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PubMed2005

Porous media matric potential and water content measurements during parabolic flight.

Control of water and air in the root zone of plants remains a challenge in the microgravity environment of space. Due to limited flight opportunities, research aimed at resolving microgravity porous media fluid dynamics must often be conducted on Earth. The NASA KC-135 reduced gravity flight program offers an opportunity for Earth-based researchers to study physical processes in a variable gravity environment. The objectives of this study were to obtain measurements of water content and matric potential during the parabolic profile flown by the KC-135 aircraft. The flight profile provided 20-25 s of microgravity at the top of the parabola, while pulling 1.8 g at the bottom. The soil moisture sensors (Temperature and Moisture Acquisition System: Orbital Technologies, Madison, WI) used a heat-pulse method to indirectly estimate water content from heat dissipation. Tensiometers were constructed using a stainless steel porous cup with a pressure transducer and were used to measure the matric potential of the medium. The two types of sensors were placed at different depths in a substrate compartment filled with 1-2 mm Turface (calcined clay). The ability of the heat-pulse sensors to monitor overall changes in water content in the substrate compartment decreased with water content. Differences in measured water content data recorded at 0, 1, and 1.8 g were not significant. Tensiometer readings tracked pressure differences due to the hydrostatic force changes with variable gravity. The readings may have been affected by changes in cabin air pressure that occurred during each parabola. Tensiometer porous membrane conductivity (function of pore size) and fluid volume both influence response time. Porous media sample height and water content influence time-to-equilibrium, where shorter samples and higher water content achieve faster equilibrium. Further testing is needed to develop these sensors for space flight applications.

Biosensing Techniques↗
PubMed1999

Premature ventricular contractions during +Gz with and without pressure breathing and extended coverage anti-G suit.

BACKGROUND: High +Gz is known to provoke cardiac dysrhythmias. Pressure breathing during G (PBG) and extended coverage anti-G suits (ECGS) are used to enhance +Gz-endurance and reduce fatigue during high +Gz flying. It is not known whether PBG in combination with ECGS increases the risk for premature ventricular contractions (PVC). HYPOTHESIS: PBG in combination with ECGS increases the risk of PVCs during high +Gz-loads. METHODS: Retrospective data were obtained from 14 subjects exposed to three different simulated aerial combat sorties each, in the centrifuge with a standard anti-G suit ensemble or with PBG in combination with ECGS. Each sortie consisted of a gradual onset G-exposure (GOR) and three simulated aerial combat maneuvers (SACM) containing four cycles of a +4.5 to +7 GzSACM; four cycles of +4 to +9 Gz tactical aerial combat maneuver (TACM) with several rapid transitions from +4 or +5 Gz to +8 or +9 Gz; and four cycles of +5 to +9 Gz SACM (5-9 SACM) with four cycles. ECG was recorded during the +Gz exposures to reveal any cardiac dysrhythmias. RESULTS AND CONCLUSIONS: No PVCs occurred during the GORs. During 4.5-7 SACMs, TACMs, and 5-9 SACMs there were 83, 50, and 24 PVCs with standard equipment, respectively, and 63, 54, and 39 PVCs with PBG and ECGS, respectively. There was no statistically significant difference between the equipment in any of the different types of +Gz exposures. No episodes of supraventricular tachycardia or relative bradycardia were found with either equipment.

Adult↗
PubMed1999

Degradation of visual pursuit during sustained +3 Gz acceleration.

BACKGROUND: During positive acceleration, there is a diminished flow of blood to all regions above the heart. This is manifested by the commonly described loss of peripheral vision, greyout and blackout, which have been investigated extensively. The ability to select appropriate scanning patterns and to efficiently process visual information is one of the important determinants of scan effectiveness. This study investigates the performance of the smooth pursuit system under sustained +3 Gz before any signs of loss of vision. METHODS: Eleven subjects with no known oculomotor and vestibular anomalies participated in the study. Horizontal and vertical pursuit at amplitudes of 10 and 20 degrees were investigated in each of the subjects over 4 separate days. During each test session, pursuit targets of a predictable sine wave, oscillating at 0.2, 0.4, 0.8, 1.2 and 1.6 Hz were presented to the subjects in a random order. Horizontal and vertical eye movements were recorded using the El-Mar eye tracking system. The subjects were tested in 4 trials: 1) at 1 G before exposure to increased acceleration; 2) during sustained +3 Gz; 3) immediately after the +3 Gz exposure; and 4) 5 min after the +3 Gz exposure. RESULTS: Breakdown in smooth pursuit in response to horizontal and vertical sinusoidal stimuli during +3 Gz is indicated by a statistically significant decrease in gain and an increase in phase lag (p < 0.01). This is most obvious when the stimulus frequency is greater than 0.4 Hz. Qualitatively, the pursuit response during acceleration was ataxic and disorganized in appearance. CONCLUSION: It is postulated that degradation of pursuit gain and phase could be due to central hypoxia, and that the increase of G loading on the vestibular system could affect the neural integration of the pursuit signal in the vestibular nuclei with its direct output to the oculomotor system.

Acceleration↗
PubMed1999

Echocardiographic evaluation of female centrifuge subjects for chronic changes in cardiac function.

BACKGROUND: High sustained G exposure as experienced in flying high performance aircraft can affect cardiac function. Numerous studies, mostly on male pilots, have evaluated the chronic effects of exposure to high G. To date, none of these studies has revealed significant positive findings in cardiac function as a result of long-term high G exposure. METHODS: A longitudinal study was conducted on six female centrifuge panel members who did not have a history of significant high +Gz exposure. Baseline echocardiographic studies were conducted prior to any +Gz exposure on the Dynamic Environment Simulator (DES) centrifuge. The echocardiograms were repeated after each panel member completed approximately 100 3-min high G (up to 9 G) exposures over the period of 7 mo. These follow-up echos were performed after all six subjects had been exposed to at least 6 h (cumulative) of sustained acceleration > 3 G. The women were protected with the COMBAT EDGE positive pressure breathing G protection ensemble. Each subject served as her own control. All studies were evaluated independently by a cardiologist who was blinded to the order in which the echos were performed. Although complete echocardiographic studies were performed, only the parameters identified as significant in prior studies were evaluated. RESULTS: No significant differences were found between the initial and follow-up echo parameters. CONCLUSIONS: We found no significant differences in cardiac function after at least 6 and up to 17 h (cumulative) of exposure to G > 3 in women. These subjects will be monitored during a longitudinal study throughout their centrifuge subject career.

Aerospace Medicine↗
PubMed1999

Visual symptoms and G-LOC in the operational environment and during centrifuge training of Turkish jet pilots.

BACKGROUND: High-performance fighter aircraft produce high-sustained +Gz forces with rapid onset rates. Because of this G-producing capability, military jet pilots are subjected to physiological stress, which may lead to visual disturbances and G-induced loss of consciousness (G-LOC). Although visual disturbances are very common in jet flights, G-LOC is relatively rare but more dangerous. The frequency and causes of G-LOC need to be determined in the interest of flight safety. METHODS: Part I. A survey was conducted on Turkish jet pilots to reveal the incidence of symptoms due to +Gz acceleration. Anonymous questionnaires were given to F-16, F-4, and F-5 pilots. They consisted of inquiries about the occurrence of visual symptoms and/or G-LOC during +Gz acceleration in the operational environment. Part II. During the years 1992-1996, 486 F-16, 801 F-4, and 256 F-5 fighter pilots underwent high "G" training at Turkish Aerospace Medical Center and they were assessed in terms of G-LOC rates. RESULTS: Part I. A total of 325 pilots who flew T-37 in undergraduate pilot training (UPT) answered the questionnaire. The pilots were divided into 3 groups according to the types of aircraft, which they fly now: 116 F-16, 182 F-4, and 27 F-5 pilots. A total of 311 pilots (95.7%) reported having experienced greyouts and/or blackouts. With 25 pilots (7.7%) experiencing G-LOC, the G-LOC frequency according to the type of aircraft was: 5.2% (T-37) [in UPT]; 4.3% (F-16), 1.6% (F-4), and 0% (F-5). Part II. In centrifuge training, the incidence of G-LOC in pilots of the various types of aircraft were: 12% (F-16), 6.4% (F-4), and 8.6% (F-5). CONCLUSIONS: Centrifuge training reduces G-LOC rates of subsequent centrifuge training; and it is hoped might reduce the G-LOC rate in the operational environment. Almost all jet pilots reported having experienced +Gz related visual symptoms, but G-LOC seems to be a more common problem for pilots who fly rapid onset rate aircraft than pilots who fly high "G" capable but lower G onset rate aircraft.

Acceleration↗
PubMedDate not supplied

[The participation of the nontraditional neuromediator nitric oxide in the mechanisms of adaptation to extreme conditions].

The investigation was performed on the medial (MMS) and lateral (LMS) magnocellular subdivisions of the hypothalamic paraventricular nuclei (HPN). The histochemical activity NO synthesizing enzyme nitric oxide synthase or NOS whose histochemical marker is NADPH-diaphorase (NADPH-D), immunocytochemical content of oxytocin (OXY), vasopressin (VP) and nucleoli sizes (squares) were studied in the mature male rats under experimental reconstruction of the both micro- and macrogravity, which are factors of the gravity field changes acting to the body during the space flight. Two experimental effects were used: B--tail suspending (imitation of the microgravity effects), C--centrifugation at 2 G (imitation of the macrogravity effects). The effect durations were designed as a time period when body is mostly affected by (1 day) and adapted (15 days) to the stress. There were 6 animal groups. 1--B(15 days), 2--B(15 days) succeeded by C(1 day), 3--B(15 days) succeeded by C(15 days), 4--C(1 day), 5--C(15 days), 6--intact animals. The histochemically and immuno-cytochemically stained neurons developing the high, moderate and small reaction intensity were counted in serial HPN sections under the light microscope and the results obtained were transformed to percent neuron contents. The nucleoli squares were examined by using the TV analyser. The histochemical staining intensity of NADPH-D in MMS is enhanced in the animals of the groups 1-4; the number of NADPH-D staining neurons with high enzyme activity was increased in 8-14 times. In the animals of group 5 the NADPH-D activity did not differ from the intact animals. The number of MMS neurons with high OXY immunoreactivities was increased up to 1.5-1.7 times in groups 1-5 if compared to those of intact controls. VP-positive neurons of LMS developed the similar increase in number of the high staining neurons in experimental animals as well as OXY-positive neurons of MMS. The nucleoli enlargement was observed in MMS (in 1.3-1.5 times) of groups 1-5 (insignificantly in group 5) and in the most magnocellular neurons LMS (in 1.5-1.7 times) of group 2-5 except group 1 where nucleoli were insignificantly decreased. The nucleoli sizes of group 4 were more than group 5. So the hypothalamo-neurohypophyseal system was activated in the animals subjected of the earthly correlates of micro- and macrogravity. The data obtained suggest involvement both the nonconventional neurotransmitter NO and stress-related peptides OXY and VP in the mechanisms subserving adaptation to the extreme factors by what a human has to be faced with during the space flight.

Adaptation, Physiological↗
PubMed1999

Patterns of physical conditioning in Royal Australian Air Force F/A-18 pilots and the implications for +Gz tolerance.

BACKGROUND: The role of physical conditioning in tolerance to +Gz remains the subject of debate, particularly in relation to the relative merits of aerobic vs. anaerobic conditioning. The purpose of this study was to document the patterns of physical conditioning in Royal Australian Air Force (RAAF) fighter pilots and to relate these findings to the question of +Gz tolerance. METHODS: A questionnaire was used to determine the physical conditioning activities of RAAF F/A-18 pilots. Aerobic fitness levels (VO2max) were determined in a sample of eight pilots using a progressive cycle ergometer protocol. RESULTS: Of the 42 F/A-18 pilots who completed the questionnaire, 86% reported regular physical conditioning, mostly three times per week. Aerobic activities were the most common (83%), with running the most popular activity (55%). Anaerobic activities were reported by 26% of respondents. Most respondents reported doing more than one activity, with an average weekly training volume of 129+/-77 min. The ergometer test results revealed a mean VO2max of 50+/-6 ml O2 x kg x min(-1). CONCLUSION: The high rates of participation in regular physical activity suggest that physical fitness is perceived as important by the fighter pilot operating in the high +Gz environment. The fighter pilots in this study participated in aerobic activities at a much higher rate than anaerobic activities. The aerobic fitness levels measured suggest that the pilots have good but not exceptionally high levels of aerobic power that are unlikely to influence +Gz tolerance.

Adult↗
PubMed1999

Thoracolumbar pain among fighter pilots.

High +Gz forces place high stress on the spinal column, and fighter pilots flying high-performance fighter aircraft frequently] report work-related thoracic and lumbar spine pain. The aim of this study was to determine whether +Gz exposure causes work-related thoracolumbar spine pain among fighter pilots. A questionnaire was used to establish the occurrence of thoracic and lumbar spine pain during the preceding 12 months and during duties over the whole working career among 320 fighter pilots and 283 nonflying controls matched for age and sex. Thirty-two percent of the pilots and 19% of the controls had experienced pain in the thoracic spine during the preceding 12 months (odds ratio [OR] = 2.3; 95% confidence interval [CI] = 1.5-3.5; p = 0.002 for the pilots). Among the pilots, the OR increased up to 6.1 (95% CI = 1.6-23.1; p = 0.0007) with the number of +Gz flight hours. There was no difference between the groups with regard to lumbar pain during the preceding 12 months, but over their whole working careers fighter pilots (58%) had experienced lumbar pain during their duties more often than controls (48%) (OR = 1.8; 95% CI = 1.3-2.6; p = 0.002). The greater the number of +Gz flight hours, the greater the occurrence of lumbar spine pain when on duty (OR = 26.9; 95% CI = 6.2-116; p = 0.0001 for the most experienced fighter pilots). The same was not true with regard to the number of +Gz flight hours and lumbar pain during the preceding 12 months. Age had no effect on pain in the thoracic or lumbar spine. Fighter pilots flying high-performance aircraft have more work-related thoracic and lumbar spine pain than controls of the same age and sex. The difference is explained by the pilots' exposure to +Gz forces.

Adult↗
PubMed1999

Gender and effect of impact acceleration on neck motion.

BACKGROUND: With the opening of the fighter cockpit to women, it became imperative to expand the current database of responses of females to both sustained and impact acceleration environments. With less upper-body strength (lean body mass) than men, it was hypothesized that women would not brace their heads as effectively against the loads occurring during high G-loading in flight and during impact and escape. This scenario creates increased potential for injury, exacerbated by the changing center of gravity and weight of helmets due to technological advances (e.g., night vision, head-up displays, etc.). METHODS: The main objective of this experimental effort was measuring the ability of subjects of both sexes to brace against an impact acceleration of -6.5 Gx or +4.0 Gy. An attempt was made to identify a correlation between such ability, static strength measurements, anthropometric measurements, or any combination thereof. RESULTS: No correlation was found between any of the static strength or anthropomorphic parameters and the amplitude of head motion. The isometric strength measurements correlated well with the size, weight, and neck circumference of the subjects, but none of these proved useful in predicting head displacement. However, there was a strong relationship between neck force exerted just before impact and head motion in the -Gx study, and somewhat less correlation for the +Gy impacts. CONCLUSION: It is useful to estimate resistance to impact by measuring neck strength, but only under conditions where the subject is highly motivated.

Acceleration↗
PubMed1999

Cognitive performance and physiological changes in females at high G while protected with COMBAT EDGE and ATAGS.

BACKGROUND: Female fighter pilots are flying the F-16 and F-15 with COMBAT EDGE, the positive pressure breathing under G (PBG) protection system. The standard CSU 13 B/P anti-G suit may soon be replaced with the Advanced Technology Anti-G suit. The purpose of this research was to compare human performance and physiological changes between the subjects protected by COMBAT EDGE with the standard anti-G suit (STD) and with the Advanced Technology Anti-G Suit (ATAGS). METHODS: Six female centrifuge subjects completed this experiment. Performance of the 3-min simulated aerial combat sorties on the Dynamic Environment Simulator. Heart rate, %SaO2 (percent arterial oxygen saturation), %rSO2 (percent regional cerebral tissue oxygen saturation) and electromyography (EMG) were compared between the two suit conditions. Subjective evaluations of the two suit conditions were also collected. RESULTS: No significant performance differences or EMG differences were found between the STD and ATAGS suits. In the ATAGS suit, %rSO2 and %SaO2 were significantly less and heart rate was significantly lower during the last minute of G exposure compared with the STD condition. Subjects rated the ATAGS suit as having provided better G tolerance, but more uncomfortable. The ATAGS were prototype suits, however, and were not custom fit to the women. CONCLUSIONS: Physiological changes did occur significantly during the last minute of G exposure, even though no significant performance differences were found between two suit conditions. Subjective comments supported the finding that the more G protection and body coverage afforded by the anti-G suit, the less comfortable the suit may be.

Adult↗
PubMed1999

MRI cervical spine findings in asymptomatic fighter pilots.

MRI of the cervical spine for evaluation concerning degenerative lesions was performed on asymptomatic experienced military high performance aircraft pilots (mean age 42 yr with mean accumulated flying time of 2600 h), and for comparison on age-matched controls without military flying experience. Young military high performance aircraft pilots (mean age 23 yr with 220 h of flying per person) were also examined. There were significantly more osteophytes, disk protrusions, compressions of the spinal cord and foraminal stenoses in the experienced pilots than in the age-matched controls. Low frequency of low grade degenerative lesions was found in the young and inexperienced pilots.

Adult↗
PubMed1999

Repetitive high G exposure is associated with increased occurrence of cardiac valvular regurgitation.

BACKGROUND: Exposure to repeated high +Gz loads and the methods to prevent loss of consciousness cause unique stresses on the cardiovascular system. The purpose of this study was to determine if the +Gz environment is associated with an increased occurrence of valvular regurgitation in pilots of high performance aircraft. METHODS: There were 247 subjects who were divided into pilot (n = 46) and non-pilot (n = 201) groups. Pilots were defined as those individuals who had flown at least 1000 h in high performance aircraft. The echocardiographic data of these subjects were examined retrospectively. RESULTS: We found a statistically significant association between pulmonic insufficiency and exposure to high +Gz stress in pilots vs. non-pilots (chi2 = 13.09, p = 0.0002). In addition, there was a greater incidence of tricuspid regurgitation (chi2 = 4.97, p = 0.025) and concurrent pulmonic insufficiency and tricuspid regurgitation (chi2 = 14.1, p = 0.0002) in the pilot group. CONCLUSIONS: There is a direct relationship between repetitive exposure to a +Gz environment and pulmonic insufficiency, tricuspid regurgitation, or concurrent pulmonic insufficiency and tricuspid regurgitation. This may be secondary to the transient increase in right ventricular pressure due to acceleration forces or straining maneuvers utilized to prevent or postpone +Gz induced loss of consciousness (G-LOC).

Adult↗
PubMed1999

Degenerative changes of the spine of fighter pilots of the Royal Netherlands Air Force (RNLAF).

HYPOTHESIS: The aim of this study was to examine whether F-16 pilots are at an increased risk of (cervical) spine degeneration. METHOD: Retrospectively, X-ray slides were examined of pilots of the Royal Netherlands Air Force who were systematically radiographed (at least twice). In total, 316 pilots were evaluated: 188 F-16 pilots and 128 pilots in the control group. Two radiologists, who were blinded as to whether the X-ray films were of F-16 pilots or the control group, examined these X-rays separately. In both groups, the time between the two X-rays was on average 6 yr. RESULTS: Though the inter-rater agreement of the X-rays was rather low, both radiologists found comparable statistically significant differences between the two groups. In the F-16 group, an increased osteophytic spurring was found at levels C4-C5 and C6-C7, and increased arthrosis deformans was found in the cervical spine. Further analysis of the data of a selected group of pilots, whereby the difference in age between both groups was minimized, showed that the higher mean age of the F-16 pilots was possibly correlated with the increased degeneration in this group. No consistent relationship was found between spinal degeneration and initial radiological status. Also, a clear relationship between spinal degeneration and flying hours could not be demonstrated. CONCLUSION: These findings suggest that frequent exposure to high +Gz forces might cause premature degeneration of the spine of F-16 pilots. Future research must demonstrate to what extent age, mission, and number of flying hours have influenced the results. An uniform international classification and coding system in combination with establishing an international database is recommended.

Adolescent↗
PubMed2000

Urinary continence in women during centrifuge exposure to high +Gz.

BACKGROUND: One earlier study and anecdotal evidence suggest a possible association between exposure to high +Gz forces and urinary incontinence in women. High +Gz could possibly contributes to the prolapse of the bladder neck, moving it into a position which decreases the leak point pressure resulting in urinary incontinence. HYPOTHESIS: We tested the hypothesis that increased urinary incontinence is associated with high +Gz. METHODS: 25 females were exposed to a high +Gz profile. Following the exposure they were asked to answer a questionnaire grading their urinary continence under high +Gz, and to provide a baseline grading of their urinary continence at +1.0 Gz and under increased abdominal stress at +1.0 Gz. Demographic data included parity and previous urogenital surgery. Graded responses were dichotomized and data was analyzed using Fischer's Exact Test for 2x2 tables with significance set at alpha = 0.05. RESULTS: At high +Gz no significant association was found between reported urine incontinence and a history of urogenital surgery or parity. Only one of twenty-five subjects had any symptoms at high +Gz despite the fact that five had a predisposition. As expected, at +1.0 Gz and under increased abdominal stress at +1.0 Gz a significant association was found between reported urine incontinence and a history of urogenital surgery, while no significant association was found for parity. CONCLUSIONS: In this simple first look there was no increase in urinary incontinence at high +Gz even among those who reported a predisposition.

Aerospace Medicine↗
PubMed2000

Heart rate and blood pressure responses to +Gz following varied-duration -Gz.

BACKGROUND: The push-pull effect has been defined previously as decreased +Gz tolerance caused by previous baseline zero or -Gz exposure. Earlier work indicates that the delay in BP (BP) recovery during +Gz is a function of time at -G7, and is due to the lengthened time-course of sympathetically mediated peripheral vasoconstriction. HYPOTHESIS: The purpose of this study was to retrospectively determine whether heart rate (HR) varies with BP as duration at preceding -Gz increased. METHODS: Continuous ECG R-R interval data from 15 s of +2.25Gz after preceding 2, 5, 10, or 15 s at 2Gz obtained from previous experiments were analyzed and compared with the previously reported BP data. Repeated measures ANOVA and regression analyses were used to compare +2.25Gz HR responses after the four -Gz conditions and one control +2.25Gz condition. RESULTS: An initial rapid rise in HR was observed for all conditions with a consistent steady-state plateau achieved after the first 7 s of +2.25Gz. However, there were significant differences in mean HR attained during the +2.25Gz plateau for preceding 15 s -2.0 Gz vs. the control, 2, 5, and 10s -Gz conditions (109+/-1.1 vs. 102+/-1.8, 100+/-2.0, 97+/-1.1 and 101+/-1.1, bpm, respectively; p<0.05). CONCLUSIONS: HR, unlike BP, increases briskly across all preceding -Gz time conditions, adapting within the initial baroreflex-compensatory time frame typically expected for +Gz exposures. These results suggest there may be a threshold effect for HR response. Consequently, vasoconstrictor response is a critical adaptive mechanism during +Gz when preceded by long (>10 s) -Gz exposures.

Adaptation, Physiological↗
PubMed2000

In-flight cerebral oxygen status: continuous monitoring by near-infrared spectroscopy.

BACKGROUND: Little is known about the in-flight cerebral oxygen status (COS) of fighter pilots. The purpose of this study was to evaluate the COS of fighter pilots during an F-15DJ flight. METHODS: Three male F-15DJ fighter pilots volunteered to serve as test subjects during aerial gunnery training (AGT) missions. During the flight, the pilots' COS was continuously monitored from the right forehead using a NIRO-300G near-infrared spectrophotometer. This new instrument is capable of measuring the concentration changes in the brain of oxygenated hemoglobin (O2Hb), reduced hemoglobin (HHb), total hemoglobin (cHb, O2Hb + HHb), and the tissue oxygenation index (TOI, O2Hb/cHb). RESULTS: Continuous changes of COS within the brain were clearly demonstrated using NIRO-300G, the changes included reductions in O2Hb, cHb, and TOI with increased +Gz, in a mirror image fashion. The maximum decreased concentration of hemoglobin during flight ranged from 12.8 to 25.6 micromol x L(-1) (of brain tissue). CONCLUSIONS: We believe this study is the first monitoring of COS during F-15 actual flight. The monitoring of COS during F-15 flight showed that the effect of +Gz was to simultaneously lower blood flow in a mirror image fashion. Our results demonstrated that near-infrared spectroscopy (NIRO-300G) provides a reliable and sensitive method for the monitoring of pilots' COS during flight.

Acceleration↗
PubMed1998

Effect of centrifugation at 2G for 14 days on metabolic enzymes of the tibialis anterior and soleus muscles.

BACKGROUND: The enzyme composition of different muscle types vary greatly, leading to different changes of enzyme level caused by exposure to various stimuli. METHODS: Male Wistar rats were centrifuged at 2G in a 12-ft radius centrifuge for 14 d. Tibialis anterior (TA) and soleus muscles from four centrifuge and four control rats were analyzed for three enzymes characteristic of fast twitch muscles (phosphofructokinase, glycerol-3-phosphate dehydrogenase, and pyruvate kinase), and four enzymes characteristic of slow twitch muscles (hexokinase, mitochondrial thiolase, B-hydroxyacyl CoA dehydrogenase, and citrate synthase). RESULTS: The centrifuged TA muscles lost 15% of their weight; the corresponding soleus muscles gained 4%. Calculated on the basis of dry weight, the fast twitch enzyme activities were reduced 3-15% in the TA muscles but increased 10-23% in the soleus muscles. The slow twitch enzymes were reduced 18-30% in TA muscles but were almost unchanged in the soleus muscles. When calculated on the basis of total muscle weight, all of the enzymes in TA muscles were significantly reduced by centrifugation. In contrast, in soleus muscles, on the basis of total muscle weight, centrifugation caused an average increase of 22% in the fast twitch enzymes but only marginal changes in the slow twitch enzymes.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1998

Adaptation of rat gastrocnemius muscles to 2 weeks of centrifugation: myofibers and extracellular matrix.

BACKGROUND: The effect of 2 wk of exposure to centrifugation (2G) on gastrocnemius muscles of rats was investigated by morphometric and computer-assisted image analysis of muscle fiber areas and non-contractile tissue components (extracellular matrix). RESULTS: Muscle atrophy was seen in the myofibers from 2G rats which had decreased in cross-sectional area by 26%. In contrast, the non-contractile tissue component actually increased by 13%. These results were compared with soleus muscle atrophy seen following 2 wk of unloading by tail-suspension. In all cases, the extracellular matrix increased in proportion to the decrease in fiber area. A theoretical model was developed to assess the effect of changes in myofiber cross-sectional area on the relative content of the extracellular matrix. The experimental results from both rat gastrocnemius and soleus muscles were consistent with the model with slight variations due to the known differences in connective tissue content of different muscles in the rat. CONCLUSION: Thus, the gastrocnemius muscle atrophy seen after 2 wk of centrifugation results from loss of contractile and other myofiber specific proteins while the extracellular matrix remains relatively constant. The loss in myofiber content was greater than expected from changes in muscle wet weight and more than required to adapt to a decrease in body weight.

Adaptation, Physiological↗