Local Vascular Adaptations after Hybrid Training in Spinal Cord–Injured Subjects

Combined L-Citrulline Supplementation and Slow Velocity Low-Intensity Resistance Training Improves Leg Endothelial Function, Lean Mass, and Strength in Hypertensive Postmenopausal Women

Hypertension is highly prevalent in postmenopausal women. Endothelial dysfunction is associated with hypertension and the age-related decreases in muscle mass and strength. L-citrulline supplementation (CIT) and slow velocity low-intensity resistance training (SVLIRT) have improved vascular function, but their effect on muscle mass is unclear. We investigated whether combined CIT and SVLIRT (CIT + SVLIRT) would have additional benefits on leg endothelial function (superficial femoral artery flow-mediated dilation (sfemFMD)), lean mass (LM), and strength in hypertensive postmenopausal women. Participants were randomized to CIT (10 g/day, n = 13) or placebo (PL, n = 11) alone for 4 weeks and CIT + SVLIRT or PL + SVLIRT for another 4 weeks. sfemFMD, leg LM and muscle strength were measured at 0, 4, and 8 weeks. CIT increased sfemFMD after 4 weeks (CIT: Δ1.8 ± 0.3% vs. PL: Δ−0.2 ± 0.5%, p < 0.05) and 8 weeks (CIT + SVLIRT: Δ2.7 ± 0.5% vs. PL + SVLIRT: Δ−0.02 ± 0.5, p = 0.003). Leg LM improved after CIT + SVLIRT compared to PL + SVLIRT (Δ0.49 ± 0.15 kg vs. Δ0.07 ± 0.12 kg, p < 0.05). Leg curl strength increased greater with CIT + SVLIRT compared to PL + SVLIRT (Δ6.9 ± 0.9 kg vs. Δ4.0 ± 1.0 kg, p < 0.05). CIT supplementation alone improved leg endothelial function and when combined with SVLIRT has additive benefits on leg LM and curl strength in hypertensive postmenopausal women.

Twelve-Week Daily Gluteal and Hamstring Electrical Stimulation Improves Vascular Structure and Function, Limb Volume, and Sitting Pressure in Spinal Cord Injury: A Pilot Feasibility Study

OBJECTIVE

We examined the long-term effects of low-intensity electrical stimulation on (micro)vasculature and sitting pressure of a home-based, wearable electrical stimulation device in a pilot feasibility study.

DESIGN

In a cohort observation before-after trial, nine middle-aged male (n = 8) and female (n = 1) individuals (48 ± 15 yrs) with American Spinal Injury Association A-C classified chronic (1-24 yrs) spinal cord injury underwent 12 wks of self-administered daily, low-intensity gluteal and hamstring electrical stimulation (50 Hz, 6 hrs [30-min electrical stimulation, 15-min rest]). Common femoral artery diameter and blood blow were determined with ultrasound, skin vascular function during local heating was assessed using Laser-Doppler flowmetry, thigh volume was estimated using leg circumferences and skinfolds, and interface sitting pressure was measured using pressure mapping.

RESULTS

Resting common femoral artery diameter increased (0.73 ± 0.20 to 0.79 ± 0.22 cm, P < 0.001) and baseline common femoral artery blood flow increased (0.28 ± 0.12 to 0.40 ± 0.15 l/min, P < 0.002). Gluteal cutaneous vascular conductance showed a time*temperature interaction (P = 0.01) with higher conductance at 42°C after 12 wks. Ischial peak pressure decreased (P = 0.003) by 32 ± 23 mm Hg and pressure gradient decreased (23 ± 7 to 16 ± 6 mm Hg, P = 0.007). Thigh volume increased (+19%, P = 0.01).

CONCLUSIONS

Twelve-week daily home-based gluteal and hamstring electrical stimulation is feasible and effective to improve (micro)vasculature and sitting pressure, and electrical stimulation may have clinical implications for ameliorating pressure ulcers and (micro)vascular complications in spinal cord injury.

Benefits and interval training in individuals with spinal cord injury: A thematic review

BACKGROUND

Arm crank ergometry (ACE), functional electrical stimulation leg cycling exercise (FES-LCE), and the combination of the two (FES hybrid exercise) have all been used as activities to help improve the fitness-related health of individuals with spinal cord injury (SCI). More recently, high-intensity interval training (HIIT) has become popular in the non-disabled community due to its ability to produce greater aerobic fitness benefits or equivalent benefits with reduced time commitment.

OBJECTIVE

This thematic review of the literature sought to determine the potential benefits and practicality of using ACE, FES-LCE, and FES hybrid exercise in an interval training format for individuals with SCI.

METHODS

Systematic literature searches were conducted in May 2020 and March 2021 focusing on interval training in individuals with SCI. Pre-defined nested search terms were used to narrow the available literature from 4273 citations to 1362 articles. The titles and abstracts were then reviewed to determine the appropriateness of the articles ending with fifteen articles.

RESULTS

The literature was limited to fifteen articles with low participant numbers (n = 1-20). However, in each article, HIIT protocols either demonstrated a greater improvement in cardiovascular, metabolic, or practicality scores compared to moderate intensity continuous training (MICT) protocols, or improvement during relatively brief time commitments.

CONCLUSION

The available literature lacked sufficient numbers of randomized control trials. However, the available evidence is encouraging concerning the potential benefits and practicality of using HIIT (ACE, FES-LCE, or FES hybrid exercise) to improve aerobic and anaerobic capacity and decrease cardiometabolic risk after SCI.

Does aerobic exercise benefit persons with tetraplegia from spinal cord injury? A systematic review

CONTEXT

This review synthesizes the findings of previous research studies on the cardiovascular and metabolic benefits of aerobic exercise for individuals with tetraplegia secondary to spinal cord injury. They are often less active due to muscular paralysis, sensory loss, and sympathetic nervous system dysfunction that result from injury. Consequently, these persons are at higher risk for exercise intolerance and secondary health conditions.

OBJECTIVE

To evaluate the evidence concerning efficacy of aerobic exercise training for improving health and exercise performance in persons with tetraplegia from cervical injury.

METHODS

The search engines PubMed and Google Scholar were used to locate published research. The final 75 papers were selected on the basis of inclusion criteria. The studies were then rank-ordered using Physiotherapy Evidence Database.

RESULTS

Studies combining individuals with tetraplegia and paraplegia show that voluntary arm-crank training can increase mean peak power output by 33%. Functional electrical stimulation leg cycling was shown to induce higher peak cardiac output and stroke volume than arm-crank exercise. A range of peak oxygen uptake (VO_2peak) values have been reported (0.57-1.32 L/min). Both VO_2peak and cardiac output may be enhanced via increased muscle pump in the legs and venous return to the heart. Hybrid exercise (arm-crank and functional electrical stimulation leg cycling) can result in greater peak oxygen uptake and cardiovascular responses.

CONCLUSION

Evidence gathered from this systematic review of literature is inconclusive due to the lack of research focusing on those with tetraplegia. Higher power studies (level 1-3) are needed with the focus on those with tetraplegia.

Vascular adaptations in nonstimulated areas during hybrid cycling or handcycling in people with a spinal cord injury: a pilot study of 10 cases

STUDY DESIGN

Sub-study of a randomized controlled trial.

OBJECTIVES

To examine if hybrid cycling (cycling with the legs via electrical stimulation combined with voluntary handcycling) compared to handcycling leads to different systemic vascular adaptations in individuals with a long-term spinal cord injury (SCI).

SETTING

Two rehabilitation centers in the Netherlands.

METHODS

Ten individuals with a SCI trained on a hybrid bicycle (N = 5) or a handcycle (N = 5) for 16 weeks twice a week. Prior to and following the training the intima media thickness (IMT) of the common coronary artery (CCA) and superficial femoral artery (SFA) were measured and the flow-mediated dilation (FMD) of the brachial artery (BA) was analyzed.

RESULTS

Before training, there were no significant differences in any of the outcome measures between the groups. We found no change in CCA IMT (pre: 0.616 mm, post: 0.586 mm), or in SFA (pre: 0.512 mm, post: 0.520 mm) after hybrid cycling. We also found no change in FMD % of BA after hybrid cycling (pre: 9.040%, post: 9.220%). There were no changes in CCA IMT, SFA IMT, and FMD% after handcycling either.

CONCLUSIONS

It appears that 16 weeks of twice-weekly training of up to 30 min on a hybrid bicycle or handcycle does not lead to systemic vascular adaptations. A larger sample size and training protocol with more frequent and higher intensity training (which might involve a home-based setting and an adapted period prior to the training) might show different results.

Functional electrical stimulation cycling exercise after spinal cord injury: a systematic review of health and fitness-related outcomes

OBJECTIVES

The objective of this review was to summarize and appraise evidence on functional electrical stimulation (FES) cycling exercise after spinal cord injury (SCI), in order to inform the development of evidence-based clinical practice guidelines.

METHODS

PubMed, the Cochrane Central Register of Controlled Trials, EMBASE, SPORTDiscus, and CINAHL were searched up to April 2021 to identify FES cycling exercise intervention studies including adults with SCI. In order to capture the widest array of evidence available, any outcome measure employed in such studies was considered eligible. Two independent reviewers conducted study eligibility screening, data extraction, and quality appraisal using Cochranes' Risk of Bias or Downs and Black tools. Each study was designated as a Level 1, 2, 3 or 4 study, dependent on study design and quality appraisal scores. The certainty of the evidence for each outcome was assessed using GRADE ratings ('High', 'Moderate', 'Low', or 'Very low').

RESULTS

Ninety-two studies met the eligibility criteria, comprising 999 adults with SCI representing all age, sex, time since injury, lesion level and lesion completeness strata. For muscle health (e.g., muscle mass, fiber type composition), significant improvements were found in 3 out of 4 Level 1-2 studies, and 27 out of 32 Level 3-4 studies (GRADE rating: 'High'). Although lacking Level 1-2 studies, significant improvements were also found in nearly all of 35 Level 3-4 studies on power output and aerobic fitness (e.g., peak power and oxygen uptake during an FES cycling test) (GRADE ratings: 'Low').

CONCLUSION

Current evidence indicates that FES cycling exercise improves lower-body muscle health of adults with SCI, and may increase power output and aerobic fitness. The evidence summarized and appraised in this review can inform the development of the first international, evidence-based clinical practice guidelines for the use of FES cycling exercise in clinical and community settings of adults with SCI. Registration review protocol: CRD42018108940 (PROSPERO).

Spinal cord injury and vascular function: evidence from diameter-matched vessels

The effect of a spinal cord injury (SCI) on vascular function has been clouded by both the physiological and mathematical bias of assessing vasodilation in arteries with differing diameters both above and below the lesion and when comparing with healthy, nondisabled controls (CTRL). Thus, we measured vascular function, with flow-mediated vasodilation (FMD), in 10 SCI and 10 CTRL with all arteries matched for diameter (≈0.5 cm): brachial artery (BA, arm, functional limb in both groups) and popliteal artery (PA, leg, disused limb in SCI, functional limb in CTRL). PA %FMD was significantly attenuated in SCI (5.6 ± 0.6%) compared with CTRL (8.4 ± 1.3%), with no difference in the BA (SCI: 8.6 ± 0.9%; CTRL: 8.7 ± 0.7%). However, unlike the arm, where muscle mass was preserved, the legs of the SCI were significantly smaller than CTRL (∼70%). Thus, reactive hyperemia (RH), which is heavily dependent on the volume of muscle occluded, in the PA was attenuated in the SCI (144 ± 22 mL) compared with CTRL (258 ± 16 mL) but not different in the BA. Consequently, shear rate was significantly diminished in the PA of the SCI, such that %FMD/shear rate (vascular responsiveness) was actually greater in the SCI (1.5 ± 0.1% · s^-1) than CTRL (1.2 ± 0.1% · s^-1). Of note, this was significantly greater than both their own BA (0.9 ± 0.1% · s^-1) and that of the CTRL (0.9 ± 0.1% · s^-1). Therefore, examining vessels of similar size, this study reveals normal vascular function above the lesion and vascular dysfunction below the lesion. However, below the lesion there was, actually, evidence of increased vascular responsiveness in this population.NEW & NOTEWORTHY This study examined the effect of a spinal cord injury (SCI) and subsequent limb disuse on vascular function, assessed by %FMD, in diameter-matched vessels above and below the lesion in subjects with SCI and controls. The results reveal normal vascular function above the lesion and vascular dysfunction below the lesion (%FMD). However, below the lesion there was, actually, evidence of increased vascular responsiveness (%FMD/shear rate) in this population.

Feasibility of overnight electrical stimulation-induced muscle activation in people with a spinal cord injury. A Pilot study

Study Design

We investigated whether overnight ES is a feasible method to activate gluteal, quadriceps, and hamstrings muscles in a two-week experiment. Electrical stimulation (ES) induced muscle contractions have proven positive effects on risk factors for developing pressure ulcers in people with a spinal cord injury (SCI). Therefore prolonged overnight ES-induced muscle activation is interesting, but has never been studied.

Objective

To study feasibility of ES-induced leg muscle activation. In eight participants with motor complete SCI gluteal, hamstrings and quadriceps muscles were activated with a 2-weeks overnight stimulation protocol, 8 h per night, using specially developed ES-shorts.

Setting

The Netherlands.

Methods

Muscle fatigue was determined with a muscle contraction sensor. Questionnaires on sleep quality (SQ) and the ES-shorts usability were taken.

Results

After 8 h of activation muscles still contracted, although fatigue occurred, and mean contraction size was lower at the end of a cycle (p = 0.03). SQ (0-100) after intervention was 75, and 66 after 4 weeks without overnight ES (p = 0.04) indicating ES improves sleep quality. The usability of the ES-shorts was good.

Conclusions

This study shows that overnight ES-induced muscle activation using ES-shorts in SCI is a new, feasible method that does not interfere with sleep. The nightly use of the ES-shorts might be considered as an important part of the daily routine in SCI.

Cycle Training improves vascular function and neuropathic symptoms in patients with type 2 diabetes and peripheral neuropathy: A randomized controlled trial

Diabetic peripheral neuropathy (DPN) is associated with peripheral arterial disease and endothelial dysfunction. We investigated the effect of exercise training on the measures of superficial femoral artery (SFA) and neuropathic symptoms in patients with DPN. In a randomized-controlled trial, 31 volunteers with established DPN were randomly assigned to experimental or control groups. Experimental group performed cycling exercise training (50%-70% of heart rate reserve, 30-45 min, 3 sessions/week) over 12 weeks. Before and 48 h after the experimental period a 5-min flow mediated dilation (FMD) response in SFA using Color Doppler Ultrasonography, fasting glucose level, HbA1c and neuropathic score were assessed. FMD% significantly increased in the experimental group (from 3.2 ± 1.1% to 5.7 ± 1.2%) compared to the control condition (P = 0.0001). However, no significant alteration occurred in baseline membrane diameter and intima media thickness (P > 0.05). We also observed a significant improvement in fasting glucose, HbA1c and Michigan Diabetic Neuropathy Score (MDNS) following exercise intervention (all P < 0.05). Linear regression analysis indicated that the change in MDNS was significantly associated with the change in HbA1c (R Square = 0.34, standardized coefficients Beta = -0.58, P = .001) and FMD (R Square = 0.37, standardized coefficients Beta = 0.61, P = .001). This finding may be clinically of considerable importance as metabolic and vascular factors have been indicated to be involved in the development of DPN.

Effects of Intermittent Pneumatic Compression on Leg Vascular Function in People with Spinal Cord Injury: A Pilot Study

Objective: The purpose of this pilot study was to determine whether 60 mins of intermittent pneumatic compression therapy (IPC) could acutely increase leg blood flow-induced shear stress and enhance vascular endothelial function in persons with spinal cord injury (SCI). Design: Pretest with multiple posttests, within subject randomized control design. Setting: University of Southern Mississippi, Spinal Cord Injury Research Program within the School of Kinesiology, recruiting from the local community in Hattiesburg, Jackson, and Gulfport, MS. Participants: Eight adults with SCI (injury level: T3 and below; ASIA class A-C; age: 41±17 yrs). Interventions: A 60-min IPC session was performed in one leg (experimental leg; EXP), with the other leg serving as a control (CON). Outcomes Measures: Posterior-tibial artery shear rate (Doppler-ultrasound) was examined at rest, and at 15 and 45 mins during IPC. Endothelial function was assessed using the flow-mediated dilation (FMD) technique, before and after IPC. Results: Resting FMD (mm) was similar between legs at rest. A two-way repeated measures ANOVA (leg x time) revealed that during IPC, peak shear rate increased in the EXP leg (215±137 to 285±164 s^-1 at 15 mins; +39±29%, P = 0.03), with no change occurring in the CON. In addition, FMD significantly increased in the EXP leg (Pre IPC: 0.36±0.14 vs. Post IPC: 0.47±0.17 mm; P = 0.011, d = 0.66), with no change occurring in the CON leg. Conclusion: These preliminary findings suggests that IPC therapy may acutely increase leg shear stress within 15 mins, with a resultant moderate-large improvement in vascular endothelial function after 60 mins in people with SCI.

Femoral Artery Blood Flow and Microcirculatory Perfusion During Acute, Low-Level Functional Electrical Stimulation in Spinal Cord Injury

OBJECTIVE

Functional electrical stimulation (FES) may help to reduce the risk of developing macrovascular and microvascular complications in people with spinal cord injury. Low-intensity FES has significant clinical potential because this can be applied continuously throughout the day. This study examines the acute effects of low-intensity FES using wearable clothing garment on vascular blood flow and oxygen consumption in people with spinal cord injury.

DESIGN

This was a cross-sectional observation study.

METHODS

Eight participants with a motor complete spinal cord injury received four 3-min unilateral FES to the gluteal and hamstring muscles. Skin and deep femoral artery blood flow and oxygen consumption were measured at baseline and during each bout of stimulation.

RESULTS

Femoral artery blood flow increased by 18.1% with the application of FES (P = 0.02). Moreover, femoral artery blood flow increased further during each subsequent block of FES (P = 0.004). Skin perfusion did not change during an individual block of stimulation (P = 0.66). Skin perfusion progressively increased with each subsequent bout (P < 0.001). There was no change in femoral or skin perfusion across time in the nonstimulated leg (all P > 0.05).

CONCLUSION

Low-intensity FES acutely increased blood flow during stimulation, with a progressive increase across subsequent FES bouts. These observations suggest that continuous, low-intensity FES may represent a practical and effective strategy to improve perfusion and reduce the risk of vascular complications.

Evidence of a limb- and shear stress stimulus profile-dependent impact of high-intensity cycling training on flow-mediated dilation

Lower limb endurance training can improve conduit artery flow-mediated dilation (FMD) in response to transient increases in shear stress (reactive hyperemia; RH-FMD) in both the upper and lower limbs. Sustained increases in shear stress recruit a partially distinct transduction pathway and elicit a physiologically relevant FMD response (SS-FMD) that provides distinct information regarding endothelial function. However, the impact of training on SS-FMD is not well understood. The purpose of this study was to determine the impact of cycling training on handgrip exercise-induced brachial artery (BA) FMD (BA SS-FMD) and calf plantar-flexion-induced superficial femoral artery (SFA) FMD (SFA SS-FMD). RH-FMD was also assessed in both arteries. Twenty-eight young males were randomized to control (n = 12) or training (n = 16) groups. The training group cycled 30 min/day, 3 days/week for 4 weeks at 80% heart rate reserve. FMD was assessed in the BA and SFA before and after the intervention via Duplex ultrasound. Results are means ± SD. Training did not impact SS-FMD in either artery, and SFA RH-FMD was also unchanged (p > 0.05). When controlling for the shear rate stimulus via covariate analysis, BA RH-FMD improved in the training group (p = 0.05) (control - pre-intervention: 5.7% ± 2.4%, post-intervention: 5.3% ± 2.4%; training - pre-intervention: 5.4% ± 2.5%, post-intervention: 7.2% ± 2.4%). Thus, endurance training resulted in nonuniform adaptations to endothelial function, with an isolated impact on the BA's ability to transduce a transient increase in shear stress. Novelty Training did not alter SS-FMD in the arm or leg. RH-FMD was augmented in the arm only. Thus training adaptations were limb- and shear stress profile-specific.

Temporal analysis of cardiovascular control and function following incomplete T3 and T10 spinal cord injury in rodents

Spinal cord injury (SCI) is a devastating condition that results in whole‐body dysfunction, notably cardiovascular (CV) disruption and disease. Injury‐induced destruction of autonomic pathways in conjunction with a progressive decline in physical fitness contribute to the poor CV status of SCI individuals. Despite the wide use of exercise training as a therapeutic option to reduce CV dysfunction, little is known about the acute hemodynamic responses to the exercise itself. We investigated CV responses to an exercise challenge (swimming) following both high and low thoracic contusion to determine if the CV system is able to respond appropriately to the challenge of swimming. Blood pressure (BP) telemetry and echocardiography were used to track the progression of dysfunction in rodents with T3 and T10 SCI (n = 8 each) for 10 weeks postcontusion. At 1 week postinjury, all animals displayed a drastic decline in heart rate (HR) during the exercise challenge, likely a consequence of neurogenic shock. Furthermore, over time, all groups developed a progressive inability to maintain BP within a narrow range during the exercise challenge despite displaying normal hemodynamic parameters at rest. Echocardiography of T10 animals revealed no persistent signs of cardiac dysfunction; T3 animals exhibited a transient decline in systolic function that returned to preinjury levels by 10 weeks postinjury. Novel evidence provided here illustrates that incomplete injuries produce hemodynamic instability that only becomes apparent during an exercise challenge. Further, this dysfunction lasts into the chronic phase of disease progression despite significant recovery of hindlimb locomotion and cardiac function.

Muscle oxygenation during hybrid arm and functional electrical stimulation-evoked leg cycling after spinal cord injury

This study compared muscle oxygenation (StO2) during arm cranking (ACE), functional electrical stimulation-evoked leg cycling (FES-LCE), and hybrid (ACE+FES-LCE) exercise in spinal cord injury individuals. Eight subjects with C7-T12 lesions performed exercises at 3 submaximal intensities. StO2 was measured during rest and exercise at 40%, 60%, and 80% of subjects' oxygen uptake (VO2) peak using near-infrared spectroscopy. StO2 of ACE showed a decrease whereas in ACE+FES-LCE, the arm muscles demonstrated increasing StO2 from rest in all of VO2) peak respectively. StO2 of FES-LCE displayed a decrease at 40% VO2 peak and steady increase for 60% and 80%, whereas ACE+FES-LCE revealed a steady increase from rest at all VO2 peak. ACE+FES-LCE elicited greater StO2 in both limbs which suggested that during this exercise, upper- and lower-limb muscles have higher blood flow and improved oxygenation compared to ACE or FES-LCE performed alone.

Non-gait-specific intervention for the rehabilitation of walking after SCI: role of the arms

Arm movements modulate leg activity and improve gait efficiency; however, current rehabilitation interventions focus on improving walking through gait-specific training and do not actively involve the arms. The goal of this project was to assess the effect of a rehabilitation strategy involving simultaneous arm and leg cycling on improving walking after incomplete spinal cord injury (iSCI). We investigated the effect of 1) non-gait-specific training and 2) active arm involvement during training on changes in over ground walking capacity. Participants with iSCI were assigned to simultaneous arm-leg cycling (A&L) or legs only cycling (Leg) training paradigms, and cycling movements were assisted with electrical stimulation. Overground walking speed significantly increased by 0.092 ± 0.022 m/s in the Leg group and 0.27 ± 0.072m/s in the A&L group after training. Whereas the increases in the Leg group were similar to those seen after current locomotor training strategies, increases in the A&L group were significantly larger than those in the Leg group. Walking distance also significantly increased by 32.12 ± 8.74 m in the Leg and 91.58 ± 36.24 m in the A&L group. Muscle strength, sensation, and balance improved in both groups; however, the A&L group had significant improvements in most gait measures and had more regulated joint kinematics and muscle activity after training compared with the Leg group. We conclude that electrical stimulation-assisted cycling training can produce significant improvements in walking after SCI. Furthermore, active arm involvement during training can produce greater improvements in walking performance. This strategy may also be effective in people with other neural disorders or diseases. NEW & NOTEWORTHY This work challenges concepts of task-specific training for the rehabilitation of walking and encourages coordinated training of the arms and legs after spinal cord injury. Cycling of the legs produced significant improvements in walking that were similar in magnitude to those reported with gait-specific training. Moreover, active engagement of the arms simultaneously with the legs generated nearly double the improvements obtained by leg training only. The cervico-lumbar networks are critical for the improvement of walking.

Body System Effects of a Multi-Modal Training Program Targeting Chronic, Motor Complete Thoracic Spinal Cord Injury

The safety and efficacy of pharmacological and cellular transplantation strategies are currently being evaluated in people with spinal cord injury (SCI). In studies of people with chronic SCIs, it is thought that functional recovery will be best achieved when drug or cell therapies are combined with rehabilitation protocols. However, any functional recovery attributed to the therapy may be confounded by the conditioned state of the body and by training-induced effects on neuroplasticity. For this reason, we sought to investigate the effects of a multi-modal training program on several body systems. The training program included body-weight-supported treadmill training for locomotion, circuit resistance training for upper body conditioning, functional electrical stimulation for activation of sublesional muscles, and wheelchair skills training for overall mobility. Eight participants with chronic, thoracic-level, motor-complete SCI completed the 12-week training program. After 12 weeks, upper extremity muscular strength improved significantly for all participants, and some participants experienced improvements in function, which may be explained by increased strength. Neurological function did not change. Changes in pain and spasticity were highly variable between participants. This is the first demonstration of the effect of this combination of four training modalities. However, balancing participant and study-site burden with capturing meaningful outcome measures is also an important consideration.

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.

Cutaneous microvascular perfusion responses to insulin iontophoresis are differentially affected by insulin resistance after spinal cord injury

NEW FINDINGS

What is the central question of this study? What impact does insulin resistance have on cutaneous perfusion responses to insulin iontophoresis in vascular beds with markedly reduced or functionally ablated sympathetic nervous system vasomotor function resulting from spinal cord injury? What is the main finding and its importance? Persons with spinal cord injury have sublesional microvascular endothelial dysfunction, as indicated by a blunted cutaneous perfusion response to acetylcholine iontophoresis, and the presence of insulin resistance has a further confounding effect on endothelium-mediated changes to cutaneous perfusion in the lower extremities. Endothelium-mediated mechanisms that regulate skin blood flow might play an integral role in optimizing skin perfusion in vascular beds with sympathetic nervous system vasomotor impairment, such as in spinal cord injury (SCI). Insulin is a vasoactive hormone and second messenger of nitric oxide that facilitates endothelium-mediated dilatation. The effects of insulin resistance (IR) on sublesional cutaneous perfusion responses to insulin provocation have yet to be described in persons with SCI. Persons with SCI and an able-bodied (AB) cohort were divided into subgroups based upon fasting plasma insulin concentration cut-offs for IR (≥13.13 mIU ml-1 ) or insulin sensitivity (IS; <13.13 mIU ml-1 ), as follows: AB, IS (ABIS, n = 21); SCI, IS (SCIS, n = 21); AB, IR (ABIR, n = 9); and SCI, IR (SCIR, n = 11). Laser Doppler flowmetry characterized peak blood perfusion unit (BPU) responses (percentage change from baseline) to insulin, acetylcholine or placebo iontophoresis in the lower extremities; BPU responses were log10 transformed to facilitate comparisons, and the net insulin response (NetIns) BPU response was calculated (insulin minus placebo BPU response). The NetIns was significantly greater in both IS groups compared with their corresponding IR group. The acetylcholine-mediated BPU responses in the SCI subgroups were significantly lower than those in the ABIS group. The proportional BPU responses of NetIns to acetylcholine in the IS cohorts (i.e. ABIS and SCIS) were significantly greater (P < 0.05) than that of each IR subgroup. The presence of IR has a confounding effect on sublesional microvascular endothelium-mediated cutaneous perfusion responses to provocation. Preservation of endothelial sensitivity to its agonists appears to be an important modifiable risk factor to optimize cutaneous perfusion in the lower extremities of persons with SCI.

MRI analysis and clinical significance of lower extremity muscle cross-sectional area after spinal cord injury

Shortly after spinal cord injury (SCI), the musculoskeletal system undergoes detrimental changes in size and composition, predominantly below the level of injury. The loss of muscle size and strength, along with increased immobility, predisposes persons with SCI to rapid and severe loss in bone mineral density and other health related consequences. Previous studies have highlighted the significance of measuring thigh muscle cross-sectional area, however, measuring the size and composition of muscles of the lower leg may provide insights on how to decrease the risk of various comorbidities. The purpose of the current review was to summarize the methodological approach to manually trace and measure the muscles of the lower leg in individuals with SCI, using magnetic resonance imaging. We also intend to highlight the significance of analyzing lower leg muscle cross-sectional area and its relationship to musculoskeletal and vascular systems in persons with SCI.

Activity-Based Restorative Therapies after Spinal Cord Injury: Inter-institutional conceptions and perceptions

This manuscript is a review of the theoretical and clinical concepts provided during an inter-institutional training program on Activity-Based Restorative Therapies (ABRT) and the perceptions of those in attendance. ABRT is a relatively recent high volume and intensity approach toward the restoration of neurological deficits and decreasing the risk of secondary conditions associated with paralysis after spinal cord injury (SCI). ABRT is guided by the principle of neuroplasticity and the belief that even those with chronic SCI can benefit from repeated activation of the spinal cord pathways located both above and below the level of injury. ABRT can be defined as repetitive-task specific training using weight-bearing and external facilitation of neuromuscular activation. The five key components of ABRT are weight-bearing activities, functional electrical stimulation, task-specific practice, massed practice and locomotor training which includes body weight supported treadmill walking and water treadmill training. The various components of ABRT have been shown to improve functional mobility, and reverse negative body composition changes after SCI leading to the reduction of cardiovascular and other metabolic disease risk factors. The consensus of those who received the ABRT training was that ABRT has much potential for enhancement of recovery of those with SCI. Although various institutions have their own strengths and challenges, each institution was able to initiate a modified ABRT program.

Functional electrical stimulation: cardiorespiratory adaptations and applications for training in paraplegia

Regular exercise can be broadly beneficial to health and quality of life in humans with spinal cord injury (SCI). However, exercises must meet certain criteria, such as the intensity and muscle mass involved, to induce significant benefits. SCI patients can have difficulty achieving these exercise requirements since the paralysed muscles cannot contribute to overall oxygen consumption. One solution is functional electrical stimulation (FES) and, more importantly, hybrid training that combines volitional arm and electrically controlled contractions of the lower limb muscles. However, it might be rather complicated for therapists to use FES because of the wide variety of protocols that can be employed, such as stimulation parameters or movements induced. Moreover, although the short-term physiological and psychological responses during different types of FES exercises have been extensively reported, there are fewer data regarding the long-term effects of FES. Therefore, the purpose of this brief review is to provide a critical appraisal and synthesis of the literature on the use of FES for exercise in paraplegic individuals. After a short introduction underlying the importance of exercise for SCI patients, the main applications and effects of FES are reviewed and discussed. Major findings reveal an increased physiological demand during FES hybrid exercises as compared with arms only exercises. In addition, when repeated within a training period, FES exercises showed beneficial effects on muscle characteristics, force output, exercise capacity, bone mineral density and cardiovascular parameters. In conclusion, there appears to be promising evidence of beneficial effects of FES training, and particularly FES hybrid training, for paraplegic individuals.

Metabolic rate and cardiorespiratory response during hybrid cycling versus handcycling at equal subjective exercise intensity levels in people with spinal cord injury

OBJECTIVE

To compare the metabolic rate and cardiorespiratory response during hybrid cycling versus handcycling at equal subjective exercise intensity levels in people with spinal cord injury (SCI).

DESIGN

Cross-sectional study.

SETTING

Amsterdam Rehabilitation Research Centre | Reade, Amsterdam, The Netherlands.

METHODS

On separate days, nine individuals with a motor complete paraplegia or tetraplegia (eight men, age 40 ± 13 years, time since injury 12 ± 10 years) performed 5-minute bouts of hybrid cycling (day 1) and handcycling (day 2) at moderate (level 3 on a 10-point rating of perceived exertion (RPE) scale) and vigorous (RPE level 6) subjective exercise intensity, while respiratory gas exchange was measured by open-circuit spirometry and heart rate was monitored using radiotelemetry.

OUTCOME MEASURES

Metabolic rate (calculated with the Weir equation) and cardiorespiratory response (heart rate, oxygen pulse, and ventilation).

RESULTS

Overall, the metabolic rate during hybrid cycling was 3.4 kJ (16%) higher (P = 0.006) than during handcycling. Furthermore, compared with handcycling, the overall heart rate and ventilation during hybrid cycling was 11 bpm (11%) and 5.3 l/minute (18%) higher (P = 0.004 and 0.024), respectively, while the oxygen pulse was the same (P = 0.26).

CONCLUSION

Hybrid cycling induces a higher metabolic rate and cardiorespiratory response at equal RPE levels than handcycling, suggesting that hybrid cycling is more suitable for fighting obesity and increasing cardiorespiratory fitness in individuals with SCI.

Passive leg movement-induced hyperaemia with a spinal cord lesion: evidence of preserved vascular function

A spinal cord injury (SCI) clearly results in greater cardiovascular risk; however, accompanying changes in peripheral vascular structure below the lesion mean that the real impact of a SCI on vascular function is unclear.

AIM

Therefore, utilizing passive leg movement-induced (PLM) hyperaemia, an index of nitric oxide (NO)-dependent vascular function and the central hemodynamic response to this intervention, we studied eight individuals with a SCI and eight age-matched controls (CTRL).

METHODS

Specifically, we assessed heart rate (HR), stroke volume (SV), cardiac output (CO), mean arterial pressure (MAP), leg blood flow (LBF) and thigh composition.

RESULTS

In CTRL, passive movement transiently decreased MAP and increased HR and CO from baseline by 2.5 ± 1 mmHg, 7 ± 2 bpm and 0.5 ± 0.1 L min(-1) respectively. In SCI, HR and CO responses were unidentifiable. LBF increased to a greater extent in CTRL (515 ± 41 ∆mL min(-1)) compared with SCI, (126 ± 25 ∆mL min(-1)) (P < 0.05). There was a strong relationship between ∆LBF and thigh muscle volume (r = 0.95). After normalizing ∆LBF for this strong relationship (∆LBF/muscle volume), there was evidence of preserved vascular function in SCI (CTRL: 120 ± 9; SCI 104 ± 11 mL min(-1) L(-1)). A comparison of ∆LBF in the passively moved and stationary leg, to partition the contribution of the blood flow response, implied that 35% of the hyperaemia resulted from cardioacceleration in the CTRL, whereas all the hyperaemia appeared peripheral in origin in the SCI.

CONCLUSION

Thus, utilizing PLM-induced hyperaemia as marker of vascular function, it is evident that peripheral vascular impairment is not an obligatory accompaniment to a SCI.

Exercise pressor reflex function following acute hemi-section of the spinal cord in cats

Cardiovascular disease is a leading cause of morbidity and mortality in patients post spinal cord injury (SCI). The prescription of exercise as a therapeutic modality for disease prevention in this population is promising. It is logical to suggest that the sooner an exercise program can begin the more benefit the patient will receive from the therapy. However, the time point after injury at which the requisite circulatory responses needed to support exercise are viable remains largely unknown. The skeletal muscle exercise pressor reflex (EPR) significantly contributes to cardiovascular control during exercise in healthy individuals. Experiments in patients with a chronic lateral hemi-section of the spinal cord (Brown-Séquard syndrome) suggest that the EPR, although blunted, is operational when examined months to years post injury. However, whether this critically important reflex remains functional immediately after lateral SCI or, in contrast, experiences a period of reduced capacity due to spinal shock has not been established. This study was designed to assess EPR function after acute lateral transection of the spinal cord. The EPR was selectively activated in seven decerebrate cats via electrically stimulated static contraction of the triceps surae muscles of each hindlimb before and after lateral hemi-section of the T₁₃–L₂ region of the spinal cord. Compared to responses prior to injury, increases in mean arterial pressure (MAP) were significantly decreased when contracting the hindlimb either ipsilateral to the lesion (MAP = 17 ± 3 mmHg before and 9 ± 2 mmHg after) or contralateral to the lesion (MAP = 22 ± 5 mmHg before and 12 ± 4 mmHg after). The heart rate (HR) response to stimulation of the EPR was largely unaffected by induction of acute SCI. The findings suggest that the EPR maintains the ability to importantly contribute to cardiovascular regulation during exercise immediately following a Brown-Séquard-like injury.

Active LifestyLe Rehabilitation interventions in aging spinal cord injury (ALLRISC): a multicentre research program

BACKGROUND

With today's specialized medical care, life expectancy of persons with a spinal cord injury (SCI) has considerably improved. With increasing age and time since injury, many individuals with SCI, however, show a serious inactive lifestyle, associated with deconditioning and secondary health conditions (SHCs) (e.g. pressure sores, urinary and respiratory tract infections, osteoporosis, upper-extremity pain, obesity, diabetes, cardiovascular disease) and resulting in reduced participation and quality of life (QoL). Avoiding this downward spiral, is crucial.

OBJECTIVES

To understand possible deconditioning and SHCs in persons aging with a SCI in the context of active lifestyle, fitness, participation and QoL and to examine interventions that enhance active lifestyle, fitness, participation and QoL and help prevent some of the SHCs.

METHODS

A multicentre multidisciplinary research program (Active LifestyLe Rehabilitation Interventions in aging Spinal Cord injury, ALLRISC) in the setting of the long-standing Dutch SCI-rehabilitation clinical research network.

RESULTS

ALLRISC is a four-study research program addressing inactive lifestyle, deconditioning, and SHCs and their associations in people aging with SCI. The program consists of a cross-sectional study (n = 300) and three randomized clinical trials. All studies share a focus on fitness, active lifestyle, SHCs and deconditioning and outcome measures on these and other (participation, QoL) domains. It is hypothesized that a self-management program, low-intensity wheelchair exercise and hybrid functional electrical stimulation-supported leg and handcycling are effective interventions to enhance active life style and fitness, help to prevent some of the important SHCs in chronic SCI and improve participation and QoL.

CONCLUSION

ALLRISC aims to provide evidence-based preventive components of a rehabilitation aftercare system that preserves functioning in aging persons with SCI.

Blood vessel remodeling and physical inactivity in humans

Physical inactivity is associated with an increase in cardiovascular risk that cannot be fully explained by traditional or novel risk factors. Inactivity is also associated with changes in hemodynamic stimuli, which exert direct effects on the vasculature leading to remodeling and a proatherogenic phenotype. In this review, we synthesize and summarize in vivo evidence relating to the impact of local and systemic models of physical inactivity on conduit arteries, resistance vessels, and the microcirculation in humans. Taken together, the literature suggests that a rapid inward structural remodeling of vessels occurs in response to physical inactivity. The magnitude of this response is dependent on the "dose" of inactivity. Moreover, changes in vascular function are found at resistance and microvessel levels in humans. In conduit arteries, a strong interaction between vascular function and structure is present, which results in conflicting data regarding the impact of inactivity on conduit artery function. While much of the cardioprotective effect of exercise is related to the nitric oxide pathway, deconditioning may primarily be associated with activation of vasoconstrictor pathways. The effects of deconditioning on the vasculature are therefore not simply the opposite of those in response to exercise training. Given the importance of sedentary behavior, future studies should provide further insight into the impact of inactivity on the vasculature and other (novel) markers of vascular health. Moreover, studies should examine the role of (hemodynamic) stimuli that underlie the characteristic vascular adaptations during deconditioning. Our review concludes with some suggestions for future research directions.

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.

Exercise and arterial adaptation in humans: uncoupling localized and systemic effects

Previous studies have established effects of exercise training on arterial wall thickness, remodeling, and function in humans, but the extent to which these changes are locally or systemically mediated is unclear. We examined the brachial arteries of the dominant (D) and nondominant (ND) upper limbs of elite racquet sportsmen and compared them to those of matched healthy inactive controls. Carotid and superficial femoral artery responses were also assessed in both groups. High-resolution duplex ultrasound was used to examine resting diameter, wall thickness, peak diameter, and blood flow. We found larger resting arterial diameter in the preferred arm of the athletes (4.9 ± 0.5 mm) relative to their nonpreferred arm (4.3 ± 0.4 mm, P < 0.05) and both arms of control subjects (D: 4.1 ± 0.4 mm; ND: 4.0 ± 0.4, P < 0.05). Similar limb-specific differences were also evident in brachial artery dilator capacity (5.5 ± 0.5 vs. 4.8 ± 0.4, 4.8 ± 0.6, and 4.8 ± 0.6 mm, respectively; P < 0.05) following glyceryl trinitrate administration and peak blood flow (1,118 ± 326 vs. 732 ± 320, 737 ± 219, and 698 ± 174 ml/min, respectively; P < 0.05) following ischemic handgrip exercise. In contrast, athletes demonstrated consistently lower wall thickness in carotid (509 ± 55 μm), brachial (D: 239 ± 100 μm; ND: 234 ± 133 μm), and femoral (D: 479 ± 38 μm; ND: 479 ± 42 μm) arteries compared with control subjects (carotid: 618 ± 74 μm; brachial D: 516 ± 100 μm; ND: 539 ± 129 μm; femoral D: 634 ± 155 μm; ND: 589 ± 112 μm; all P < 0.05 vs. athletes), with no differences between the limbs of either group. These data suggest that localized effects of exercise are evident in the remodeling of arterial size, whereas arterial wall thickness appears to be affected by systemic factors.

The effects of stimulating lower leg muscles on the mechanical work and metabolic response in functional electrically stimulated pedaling

Functional electrical stimulation (FES) pedaling with the muscles of the upper leg has been shown to provide benefit to spinal cord injured (SCI) individuals. FES pedaling with electrical stimulation timing patterns that minimize the stress-time integral of activated muscles has been shown to increase the work individuals can perform during the exercise compared to existing FES stimulation timing patterns. Activation of the lower leg muscles could further enhance the benefit of FES pedaling by increasing the metabolic response to the exercise. For SCI individuals, the objectives of this study were to experimentally determine whether FES pedaling with the upper and lower leg muscles would affect the work generated and increase the physiological responses compared to pedaling with the upper leg muscles alone. Work, rate of oxygen consumption ·VO₂, and blood lactate data were measured from nine SCI subjects (injury level T4-T12) as they pedaled using upper leg and upper and lower leg muscle groups on repeated trials. The subjects performed 6% more work with the upper and lower legs than with the upper legs alone, but the difference was not significant (p = 0.2433). The average rate of oxygen consumption associated with the upper leg muscles (441 ±231 mL/min) was not significantly different from the corresponding average for the upper and lower legs (473 ±213 mL/min) (p = 0.1176). The blood lactate concentration associated with the upper leg muscles (5.9 ±2.3 mmoles/L) was significantly lower than the corresponding average for the upper and lower legs (6.8 ±2.3 mmoles/L) (p = 0.0049). The results indicate that electrical stimulation timing patterns that incorporate the lower leg muscles do increase the blood lactate concentrations. However, there was not enough evidence to reject the null hypothesis that stimulating the lower leg muscles affected the work accomplished or increased the rate of oxygen consumption. In conclusion, incorporating the lower leg muscles in the exercise does not lead to negative effects and could result in enhanced exercise outcomes in the long term.

Impact of bed rest on conduit artery remodeling: effect of exercise countermeasures

Physical inactivity is a potent stimulus for vascular remodeling, leading to a marked decrease in conduit artery diameter. However, little is known about the impact of physical inactivity on artery wall thickness or wall:lumen ratio or the potential of exercise countermeasures to modify artery wall thickness. The purpose of the study was to examine the impact of 60 days of bed rest, with or without exercise countermeasures, on carotid and superficial femoral artery wall thickness. Eighteen men were assigned to bed rest (second Berlin Bed Rest Study) and randomly allocated to control, resistive exercise, or resistive vibration exercise. Both exercise countermeasures were applied 3 times per week while the subjects were in the supine position on the bed. Sonography was used to examine baseline diameter and wall thickness of the carotid and femoral arteries. Bed rest decreased diameter of the superficial femoral artery (P=0.001) but not the carotid artery (P=0.29). Bed rest induced a significant increase in carotid and superficial femoral artery wall thickness (P=0.007 and 0.03) and wall:lumen ratio (P=0.009 and 0.001). Exercise prevented the increase in wall thickness of the carotid artery. In addition, exercise partly prevented the increased wall:lumen ratio in the superficial femoral artery. In conclusion, 8 weeks of bed rest resulted in approximately 20% increase in conduit artery wall thickness. Exercise countermeasures completely (carotid artery) or partly (superficial femoral artery) abolished the increase in wall thickness. These findings suggest that conduit artery wall thickness, a vascular characteristic associated previously with atherosclerosis, can rapidly adapt to physical inactivity and exercise in humans.

Impact of inactivity and exercise on the vasculature in humans

The effects of inactivity and exercise training on established and novel cardiovascular risk factors are relatively modest and do not account for the impact of inactivity and exercise on vascular risk. We examine evidence that inactivity and exercise have direct effects on both vasculature function and structure in humans. Physical deconditioning is associated with enhanced vasoconstrictor tone and has profound and rapid effects on arterial remodelling in both large and smaller arteries. Evidence for an effect of deconditioning on vasodilator function is less consistent. Studies of the impact of exercise training suggest that both functional and structural remodelling adaptations occur and that the magnitude and time-course of these changes depends upon training duration and intensity and the vessel beds involved. Inactivity and exercise have direct "vascular deconditioning and conditioning" effects which likely modify cardiovascular risk.

Effect of functional electrostimulation on impaired skin vasodilator responses to local heating in spinal cord injury

Spinal cord injury (SCI) induces vascular adaptations below the level of the lesion, such as impaired cutaneous vasodilation. However, the mechanisms underlying these differences are unclear. The aim of this study is to examine arm and leg cutaneous vascular conductance (CVC) responses to local heating in 17 able-bodied controls (39 +/- 13 yr) and 18 SCI subjects (42 +/- 8 yr). SCI subjects were counterbalanced for functional electrostimulation (FES) cycling exercise (SCI-EX, n = 9) or control (SCI-C, n = 9) and reanalyzed after 8 wk. Arm and leg skin blood flow were measured by laser-Doppler flowmetry during local heating (42 degrees C), resulting in an axon-reflex mediated first peak, nadir, and a primarily nitric oxide-dependent plateau phase. Data were expressed as a percentage of maximal CVC (44 degrees C). CVC responses to local heating in the paralyzed leg, but also in the forearm of SCI subjects, were lower than in able-bodied controls (P < 0.05 and 0.01, respectively). The 8-wk intervention did not change forearm and leg CVC responses to local heating in SCI-C and SCI-EX, but increased femoral artery diameter in SCI-EX (P < 0.05). Interestingly, findings in skin microvessels contrast with conduit arteries, where physical (in)activity contributes to adaptations in SCI. The lower CVC responses in the paralyzed legs might suggest a role for inactivity in SCI, but the presence of impaired CVC responses in the normally active forearm suggests other mechanisms. This is supported by a lack of adaptation in skin microcirculation after FES cycle training. This might relate to the less frequent and smaller magnitude of skin blood flow responses to heat stimuli, compared with controls, than physical inactivity per se.

Sympathetic vasomotor control does not explain the change in femoral artery shear rate pattern during arm-crank exercise

During lower limb exercise, blood flow through the resting upper limbs exhibits a change characterized by increased anterograde flow during systole, but also large increases in retrograde diastolic flow. One explanation for the retrograde flow is that increased sympathetic nervous system (SNS) tone and concomitant increased peripheral resistance generate a rebound during diastole. To examine whether the SNS contributes to retrograde flow patterns, we measured femoral artery blood flow during arm-crank exercise in 10 healthy men (31 ± 4 yr) and 10 spinal cord-injured (SCI) subjects who lack sympathetic innervation in the legs (33 ± 5 yr). Before, and every 5 min during 25-min arm-crank exercise at 50% maximal capacity, femoral artery blood flow and peak anterograde and retrograde shear rate were assessed using echo Doppler sonography. Femoral artery baseline blood flow was significantly lower in SCI compared with controls. Exercise increased femoral artery blood flow in both groups (ANOVA, P < 0.05), whereas leg vascular conductance did not change during exercise in either group. Mean shear rate was lower in SCI than in controls ( P < 0.05). Peak anterograde shear rate was higher in SCI than in controls ( P < 0.05), whereas peak retrograde shear rate did not differ between groups. Arm-crank exercise induced an increase in peak anterograde and retrograde shear rate in the femoral artery in controls and SCI subjects ( P < 0.05). This suggests that the SNS is not obligatory to change the flow pattern in inactive regions during exercise. Local mechanisms may play a role in the arm-crank exercise-induced changes in flow pattern in the femoral artery.

Endothelium-dependent and -independent vasodilation of the superficial femoral artery in spinal cord-injured subjects

Extreme inactivity of the legs in spinal cord-injured (SCI) individuals does not result in an impairment of the superficial femoral artery flow-mediated dilation (FMD). To gain insight into the underlying mechanism, the present study examined nitric oxide (NO) responsiveness of vascular smooth muscles in controls and SCI subjects. In eight healthy men (34 +/- 13 yr) and six SCI subjects (37 +/- 10 yr), superficial femoral artery FMD response was assessed by echo Doppler. Subsequently, infusion of incremental dosages of sodium nitroprusside (SNP) was used to assess NO responsiveness. Peak diameter was examined on a second day after 13 min of arterial occlusion in combination with sublingual administration of nitroglycerine. Resting and peak superficial femoral artery diameter in SCI subjects were smaller than in controls (P < 0.001). The FMD response in controls (4.2 +/- 0.9%) was lower than in SCI subjects (8.2 +/- 0.9%, P < 0.001), but not after correcting for area under the curve for shear rate (P = 0.35). When expressed as relative change from baseline, SCI subjects demonstrate a significantly larger diameter increase compared with controls at each dose of SNP. However, when expressed as a relative increase within the range of diameter changes [baseline (0%) - peak diameter (100%)], both groups demonstrate similar changes in response to SNP. Changes in diameter during SNP infusion and FMD response are larger in SCI subjects compared with controls. When these results are corrected, superficial femoral artery FMD and NO sensitivity in SCI subjects are not different from those in controls. This illustrates the importance of appropriate data presentation and suggests that, subsequent to structural inward remodeling of conduit arteries as a consequence of extreme physical inactivity, arterial function is normalized.

Flow-mediated dilatation in the superficial femoral artery is nitric oxide mediated in humans

Flow-mediated dilatation (FMD) of the brachial and radial arteries is an important research tool for assessment of endothelial function in vivo, and is nitric oxide (NO) dependent. The leg skeletal muscle vascular bed is an important territory for studies in exercise physiology. However, the role of endothelial NO in the FMD response of lower limb arteries has never been investigated. The purpose of this study was to examine the contribution of NO to FMD in the superficial femoral artery in healthy subjects. Since physical inactivity may affect endothelial function, and therefore NO availability, spinal cord-injured (SCI) individuals were included as a model of extreme deconditioning. In eight healthy men (34 +/- 13 years) and six SCI individuals (37 +/- 10 years), the 5 min FMD response in the superficial femoral artery was assessed by echo-Doppler, both during infusion of saline and during infusion of the NO synthase blocker N(G)-monomethyl-L-arginine (L-NMMA). In a subset of the controls (n = 6), the 10 min FMD response was also examined using the same procedure. The 5 min FMD response in controls (4.2 +/- 0.3%) was significantly diminished during L-NMMA infusion (1.0 +/- 0.2%, P < 0.001). In SCI, L-NMMA also significantly decreased the FMD response (from 8.2 +/- 0.4% during saline to 2.4 +/- 0.5% during L-NMMA infusion). The hyperaemic flow response during the first 45 s after cuff deflation was lower in both groups during infusion of L-NMMA, but the effect of L-NMMA on FMD persisted in both groups after correction for the shear stress stimulus. The 10 min FMD was not affected by L-NMMA (saline: 5.4 +/- 1.6%, L-NMMA: 5.6 +/- 1.5%). Superficial femoral artery FMD in response to distal arterial occlusion for a period of 5 min is predominantly mediated by NO in healthy men and in the extremely deconditioned legs of SCI individuals.

Vascular adaptations to 8-week cycling training in older men

AIM

Because age-related changes in the large conduit arteries (increased wall thickness, and attenuated arterial compliance and endothelial function) are associated with cardiovascular pathology, prevention is of paramount importance. The effects of endurance training (i.e. walking or cycling) in older humans are assessed in cross-sectional studies, examining the brachial and carotid arteries (supplying non-trained areas). The purpose of this study was to assess the effects of 8-week endurance training in older men on conduit artery characteristics in the trained and non-trained vascular beds.

METHODS

In eight healthy sedentary older men (70 +/- 3 years), characteristics of the large conduit arteries [common femoral (CFA), superficial femoral (SFA), carotid (CA), and brachial artery (BA)] were measured before and after 8-week cycling training. Functional [arterial compliance and flow-mediated dilation (FMD)] and structural (diameter and intima-media thickness) conduit artery properties were measured using echo-Doppler. Peak blood flow, representing structural peripheral adaptations, was measured using venous occlusion plethysmography.

RESULTS

After training, peak leg blood flow was increased (P < 0.01) and baseline diameter and flow were increased in the CFA (P < 0.05). Cycling training enhanced arterial compliance of the SFA (P = 0.03), but did not affect the FMD (P = 0.32) or the intima-media thickness of the SFA. Exercise training did not alter characteristics of the BA or CA.

CONCLUSION

Eight weeks of endurance training in older men altered functional and structural characteristics of the lower extremity vasculature, whereas no changes are reported for the conduit arteries in the non-trained areas (BA or in the CA).

Effects of training programs for spinal cord injury

INTRODUCTION

Endurance exercise training programs in patients with spinal cord injury (SCI) were largely studied to determine different types of adaptations. The aim of specific rehabilitation is to obtain maximal gains in quality-of-life (QoL) after SCI.

OBJECTIVE

To review the literature on the efficiency of training programs for SCI.

METHODS

We searched the MEDline database with the keywords SCI, paraplegia and quadriplegia and synonyms, then combined them with one of the following terms: rehabilitation, training, exercise conditioning, physical fitness, exercise prescription, adaptation, effect, or benefit. We found 65 articles related to the physiological and psychological effects of training programmes on patients with SCI.

RESULTS AND DISCUSSION

Training programs after SCI offer reconditioning cardiorespiratory, cardiovascular, cardiac, metabolic, bone, biomechanical, muscle adaptation, and QoL benefits. Reconditioning training increases VO2 max, reverses leg vascular resistance in the paralyzed legs and has possible cardiac and neural adaptations, favorable catecholamine responses and effects on platelet aggregation. Reconditioning can also modify lipid profile, reduce risk for cardiovascular diseases, prevent osteoporosis and increase maximal upper-extremity muscle strength, sprint power output and maximal power output. This effect allows for considerable improvement in mechanical efficiency and wheelchair propulsion technique.

CONCLUSIONS

Reconditioning training programs after SCI have a direct impact on function and QoL, permitting participation in physical activities in addition to daily living activities in subjects with SCI.