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Biomedical subjects

I Jacobs

Publications and source records attributed to I Jacobs.

At least 145 records · Page 8Linked to original sources
PubMed1985

Relationship of ergometer-specific VO2 max and muscle enzymes to blood lactate during submaximal exercise.

This study compared the relationship of maximum oxygen uptake and skeletal muscle enzyme activities to the submaximal exercise intensity eliciting 4 mM blood lactate (OBLA). Twelve subjects performed both cycle (Cy) and treadmill (Tr) submaximal exercise with step-wise increments each fourth minute. Blood lactate concentration and oxygen uptake (VO2) were determined during the final minute of each step. Peak VO2 during exhaustive exercise was also measured on each ergometer. Biopsies were taken from the gastrocnemius (gast) and vastus lateralis (vl) muscles as representatives of muscles recruited during Tr and Cy exercise, respectively. Citrate synthase (CS), phosphofructokinase (PFK), and lactate dehydrogenase (LDH) activities were assayed. Peak VO2 was 10% greater and the VO2 at OBLA was 16% greater during Tr compared to Cy exercise. The percent of peak VO2 at OBLA was 85% and 79% for Tr and Cy exercise, respectively. The absolute enzyme activities were not different in the two muscles, however the ratio LDH/CS was greater in the vl than in the gast. The results indicate that the absolute differences between Cy and Tr exercise in peak VO2 are not commensurate with the differences in the relative exercise intensity at which OBLA occurs.

Biopsy↗
PubMed1984

Lipoproteins, lipoprotein lipase, and glycogen after prolonged physical activity.

The effect of strenuous exercise on lipoprotein level and composition as well as on lipoprotein lipase activity (LPLA) and glycogen stores in skeletal muscle was studied in 16 healthy young men after military field maneuvers. Body weight was reduced by 1 kg after the maneuvers and was gradually restored during a 5-day recovery phase. Glycogen levels were reduced by 50% and LPLA increased threefold immediately after the exercise, and neither were restored until 3-5 days of recovery. Serum triglycerides were decreased by about 50% after 1 day of recovery and the cholesterol concentration in high-density lipoproteins increased but only immediately after exercise. In contrast, the apolipoproteins A-I and A-II, the main protein constituents, were both decreased and remained so for 3-5 days. The results indicate that significant alterations of plasma lipoprotein level and composition as well as of muscle metabolism occur after prolonged physical exertion and that some changes are still evident after 5 days of recovery.

Adult↗
PubMed1984

Effects of endurance fitness on responses to cold water immersion.

The purpose of this study was to determine if the changes in selected blood hormones and substrates, metabolic rate, and rectal temperature (Tre) in nine males after immersion in 10 degrees C water, while clad in standard flight suits, were related to the level of aerobic fitness. Fitness was evaluated by the blood lactate response to submaximal exercise. Immersion time (IT) was defined as the time required for a 1 degrees C decrease in Tre and averaged 38.5 (range: 21-62) min. Metabolic rate increased 3.4 times the resting rate. Lactate, free fatty acids, triiodothyronine and thyroxine increased by 81%, 38%, 11%, and 8%, respectively, in contrast to insulin which decreased by 32%, with all changes being statistically significant (p less than 0.05). Glucagon increased slightly but not significantly (p = 0.11) while glucose levels did not change. The IT was correlated directly with a measure of aerobic fitness, with relative body fat, and with the T3 levels postimmersion (p less than 0.05). The results suggest that the aerobic fitness level can significantly influence the cooling rate during water immersion.

Adult↗
PubMed1984

Exaggerated systolic blood pressure response to exercise in a water polo team.

Twenty-three top-level water polo players (WP) were examined for blood pressure (BP) response to graded and continuous cycle ergometry. Testing also included resting muscle biopsy for fiber typing, exercise ECG recording for heart rate (HR), exercise concentrations of blood lactate (LA), measured VO2max, and ratings of perceived exertion (RPE). A control group (C), whose subjects were physically active in endurance sports, but were older and less fit than the experimental subjects, was tested by an identical protocol. The BP response to exercise was significantly higher in the WP group at all comparison criteria including onset of blood lactate accumulation, absolute HR, percent of HRmax, and power loads (including loadless pedaling). To date, we are unaware of other reports on whole groups of sportsmen showing an exaggerated BP response to exercise. While it would appear from previous studies that normotensive individuals showing such a response are at a greater risk of developing hypertension, the significance of this BP response in highly-trained athletes in a specific sport remains unclear.

Adolescent↗
PubMed1983

Semi-automatic blood lactate assay: experiences from an exercise laboratory.

A semi-automatic system based on flow injection analysis (FIA) for the transportation of small sample aliquots has been combined with fluorometric, enzymatic methods for blood lactate determination and has been described earlier. In the present study duplicate blood samples were obtained from exercising subjects to enable a comparison of lactate concentrations between neutralized and non-neutralized samples. Duplicate samples were also obtained to enable FIA lactate values to be compared to those obtained with a manual enzymatic method, and with a colorimetric method. No significant change was observed if the sample was not neutralized, enabling a more rapid sample turnover. The FIA method was reliable, with a coefficient of variation of 4.9% between duplicate blood samples. FIA lactate values were valid when compared to two other manual assays. FIA has been shown to be a rapid (60 samples x h-1) means of accurately determining blood lactate concentrations with 25 microliter blood samples and is of particular relevance to the exercise laboratory.

Automation↗
PubMed1983

Influence of lactate accumulation of EMG frequency spectrum during repeated concentric contractions.

One hundred and twenty consecutive maximal leg extensions at a constant angular velocity of 1.5 radians . s-1 were performed by nine physical education students. Integrated electromyographic (IEMG) activity and power spectrum density function (PSDF) of the EMG were recorded from m. vastus lateralis, vastus medialis and m. rectus femoris using bipolar surface electrodes. Muscle biopsies were obtained from m. vastus lateralis before and after exercise. Tissue samples were analyzed for muscle fiber type distribution and lactate and glycogen concentration. Muscle force and IEMG decreased in parallel over the exercise period. Thus, the IEMG/force ratio was unchanged. Mean power frequency (MPF) of PSDF of the three nucleus decreased by 10% (p less than 0.001) during the initial 25 contractions with no further decline during the latter part of exercise. The relative contribution of the highest bandwidth (130-500 Hz) of the PSDF decreased (p less than 0.001) between the first and final contractions. Muscle glycogen concentration decreased from 85 +/- 23 to 68 +/- 22 mmol . kg-1 w.w. during the exercise. Muscle and blood lactate concentration averaged 12.1 +/- 8.8 mmol . kg-1 w.w. and 3.8 +/- 0.8 mmol . l-1, respectively. The relative changes in MPF and in the highest bandwidth were correlated with muscle lactate concentration and fiber type distribution: in individuals with a high proportion of fast twitch muscle fibres and/or the greatest lactate accumulation, MPF and high frequency components of EMG PSDF decreased most markedly. Reductions in muscle force and IEMG are suggested to be partly due to a decreased motor neuron firing rate. It is discussed whether lactate or associated metabolic changes are influencing the motor unit action potential through feedback processes.

Action Potentials↗
PubMed1983

Lactate in human skeletal muscle after 10 and 30 s of supramaximal exercise.

The purpose of this study was to evaluate the extent of anaerobic glycogenolysis, as indicated by intramuscular lactate concentration, after 10 and 30 s of supramaximal exercise and to compare male and female subjects in this regard. Fifteen males and seven females performed two cycle exercise bouts against a resistance which was standardized so that one pedal revolution resulted in 4.90 J work X kg body wt-1. A muscle biopsy was obtained after 10- and 30-s exercise bouts and analyzed for lactate concentration. The lactate concentrations averaged 36 and 61 mmol X kg dry wt-1 after the 10- and 30-s exercise bouts, respectively. The male subjects had higher (P less than 0.005) lactate concentrations and generated higher (P less than 0.001) power outputs for both exercise bouts. When the mean lactate concentrations were statistically adjusted after controlling for between-group variation in power output, no difference was evident between groups for the 10- or the 30-s lactate value. The results are evidence that pronounced lactate accumulation occurs during supramaximal exercise of a 10-s duration, suggesting that glycolysis can occur within this time frame. This is in contrast to the theory that glycolysis does not occur until endogenous phosphagen levels reach some critically low value, not thought to be obtainable within the first 10 s of supramaximal exercise.

Female↗
PubMed1983

Muscle glycogen in soldiers on different diets during military field manoeuvres.

Severe skeletal muscle glycogen depletion has been previously reported for soldiers participating in field exercises. The purpose of the present study was to determine if the distribution of amplified food rations would reduce the extent of glycogen depletion during military field manoeuvres. Needle biopsy samples were obtained from the m. vastus lateralis of soldiers both before and immediately after their participation in 4.5 d of field exercises. Eight soldiers received normal rations while a second group of eight soldiers received rations which were amplified in both caloric value and the proportion of carbohydrates. Intramuscular glycogen concentrations before and after the manoeuvres averaged 120 and 55 mmol glucose units . kg-1, respectively. The group which received amplified rations did not exhibit glycogen levels significantly different from those using normal rations.

Adult↗
PubMed1983

A category-ratio perceived exertion scale: relationship to blood and muscle lactates and heart rate.

The purpose of this investigation was to study the relationship between perceptual ratings from Borg's new category-ratio scale and some physiological variables during exercise. To accomplish this, scale ratings were related to blood and muscle lactate accumulation and heart rates during a progressive, maximal exercise test on the cycle ergometer. Ten physically active males were utilized as subjects; lactate data were recorded on only 7 of the 10 subjects. Three ratings of perceived exertion were made at each stage of the exercise test: leg effort (LE), cardiorespiratory effort (CE), and leg pain (LP). All ratings showed a positively accelerating increase with exercise intensity as did both blood and muscle lactate, while heart rate increased linearly. The exponents of the power functions describing the perceptual variation ranged from 1.63-1.67 compared to 2.2 for blood lactate and 2.7 for muscle lactate. Polynomial analysis revealed a similar quadratic trend for both perceptual and blood lactate data; however, muscle lactate demonstrated a cubic trend. No significant differences were found between CE and LE at 100, 200, and 300 W (P greater than 0.05). Subjects with the highest percentage of slow-twitch muscle fibers (mean ST%=51.14) rated LE and CE significantly lower ( mean of all power outputs, 0-300 W) than those with the lowest ST% (mean=34.52). It is concluded that the ratings from the category-ratio scale correspond very well with glycogenolytic metabolism leading to lactate accumulation during exercise.

Adolescent↗
PubMed1982

Changes in onset of blood lactate accumulation (OBLA) and muscle enzymes after training at OBLA.

Eight well-trained middle and long distance male runners added to their regular training program a weekly 20-min treadmill run at a velocity calculated to elicit a blood lactate concentration of 4 mmol X 1-1. VO2 max, the running velocity eliciting 4 mmol X 1-1 blood lactate (VOBLA), and the activities of citrate synthase (CS), phosphofructokinase (PFK), lactate dehydrogenase (LDH) and LDH isozymes in the M. vastus lateralis were determined before and after 14 weeks of this training. Significant increases were observed in VOBLA and the relative fraction of heart-specific LDH, while the activity of PFK and the ratio of PFK/CS decreased after training. The change in VOBLA was negatively correlated to the mean rate of blood lactate accumulation during the last 15 min of the treadmill training runs, and positively correlated to the percentage of slow twitch fibers in the M. vastus lateralis. The data support the hypothesis that a steady state training intensity which approximates VOBLA will increase VOBLA, and will result in measureable local metabolic adaptations in the active skeletal muscles of well-trained runners without a significant change in maximal aerobic power. Muscle fiber type composition may be an indicator of the "trainability" of the musculature.

Adolescent↗
PubMed1982

Muscle glycogen and diet in elite soccer players.

The top players in an elite soccer team volunteered as subjects in a study to determine intramuscular glycogen concentrations after a regular season match, and whether optimal glycogen levels could be re-attained prior to the team's next match. Fifteen players were biopsied in the M. vastus lateralis following a regular season game (Day I). Of these, eight were biopsied 24 h later in the evening of a free day during which no training session was held (Day II), and again 24 h later after a very light training session (Day III). Muscle glycogen concentrations for the eight players averaged (+/- SD) 45.9 +/- 7.9, 68.9 +/- 2.7, and 72.8 +/- 8.3 mmol glucose units x kg-1 wet muscle weight on Day I, Day II, and Day III respectively. Dietary records were analysed during a week of peak, season competition and training. The average daily total energy consumption and total quantity of carbohydrates consumed were less than what is normally consumed by athletes in similar sports. The inability of the players to maintain even normal, resting levels of muscle glycogen is probably related to their dietary practices.

Adult↗
PubMed1982

Decrease of lipoprotein lipase activity in skeletal muscle in man during a short-term carbohydrate-rich dietary regime. With special reference to HDL-cholesterol, apolipoprotein and insulin concentrations.

Seven men took part in a study in which the diet was changed from an ordinary mixed one to a fat-rich diet [greater than 70% energy (E)] for 3 days followed by a carbohydrate-rich diet (greater than 70% E) for 3 days. Blood was drawn and muscle biopsies [for analysis of lipoprotein-lipase (LPL) activity] were taken before the study and at the end of each diet period. Insulin, apolipoprotein (apo) B, A-I and A-II, cholesterol and triglyceride concentrations were determined in serum and the lipids also in the high density lipoproteins (HDL). Serum insulin was higher (p less than 0.01) during the carbohydrate-rich diet than during the fat-rich diet (12.0 +/- 0.9 vs. 7.5 +/- 0.5 microunits/l, mean +/- SEM), as were serum-triglycerides (2.42 +/- 0.27 vs. 0.98 +/- 0.07 mmole/1, p less than 0.001). Muscle LPL activity, on the other hand, was lower (p less than 0.01), 27.3 +/- 6.1 vs. 75.1 +/- 13.2 microunits/g. HDL-cholesterol was 1.22 +/- 0.08 during the carbohydrate-rich diet which was lower (p less than 0.01) than during the fat-rich diet, 1.45 +/- 0.11. The concentration of apo A-I and A-II did not vary significantly. It is suggested that the increased insulin concentrations during a short-term, carbohydrate-rich diet may have a down-regulating effect on muscle LPL activity. Low muscle LPL activity may account for part of the elevation of serum triglycerides. An ineffective hydrolysis of VLDL-triglycerides may contribute to the variation in HDL-cholesterol concentration seen under these circumstances.

Adolescent↗
PubMed1982

Lactate in blood, mixed skeletal muscle, and FT or ST fibres during cycle exercise in man.

The relationship between muscle and blood lactate levels during progressively step-wise incrementing cycle exercise has been investigated in 10 male subjects. Steps between power outputs during exercise were 50 W and each stage, from loadless pedalling until voluntary exhaustion, lasted 4 min. Blood samples and biopsies (m. vastus lateralis) were taken for lactate determination at each power output beginning with the exercise intensity perceived by the subject as being "rather moderate". The ratio muscle:blood lactate was greater than one at all power outputs and increased most markedly at the power output closest to that eliciting 4 mmol x 1(-1) blood lactate (WOBLA). At WOBLA, blood lactate was positively correlated to muscle lactate concentrations which covaried widely among subjects (mean 8.3, range 4.5-14.4 mmol x kg-1 wet weight). Muscles fibres from the WOBLA biopsy in 6 subjects were dissected out and identified as fast twitch (FT) or slow twitch (ST). No significant difference in lactate concentration was observed between pools of FT or ST fibres.

Adolescent↗
PubMed1982

Dietary effects on glycogen and lipoprotein lipase activity in skeletal muscle in man.

The influence of short-term adaptation to a fat and protein enriched diet (F + P) and a carbohydrate enriched diet (CHO) on skeletal muscle lipoprotein lipase (LPL) activity and muscle glycogen levels was evaluated in 7 males. Muscle biopsies were taken from the m. vastus lateralis after an uncontrolled, mixed diet (M), after a 3 day F + P) diet preceded by intense exercise, and after a 3 day CHO diet. After the F + P diet glycogen concentration was 55% that of the M diet while LPL activity increased by 21% (n.s.). After the CHO diet glycogen levels increased by 82% and LPL activity decreased by 55% compared to the M diet (p less than 0.01). The changes in LPL after the CHO diet were related to the changes in glycogen concentration (r = 0.98, p less than 0.01). LPL activity in the control situation was directly related to percent slow twitch (ST) muscle fibre type (r = 0.95, p less than 0.01). The results suggest that the uptake of fat from the circulation may be actively regulated by the muscle as a function of intramuscular substrate availability and that this regulation may be related to muscle fibre type composition.

Adolescent↗
PubMed1982

Changes in muscle metabolites in females with 30-s exhaustive exercise.

The purpose of this study was to quantify the changes in selected intramuscular metabolites associated with non-oxidative energy metabolism after performance of the Wingate Test (WT), a widely used, exhaustive, 30-s cycle test of short-time muscular power. Muscle biopsies were taken from the m. vastus lateralis of nine female physical education students at rest and immediately after performance of the WT. The concentrations of adenosine triphosphate (ATP), creatine phosphate (CP), lactate, and glycogen were determined. The ATP decreased from 20.9 to 13.8; CP decreased from 62.7 to 25.1; lactate increased from 9.0 to 60.5; and glycogen decreased from 360 to 278 (all concentrations are mmol X kg-1 dry muscle). The absolute changes in CP and lactate were not as large as those reported in other exercise studies. Based on the metabolite changes, it was concluded that the WT is a satisfactory test of the maximal muscular power that can be generated from non-oxidative metabolism, but that the 30-s duration of the test probably does not tax the maximal capacity of such energy metabolism.

Adenosine Triphosphate↗
PubMed1981

Relevance of muscle fibre type to fatigue in short intense and prolonged exercise in man.

It has been suggested that the histological and histochemical features of human muscle are important in determining performance capacity. The relationship between muscle fibre types (Type I, slow twitch fibres; Type II, fast twitch fibres) and performance on standardized tests has been studied in subjects accustomed to physical exercise, and related to their patterns of lactate metabolism, expressed as the onset of blood lactate accumulation (OBLA). This variable was found to be the best predictor of endurance capacity of the variables studied. It is suggested that in healthy male subjects muscle lactate is crucial in short, intense forms of exercise (the higher the lactate formation, the better the performance) and also in prolonged, "endurance' forms of exercise (the later the onset of lactate formation, the higher the sustainable exercise intensity). In subjects with a high proportion of fast twitch fibres, more lactate will be formed at the same exercise intensity. This is advantageous for short intense exercise but impairs endurance performance. The deleterious effects induced by glycogen depletion were studied and found to be most pronounced in subjects rich in fast twitch (glycogen-dependent) fibres. Indications were also obtained that muscular performance is regulated in different ways in males and females. In women an inverse relationship was found between fast twitch fibres and muscle power, and between fatigue and lactate concentration, whereas direct relations were found in men.

Biopsy↗