Increasing blood flow before exercise in spinal cord-injured individuals does not alter muscle fatigue

Cardiorespiratory and Muscle Metabolic Responses During Conventional Versus Motion Sensor-Assisted Strategies for Functional Electrical Stimulation Standing After Spinal Cord Injury

This is a case series study with the objective of comparing two motion sensor automated strategies to avert knee buckle during functional electrical stimulation (FES)-standing against a conventional hand-controlled (HC) FES approach. The research was conducted in a clinical exercise laboratory gymnasium at the University of Sydney, Australia. The automated strategies, Aut-A and Aut-B, applied fixed and variable changes of neurostimulation, respectively, in quadriceps amplitude to precisely control knee extension during standing. HC was an "on-demand" increase of stimulation amplitude to maintain stance. Finally, maximal FES amplitude (MA) was used as a control condition, whereby knee buckle was prevented by maximal isometric muscle recruitment. Four AIS-A paraplegics undertook 4 days of testing each, and each assessment day comprised three FES standing trials using the same strategy. Cardiorespiratory responses were recorded, and quadriceps muscle oxygenation was quantified using near-infrared spectroscopy. For all subjects, the longest standing times were observed during Aut-A, followed by Aut-B, and then HC and MA. The standing times of the automated strategies were superior to HC by 9-64%. Apart from a lower heart rates during standing (P = 0.034), the automation of knee extension did not promote different cardiorespiratory responses compared with HC. The standing times during MA were significantly shorter than during the automated or "on-demand" strategies (by 80-250%). In fact, the higher isometric-evoked quadriceps contraction during MA resulted in a greater oxygen demand (P < 0.0001) and wider arteriovenous oxygen extraction (P = 0.08) when compared with the other strategies. In conclusion, even though increased standing times were demonstrated using automated control of knee extension, physiological benefits compared with HC were not evident.

Skeletal muscle fatigue

Skeletal muscle fatigue is defined as the fall of force or power in response to contractile activity. Both the mechanisms of fatigue and the modes used to elicit it vary tremendously. Conceptual and technological advances allow the examination of fatigue from the level of the single molecule to the intact organism. Evaluation of muscle fatigue in a wide range of disease states builds on our understanding of basic function by revealing the sources of dysfunction in response to disease.

Muscle after spinal cord injury

The morphological and contractile changes of muscles below the level of the lesion after spinal cord injury (SCI) are dramatic. In humans with SCI, a fiber-type transformation away from type I begins 4-7 months post-SCI and reaches a new steady state with predominantly fast glycolytic IIX fibers years after the injury. There is a progressive drop in the proportion of slow myosin heavy chain (MHC) isoform fibers and a rise in the proportion of fibers that coexpress both the fast and slow MHC isoforms. The oxidative enzymatic activity starts to decline after the first few months post-SCI. Muscles from individuals with chronic SCI show less resistance to fatigue, and the speed-related contractile properties change, becoming faster. These findings are also present in animals. Future studies should longitudinally examine changes in muscles from early SCI until steady state is reached in order to determine optimal training protocols for maintaining skeletal muscle after paralysis.

Effects of Graduated Compression Stockings on Cardiovascular and Metabolic Responses to Exercise and Exercise Recovery in Persons With Spinal Cord Injury

OBJECTIVE

To investigate whether reporting blood redistribution by means of graduated elastic stockings affects exercise and postexercise responses in people with spinal cord injury (SCI).

DESIGN

Crossover trial.

SETTING

Physical medicine and rehabilitation department in France.

PARTICIPANTS

Fourteen men with traumatic SCI, grouped according to their level of injury.

INTERVENTIONS

Subjects performed 2 maximal wheelchair exercise tests 1 week apart, in random order and under a counter-balanced design. One test was done with and the other without graduated elastic stockings (21 mmHg).

MAIN OUTCOME MEASURES

Blood lactate, blood pressure, heart rate, maximal power output, and oxygen consumption (Vo2).

RESULTS

Postexercise venous lactate concentration was reduced in SCI subjects with lesion levels below T6 while wearing graduated elastic stockings during both exercise and recovery (10.9+/-3.9 mmol/L vs 12.5+/-4.6 mmol/L, P<.05). There were no significant differences in submaximal and maximal values (heart rate, Vo2, power output) between subjects tested with and without graduated elastic stockings.

CONCLUSIONS

Wearing elastic stockings affects postexercise responses by decreasing lactate concentration in well-trained, low-level paraplegic patients after a maximal exercise. The relatively low pressure generated by the stockings may not, however, influence the venous system enough to produce improved performance and cardiovascular responses.

Muscle oxygenation during prolonged electrical stimulation-evoked cycling in paraplegics

This study investigated cardiorespiratory responses and muscle oxygenation during prolonged electrical stimulation (ES)-evoked leg cycling in individuals with paraplegia (PARA). Four PARA and 6 able-bodied (AB) persons participated in this study. Subjects performed 10 min of passive cycling and 40 min of active cycling (PARA, ES cycling; AB, voluntary cycling) at workloads selected to elicit an equivalent oxygen uptake between groups. Cycling power output, cardiorespiratory responses, mechanical efficiency, and quadriceps muscle oxygenation (measured with near-infrared spectroscopy) were measured over the duration of the exercise. Oxygen uptake was similar in both groups during active cycling (PARA, 737 ± 177 mL·min–1; AB, 840 ± 90 mL·min–1). The cycling power output for PARA individuals commenced at 8.8 W, but varied considerably over 40 min. PARA individuals demonstrated markedly lower gross mechanical efficiency (~1.3%) during ES cycling compared with AB individuals performing voluntary exercise (~12.6%). During ES cycling, muscle oxygen saturation (SO2) decreased to approximately 72 ± 19%, whereas SO2 during volitional cycling was unaltered from resting levels. Muscle oxygenated haemoglobin initially decreased (–23%) during ES cycling, but returned to resting levels after 10 min. Deoxygenated haemoglobin initially rose during the first 5 min of ES cycling, and remained elevated by 28% thereafter. Upon cessation of ES cycling, lower-limb muscle oxygenation increased (+93%), suggesting reactive hyperaemia in PARA individuals after such exercise. During ES cycling, muscle oxygenation followed a different pattern to that observed in AB individuals performing voluntary cycling at an equivalent VO2. Equilibrium between oxygen demand and oxygen delivery was reached during prolonged ES cycling, despite the lack of neural adjustments of leg vasculature in the paralyzed lower limbs.

La fatigue du blessé médullaire

OBJECTIVES

To identify variables increasing fatigue following spinal cord injury (SCI) and their functional consequences.

METHODS

A search of the Medline and Reedoc databases with the keywords SCI, fatigue, intrinsic muscular fatigue, chronic fatigue, aging, training, electrostimulation, quality of life and the same words in French.

RESULTS

Two kinds of fatigue are identified following SCI. Intrinsic fatigue in muscles totally or partially paralysed at the level of or below the spinal cord lesion; this peripheral fatigue is due to denervation, total or partial loss of motoneurons, or histological and metabolical changes in muscle; it is well-defined by electrophysiological technology; spasticity and spasms have little influence on its development; it is reversible in part with long term electrostimulation, but at this time, electroneuroprosthetic techniques do not reduce the excessive energetic cost to stand up and walk. Chronic fatigue appears in the long term following SCI; it is linked with aging, physiological, and psychological deconditioning; some data point to chronic fatigue after SCI similar to post-polio syndrome and chronic fatigue syndrome, which may explain the central nature of the fatigue; training programs could be useful in delaying this chronic fatigue and as a consequence, increasing the latent quality of life.

CONCLUSION

Muscular intrinsic fatigue after SCI is always of a peripherical nature in muscles partially or totally paralysed. Chronic fatigue during aging greatly decreases quality of life. Both intrinsic and chronic fatigue could be anticipated by electrostimulation technique on the one hand and long term training on the other.

Electrically stimulated resistance training in SCI individuals increases muscle fatigue resistance but not femoral artery size or blood flow

STUDY DESIGN

Longitudinal.

OBJECTIVES

The purpose of this study was to evaluate the effect of lower extremity resistance training on quadriceps fatigability, femoral artery diameter, and femoral artery blood flow.

SETTING

Academic Institution.

METHODS

Five male chronic spinal cord injury (SCI) individuals (American Spinal Injury Association (ASIA): A complete; C5-T10; 36+/-5 years old) completed 18 weeks of home-based neuromuscular electrical stimulation (NMES) resistance training. Subjects trained the quadriceps muscle group twice a week with four sets of 10 dynamic knee extensions against resistance while in a seated position. All measurements were made before training and after 8, 12, and 18 weeks of training. Ultrasound was used to measure femoral artery diameter and blood flow. Blood flow was measured before and after 5 and 10 min of distal cuff occlusion, and during a 4-min isometric electrical stimulation fatigue protocol.

RESULTS

Training resulted in significant increases in weight lifted and muscle mass, as well as a 60% reduction in muscle fatigue (P = 0.001). However, femoral arterial diameter did not increase. The range was 0.44+/-0.03 to 0.46+/-0.05 cm over the four time points (P = 0.70). Resting, reactive hyperemic, and exercise blood flow did not appear to change with training.

CONCLUSION

NMES resistance training improved muscle size and fatigue despite an absence of response in the supplying vasculature. These results suggest that the decreases in arterial caliber and blood flow seen with SCI are not tightly linked to muscle mass and fatigue resistance. In addition, muscle fatigue in SCI patients can be improved without increases in arterial diameter or blood flow capacity.

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

PURPOSE

Studies investigating vascular adaptations in non-exercised areas during whole body exercise training show conflicting results. Individuals with spinal cord injury (SCI) provide a unique model to examine vascular adaptations in active tissue vs adjacent inactive areas. The purpose of this study is to assess the effects of 4 wk of voluntary arm and electrically stimulated leg exercise (8-12 sessions) on vascular adaptations in active areas (thigh and arms) and inactive areas (calf).

METHODS

Vascular characteristics were measured by plethysmography (blood flow and vascular resistance) and echo Doppler (diameter and flow-mediated dilation (FMD) after 13 min of ischemia).

RESULTS

After training, increased thigh baseline and peak blood flow, decreased thigh baseline vascular resistance, and increased diameter of the common femoral artery were found in the stimulated thigh tissue. Forearm and calf arterial parameters and FMD, in both superficial femoral artery and brachial artery, did not change. The lack of activity in the calf and concomitant insufficient elevation of blood flow during training, and the high initial training status of the arms are suggested to explain the absence of vascular adaptations in these areas.

CONCLUSION

The presence of vascular adaptations after only 4 wk of FES cycling indicates that adaptations occur in an early phase. In addition, 4 wk of whole body exercise training in SCI individuals leads to vascular adaptations in the exercised tissues (thigh) but not in nonstimulated passive tissue (calf).