Biomedical subjects

Robert R Kraemer

Publications and source records attributed to Robert R Kraemer.

12 recordsLinked to original sources

PubMed2006

Comparison of hormone responses following light resistance exercise with partial vascular occlusion and moderately difficult resistance exercise without occlusion.

Previous studies of contracting muscle with low loading and partial vascular occlusion demonstrated hypertrophy and strength adaptations similar to and exceeding those observed with traditional moderate to high resistance (Shinohara M, Kouzaki M, Yoshihisa T, and Fukunaga T. Eur J Physiol 77: 189-191, 1998; Takarada Y, Takazawa H, Sato Y, Takebayashi S, Tanaka Y, and Ishii N. J Appl Physiol 88: 2097-2106, 2000; Takarada Y, Sato Y, and Ishii N. Eur J Physiol 86: 308-314, 2002). The purpose of the study was to determine the anabolic and catabolic hormone responses to light resistance exercise combined with partial vascular occlusion. Three experimental conditions of light resistance with partial occlusion (LRO), moderate resistance with no occlusion (MR), and partial occlusion without exercise (OO) were performed by eight healthy subjects [mean 21 yr (SD 1.8)]. Three sets of single-arm biceps curls and single-leg calf presses were completed to failure with 1-min interset rest periods. Workloads of 30 and 70% one repetition maximum for each exercise were lifted for the LRO and MR trials, respectively. Blood samples were taken preexercise, postexercise, and 15 min postexercise for each experimental condition. Lactate increased significantly in the LRO and MR trials and was not significantly different from each other at any time point. Growth hormone (GH) increased significantly by fourfold from pre- to postexercise in the LRO session but did not change significantly during this time period in the MR and OO trials (8.3 +/- 2.3 vs. 2.1 +/- 1.2 and 2.6 +/- 0.94 microg/l; respectively, P < 0.05). There were no changes in resting total testosterone [T; mean 15.7 +/- 1.6 (SE) nmol/l], free testosterone (FT; 54.1 +/- 4.5 pmol/l), or cortisol (267.6 +/- 22 nmol/l) across all trials and times. In conclusion, with similar lactate responses, light exercise combined with partial vascular occlusion elicits a greater GH response than moderate exercise without occlusion but does not affect T, FT, or cortisol.

Adolescent↗

PubMed2006

Interrelationships of serum estradiol, estrone, and estrone sulfate, adiposity, biochemical bone markers, and leptin in post-menopausal women.

OBJECTIVE: The aim of this study was to examine the relationships between endogenous estrogens and adiposity, bone markers, and leptin in post-menopausal (PM) women. DESIGN: Seventy-three post-menopausal (PM) women participated in a clinical correlational study. Weight, height, waist-hip ratio, fasted morning serum and first morning voided urine samples were obtained to compare body mass index (BMI), waist-hip ratio, endogenous estrogens, leptin, and bone markers. Serum estradiol, estrone (E1), estrone sulfate (E1S), leptin, osteocalcin, and urinary deoxypyridinoline (Dpd) were determined. RESULTS: Significant positive relationships were found between BMI and estradiol, E1, and E1S (r = 0.52, 0.38, and 0.29; P < or = 0.001, 0.001, and 0.013 respectively). Significant relationships between leptin and estrogens were revealed, but were not significant when BMI was used as a covariate. Although many subjects revealed elevated bone marker levels, no correlation between estrogens or BMI and bone markers (Dpd and osteocalcin) was found. CONCLUSIONS: There are significant positive correlations between estrogens and BMI in PM women. Increasing levels of estradiol, E1, and E1S with increasing BMI may be an indicator of adiposity, but are without effect as a stimulatory factor on leptin production. Waist-hip ratio did not significantly affect leptin concentrations when accounting for BMI. Due to assay sensitivity in the present study, data represent a more precise representation of these relationships. The lack of correlation between estrogens and bone marker levels may have been due to low estrogen levels in PM women.

Adipose Tissue↗

PubMed2005

Similar hormonal responses to concentric and eccentric muscle actions using relative loading.

Conventional resistance exercise is performed using sequential concentric (CON) and eccentric (ECC) contractions, utilizing the same muscle load. Thus, relative to maximal CON and ECC resistance, the ECC contraction is loaded to a lesser degree. We have recently shown that at the same absolute load, CON contractions are associated with greater growth hormone (GH) but similar total testosterone (TT) and free testosterone (FT) responses compared with ECC contractions and attributed the larger GH response to greater relative CON loading. In the present study, we have examined the same endocrine parameters to six different upper and lower body exercises using relative loading rather than absolute loading, hypothesizing that GH responses would be similar for CON and ECC actions, but TT and FT responses would be greater after ECC contractions. Seven young men with recreational weight training experience completed an ECC and CON muscle contraction trial on two different occasions in a counterbalanced fashion. The exercises consisted of four sets of 10 repetitions of lat pull-down, leg press, bench press, leg extension, military press, and leg curl exercises at 65% of an ECC or CON 1-RM with 90 s between sets and exercises. CON and ECC actions were performed at the same speed. ECC 1-RMs were considered to be 120% of the CON 1-RM for the same exercise. Blood samples were collected before, immediately after, and 15 min after the exercise. GH significantly increased across both trials but was not different between the two trials. Total testosterone was not significantly altered in response to either trial; however, free testosterone concentrations increased in response to both ECC and CON trials. Data suggest that CON and ECC muscle contractions produce similar GH, T, and free testosterone responses with the same relative loading.

Adaptation, Physiological↗

PubMed2003

Responses of growth hormone aggregates to different intermittent exercise intensities.

The purpose of this study was to determine the impact of high-intensity intermittent exercise on the presence of circulating growth hormone (GH) aggregates measured using two different assay techniques. Six male subjects with endurance training background participated in this study under both exercise and no-exercise control conditions. After resting blood sampling, subjects completed an intermittent treadmill exercise protocol at four speeds predicted to elicit a specific VO(2):60% VO(2max) for 10 min, 75% for 10 min, 90% for 5 min, and 100% for 2 min. After each exercise intensity was completed treadmill speed was reduced to a walk (3.5-4 min) for blood sampling. Sampling continued every 15 min for 1 h into recovery. All samples were then measured for GH concentrations using Nichols immunoradiometric assay (IRMA) and Diagnostic Systems Laboratory's immunofunctional assay (IFA). A second set of samples was chemically reduced using reduced glutathione (GSH; 10 mM for 18 h at room temperature) to break disulfide bonds between possible oligomeric GH complexes, and subsequently assayed using the same GH assays. With the IRMA, GH was significantly elevated ( P<0.05) after the 75% workload and remained elevated through 30 min post-exercise. After adding GSH to the sample, the IRMA indicated significant increases in GH as early as the 60% exercise intensity and remained elevated through 45 min into recovery. At 75%, the GSH assay run was significantly higher than the non-GSH assay run. With the IFA, GH was significantly elevated at 60% in the non-GSH condition, whereas the GSH assay run indicated significant elevations at 75%. Both GSH and non-GSH conditions remained elevated through 30 min into recovery. These data indicate that the addition of GSH to serum samples prior to assay via an IRMA may break existing disulfide bonds between aggregated GH molecules, thus altering the apparent assay signal to reveal greater total GH in the sample.

Adult↗

PubMed2003

Variability of serum estrogens among postmenopausal women treated with the same transdermal estrogen therapy and the effect on androgens and sex hormone binding globulin.

OBJECTIVE: To examine the variability of serum estrogens in response to transdermal estrogen replacement therapy (ET), and to determine the effects on androgens and sex hormone binding globulin (SHBG). DESIGN: Randomized, double-blind, placebo-controlled study. SETTING: Women's hospital. PATIENT(S): Two groups of postmenopausal women: [1] 21 women not on ET enrolled and 17 completed the study; [2] 19 women on continuous transdermal ET enrolled and 13 completed the study. INTERVENTION(S): Women not on ET were administered a placebo patch or a newly initiated estrogen patch, then crossed over to the alternate treatment. Serum samples were obtained at baseline and the subsequent 3 days from the placebo and new-patch groups and from a separate group of women receiving continuous estrogen patch treatment. MAIN OUTCOME MEASURE(S): Estradiol (E(2)), estrone, estrone sulfate, T, dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEAS), androstenedione, free androgen index, and SHBG. RESULT(S): There was considerable intrapatient and interpatient variability in the estrogen response to identical treatment doses, with E(2) values differing between women as much as 138 pg/mL and E(2) increases above baseline differing as much as 90 pg/mL. Continuous treatment increased SHBG and decreased androstenedione levels; however, levels of T, DHEA, DHEAS, and free androgen index did not change. CONCLUSION(S): There is great variability of estrogen in response to transdermal ET, but minimal effect on circulating androgens.

Administration, Cutaneous↗

PubMed2003

Hormonal responses from concentric and eccentric muscle contractions.

UNLABELLED: Intense resistance exercise can acutely increase testosterone (T), free testosterone (FT), and growth hormone (GH) concentrations, but there are few investigations concerning acute endocrine responses to concentric (CON) and eccentric (ECC) contractile actions. PURPOSE: The purpose of the study was to compare acute anabolic hormonal responses to bouts of dynamic CON and ECC contractions from multiple exercises at the same absolute load. METHODS: Ten young men (age: 24.7 +/- 1.2 yr, weight: 85.45 +/- 24.2 kg, and height: 178 +/- 0.2 cm) completed two trials in counterbalanced fashion consisting of only CON or ECC contractions at the same absolute workload. Subjects performed four sets of 12 repetitions of bench press, leg extension, military press, and leg curl at 80% of a 10-repetition maximum with 90-s rest periods. Blood samples were collected pre-, post-, and 15-min postexercise. RESULTS: There were significant increases in GH, T, and FT and lactate for both trials, but only GH and lactate were greater for the CON trial. CONCLUSION: CON exercise increases GH concentrations to a much greater extent than ECC exercise at the same absolute load, and it is likely that greater GH responses were related to intensity rather than mode of contraction. Also, CON and ECC dynamic contraction trials at the same absolute workload elicited similar small but significant increases in T and FT, indicating that the greater metabolic stress produced by during the CON trial did not affect these hormone responses.

Adult↗

PubMed2003

RPE, pain, and physiological adjustment to concentric and eccentric contractions.

PURPOSE: The purpose of the study was to compare perceptual (RPE and pain), cardiac (heart rate), lactate, and endocrine (cortisol) responses with concentric (CON) and eccentric (ECC) resistance exercise protocols using the same absolute workload. METHODS: Eight healthy men with resistance-training experience participated in the study. Subjects completed two experimental trials consisting of either CON contractions or ECC contractions at the same absolute workload for each of four exercises: bench press, leg extension, military press, and leg curl. Subjects performed four sets of 12 repetitions at 80% of 10-RM with 90-s rest periods. Blood samples were taken before, immediately after, and 15-min postexercise. RESULTS: There was a significant trial effect for RPE, with CON exercise eliciting a higher RPE than ECC exercise (6.71 +/- 0.51 and 4.10 +/- 0.27, respectively). A significant trial effect was also demonstrated for pain, with CON exercise producing a higher pain rating than ECC exercise (5.59 +/- 0.41 and 3.23 +/- 0.27, respectively). Significantly higher heart rates and lactates were also demonstrated during the CON trial. For cortisol, a significant interaction was revealed between the pre- and immediate posttrial measures but not an overall trial effect. Correlational analyses revealed a significant relationship between RPE and pain for both trials. CONCLUSIONS: CON exercise elicits greater perceptual (higher RPE and pain rating), cardiac, lactate and cortisol response than ECC exercise at the same absolute workload. Data demonstrate that relative to absolute load, RPE and pain respond to resistance exercise in a similar fashion. Additionally, physiological cues are consistent with these perceptual data.

Adolescent↗

PubMed2003

Adiponectin responses to continuous and progressively intense intermittent exercise.

PURPOSE: Adiponectin is a recently discovered adipocyte protein that is lower in patients with coronary artery disease and in Type II diabetics who have insulin resistance. Regular exercise is known to be a preventative factor in the development of atherosclerosis and Type II diabetes. Acute exercise increases insulin sensitivity; however, it also increases beta-adrenergic and glucocorticoid activities that may suppress adiponectin expression. Two experiments were conducted to determine whether acute exercise affects adiponectin concentrations. METHODS: In the first experiment, six healthy male subjects completed 30 min of heavy continuous running exercise at 79% of VO (2max). In the second experiment, well-trained runners completed strenuous intermittent exercise consisting of treadmill running at 60, 75, 90, and 100% VO (2max). A resting control trial for the second experiment was also conducted. RESULTS: Glucose and insulin were not altered significantly in the first experiment, but both increased significantly (P < 0.05) in the second experiment. A significant increase (P < 0.05) in adiponectin in the first experiment was no longer significant after correction for plasma volumes shifts. In the second experiment, there were significant (P < 0.05) changes in adiponectin concentrations over time but not a significant difference between adiponectin responses in exercise and control trials. CONCLUSIONS: The data suggest that 30 min of heavy continuous running or more strenuous intermittent running does not stimulate an increase in production and release of adiponectin, and small increases in adiponectin concentrations resulting from the exercise may be attributed to normal plasma volume shifts.

Adiponectin↗

PubMed2003

Effects of high-intensity exercise on leptin and testosterone concentrations in well-trained males.

OBJECTIVE: A number of investigations have examined the effect of exercise on leptin concentrations, because leptin is associated with obesity, satiety, and reproductive function. High-intensity exercise is known to increase testosterone, an inhibitor of leptin. The objective of the study was to determine whether the leptin responses to a progressive, intermittent exercise protocol were related to serum testosterone concentrations. Most previous studies have examined leptin responses to low or moderately high exercise intensities. A second objective was to determine whether leptin responses were different than previous experiments using intermittent moderate and high-intensity exercise. METHODS: Well-trained runners completed strenuous intermittent exercise consisting of treadmill running at 60, 75, 90, and 100% VO(2 max) and a subsequent resting control trial was also conducted. RESULTS: There were significant increases in mean serum levels of leptin and testosterone with both quickly returning to baseline during recovery, but no relationship between the two hormones was found. After examining individual data for both hormones, it was discovered that subjects could be classified as leptin responders or nonresponders, whereas testosterone increased in all subjects. Responders had elevated serum leptin levels at baseline and exhibited increases after high-intensity exercise, whereas nonresponders did not show changes in leptin during exercise. CONCLUSIONS: Data suggest testosterone levels do not acutely affect leptin responses to exercise or 1-h of recovery. Moreover, varied leptin responses to intense exercise in comparable well-trained runners was observed and was associated with baseline leptin concentrations.

Adult↗

PubMed2003

Different effects of concentric and eccentric muscle actions on plasma volume.

The effects of concentric (CON) and eccentric (ECC) contractions on Delta plasma volume (PV), heart rate (HR), and lactate in responses to protocols in different body positions were investigated. CON or ECC contractions were performed in either a single-exercise (6 sets of 12 repetitions of leg extensions completed at 80% of 12 repetition maximum [12RM] with 3-minute rest periods) or multiexercise (4 sets of 10 repetitions for both CON and ECC trials of bench press, leg extension, military press, and leg curl at 80% of 10RM with 90-second rest periods) protocols. HR and lactate increased significantly for both protocols from pre- to postexercise for CON but not ECC trials. DeltaPV was greater following both CON single-exercise (-11.48 +/- 1.38%) and multiexercise (-4.64 +/- 0.33%) trials vs. ECC single-exercise (-1.62 +/- 1.69%) and multiexercise (-1.26 +/- 1.20) trials. Data demonstrate ECC exercise in response to single and multiexercise protocols at the same absolute workload as CON exercise produces less cardiovascular stress.

Adult↗

PubMed2002

Substrate utilization during exercise in postmenopausal women on hormone replacement therapy.

It has been suggested that due to the slight direct or indirect effect of estrogen on lipolytic activity, the age-related decrease in production associated with the menopause may heighten the risk of cardiovascular and metabolic disease in women. While hormone replacement therapy (HRT) alone may have little or no effect on body mass in postmenopausal women, data suggest it can alter the shift toward abdominal adiposity. Furthermore, estrogen may have a synergistic effect on exercise-induced reduction in fat mass. Accordingly, the purpose of this investigation was to examine the potential influence of HRT on substrate utilization during 30 min of treadmill exercise at approximately 80% maximal oxygen uptake (VO(2max)) in postmenopausal women. Eight women were receiving HRT and nine women were not (NHRT). No significant differences between the HRT and NHRT groups were noted for age, body mass, body fat, VO(2max) or the percentage of VO(2max) maintained during exercise. Expired gas samples were analyzed every 30 s to determine respiratory exchange ratio (R) and % VO(2max). The R, total energy expended and percentage contributions from fats and carbohydrate were averaged over three periods during the exercise (min 1-10, 11-20, and 21-30). There was no effect of HRT on R, total energy expended or substrate contribution. Thus, treatment of postmenopausal women using HRT (primarily conjugated equine estrogens in doses of 0.625-1.25 mg x day(-1)) did not appear to affect the percentages of fat and carbohydrate utilized during 30 min of treadmill exercise at 80% of VO(2max). However, the exercise responses in this group of menopausal women were consistent with a duration-dependent increased reliance on fat as an energy source during exercise of moderate to vigorous intensity as has been demonstrated in younger populations.

Aged↗

PubMed2002

Leptin and exercise.

Short-term exercise (<60 min) studies suggest that leptin concentrations are not acutely affected in healthy males and females. Most reports of reductions in serum leptin may be attributed to circadian rhythms or hemoconcentration. For long-term (> or =60 min) exercise, a reduction in leptin concentrations reported from 1 to 3 hr of running or cycling has been attributed to diurnal reduction in circulating leptin, independent of exercise. Exercise that produces a sufficient energy imbalance (kilocalorie intake versus kilocalorie expenditure) suppresses 24-hr mean and amplitude of the diurnal rhythm of leptin in women. Suppression of leptin concentrations may be counterbalanced by feeding and may explain consistent reports of reductions in leptin concentrations following extreme bouts of exercise such as marathons or ultramarathons. In addition, leptin concentrations are reduced 48 hr after long-term aerobic exercise and long-term resistance exercise is associated with delayed leptin reduction 9 hr postexercise. Training studies have documented that short-term exercise training (< or =12 weeks) does not affect leptin levels, with the exception of patients with type 2 diabetes. Exercise training protocols that result in reduced fat mass will lower leptin concentrations, thus, most investigators have reported leptin concentrations after accounting for fat loss. There are disparate findings concerning long-term (>12 weeks) training studies, with a number of studies finding no effect of training on leptin concentrations other than effects induced by fat loss, and other studies finding reductions in leptin concentrations after accounting for fat loss. Exercise training-induced reductions in leptin levels have been attributed to alterations in energy balance, improvements in insulin sensitivity, alterations in lipid metabolism, and unknown factors. Hormone replacement does not seem to affect leptin adaptations to training. Patients with type 2 diabetes show delayed effects of short-term resistance exercise on leptin concentrations, reduced leptin levels with long-term training, and appear to be more sensitive to training-induced leptin adaptations than other populations.

Energy Metabolism↗