Muscle oxygenation during incremental arm and leg exercise in men and women

The purpose of this study was to compare the rates of muscle deoxygenation in the exercising muscles during incremental arm cranking and leg cycling exercise in healthy men and women. Fifteen men and 10 women completed arm cranking and leg cycling tests to exhaustion in separate sessions in a counterbalanced order. Cardiorespiratory measurements were monitored using an automated metabolic cart interfaced with an electrocardiogram. Tissue absorbency was recorded continuously at 760 nm and 850 nm during incremental exercise and 6 min of recovery, with a near infrared spectrometer interfaced with a computer. Muscle oxygenation was calculated from the tissue absorbency measurements at 30%, 45%, 60%, 75% and 90% of peak oxygen uptake (V˙O₂) during each exercise mode and is expressed as a percentage of the maximal range observed during exercise and recovery (%Mox). Exponential regression analysis indicated significant inverse relationships (P < 0.01) between %Mox and absolute V˙O₂ during arm cranking and leg cycling in men (multiple R = −0.96 and −0.99, respectively) and women (R =−0.94 and −0.99, respectively). No significant interaction was observed for the %Mox between the two exercise modes and between the two genders. The rate of muscle deoxygenation per litre of V˙O₂ was 31.1% and 26.4% during arm cranking and leg cycling, respectively, in men, and 26.3% and 37.4% respectively, in women. It was concluded that the rate of decline in %Mox for a given increase in V˙O₂ between 30% and 90% of the peak V˙O₂ was independent of exercise mode and gender. Accepted: 31 March 1998     

Muscle activation during maximal voluntary eccentric and concentric knee extension

The aim of this investigation was to study the relationships among movement velocity, torque output and electromyographic (EMG) activity of the knee extensor muscles under eccentric and concentric loading. Fourteen male subjects performed maximal voluntary eccentric and concentric constant-velocity knee extensions at 45, 90, 180 and 360 degrees.s-1. Myoelectric signals were recorded, using surface electrodes, from the vastus medialis, vastus lateralis and rectus femoris muscles. For comparison, torque and full-wave rectified EMG signals were amplitude-averaged through the central half (30 degrees-70 degrees) of the range of motion. For each test velocity, eccentric torque was greater than concentric torque (range of mean differences: 20%-146%, P less than 0.05). In contrast, EMG activity for all muscles was lower under eccentric loading than velocity-matched concentric loading (7%-31%, P less than 0.05). Neither torque output nor EMG activity for the three muscles changed across eccentric test velocities (P greater than 0.05). While concentric torque increased with decreasing velocity, EMG activity for all muscles decreased with decreasing velocity (P less than 0.05). These data suggest that under certain high-tension loading conditions (especially during eccentric muscle actions), the neural drive to the agonist muscles was reduced, despite maximal voluntary effort. This may protect the musculoskeletal system from an injury that could result if the muscle was to become fully activated under these conditions.     

Muscle and femoral vein temperatures during short-term maximal exercise in heart failure

Core temperature decreases throughout short-term maximal exercise in heart-failure patients. To investigate possible causes for this unusual response to exercise, we studied core (pulmonary arterial blood), femoral vein, muscle, and skin temperatures in eight patients with severe heart failure who performed maximal upright incremental bicycle exercise to 50 W. A normal group (n = 4) was exercised for comparison. In the heart-failure patients, core temperature was 36.95 +/- 0.37 degrees C at rest, significantly (P less than 0.05) decreased at 25 W of exercise to 36.59 +/- 0.40 degrees C, and at 50 W remained decreased to 36.57 +/- 0.40 degrees C. In comparison, we found that the resting core temperature in the normal subjects was 37.28 +/- 0.34 degrees C, was the same at 25 W (37.29 +/- 0.41 degrees C), and increased significantly (P less than 0.05) to 37.50 +/- 0.32 degrees C at 50 W of exercise. Femoral vein temperature in heart-failure patients (n = 6) was below core temperature throughout exercise to 25 and 50 W (36.22 +/- 0.62 and 36.34 +/- 0.65 degrees C, respectively). Muscle temperature (n = 7) was significantly (P less than 0.05) lower in the heart-failure patients (34.8 +/- 1.1 degrees C) at rest compared with the normal subjects (36.2 +/- 1.0 degrees C). During exercise, muscle temperature increased above core temperature in only four of the heart-failure patients and was significantly (P less than 0.05) lower (36.5 +/- 1.3 degrees C) compared with the normal subjects (38.0 +/- 0.2 degrees C).(ABSTRACT TRUNCATED AT 250 WORDS)     

Muscle power and metabolism in maximal intermittent exercise

Muscle power and the associated metabolic changes in muscle were investigated in eight male human subjects who performed four 30-s bouts of maximal isokinetic cycling at 100 rpm, with 4-min recovery intervals. In the first bout peak power and total work were (mean +/- SE) 1,626 +/- 102 W and 20.83 +/- 1.18 kJ, respectively; muscle glycogen decreased by 18.2 mmol/kg wet wt, lactate increased to 28.9 +/- 2.7 mmol/kg, and there were up to 10-fold increases in glycolytic intermediates. External power and work decreased by 20% in both the second and third exercise periods, but no further change occurred in the fourth bout. Muscle glycogen decreased by an additional 14.8 mmol/kg after the second exercise and thereafter remained constant. Muscle adenosine triphosphate (ATP) was reduced by 40% from resting after each exercise period; creatine phosphate (CP) decreased successively to less than 5% of resting; in the recovery periods ATP and CP increased to 76 and 95% of initial resting levels, respectively. Venous plasma glycerol increased linearly to 485% of resting; free fatty acids did not change. Changes in muscle glycogen, lactate, and glycolytic intermediates suggested rate limitation at phosphofructokinase during the first and second exercise periods, and phosphorylase in the third and fourth exercise periods. Despite minimal glycolytic flux in the third and fourth exercise periods, subjects generated 1,000 W peak power and sustained 400 W for 30 s, 60% of the values recorded in the first exercise period.(ABSTRACT TRUNCATED AT 250 WORDS)     

Muscle protein changes following eccentric exercise in humans

This study characterized changes in the protein composition of human muscle tissue after eccentric exercise. Four subjects performed 70 maximum eccentric, isokinetic actions of the forearm flexors with one arm. The other arm served as control. A biopsy of the biceps muscle of each arm was taken 2 days after exercise when muscles were very sore (mean = 8.0; 1 = normal; 10 = very, very sore), and muscle damage was documented by a mean decrease of 0.2 radians in the relaxed elbow angle. Proteins from the biopsy tissue were solubilized in a high ionic strength buffer containing several proteolytic inhibitors. Protein concentrations of the extracts were determined and identical amounts loaded onto sodium dodecyl sulfate (SDS) polyacrylamide gels (7.5, 12.5, and 17.5%). Densitometric analysis of the Coomassie brilliant blue stained gels revealed alterations in the amounts of three protein bands in the exercised tissue relative to the control. These changes were in the linear portion of the graph of absorbance versus protein amount. Wilcoxon's signed rank test showed the first two of the following bands to increase significantly in amount (P less than 0.062). The average percentage changes [mean (SEM)] for these bands were 63 (21), 39 (5), and 82 (35). The corresponding molecular weights determined from known standards were 76300 (860), 33200 (310), and 12000 (80) daltons, respectively. These changes imply that the increased synthesis, decreased degradation, or some combination thereof, of these three proteins may be necessary for the repair or regeneration response to exercise-induced muscle damage.     

The maximal exercise ECG in asymptomatic men

Lead MC5 bipolar exercise ECG was obtained in 510 asymptomatic males, aged 40 to 65, utilizing the bicycle ergometer, with maximal stress in 71% of the subjects. “Ischemic changes” occurred in 61 subjects, the frequency increasing from 4% at age 40 to 45, to 20% at age 50 to 55, to 37% at age 61 to 65. Subjects having an ischemic type ECG change on exercise had more frequent minor resting ECG changes, more resting hypertension, and a greater incidence of high cholesterol values than subjects with a normal ECG response to exercise, but there was no difference in the incidence of obesity, low fitness, or high systolic blood pressure after exercise. Current evidence suggests that asymptomatic male subjects with an abnormal exercise ECG develop clinical coronary heart disease from 2.5 to over 30 times more frequently than those with a normal exercise ECG.     

Muscle adenine nucleotide metabolism during and in recovery from maximal exercise in humans.

The relationship between changes in the muscle total adenine nucleotide pool (TAN = ATP + ADP + AMP) and IMP during and after 30 s of sprint cycling was examined. Skeletal muscle samples were obtained from the vastus lateralis muscle of seven untrained men (23. 9 +/- 2.3 yr, 74.4 +/- 3.6 kg, and 55.0 +/- 2.9 ml. kg(-1). min(-1) peak oxygen consumption) before and immediately after exercise and after 5 and 10 min of passive recovery. The exercise-induced increase in muscle IMP was linearly related to the decrease in muscle TAN (r = -0.97, P < 0.01), and the slope of this relationship (-0.83) was not different from 1.0 (P > 0.05), indicating a 1:1 stoichiometric relationship. This interpretation must be treated cautiously, because all subjects displayed a greater decrease in TAN compared with the increase in IMP content, and the TAN + IMP + inosine + hypoxanthine content was lower (P < 0.05) immediately after exercise compared with during rest. During the first 5 min of recovery, the increase in TAN was not correlated with the decrease in IMP (r = -0.18, P > 0.05). In all subjects, the magnitude of TAN increase was higher than the magnitude of IMP decrease over this recovery period. In contrast, the increase in TAN was correlated with the decrease in IMP throughout the second 5 min of recovery (r = -0.80, P < 0.05), and it was a 1:1 stoichiometric relationship (slope = -1.12). These data indicate that a small proportion of the TAN pool was temporarily lost from the muscle purine stores during sprinting but was rapidly recovered after exercise.     

Maximal eccentric and concentric strength discrepancies between young men and women for dynamic resistance exercise

Although research has demonstrated that isokinetic eccentric (ECC) strength is 20-60% greater than isokinetic concentric (CON) strength, few data exist comparing these strength differences in standard dynamic resistance exercises. The purpose of the study was to determine the difference in maximal dynamic ECC and CON strength for 6 different resistance exercises in young men and women. Ten healthy young men (mean +/- SE, 25.30 +/- 1.34 years), and 10 healthy young women (mean +/- SE, 23.40 +/- 1.37 years) who were regular exercisers with resistance training experience participated in the study. Two sessions were performed to determine CON and ECC 1 repetitions maximum for latissimus pull-down (LTP), leg press (LP), bench press (BP), leg extension (LE), seated military press (MP), and leg curl (LC) exercises. Maximal ECC and maximal CON strength were determined on weight stack machines modified to isolate ECC and CON contractions using steel bars and pulleys such that only 1 type of contraction was performed. Within 2 weeks, participants returned and completed a retest trial in a counterbalanced fashioned. Test-retest reliability was excellent (r = 0.99) for all resistance exercise trials. Men demonstrated 20-60% greater ECC than CON strength (LTP = 32%, LP = 44%, BP = 40%, LE = 35%, MP = 49%, LC = 27%). Women's strength exceeded the proposed parameters for greater ECC strength in 4 exercises, p < 0.05 (LP = 66%, BP = 146%, MP = 161%, LC = 82%). The ECC/CON assessment could help coaches capitalize on muscle strength differences in young men and women during training to aid in program design and injury prevention and to enhance strength development.     

Fuel metabolism in men and women during and after long-duration exercise

This study aimed to determine gender-baseddifferences in fuel metabolism in response to long-duration exercise.Fuel oxidation and the metabolic response to exercise were compared inmen (n = 14) and women(n = 13) during 2 h (40% of maximalO₂ uptake) of cycling and 2 h ofpostexercise recovery. In addition, subjects completed a separatecontrol day on which no exercise was performed. Fuel oxidation wasmeasured using indirect calorimetry, and blood samples were drawn forthe determination of circulating substrate and hormone levels. Duringexercise, women derived proportionally more of the total energyexpended from fat oxidation (50.9 ± 1.8 and 43.7 ± 2.1% forwomen and men, respectively, P < 0.02), whereas men derived proportionally more energy from carbohydrateoxidation (53.1 ± 2.1 and 45.7 ± 1.8% for men and women,respectively, P < 0.01). Thesegender-based differences were not observed before exercise, afterexercise, or on the control day. Epinephrine(P < 0.007) and norepinephrine(P < 0.0009) levels weresignificantly greater during exercise in men than in women (peakepinephrine concentrations: 208 ± 36 and 121 ± 15 pg/ml in menand women, respectively; peak norepinephrine concentrations: 924 ± 125 and 659 ± 68 pg/ml in men and women, respectively). Ascirculating glycerol levels were not different between the two groups,this suggests that women may be more sensitive to the lipolytic action of the catecholamines. In conclusion, these data support the view thatdifferent priorities are placed on lipid and carbohydrate oxidationduring exercise in men and women and that these gender-based differences extend to the catecholamine response to exercise.

     

Metabolic changes following eccentric exercise in trained and untrained men

The effects of one 45-min bout of high-intensity eccentric exercise (250 W) were studied in four male runners and five untrained men. Plasma creatine kinase (CK) activity in these runners was higher (P less than 0.001) than in the untrained men before exercise and peaked at 207 IU/ml 1 day after exercise, whereas in untrained men the maximum was 2,143 IU/ml 5 days after exercise. Plasma interleukin-1 (IL-1) in the trained men was also higher (P less than 0.001) than in the untrained men before exercise but did not significantly increase after exercise. In the untrained men, IL-1 was significantly elevated 3 h after exercise (P less than 0.001). In the untrained group only, 24-h urines were collected before and after exercise while the men consumed a meat-free diet. Urinary 3-methylhistidine/creatinine in the untrained group rose significantly from 127 mumol/g before exercise to 180 mumol/g 10 days after exercise. The results suggest that in untrained men eccentric exercise leads to a metabolic response indicative of delayed muscle damage. Regularly performed long distance running was associated with chronically elevated plasma IL-1 levels and serum CK activities without acute increases after an eccentric exercise bout.     

Leg free fatty acid kinetics during exercise in men and women

We previously reported that epinephrine stimulates leg free fatty acid (FFA) release in men but not in women. The present studies were conducted to determine whether the same is true during exercise. Six men and six women bicycled for 90 min at 45% of peak O(2) consumption, during which time systemic and leg FFA kinetics ([9, 10-(3)H]palmitate) were measured. The catecholamine and hormonal responses to exercise were not different in men and women. The baseline systemic and leg palmitate release was 94 +/- 15 vs. 114 +/- 5 micromol/min and 16 +/- 2 and 20 +/- 3 micromol/min, respectively, in men and women [P = nonsignificant (NS)]. Systemic and leg palmitate release increased (both P < 0.001) to 251 +/- 18 vs. 212 +/- 16 micromol/min and 73 +/- 19 vs. 80 +/- 12 micromol/min in men and women, respectively, during the last 30 min of exercise (P = NS, men vs. women). We conclude that the systemic and leg adipose tissue lipolytic response to exercise is not different in nonobese men and women.     

Energy metabolism and regulatory hormones in women and men during endurance exercise

Gender differences in the changes substrates of carbohydrate and lipid metabolism as well as in adrenaline, noradrenaline, growth hormone, insulin and cortisol were investigated in 24 women and 24 men during exhaustive endurance exercise. Training history and current performance capacity were taken into consideration in the design of the study. Since previous papers present conflicting results the purpose of the present study was to obtain further information regarding possible gender differences in lipid metabolism and its regulation by hormones. Non-endurance-trained women and men each ran 10 km on a treadmill at an intensity of 75% of VO2max; endurance-trained women and men ran 14 and 17 km, respectively, at an intensity of 80% of VO2max. Blood glucose levels in non-endurance-trained women were higher when compared to non-endurance-trained men. This might be explained by increased mobilization of free fatty acids from intramuscular fat depots during energy production in non-specifically trained women. In contrast, no substantial gender differences in endurance-trained persons were seen in lipid metabolism. The changes in substrates of lipid metabolism confirm the higher lipolytic activity and greater utilization of free fatty acids in endurance-trained persons. During endurance exercise, changes in adrenaline, noradrenaline, growth hormone, insulin and cortisol were not substantially affected by the sex of the subjects. This study does not present any conclusive results that endurance-trained persons show gender differences in lipid metabolism and major regulatory hormones.     

Enhanced protein breakdown after eccentric exercise in young and older men

The effects of eccentric exercise on whole body protein metabolism were compared in five young untrained [age 24 +/- 1 yr, maximal O2 uptake (VO2max) = 49 +/- 6 ml.kg-1.min-1] and five older untrained men (age 61 +/- 1 yr, VO2max = 34 +/- 2 ml.kg-1.min-1). They performed 45 min of eccentric exercise on a cycle ergometer at a power output equivalent to 80% VO2max (182 +/- 18 W). Beginning 5 days before exercise and continuing for at least 10 days after exercise, they consumed a eucaloric diet providing 1.5 g.kg-1.day-1 of protein. Leucine metabolism in the fed state was measured before, immediately after, and 10 days after exercise, with intravenous L-[1-13C]leucine as a tracer (0.115 mumol.kg-1.min-1). Leucine flux increased 9% immediately after exercise (P less than 0.011) and remained elevated 10 days later, with no effect of age. Leucine oxidation increased 19% immediately after exercise and remained 15% above baseline 10 days after exercise (P less than 0.0001), with no effect of age. In the young men, urinary excretion of 3-methylhistidine per gram of creatinine did not increase until 10 days postexercise (P less than 0.05), but in the older men, it increased 5 days after exercise and remained high through 10 days postexercise (P less than 0.05), averaging 37% higher than in the young men. These data suggest that eccentric exercise produces a similar increase in whole body protein breakdown in older and young men, but myofibrillar proteolysis may contribute more to whole body protein breakdown in the older group.     

Effects of eccentric exercise on the immune system in men

The effects of eccentric exercise on changes innumbers of circulating leukocytes, cell activation, cell adhesion, andcellular memory function were investigated in 12 men, aged 22-35yr. The immunologic effects of postexercise epidermal treatment withmonochromatic, infrared light were also evaluated. Blood was drawnbefore and 6, 24, and 48 h after exercise for phenotyping and analysisof creatine kinase activity. There was an increase in leukocyte, monocyte, and neutrophil number, no change in the number of basophils, eosinophils, B cells, and T cells, and a decrease in natural killer cell number postexercise. Some markers of lymphocyte and monocyte activation remained unchanged or decreased, whereas the expression ofadhesion molecules 62L and 11b increased on monocytes. It is concludedthat eccentric exercise induced decreased activation, and increasedcell adhesion capacity, of monocytes. Altered trafficking of cellsbetween lymphoid tissue and blood, selective apoptosis, orattachment/detachment from the endothelial wall can explain theobserved phenotypic changes. Treatment with monochromatic, infraredlight did not significantly affect any of the investigated variables.Correlations between immunologic and physiological parameters indicatea role of the immune system in adaptation to physical exercise.