above the Sixth Thoracic Vertebra

Objective: To test whether passive leg cycling (PLC) during arm cycling ergometry (ACE) affects peak oxygen uptake (VO2peak) differently in individuals with spinal cord injury (SCI) at/above the 6th thoracic vertebra (T6) and below T6. Methods: We conducted a cross-sectional study, analyzed by univariate and multivariate regression models. Between- and within-group differences were examined during (a) ACE only, (b) ACE combined with PLC (ACE-PLC), and (c) ACE combined with functional electrical stimulation cycling (FES hybrid). Fifteen SCI subjects were recruited and grouped according to injury level: at/above T6 (SCI-high, n = 8) or below T6 (SCI-low, n = 7). VO2peak tests during ACE only, ACE-PLC, and FES hybrid were performed in random order on separate days. Results: In the SCI-high group, mean (SD) VO2peak was 19% higher during ACE-PLC than during ACE only [21.0 (3.8) vs 17.7 (5.0) mL·kg-1·min-1; p = .002], while VO2peak during FES hybrid cycling was 16% higher than during ACE-PLC [24.4 (4.1) mL·kg-1·min-1; p = .001]. No significant differences among exercise modalities were found for the SCI-low group. Conclusion: Additional training modalities (eg, PLC) during ACE facilitate exercise in SCI-high individuals, but not to the level of the FES hybrid method. Conversely, additional training modalities may not increase training load in SCI-low individuals.

Ventilation Limits Aerobic Capacity after Functional Electrical Stimulation Row Training in High Spinal Cord Injury

PURPOSE

In the able-bodied, exercise training results in increased ventilatory capacity to meet increased aerobic demands of trained skeletal muscle. However, after spinal cord injury (SCI), peak ventilation can be limited by pulmonary muscle denervation. In fact, peak ventilation may restrict aerobic capacity in direct relation to injury level. Hybrid functional electrical stimulation (FES) exercise training results in increased aerobic capacity and dissociation between aerobic capacity and injury level in those with injuries at T3 and below. However, injuries above T3 have the greatest pulmonary denervation, and ventilatory capacity may restrict the increase in aerobic capacity with hybrid FES training.

METHODS

We assessed relationships among injury level, peak ventilation, and peak aerobic capacity and calculated oxygen uptake efficiency slope during hybrid FES exercise in 12 individuals (1 female) with SCI at level T2 to C4 (injury duration = 0.33-33 yr, age = 20-60 yr), before and after 6 months of FES-row training (FES-RT).

RESULTS

Training increased peak aerobic capacity by 12% (P = 0.02) with only a modest increase in peak ventilation (7 of 12 subjects, P = 0.09). Both before and after training, injury level was directly related to peak ventilation (R = 0.48 and 0.43) and peak aerobic capacity (R = 0.70 and 0.55). Before training, the relationship of peak aerobic capacity to peak ventilation was strong (R = 0.62), however, after training, this relationship became almost completely linearized (R = 0.84). In addition, oxygen uptake efficiency slope increased by 11% (P < 0.05) after FES-RT.

CONCLUSION

Despite the ability to increase exercise capacity via hybrid FES exercise, the inability to increase peak ventilation beyond limits set by SCI level in those with high-level injuries (above T3) appears to restrict aerobic capacity.

Implications of altered autonomic control on sports performance in athletes with spinal cord injury

It is well known that athletes with spinal cord injury (SCI) may experience altered autonomic physiology that impacts their exercise capacity and sports performance. This is particularly relevant given the ever-increasing number of individuals with SCI who are actively engaged in sports at all levels, from community-based adaptive sports to elite Paralympic competitions. As such, the purpose of this article is to review the present literature regarding the implications of altered autonomic control on the safety and performance of athletes with SCI. A particular emphasis will be placed on the autonomic aspects of cardiovascular and thermoregulatory control in the athlete population, as well as the implications of autonomic dysreflexia in enhancing sports performance. Further research is needed to understand the autonomic factors that influence athletes with SCI in order to ensure optimal and safe sports competition. Additionally, this information is crucially relevant to the coaches, sports administrators, and team medical staff who work closely with athletes with SCI.

Cardiac Consequences of Autonomic Dysreflexia in Spinal Cord Injury

Autonomic dysreflexia (AD), which describes episodic hypertension, is highly prevalent in people with spinal cord injury (SCI). In non-SCI, primary hypertension depresses cardiac contractile reserve via β-adrenergic mechanisms. In this study, we investigated whether AD contributes to the impairment in cardiac contractile function that accompanies SCI. We induced SCI in rodents and stratified them into sham, SCI, or SCI plus repetitive induction of AD. At 6-week post-SCI, we assessed cardiac function using in vivo (speckle-tracking echocardiography), ex vivo (working heart), and molecular approaches (Western blot). We also provide unique translational insight by comparing the relationship between the number of daily AD events and cardiac function in 14 individuals with cervical SCI. We found SCI and SCI plus repetitive induction of AD exhibited a reduction in left ventricular dimensions at 6-week post-SCI versus preinjury (P<0.049). Compared with sham, SCI exhibited a reduction in peak radial strain along with a down and rightward shift in the Starling curve (P<0.037), both of which were further depressed in SCI plus repetitive induction of AD (P<0.042). In response to β-adrenergic stimulation, SCI plus repetitive induction of AD exhibited an attenuated increase in contractile indices (P<0.001), despite no differences in β-receptor expression within the left ventricle. Our clinical data confirm our experimental findings by demonstrating significant associations between the number of daily AD events and markers of systolic and diastolic function along with left ventricular mechanics. Here, we provide the first evidence from a translational perspective that AD exerts insidious effects on cardiac function in rodents and humans with SCI.

Cardiovascular control during whole body exercise

It has been considered whether during whole body exercise the increase in cardiac output is large enough to support skeletal muscle blood flow. This review addresses four lines of evidence for a flow limitation to skeletal muscles during whole body exercise. First, even though during exercise the blood flow achieved by the arms is lower than that achieved by the legs (∼160 vs. ∼385 ml·min(-1)·100 g(-1)), the muscle mass that can be perfused with such flow is limited by the capacity to increase cardiac output (42 l/min, highest recorded value). Secondly, activation of the exercise pressor reflex during fatiguing work with one muscle group limits flow to other muscle groups. Another line of evidence comes from evaluation of regional blood flow during exercise where there is a discrepancy between flow to a muscle group when it is working exclusively and when it works together with other muscles. Finally, regulation of peripheral resistance by sympathetic vasoconstriction in active muscles by the arterial baroreflex is critical for blood pressure regulation during exercise. Together, these findings indicate that during whole body exercise muscle blood flow is subordinate to the control of blood pressure.

Differences in Left Ventricular Global Function and Mechanics in Paralympic Athletes with Cervical and Thoracic Spinal Cord Injuries

Following a spinal cord injury, there are changes in resting stroke volume (SV) and its response to exercise. The purpose of the following study was to characterize resting left ventricular structure, function, and mechanics in Paralympic athletes with tetraplegia (TETRA) and paraplegia (PARA) in an attempt to understand whether the alterations in SV are attributable to inherent dysfunction in the left ventricle. This retrospective study compared Paralympic athletes with a traumatic, chronic (>1 year post-injury), motor-complete spinal cord injury (American Spinal Injury Association Impairment Scale A-B). Eight male TETRA wheelchair rugby players (34 ± 5 years, C5-C7) and eight male PARA alpine skiers (35 ± 5 years, T4-L3) were included in the study. Echocardiography was performed in the left lateral decubitus position and indices of left ventricular structure, global diastolic and systolic function, and mechanics were derived from the average across three cardiac cycles. Blood pressure was measured in the supine and seated positions. All results are presented as TETRA vs. PARA. There was no difference in left ventricular dimensions between TETRA and PARA. Additionally, indices of global diastolic function were similar between groups including isovolumetric relaxation time, early (E) and late (A) transmitral filling velocities and their ratio (E/A). While ejection fraction was similar between TETRA and PARA (59 ± 4 % vs. 61 ± 7 %, p = 0.394), there was evidence of reduced global systolic function in TETRA including lower SV (62 ± 9 ml vs. 71 ± 6 ml, p = 0.016) and cardiac output (3.5 ± 0.6 L/min vs. 5.0 ± 0.9 L/min, p = 0.002). Despite this observation, several indices of systolic and diastolic mechanics were maintained in TETRA but attenuted in PARA including circumferential strain at the level of the papillary muscle (−23 ± 4% vs. −15 ± 6%, p = 0.010) and apex (−36 ± 10% vs. −23 ± 5%, p = 0.010) and their corresponding diastolic strain rates (papillary: 1.90 ± 0.63 s⁻¹ vs. 1.20 ± 0.51 s⁻¹, p = 0.028; apex: 3.03 ± 0.71 s⁻¹ vs. 1.99 ± 0.69 s⁻¹, p = 0.009). All blood pressures were lower in TETRA. The absence of an association between reduced global systolic function and mechanical dysfunction in either TETRA or PARA suggests any reductions in SV are likely attributed to impaired loading rather than inherent left ventricular dysfunction.

The role of autonomic function on sport performance in athletes with spinal cord injury

Devastating paralysis, autonomic dysfunction, and abnormal cardiovascular control present significant hemodynamic challenges to individuals with spinal cord injury (SCI), especially during exercise. In general, resting arterial pressure after SCI is lower than with able-bodied individuals and is commonly associated with persistent orthostatic intolerance along with transient episodes of life-threatening hypertension, known as "autonomic dysreflexia." During exercise, the loss of central and reflexive cardiovascular control attenuates maximal heart rate and impairs blood pressure regulation and blood redistribution, which ultimately reduces venous return, stroke volume, and cardiac output. Thermoregulation also is severely compromised in high-lesion SCI, a problem that is compounded when competing in hot and humid conditions. There is some evidence that enhancing venous return via lower body positive pressure or abdominal binding improves exercise performance, as do cooling strategies. Athletes with SCI also have been documented to self-induce autonomic dysreflexia before competition with a view of increasing blood pressure and improving their performance, a technique known as "boosting." For health safety reasons, boosting is officially banned by the International Paralympics Committee. This article addresses the complex issue of how the autonomic nervous system affects sports performance in athletes with SCI, with a specific focus on the potential debilitating effects of deranged cardiovascular control.

Effect of abdominal binding on respiratory mechanics during exercise in athletes with cervical spinal cord injury

We asked whether elastic binding of the abdomen influences respiratory mechanics during wheelchair propulsion in athletes with cervical spinal cord injury (SCI). Eight Paralympic wheelchair rugby players with motor-complete SCI (C5-C7) performed submaximal and maximal incremental exercise tests on a treadmill, both with and without abdominal binding. Measurements included pulmonary function, pressure-derived indices of respiratory mechanics, operating lung volumes, tidal flow-volume data, gas exchange, blood lactate, and symptoms. Residual volume and functional residual capacity were reduced with binding (77 ± 18 and 81 ± 11% of unbound, P < 0.05), vital capacity was increased (114 ± 9%, P < 0.05), whereas total lung capacity was relatively well preserved (99 ± 5%). During exercise, binding introduced a passive increase in transdiaphragmatic pressure, due primarily to an increase in gastric pressure. Active pressures during inspiration were similar across conditions. A sudden, sustained rise in operating lung volumes was evident in the unbound condition, and these volumes were shifted downward with binding. Expiratory flow limitation did not occur in any subject and there was substantial reserve to increase flow and volume in both conditions. V̇o2 was elevated with binding during the final stages of exercise (8-12%, P < 0.05), whereas blood lactate concentration was reduced (16-19%, P < 0.05). V̇o2/heart rate slopes were less steep with binding (62 ± 35 vs. 47 ± 24 ml/beat, P < 0.05). Ventilation, symptoms, and work rates were similar across conditions. The results suggest that abdominal binding shifts tidal breathing to lower lung volumes without influencing flow limitation, symptoms, or exercise tolerance. Changes in respiratory mechanics with binding may benefit O2 transport capacity by an improvement in central circulatory function.

Peripheral circulation

Blood flow (BF) increases with increasing exercise intensity in skeletal, respiratory, and cardiac muscle. In humans during maximal exercise intensities, 85% to 90% of total cardiac output is distributed to skeletal and cardiac muscle. During exercise BF increases modestly and heterogeneously to brain and decreases in gastrointestinal, reproductive, and renal tissues and shows little to no change in skin. If the duration of exercise is sufficient to increase body/core temperature, skin BF is also increased in humans. Because blood pressure changes little during exercise, changes in distribution of BF with incremental exercise result from changes in vascular conductance. These changes in distribution of BF throughout the body contribute to decreases in mixed venous oxygen content, serve to supply adequate oxygen to the active skeletal muscles, and support metabolism of other tissues while maintaining homeostasis. This review discusses the response of the peripheral circulation of humans to acute and chronic dynamic exercise and mechanisms responsible for these responses. This is accomplished in the context of leading the reader on a tour through the peripheral circulation during dynamic exercise. During this tour, we consider what is known about how each vascular bed controls BF during exercise and how these control mechanisms are modified by chronic physical activity/exercise training. The tour ends by comparing responses of the systemic circulation to those of the pulmonary circulation relative to the effects of exercise on the regional distribution of BF and mechanisms responsible for control of resistance/conductance in the systemic and pulmonary circulations.

Avaliação da potência aeróbia de praticantes de Rugby em Cadeira de Rodas através de um teste de quadra

O presente estudo teve por finalidade estimar a potência aeróbia em atletas com LME praticantes de RCR, correlacionar os níveis de VO2máx com a classificação funcional (CF) dos atletas e analisar o comportamento da FC antes e pós-teste. A amostra foi composta por 10 atletas com LME, do sexo masculino e idade média de 29,6±6,5anos. Os atletas foram submetidos ao teste de corrida de 12 minutos e monitorados com o frequêncimetro cardíaco. A média do VO2máx foi de 18,3±8,1ml(kg.min)-1 e da FCmáx de 114,6±25,3bpm. Os valores de VO2máx obtidos no estudo são classificados como médio para a população com tetraplegia. Observou-se que existe correlação moderada (r=0,77) entre a CF e o VO2máx entre atletas praticantes de RCR e por fim, observou-se baixos valores de FC frente á um teste submáximo, fato que pode estar relacionado à diminuição da atuação simpática após LME.

Cardiovascular drift in trained paraplegic and able-bodied individuals during prolonged wheelchair exercise: effect of fluid replacement

The progressive heart rate (HR) increase and stroke volume (SV) decline during prolonged constant-load leg exercise signifies cardiovascular drift (CVdrift); fluid replacement is known to minimize this phenomenon. Like their able-bodied counterparts (AB), paraplegic athletes undergo prolonged exercise during training and competition, which could result in CVdrift. The aim of this study is to address the role of rehydration on preventing CVdrift in spinal cord injured (SCI) paraplegic athletes. Eight SCI athletes with an injury level between C7 and T6 and 9 AB subjects performed 60-min constant-load exercise on a wheelchair ergometer in a thermo-neutral environment. No fluid was taken in 1 trial, whereas 85% of sweat losses were replaced by drinking water in another trial. Cardic output (CO), SV, HR, and oral temperature (Tor) were determined during exercise. Prolonged exercise resulted in similar HR (18 beats·min(-1) for AB and 12 beats·min(-1) for SCI) and Tor (0.63 °C for AB and 0.71 °C for SCI) elevation and SV decline (-8.5 mL·beat(-1) for AB and -5.5 mL·beat(-1) for SCI), whereas CO remained unchanged. Water intake restrained the exercise-induced hyperthermia and resulted in smaller SV decline (-4.0 mL for AB and -3.0 mL for SCI, p < 0.01). In conclusion, CVdrift was similar in SCI and AB subjects during prolonged wheelchair exercise. Likewise, the beneficial effects of hydration in both groups were analogous.

The impact of obesity on cardiac troponin levels after prolonged exercise in humans

Elevated cardiac troponin I (cTnI), a marker for cardiac damage, has been reported after high-intensity exercise in healthy subjects. Currently, little is known about the impact of prolonged moderate-intensity exercise on cTnI release, but also the impact of obesity on this response. 97 volunteers (55 men and 42 women), stratified for BMI, performed a single bout of walking exercise (30-50 km). We examined cTnI-levels before and immediately after the exercise bout in lean (BMI < 25 kg/m(2), n = 30, 57 ± 19 years), overweight (25 ≤ BMI < 30 kg/m(2), n = 29, 56 ± 11 years), and obese subjects (BMI ≥ 30 kg/m(2), n = 28, 53 ± 9 years). Walking was performed at a self-selected pace. cTnI was assessed using a high-sensitive cTnI-assay (Centaur; clinical cut-off value ≥ 0.04 μg/L). We recorded subject characteristics (body weight, blood pressure, presence of cardiovascular risk) and examined exercise intensity by recording heart rate. Mean cTnI-levels increased significantly from 0.010 ± 0.006 to 0.024 ± 0.046 μg/L (P < 0.001). The exercise-induced increase in cTnI was not different between lean, overweight and obese subjects (two-way ANOVA interaction; P = 0.27). In 11 participants, cTnI was elevated above the clinical cut-off value for myocardial infarction. Logistic regression analysis identified exercise intensity (P < 0.001), but not BMI, body fat percentage or waist circumference to significantly relate to positive troponin tests. In conclusion, prolonged, moderate-intensity exercise results in a comparable increase in cTnI-levels in lean, overweight and obese subjects. Therefore, measures of obesity unlikely relate to the magnitude of the post-exercise elevation in cTnI.

Muscle perfusion of posterior trunk and lower-limb muscles at rest and during upper-limb exercise in spinal cord-injured and able-bodied individuals

STUDY DESIGN

Nonrandomized-controlled trial.

OBJECTIVES

To assess muscle perfusion at rest and during arm-cranking exercise (ACE) in upper and lower posterior trunk and vastus lateralis (VL) muscles in individuals with spinal cord injury (SCI) and controls (C).

SETTING

Exercise Physiology-Biochemistry Laboratory.

METHODS

Eight SCI with thoracic lesion and eight C received injections of radioactive tracer to trapezius (TRAP), latissimus dorsi (LAT) and VL. Radioactive counts were recorded with a γ-camera for 10 min at rest and during ACE (60% VO(2max) for 20 min). Time-count curves were generated and the isotope clearance rate, expressed as half-life time (T(1/2),min), was calculated to assess muscle perfusion.

RESULTS

Resting T(1/2) was lower in TRAP and LAT vs VL (P<0.05) in SCI, however, there were no differences among muscles in C. Arm-cranking increased (P<0.001) the isotope clearance in TRAP and LAT in SCI and C, whereas no effect was found on T(1/2) in VL in both groups. T(1/2) was longer (P<0.05) in SCI vs C in VL at rest and during ACE, whereas there were no differences between groups in posterior trunk muscles.

CONCLUSIONS

Resting muscle perfusion was reduced in the paralyzed limbs of SCI compared with C, whereas there was no evidence of impaired microcirculation in upper and lower back muscles in SCI. Although ACE did not induce a hyperemic response in VL, it increased hyperemia in upper and lower posterior trunk muscles in SCI, suggesting beneficial effects of this type of activity on muscle microvasculature in this region.

Review article: the pathophysiology and management of gastrointestinal symptoms during physical exercise, and the role of splanchnic blood flow

BACKGROUND

The prevalence of exercise-induced gastrointestinal (GI) symptoms has been reported up to 70%. The pathophysiology largely remains unknown.

AIM

To review the physiological and pathophysiological changes of the GI-tract during physical exercise and the management of the most common gastrointestinal symptoms.

METHODS

Search of the literature published in the English and Dutch languages using the Pubmed database to review the literature that focused on the relation between splanchnic blood flow (SBF), development of ischaemia, postischaemic endotoxinemia and motility.

RESULTS

During physical exercise, the increased activity of the sympathetic nervous system (SNS) redistributes blood flow from the splanchnic organs to the working muscles. With prolonged duration and/or intensity, the SBF may be decreased by 80% or more. Most studies point in the direction of increased SNS-activity as central driving force for reduction in SBF. A severely reduced SBF may frequently cause GI ischaemia. GI-ischaemia combined with reduced vagal activity probably triggers changes in GI-motility and GI absorption derangements. GI-symptoms during physical exercise may be prevented by lowering the exercise intensity, preventing dehydration and avoiding the ingestion of hypertonic fluids.

CONCLUSIONS

Literature on the pathophysiology of exercise-induced GI-symptoms is scarce. Increased sympathetic nervous system activity and decreased splanchnic blood flow during physical exercise seems to be the key factor in the pathogenesis of exercise-induced GI-symptoms, and this should be the target for symptom reduction.

Cardiovascular determinants of exercise capacity in the Paralympic athlete with spinal cord injury

This report briefly summarizes the cardiovascular factors that influence exercise physiology and, eventually, sports performance of athletes with a spinal cord injury (SCI). The consequences of an SCI are numerous and concern voluntary muscle function, deep and superficial sensitivity, and autonomic function to a degree determined by the level and completeness of the spinal lesion. Athletes with SCI perform with their upper body, which limits their maximal exercise capacity and puts them at a disadvantage compared with leg exercise in terms of mechanical efficiency and physiological adaptations to exercise. Studies generally find that maximal oxygen consumption and mechanical power output are inversely related to spinal lesion level. Athletes with cervical or dorsal lesions down to Th6 have limited maximal heart rates owing to a lack of sympathetic drive to the heart. Blood redistribution from body areas lacking autonomic control is impaired, thus reducing venous return and limiting cardiac stroke volume during exercise. Thermoregulatory function is affected through a lack of afferent neural feedback and limited efferent vasomotor and sudomotor control below the lesion. Strategies to support venous return and to promote body cooling potentially improve physiological responses and athletic performance, especially in individuals with high lesion levels. The latter are subject to autonomic dysreflexia, a generalized sympathetic vasoconstriction below the lesion resulting from nociceptive stimulations in insensate body regions. Acute episodes induce high blood pressure, may enhance exercise performance and must be treated as a clinical emergency. Deliberate triggering of this reflex is prohibited by the International Paralympic Committee.

Evidence for greater burden of peripheral arterial disease in lower extremity arteries of spinal cord-injured individuals

Spinal cord injury leads to increased risk for cardiovascular disease and results in greater risk of death. Subclinical markers of atherosclerosis have been reported in carotid arteries of spinal cord-injured individuals (SCI), but the development of lower extremity peripheral arterial disease (PAD) has not been investigated in this population. The purpose of this study was to determine the effect of spinal cord injury on ankle-brachial index (ABI) and intima-media thickness (IMT) of upper-body and lower-extremity arteries. We hypothesized that the aforementioned measures of lower-extremity PAD would be worsened in SCI compared with controls and that regular participation in endurance exercise would improve these in both groups. To test these hypotheses, ABI and IMT were determined in 105 SCI and compared with 156 able-bodied controls with groups further subdivided into physically active and sedentary. ABIs were significantly lower in SCI versus controls (0.96 ± 0.12 vs. 1.06 ± 0.07, P < 0.001), indicating a greater burden of lower-extremity PAD. Upper-body IMTs were similar for brachial and carotid arteries in controls versus SCI. Lower extremity IMTs revealed similar thicknesses for both superficial femoral and popliteal arteries, but when normalized for artery diameter, individuals with SCI had greater IMT than controls in the superficial femoral (0.094 ± 0.03 vs. 0.073 ± 0.02 mm/mm lumen diameter, P < 0.01) and popliteal (0.117 ± 0.04 vs. 0.091 ± 0.02 mm/mm lumen diameter, P < 0.01) arteries. The ABI and normalized IMT of SCI compared with controls indicate that subclinical measures of lower-extremity PAD are worsened in individuals with SCI. These findings should prompt physicians to consider using the ABI as a screening method to detect lower-extremity PAD in SCI.

Cardiovascular responses to arm static exercise in men with thoracic spinal cord lesions

Isometric muscle contraction (static exercise) induces circulatory response. Static exercise in individuals with thoracic spinal cord injury (TSCI) induces cardiovascular response and blood redistribution to the non-exercising muscles. The aim of our study was to determine the circulatory response during arm static exercise in individuals with TSCI and able-bodied (AB) controls. Mean blood pressure (MBP), heart rate (HR), cardiac output (CO), leg skin blood flow (SBF), and leg muscle blood flow (MBF) were recorded noninvasively, total peripheral resistance (TPR) was estimated by dividing MBP by CO, and hormonal changes were measured before, during and after static 35% maximal voluntary contraction (MVC) of the arm flexor muscles in seven male individuals with TSCI (T7-T11) and seven age-comparable AB control (32.2 ± 7.6 and 31.0 ± 4.7 years, respectively). The 35% MVC was similar in TSCI and AB individuals (107.3 ± 28.2 and 101.0 ± 22.5 N, respectively). HR, CO, MBP, TPR, SBF and MBF increased in both groups during arm static exercise. Plasma epinephrine concentration increased during arm static exercise in AB controls only (P < 0.05). Circulation to leg muscles was similar in TSCI and AB individuals and the lack of sympathetic vasoconstriction in the paralyzed leg area did not alter the cardiovascular responses during 35% MVC of arm static exercise. We conclude that sympathetic vasoconstriction in the resting leg area did not contribute to the pressor reflex during 35% MVC of arm static exercise.

Vascular effects of exercise: endothelial adaptations beyond active muscle beds

Endothelial adaptations to exercise training are not exclusively conferred within the active muscle beds. Herein, we summarize key studies that have evaluated the impact of chronic exercise on the endothelium of vasculatures perfusing nonworking skeletal muscle, brain, viscera, and skin, concluding with discussion of potential mechanisms driving these endothelial adaptations.