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All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Evaluation of Treadmill Exercise in a Lower Body Negative Pressure Chamber as a Countermeasure for Weightlessness-Induced Bone Loss: a Bed Rest Study with Identical Twins

Counteracting bone loss is required for future space exploration. We evaluated the ability of treadmill exercise in a LBNP chamber to counteract bone loss in a 30-day bed rest study. Eight pairs of identical twins were randomly assigned to sedentary control or exercise groups. Exercise within LBNP decreased the bone resorption caused by bed rest and may provide a countermeasure for spaceflight. INTRODUCTION: Bone loss is one of the greatest physiological challenges for extended-duration space missions. The ability of exercise to counteract weightlessness-induced bone loss has been studied extensively, but to date, it has proven ineffective. We evaluated the effectiveness of a combination of two countermeasures-treadmill exercise while inside a lower body negative pressure (LBNP) chamber-on bone loss during a 30-day bed rest study. MATERIALS AND METHODS: Eight pairs of identical twins were randomized into sedentary (SED) or exercise/LBNP (EX/LBNP) groups. Blood and urine samples were collected before, several times during, and after the 30-day bed rest period. These samples were analyzed for markers of bone and calcium metabolism. Repeated measures ANOVA was used to determine statistical significance. Because identical twins were used, both time and group were treated as repeated variables. RESULTS: Markers of bone resorption were increased during bed rest in samples from sedentary subjects, including the collagen cross-links and serum and urinary calcium concentrations. For N-telopeptide and deoxypyridinoline, there were significant (p < 0.05) interactions between group (SED versus EX/LBNP) and phase of the study (sample collection point). Pyridinium cross-links were increased above pre-bed rest levels in both groups, but the EX/LBNP group had a smaller increase than the SED group. Markers of bone formation were unchanged by bed rest in both groups. CONCLUSIONS: These data show that this weight-bearing exercise combined with LBNP ameliorates some of the negative effects of simulated weightlessness on bone metabolism. This protocol may pave the way to counteracting bone loss during spaceflight and may provide valuable information about normal and abnormal bone physiology here on Earth.

Twin Study↗
NASA NTRS2006

Supine Treadmill Exercise in Lower Body Negative Pressure Combined with Resistive Exercise Counteracts Bone Loss, Reduced Aerobic Upright Exercise Capacity and Reduced Muscle Strength

Long-term exposure to weightlessness leads to cardiovascular and musculoskeletal deconditioning. In this report, the effectiveness of combined supine treadmill exercise in a lower body negative pressure chamber (LBNPex) and flywheel resistive exercise (Rex) countermeasures was determined to prevent bone loss, reduced aerobic upright exercise capacity and reduced muscle strength. We hypothesized that exercise subjects would show less decrease in bone mineral density (BMD), peak oxygen consumption (VO2pk) and knee extensor strength (KES) than control subjects. Sixteen healthy female subjects participated in a 60-d 6(sup 0) head-down tilt bed rest (BR) study after providing written informed consent. Subjects were assigned to one of two groups: a non-exercising control group CON or an exercise group EX performing LBNPex 2-4 d/wk and Rex every 3rd-d. VO2pk was measured with a maximal, graded, upright treadmill test performed pre-BR and on 3-d after BR. BMD was assessed before and 3-d after BR. Isokinetic KES was measured before and 5-d after BR. Two-way repeated measures ANOVA were performed. Statistical significance was set at p less than 0.05. CON experienced a significant decrease in BMD in the trochanter (PRE: 0.670 plus or minus 0.045; POST: 0.646 plus or minus 0.352 g (raised dot) per square centimeter) and in the whole hip (PRE=0.894 plus or minus 0.059; POST: 0.858 plus or minus 0.057 g (raised dot) per square centimeter). BMD also decreased significantly in EX in the trochanter (PRE: 0.753 plus or minus 0.0617; POST: 0.741 plus or minus 0.061 g (raised dot) per square centimeter) and whole hip (PRE: 0.954 plus or minus 0.067; POST: 0.935 plus or minus 0.069 g (raised dot) per square centimeter). BMD losses were significantly less in EX than in CON subjects. VO2pk was significantly decreased in the CON after BR (PRE: 38.0 plus or minus 4.8; POST: 29.9 plus or minus 4.2 ml (raised dot) per kilogram per minute), but not in the EX (PRE: 39.0 plus or minus 2.0; POST: 37.8 plus or minus 1.9 ml (raised dot) per kilogram per minute). KES was significantly reduced by 30% in Con (PRE: 113 plus or minus 12; POST: 78 plus or minus 8 N-m), but was not different in EX (PRE: 126 plus or minus 25; POST: 115 plus or minus 25 N-m). The combination LBNPex and Rex during 60-d BR protects against cardiovascular and musculoskeletal deconditioning and may be efficacious countermeasure for prolonged space flight.

Meuche, Sabine↗
NASA NTRS2006

The Interplay Between Strategic And Adaptive Control Mechanisms In Plastic Recalibration Of Locomotor Function

We have previously shown that viewing simulated rotary self-motion during treadmill locomotion causes immediate strategic modifications (Richards et al. 2004) as well as an after effect reflecting adaptive modification of the control of position and trajectory during over-ground locomotion (Mulavara et al. 2005). The process of sensorimotor adaptation is comprised of both strategic and adaptive control mechanisms. Strategic control involves cognitive, on-line corrections to limb movements once one is aware of a sensory discordance. Over an extended period of exposure to the sensory discordance, new strategic sensorimotor coordination patterns are reinforced until they become more automatic, and therefore adaptive, in nature. The objective of this study was to investigate how strategic changes in trunk control during exposure to simulated rotary self-motion during treadmill walking influences adaptive modification of locomotor heading direction during over-ground stepping. Subjects (n = 10) walked on a motorized linear treadmill while viewing a wide field-of-view virtual scene for 24 minutes. The scene was static for the first 4 minutes and then, for the last 20 minutes, depicted constant rate self-motion equivalent to walking in a counter-clockwise, circular path around the perimeter of a room. Subjects performed five stepping trials both before and after the exposure period to assess after effects. Results from our previous study showed a significant change in heading direction (HD) during post-exposure step tests that was opposite the direction in which the scene rotated during the adaptation period. For the present study, we quantified strategic modifications in trunk movement control during scene exposure using normalized root mean square (R(sub p)) variation of the subject's 3D trunk positions and normalized sum of standard deviations (R(sub o)) variation of 3D trunk orientations during scene rotation relative to that during static scene presentation. Associated 95% confidence intervals, CI(sub P) and CI(sub O), were calculated to investigate the variation of strategic modifications during scene exposure. Repeated measures ANOVA and individual subject regression analyses showed that R(sub P) and R(sub O) (i.e. strategic modifications) for trunk fore/aft (X) and yaw movements, respectively, decreased significantly over the exposure period. Furthermore, we found a significant correlation between the magnitude change in HD and the rate at which the variation of strategic modifications in trunk X decreased. We also found evidence of a correlation between HD and the rate at which strategic modifications in trunk yaw decreased (p = .06). We infer that adaptive recalibration of locomotor trajectory using optic flow stimuli depends on the rate at which strategic intervention is reduced.

Richards, J. T.↗
NASA NTRS2006

WISE 2005: LBNP Exercise and Flywheel Resistive Exercise as an Effective Countermeasure Combination

Long-term exposure to microgravity can cause a severe musculoskeletal loss and cardiovascular deconditioning in astronauts. In this report, the effectiveness of combined supine treadmill exercise in a lower body negative pressure chamber (LBNPex) and flywheel resistive exercise (Rex) countermeasures was determined to prevent bone loss, reduced aerobic upright exercise capacity and reduced muscle strength. We hypothesized that exercise subjects (EX) would show less decrease in bone mineral density (BMD), peak oxygen consumption (VO2pk) and knee extensor strength (KES) than control subjects (CON). Sixteen healthy female subjects (34 plus or minus 4yrs, 164 plus or minus 6.5cm, 58 plus or minus 5kg; mean plus or minus SD) participated in a 60-d 6 degree head-down tilt bed rest (BR) study after providing written informed consent. Subjects were assigned to one of two groups: a non- exercising CON group or an EX group performing LBNPex 2-4 d/wk and Rex every 3rd-d. VO2pk was measured with a maximal, graded, upright treadmill test performed pre-BR and on 3-d after BR. BMD was assessed pre-BR and 3-d after BR by dual energy x-ray absorptiometry total body DEXA scan (DEXA; HOLOGIC QDR 4500 Elite ). A Cybex dynamometer was employed to measure the isokinetic KES before and 5-d after BR. Two-way repeated measures ANOVA were performed with time as the repeated factor. Statistical significance was set at p less than 0.05. CON experienced a significant decrease in BMD in the trochanter (PRE: 0.670 0.045; POST: 0.646 0.352 g(raised dot) per square centimeter) and in the whole hip (PRE: 0.894 0.059; POST: 0.858 0.057 g(raised dot) per square centimeter). BMD also decreased significantly in EX in the trochanter (PRE: 0.753 plus or minus 0.0617; POST: 0.741 plus or minus 0.061 g(raised dot) per square centimeter) and whole hip (PRE: 0.954 plus or minus 0.067; POST: 0.935 plus or minus 0.069 g(raised dot) per square centimeter). BMD losses were significantly less in EX than in CON subjects. VO2pk was significantly decreased in the CON after BR (PRE: 38.0 plus or minus 4.8; POST: 29.9 plus or minus 4.2 ml(raised dot) per kilogram per minute), but not in the EX (PRE: 39.0 plus or minus 2.0; POST: 37.8 plus or minus 1.9 ml(raised dot) per kilogram per minute). KES was significantly reduced by 30% in CON (PRE: 113 plus or minus 12; POST: 78 plus or minus 8 N-m), but was not different in EX (PRE: 126 plus or minus 25; POST: 115 plus or minus 25 N-m). The combination LBNPex and Rex during 60-d BR protects against cardiovascular and musculoskeletal deconditioning and may be an efficacious countermeasure for prolonged space flight.

Meuche, S.↗
NASA NTRS2007

Adaptive Responses in Eye-Head-Hand Coordination Following Exposures to a Virtual Environment as a Possible Space Flight Analog

Virtual environments (VE) offer unique training opportunities, particularly for training astronauts and preadapting them to the novel sensory conditions of microgravity. Sensorimotor aftereffects of VEs are often quite similar to adaptive sensorimotor responses observed in astronauts during and/or following space flight. The purpose of this research was to compare disturbances in sensorimotor coordination produced by dome virtual environment display and to examine the effects of exposure duration, and repeated exposures to VR systems. The current study examined disturbances in eye-head-hand (EHH) and eye-head coordination. Preliminary results will be presented. Eleven subjects have participated in the study to date. One training session was completed in order to achieve stable performance on the EHH coordination and VE tasks. Three experimental sessions were performed each separated by one day. Subjects performed a navigation and pick and place task in a dome immersive display VE for 30 or 60 min. The subjects were asked to move objects from one set of 15 pedestals to the other set across a virtual square room through a random pathway as quickly and accurately as possible. EHH coordination was measured before, immediately after, and at 1 hr, 2 hr, 4 hr and 6 hr following exposure to VR. EHH coordination was measured as position errors and reaction time in a pointing task that included multiple horizontal and vertical LED targets. Repeated measures ANOVAs were used to analyze the data. In general, we observed significant increases in position errors for both horizontal and vertical targets. The largest decrements were observed immediately following exposure to VR and showed a fairly rapid recovery across test sessions, but not across days. Subjects generally showed faster RTs across days. Individuals recovered from the detrimental effects of exposure to the VE on position errors within 1-2 hours. The fact that subjects did not significantly improve across days suggests that in order to achieve dual adaptation of EHH coordination may require more than three training sessions. These findings provide some direction for developing training schedules for VE users that facilitate adaptation, support the idea that preflight training of astronauts may serve as useful countermeasure for the sensorimotor effects of space flight, and support the idea that VEs may serve as an analog for sensorimotor effects of spaceflight.

Harm, Deborah L.↗
NASA NTRS2007

Effect of Head-Down Bed Rest and Artificial Gravity Countermeasure on Cardiac Autonomic and Advanced Electrocardiographic Function

To study the effects of 21 days of head-down bed rest (HDBR), with versus without an artificial gravity (AG) countermeasure, on cardiac autonomic and advanced electrocardiographic function. Fourteen healthy men participated in the study: seven experienced 21 days of HDBR alone ("HDBR controls") and seven the same degree and duration of HDBR but with approximately 1hr daily short-arm centrifugation as an AG countermeasure ("AG-treated"). Five minute supine high-fidelity 12-lead ECGs were obtained in all subjects: 1) 4 days before HDBR; 2) on the last day of HDBR; and 3) 7 days after HDBR. Besides conventional 12-lead ECG intervals and voltages, all of the following advanced ECG parameters were studied: 1) both stochastic (time and frequency domain) and deterministic heart rate variability (HRV); 2) beat-to-beat QT interval variability (QTV); 3) T-wave morphology, including signal-averaged T-wave residua (TWR) and principal component analysis ratios; 4) other SAECG-related parameters including high frequency QRS ECG and late potentials; and 5) several advanced ECG estimates of left ventricular (LV) mass. The most important results by repeated measures ANOVA were that: 1) Heart rates, Bazett-corrected QTc intervals, TWR, LF/HF power and the alpha 1 of HRV were significantly increased in both groups (i.e., by HDBR), but with no relevant HDBR*group differences; 2) All purely "vagally-mediated" parameters of HRV (e.g., RMSSD, HF power, Poincare SD1, etc.), PR intervals, and also several parameters of LV mass (Cornell and Sokolow-Lyon voltages, spatial ventricular activation times, ventricular gradients) were all significantly decreased in both groups (i.e., by HDBR), but again with no relevant HDBR*group differences); 3) All "generalized" or "vagal plus sympathetic" parameters of stochastic HRV (i.e., SDNN, total power, LF power) were significantly more decreased in the AG-treated group than in the HDBR-only group (i.e., here there was a relevant HDBR*group difference); and 4) QTV index was also significantly more changed (increased) in the AG-treated group than in the HDBR-only group, although this was clearly due to a greater decrease in generalized HRV and not to a greater increase in QTV proper because there was no relevant HDBR*group effect for either the SDNN or the RMSSD of QTV. Brief daily AG treatment by short-arm centrifuge during each of 21 days of HDBR does not appear to protect against HDBR-related losses of cardiac autonomic function or of LV mass as estimated by ECG.

Schlegel, T. T.↗
NASA NTRS2007

Relative Bioavailability of Scopolamine Dosage Forms and Interaction with Dextroamphetamine

The NASA Reduced Gravity Office (RGO) uses scopolamine (SCOP) and in combination with dextoamphetamine (DEX) to manage motion sickness symptoms during parabolic flights. The medications are dispensed as custom dosage forms as gelatin capsules. Anecdotal evidence of efficacy suggests that these formulations are unreliable and less efficacious for the treatment of motion sickness. We estimated bioavailability of four different oral formulations used by NASA for the treatment of motion sickness. Twelve healthy, non-smoking subjects between 21and 48 years of age received four treatments on separate days in a randomized fashion; the treatments were 0.8 mg SCOP alone as tablet, 0.8 mg SCOP alone in gel cap, 0.8 mg SCOP and 10 mg DEX as tablets, and 0.8 mg SCOP and 10 mg DEX in gel cap. After each treatment, blood, saliva, and urine samples were collected at scheduled time intervals for 24 h after dosing. Bioavailability and pharmacokinetic parameters were calculated and compared using ANOVA. After administration of SCOP tablets alone, maximum concentration (C(sub max)) and time for maximum concentration (t(sub max)) were 0.26 plus or minus 0.04 ng/mL and 0.71 plus or minus 0.02 h, respectively; volume of distribution, and clearance were 47.6 plus or minus 4.72 L/kg and 23.0 plus or minus 4.58 L/h/kg, respectively. SCOP t(sub max) after administration as gelcaps was significantly longer than that with tablets (1.04 h, p less than 0.05), but no significant differences in other pharmacokinetic parameters of SCOP were observed between the two dosage forms. When coadministered with DEX, the area underneath the concentration versus time curve (AUC) of SCOP was significantly reduced to 0.61 plus or minus 0.09 and 0.64 plus or minus 0.11 ng (raised dot) h/mL after administration as a tablet or gelcap formulation, respectively; SCOP C(sub max) was lower after coadministration with DEX, this difference, however, was not statistically significant. Delayed absorption with gelcaps coupled with reduced bioavailability with DEX coadministration may have resulted in the observed treatment failure with some of these formulations. This could result from failure to reach minimum effective concentrations after treatment with gelcap formulations before parabolic flights. A new nomogram for dosing is proposed for treatment with SCOP gelcaps or SCOP-DEX combination.

Boyd, Jason L.↗
NASA NTRS2007

Skeletal Adaptations to Different Levels of Eccentric Resistance Following Eight Weeks of Training

Coupled concentric-eccentric resistive exercise maintains bone mineral density (BMD) during bed rest and aging. PURPOSE: We hypothesized that 8 wks of lower body resistive exercise training with higher ratios of eccentric to concentric loading would enhance hip and lumbar BMD. METHODS: Forty untrained male volunteers (34.9+/-7.0 yrs, 80.9+/-9.8 kg, 178.2+/-7.1 cm; mean+/-SD) were matched for leg press (LP) 1-Repetition Maximum (1-RM) strength and randomly assigned to one of 5 training groups. Concentric load (% 1-RM) was constant across groups, but each group trained with different levels of eccentric load (0, 33, 66, 100, or 138% of concentric) for all training sessions. Subjects performed a periodized supine LP and heel raise (HR) training program 3 d wk-1 for 8 wks using a modified Agaton Fitness System (Agaton Fitness AB, Boden, Sweden). Hip and lumbar BMD (g/sq cm) was measured in triplicate pre- and post-training using DXA (Hologic Discovery ). Pre- and post-training means were compared using the appropriate ANOVA and Tukey's post hoc tests. Within group pre- to post-training BMD was compared using paired t-tests with a Bonferroni adjustment. RESULTS: There was a main effect of training on L1, L2, L3, L4, total lumbar, and greater trochanter BMD, but there were no differences between groups. CONCLUSION: Eights wks of lower body resistive exercise increased greater trochanter and lumbar BMD. Inability to detect group differences may have been influenced by a potentially osteogenic vibration associated with device operation in the 0, 33, and 66% groups.

English, Kirk L.↗
NASA NTRS2007

Comparison of the US and Russian Cycle Ergometers

The purpose of this study was to compare the U.S. and Russian cycle ergometers focusing on the mechanical differences of the devices and the physiological differences observed while using the devices. Methods: First, the mechanical loads provided by the U.S. Cycle Ergometer with Vibration Isolation System (CEVIS) and the Russian Veloergometer were measured using a calibration dynamometer. Results were compared and conversion equations were modeled to determine the actual load provided by each device. Second, ten male subjects (32.9 +/- 6.5 yrs, 180.6 +/- 4.4 cm; 81.9 +/- 6.9 kg) experienced with both cycling and exercise testing completed a standardized submaximal exercise test protocol on CEVIS and Veloergometer. The exercise protocol involved 8 sub-maximal workloads each lasting 3 minutes for a total of 24 minutes per session, or until the end of the stage when the subject reached 85% of peak oxygen consumption or age-predicted maximum heart rate (220 - age). The workload started at 50 Watts (W), increased to 100 W, and then increased 25 W every 3 minutes until reaching a peak workload of 250 W. Physiological variables were then compared at each workload by repeated measures ANOVA or paired t-tests (p<0.05). Results: While both CEVIS and Veloergometer produced significantly lower workloads than the displayed workload, CEVIS produced even lower loads than Veloergometer (p<0.05) at each indicated workload. Despite this fact, the only physiological variables that showed a significant difference between the ergometers were VE (125 - 250W), VO2 (175 and 250 W), and VCO2 (175 W). All other physiological data were not statistically different between CEVIS and Veloergometer. Conclusion: Although workloads were different between ergometers, relatively few physiological differences were observed. Therefore, CEVIS workloads of 87.5 - 262.5 W can be rounded to the nearest 25 W increment and performed on the Veloergometer.

Norcross, Jason↗
NASA NTRS2008

Different Levels of Eccentric Resistance during Eight Weeks of Training Affect Muscle Strength and Lean Tissue Mass

Coupling concentric and eccentric muscle contractions appears to be important in the development of muscle strength and hypertrophy. The interim Resistive Exercise Device (iRED) currently used aboard the International Space Station does not seem to be as effective as free weight training in ambulatory subjects and has not completely protected against muscular deconditioning due to space flight. The lack of protection during space flight could be caused by iRED's proportionally lower eccentric resistance (60-70%) compared to concentric resistance. PURPOSE: To determine the effects of 8 wks of lower body resistive exercise training using five levels of eccentric resistance on muscle strength and lean tissue mass. METHODS: Forty untrained males (34.9 +/- 7 yrs, 80.9 +/- 9.8 kg, 178.2 +/- 7.1 cm; mean +/- SD) completed three 1-repetition maximum (1-RM) strength tests for both the supine leg press (LP) and supine heel raise (HR) prior to training; subjects were matched for LP strength and randomly assigned to one of five training groups. Concentric load (% 1-RM) was constant across groups during training, but each group trained with different levels of eccentric load (0%, 33%, 66%, 100%, or 138% of concentric). Subjects trained 3 d / wk for 8 wks using a periodized program for LP and HR based on percentages of the highest pre-training 1-RM. LP and HR 1-RM and leg lean mass (LLM; assessed by DEXA) were measured pre- and post-training. A two-way ANOVA was used to analyze all dependent measures. Tukey's post hoc tests were used to test significant main effects. Within group pre- to post-training changes were compared using paired t-tests with a Bonferroni adjustment. Statistical significance was set a priori at p 0.05. All data are expressed as mean +/- SE. RESULTS: LP 1-RM strength increased significantly in all groups pre- to post-training. The 138% group increase (20.1 +/- 3.7%) was significantly greater than the 0% (7.9 +/- 2.8%), 33% (7.7 +/- 4.6%), and 66% (7.5 +/- 4.3%) groups. All groups significantly increased HR strength pre- to posttraining (33%: 7.5 +/- 6.1%; 66%: 6.6 +/- 3.7%; 100%: 12.2 +/- 1.8%; 138%: 11.0 +/- 6.4%) except for the 0% (4.9 +/- 9.1%) group. There were no differences between groups. LLM increased significantly pre- to post-training in only the 138% group; there were no differences between groups. CONCLUSIONS: Eight wks of lower body resistive exercise training with eccentric overload resulted in greater increases in LP strength than training with eccentric loads of 66% or less. Post-training HR strength was not affected by eccentric training load, perhaps because of the predominance of Type I fibers typical in the gastrocnemius. Only 138% eccentric training significantly increased LLM. PRACTICAL APPLICATIONS: For athletes or others desiring to maximize muscle strength and hypertrophy gains, training with eccentric loads greater than 100% of concentric resistance will provide greater increases in muscle strength and lean tissue mass in some muscle groups. In a rehabilitation or geriatric exercise setting that places primary emphasis on program adherence and moderate strength gains, training with an eccentric underload may provide strength increases comparable to those of traditional 1:1 training but with less muscle soreness and physiologic insult to the patient, but this has yet to be proven.

English, K. L.↗
NASA NTRS2006

Nutritional Status in Humans during Long-Duration Bed Rest

Bed rest is a valuable ground-based model for many of the physiological changes associated with space flight. A series of studies was undertaken to evaluate nutritional changes during and after 60 or 90 days of -6 head-down-tilt bed rest. A total of 11 subjects (8 M, 3 F; age 26-55 y) participated in the studies. Blood and urine were collected twice before bed rest and once per month during bed rest. Samples were analyzed in batch at the end of each study. Data were analyzed using repeated-measures ANOVA. Markers of bone resorption (such as n-telopeptide excretion, p less than 0.05) increased during bed rest, and 25-OH vitamin D status tended to decline (p=0.06). During bed rest oxidative damage markers, such as superoxide dismutase increased (p less than 0.01) and 8-(OH)-2'-deoxyguanosine tended to increase (p=0.07); whereas total antioxidant capacity decreased (p less than 0.02). Iron status indices showed patterns of increased iron stores, with decreased transferrin receptors (p less than 0.001). Biochemical markers revealed a tendency toward a loss of muscle mass, by lower excretion of creatinine and 3-methyl-histidine during bed rest. All of these changes are very similar to those observed during space flight, and further document the utility of bed rest as a model of space flight.

Smith, Scott M.↗
NASA NTRS2006

Vitamin D in Real and Simulated Weightlessness: Implications for Earth

Vitamin D deficiency has reemerged as a public health concern in the United States. It is also a concern for astronauts because spacecraft are shielded from ultraviolet light, leaving diet as the sole source of vitamin D. We report here the findings from four studies: one evaluation of astronauts before and after 4- to 6-month missions to the International Space Station, and the other three from a ground-based analog for space flight, long-term bed rest. For the space flight study, blood samples were collected before the flight and within hours of landing after it. Crewmembers (n = 11) were provided vitamin D supplements (as cholecalciferol (10 g/d) throughout the mission. The average number of vitamin D supplements reported to be consumed per week was 5.7 plus or minus 4.0. The vitamin D status indicator serum 25-hydroxycholecalciferol was 25% less after landing (48 plus or minus 20) than before flight (63 plus or minus 16) (P less than 0.01). A series of three studies was undertaken to evaluate nutritional changes during and after 60 or 90 days of -6 deg. head-down-tilt bed rest. A total of 11 subjects (8 M, 3 F; age 26-55 y) participated in the studies. Blood and urine were collected twice before bed rest and once per month during bed rest. During bed rest the average dietary intake of vitamin D for the three studies was 4.84 plus or minus 0.16 (study 1), 6.24 plus or minus 0.81 (study 2), and 7.16 plus or minus 1.40 (study 3) micrograms/day. In study 1 only, subjects were given a daily supplement of 10 g vitamin D (as ergocalciferol). Data were analyzed using repeated-measures ANOVA. In the first study, 7 days after the end of the bed rest, serum 25-hydroxycholecalciferol was 30% less than it was before bed rest (p less than 0.05). In the second and third studies, during or after bed rest the serum 25-hydroxycholecalciferol concentration was not significantly different from its concentration before bed rest. These data demonstrate that vitamin D intake is critical for individuals not exposed to the sun. Although we studied astronauts and healthy subjects in bed rest, the implications of our results also apply to people living in northern latitudes and others who receive little exposure to sunlight, such as elderly people who seldom go outdoors. The inability of supplements to maintain vitamin D status is also an important finding, and highlights the need for careful food selection to ensure adequate vitamin D intake.

Rice, Barbara L.↗
NASA NTRS2009

Using Maximal Isometric Force to Determine the Optimal Load for Measuring Dynamic Muscle Power

Maximal power output occurs when subjects perform ballistic exercises using loads of ~30-50% of one-repetition maximum (1-RM). However, performing 1-RM testing prior to power measurement requires considerable time, especially when testing involves multiple exercises. Maximal isometric force (MIF), which requires substantially less time to measure than 1-RM, might be an acceptable alternative for determining the optimal load for power testing. PURPOSE: To determine the optimal load based on MIF for maximizing dynamic power output during leg press and bench press exercises. METHODS: Twenty healthy volunteers (12 men and 8 women; mean +/- SD age: 31+/-6 y; body mass: 72 +/- 15 kg) performed isometric leg press and bench press movements, during which MIF was measured using force plates. Subsequently, subjects performed ballistic leg press and bench press exercises using loads corresponding to 20%, 30%, 40%, 50%, and 60% of MIF presented in randomized order. Maximal instantaneous power was calculated during the ballistic exercise tests using force plates and position transducers. Repeated-measures ANOVA and Fisher LSD post hoc tests were used to determine the load(s) that elicited maximal power output. RESULTS: For the leg press power test, six subjects were unable to be tested at 20% and 30% MIF because these loads were less than the lightest possible load (i.e., the weight of the unloaded leg press sled assembly [31.4 kg]). For the bench press power test, five subjects were unable to be tested at 20% MIF because these loads were less than the weight of the unloaded aluminum bar (i.e., 11.4 kg). Therefore, these loads were excluded from analysis. A trend (p = 0.07) for a main effect of load existed for the leg press exercise, indicating that the 40% MIF load tended to elicit greater power output than the 60% MIF load (effect size = 0.38). A significant (p . 0.05) main effect of load existed for the bench press exercise; post hoc analysis indicated that the effect of load on power output was: 30% > 40% > 50% = 60%. CONCLUSION: Loads of 40% and 30% of MIF elicit maximal power output during dynamic leg presses and bench presses, respectively. These findings are similar to those obtained when loading is based on 1-RM.

Spiering, Barry A.↗
NASA NTRS2009

Time-to-Fatigue and Intramuscular pH Measured via NIRS During Handgrip Exercise in Trained and Sedentary Individuals

In exercising muscles force production and muscular endurance are impaired by a decrease in intramuscular pH. The effects of aerobic training (AT) on preventing acidosis and prolonging exercise time in muscles not specifically targeted by the training are unknown. Purpose: To compare interstitial pH, measured non-invasively with near infrared spectroscopy (NIRS), in the flexor digitorum profundus (FDP) during rhythmic handgrip exercise in sedentary subjects and those who participate in AT activities that target the lower body. Methods: Maximal isometric force (MIF) was measured on three separate days in AT (n=5) and sedentary (n=8) subjects using a handgrip dynamometer (HGD). Isometric muscular endurance (IME) was measured during five trials, each separated by at least 48 hrs. For each IME trial subjects rhythmically squeezed (4 sec at 40% of MVC) and relaxed (2 sec) to fatigue or failure to reach the target force in three consecutive contractions or four non-consecutive contractions. Interstitial pH was derived from spectra collected using a NIRS sensor adhered to the skin over the FDP. The first four IME trials served to familiarize subjects with the protocol; the fifth trial was used for analysis. NIRS-derived pH was averaged in 30 sec increments. Between group differences in MIF and exercise time were tested using paired t-tests. A repeated measures ANOVA was used to analyze effects of AT and exercise time on pH. Results: MIF was not different between groups (mean SD; aerobic=415.6 95.4 N vs. sedentary =505.1 107.4 N). Time to fatigue was greater in the AT than in the sedentary group (mean SD: 611 173 sec vs. 377 162 sec, p<0.05). pH was not different between groups at any time point. Average pH decreased (p<0.05) in both groups from rest (pH=7.4) through 90 sec of exercise (pH=6.9), but did not decrease further throughout the remainder of exercise. Conclusion: Although between group differences in pH were not detected, differences during the onset of exercise may exist with a more frequent sampling. AT individuals appear to better tolerate decreased interstitial pH and are able to continue submaximal muscular work, possibly due to psychological familiarization to muscular fatigue and/or systemic physiological benefits.

Everett, M. E.↗
NASA NTRS2008

Arterial Structure and Function in Women and Men Following Long Duration Bed Rest

Orthostatic intolerance is a well-recognized consequence of space flight and bed rest (BR), with a greater incidence reported in women. We hypothesized that leg, but not arm, arterial structure and function would be altered following prolonged BR, as a model of space flight, and that women would be more susceptible to BR-induced deconditioning than men. METHODS: Ten volunteers (5 males, 5 females) completed 90 d of 6 head-down BR. Subjects participated in tests of brachial (BA) and anterior tibial (AT) artery endothelium-dependent (flow mediated dilation [FMD] following 5-7 min of arterial occlusion) and endothelium-independent (0.4 mg sublingual nitroglycerin [SN]) vasodilation before BR (PRE) and on days 7 (BR7), 21 (BR21), and 90 (BR90) of BR. Vessel diameter and intimal medial thickness (IMT) were measured by ultrasound. IMT, baseline diameter, and percent change in diameter from baseline during FMD and SN tests were compared across BR and between genders using repeated measures two-way ANOVA with Bonferroni post-hoc tests in which PRE and women were control conditions. RESULTS: Baseline vessel diameter was lower in women than in men in both the BA (p=0.005) and AT (p=0.01) across all days. Baseline AT diameter decreased during BR (p=0.01) and tended to be more profound in women (interaction, p=0.06). AT diameter was reduced in women at BR21 and BR90 (p<0.01) but not in men. In contrast, there was no BR effect on baseline BA diameter. IMT also decreased in the AT (p<0.001) but not in the BA during BR; AT IMT was reduced by BR21 (p<0.05). As a group, there was no effect of BR on AT FMD, BA FMD, and AT SN-dilation, although BA SN-dilation was significantly reduced on BR21 (p=0.01). Across all BR days, women exhibited higher AT FMD (p=0.03), BA FMD (p=0.02), and BA SN-dilation (p=0.01) and tended to demonstrate greater AT SN-dilation (p=0.11). CONCLUSIONS: These preliminary results suggest that arterial remodeling occurs during BR in the leg (decreased diameter and IMT), but not in the arm, and that women appear to be more responsive to BR than men. These changes in the leg, coupled with larger responses to direct and indirect stimulation of the arterial smooth muscle, may be related to the greater incidence of orthostatic intolerance in women after BR and space flight.

Lee, Stuart M. C.↗
NASA NTRS2008

Near-Infrared Spectroscopic Measurements of Calf Muscle during Walking at Simulated Reduced Gravity - Preliminary Results

Consideration for lunar and planetary exploration space suit design can be enhanced by investigating the physiologic responses of individual muscles during locomotion in reduced gravity. Near-infrared spectroscopy (NIRS) provides a non-invasive method to study the physiology of individual muscles in ambulatory subjects during reduced gravity simulations. PURPOSE: To investigate calf muscle oxygen saturation (SmO2) and pH during reduced gravity walking at varying treadmill inclines and added mass conditions using NIRS. METHODS: Four male subjects aged 42.3 +/- 1.7 years (mean +/- SE) and weighing 77.9 +/- 2.4 kg walked at a moderate speed (3.2 +/- 0.2 km/h) on a treadmill at inclines of 0, 10, 20, and 30%. Unsuited subjects were attached to a partial gravity simulator which unloaded the subject to simulate body weight plus the additional weight of a space suit (121 kg) in lunar gravity (0.17G). Masses of 0, 11, 23, and 34 kg were added to the subject and then unloaded to maintain constant weight. Spectra were collected from the lateral gastrocnemius (LG), and SmO2 and pH were calculated using previously published methods (Yang et al. 2007 Optics Express ; Soller et al. 2008 J Appl Physiol). The effects of incline and added mass on SmO2 and pH were analyzed through repeated measures ANOVA. RESULTS: SmO2 and pH were both unchanged by added mass (p>0.05), so data from trials at the same incline were averaged. LG SmO2 decreased significantly with increasing incline (p=0.003) from 61.1 +/- 2.0% at 0% incline to 48.7 +/- 2.6% at 30% incline, while pH was unchanged by incline (p=0.12). CONCLUSION: Increasing the incline (and thus work performed) during walking causes the LG to extract more oxygen from the blood supply, presumably to support the increased metabolic cost of uphill walking. The lack of an effect of incline on pH may indicate that, while the intensity of exercise has increased, the LG has not reached a level of work above the anaerobic threshold. In these preliminary studies, 30% incline walking at reduced gravity may not require anaerobic LG activity due to the low exercise intensity (42.8 +/- 1.6% of VO(sub 2max)). It is also possible that at reduced gravity additional work is being done by muscle groups other than the calf.

Ellerby, Gwenn E. C.↗
NASA NTRS2009

Muscle Volume Increases Following 16 Weeks of Resistive Exercise Training with the Advanced Resistive Exercise Device (ARED) and Free Weights

Space flight-induced muscle atrophy, particularly in the postural and locomotorymuscles, may impair task performance during long-duration space missions and planetary exploration. High intensity free weight (FW) resistive exercise training has been shown to prevent atrophy during bed rest, a space flight analog. NASA developed the Advanced Resistive Exercise Device (ARED) to simulate the characteristics of FW exercise (i.e. constant mass, inertial force) and to be used as a countermeasure during International Space Station (ISS) missions. PURPOSE: To compare the efficacy of ARED and FW training to induce hypertrophy in specific muscle groups in ambulatory subjects prior to deploying ARED on the ISS. METHODS: Twenty untrained subjects were assigned to either the ARED (8 males, 3 females) or FW (6 males, 3 females) group and participated in a periodizedtraining protocol consisting of squat (SQ), heel raise (HR), and deadlift(DL) exercises 3 d wk-1 for 16 wks. SQ, HR, and DL muscle strength (1RM) was measured before, after 8 wks, and after 16 wks of training to prescribe exercise and measure strength changes. Muscle volume of the vastigroup (V), hamstring group (H), hip adductor group (ADD), medial gastrocnemius(MG), lateral gastrocnemius(LG), and deep posterior muscles including soleus(DP) was measured using MRI pre-and post-training. Consecutive cross-sectional images (8 mm slices with a 2 mm gap) were analyzed and summed. Anatomical references insured that the same muscle sections were analyzed pre-and post-training. Two-way repeated measures ANOVAs (p<0.05) were used to test for differences in muscle strength and volume between training devices. RESULTS: SQ, HR, and DL 1RM increased in both FW (SQ: 49+/-6%, HR: 12+/-2%, DL: 23+/-4%) and ARED (SQ: 31+/-4%, HR: 18+/-2%, DL: 23+/-3%) groups. Both groups increased muscle volume in the V (FW: 13+/-2%, ARED: 10+/-2%), H (FW: 3+/-1%, ARED: 3+/-1 %), ADD (FW: 15=/-2%, ARED: 10+/-1%), LG (FW: 7+/-2%, ARED: 4+/-1%), MG (FW: 7+/-2%, ARED: 5+/-2%), and DP (FW: 2+/-1%; ARED: 2+/-1%) after training. There were no between group differences in muscle strength or volume. CONCLUSIONS: The increase in muscle volume and strength following ARED training is not different than FW training. With the training effects similar to FW and a 600 lb load capacity, ARED likely will protect against muscle atrophy in microgravity.

Nash, R. E.↗
NASA NTRS2009

Effect of Pharmacologically-Induced Hypovolemia on Aerobic Capacity

Decreased peak oxygen consumption (VO2pk) and an elevated exercise heart rate (HR) response are associated with a reduction in plasma volume (PV) after space flight and bed rest, a space flight analog. Reduced VO2pk and submaximal exercise tolerance would negatively impact an astronaut s ability to perform near maximal work that would be required in the event of an emergency. We previously have administered IV furosemide followed by a low salt diet to model PV loss and orthostatic intolerance observed after spaceflight. Purpose: To determine whether a pharmacologically-induced reduction in PV results in decreased VO2pk and elevated exercise HR response. Methods: Six subjects (5M, 1F) performed two graded peak cycle tests (work rate increased by 35 or 50 W every 3 min), once while normovolemic and once while hypovolemic. HR and expired respiratory gases were continuously measured. To induce hypovolemia, subjects were administered a single dose of IV furosemide (0.5 mg.kg-1) 30 hr before exercise testing and then consumed a low-salt diet (10 mEq.d(sup -1)). PV was measured using carbon monoxide rebreathing. Exercise HR and VO2 responses were quantified as the area under the curve (AUC) calculated over each quartile of the peak test, based on test time in the hypovolemia condition. Paired t-tests were used to test for differences in PV, VO2pk, and peak HR between conditions. Repeated-measures ANOVAs were used to test for differences in AUC between conditions. Results: PV (3.32+/-0.12 vs. 2.77+/-0.16 L, p<0.05) and VO2pk (3.30+/-0.67 vs. 2.90+/-0.57 L.min(sup -1), p<0.05) were lower during hypovolemia than during normovolemia, but peak HR was not different (187+/-5 vs. 187+/-5 bpm). The AUC for VO2 and HR was different (p<0.05) between conditions only in the highest quartile: HR was 4% higher and VO2 was 5% lower during the hypovolemia condition. Conclusion: The mean difference in VO2pk (-12%) between normovolemia and hypovolemia was similar to the mean difference in PV (-17%). Similar decreases in PV and VO2pk have been observed following short duration space flight, suggesting that pharmacologically-induced PV loss can be used to model microgravity-induced reductions in VO2pk.

Everett, Meghan E.↗