Biomedical subjects

J Bangsbo

Publications and source records attributed to J Bangsbo.

At least 55 records · Page 3Linked to original sources

PubMed1997

Dissociation between lactate and proton exchange in muscle during intense exercise in man.

1. Transport of lactate, H+ and fluid across muscle sarcolemma was studied in contracting muscles under varying blood acid-base conditions. 2. Subjects performed two-legged submaximal knee-extensor exercise for 29-35 min consisting of warming up for 5 min followed by 10 min of leg exercise (L1), leg and arm exercise for 6-10 min (L2 + A) and leg exercise for 10 min (L3). The experimental protocol was performed on two occasions; inspiring air (normoxia, N) or breathing 14% O2 in N2 (hypoxia, H). Leg blood flow was measured and femoral arterial and venous blood was sampled before and during each phase of exercise. 3. Arterial blood lactate concentration increased progressively during exercise to 5.9 +/- 0.8 (N) and 8.2 +/- 0.8 mmol l-1 (H) (P < 0.05) after 5.5 min of L2 + A. Arterial blood pH was higher (P < 0.05) in H than in N, whereas arterial blood HCO3- concentrations were the same. Leg lactate release was higher in H than in N (3.1 +/- 0.7 vs. 2.0 mmol l-1 (P < 0.05) during L1. In L2 + A a net uptake of lactate was observed in both N and H. The concentration of lactate in the red blood cells increased during exercise to 2.3 +/- 0.4 (N) and 4.3 +/- 0.7 mmol l-1 (H) (P < 0.05) after 5.5 min of L2 + A, but no red blood cell femoral arterial-venous lactate difference was observed. 4. Net proton release, estimated from actual base excess (ABE) adjusted for changes in reduced haemoglobin, was significant (P < 0.05) both at rest and during each phase of exercise. Furthermore, the difference between net proton and lactate release was positive throughout exercise and of similar magnitude in N and H. 5. The present data suggest that (1) H+ exchange in muscle during submaximal exercise can to a large extent occur through mechanisms other than via coupling to lactate; (2) muscle transport of H+ is insensitive to changes in blood pH in the range of 0.02-0.08 pH units; (3) transport of lactate across the membrane of red blood cells appears to be of minor importance for lactate release from active muscles.

Acid-Base Equilibrium↗

PubMed1997

Oxidation of urate in human skeletal muscle during exercise.

The purpose of the present study was to investigate whether high metabolic stress to skeletal muscle, induced by intensive exercise, would lead to an oxidation of urate to allantoin in the exercised muscle. Seven healthy male subjects performed short term (4.39 +/- 0.04 [+/-SE] min) exhaustive cycling exercise. Muscle samples were obtained from m. v. lateralis before and during the first few minutes after the exercise. Venous blood samples were obtained before and up to 45 min after the exercise. The concentration of urate in muscle decreased from a resting level of 0.26 +/- 0.023 to 0.084 +/- 0.016 mumol.g-1 w.w. (p < .05) during the exercise and then rapidly increased during recovery to reach the resting level within 3 min after exercise. The concentration of allantoin in the muscle increased from a resting value of 0.03 +/- 0.007 to 0.10 +/- 0.014 mumol.g-1 w.w. immediately after exercise (p < .05) and then decreased to 0.079 +/- 0.002 mumol.g-1 w.w. during the first 3 min after exercise (p < .05). Plasma urate levels increased slowly from 305 +/- 16 to 426 +/- 20 mumol.liter-1 at 45 min in recovery (p < .05). Plasma allantoin was 11.9 +/- 2.6 mumol.liter-1 at rest and by 5 min the level was more than twofold higher and remained elevated throughout recovery (p < .05). The present results indicate that urate is oxidized to allantoin in the muscle during exercise, probably due to generation of free radicals. Furthermore, the findings support the suggested importance of urate as a free radical scavenger in vivo.

Adult↗

PubMed1997

Long-term adaptation to electrically induced cycle training in severe spinal cord injured individuals.

Spinal cord injured (SCI) individuals most often contract their injury at a young age and are deemed to a life of more or less physical inactivity. In addition to the primary implications of the SCI, severe SCI individuals are stigmatized by conditions related to their physically inactive lifestyle. It is unknown if these inactivity related conditions are potentially reversible and the aim of the present study was, therefore, to examine the effect of exercise on SCI individuals. Ten such individuals (six with tetraplegia and four with paraplegia; age 27-45 years; time since injury 3-23 years) were exercise trained for 1 year using an electrically induced computerized feedback controlled cycle ergometer. They trained for up to three times a week (mean 2.3 times), 30 min on each occasion. The gluteal, hamstring and quadriceps muscles were stimulated via electrodes placed on the skin over their motor points. During the first training bouts, a substantial variation in performance was seen between the subjects. A majority of them were capable of performing 30 min of exercise in the first bout; however, two individuals were only able to perform a few minutes of exercise. After training for 1 year all of the subjects were able to perform 30 min of continuous training and the work output had increased from 4 +/- 1 (mean +/- SE) to 17 +/- 2 Kilo Joules per training bout (P < 0.05). The maximal oxygen uptake during electrically induced exercise increased from 1.20 +/- 0.08 litres per minute measured after a few weeks habituation to the exercise to 1.43 +/- 0.09 litres per minute after training for 1 year (P < 0.05). Magnetic resonance cross sectional images of the thigh were performed to estimate muscle mass and an increase of 12% (mean, P < 0.05) was seen in response to 1 year of training. In biopsies taken before exercise various degrees of atrophy were observed in the individual muscle fibres, a phenomenon that was partially normalized in all subjects after training. The fibre type distribution in skeletal muscles is known to shift towards type IIB fibres (fast twitch, fast fatiguable, glycolytic fibres) within the first 2 years after the spinal cord injury. The muscle in the present investigation contained of 63% myosin heavy chain (MHC) isoform IIB, 33% MHC isoform IIA (fast twitch, fatigue resistant) and less than 5% MHC isoform I (slow twitch) before training. A shift towards more fatigue resistant contractile proteins was found after 1 year of training. The percentage of MHC isoform IIA increased to 61% of all contractile protein and a corresponding decrease to 32% was seen in the fast fatiguable MHC isoform IIB, whereas MHC isoform I only comprised 7% of the total amount of MHC. This shift was accompanied by a doubling of the enzymatic activity of citrate synthase, as an indicator of mitochondrial oxidative capacity. It is concluded that inactivity-associated changes in exercise performance capacity and skeletal muscle occurring in SCI individuals after injury are reversible, even up to over 20 years after the injury. It follows that electrically induced exercise training of the paralysed limbs is an effective rehabilitation tool that should be offered to SCI individuals in the future.

Adaptation, Physiological↗

PubMed1997

Muscle glycogen synthesis in recovery from intense exercise in humans.

The present study examined the role of lactate and glucose as substrates for glyconeogenesis in muscle in recovery from high-intensity exercise in humans. Seven subjects performed approximately 100 min of intense intermittent one-legged knee extensor exercise on two occasions: with [high lactate (HL)] and without [control (C)] intense arm exercise between the leg exercise bouts, leading to end exercise arterial plasma lactate concentrations of 16.0 +/- 1.6 and 9.2 +/- 1.6 mmol/l, respectively (P < 0.05). At the end of exercise, muscle lactate and glycogen were similar in HL and C (20.5 +/- 1.3 vs. 17.3 +/- 2.0 mmol/kg wet wt and 48.1 +/- 11.3 vs. 56.3 +/- 8.6 mmol/kg wet wt, respectively). Muscle glycogen increased (P < 0.05) during the first 5 min of recovery only in HL, but after 90 min of recovery the muscle glycogen concentration was the same in C and HL (61.2 +/- 12.0 vs. 71.5 +/- 10.9 mmol/kg wet wt). Muscle lactate not released to the blood could maximally account for 28 (C) and 54% (HL) of the increase in muscle glycogen during 90 min of recovery or < 10% of glycogen synthesis after full recovery. The total net glucose uptake corresponded to 84 (C) and 57% (HL) of the glycogen synthesized. Apparently, muscle glyconeogenesis may occur in humans, but the role of lactate as a substrate is minor. Instead, blood glucose appears to be the most important precursor for muscle glycogen synthesis after intense exercise.

Adult↗

PubMed1996

Effect of muscle acidity on muscle metabolism and fatigue during intense exercise in man.

1. The aim of this study was to examine the effect of muscle pH on muscle metabolism and development of fatigue during intense exercise. 2. Seven subjects performed intense exhaustive leg exercise on two occasions: with and without preceding intense intermittent arm exercise leading to high or moderate (control) blood lactate concentrations (HL and C, respectively). Prior to and immediately after each exercise bout, a muscle biopsy was taken from m. vastus lateralis of the active leg. Leg blood flow was measured and femoral arterial and venous blood samples were collected before and frequently during the exhaustive exercises. 3. The duration of the exercise was shorter in HL than in C (3.46 +/- 0.28 vs. 4.67 +/- 0.55 min; means +/- S.E.M.; P < 0.05). Before exercise muscle pH was the same in C and HL (7.17 vs. 7.10), but at the end of exercise muscle pH was lower in HL than in C (6.82 vs. 6.65; P < 0.05). The release of potassium during exercise was higher (P < 0.05) in HL compared with C, but the arterial and femoral venous plasma potassium concentrations were the same at exhaustion in HL and C. 4. Muscle lactate concentration was higher in HL compared with C (3.7 +/- 0.4 vs. 1.6 +/- 0.2 mmol (kg wet weight)-1; P < 0.05), but the same at exhaustion (26.5 +/- 2.7 vs. 25.4 +/- 2.4 mmol (kg wet weight)-1). Total release of lactate in HL was lower than in C (18.7 +/- 4.5 vs. 50.4 +/- 11.0 mmol; P < 0.05), but rate of lactate production was not different (9.0 +/- 1.0 vs. 10.2 +/- 1.3 mmol (kg wet weight)-1 min-1). The rate of muscle glycogen breakdown was the same in C and HL (8.1 +/- 1.2 vs. 8.2 +/- 1.0 mmol (kg wet weight)-1 min-1). 5. The present data suggest that elevated muscle acidity does not reduce muscle glycogenolysis/glycolysis and is not the only cause of fatigue during intense exercise in man. Instead, accumulation of potassium in muscle interstitium may be an important factor in the development of fatigue.

Adult↗

PubMed1996

Specificity of training velocity and training load on gains in isokinetic knee joint strength.

The present study investigated the effects of three different strength training regimes on the isokinetic strength profile of the knee extensors (quadriceps, Q) and flexors (hamstrings, H) and if increases in isokinetic strength were accompanied by an enhanced performance during a more complex leg movement, the soccer kick. Twenty-two elite soccer players performed 12 weeks of strength training (three times per week) at either high resistance (HR group: 4 sets, 8 reps, 8RM loading), low resistance (LR group: 4 sets, 24 reps, 24RM loading), loaded kicking movements (LK group: 4 sets, 16 reps, 16RM loading) while one group served as controls (CO group). Isokinetic concentric and eccentric moment of force was obtained (KinCom) as peak moment (Mpeak) and moment at 50 degrees knee flexion (M50) at angular velocities of 30, 120, 240 degrees s-1. Isokinetic knee joint strength was unchanged in groups LR, LK, CO. However, after the HR strength training, concentric Mpeak (+/- SD) increased (P < 0.01) at 30 degrees s-1 (Q, 258 +/- 37 to 297 +/- 57 Nm; H, 122 +/- 22 to 140 +/- 21 Nm). Furthermore, eccentric Mpeak increased at 30, 120 and 240 degrees s-1 (Q, 274 +/- 60 to 345 +/- 57 Nm (P < 0.01), 291 +/- 56 to 309 +/- 49 Nm and 275 +/- 43 to 293 +/- 36 Nm (P < 0.05), respectively; H, 143 +/- 32 to 158 +/- 25 Nm, 152 +/- 39 to 169 +/- 31 Nm and 148 +/- 27 to 163 +/- 19 Nm (P < 0.05)). Corresponding increases (P < 0.05) were observed for M50. The H/Q ratio calculated as eccentric hamstring strength divided by concentric quadriceps strength (Hecc/Qcon, representative for knee extension) at 240 degrees s-1 increased (P < 0.05) from 107 to 118% (based on Mpeak) and from 90 to 105% (M50). Kicking performance estimated by maximal ball flight velocity was unaffected by any of the strength training regimes investigated. In conclusion, only heavy-resistance strength training induced increases in isokinetic muscle strength in the absence of learning effects. Concentric strength gains were observed at the actual velocity of training, while eccentric strength gains were found over the entire range of velocities examined. The capacity of the hamstring muscles for providing stability to the knee joint during fast extension was augmented as a result of the heavy-resistance strength training. Strength training should be integrated with other types of training involving the actual movement pattern in order to increase the performance within more complex movement patterns.

Adult↗

PubMed1996

Oxygen deficit: a measure of the anaerobic energy production during intense exercise?

Several findings in studies of whole-body exercise indicate that the energy provided from anaerobic sources during intense whole-body exercise cannot be quantified from oxygen deficit determinations when energy demand for the supramaximal exercise is estimated from a linear relationship between work intensity and energy production during submaximal exercise. It is likely that the energy demand during high-intensity exercise is underestimated by this procedure; these errors are probably greatest for very high power outputs (shorter exercise time to exhaustion). It is clear that further studies are needed to characterize the energy demand during intense exercise before the oxygen deficit can be used as a measure of the anaerobic energy production.

Anaerobic Threshold↗

PubMed1996

Ammonia uptake in inactive muscles during exercise in humans.

The present study examined NH3 (ammonia and ammonium) uptake in resting leg muscle. Six male subjects performed intermittent arm exercise at various intensities in two separate 32-min periods (part I and part II) and in one subsequent 20-min period in which one-legged exercise was also performed (part III). The arterial plasma NH3 concentration was 79.6 +/- 9.6 (SE) mumol/l at rest and 88.1 +/- 9.1, 98.1 +/- 8.1, and 210.2 +/- 7.5 mumol/l after 10 min of exercise in parts I, II, and III, respectively. The corresponding NH3 uptakes in the resting leg were 3.3 +/- 1.3 (rest), 7.8 +/- 1.5, 14.0 +/- 4.5, and 57.7 +/- 18.3 mumol/min. Throughout each exercise period a net uptake of NH3 was observed in the resting leg (P < 0.05), but uptake decreased to resting values within 5 min of termination of exercise. The muscle NH3 concentration of 195.1 +/- 15.0 mumol/kg wet wt at rest was largely unchanged throughout the experiment. The present data suggest that resting muscles extract NH3 and contribute significantly to clearance of NH3 during exercise and in early recovery from exercise. The extracted NH3 appears to be metabolized within the resting muscles.

Adult↗

PubMed1996

Hormonal and metabolic responses to electrically induced cycling during epidural anesthesia in humans.

Hormonal and metabolic responses to electrically induced dynamic exercise were investigated in eight healthy young men with afferent neural influence from the legs blocked by epidural anesthesia (25 ml of 2% lidocaine) at L3-L4. This caused cutaneous sensory anesthesia below T8-T9 and complete paralysis of the legs. Cycling increased oxygen uptake to 1.90 +/- 0.13 (SE) l/min, and fatigue developed after 22.7 +/- 2.7 min. Compared with voluntary exercise at the same oxygen uptake and heart rate, concentrations of blood and muscle lactate (musculus vastus lateralis) as well as plasma potassium increased more while muscle glycogen decreased more during electrically induced exercise. Hepatic glucose production always rose during exercise. However, during involuntary exercise with sensory blockade, it did not match the rise in peripheral glucose uptake and plasma glucose decreased (P < 0.05). Plasma glycerol increased less in electrically induced vs. voluntary exercise, and free fatty acids and beta-hydroxybutyrate decreased only during electrically induced exercise. Epinephrine, growth hormone, adrenocorticotropic hormone, and cortisol levels were higher during involuntary vs. voluntary exercise (P < 0.05). In conclusion, neural and humoral mechanisms exert redundant control with regard to responses of catecholamines and pituitary hormones (growth hormone and adrenocorticotropic hormone). In contrast, neural input from motor centers and feedback from working muscle are important for glucose production and lipolysis during exercise in humans. Humoral feedback is apparently not sufficient to trigger normal mobilization of extramuscular fuel stores.

Adult↗

PubMed1996

Physiological factors associated with efficiency in high intensity exercise.

Information about mechanical efficiency during intense exercise is limited, which is partly due to the difficulties that exist in quantifying anaerobic energy production. Based on human studies examining the isolated quadriceps muscle, the mechanical efficiency during intense dynamic exercise has been estimated to be around 22 to 26%. For cycling, the mechanical efficiency shows a wider range (14 to 34%) which, to a large extent, can be attributed to the uncertainties regarding the mass of the muscles used and whether muscle biopsy material is representative for the muscles involved in the exercise. Data from studies of the isolated quadriceps muscle suggest that mechanical efficiency increases as intense exercise is continued and that mechanical efficiency is greater when high intensity exercise is repeated, even with a rest period of 1 hour between exercise bouts. It is unclear whether a period of training can affect mechanical efficiency during intense exercise.

Energy Metabolism↗

PubMed1995

Lactate and H+ uptake in inactive muscles during intense exercise in man.

1. The present study examined how uptake of lactate and H+ in resting muscle is affected by blood flow, arterial lactate concentration and muscle metabolism. 2. Six males subjects performed intermittent arm exercise in two separate 32 min periods (Part I and Part II) and in one subsequent 20 min period in which one leg knee-extensor exercise was also performed (Part III). The exercise was performed at various intensities in order to obtain different steady-state arterial blood lactate concentrations. In the inactive leg, femoral venous blood flow (draining about 7.7 kg of muscles) was measured and femoral arterial and venous blood was collected frequently. Biopsies were taken from m. vastus lateralis of the inactive leg at rest and 10 and 30 min into both Part I and Part II as well as 10 min into recovery from Part II. 3. The arterial plasma lactate concentrations were 7, 9 and 16 mmol l-1 after 10 min of Parts I, II and III, respectively, and the corresponding arterial-venous difference (a-vdiff) for lactate in the resting leg was 1.3, 1.4 and 2.0 mmol l-1. The muscle lactate concentration was 2.8 mmol (kg wet wt)-1 after 10 min of Part I and remained constant throughout the experiment. During Parts I and II, a-vdiff lactate decreased although the arterial lactate concentration and plasma-muscle lactate gradient were unaltered throughout each period. Thus, membrane transport of lactate decreased during each period. 4. Blood flow in the inactive leg was about 2-fold higher during arm exercise compared to the rest periods, resulting in a 2-fold higher lactate uptake. Thus, lactate uptake by inactive muscles was closely related to blood flow. 5. Throughout the experiment a-vdiff for actual base excess and for lactate were of similar magnitude. Thus, in inactive muscles lactate uptake appears to be coupled to the transport of H+.

Acid-Base Equilibrium↗

PubMed1995

Aerobic exercise capacity at sea level and at altitude in Kenyan boys, junior and senior runners compared with Scandinavian runners.

The aim of this study was to characterize Kenyan runners in regard to their oxygen uptake and blood and ammonia responses when running. Untrained Kenyan boys (14.2 +/- 0.2 years) and Scandinavian runners were included for comparison. The studies were performed at altitude (approximately 2.000 m.a.s.l.) and, for several Kenyan and Scandinavian runners, at sea level as well. At altitude sedentary adolescent Kenyan boys had a mean maximal oxygen uptake (VO2max) of 47 (44-51) ml.kg-1.min-1, whereas similarly aged boys regularly walking or running but not training for competition reached above 62 (58-71) ml.kg-1.min-1 in VO2max. Kenyan runners in active training had 68 +/- 1.4 ml.kg-1.min-1 at altitude and 79.9 +/- 1.4 ml.kg-1.min-1 at sea level, with individuals reaching 85 ml.kg-1.min-1. The best Scandinavian runners were not significantly different from the Kenyan runners in VO2max both at altitude and at sea level, but none of the Scandinavians reached as high individual values as observed for some Kenyan runners. The running efficiency, determined as the oxygen cost at a given running speed, was less in the Kenyan runners, and the difference became more pronounced when body weight was expressed in ml.kg-0.75 min-1. Blood lactate concentration was in general lower in the Kenyan than in the Scandinavian runners, and the Kenyans also had extremely low ammonia accumulation in the blood even at very high exercise intensities. It is concluded that it is the physical activity during childhood, combined with intense training as teenagers that brings about the high VO2max observed in some Kenyan runners. Their high aerobic capacity, as well as their good running economy, makes them such superior runners. In addition, their low blood lactate and ammonia accumulation in blood when running may also be contributing factors.

Adolescent↗

PubMed1995

Skeletal muscle perfusion in electrically induced dynamic exercise in humans.

Leg blood flow, blood pressure and metabolic responses were evaluated in six men during incremental one-legged dynamic knee extension exercise tests (no load exercise-40 W); one performed with voluntary contractions (VOL) and one with electrically induced contractions (EMS). Pulmonary oxygen uptake was the same in both exercise modes, but the ventilatory coefficient was 2-5 L per L O2 higher in EMS than VOL (P < 0.05). Heart rate and mean arterial pressure were slightly higher with EMS than VOL at all exercise intensities reaching 138 (EMS) and 126 bpm (VOL), as well as 148 (EMS) and 137 mmHg (VOL) at 40 W, respectively (P < 0.05). Leg blood flow, oxygen uptake and conductance were similar in the two exercise modes. At 40 W, mean muscle blood flow was close to 200 (range: 165-220) mL 100 g-1 min-1, mean peak muscle oxygen uptake reached 230 mL kg-1 min-1, and mean conductance became as high as around 45 mL min-1 mmHg-1, and normalized for muscle size and arterial pressure it approached 100 mL min-1 100 g-1 100 mmHg-1. Lactate and ammonia efflux from the leg were higher with EMS than with VOL and the difference became larger with increasing exercise intensity (P < 0.05). Muscle glucose uptake was the same in each exercise mode. Femoral venous K+ concentration increased with exercise intensity and was higher with EMS than with VOL, reaching 5.1 (EMS) and 4.7 mmol L-1 (VOL) at 40 W (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1995

Isokinetic hamstring/quadriceps strength ratio: influence from joint angular velocity, gravity correction and contraction mode.

This study investigated isokinetic peak- and angle-specific hamstring/quadriceps strength ratios (conventional H/Q ratio) obtained during concentric and eccentric muscle contraction and examined the influence of joint angular velocity and the effect of gravity correction on these ratios. Also, a 'functional' H/Q ratio was defined by calculating eccentric hamstring strength relative to concentric quadriceps strength (Hecc/Qcon' representative for knee extension) and calculating concentric hamstring strength relative to eccentric quadriceps strength (Hcon/Qecc' representative for knee flexion). The H/Q ratio was calculated based on isokinetic peak moment and 50 degree-moment (0 degree = full extension) obtained at joint angular velocities 30, 120 and 240 degrees s-1. Gravity corrected conventional H/Q ratio remained constant across speeds and contraction mode, ranging from 0.47 to 0.54 and from 0.49 to 0.56 based on peak and 50 degree moment, respectively. In contrast, non-corrected H/Q ratio increased during concentric contraction from 0.58 at 30 degrees s-1 to 0.74 at 240 degree s-1 (P < 0.01). For knee extension at 240 degrees s-1 an Hecc/Qcon of 1.05 (peak) and 0.89 (50 degrees) was observed while for flexion at 240 degrees s-1 an Hcon/Qecc of 0.27 (peak) and 0.28 (50 degrees) was observed. In conclusion, gravity correction had high influence on the change in H/Q ratio with variation in extension velocity. A potential 1:1 hamstring/quadriceps strength relationship was demonstrated for fast knee extension, indicating a significant functional capacity of the hamstring muscles for providing muscular stability at the knee joint in such situations.

Adult↗

PubMed1995

Effect of blood flow on muscle lactate release studied in perfused rat hindlimb.

The influence of blood flow on muscle lactate and H+ release as well as muscle glyconeogenesis was studied in the perfused rat hindlimb. After 2 min of supramaximal stimulation the perfusate flow rate was 7 (F7), 12 (F12), or 18 (F18) ml/min for 30 min. Perfusate samples were drawn frequently and muscle samples were obtained before stimulation, immediately after stimulation, and at 3, 10, and 30 min of recovery from soleus, white gastrocnemius (WG) and red gastrocnemius. During the first 5 min of recovery lactate release was 35-39% lower (P < 0.05) in F7 than in F12 and F18 but with no differences in total release during recovery. In F7 the concentration of lactate was higher (P < 0.05) in soleus after 10 min (18-20%) and in WG after 30 min (63-67%) than in F12 and F18. During the first 2 min of recovery H+ release was 23-34% lower (P < 0.05) in F7 than in F12 and F18. The difference between H+ and lactate release was larger (P < 0.05) in F7 than in F12 and F18 from 3 to 10 min and from 5 to 10 min of recovery, respectively. Muscle glycogen concentrations after 30 min of recovery were independent of flow in each of the muscles. The present data suggest that 1) in the range of blood flow rates from 0.61 to 0.92 ml.min-1.g-1, lactate and H+ release are independent of the flow rate, whereas at a lower flow rate (0.36 ml.min-1.g-1) release of these substances is decreased; 2) low blood flow influences lactate efflux more than H+ release; and 3) muscle glyconeogenesis from lactate is of minor importance.

Acid-Base Equilibrium↗

PubMed1995

IMP metabolism in human skeletal muscle after exhaustive exercise.

This study addressed whether AMP deaminase (AMPD)myosin binding occurs with deamination during intense exercise in humans and the extent of purine loss from muscle during the initial minutes of recovery. Male subjects performed cycle exercise (265 +/- 2 W for 4.39 +/- 0.04 min) to stimulate muscle inosine 5'-monophosphate (IMP) formation. After exercise, blood flow to one leg was occluded. Muscle biopsies (vastus lateralis) were taken before and 3.6 +/- 0.2 min after exercise from the occluded leg and 0.7 +/- 0.0, 1.1 +/- 0.0, and 2.9 +/- 0.1 min postexercise in the nonoccluded leg. Exercise activated AMPD; at exhaustion IMP was 3.5 +/- 0.4 mmol/kg dry muscle. Before exercise, 16.0 +/- 1.6% of AMPD cosedimented with the myosin fraction; the extent of AMPD:myosin binding was unchanged by exercise. Inosine content increased about threefold during exercise and twofold more during recovery; by 2.9 min postexercise it was 0.43 +/- 0.02 mmol/kg dry muscle. IMP decreased 2.1 +/- 0.3 mmol/kg dry muscle with no change in total adenylates. Total purines declined significantly (P < 0.05) during the recovery period in the nonoccluded leg, consistent with a loss of purines to the circulation, whereas total purines were unchanged in the occluded leg. Regulation of muscle purine content is a dynamic process that must accommodate rapid changes due to degradation and efflux.

AMP Deaminase↗

PubMed1995

Metabolic response and muscle glycogen depletion pattern during prolonged electrically induced dynamic exercise in man.

Muscle glycogen depletion pattern and metabolic responses during voluntary (VOL) and functional electrical stimulated (FES) dynamic knee-extensor exercise with one leg were evaluated. Seven healthy men exercised for 60 minutes at 30 W with an pulmonary oxygen uptake of 0.8 and 1.01 min-1, and respiratory exchange ratios of 0.90 and 0.95 in VOL and FES, respectively. Heart rate reached a level around 90 beats min-1 (VOL) and up to 110 beats min-1 (FES). Muscle glycogen decreased in FES with 260 and 290 mmol kg-1 d.w. in vastus lateralis and m. rectus femoris, respectively, compared with 45 and 160 mmol kg-1 d.w. in VOL (p < 0.05). In FES the percentage of empty and almost empty fibres determined by periodic acid-Schiff staining in vastus lateralis and rectus femoris was 50 and 77% of type I, 63 and 90% of type IIa, and 59 and 84% of type IIb fibres, respectively, whereas in VOL it was 24 and 26% of type I, 7 and 19% of type IIa, and 2 and 3% of type IIb fibres. Muscle lactate reached 30 mmol kg-1 d.w. in FES and was 9 mmol kg-1 d.w. lower in VOL. The changes in blood lactate and NH3 during the exercise were slightly higher in FES than in VOL, whereas the alterations in glucose, FFA, and K+ were small in both exercise modes. The pressure in the two muscle portions at different locations (proximal-distal) and depths was always higher (approximately 50%) in FES than in VOL, reaching levels around 55 mmHg.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

Maximal oxygen deficit of sprint and middle distance runners.

Anaerobic energy capacity was evaluated by maximal oxygen deficit (MOD) as well as by blood gas and muscle biopsy variables during short exhausting running in six recreational (RR) and eight competitive sprint and middle distance runners (SMDR). On 3 days runs to exhaustion were executed. Two runs were performed at a treadmill gradient of 15% at speeds which resulted in exhaustion after approximately 1 (R15%,1 min) and 2-3 min (R15%,2-3 min), respectively. On the 3rd day, the subjects ran with the treadmill at a gradient of 1% at a speed which caused exhaustion after 2-3 min (R1%,2-3 min). The runner performance was assessed from 400 m [RR, median 64.8 (range 62.2-69.6) s; SMDR, median 49.4 (range 48.5-52.0) s] and 800 m [RR, median 158.8 (range 153.3-170.2) s; SMDR, median 115.2 (range 113.3-123.3) s] track times. Muscle biopsies from gastrocnemius muscle were obtained before and immediately after R15%,2-3 min, from which muscle lactate and creatine phosphate (CP) concentrations, fibre type distribution, capillaries per fibre, total lactate dehydrogenase (LDH) activity and the LDH isoenzyme pattern were determined. The MOD increased with the treadmill gradient and duration. During both treadmill and track runs, SMDR performance was superior to that of RR, but no significant differences were observed with respect to MOD, muscle fibre type distribution, total LDH activity, its iso-enzyme pattern, changes in muscle lactate or CP concentrations. However, after treadmill runs, peak venous lactate concentration and partial pressures of carbon dioxide were higher, and pH lower in SMDR. Also the number of capillaries per muscle fibre and the maximal oxygen uptake were larger in SMDR. These findings would suggest that the superior performance of SMDR depended more on their aerobic than on their anaerobic capacity.

Adult↗