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Biomedical subjects

H G Knuttgen

Publications and source records attributed to H G Knuttgen.

At least 19 recordsLinked to original sources
PubMed2000

Effect of acute postexercise ethanol intoxication on the neuroendocrine response to resistance exercise.

This investigation was conducted to determine the effect of postexercise ethanol intoxication (21.97 +/- 1.09 mmol/l blood) on the response of selected aspects of the neuroendocrine system to a resistance exercise (Ex) session. Nine resistance-trained men (25.0 +/- 1.4 yr, 179.4 +/- 3.4 cm, 79.7 +/- 3.3 kg) were used to compare three 3-day treatments: control, Ex, and ethanol after exercise (ExEt). Blood was collected serially from an antecubital vein before exercise, immediately after exercise, and for pooled analysis at 20-40 (2 samples), 60-120 (4 samples), and 140-300 (9 samples) min after exercise on day 1 and in the morning (2 samples each) on days 2 and 3. Ethanol did not increase circulating epinephrine, norepinephrine, or cortisol concentration (Cort) above Ex elevations. At 60-120 min, only ExEt Cort was greater than control Cort. Concentrations of testosterone, luteinizing hormone, and corticotropin were not affected by either treatment. It is concluded that, although this blood ethanol concentration is insufficient to acutely increase Cort above that caused by Ex alone, it appears that ethanol may have a prolonged effect beyond the Ex response. This blood ethanol concentration does not further stimulate the sympathoadrenal system during the postexercise response.

Adrenocorticotropic Hormone↗
PubMed1999

Exercise and recovery responses of adrenal medullary neurohormones to heavy resistance exercise.

PURPOSE: The purpose of this study was to examine the effect of dynamic resistance exercise on the response patterns of adrenal medullary neurohormones in strength-trained men. METHODS: Ten strength-trained men (21.7+/-0.58 yr) gave informed consent and performed two resistance exercise protocols, high force and high power, of equal total work in a randomized order separated by 1 wk. Blood samples were obtained pre-exercise (baseline), 0 (R-0), 15 (R-15), and 240 (R-240) min postexercise and under resting control conditions for each time point. RESULTS: There were no significant differences in control concentrations for each time point and no difference in pre-exercise values between the two resistance exercise protocols for plasma lactate, epinephrine, plasma peptide F (P-F), or norepinephrine (NE). Plasma lactate significantly (P< or = 0.05) increased from baseline for both protocols; however, concentrations were higher in response to the high force protocol. Plasma epinephrine was significantly increased from baseline at R-0 and returned to baseline at R-15 for both protocols. In contrast, plasma P-F was significantly decreased at R-0 from baseline; however, at R-240 P-F had significantly increased to >80% baseline for both protocols. CONCLUSIONS: These results indicate that the adrenal medulla was activated in response to the acute stress of both types of heavy resistance exercise. Furthermore, during longer recovery periods, the adrenal medulla was also active above baseline conditions as increased concentrations of proenkephalin fragments (i.e., P-F) were detected in the circulation.

Adrenal Medulla↗
PubMed1994

Effect of acid-base balance on the growth hormone response to acute high-intensity cycle exercise.

To investigate the effect of acid-base balance on serum human growth hormone (hGH) concentration after an acute high-intensity anaerobic exercise bout, 10 untrained but normally active men [age, 24.6 +/- 1.5 (SE) yr] participated in a randomized double-blind counterbalanced experiment. Each subject reported in a fasted state at the same time of day for two experimental sessions separated by 1 wk. For each session, subjects were administered a decaffeinated tea solution containing either 0.3 g NaHCO3/kg body wt [alkalosis (ALK)] or 0.04 g NaCl/kg body wt [control (CTRL)] over a 45-min ingestion period. Venous blood samples were obtained before [baseline (BL)] and 75 min after the ingestion period, as well as postexercise at 0, 5, 10, 15, 20, and 30 min. The exercise task immediately followed the preexercise blood draw and consisted of 90 s of maximal-effort cycle ergometry against an opposing force of 0.49 N (0.05 kg)/kg body wt. There were no differences between the ALK and CTRL conditions in mean or peak power output or total work during the exercise task. Whole blood pH was significantly (P < or = 0.05) elevated in ALK above CTRL at all time points except BL. Postexercise serum hGH concentration significantly increased above BL at 10, 15, 20, and 30 min in CTRL and at 20 and 30 min in ALK. The hGH concentration was significantly lower in ALK than in CTRL at 15, 20, and 30 min postexercise. These data indicate that an increase in blood hydrogen ion concentration may be partly responsible for the hGH response to acute high-intensity anaerobic exercise.

Acid-Base Equilibrium↗
PubMed1994

Performance decrements with high-intensity resistance exercise overtraining.

The purpose of this investigation was to study a high-intensity resistance exercise overtraining protocol resulting in muscular strength decrements. Seventeen weight-trained males were divided into an overtraining group (OT; N = 11; mean +/- SE, age = 22.0 +/- 0.9 yr,) that exercised on a squat machine daily for 2 wk with 100% of 1 repetition maximum (RM) relative intensity, and a control group (CON; N = 6; age = 23.7 +/- 2.4 yr) that exercised 1 d.wk-1 with low intensity (50% 1 RM). Test batteries were conducted at the beginning (test 1), after 1 wk (test 2), and after 2 wk (test 3) of the study. One RM performance significantly decreased from test 1 to test 3 (P < 0.05) for the OT group (mean = -12.2 +/- 3.8 kg), but not the CON group (mean = -1.1 +/- 0.8 kg). Isokinetic and stimulated isometric muscle force significantly decreased for the OT group compared with the CON group by test 3. The primary site of maladaptation appeared to be in the periphery as indicated by changes in stimulated force, circulating CK activity, and exercise-induced lactate responses. This protocol produced a significant decrease in 1 RM performance, thus providing a model for the study of short-term, high-intensity resistance exercise overtraining.

Adaptation, Physiological↗
PubMed1991

Effects of high-intensity cycle exercise on sympathoadrenal-medullary response patterns.

Plasma proenkephalin peptide F immunoreactivity and catecholamines were examined on separate days in nine healthy males before and after maximal exercise to exhaustion at four intensities [36, 55, 73, and 100% of maximal leg power (MLP)] by use of a computerized cycle ergometer. The mean duration of 36, 55, 73, and 100% MLP was 3.31, 0.781, 0.270, and 0.1 min, respectively. All intensities were greater than those eliciting peak O2 uptake for the individual subjects. Blood samples were obtained before, immediately after exercise, and 5 and 15 min after exercise. Significant (P less than 0.05) increases in plasma peptide F immunoreactivity (i.e., from mean resting value of 0.18 to 0.43 pmol/ml) were observed immediately after exercise at 36% MLP. Significant increases in plasma epinephrine were observed immediately after exercise at 36% MLP (i.e., from mean resting value of 2.22 to 3.11 pmol/ml) and 55% MLP (i.e., from mean resting value of 1.67 to 2.98 pmol/ml) and 15 min after exercise at 100% MLP (i.e., from mean resting value of 1.92 to 3.88 pmol/ml). Significant increases for plasma norepinephrine were observed immediately after exercise (36, 55, 73, and 100% MLP), 5 min after exercise (36, 55, and 73% MLP), and 15 min after exercise (36% MLP). Increases in whole blood lactate were observed at all points after exercise for 36, 55, and 73% MLP and 5 min after exercise for 100% MLP. These data show that brief high-intensity exercise results in differential response patterns of catecholamines and proenkephalin peptide F immunoreactivity.

Adrenal Medulla↗
PubMed1990

Factors in maximal power production and in exercise endurance relative to maximal power.

The relationship of muscle fiber type and mass to maximal power production and the maintenance of power (endurance time to exhaustion) at 36%, 55%, and 73% of maximal power was investigated in 18 untrained but physically active men. Power output was determined at constant pedalling rate (60 rev.min-1) on a cycle ergometer instrumented with force transducers and interfaced with a computer. Maximal power was determined for each subject as the highest one-revolution average power. Fat-free mass was determined by hydrostatic weighing, fat-free thigh volume by water displacement and skinfold measurement, and percentage and area of type II fibers from biopsy specimens taken from the vastus lateralis. Maximal power averaged 771 +/- 149 W with a range of 527-1125 W. No significant correlations were found among percentage of type II fibers, relative area of type II fibers, or fat-free thigh volume and maximal power or endurance times to exhaustion at any percentage of maximal power. Weak but significant relationships were found for fat-free mass with both maximal power (r = 0.57) and endurance time at 73% of maximal power (r = -0.47). These results show maximal power to be more dependent on factors related to body size than muscle-fiber characteristics. The low correlations for so many of the relationships, however, suggest that individuals employ either different combinations of these factors or utilize other strategies for the generation of high power.

Ergonomics↗
PubMed1989

Hypothalamic-pituitary-adrenal responses to short-duration high-intensity cycle exercise.

beta-Endorphin (beta-EP), adrenocorticotropin (ACTH), and cortisol plasma concentrations were examined before and after maximal exercise at four intensities [36, 55, 73, and 100% of maximal leg power (MLP)] by means of a computerized cycle ergometer. All intensities were greater than those eliciting peak O2 uptake for the individual subjects. Blood samples were collected at rest, immediately after exercise, and at 5 and 15 min postexercise. Significant (P less than 0.05) increases were observed at 36% MLP for beta-EP and ACTH immediately after exercise and at 5 and 15 min postexercise. Plasma cortisol increased at 36% MLP at 15 min postexercise. Blood lactate significantly increased at all postexercise collection points for exercise intensities of 36, 55, and 73% MLP and at 5 min postexercise for 100% MLP. beta-EP concentrations at 36% MLP were significantly correlated (r = 0.75) with capillary density (mm-2), and cortisol concentrations at 36% MLP were significantly correlated (r = 0.89) with percentage of type II muscle fibers. No other significant relationships were observed. These data show that brief, high-intensity exercise up to maximal power production results in a nonlinear response pattern in peripheral blood hormone concentrations. Furthermore, blood lactate levels do not appear to be related to hypothalamic-pituitary-adrenal hormone plasma concentrations at high exercise intensities.

Adrenocorticotropic Hormone↗
PubMed1988

Strength conditioning in older men: skeletal muscle hypertrophy and improved function.

The effects of strength conditioning on skeletal muscle function and mass were determined in older men. Twelve healthy untrained volunteers (age range 60-72 yr) participated in a 12-wk strength training program (8 repetitions/set; 3 sets/day; 3 days/wk) at 80% of the one repetition maximum (1 RM) for extensors and flexors of both knee joints. They were evaluated before the program and after 6 and 12 wk of training. Weekly measurements of 1 RM showed a progressive increase in strength in extensors and flexors. By 12 wk extensor and flexor strength had increased 107.4 (P less than 0.0001) and 226.7% (P less than 0.0001), respectively. Isokinetic peak torque of extensors and flexors measured on a Cybex II dynamometer increased 10.0 and 18.5% (P less than 0.05) at 60 degrees/s and 16.7 and 14.7% (P less than 0.05) at 240 degrees/s. The torque-velocity relationship showed an upward displacement of the curve at the end of training, mainly in the slow-velocity high-torque region. Midthigh composition from computerized tomographic scans showed an increase (P less than 0.01) in total thigh area (4.8%), total muscle area (11.4%), and quadriceps area (9.3%). Biopsies of the vastus lateralis muscle revealed similar increases (P less than 0.001) in type I fiber area (33.5%) and type II fiber area (27.6%). Daily excretion of urinary 3-methyl-L-histidine increased with training (P less than 0.05) by an average 40.8%. Strength gains in older men were associated with significant muscle hypertrophy and an increase in myofibrillar protein turnover.

Aged↗
PubMed1987

Automated data collection and processing for a cycle ergometer.

A system is described for collection and processing of data from a cycle ergometer. Cycle pedals, specially made to withstand the extremely high forces exerted during maximal power cycling, contain transducers to measure pedal angle relative to the crank and foot forces both perpendicular and parallel to the pedal surface. An additional transducer monitors crank position. Output signals are conditioned, amplified, digitized by a 12-bit analog-to-digital converter, fed into a computer at 100 Hz/channel, and mathematically smoothed to attenuate noise. For each sample interval, foot force components perpendicular and parallel to the crank arm are calculated. Power generated on each crank revolution is determined from transducer information. Computer graphics display pedaling parameters vs. crank angle in both rectangular and circular format. Data files containing variables descriptive of pedaling force curves are produced to enable computerized statistical analysis of cycling performance.

Computer Graphics↗
PubMed1987

Exercise endurance time as a function of percent maximal power production.

To develop and validate a mathematical model of the relationship between endurance time (T) and power production, 15 male subjects were first tested for maximal power on an instrumented cycle ergometer at 60 rpm. On subsequent days, they were tested for T at various percentages of maximal power. Curves of T as a function of percent maximal power were curvilinear, and could be made to overlap among subjects by individual abscissa scaling, which resulted in the appearance of horizontal stretching or compression of the curves. The degree of stretching-compression was defined by a statistically obtained scaling factor (F) which served to quantify each subject's endurance ability at fractions of maximal power. F was used to transform percent of maximal power to a scaled power variable (Psc). A curve of the form T = a(Psc)b was developed on 10 of the subjects and validated on the remaining five. Correlation between predicted and actual T was 0.967 for the fitting group and 0.980 for the validation group. A maximal power test and a single endurance test at 40 to 50% of maximal power were found to establish individual endurance-power curves fairly well, with a correlation of 0.828 between actual and predicted T. The combination of F and maximal power for a given physical activity provide a useful profile of an individual's ability to perform at constant exercise intensity.

Adult↗
PubMed1986

Metabolic and ventilatory responses to steady state exercise relative to lactate thresholds.

The metabolic and ventilatory responses to steady state submaximal exercise on the cycle ergometer were compared at four intensities in 8 healthy subjects. The trials were performed so that, after a 10 min adaptation period, power output was adjusted to maintain steady state VO2 for 30 min at values equivalent to: (1) the aerobic threshold (AeT); (2) between the aerobic and the anaerobic threshold (AeTAnT); (3) the anaerobic threshold (AnT); and (4) between the anaerobic threshold and VO2max (AnTmax). Blood lactate concentration and ventilatory equivalents for O2 and CO2 demonstrated steady state values during the last 20 min of exercise at the AeT, AeAnT and AnT intensities, but increased progressively until fatigue in the AnTmax trial (mean time = 16 min). Serum glycerol levels were significantly higher at 40 min of exercise on the AeAnT and the AnT when compared to AeT, while the respiratory exchange ratios were not significantly different from each other. Thus, metabolic and ventilatory steady state can be maintained during prolonged exercise at intensities up to and including the AnT, and fat continues to be a major fuel source when exercise intensities are increased from the AeT to the AnT in steady state conditions. The blood lactate response to exercise suggests that, for the organism as a whole, anaerobic glycolysis plays a minor role in the energy release system at exercise intensities upt to and including the AnT during steady state conditions.

Adult↗
PubMed1986

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.

Creatine Kinase↗
PubMed1985

Heart rate break point may coincide with the anaerobic and not the aerobic threshold.

Recently, Conconi et al. (4) proposed that the point where heart rate departs from linearity in an incremental exercise test is a good predictor of the aerobic threshold (AeT, i.e., the exercise intensity at which blood lactate concentration increases systematically above resting levels). We hypothesized that this heart rate break point (BrP) is a better predictor of the anaerobic threshold (AnT, i.e., the exercise intensity at which blood lactate concentration shows a rapid rise during an incremental test). To test this hypothesis, 11 subjects with different levels of conditioning were tested on a cycle ergometer using a progressive incremental exercise protocol. Heart rate from EKG tracings and blood samples for lactate determination were taken every minute. The results showed the following significant correlation coefficients when the variables were expressed in watts: AeT and AnT = 0.92; AeT and BrP = 0.89; AnT and BrP = 0.97. The AeT was significantly lower than the BrP (166.4 +/- 52.6 W and 234.5 +/- 69.5 W). There was no significant difference between the AnT and BrP (240.0 +/- 67.1 W and 234.5 +/- 69.5 W). Another group consisting of 16 subjects performed two tests to evaluate the reproducibility of the BrP. Although a ventilatory AnT (defined as a consistent decrease in the fraction of expired CO2) was noted in all the tests, eight subjects failed to demonstrate a BrP in at least one of the evaluations, even though post-exercise blood lactate levels and peak heart rates were consistent with a maximal effort.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1982

Effects of training with eccentric muscle contractions on exercise performance, energy expenditure, and body temperature.

To study the effects of exercise training with eccentric muscle contractions on body temperatures, energy cost, and performance capacity, six human subjects were tested before and after a 5-week training program of eccentric exercise. Exercise was performed as leg cycling on a motor-driven ergometer at power levels ranging 252-316 W. Training consisted of three sessions/week for 1 h/session. As a result of the training, VO2, fH, and mean skin temperature were lowered for each subject at the same absolute exercise intensities. Ability to continue exercise as indicated by endurance time improved with training. Before training, four subjects terminated exercise after 30 min because of localized leg exhaustion and one subject could not continue longer than 45 min. After training, all six subjects completed 45 min of the exercise test without difficulty. Esophageal and muscle temperatures evidenced no changes as a result of training. It was concluded that the inability of subjects to perform eccentric exercise in the untrained state was not related to muscle temperature.

Adult↗
PubMed1981

Performance and muscle metabolite changes in exercise with repeated maximal dynamic contractions.

Maximal voluntary contractions (MVC) were performed by five male subjects as repeated knee extensions separated by 13-s rest periods for the purposes of studying performance capability, physiologic responses, and recruitment patterns among fast-twitch (FT) and slow-twitch (ST) extrafusal muscle fibers for this type of exercise. Exercise was performed on an isokinetic ergometer (Cybex II) as 4 MVC per min for 1 h, each contraction lasting 2 s and resulting in knee extension at a velocity of 18 degrees x s-1 from 90 forward to 57. Biopsies were taken from the m. vastus lateralis before, at the midpoint, and at the end of the 60-min period of exercise and analyzed for ATP, CP, lactate, and glycogen. Fiber type was determined by staining sections for myofibrillar ATPase and fiber glycogen content by PAS stain. Ability to produce force (torque) declined form an average of 250 Nm during the first minute to 200 Nm during the last minute of exercise. Oxygen uptake and heart rate were relatively constant for each subject and averaged 0.94 l x min-1 and 110 beat x min-1 throughout exercise. Muscle values in mmol x kg-1 at rest, at midpoint, and at end of exercise were for ATP 5.3, 5.4, and 4.1; for CP 19.4, 15.7, and 12.1; and for lactate 1.7, 3.9, and 4.5, respectively. It was estimated that approximately one third of the energy requirement for exercise was obtained from the endogenous muscle glycogen. Glycogen depletion patterns indicated the involvement of both FT and ST fibers in this type of exercise.

Adenosine Triphosphate↗