Bertram N. Ezenwa

Musculoskeletal responses of spinal cord injured individuals to functional neuromuscular stimulation-induced knee extension exercise training.

This study was conducted to evaluate a newly designed functional neuromuscular stimulation (FNS)-induced knee extension (KE) exercise system that incorporates the most desired features of previously described systems by determining the musculoskeletal responses of spinal cord injured (SCI) individuals to training. A specially designed chair and electrical stimulator were fabricated for FNS-induced KE resistance exercise. Surface electrodes were placed over motor points of the quadriceps muscles, and KE was alternated between legs at an average rate of 6 KE/min/leg. KE testing protocols were developed for pre- and post-training evaluations of performance, and 12 SCI subjects exercise-trained up to three times per week for 36 sessions using a progressive resistance load at ankle level. Pre- and post-training evaluation data were statistically compared using a 0.05 level for significance. Quadriceps muscle performance (strength x repetitions) improved for both legs in all subjects as indicated by significant increases in load resistance and repetitions over the 36-session training period (right leg mean = 1156.0 versus 1624.8 kg.reps, left leg mean = 1127.3 versus 1721.1 kg.reps). In addition, knee range of motion significantly increased (right leg mean = 134 versus 146 degrees, left leg mean = 133 versus 144 degrees). Thigh skinfold, thigh girth, body weight and bone density were not significantly changed. The lack of decrease in bone density in some subjects suggests that the training may retard the rate of bone loss which typically occurs with SCI. No injuries or problems were encountered during testing and training.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiologic responses of paraplegics and quadriplegics to passive and active leg cycle ergometry.

The purposes of this study were three-fold: (a) to determine acute physiologic responses of spinal cord injured (SCI) subjects to peak levels of leg cycle ergometry utilizing functional neuromuscular stimulation (FNS) of paralyzed leg muscles, (b) to determine the relative contributions of passive and active components of FNS cycling to the peak physiologic responses, and (c) to compare these physiologic responses between persons who have quadriplegia and those who have paraplegia. Thirty SCI subjects (17 quadriplegics and 13 paraplegics) performed a discontinuous graded FNS exercise test from rest to fatigue on an ERGYS 1 ergometer. Steady-state physiologic responses were determined by open-circuit spirometry, impedance cardiography with ECG, and auscultation. In the combined statistics of both groups, it was noted that peak FNS cycling significantly increased (from rest levels) mean oxygen uptake by 255%, arteriovenous O2 difference VO2 and VE, Q and a-vO2 and VCO by 69%, and stroke volume by 45%, while total peripheral vascular resistance decreased by 43%. Mean peak power output for paraplegics (15 W) was significantly higher than for quadriplegics (9 W), eliciting higher peak levels of pulmonary ventilation and sympathetically mediated hemodynamic responses such as cardiac output, heart rate, and systolic and diastolic arterial blood pressure. Passive cycling without FNS produced no statistically significant increases in physiologic responses above the resting level in either group.

Acute hemodynamic responses of spinal cord injured individuals to functional neuromuscular stimulation-induced knee extension exercise

The purpose of this study was to determine and compare acute hemodynamic responses of spinal cord injured (SCI) quadriplegics (quads), and paraplegics (paras) during a graded-intensity knee extension (KE) exercise test utilizing functional neuromuscular stimulation (FNS) of paralyzed quadriceps muscles. Seven quads and seven paras (N = 14) performed a series of 4-minute stages of bilateral alternating FNS-KE exercise (approximately zero to 70 degree range of motion at the knee and 6 KE/min/leg) at ankle loads of 0, 5, 10, and 15 kg/leg. Physiologic responses were determined with open-circuit spirometry, impedance cardiography, and auscultation. Comparing rest with peak FNS-KE for both groups combined, FNS-KE exercise elicited significant (p less than 0.05) increases in oxygen uptake (130 percent), pulmonary ventilation (120 percent), respiratory exchange ratio (37 percent), arteriovenous oxygen difference (57 percent), cardiac output (32 percent), stroke volume (41 percent), mean arterial pressure (18 percent), and rate-pressure product (23 percent). Heart rate increased significantly by 11 percent from the 5- to the 15-kg/leg stages. Physiologic responses of quads and paras were very similar, except for lower (p less than 0.05) arterial pressures, rate-pressure product, and peripheral vascular resistance in quads. This graded FNS-KE exercise up to the 15-kg/leg load induced relatively small but appropriate increases in aerobic metabolism and cardiopulmonary responses that appear to be safe and easily tolerated by quads and paras. Arterial pressure needs to be monitored carefully in quads to prevent excessive hypertension or hypotension. Although FNS-KE exercise has been shown to elicit peripheral adaptations to improve muscle strength and endurance, it is probably not an effective central cardiovascular training tool for all but the least fit SCI individuals. This information is important for understanding the effects of FNS use during more complex activities such as cycling and ambulation.

Efficiency of FNS leg cycle ergometry

The efficiency of electrically induced leg cycle ergometry performed by spinal-cord-injured (SCI) subjects was compared to voluntary leg cycle ergometry performed by able-bodied (AB) subjects at power output (PO) levels of 6-42 W. Twenty SCI (nine quadriplegics and 11 paraplegics) and twenty AB subjects exercised on a leg cycle ergometer. SCI subjects received functional neuromuscular stimulation (FNS) of paralyzed leg musculature, while AB subjects pedaled voluntarily. Subjects performed a discontinuous, progressive intensity exercise test with 6-W (for SCI) or 12-W (for AB) PO increments between stages. Each exercise bout was 5 min in duration and was followed by a 5-min rest period. Steady-rate oxygen uptake (VO/sub 2/) and respiratory exchange ratio (RER) values were determined by open-circuit spirometry during the final minute of each stage. Gross, net, work, and data efficiencies were calculated for each PO. These efficiencies ranged from 2 to 14% for FNS cycling by SCI subjects and from 4 to 34% during voluntary cycling by AB subjects. At most POs, efficiencies for FNS cycling were significantly lower (by approximately one-half) than those for voluntary cycling. Despite the apparent energy-wastefulness or inefficiency of FNS leg cycle ergometry, the relatively high metabolic rates elicited by the exercise may be advantageous to SCI individuals seeking aerobic (cardiopulmonary) training effects.<<ETX>>

Multiple vibration displacements at multiple vibration frequencies stress impact on human femur computational analysis

Whole-body vibration training using single-frequency methods has been reported to improve bone mineral density. However, the intensities can exceed safe levels and have drawn unfavorable comments from subjects. In a previous article, whole-body vibration training using multiple vibration displacements at multiple vibration frequencies (MVDMVF) was reported. This article presents the computational simulation evaluation of stress dispersion on a femur with and without the MVDMVF input. A model of bone femur was developed from a computed tomography image of the lower limb with Mimics software from Materialise (Plymouth, Michigan). We analyzed the mesh model in COMSOL Multiphysics (COMSOL, Inc; Burlington, Massachusetts) with and without MVDMVF input, with constraints and load applied to the femur model. We compared the results with published joint stresses during walking, jogging, and stair-climbing and descending and with standard vibration exposure limits. Results showed stress levels on the femur are significantly higher with MVDMVF input than without. The stress levels were within the published levels during walking and stair-climbing and descending but below the stress levels during jogging. Our computational results demonstrate that MVDMVF generates stress level equivalent to the level during walking and stair-climbing. This evidence suggests that MVDMVF is safe for prolonged use in subjects with osteoporosis who ambulate independently.

Hemodynamic responses of quadriplegics to maximal arm-cranking and FNS leg cycling exercise

The purpose of this study was to compare maximal central hemodynamic responses of spinal-cord-injured quadriplegic subjects to voluntary arm-crank exercise (ACE) and to electrically induced leg cycling exercise. Six C6-C7 quadriplegic men performed graded exercises to maximum with both an arm-crank ergometer and a leg-cycle ergometer, utilizing functional neuromuscular stimulation (FNS) of paralyzed leg musculature. Both exercise modes produced a V-dot O/sub 2/ peak of approximately 1 l/min, with peak power outputs for the arm and leg exercises of 38 and 11 W, respectively. Compared with voluntary ACE, FNS cycling elicited a significantly higher mean cardiac output, stroke volume, and mean arterial blood pressure, and significantly lower mean heart rate and rate-pressure product. While maximal FNS cycling is mechanically less efficient than ACE, it appears to produce a more desirable hemodynamic response pattern, i.e. greater venous return and cardiac volume-load with less myocardial stress. Thus, FNS leg cycling may be more effective than ACE for aerobic cardiovascular training of quadriplegics.<<ETX>>

Multiple frequency system for body composition measurement

This paper describes a multiple frequency system for body composition measurement. The system uses a fixed reference frequency method of phase locked loop to control the frequeocy of the excitation signal. It also use8 a synchronous technique to ensure that the excitation signal is stable under varying load at eleven frequencies. Pilot results indicate that the system could be used for body composition determination such as bladder fluid volume.

Automated autonomic nervous system function analysis

The automated system was used to evaluated autonomic nervous-system function for four conditions: (1) valsalva maneuver; (2) beat-beat variation in heart rate during deep breathing; (3) isometric muscular contraction; and (4) heart-rate response to standing and orthostatic tolerance. Interrupt routines were used to collect electrocardiogram (ECG) data through a computer during the four recording conditions and, in certain cases, special interrupt routines were used to synchronize with minute-to-minute blood pressure measurements. Paper tracings were recorded at the same time for hand calculation. The R-R interval and heart rate were calculated by hand from the ECG tracings and compared to the results of the automated analysis system. No statistically significant (p>0.05) differences were observed between the two methods. Also significant correlations (p<0.05) ranging from 0.98 to 0.99 were found between them. The advantages of the automated system include the elimination of the need for recording papers and observer subjectivity and the higher speed of analysis.<<ETX>>

Muscle fiber excitation system

Persons unable to exercise due to old age, immobility or medical condition may develop low bone density, decline in muscle contraction, blood pooling or clot. Due to musculoskeletal fragility caution is required in bone and muscle strengthening. Similarly, caution is required to use anticoagulant drug to prevent blood clot due to side effect, and compression devices are not as effective as drug. This paper presents a transcutaneous muscle fiber excitation system adaptable for use in seated, walking or lying position. Clinical trials will determine performance in pathological cases.Persons unable to exercise due to old age, immobility or medical condition may develop low bone density, decline in muscle contraction, blood pooling or clot. Due to musculoskeletal fragility caution is required in bone and muscle strengthening. Similarly, caution is required to use anticoagulant drug to prevent blood clot due to side effect, and compression devices are not as effective as drug. This paper presents a transcutaneous muscle fiber excitation system adaptable for use in seated, walking or lying position. Clinical trials will determine performance in pathological cases.

A technique to monitor muscle performance during L1/M1 anti-G straining maneuvers

A relatively simple noninvasive method for continuous monitoring of human muscle performance and reserve capability, as well as for prediction of physical competence during repetitive execution of the L1/M1 anti-G straining maneuver (AGSM) is discussed. A computer-based system is used to quantify the force output (F/sub 0/) and integrated surface electromyographic (EMG) activity of major muscle groups of the arms, abdomen and legs. Ten healthy volunteers performed up to 40 repetitive AGSMs. A significant (p<0.05) correlation coefficient of 0.70 was found between F/sub 0/ and the EMG, indicating that either variable can be used to predict human performance independently. Plots of the two variables demonstrate similar trends among individuals. It is observed that when an individuals muscle is performance below 60% of the initial value, that individual is no longer able to continue performing AGSMs.<<ETX>>