Short-duration swimming exercise decreases penicillin-induced epileptiform ECoG activity in rats

The aim of the present study is to understand the basic relationship between swimming exercise and natural course of epilepsy in animals by performing an electrophysiological study. For this purpose, male Wistar rats were submitted to daily swimming exercise program of three different durations. Animals were swim-exercised for 90 days with either 15 minutes, 30 minutes or 60 minutes/day. Thereafter, the epileptiform activity was induced by a single microinjection of penicillin (500 units) into the left somatomotor cortex. Short-duration swimming exercise (15 min per day for 90 days) decreased the mean frequency and amplitude of penicillin-induced epileptiform activity in the 70 and 90 minutes after penicillin injection compared to penicillin administered group, respectively. Moderate-duration (30 min per day for 90 days) and long-duration (60 min per day for 90 days) swimming exercise did not alter either the frequency or amplitude of epileptiform activity. The results of the present study provide electrophysiologic evidence that short-duration swimming exercise partially inhibits penicillin-induced epileptiform activity. These data also suggest that moderate and long-duration swimming exercise do not increase either the frequency or severity of seizure in the model of penicillin-induced epilepsy.     

Long-term swimming in an inescapable stressful environment attenuates the stimulatory effect of endurance swimming on duodenal calcium absorption in rats

Endurance swimming is known to increase duodenal calcium absorption in normal rats and bone strength in estrogen-deficient rats. Because the stress resulting from forced training often attenuates the stimulatory effect of exercise, swimming in an inescapable chamber should reveal both the positive effect of the exercise and the negative effect of stress. In the work reported herein, swimming rats showed no signs of stress during 2 weeks of training. However, stress response gradually developed thereafter and peaked at weeks 6 and 7. In rats swimming for 2 weeks, transcellular duodenal calcium transport was enhanced ~2-fold. In contrast, calcium absorption was reduced in rats swimming for 8 weeks, consistent with the absence of swimming-induced upregulation of calcium transporter genes in the 8-week group. In conclusion, prolonged stress hindered the stimulatory effect of swimming on duodenal calcium absorption, and thus endurance exercise should be performed without forced training or stress to retain its beneficial effect on calcium metabolism.     

Changes in serum and erythrocyte magnesium and blood lipids after distance swimming

The effect of a 30 min. swimming exercise (freestyle) on plasma magnesium and other biochemical variables was assessed on 6 well trained swimmers. Blood samples were taken before, right after, 30 min. and 24 hours after exercise. Serum Mg concentration decreased significantly during exercise, returning to base line 24 hours after. Erythrocyte content in Mg did not show any significant changes. Plasma total cholesterol level decreased significantly 30 min. after exercise. A significant positive correlation found at rest between plasma Mg levels and plasma total H.D.L. cholesterol disappeared after exercise but was observed again 24 hours later.     

The effect of high-intensity intermittent swimming on post-exercise glycogen supercompensation in rat skeletal muscle

A single bout of prolonged endurance exercise stimulates glucose transport in skeletal muscles, leading to post-exercise muscle glycogen supercompensation if sufficient carbohydrate is provided after the cessation of exercise. Although we recently found that short-term sprint interval exercise also stimulates muscle glucose transport, the effect of this type of exercise on glycogen supercompensation is uncertain. Therefore, we compared the extent of muscle glycogen accumulation in response to carbohydrate feeding following sprint interval exercise with that following endurance exercise. In this study, 16-h-fasted rats underwent a bout of high-intensity intermittent swimming (HIS) as a model of sprint interval exercise or low-intensity prolonged swimming (LIS) as a model of endurance exercise. During HIS, the rats swam for eight 20-s sessions while burdened with a weight equal to 18% of their body weight. The LIS rats swam with no load for 3 h. The exercised rats were then refed for 4, 8, 12, or 16 h. Glycogen levels were almost depleted in the epitrochlearis muscles of HIS- or LIS-exercised rats immediately after the cessation of exercise. A rapid increase in muscle glycogen levels occurred during 4 h of refeeding, and glycogen levels had peaked at the end of 8 h of refeeding in each group of exercised refed rats. The peak glycogen levels during refeeding were not different between HIS- and LIS-exercised refed rats. Furthermore, although a large accumulation of muscle glycogen in response to carbohydrate refeeding is known to be associated with decreased insulin responsiveness of glucose transport, and despite the fact that muscle glycogen supercompensation was observed in the muscles of our exercised rats at the end of 4 h of refeeding, insulin responsiveness was not decreased in the muscles of either HIS- or LIS-exercised refed rats compared with non-exercised fasted control rats at this time point. These results suggest that sprint interval exercise enhances muscle glycogen supercompensation in response to carbohydrate refeeding as well as prolonged endurance exercise does. Furthermore, in this study, both HIS and LIS exercise prevented insulin resistance of glucose transport in glycogen supercompensated muscle during the early phase of carbohydrate refeeding. This probably led to the enhanced muscle glycogen supercompensation after exercise.     

Blood metabolites during prolonged exercise in swimming and leg cycling

Summary This study was designed to compare the influence of two modes of exercise (swimming and leg cycling) on the blood concentrations of metabolic substrates and metabolites during a 45-min exercise period. Eight college students (mean age=21.6±1.2 year) exercised at 70% of O₂ max, in water using the front crawl on one occasion, and on a cycle ergometer using the legs on another. Blood samples were drawn at 0,15, 30, and 45 min and analyzed for free fatty acids, glycerol, glucose, pyruvate, and lactate concentrations. Mean oxygen uptakes (2.23 vs 2.12 l·min^–1) and heart rates (152 vs 150 b·min^–1) for cycling and swimming respectively were not significantly different. Lactate and pyruvate were significantly (p<0.01) higher during swimming as compared to cycling. Free fatty acids, glycerol, and glucose were not significantly different between the two modes of exercise (p>0.05). Assuming venous blood concentrations provide some indication of metabolic events, these data are compatible with a tendency to a higher relative carbohydrate oxidation rate during swimming as compared to cycling during prolonged exercise at the same relative work intensities.Supported by grand from C.A.F.I.R., Université de Montréal     

Metabolic changes in man during long-distance swimming

Summary Sixteen young adults were investigated before, immediately after and 24 h after swimming 5,200±618 m in 90 min. Mean pulse rate at the end of exercise was 151.3 min^–1; skin and rectal temperature both slightly increased. Except for a marked leukocytosis, no changes were observed in other blood parameters (hematocrit, hemoglobin, erythrocytes). Serum enzyme activities showed (except for triosephosphate dehydrogenase) marked increases which in the case of creatine kinase and of malate dehydrogenase did not return to preexercise level on the next day. No hypoglycemia occurred in any of the subjects. Blood lactate increased to 4.2 mmol/l at the 15th min of exercise and at the end was still slightly above the resting value. Free fatty acids, free glycerol, 3-hydroxybutyrate, serum urea and uric acid rose markedly after swimming, whereas -amino nitrogen, triglycerides, and serum magnesium significantly decreased.The electrical excitability of the two investigated muscles (M. vastus med. quadr. and M. deltoides) showed opposite changes, which was ascribed to their different involvement during swimming.     

Capsiate, a non-pungent capsaicin analog, reduces body fat without weight rebound like swimming exercise in mice

Enhancement of energy expenditure and reducing energy intake are crucial for weight control. Capsiate, a non-pungent capsaicin analog, is known to suppress body fat accumulation and reduce body weight by enhancing of energy expenditure in both mice and humans. However, it is poorly understood whether suppressing body fat accumulation by capsiate administration is equal to exercise or not. The aim of this study is to compare the effects of repeated administration of capsiate and exercise and to investigate the weight rebound after repeated capsiate administration and/or exercise. In the present study, we report that 2 weeks treatment of capsiate and exercise increased energy metabolism and suppressed body fat accumulation during 4 more weeks of ad libitum feeding. The body weight in capsiate and exercise groups was significantly lower than that of control group. The oxygen consumption was significanlty increased in capsiate and exercise groups than in the vehicle administered mice. In addition, the abdominal adipose tissue weight in capsiate and exercise groups was significantly lower than that of control group. These results indicate that suppressing body fat accumulation by capsiate intake is beneficial for maintaining an ideal body weight as exercise.     

Biochemical responses during recovery from maximal and submaximal swimming exercise

Summary We set out to demonstrate whether changes in plasma volume, haematocrit and some important blood constituents occurred after swimming 100 m and 800 m, as well as monitoring the duration of these changes. We measured exercise-induced changes in concentration of plasma constituents in eight subjects, and determined the expected effects of haemoconcentration on these constituents. We also investigated the different biochemical responses occurring after maximal exercise (100 m), as compared to submaximal exercise (800 m). The haematocrit increased significantly after the 100 m swim and to a lesser extent after the 800-m swim, returning to basal levels within 30 min. The plasma volume decreased by 16% on completion of the 100 m and by 8% on completion of the 800 m. The blood lactate concentration increased 15-fold and 10-fold after the 100-m and 800-m swims respectively. The plasma potassium concentration increased significantly immediately on completion of the 100-m swim, then decreased significantly at 2 1/2 and 5 min post-exercise, returning to near-basal values at 30 min. The potassium concentration measured after the 800-m event did not differ significantly from basal levels, however the measured concentrations were significantly lower than the concentrations expected on the basis of haemoconcentration. The plasma sodium concentrations measured after both 100-m and 800-m swims were significantly increased. However, calculations correcting for haemoconcentration showed significant losses in toal circulating sodium. Our study demonstrates marked changes in plasma volume and certain blood constituents after maximal intensity swimming, and less marked changes after submaximal exercise. We also demonstrated the importance of taking the effects of haemoconcentration into account when evaluating changes in concentration of plasma constituents.     

Phenylephrine-induced vasoconstriction of the rat superior mesenteric artery is decreased after repeated swimming.

This study was performed to determine the effect of forced swimming on the vascular responsiveness of the rat superior mesenteric artery to phenylephrine, focusing on the involvement of locally produced substances. Repeated but not single sessions of forced swimming exercise reduced the vasoconstrictor potency of phenylephrine in the studied arteries, regardless of the presence of intact endothelium. No significant changes were observed in the maximal response to phenylephrine. Treatment with indomethacin (1 microM) did not affect the exercise-induced reduction in vascular responsiveness to phenylephrine. However, the reduction of vascular reactivity to phenylephrine due to repeated exercise was no longer observed after treatment with N(G)-monomethyl-L-arginine (L-NMMA, 100 microM). The results suggest that repeated exercise reduces vasomotor responses to phenylephrine in rat superior mesenteric arteries through a non-endothelial nitric oxide (NO)-related mechanism.     

Effect of high-intensity intermittent swimming training on fatty acid oxidation enzyme activity in rat skeletal muscle

We previously reported that high-intensity exercise training significantly increased citrate synthase (CS) activity, a marker of oxidative enzyme, in rat skeletal muscle to a level equaling that attained after low-intensity prolonged exercise training (Terada et al., J Appl Physiol 90: 2019-2024, 2001). Since mitochondrial oxidative enzymes and fatty acid oxidation (FAO) enzymes are often increased simultaneously, we assessed the effect of high-intensity intermittent swimming training on FAO enzyme activity in rat skeletal muscle. Male Sprague-Dawley rats (3 to 4 weeks old) were assigned to a 10-day period of high-intensity intermittent exercise training (HIT), low-intensity prolonged exercise training (LIT), or sedentary control conditions. In the HIT group, the rats repeated fourteen 20 s swimming sessions with a weight equivalent to 14-16% of their body weight. Between the exercise sessions, a 10 s pause was allowed. Rats in the LIT group swam 6 h/day in two 3 h sessions separated by 45 min of rest. CS activity in the triceps muscle of rats in the HIT and LIT groups was significantly higher than that in the control rats by 36 and 39%, respectively. Furthermore, 3-beta hydroxyacyl-CoA dehydrogenase (HAD) activity, an important enzyme in the FAO pathway in skeletal muscle, was higher in the two training groups than in the control rats (HIT: 100%, LIT: 88%). No significant difference in HAD activity was observed between the two training groups. In conclusion, the present investigation demonstrated that high-intensity intermittent swimming training elevated FAO enzyme activity in rat skeletal muscle to a level similar to that attained after 6 h of low-intensity prolonged swimming exercise training.     

Cardiac output and heart rate in man during simulated swimming while breath-holding

We measured stroke volume (SV), heart rate (HR), cardiac output (Q), arterial pressure and intrapulmonic (mouth) pressure in four healthy, male subjects during simulated swimming (i.e., performing crawl movements with the legs continuously at a constant rhythm) with and without apnea (water temperature: 31 degrees C). We wanted to see whether the exercise tachycardia response persisted, or whether the HR decreased during apnea, just as in the "diving response" of diving animals. The SV and the Q fell to half its value in the control phase (i.e., swimming with normal breathing), when the 15-s apnea was performed at a high mouth-pressure; at low mouth-pressure, SV and Q hardly changed. These results are replicates of our previous findings in man during rest in air. Due to the light work, HR increased slightly from rest, but the exercise HR did not change much during apnea with or without high mouth-pressure. The results show that man tends to preserve his exercise HR response, and does not react as an oxygen-conserving animal, whether he is in air or in water under these conditions. However, man, as well as diving animals, may well have a "diving response" as an emergency reaction, which may not be restricted to only the water environment.     

Increase in serum S100B protein level after a swimming race.

Physical activity has been shown to be a beneficial stimulus to the central and peripheral nervous systems. The S100B is a cytokine physiologically produced and released predominantly by astrocytes on the central nervous system (CNS). In order to study the possible influence of a nonimpact exercise on S100B serum levels, we measured this protein serum level after a 7,600-meter swimming race. We observed an increase in S100B levels in athletes post-race compared with their baseline values, pointing to a potential acute influence of physical exercise on serum S100B levels not related with CNS injury. We discuss this result and emphasize the possible central and peripheral origins of S100B serum levels.     

Breathing dry or humid air and exercise-induced asthma during swimming

Summary With a view to investigating the aerobic and anaerobic proportions of oxygen supply during different grades of muscular activity in varying thermal stress, studies have been conducted on six young healthy Indians naturally acclimatized to heat. The subjects were given submaximal exercises of 400, 500, and 600 kgm/min (equivalent to 65.40, 81.75, and 98.10 W) for 6 min on a bicycle ergometer in three different simulated conditions, i.e., comfortable, hot humid, and very hot humid. Their O₂ consumption (VO₂), pulmonary ventilation (V _E) and heart rate (HR) were measured during rest and throughout the exercise period (6 min) and for 30 min post exercise. Blood lactate level (LA) was measured during rest and recovery. From these, the total O₂ cost with aerobic and anaerobic proportions were calculated. Results indicated a significant increase in the total O₂ cost for each exercise with increasing thermal stress, along with a significant increase in the anaerobic fraction and a decrease in the aerobic fraction. The increase in anaerobic contribution to the energy supply processes was further confirmed by a significant increase in relative O₂ debt (l/kg) and in blood lactate level at each work load. Thus, a highly significant correlation (P<0.001) was found between O₂ debt contracted and increase in thermal stress. A significant fall in VO₂ max was also observed in hot humid and very hot humid conditions as against comfortable temperature, with no change in HR max and V _E max.     

Effects of nonexhaustive bouts of high-intensity intermittent swimming training on GLUT-4 expression in rat skeletal muscle

We previously reported that 14 bouts of exhaustive high-intensity intermittent training [20 s periods of swimming while carrying a weight (14% of body weight), separated by pauses of 10 s] is the highest stimuli in terms of exercise training-induced glucose transporter 4 (GLUT-4) expression in rat epitrochlearis (EPI) muscles. In the present study, we found that the GLUT-4 protein content in the skeletal muscle of male Sprague-Dawley rats (age 5 weeks old; body weight 90–110 g) that underwent intermittent exercise training of 3 and 14 bouts of 20 s swimming for 5 days was increased over age-matched sedentary control rats by 75 and 71%, respectively, 18 h after the last bout of exercise. These results suggest that GLUT-4 content in rat EPI muscle increases dramatically after very short (60 s) and nonexhaustive high-intensity intermittent exercise training.     

Sodium bicarbonate ingestion improves performance in interval swimming

Summary In an effort to determine the effects of bicarbonate (NaHCO₃) ingestion on exercise performance, ten male college swimmers were studied during five different trials. Each trial consisted of five 91.4m (100-yd) front crawl swims with a two-minute rest interval between each bout. The trials consisted of two NaHCO₃ treatments, two placebo trials and one test with no-drink. One hour before the onset of swimming, the subjects were given 300 ml of citric acid flavored solution containing either 17 mmol of NaCl (placebo) or 2.9 mmol of NaHCO₃ · kg^–1 body weight (experimental), or received no drink (no-drink). Performance times for each 91.4 m swim were recorded. Blood samples were obtained before and one hr after treatment, two min after warmup, and two min after the final 91.4 m sprint. Blood pH, lactate, standard bicarbonate (SBC) and base excess (BE) were measured. No differences were found for performance or the blood measurements between the placebo and no-drink trials. Bicarbonate feedings, on the other hand, produced a significant (P<0.05) improvement in performance on the fourth and fifth swimming sprints. Blood lactate, pH, SBC and BE were significantly higher (P<0.05) at post-exercise in NaHCO₃ treatments. These data are in agreement with previous findings that during repeated bouts of exercise pre-exercise administration of NaHCO₃ improves performance, possibly by facilitating the efflux of hydrogen ions from working muscles and thereby delaying the onset of fatigue.     

Effects of high-intensity intermittent swimming on PGC-1alpha protein expression in rat skeletal muscle

AIM: The aim of the present investigation was to elucidate the effects of exercise intensity on exercise-induced expression of peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha) protein in rat skeletal muscle. METHODS: We measured PGC-1alpha content in the skeletal muscles of male Sprague-Dawley rats (age: 5-6 weeks old; body weight: 150-170 g) after a single session of high-intensity intermittent exercise (HIE) or low-intensity prolonged swimming exercise (LIE). During HIE, the rats swam for fourteen 20-s periods carrying a weight (14% of body weight), and the periods of swimming were separated by a 10-s pause. LIE rats swam with no load for 6 h in two 3-h sessions, separated by 45 min of rest. RESULTS: After HIE, the PGC-1alpha protein content in rat epitrochlearis muscle had increased by 126, 140 and 126% at 2, 6 and 18 h, respectively, compared with that of the age-matched sedentary control rats' muscle. Immediately, 6 and 18-h after LIE, the PGC-1alpha protein content in the muscle was significantly elevated by 84, 95 and 67% respectively. The PGC-1alpha protein content observed 6 h after HIE tended to be higher than that observed after LIE. However, there was no statistically significant difference between the two values (P = 0.12). CONCLUSION: The present investigation suggests that irrespective of the intensity of the exercise, PGC-1alpha protein content in rat skeletal muscle increases to a comparable level when stimuli induced by different protocols are saturated. Further, HIE is a potent stimulus for enhancing the expression of PGC-1alpha protein, which may induce mitochondrial biogenesis in exercise-activated skeletal muscle.     

Changes in plasma, erythrocyte, and urinary magnesium with prolonged swimming exercise

Erythrocyte, plasma and urinary magnesium were observed in a group of 8 well-trained swimmers and in a group of 10 untrained subjects before, 2 minutes after and 30 minutes after a swimming test. After effort, plasma Mg (pMg) decreased significantly in both groups. Erythrocyte and urinary Mg variations were not significant in this study. PMg decrease after effort was more important in the swimmers group than in the untrained group (12% versus 6% after 2 minutes; 21% versus 4% after 30 minutes). The observed fall in plasma Mg concentration after exercise cannot be explained by a shift into erythrocytes during exercise, since the Mg content of these blood cells did not suffer significant alterations. The possible causes of the observed phenomena are discussed.     

Plasma renin activity,aldosterone and catecholamine levels when swimming and running

Summary The purpose of this study was to determine the response of plasma renin activity (PRA), plasma aldosterone concentration (PAC) and catecholamines to two graded exercises differing by posture. Seven male subjects (19–25 years) performed successively a running rest on a treadmill and a swimming test in a 50-m swimming pool. Each exercise was increased in severity in 5-min steps with intervals of 1 min. Oxygen consumption, heart rate and blood lactate, measured every 5 min, showed a similar progression in energy expenditure until exhaustion, but there was a shorter time to exhaustion in the last step of the running test. PRA, PAC and catecholamines were increased after both types of exercise. The PRA increase was higher after the running test (20.9 ng AngI · ml^–1 · h^–1) than after swimming (8.66 ng AngI · ml^–1 · h^–1). The PAC increase was slightly greater after running (123 pg · ml^–1) than swimming (102 pg · ml^–1), buth the difference was not significant. Plasma catecholamine was higher after the swimming test. These results suggest that the volume shift induced by the supine position and water pressure during swimming decreased the PRA response. The association after swimming compared to running of a decreased PRA and an enhanced catecholamine response rule out a strict dependence of renin release under the effect of plasma catecholamines and is evidence of the major role of neural pathways for renin secretion during physical exercise.     

Forced swimming alters vaginal estrous cycles, body composition, and steroid levels without disrupting lordosis behavior or fertility in rats

The purpose of the present studies was to examine how exercise affects reproductive physiology and behavior. In four separate experiments, exercise regimens of forced swimming or swimming plus running, were gradually increased in duration to a maximum of 2.5 hours. Vaginal cycles were monitored daily and after eight weeks animals were tested for sexual behavior, ability to breed, changes in body composition, circulating levels of estradiol, progesterone, and corticosterone. Total body lipids were lowered in animals that both ran and swam and parametrial fat pad weight was reduced in all exercising animals. Although exercise lowered circulating levels of ovarian steroids, elevated corticosterone levels and disrupted vaginal cycles, exercised animals exhibited normal sexual behavior and bred successfully. These data indicate that intense exercise can, under certain conditions, disrupt the mechanisms controlling vaginal cycles while the neuroendocrine mechanisms controlling sexual receptivity, ovulation, and fertility remain intact.     

The critical velocity in swimming

In supra-maximal exercise to exhaustion, the critical velocity (cv) is conventionally calculated from the slope of the distance (d) versus time (t) relationship: d = I + St. I is assumed to be the distance covered at the expense of the anaerobic capacity, S the speed maintained on the basis of the subject’s maximal O₂ uptake This approach is based on two assumptions: (1) the energy cost of locomotion per unit distance (C) is constant and (2) is attained at the onset of exercise. Here we show that cv and the anaerobic distance (d _anaer) can be calculated also in swimming, where C increases with the velocity, provided that its on-response, and the C versus v relationship are known. d _anaer and cv were calculated from published data on maximal swims for the four strokes over 45.7, 91.4 and 182.9 m, on 20 elite male swimmers (18.9 ± 0.9 years, 75.9 ± 6.4 kg), whose and C versus speed relationship were determined, and compared to I and S obtained from the conventional approach. cv was lower than S (4, 16, 7 and 11% in butterfly, backstroke, breaststroke and front crawl) and I (=11.6 m on average in the four strokes) was lower than d _anaer. The latter increased with the distance: average, for all strokes: 38.1, 60.6 and 81.3 m over 45.7, 91.4 and 182.9 m. It is concluded that the d versus t relationship should be utilised with some caution when evaluating performance in swimmers.