In vivo human tendinous tissue stretch upon maximum muscle force generation

In the present study, we examined the hypothesis that stretch of tendinous tissue in the human tibialis anterior (TA) muscle-tendon unit upon isometric dorsiflexion maximum voluntary contraction (MVC) varies along the entire tendinous component length. Ultrasound-based measurements of the excursions of the TA tendon origin and proximal end of the TA central aponeurosis were taken in the transition from rest to MVC in six men. Subtracting the TA tendon origin excursion from the excursion of the aponeurosis proximal end, the aponeurosis excursion was estimated. Estimation of the aponeurosis proximal region excursion was obtained subtracting the excursion of the insertion point of a central region fascicle on the aponeurosis from the whole aponeurosis excursion. Subtracting tendon excursion from the excursion of the central fascicle insertion point, the aponeurosis distal region excursion was estimated. Strain values were calculated dividing the excursions obtained by the original resting lengths. All excursions and lengths were measured in the mid-longitudinal axis of the TA muscle-tendon unit at the neutral anatomical ankle position. Tendon excursion and strain were 0.5+/-0. 08 cm (mean+/-SE) and 3.1+/-0.2%, respectively. Aponeurosis excursion and strain were 1.1+/-0.15 cm and 6.5+/-0.6%, respectively. Aponeurosis distal region excursion and strain were 0.3+/-0.05 cm and 3.5+/-0.3%, respectively. Aponeurosis proximal region excursion and strain were 0.8+/-0.12 cm and 9.2+/-1%, respectively. Aponeurosis excursion and strain were larger by 110-120% (P<0.05) compared with tendon. Aponeurosis proximal region excursion and strain were larger by 165-170% (P<0.05) compared with aponeurosis distal region. These findings are in line with results from in vitro animal material testing and have important implications for theoretical models of muscle function.     

Pyruvate overrides inhibition of PDH during exercise after a low-carbohydrate diet

The effects of carbohydrate deprivation on the regulation of pyruvate dehydrogenase (PDH) were studied at rest and during moderate-intensity exercise. An inhibitory effect of a chronic low-carbohydrate diet (LCD) on the active form of PDH (PDHa) mediated by a stable increase in PDH kinase (PDHK) activity has recently been reported (Peters SJ, Howlett RA, St. Amand TA, Heigenhauser GJF, and Spriet LL. Am J Physiol Endocrinol Metab 275: E980-E986, 1998.). In the present study, seven males cycled at 65% maximal O(2) uptake for 30 min after a 6-day LCD. Exercise was repeated 1 wk later after a mixed diet (MD). Muscle biopsies were sampled from the vastus lateralis at rest and at 2 and 30 min of exercise. At rest, PDHa activity (0.18 +/- 0.04 vs. 0.63 +/- 0.18 mmol x min(-1) x kg wet wt(-1)), muscle glycogen content (310.2 +/- 36.9 vs. 563.9 +/- 32.6 mmol/kg dry wt), and muscle lactate content (2.6 +/- 0.3 vs. 4.2 +/- 0.6 mmol/kg dry wt) were significantly lower after the LCD. Resting muscle acetyl-CoA (10.8 +/- 1.9 vs. 7.4 +/- 0.8 micromol/kg dry wt) and acetylcarnitine (5.3 +/- 1.4 vs. 1.6 +/- 0.3 mmol/kg dry wt) contents were significantly elevated after the LCD. During exercise, PDHa, glycogenolytic rate (LCD 5.8 +/- 0.4 vs. MD 6.9 +/- 0.2 mmol x min(-1) x kg dry wt(-1)), and muscle concentrations of acetylcarnitine, pyruvate, and lactate increased to the same extent in both conditions. The results of the present study suggest that inhibition of resting PDH by elevated PDHK activity after a LCD may be overridden by the availability of muscle pyruvate during exercise.     

Myofibrillar and collagen protein synthesis in human skeletal muscle in young men after maximal shortening and lengthening contractions

We aimed to determine whether there were differences in the extent and time course of skeletal muscle myofibrillar protein synthesis (MPS) and muscle collagen protein synthesis (CPS) in human skeletal muscle in an 8.5-h period after bouts of maximal muscle shortening (SC; average peak torque = 225 +/- 7 N.m, means +/- SE) or lengthening contractions (LC; average peak torque = 299 +/- 18 N.m) with equivalent work performed in each mode. Eight healthy young men (21.9 +/- 0.6 yr, body mass index 24.9 +/- 1.3 kg/m2) performed 6 sets of 10 maximal unilateral LC of the knee extensors on an isokinetic dynamometer. With the contralateral leg, they then performed 6 sets of maximal unilateral SC with work matched to the total work performed during LC (10.9 +/- 0.7 vs. 10.9 +/- 0.8 kJ, P = 0.83). After exercise, the participants consumed small intermittent meals to provide 0.1 g.kg(-1).h(-1) of protein and carbohydrate. Prior exercise elevated MPS above rest in both conditions, but there was a more rapid rise after LC (P < 0.01). The increases (P < 0.001) in CPS above rest were identical for both SC and LC and likely represent a remodeling of the myofibrillar basement membrane. Therefore, a more rapid rise in MPS after maximal LC could translate into greater protein accretion and muscle hypertrophy during chronic resistance training utilizing maximal LC.     

Interstitial pH, K(+), lactate, and phosphate determined with MSNA during exercise in humans

The purpose of the present study was to use the microdialysis technique to simultaneously measure the interstitial concentrations of several putative stimulators of the exercise pressor reflex during 5 min of intermittent static quadriceps exercise in humans (n = 7). Exercise resulted in approximately a threefold (P < 0.05) increase in muscle sympathetic nerve activity (MSNA) and 13 +/- 3 beats/min (P < 0.05) and 20 +/- 2 mmHg (P < 0.05) increases in heart rate and blood pressure, respectively. During recovery, all reflex responses quickly returned to baseline. Interstitial lactate levels were increased (P < 0.05) from rest (1.1 +/- 0.1 mM) to exercise (1. 6 +/- 0.2 mM) and were further increased (P < 0.05) during recovery (2.0 +/- 0.2 mM). Dialysate phosphate concentrations were 0.55 +/- 0. 04, 0.71 +/- 0.05, and 0.48 +/- 0.03 mM during rest, exercise, and recovery, respectively, and were significantly elevated during exercise. At the onset of exercise, dialysate K(+) levels rose rapidly above resting values (4.2 +/- 0.1 meq/l) and continued to increase during the exercise bout. After 5 min of contractions, dialysate K(+) levels had peaked with an increase (P < 0.05) of 0.6 +/- 0.1 meq/l and subsequently decreased during recovery, not being different from rest after 3 min. In contrast, H(+) concentrations rapidly decreased (P < 0.05) from resting levels (69.4 +/- 3.7 nM) during quadriceps exercise and continued to decrease with a mean decline (P < 0.05) of 16.7 +/- 3.8 nM being achieved after 5 min. During recovery, H(+) concentrations rapidly increased and were not significantly different from baseline after 1 min. This study represents the first time that skeletal muscle interstitial pH, K(+), lactate, and phosphate have been measured in conjunction with MSNA, heart rate, and blood pressure during intermittent static quadriceps exercise in humans. These data suggest that interstitial K(+) and phosphate, but not lactate and H(+), may contribute to the stimulation of the exercise pressor reflex.     

Contribution of erythrocytes to the control of the electrolyte changes of exercise

Five healthy males performed four 30-s bouts of maximal isokinetic cycling with 4 min rest between each bout. Arterial and femoral venous blood was sampled during and for 90 min following exercise. During exercise, arterial erythrocyte [K+] increased from 117.0 +/- 6.6 mequiv./L at rest to 124.2 +/- 5.9 mequiv./L after the second exercise bout. Arterial erythrocyte [K+] returned to the resting values during the first 5 min of recovery. No significant change was observed in femoral venous erythrocyte [K+]. Arterial erythrocyte lactate concentration ([Lac-]) increased during exercise from 0.2 +/- 0.1 mequiv./L peaking at 9.5 +/- 1.5 mequiv./L at 5 min of recovery, after which the values returned to control. Femoral venous erythrocyte [Lac-] changed in a similar fashion. Arterial erythrocyte [Cl-] rose during exercise to 76 +/- 3 mequiv./L and returned to resting values (70 +/- 2 mequiv./L) by 25 min recovery. During exercise there was a net flux of Cl- into the erythrocyte. We conclude that erythrocytes are a sink for K+ ions leaving working muscles. Furthermore, erythrocytes function to transport Lac- from working muscle and reduce plasma acidosis by uptake of Cl-. The erythrocyte uptake of K+, Lac-, and Cl- helps to maintain a concentration difference between plasma and muscle, facilitating diffusion of Lac- and K+ from the interstitial space into femoral venous plasma.     

Testicular and epididymal function during the peripuberal period in Brahman bulls receiving various amounts of protein degradable in the rumen

Thirty-nine Brahman bulls with an initial age and weight of 301.7 +/- 4.1 d and 202.7 +/- 4.7 kg, respectively, were randomly allocated to 1 of 2 dietary treatment groups within age, weight and sire in order to study the influence of source of protein and stage of peripuberal period on testicular and epididymal function. In the soybean meal treatment the amount of protein undegradable in the rumen averaged 47%, while it was 72% in the fish meal treatment. The supplements were isocaloric and isonitrogenous. Bulls were electroejaculated, and castrations were performed randomly in a predetermined order when the first ejaculate with the first motile sperm cells (Stage 1), 10 to 25 million (Stage 2), and 50 million or more sperm cells (Stage 3 - puberty) was obtained. Testicular and epididymal traits were analyzed for a single testicle and epididymis. Daily sperm production, daily sperm production per gram of testicular parenchyma, testicular weight and testicular parenchyma weight were not affected by treatment. Bulls receiving fish meal had heavier (P < 0.01) epididymis than soybean meal-fed bulls (6.6 +/- 1.0 vs 3.9 +/- 0.6 g) but similar (P > 0.05) epididymal sperm reserves. Daily sperm production (1 testicle) was 115.2 +/- 0.1, 447.4 +/- 0.1, 792.7 +/- 0.1 million sperm cells, and daily sperm production per gram of testicular parenchyma was 1.5 +/- 0.5, 3.2 +/- 0.6 and 6.4 +/- 0.6 million sperm cells for bulls at Stage 1, 2 and 3, respectively. Sire and amount of undegradable intake protein had significant (P < 0.05) affects on the distribution of epididymal sperm reserves, with soybean meal-fed bulls having the higher proportions of epididymal sperm reserves in the cauda epididymis.     

Isometric handgrip training reduces arterial pressure at rest without changes in sympathetic nerve activity

The purpose of this study was to determine whether isometric handgrip (IHG) training reduces arterial pressure and whether reductions in muscle sympathetic nerve activity (MSNA) mediate this drop in arterial pressure. Normotensive subjects were assigned to training (n = 9), sham training (n = 7), or control (n = 8) groups. The training protocol consisted of four 3-min bouts of IHG exercise at 30% of maximal voluntary contraction (MVC) separated by 5-min rest periods. Training was performed four times per week for 5 wk. Subjects' resting arterial pressure and heart rate were measured three times on 3 consecutive days before and after training, with resting MSNA (peroneal nerve) recorded on the third day. Additionally, subjects performed IHG exercise at 30% of MVC to fatigue followed by muscle ischemia. In the trained group, resting diastolic (67 +/- 1 to 62 +/- 1 mmHg) and mean arterial pressure (86 +/- 1 to 82 +/- 1 mmHg) significantly decreased, whereas systolic arterial pressure (116 +/- 3 to 113 +/- 2 mmHg), heart rate (67 +/- 4 to 66 +/- 4 beats/min), and MSNA (14 +/- 2 to 15 +/- 2 bursts/min) did not significantly change following training. MSNA and cardiovascular responses to exercise and postexercise muscle ischemia were unchanged by training. There were no significant changes in any variables for the sham training and control groups. The results indicate that IHG training is an effective nonpharmacological intervention in lowering arterial pressure.     

Hypohydration does not impair skeletal muscle glycogen resynthesis after exercise

The purpose of this investigation was to examine the effects of moderate hypohydration (HY) on skeletal muscle glycogen resynthesis after exhaustive exercise. On two occasions, eight males completed 2 h of intermittent cycle ergometer exercise (4 bouts of 17 min at 60% and 3 min at 80% of maximal O2 consumption/10 min rest) to reduce muscle glycogen concentrations (control values 711 +/- 41 mumol/g dry wt). During one trial, cycle exercise was followed by several hours of light upper body exercise in the heat without fluid replacement to induce HY (-5% body wt); in the second trial, sufficient water was ingested during the upper body exercise and heat exposure to maintain euhydration (EU). In both trials, 400 g of carbohydrate were ingested at the completion of exercise and followed by 15 h of rest while the desired hydration level was maintained. Muscle biopsy samples were obtained from the vastus lateralis immediately after intermittent cycle exercise (T1) and after 15 h of rest (T2). During the HY trial, the muscle water content was lower (P less than 0.05) at T1 and T2 (288 +/- 9 and 265 +/- 5 ml/100 g dry wt, respectively; NS) than during EU (313 +/- 8 and 301 +/- 4 ml/100 g dry wt, respectively; NS). Muscle glycogen concentration was not significantly different during EU and HY at T1 (200 +/- 35 vs. 251 +/- 50 mumol/g dry wt) or T2 (452 +/- 34 vs. 491 +/- 35 mumol/g dry wt). These data indicate that, despite reduced water content during the first 15 h after heavy exercise, skeletal muscle glycogen resynthesis is not impaired.     

Muscle glycogenolysis and H+ concentration during maximal intermittent cycling

The relationships between muscle glycogenolysis, glycolysis, and H+ concentration were examined in eight subjects performing three 30-s bouts of maximal isokinetic cycling at 100 rpm. Bouts were separated by 4 min of rest, and muscle biopsies were obtained before and after bouts 2 and 3. Total work decreased from 20.5 +/- 0.7 kJ in bout 1 to 16.1 +/- 0.7 and 13.2 +/- 0.6 kJ in bouts 2 and 3. Glycogenolysis was 47.2 and 15.1 mmol glucosyl U/kg dry muscle during bouts 2 and 3, respectively. Lower accumulations of pathway intermediates in bout 3 confirmed a reduced glycolytic flux. In bout 3, the work done represented 82% of the work in bout 2, whereas glycogenolysis was only 32% of that in bout 2. Decreases in ATP and phosphocreatine contents were similar in the two bouts. Muscle [H+] increased from 195 +/- 12 to 274 +/- 19 nmol/l during bout 2, recovered to 226 +/- 8 nmol/l before bout 3, and increased to 315 +/- 24 nmol/l during bout 3. Muscle [H+] could not be predicted from lactate content, suggesting that ion fluxes are important in [H+] regulation in this exercise model. Low glycogenolysis in bout 3 may be due to an inhibitory effect of increased [H+] on glycogen phosphorylase activity. Alternately, reduced Ca2+ activation of fast-twitch fibers (including a possible H+ effect) may contribute to the low overall glycogenolysis. Total work in bout 3 is maintained by a greater reliance on slow-twitch fibers and oxidative metabolism.     

Purine loss after repeated sprint bouts in humans.

The influence of the number of sprint bouts on purine loss was examined in nine men (age 24.8 +/- 1.6 yr, weight 76 +/- 3.9 kg, peak O(2) consumption 3.87 +/- 0.16 l/min) who performed either one (B1), four (B4), or eight (B8) 10-s sprints on a cycle ergometer, 1 wk apart, in a randomized order. Forearm venous plasma inosine, hypoxanthine (Hx), and uric acid concentrations were measured at rest and during 120 min of recovery. Urinary inosine, Hx, and uric acid excretion were also measured before and 24 h after exercise. During the first 120 min of recovery, plasma inosine and Hx concentrations, and urinary Hx excretion rate, were progressively higher (P < 0.05) with an increasing number of sprint bouts. Plasma uric acid concentration was higher (P < 0.05) in B8 compared with B1 and B4 after 45, 60, and 120 min of recovery. Total urinary excretion of purines (inosine + Hx + uric acid) was higher (P < 0. 05) at 2 h of recovery after B8 (537 +/- 59 micromol) compared with the other trials (B1: 270 +/- 76; B4: 327 +/- 59 micromol). These results indicate that the loss of purine from the body was enhanced by increasing the number of intermittent 10-s sprint bouts.     

Variations in running activity and enzymatic adaptations in voluntary running rats

The running behavior and biochemical markers of oxidative and glycolytic activities associated with voluntary running activity were studied in male Sprague-Dawley rats after 6 wk of training in exercise wheel cages. Twenty-four-hour recordings of running activity were used to quantify the number of individual running bouts, their duration and running speed, and the distance run per day. We then established three categories of voluntary running activity based on the mean distance run per day during the last 3 wk of training: low-activity runners averaged 2-5 km/day, medium runners 6-9 km/day, and high runners greater than 11 km/day. Each group demonstrated an intermittent, nocturnal running pattern, at relatively high intensities, with a similar mean running speed for all groups (avg approximately 45 m/min). Differences in total distance run per day were the result of variations in both the number and duration of individual running bouts. Specifically, high runners (n = 7) had 206 +/- 30 individual running bouts per 24 h, each lasting 87 +/- 7 s; medium runners (n = 7) 221 +/- 22 running bouts, lasting 47 +/- 5 s; and low runners (n = 7) 113 +/- 7 bouts, each lasting 40 +/- 7 s. Voluntary running depressed the rate of body weight gain compared with sedentary control rats, despite an increased food and water intake for all runners. Furthermore, drinking activity was temporally associated with running periods.(ABSTRACT TRUNCATED AT 250 WORDS)     

The relationship between creatine kinase kinetics and exercise intensity in human forearm is unchanged by age

Using (31)P magnetic resonance spectroscopy, creatine kinase (CK) reaction kinetics was assessed in the forearm flexor digitorum profundus muscle of healthy young (n = 11, age 34.7 +/- 5 yr) and older (n = 20, age 73.5 +/- 8 yr) subjects at rest, intermittent exercise at 20% maximum voluntary contraction (MVC), and 40% MVC. Exercise resulted in a significant increase in the average ratio of inorganic phosphate (P(i)) to phosphocreatine (PCr) from resting values of 0.073 +/- 0.031 (young) and 0.082 +/- 0.037 (older) to 0. 268 +/- 0.140 (young, P < 0.01) and 0.452 +/- 0.387 (older, P < 0. 01) at 40% MVC. At 40% MVC, intracellular pH decreased significantly, from resting values of 7.08 +/- 0.08 (young) and 7.08 +/- 0.11 (older) to 6.84 +/- 0.19 (young, P < 0.05) and to 6.75 +/- 0.25 (older, P < 0.05). Average values of the pseudo-first-order reaction rate k((PCr-->ATP)) at rest were 0.07 +/- 0.04 s(-1) in the young and 0.07 +/- 0.03 s(-1) in the older group. At both exercise levels, the reaction rate constant increased compared with the resting value, but only the difference between the resting value and the 20% MVC value, which showed an 86% higher reaction rate constant in both groups, reached statistical significance (P < 0.05). No difference in the reaction rate constant between the young and older groups was observed at either exercise level. As with k((PCr-->ATP)), the average phosphorus flux through the CK reaction increased during exercise at 20% MVC (P < 0.05 in the older group) but decreased toward resting values at 40% MVC in both groups. The data in our study suggest that normal aging does not significantly affect the metabolic processes associated with the CK reaction.     

Hormone-sensitive lipase activity and fatty acyl-CoA content in human skeletal muscle during prolonged exercise.

Hormone-sensitive lipase (HSL) catalyzes the hydrolysis of intramuscular triacylglycerols (IMTGs), but HSL regulation is poorly understood in skeletal muscle. The present study measured human skeletal muscle HSL activity at rest and during 120 min of cycling at 60% of peak O2 uptake. Several putative HSL regulators were also measured, including muscle long-chain fatty acyl-CoA (LCFA CoA) and free AMP contents and plasma epinephrine and insulin concentrations. HSL activity increased from resting levels by 10 min of exercise (from 2.09 +/- 0.19 to 2.56 +/- 0.22 mmol. min-1x kg dry mass-1, P < 0.05), increased further by 60 min (to 3.12 +/- 0.27 mmol x min-1x kg dry mass-1, P < 0.05), and decreased to near-resting rates after 120 min of cycling. Skeletal muscle LCFA CoA increased (P < 0.05) above rest by 60 min (from 15.9 +/- 3.0 to 50.4 +/- 7.9 micromol/kg dry mass) and increased further by 120 min. Estimated free AMP increased (P < 0.05) from rest to 60 min and was approximately 20-fold greater than that at rest by 120 min. Epinephrine was increased above rest (P < 0.05) at 60 (1.47 +/- 0.15 nM) and 120 min (4.87 +/- 0.76 nM) of exercise. Insulin concentrations decreased rapidly and were lower than resting levels by 10 min and continued to decrease throughout exercise. In summary, HSL activity was increased from resting levels by 10 min, increased further by 60 min, and decreased to near-resting values by 120 min. The increased HSL activity at 60 min was associated with the stimulating effect of increased epinephrine and decreased insulin levels. After 120 min, the decreased HSL activity was associated with the proposed inhibitory effects of increased free AMP. The accumulation of LCFA CoA in the 2nd h of exercise may also have reduced the flux through HSL and accounted for the reduction in IMTG utilization previously observed late in prolonged exercise.     

Muscle sympathetic nerve responses to physiological changes in prostaglandin production in humans.

Previous studies suggest that prostaglandins may contribute to exercise-induced increases in muscle sympathetic nerve activity (MSNA). To test this hypothesis, MSNA was measured at rest and during exercise before and after oral administration of ketoprofen, a cyclooxygenase inhibitor, or placebo. Twenty-one subjects completed two bouts of graded dynamic and isometric handgrip to fatigue. Each exercise bout was followed by 2 min of postexercise muscle ischemia. The second exercise bouts were performed after 60 min of rest in which 11 subjects were given ketoprofen (300 mg) and 10 subjects received a placebo. Ketoprofen significantly lowered plasma thromboxane B(2) in the drug group (from 36 +/- 6 to 22 +/- 3 pg/ml, P < 0.04), whereas thromboxane B(2) in the placebo group increased from 40 +/- 5 to 61 +/- 9 pg/ml from trial 1 to trial 2 (P < 0.008). Ketoprofen and placebo did not change sympathetic and cardiovascular responses to dynamic handgrip, isometric handgrip, and postexercise muscle ischemia. There was no relationship between thromboxane B(2) concentrations and MSNA or arterial pressure responses during both exercise modes. The data indicate that physiological increases or decreases in prostaglandins do not alter exercise-induced increases in MSNA and arterial pressure in humans. These findings suggest that contraction-induced metabolites other than prostaglandins mediate MSNA responses to exercise in humans.     

Effect of isometric exercise on catecholamines in the coronary circulation.

Arterial and coronary sinus blood levels of catecholamines, adenosine 3', 5'-cyclic monophosphate (c-AMP) and lactate were measured during isometric exercise in fourteen patients. In no patient did lactate production occur. Mean resting total catecholamine levels both arterial (0.53 +/- 0.07 ng/ml; 2.94 +/- 0.38 nmol/l) and coronary sinus (0.4 +/- 0.08 ng/ml; 2.22 +/- 0.44 nmol/l), did not change significantly on exercise. Coronary sinus c-AMP levels fell on exercise from 11.5 +/- 0.8 nmol/l (resting) to 9.9 +/- 0.8 nmol/l (exercise) (P less than 0.01) with an arterial-coronary sinus difference of 1.2 nmol/l (P less than 0.01) on exercise. Our findings suggest that isometric exercise does not normally result in excessive cardiac symphathetic activity.     

Rib cage and abdominal expiratory muscle responses to CO2 and esophageal distension

The present study compared the responses of rib cage and abdominal expiratory muscles to chemical and mechanical stimuli. In pentobarbital-anesthetized spontaneously breathing dogs, electromyograms (EMG) were recorded from the triangularis sterni (TS) and transverse abdominis (TA) muscles using bipolar intramuscular wire electrodes. During resting oxygen breathing, both muscles were electrically active during expiration. Progressive hyperoxic hypercapnia significantly augmented the expiratory activity of both the TA and the TS. However, the mean percent increases in electrical activity in response to CO2 were substantially greater for the TA than for the TS at all PCO2 levels greater than 50 Torr (P less than 0.01). Occlusion of the airway at end inspiration significantly delayed the onset of TS EMG (from 0.35 +/- 0.07 to 3.35 +/- 0.67 sec; P less than 0.002) and decreased TS EMG rate of rise (P less than 0.002), but did not significantly alter these parameters for the TA. Esophageal distension increased TS EMG in all dogs (by mean of 220 +/- 64%; P less than 0.01), but in contrast decreased TA EMG in all dogs (by a mean of 63 +/- 12%; P less than 0.001). The response to esophageal distention occurred in a graded manner and appeared to be mediated predominantly via vagal afferents. We concluded that expiratory muscles of the rib cage and abdomen manifest substantial differences in their electrical responses to chemoreceptor, pulmonary stretch receptor, and esophageal mechanoreceptor stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)     

Preferences of farmed blue foxes for different floor types

In the first experiment, farmed blue foxes were allowed to choose for 1 week between four standard farm cages equipped with different floor materials: plastic-coated wire mesh, dry wood, dry sand and wet (summer) or icy (winter) sand. Resting consisted of 10-15 separate bouts/day occupying 50-60% of the total 24-h. There were no other differences in the use of the cages except that the time spent on, and the duration and number of resting bouts were lower on wet or icy sand, resting periods being more affected than activity. In the second experiment, two cages were connected with a 1.2 m tunnel. One cage was always elevated (50 cm) compared to that one which was lower. One cage of each pair had a wire floor whereas the other cage either had sand or wire floor. Sand floor was preferred for active behaviours and wire floor for resting if these were on elevated level. Of two identical wire-floored cages, the elevated one had the priority. Foxes preferred to rest on the same floor where they had finished their previous resting bout, often exclusively and independently of floor material or floor level.     

Limb congestion enhances the synchronization of sympathetic outflow with muscle contraction

In this report, we examined if the synchronization of muscle sympathetic nerve activity (MSNA) with muscle contraction is enhanced by limb congestion. To explore this relationship, we applied signal-averaging techniques to the MSNA signal obtained during short bouts of forearm contraction (2-s contraction/3-s rest cycle) at 40% maximal voluntary contraction for 5 min. We performed this analysis before and after forearm venous congestion; an intervention that augments the autonomic response to sustained static muscle contractions via a local effect on muscle afferents. There was an increased percentage of the MSNA noted during second 2 of the 5-s contraction/rest cycles. The percentage of total MSNA seen during this particular second increased from minute 1 to 5 of contraction and was increased further by limb congestion (control minute 1 = 25.6 +/- 2.0%, minute 5 = 32.8 +/- 2.2%; limb congestion minute 1 = 29.3 +/- 2.1%, minute 5 = 37.8 +/- 3.9%; exercise main effect <0.005; limb congestion main effect P = 0.054). These changes in the distribution of signal-averaged MSNA were seen despite the fact that the mean number of sympathetic discharges did not increase over baseline. We conclude that synchronization of contraction and MSNA is seen during short repetitive bouts of handgrip. The sensitizing effect of contraction time and limb congestion are apparently due to feedback from muscle afferents within the exercising muscle.     

BODY SIZE,SPERM COMPETITION,AND DETERMINANTS OF REPRODUCTIVE SUCCESS IN MALE SAVANNA BABOONS

One component of sexual selection is sperm competition. It has been reasoned that the intensity of sperm competition may be reflected in the relative testicular sizes of animals. Among males residing in multimale breeding systems, testicular size is relatively larger than among males residing in unimale mating systems. Information on whether differences in testicular size within a species can account for differences in male reproductive success is unavailable for natural populations of primates. A population of six troops of savanna baboons in Kenya was surveyed for morphometric analysis, and one of these troops was the subject of extensive behavioral observations afterwards. Testicular weights could not be obtained, but measurements of linear dimensions were transformed into volumetric estimates. Male weight accounted for 30% of the variance in testicular volume. Neither body size nor testicular volume was associated with differences in male reproductive activity. The outcome of fights over access to females could not be related to male body size, and ejaculatory patterns of males were independent of testicle size. Both sperm competition and aggressive competition intensified during the four-day optimum conception period, but fights over access to consort females were infrequent. Among savanna baboons, the probability of an ejaculation resulting in a conception is fairly low, which may account for the infrequency of injurious fights. Although testicle size influences sperm production, it does not influence either the timing of mating or the fertilizing capacity of spermatozoa, and both of these factors probably account for a substantial fraction of the variance in male baboon paternity. Sperm competition is an adjunct to agonistic competition as a mechanism affecting male baboon reproductive success. It is concluded that male reproductive success in baboons is affected more by social factors than by morphological traits associated with size.     

Effects of high-intensity swimming training on GLUT-4 and glucose transport activity in rat skeletal muscle.

This study was performed to assess the effects of short-term, extremely high-intensity intermittent exercise training on the GLUT-4 content of rat skeletal muscle. Three- to four-week-old male Sprague-Dawley rats with an initial body weight ranging from 45 to 55 g were used for this study. These rats were randomly assigned to an 8-day period of high-intensity intermittent exercise training (HIT), relatively high-intensity intermittent prolonged exercise training (RHT), or low-intensity prolonged exercise training (LIT). Age-matched sedentary rats were used as a control. In the HIT group, the rats repeated fourteen 20-s swimming bouts with a weight equivalent to 14, 15, and 16% of body weight for the first 2, the next 4, and the last 2 days, respectively. Between exercise bouts, a 10-s pause was allowed. RHT consisted of five 17-min swimming bouts with a 3-min rest between bouts. During the first bout, the rat swam without weight, whereas during the following four bouts, the rat was attached to a weight equivalent to 4 and 5% of its body weight for the first 5 days and the following 3 days, respectively. Rats in the LIT group swam 6 h/day for 8 days in two 3-h bouts separated by 45 min of rest. In the first experiment, the HIT, LIT, and control rats were compared. GLUT-4 content in the epitrochlearis muscle in the HIT and LIT groups after training was significantly higher than that in the control rats by 83 and 91%, respectively. Furthermore, glucose transport activity, stimulated maximally by both insulin (2 mU/ml) (HIT: 48%, LIT: 75%) and contractions (25 10-s tetani) (HIT: 55%, LIT: 69%), was higher in the training groups than in the control rats. However, no significant differences in GLUT-4 content or in maximal glucose transport activity in response to both insulin and contractions were observed between the two training groups. The second experiment demonstrated that GLUT-4 content after HIT did not differ from that after RHT (66% higher in trained rats than in control). In conclusion, the present investigation demonstrated that 8 days of HIT lasting only 280 s elevated both GLUT-4 content and maximal glucose transport activity in rat skeletal muscle to a level similar to that attained after LIT, which has been considered a tool to increase GLUT-4 content maximally.