Assembly of high-areal-density deuterium-tritium fuel from indirectly driven cryogenic implosions.

The National Ignition Facility has been used to compress deuterium-tritium to an average areal density of ~1.0±0.1 g cm(-2), which is 67% of the ignition requirement. These conditions were obtained using 192 laser beams with total energy of 1-1.6 MJ and peak power up to 420 TW to create a hohlraum drive with a shaped power profile, peaking at a soft x-ray radiation temperature of 275-300 eV. This pulse delivered a series of shocks that compressed a capsule containing cryogenic deuterium-tritium to a radius of 25-35 µm. Neutron images of the implosion were used to estimate a fuel density of 500-800 g cm(-3).

The restorative effects of pulsed infrared light therapy on significant loss of peripheral protective sensation in patients with long-term type 1 and type 2 diabetes mellitus.

Pulsed infrared light therapy (PILT) has been shown to increase peripheral sensation in diabetic patients with diabetic peripheral neuropathy (DPN). However, most studies last for very short periods, with the subjects receiving only 6-20 treatments. The purpose of this study was to evaluate the effectiveness of an eight-week course of PILT in reversing long-standing, profound DPN in patients with type 1 and type 2 diabetes. Twenty-two subjects with a diagnosis of type 1 (n=2) or type 2 (n=20) diabetes participated in the study. PILT was administered to one foot chosen at random with the other foot serving as a within-subject control (no treatment). Patients underwent 24 treatments (3 times/week, for eight weeks) for 30 min per treatment. Changes in peripheral protective sensation (PPS) were measured using Semmes-Weinstein monofilaments (SWM) ranging from 3.7 to 6.48. PILT improved PPS even in patients with long-standing chronic neuropathies whose initial pre-study sensation was not measurable with a 200-g SWM. PILT significantly improves PPS. While the exact mechanism of action is not understood, infrared light may improve peripheral neuropathies by improving foot perfusion by stimulating nitric oxide production.

Aerobic exercise in water versus walking on land: effects on indices of fat reduction and weight loss of obese women.

AIM: It has been suggested, that water exercise is less effective than weight-bearing exercise on land for body fat reduction. METHODS: To test this hypothesis 38 middle-aged obese women (25-47% body fat) participated in a 13 week exercise-diet program to compare the effects of aerobic exercise in water versus walking on land on indices of fat reduction and weight loss changes. Subjects were randomly assigned to 1 of 3 exercise groups: 1) walking on land (WL), 2) swimming (SW) at 27 degrees C water temperature and 3) walking in 29 degrees C water (WW) at the shallow end of a declining pool with the water at navel height. Subjects in the SW group alternated breast-, side-, and backstroke swimming without face immersion. Exercise parameters were kept constant for all three groups. Subjects participated in supervised exercise sessions for 40 min, 4 times a week at 70% of age-predicted maximum heart rate. Subjects were tested before and after the 13-week experimental period. RESULTS: Significant reductions in body weight, (5.9 kg), percent body fat, (3.7%), and skinfold and girth measurements, occurred in all groups. There where no significant differences between groups. CONCLUSIONS: The results of this study indicate that there are no differences in the effect of aerobic activities in the water versus weight-bearing aerobic exercise on land on body composition components as long as similar intensity, duration and frequency are used.

The prolonged hematologic effects of a single injection of PEG-rHuMGDF in normal and thrombocytopenic mice.

A single injection of > or =10 microg/kg PEG-rHuMGDF in mice causes a dose-dependent increase in circulating platelets beginning on day 3 and peaking on days 5-6. The mean platelet volume and platelet distribution width at doses > or =100 microg/kg initially increase in a dose-dependent fashion and later decrease. However, the mean platelet volume does not change when platelets are incubated with PEG-rHuMGDF in vitro. The number of marrow megakaryocytes increases in a dose-dependent fashion as early as day 1 and peaks on day 3. Marrow megakaryocyte colony-forming units (CFU-Meg) do not increase on days 1-3 at a dose of 100 microg/kg (a dose that increases platelet numbers two- to threefold and may be clinically relevant), but the relative frequency of high ploidy megakaryocytes and the proportion of large marrow megakaryocytes (29-50 microm in diameter) increases. After a dose of 1,000 microg/kg the percentage of megakaryocytes in mitosis peaks at 24-48 hours and the percentage of megakaryocytes incorporating BrdU is maximal at 48 hours, the relatively delayed peak of BrdU incorporation most likely representing endomitosis. The relative frequency of type II and III megakaryocytes peaks on days 3 and 4, respectively. Pharmacokinetic analysis of PEG-rHuMGDF shows peak serum concentrations at 2-4 hours and a terminal half-life of 11.4+/-2.5 hours. A single injection of PEG-rHuMGDF ameliorates carboplatin-induced megakaryocytopenia and thrombocytopenia in a dose-response dependent fashion. In conclusion, a single injection of PEG-rHuMGDF increases megakaryocyte and platelet production in normal and myelo-suppressed mice.

Noninvasive evaluation of world class athletes engaged in different modes of training.

This study evaluated by noninvasive methods the cardiac structure and functional characteristics of world class athletes participating in different types of training programs. Fourteen subjects, including 4 strength-trained (discus and shot put), 4 endurance-trained (long distance runners), 4 decathlon-trained (strength and endurance), 2 wheelchair athletes and 31 college-age control subjects were evaluated using electrocardiography, M-mode echocardiography and maximal oxygen consumption. M-mode echocardiography measurements of left ventricular structure and function were compared before and after normalization for lean body weight. As expected, endurance athletes had greater maximal O2 consumption than the other groups (p less than 0.05). Before normalization for lean body weight, there were no significant differences in end-diastolic dimensions. After normalization, the endurance, wheelchair and control subjects had end-diastolic dimensions larger than those of strength athletes. Strength athletes appeared to have a much larger posterior wall and septal thickness than all groups except the decathlon athletes. However, when normalized, there was no difference among any of the groups. Previous investigators have attempted to determine "normalcy" of cardiac hypertrophy by looking at the ratio of left ventricular wall thickness to left ventricular radius. In the present study, the thickness to radius ratio in strength athletes was 33% greater than that in endurance athletes. It appears that the left ventricular wall thickness in the strength athletes occurred without a concomitant increase in left ventricular radius and that the left ventricular hypertrophy of world class athletes is related to the total increase in lean body weight. However, ventricular dimensions may be related more to the type of overload experienced.

Glycogen repletion and exercise endurance in rats adapted to a high fat diet.

It is well accepted that exercise endurance is directly related to the amount of carbohydrate stored in muscle and that a low carbohydrate diet reduces glycogen storage and exercise performance. However, more recent evidence has shown that when the organism adapts to a high fat diet endurance is not hindered. The present study was designed to test that claim and to further determine if animals adapted to a high fat diet could recover from exhausting exercise and exercise again in spite of carbohydrate deprivation. Fat-adapted (3 to 4 weeks, 78% fat, 1% carbohydrates) rats (FAT) ran (28 m/min, 10% grade) as long as carbohydrate-fed (69% carbohydrates) animals (CHO) (115 v 109 minutes, respectively) in spite of lower pre-exercise glycogen levels in red vastus muscle (36 v 54 mumols/g) and liver (164 v 313 mumols/g) in the FAT group. Following 72 hours of recovery on the FAT diet, glycogen in muscle had replenished to 42 mumols/g (v 52 for CHO) and liver glycogen to 238 mumols/g (v 335 for CHO). The animals were run to exhaustion a second time and run times were again similar (122 v 132 minutes FAT v CHO). When diets were switched after run 1, FAT-adapted animals, which received carbohydrates for 72 hours, restored muscle and liver glycogen (48 and 343 mumols/g, respectively) and then ran longer (144 minutes) than CHO-adapted animals (104 minutes) that ate fat for 72 hours and that had reduced glycogen repletion. We conclude that, in contrast to the classic CHO loading studies in humans that involved acute (72 hours) fat feedings and subsequently reduced endurance, rats adapted to a high fat diet do not have a decrease in endurance capacity even after recovery from previous exhausting work bouts. Part of this adaptation may involve the increased storage and utilization of intramuscular triglycerides (TG) as observed in the present experiment.

Cocaine alters myosin isoform expression in the rat soleus.

The purpose of this study was to determine whether chronic cocaine administration alters the expression of myosin isoforms in the rat soleus. Forty-five adult Sprague-Dawley rats were divided into three groups: chronic cocaine (n = 15), 12.5 mg/kg cocaine-HCl injected intraperitoneally twice daily for 14 days and one injection of cocaine (12.5 mg/kg ip) on day 15; acute cocaine (n = 15), saline injections twice daily for 14 days and one injection of cocaine (12.5 mg/kg ip) on day 15; and chronic saline (n = 15), saline injections twice daily for 14 days and one saline injection on day 15. Myosin isoform content of the soleus (native and heavy chains) was identified by electrophoresis. The solei samples from the chronic saline and acute cocaine animals contained slow myosin only. However, solei samples from the chronic cocaine group contained slow myosin and two to three other myosin isoforms and the associated heavy chains IIa and IIx. Therefore, chronic cocaine administration causes in the rat soleus a shift in myosin expression from slow isoforms to fast isoforms.

Effect of cocaine on exercise endurance and glycogen use in rats.

To determine the effects of cocaine on exercise endurance, male rats were injected intraperitoneally with cocaine (20 mg/kg body wt) or saline and then run to exhaustion 20 min later at 22 m/min and 15% grade. Saline-injected animals ran 74.9 +/- 16.5 (SD) min, whereas cocaine-treated rats ran only 29 +/- 11.6 min. The drug had no effect on resting blood glucose or lactate levels, nor did it affect resting glycogen levels in liver or red and white vastus muscle. However, it did reduce resting soleus glycogen content by 30%. During exercise liver and soleus glycogen depletion occurred at the same rate in saline- and cocaine-treated animals. In contrast, the rate of glycogen depletion during exercise in red and white vastus was markedly increased in cocaine-treated rats with a corresponding elevation in blood lactate (12 vs. only 5 mM in saline group) at exhaustion. These data suggest that cocaine administration (20 mg/kg) before submaximal exercise dramatically alters glycogen metabolism during exercise, and this effect has a negative impact on exercise endurance.

Effects of 24-hour fast on cycling endurance time at two different intensities.

Ten competitive cyclists were exercised to exhaustion to test the potential of a 24-h fast for increasing endurance. One group (n = 4) was tested at an initial intensity of 86% maximum O2 uptake (VO2max) (HI) and a second group (n = 6) at 79% VO2max (MI). Both groups repeated test rides in fasted and normal-diet conditions. Time to fatigue was designated at two points: fatigue 1 occurred when pedal frequency could not be maintained at the initial percent VO2max; fatigue 2 occurred when pedal frequency could not be maintained at a workload of approximately 65% VO2max. In both HI and MI the 24-h fast had no effect on resting muscle glycogen stores but significantly increased plasma free fatty acid (FFA) levels. Despite the increased FFA availability, time to fatigue was reduced in the fasted groups. Fatigue 1 and 2 times (mean +/- SE) for HI-fasted were 42.0 +/- 6.2 and 170.0 +/- 20.4 min, respectively, compared with those of the HI-normal diet of 115.3 +/- 25.6 and 201.0 +/- 14.8 min. Fatigue 1 and 2 times for MI-fasted were 142.0 +/- 19.6 and 167.5 +/- 10.5 min compared with those of the MI-normal diet of 191.3 +/- 25.0 and 214.3 +/- 18.9 min. The cause of fatigue at fatigue 1 was not readily apparent. Fatigue 2 in all groups seemed to be related to hypoglycemia as well as muscle glycogen depletion.

Morderate diabetes alters myosin isoenzyme distribution in cardiac but not skeletal muscle of male rats.

Diabetes is known to alter the myosin phenotype of striated muscle, but the impact of the same diabetic state on different types of striated muscles remains unknown. Therefore, this study determined the myosin isoenzyme profile in the left ventricle, soleus, plantaris, and extensor digitorium longus (EDL) of young male rats made moderately diabetic with streptozotocin, (45 mg/kg, ip). Eight weeks after the single streptozotocin injection, tissues were collected and subsequently electrophoretically analyzed for native myosin isoenzyme distribution. Skeletal muscles were additionally analyzed for myosin heavy chain distribution. Neither the native myosin isoform nor the myosin heavy chain (MHC) distribution profiles of the skeletal muscles were altered by the diabetic state. In contrast, the high ATPase cardiac isoform, VI, was significantly replaced by the low ATPase isoform, V3 (p < 0.05). These results demonstrate that striated muscle responds to a moderate diabetic state in a limited and muscle specific fashion. Significantly, the change in the cardiac myosin isoform profile is comparable to that which occurs in a more severe diabetic state.

BIBP3226 inhibits neuropeptide Y and pancreatic polypeptide potentiated neurogenic vasoconstriction.

Neuropeptide Y (NPY) potentiates the contractile response of the rat caudal artery to adrenergic nerve stimulation in-vitro. The NPY Y1 selective antagonist BIBP3226 ((R)-N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]-argininami de), inhibited the vascular effects of NPY in rat caudal artery preparations in-vitro (IC50 =126 nM). BIBP3226 also inhibited the effects of the selective Y1 agonist [Leu31,Pro34]NPY and completely abolished the effects of avian pancreatic polypeptide that was shown to be capable of potentiating neurogenic vasoconstriction in this preparation. These effects were reversible and are most likely mediated by the Y1 receptor subtype since we failed to observe any functional evidence of a Y2 receptor subtype in rat caudal artery. The caudal artery provides a useful functional assay for pharmacological analysis of NPY and NPY antagonists.

Muscle glycogen supercompensation is enhanced by prior creatine supplementation.

PURPOSE: Recently, it was shown that glycogen supercompensation tended (P = 0.06) to be greater if creatine and glycogen were loaded simultaneously. Because the authors suggested that creatine loading increased cell volumes and, therefore, enhanced glycogen supercompensation, we decided to determine whether an enhanced glycogen supercompensation could be realized if the glycogen loading protocol was preceded by a 5-d creatine load. METHODS: Twelve men (19-28 yr) performed two standard glycogen loading protocols interspersed with a standard creatine load of 20 g.d(-1) for 5 d. The vastus lateralis muscle was biopsied before and after each loading protocol. RESULTS: The initial glycogen loading protocol showed a significant 4% increase (P < 0.05) in muscle glycogen (Delta upward arrow 164 +/- 87 mmol.kg(-1) d.m.), and no change (P > 0.05) in total muscle creatine. Biopsies pre- and post-creatine loading showed significant increases in total muscle creatine levels in both the left leg (Delta upward arrow 41.1 +/- 31.1 mmol.kg(-1) d.m.) and the right leg (Delta upward arrow 36.6 +/- 19.8 mmol.kg(-1) d.m.), with no change in either leg's muscle glycogen content. After the final glycogen loading, a significant 53% increase in muscle glycogen (Delta upward arrow 241 +/- 150 mmol.kg-1 d.m.) was detected. Finally, the postcreatine load total glycogen content (694 +/- 156 mmol.kg(-1) d.m.) was significantly (P < 0.05) greater than the precreatine load total glycogen content (597 +/- 142 mmol.kg(-1) d.m.). CONCLUSION: It is suggested that a muscle's glycogen loading capacity is influenced by its initial levels of creatine and the accompanying alterations in cell volume.

Consequences of combining strength and endurance training regimens.

A common belief among many clinicians and trainers is that intensive simultaneous training for muscle strength and cardiovascular endurance is counterproductive. To test this premise, 14 healthy, untrained men trained four days per week for 20 weeks on a bicycle ergometer for endurance (END Group, n = 4), on an isokinetic device for increased torque production (ITP Group, n = 5), or on both devices (COMBO Group, n = 5). The ITP and COMBO groups had equal torque gains throughout the study (234 +/- 45 and 232 +/- 23 N.m, respectively). After 11 weeks, both END and COMBO groups had similar gains in maximal oxygen consumption (VO2max) (in milliliters per kilogram of body weight per minute). During the last half of the study, however, the END Group had a significant gain in VO2max (p less than .05) of 4.7 +/- 1.2 mL.kg-1.min-1, whereas the COMBO Group had a nonsignificant gain (p greater than .05) of 1.8 +/- 0.6 mL.kg-1.min-1. In harmony with this finding, the END Group showed a significant increase (p less than .05) in citrate synthase activity (15.5 +/- 7.9 mumol.g-1.min-1), whereas the COMBO Group had no significant increase. The authors concluded that simultaneous training may inhibit the normal adaptation to either training program when performed alone. The extent of the interference probably depends on the nature and intensity of the individual training program. [Nelson AG, Arnall DA, Loy SF, et al: Consequences of combining strength and endurance training regimens.

Proprioceptive neuromuscular facilitation versus weight training for enhancement of muscular strength and athletic performance*.

This study was designed to examine the effects of proprioceptive neuromuscular facilitation (PNF) and weight training (WT) on muscular strength and athletic performance. Thirty college women were randomly assigned to one of three groups: WT, PNF, and control. WT and PNF subjects trained 3 days a week for 8 weeks. All subjects were tested for changes in knee and elbow extensor strength, throwing distance, and vertical jump. The WT group increased strength by 19.3% for knee extension and 20.4% for elbow extension while the PNF group increaseil22.1 and 29.1 %, respectively. PNF also increased throwing distance by 25% and vertical jump by 16% while WT had increases of 12.8 and 9.9% respectively. These findings indicate PNF might be superior to WT in athletic performance enhancement and, therefore, the better modality for athletic conditioning and injury rehabilitation. J Orthop Sports Phys Ther 1986;7(5):250-253.

Effects of prior strength exercise on the heart rate oxygen uptake relationship during submaximal exercise.

Fourteen young males (mean age 26.7 yrs) were tested to determine if there was an alteration, in the heart rate-oxygen uptake relationship during submaximal cycle ergometer exercise following isokinetic strength training activity as has been documented following high intensity endurance activity. Results indicated that there was a significant increase rate without a concomitant increase in heart oxygen uptake during the first five minutes of submaximal cycle riding at 73% VO2max after heavy strength leg exercise, angular velocity of 30 degrees/second, when compared to no prior exercise. This alteration in the heart rate-oxygen uptake relation is not apparent by 20 minutes of the same submaximal exercise despite higher lactate values and greater ratings of perceived exertion. For individuals using heart rate as a guide to exercise intensity, the elevated heart rate at five minutes of submaximal exercise following heavy strength leg exercise does not exceed the 20 minute value which is an accurate reflection of energy cost and intensity.

Thermal and metabolic responses of high and low fat women to cold water immersion.

BACKGROUND: At rest during cold exposure, the amount of body fat plays an important role in the maintenance of core temperature. High fat (HF) individuals would therefore have an advantage as compared with their low fat (LF) counterparts. Since females usually have a higher amount of body fat than males they are expected to maintain core temperature at a lower energy cost. METHODS: The purpose of the present investigation was to dichotomize female subjects by percent fat (LF = 20.5 +/- 2%, n = 6 vs. HF = 30 +/- 3%, n = 6) to elucidate the thermal and metabolic responses during acute exposure to 17 degrees C water for 120 min. The following variables were measured: rectal temperature (Tre; degrees C), mean skin temperature (Tsk; degrees C), oxygen consumption (VO2; ml x kg(-1) x min(-1)), and tissue insulation (I; degrees C x m2 x W(-1)). The experiment-wise error rate was set a priori at p = 0.05. RESULTS: Unexpectedly, only one of the variables demonstrated a main effect for fat (p < 0.05). Tre demonstrated a significant (p < 0.05) group by time interaction. However, Tsk and I demonstrated a main effect for time (p < 0.05). While VO2 demonstrated an increase across time, these changes were non-significant (p > 0.05). It appears that the HF group demonstrated a similar thermal (I and Tsk) and metabolic (VO2) response as compared with the LF counterparts. However, the LF groups maintained a lower Tre as compared with the HF subjects. Perhaps leaner subjects or colder water temperatures would elucidate the value of body fat in females, and demonstrate a differential response with respect to females varying in percent body fat.

Does capsaicin affect physiologic and thermal responses of males during immersion in 22 degrees C?

BACKGROUND: Capsaicin alters thermoregulation in adult rats by producing a dose-dependent fall in body temperature and metabolism. The present investigation examined the thermal and metabolic responses in males who were fed capsaicin (CAP: 2 mg.kg(-1) body weight) vs. a placebo (PL: a maltodextrin capsule) prior to immersion in cold water. METHODS: Seven Caucasian males aged 20-28 yr were immersed in 22 degrees C twice (PL vs. CAP), for 120 min. The following were examined: metabolism (M; W.m(-2)), rectal temperature (Tre; degrees C), mean skin temperature (Tsk; degrees C), tissue insulation (I; degrees C.m(-2).W(-1) and proportion of energy derived from carbohydrate (%CHO). RESULTS: For M, Tre, I, and Tsk there was no significant differences between treatments (PL vs. CAP) when the variables were pooled jointly over time. However, significant differences across time was detected for Tre (p = 0.0003), Tsk (p = 0.0147), and M (p = 0.0036). Values for %CHO demonstrate a main effect for treatment (p = 0.0210) suggesting the CAP (46.7-/+25.9%) treatment demonstrated a decreased reliance on carbohydrate utilization for energy provision as compared to the PL (75.0+/-21.9%) treatment. Additionally, the treatment x time interaction was significant (p = 0.0096) whereby, PL differed from CAP at 5 min only. CONCLUSION: From these data it appears that while M, Tre, and Tsk differed across time, a CAP (which differentially affected percent of energy derived from carbohydrate) feeding did not differentially affect the thermal and metabolic responses of males during acute cold water immersion.

Thermal and metabolic responses of women with high fat versus low fat body composition during exposure to 5 and 27 degrees C for 120 min.

BACKGROUND: Men with high fat body composition maintain higher core temperatures, and lower aerobic metabolic rates than their low fat counterparts thus, verifying the insulatory benefit of body fat. Females, on average have more body fat and less muscle mass than males, and may maintain rectal temperature (Tre) at a lower energy cost. METHODS: The present investigation dichotomized female subjects by percent fat (low fat; n = 3, LF = 19.2+/-3% vs. high fat; n = 4 HF: 29.9+/-3%) to elucidate the thermal and metabolic responses during acute exposure to 5 and 27 degrees C air for 120 min. An ANOVA was used to examine the following: Tre (degrees C), mean skin temperature (Tsk; degrees C), oxygen consumption (VO2; ml x kg(-1) x min(-1)) and tissue insulation (I; degrees C x m2 x W(-1)). For Tre, a significant fat x time interaction (p < 0.05) was demonstrated at both 5 and 27 degrees C, whereby Tre tended to be lower in the LF group than the HF group. VO2 at 5 degrees C demonstrated a main effect for time only. For I, a main effect for time was noted at 5 degrees C. Also for I, a trend (p = 0.06) toward a main effect of fat during exposure to 5 degrees C was noted while at 27 degrees C a main effect (p < 0.05) was demonstrated. RESULTS: From this data it appears that under these conditions, the HF group demonstrated higher Tre and I values than their LF counterparts that was not accompanied with a differential response with respect to aerobic metabolic rate. Thus, the impact of body composition on energy expenditure to maintain Tre differs between LF and HF males and females.

Influence of delayed hyperbaric oxygenation on recovery from mechanically induced damage.

This study examined whether subjecting a crushed muscle to a delayed intermittent hyperbaric oxygenation protocol would facilitate healing, the marker for healing being a return toward 100% uncrushed muscle in selected mechanical, morphologic, and biochemical parameters. Thirty-six rabbits (4 groups of 9) had the right lateral head of their gastrocnemius muscle surgically crushed. After surgery, the rabbits were exposed daily for 90 min 5 days/wk to either 100% O2 at 243 kPa, 8.5% O2 and 91.5% N2 at 243 kPa, 100% O2 at 101 kPa, or 21% O2 at 101 kPa. Initial treatments were administered 16-18 h post-muscle crush. After 10 days of treatment, maximal twitch and tetanic tension of the crushed muscle and its contralateral counterpart were measured. The muscles were then removed and analyzed morphologically, and the activity of citrate synthase, phosphofructokinase, and glucose-6-phosphate dehydrogenase were measured. The treatment group means for any of the parameters measured were not significantly different from each other. The extent of muscle damage, however, was determined to be minor as the control group recovery threshold was approximately 80%. Thus, it seems that the treatment protocol used does not facilitate healing for this type of muscle crush injury.

Hyperbaric oxygenation treatments and metabolic enzymes in the heart and diaphragm.

We previously found that intermittent hyperbaric oxygen exposure increases metabolic enzyme activity in soleus muscle. Since the metabolic enzyme activities of the heart and diaphragm of healthy animals are difficult to alter, we questioned whether intermittent hyperbaric oxygenation would provide a stimulus sufficient to increase metabolic enzyme activity. Therefore, we exposed 36 rabbits (4 groups of 9) twice daily for 90 min 5 days/wk to either 100% O2 at 243 kPa, 8.5% O2, and 91.5% N2 at 243 kPa, 100% O2 at 101 kPa, or 21% O2 at 101 kPa. After 4 wk of treatment, the activities of citrate synthase, succinate dehydrogenase, alpha-glycerophosphate dehydrogenase, phosphofructokinase, and glyceraldehyde-3-phosphate dehydrogenase were measured. In both the heart and the diaphragm, none of the treatments significantly altered the mean enzyme activities for any of the enzymes measured. Therefore, it seems that the hyperbaric oxygenation treatment protocols used do not induce an increase in metabolic enzyme activity in the heart and diaphragm in healthy animals.