Prediction of muscle performance during dynamic repetitive movement.

BACKGROUND: During long-duration spaceflight, astronauts experience progressive muscle atrophy and often perform strenuous extravehicular activities. Post-flight, there is a lengthy recovery period with an increased risk for injury. Currently, there is a critical need for an enabling tool to optimize muscle performance and to minimize the risk of injury to astronauts while on-orbit and during post-flight recovery. Consequently, these studies were performed to develop a method to address this need. METHODS: Eight test subjects performed a repetitive dynamic exercise to failure at 65% of their upper torso weight using a Lordex spinal machine. Surface electromyography (SEMG) data was collected from the erector spinae back muscle. The SEMG data was evaluated using a 5th order autoregressive (AR) model and linear regression analysis. RESULTS: The best predictor found was an AR parameter, the mean average magnitude of AR poles, with r = 0.75 and p = 0.03. This parameter can predict performance to failure as early as the second repetition of the exercise. CONCLUSION: A method for predicting human muscle performance early during dynamic repetitive exercise was developed. The capability to predict performance to failure has many potential applications to the space program including evaluating countermeasure effectiveness on-orbit, optimizing post-flight recovery, and potential future real-time monitoring capability during extravehicular activity.

Safety and efficacy evaluation of a fitness club weight-loss program.

It is well documented that excess weight is a major risk factor for many chronic diseases, and, despite considerable expenditure of time, money, and effort, little or no progress has been made in reversing the trend toward increased weight. Although fitness and athletic clubs offer one potential for tackling this problem, few provide information about the efficacy of their weight-loss programs. There is general agreement that an efficacious weight-loss program should reduce body fat, maintain or increase fat-free mass (FFM), and lower total and low-density lipoprotein (LDL) cholesterol. This study was designed to compare changes in body composition and serum cholesterol associated with participation in a fitness club program (EXP) versus changes that occurred when participants pursued a program of their own choosing (CTL). The EXP group participated in the Bally's Total Fitness program that included exercise, behavior modification, and dietary supplements. Although only small differences in body weight were noted between groups, participation in the EXP program led to significant (sixfold) reductions in fat mass, increases in FFM, and improvements in body composition. These data highlight the importance of using measures of body composition rather than scale weight in evaluating the efficacy of weight-loss programs. Additionally, the EXP group achieved significant reductions in total and LDL cholesterol, particularly among individuals with baseline total cholesterol levels above 200 micrograms/dL. It is also worth noting that respective cholesterol levels were maintained for participants with total cholesterol levels between 150 and 199 micrograms/dL and were increased for those with levels at or below 150 micrograms/dL.

Cerebral artery blood flow velocity changes following rapid release of lower body negative pressure.

BACKGROUND: Circulatory changes occur during exposure to Lower Body Negative Pressure (LBNP). These changes may have some similarities to exposure to moderately and slowly increased G-loads in a relaxed subject without anti-G suit. HYPOTHESIS: Changes will also occur in cerebral blood circulation during a rapid release of LBNP. METHODS: Transcranial Doppler ultrasound (TCD) was used to measure middle cerebral artery blood flow velocity (CBFV) in 14 human subjects following rapid release of a ramped lower body negative pressure (LBNP) (0.33 mm Hg.s) to presyncope (mean peak negative pressure of -124 mm Hg). RESULTS: The mean CBFV decreased to an average of 60% (p < 0.05) of the baseline value at peak LBNP. Mean CBFV was still decreased to 65% and 84% of the baseline value (p < 0.05) at the third heart beat and 30 s, respectively, after pressure release. The systolic CBFV decreased similarly to 57% (p < 0.05) of baseline during peak LBNP, and was still 63% (p < 0.05) at the third heart beat after pressure release. Heart rate increased by a mean of 51% (p < 0.001) and systolic heart level blood pressure decreased by 28% (p < 0.001) during peak negative pressure. Both heart rate and blood pressure returned to baseline levels within 30 s after pressure release. CONCLUSIONS: Following a presyncopal LBNP, the CBFV is not fully restored up to 30 s after the release of the negative pressure. This delayed returning of cerebral circulation following orthostatic stress may have some similarities to what occurs after the release of a gradual onset G-load in a relaxed subject without anti-G suit.

Hormonal responses during orthostasis following 4 hours of head-down tilt.

The purpose of this investigation was to test the hypothesis that endurance exercise trained (ET) subjects would demonstrate a greater reduction in orthostatic tolerance as compared to untrained (UT) subjects following prior exposure to -6 degrees head-down tilt (HDT) because vasoactive hormone and enzyme responses to head-up tilt (HUT) would be decreased following HDT so as to predispose ET subjects to orthostatic intolerance. Six ET subjects (VO2peak = 4.52 +/- 0.20 L/min) were matched for age and height with six UT subjects (VO2peak = 3.26 +/- 0.22 L/min; p < 0.01). After 30 min of supine rest, subjects were exposed to 30 min of head-up tilt (HUT) at 70 degrees, then on a separate occasion, 4 h of HDT (-6 degrees) followed by 30 min of HUT. The HUT involved passive standing for 30 min or until subjects became presyncopal. Blood sampled from the antecubital vein at min 1, 15, and 30, or at presyncope was analyzed for atrial natriuretic peptide (ANP), aldosterone (PA), arginine vasopressin (AVP), plasma renin activity (PRA), and norepinephrine (NE), while BP and HR were continuously monitored. All subjects tolerating 30 min of HUT, after either condition, had significantly increased (p < 0.05) levels of PRA at the 30th min. Following 4 h of HDT, five of six UT subjects and only one of six ET subjects endured 30 min of HUT. The most marked difference during HUT after prior exposure to HDT was a significant increase in AVP (p < 0.05) at the onset of HUT observed only for the UT subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Psychological profile of college students who use smokeless tobacco.

The purpose of this study was to develop a psychological profile of smokeless tobacco users. We surveyed 1991 college students regarding their use of tobacco products. Twenty-one percent of the white males used smokeless tobacco compared to only 10.4% of blacks, 5.4% of Hispanics, and 5.4% of others, primarily Asians. Although the prevalence of smokeless tobacco use reported by Asians was relatively low, their rate of reported smoking was over twice as high as any other ethnic group, 43.6%. The most important reasons for beginning to use smokeless tobacco were to "see if I would enjoy it," "most friends used it," and "try something new." The personality profile of the smokeless tobacco users differed from that of smokers and non-users of tobacco. College students with the highest probability of being a smokeless tobacco user were white males who scored higher in extraversion and neuroticism but lower on state anxiety than non-users.

Aerobic fitness: I. Response of volume regulating hormones to head-down tilt.

We investigated the relationship of aerobic fitness to the response of volume-regulating hormones to acute simulated microgravity. Six untrained (UT) and six endurance-trained (ET) healthy young males were studied in the head-down tilt (HDT) position of -6 degrees for 4 h. Peak oxygen uptake (VO2peak) and plasma volume (PV) were significantly greater in the ET (VO2peak = 61.7 +/- 1.6 ml.min-1.kg-1 and PV = 53.1 +/- 2.8 ml.kg-1) than in the UT (VO2peak = 38.4 +/- 1.7 ml.min-1.kg-1 and PV = 38.8 +/- 1.0 ml.kg-1). Plasma concentrations of atrial natriuretic peptide (ANP), arginine vasopressin (AVP), norepinephrine (NE), renin activity (PRA), and aldosterone (PA) were measured prior to HDT and at minutes 2, 5, 15, 30, 60, 120, 180, and 240 during HDT. PRA and PA significantly decreased during the time of HDT in both groups. The changes in ANP and NE concentrations were not significantly different between the groups nor across time. However, in the ET subjects, the changes in PRA and NE were significantly correlated with the changes in ANP (r = 0.49, P less than 0.01; and r = 0.86, P less than 0.001, respectively); in the UT subjects, the changes in AVP, PRA, and PA were significantly associated with changes in NE (r = 0.34, P less than 0.03; and r = 0.59; and r = 0.53, P less than 0.01, respectively). PV significantly decreased during HDT, and was primarily related to the decrease in PA in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerobic fitness: II. Orthostasis and VO2peak following head-down tilt.

To determine whether endurance exercise trained (ET) subjects would experience greater reductions in peak oxygen delivery and orthostatic tolerance (OT) than untrained (UT) subjects, both peak oxygen uptake (VO2peak) during upright bicycle ergometry and tolerance time during 70 degrees head-up tilt (HUT) were compared within and between groups before and after 4 h of -6 degrees head-down tilt (HDT). Eight ET subjects with a mean VO2peak of 61.7 +/- 1.6 ml.kg-1.min-1 were matched for age, height, and weight with eight UT subjects (VO2peak = 38.4 +/- 1.7 ml.kg-1.min-1). Following HDT, decreases in plasma volume (PV) were larger for ET subjects (-3.7 +/- 0.5 ml.kg-1) than for UT subjects (-2.3 +/- 0.3 ml.kg-1), P less than 0.03. Reductions in VO2peak for ET subjects (-5.4 +/- 1.1 ml.kg-1.min-1) were also greater than for UT subjects (-2.4 +/- 0.8 ml.kg-1.min-1), P less than 0.05. The ET (N = 6) subjects also had a significant decrease in OT time (-13.0 +/- 4.2 min) during post-HDT HUT, which was not observed for the UT group (N = 6). A significant inverse correlation was found pre-HDT VO2peak and the change in OT time, r = -0.74, P less than 0.01. The decrease in OT was also significantly correlated to the PV decrease, r = 0.59, P less than 0.04. The UT subjects had significantly augmented pressor responses to HUT manifested by the increases in both HR and MAP following HDT.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic responses to 6 degree head-down rest in dogs: effect of aerobic conditioning.

The -6 degree head-down position is used in humans to produce fluid shifts that resemble those occurring in microgravity. Alternative animal models of microgravity may be helpful for extensive exploration of this unique condition. The dog may be a viable candidate. Sixteen dogs were assigned to one of three conditions: anesthetized open chest, anesthetized closed chest, and awake. Dogs in groups 1 (N = 6) and 2 (N = 6) were divided into an exercise or a sedentary treatment, and dogs in group 3 (N = 4) served as their own controls. Following instrumentation the dogs were put in the head-down position for 1 h. Measurements included right atrial pressure, heart rate, and mean arterial pressure for all groups, left ventricular pressure and LV dp/dt for group 1, and cardiac output and iliac flow for group 2. Right atrial pressure increased for all groups. Heart rate demonstrated non-significant changes over time or group. Significant differences were noted for mean arterial pressure, left ventricular pressure and LV dp/dt for exercise condition in response to HDR. It appears that -6 degrees of head-down rest produces similar cardiovascular responses in dogs as those observed in humans and that exercise has a minor effect on those responses.

Analysis of commercial samples of dimethyl sulfoxide.

Refractive index measurements and spectral data (IR and NMR) were used to verify the purity claimed by commercial samples of dimethyl sulfoxide.

Effect of 60-minute head-down tilt on arterial baroreflex function in anesthetized dogs.

Arterial baroreflex control of heart rate was assessed in 6 anesthetized dogs with a bolus infusion of phenylephrine before and during cardiopulmonary receptor stimulation by 6 degrees head-down tilt (HDT) for 60 min. No difference in arterial baroreflex function was observed between the control and HDT conditions. It appears that the attenuation of baroreflex function that occurs during acute stimulation of cardiopulmonary baroreceptors disappears when cardiopulmonary baroreceptors reset after prolonged stimulation.

Benefits of aerobic exercise for the paraplegic: a brief review.

The importance of exercise for the general population is emphasized widely; therefore, it must be even more important for paralegics who are already threatened with poor health due to the sedentary nature of their lifestyle. The effects of functional degeneration are vast and greatly reduce the overall health of paraplegics, particularly within the musculoskeletal and cardiovascular systems, thereby increasing their risk for cardiovascular disease. Recent investigations suggest that this process may be reversible through exercise training and that paraplegics respond to exercise training in essentially the same manner as the non-handicapped individual. In addition, exercise training has been reported to decrease the resorptive process of the skeleton by decreasing bone and collagen catabolism and possibly aiding in new bone formation. This review attempts to summarize the available literature on the effects of exercise on the paraplegic and will hopefully provide some direction not only for further research but also recommendations for practitioners working in the field.

Comparison of exercise blood pressure measured by technician and an automated system.

We evaluated the automated system Blood Pressure Measuring System (BPMS) developed by NASA on 277 adult males who elected to have a treadmill test as part of their annual physical. The BPMS uses acoustic transduction with a computer-assisted ECG gating to detect nonsynchronous noise. The BPMS readings were compared to pressures simultaneously measured by trained technicians. For all stages of work, BPMS readings were higher for systolic and lower for diastolic than technician readings. At peak stages of work, BPMS systolic pressures were about 20 mmHg higher than technician readings. Within each 3-min workstage, BPMS readings were found to be more inconsistent than technician readings. The standard errors of measurement for BPMS were from two to three times higher than technician values. These data showed automated blood pressure readings were significantly different than technician values and subject to more random fluctuations. These findings demonstrate the need to view exercise blood pressure measured by automated systems with caution.

Hemodynamic effects of oral smokeless tobacco in dogs and young adults.

Oral smokeless tobacco (snuff) is increasingly used among the young male population. To determine cardiovascular effects of an oral smokeless tobacco product, 10 anesthetized dogs were instrumented to measure blood pressure, heart rate, left ventricular end diastolic pressure, and circumflex coronary, renal, and femoral flows. After a 5-min baseline, a 2.5-g, approximately 1.2% nicotine bolus dose was placed in the buccal space, and measurements were made for 20 min. Significant increases were seen in heart rate, blood pressure, left ventricular pressure, left ventricular end diastolic pressure, and left ventricular dP/dt. Significant decreases in flow were noted in the coronary circumflex, renal, and femoral arteries. The flow reduction was thought to have been mediated by an alpha-adrenergic mechanism. Additionally, 20 human males, mean age 20 years, without nicotine exposure for 72 hr, were given a 2.5-g dose of the same oral smokeless product. From baseline to 20 min, heart rate increased from 69 to 88 beats/min (P less than 0.05), blood pressure from 118/72 to 126/78 mm Hg (P less than 0.05). Thus, oral smokeless tobacco use can produce significant hemodynamic changes in both dogs and normal humans.

Demonstration of training effect during chronic beta-adrenergic blockade in patients with coronary artery disease.

Attenuation of exercise-induced increases in heart rate and cardiac output by chronic beta-adrenergic blockade has been thought to compromise benefit of exercise training in patients with coronary artery disease (CAD). To assess this important issue, 35 CAD patients were evaluated by a 3-month walk-jog-cycle training program: 14 patients received no beta blocker (group 1), 14 received propranolol, 30-80 mg/day (group 2), and seven patients received propranolol, 120-240 mg/day (group 3). The extent of CAD, resting heart rate before training blood pressure and VO2 max were similar (p = NS) in each group. The maximal exercise heart rate (mean +/- SD, 147 +/- 21 beats/min in group 1 vs 120 +/- 10 beats/min in group 2 and 115 +/- 12 beats/min in group 3 (both p less than 0.05 vs group 1). The VO2 max before training was 25 +/- 5.0 ml/kg/min in group 1 vs 23 +/- 3.2 ml/kg/min in group 2 and 26 +/- 2.8 ml/Kg/min in group 3 (all p = NS). Training consisted of three 1-hour periods per week at a heart rate of 70-85% of the maximal pretraining heart rate. In each group, VO2 increased (p less than 0.05) after training: group 1, 27%; group 2, 30%; group 3, 46%. The double product was unchanged after training (p = NS) in each group. These data indicate that substantial training effects may be achieved in CAD patients despite therapeutic doses of beta blockers and a reduced training HR. Thus, there appears to be no indication to reduce beta blockers in CAD patients engaged in cardiac rehabilitation.