Biomedical subjects

Thomas W Storer

Publications and source records attributed to Thomas W Storer.

17 recordsLinked to original sources

PubMed2026

Effects of testosterone-augmented multimodal exercise intervention in spinal cord injury: a randomized controlled trial.

CONTEXT: Spinal cord injury (SCI) leads to profound muscle atrophy, aerobic deconditioning, and metabolic dysfunction. Exercise-based interventions alone produce modest benefits. Whether testosterone can augment physiologic responses to exercise in this population remains untested. OBJECTIVE: To evaluate efficacy and safety of home-based intervention combining functional electrical stimulation-assisted leg cycling (FES-LC), arm ergometry (AE), and testosterone compared with FES-LC, AE plus placebo in adults with SCI. METHODS: This randomized, placebo-controlled, double-blind trial enrolled 84 adults (76 males and 8 females) aged 19-70 years with SCI (neurologic levels C4-T12; AIS grades A-D). Participants were randomized to multimodality intervention (home-based FES-LC, AE and intramuscular testosterone undecanoate) (n = 38) or control intervention (FES-LC, AE plus placebo) (n = 46) for 16 weeks. The primary outcome was change in aerobic capacity (peak VO2) during AE cardiopulmonary exercise testing. Secondary outcomes included lean mass, hemoglobin, cardiometabolic markers, and safety. RESULTS: Mean (SD) age was 44 (13) years and time since injury was 13.9 (13) years). Between-group changes in peak VO2 were not statistically significant. Within-group improvements were larger in multimodality (∼19% increase; 0.10 L/min; 95% CI, 0.02-0.18 L/min) compared to controls (∼6% increase; 0.06 L/min; 95% CI, -0.01-0.13). The multimodality group gained significantly more lean mass (whole-body:1.84 kg, 95% CI: 0.52-3.16, P = .007; lower extremity 0.92 kg, 95% CI: 0.38-1.45, P = .001), and anemia was corrected in a greater proportion of participants. Adverse event rates were similar between groups. CONCLUSION: A home-based multimodality intervention combining FES-LC, AE, and testosterone was safe and associated with greater improvements in lean mass and hemoglobin. Although between-group differences in aerobic capacity were not statistically significant, greater within-group increases were observed in the multimodality group. These findings may inform future studies of testosterone-augmented exercise interventions for individuals living with SCI.

Humans↗

PubMed2006

Drug insight: Testosterone and selective androgen receptor modulators as anabolic therapies for chronic illness and aging.

Several regulatory concerns have hindered development of androgens as anabolic therapies, despite unequivocal evidence that testosterone supplementation increases muscle mass and strength in men; it induces hypertrophy of type I and II muscle fibers, and increases myonuclear and satellite cell number. Androgens promote differentiation of mesenchymal multipotent cells into the myogenic lineage and inhibit their adipogenic differentiation, by facilitating association of androgen receptors with beta-catenin and activating T-cell factor 4. Meta-analyses indicate that testosterone supplementation increases fat-free mass and muscle strength in HIV-positive men with weight loss, glucocorticoid-treated men, and older men with low or low-normal testosterone levels. The effects of testosterone on physical function and outcomes important to patients have not, however, been studied. In older men, increased hematocrit and increased risk of prostate biopsy and detection of prostate events are the most frequent, testosterone-related adverse events. Concerns about long-term risks have restrained enthusiasm for testosterone use as anabolic therapy. Selective androgen-receptor modulators that are preferentially anabolic and that spare the prostate hold promise as anabolic therapies. We need more studies to determine whether testosterone or selective androgen-receptor modulators can induce meaningful improvements in physical function and patient-important outcomes in patients with physical dysfunction associated with chronic illness or aging.

Aging↗

PubMed2006

Maximal oxygen uptake at the same fat-free mass is greater in men than women.

Maximal oxygen uptake (VO(2max)) is commonly divided by body mass or fat-free mass (body mass minus fat mass) in order to make it size independent so that comparisons among persons of different size can be made. However, numerous studies have shown that the ratio created is not size-independent. Analysis of covariance (ANCOVA) allows a dependent variable to be compared between groups at a common value of a covariate. The purpose of this study was to compare VO(2max) at the same fat-free mass (FFM) in 230 sedentary subjects (half men) who ranged in age from 20 to 70 years. The subjects underwent maximal cardiopulmonary exercise testing on a cycle ergometer as ventilation and the expired gas fractions were being measured. Two ANCOVA models were evaluated. The dependent variable, fixed factor and covariate(s) in the linear model were VO(2max), sex and FFM, respectively. The corresponding terms in the log-linear model were ln VO(2max), sex, and ln FFM and age. Sex made a significant contribution to both models. In the linear model, the mean VO(2max) at the same FFM was 27% higher in men (2,444 versus 1,929 ml min(-1); P<0.001). In the log-linear model, the corresponding value at the same FFM and age was 32% higher in men (2,368 versus 1,794 ml min(-1); P<0.001). The goodness of fit indices of squared multiple correlation coefficient and standard error of estimate were significantly better for the log-linear model. We conclude that VO(2max) at the same FFM is considerably higher in men than in women who have a sedentary lifestyle.

Adult↗

PubMed2005

A randomized, placebo-controlled trial of nandrolone decanoate in human immunodeficiency virus-infected men with mild to moderate weight loss with recombinant human growth hormone as active reference treatment.

OBJECTIVE: We compared the effectiveness of a biweekly regimen of 150 mg nandrolone with placebo in HIV-infected men with mild to moderate weight loss and contrasted its effects against a Food and Drug Administration-approved regimen of recombinant human (rh)GH. METHODS: In this placebo-controlled, randomized, 12-wk trial, placebo and nandrolone (150 mg im biweekly) were administered double blind, and rhGH (6 mg sc daily) was administered in an open-label manner. Participants were HIV-infected men with 5-15% weight loss over 6 months and on stable antiretroviral therapy for more than 12 wk. Lean body mass (LBM), muscle performance, physical function, endurance, hormone levels, insulin sensitivity, sexual function, quality of life, and appetite were assessed at baseline and after 12 wk. RESULTS: Nandrolone administration was associated with a greater increase in LBM (+1.6 +/- 0.3 kg) by dual-energy x-ray absorptiometry scan than placebo (+0.4 +/- 0.3 kg; P < 0.05); however, the change in LBMs with nandrolone was not significantly different from rhGH (+2.5 +/- 0.3 kg). Nandrolone administration was also associated with significantly greater gains in fat-free mass (+1.6 +/- 0.3 kg), body cell mass (+1.0 +/- 0.2 kg), and intracellular water (+0.9 +/- 0.2 kg) than placebo; these changes in the nandrolone group were not significantly different from the rhGH group. rhGH administration was associated with greater loss of whole body fat mass and higher frequency of drug-related adverse effects and treatment discontinuations than nandrolone and placebo and a greater increase in extracellular water than nandrolone. Nandrolone treatment was associated with greater improvements in perception of health than rhGH and sexual function than placebo. The cachexia/anorexia scores, health care resource use, and insulin sensitivity did not significantly change. CONCLUSION: We conclude that nandrolone is superior to placebo and not significantly different from a Food and Drug Administration-approved regimen of rhGH in improving lean body mass in HIV-infected men with mild to moderate weight loss.

Adipose Tissue↗

PubMed2005

Endurance exercise training during haemodialysis improves strength, power, fatigability and physical performance in maintenance haemodialysis patients.

BACKGROUND: Endurance training improves cardiopulmonary fitness in maintenance haemodialysis (MHD). Because many MHD patients are profoundly deconditioned and exhibit significant muscle weakness, endurance training may also improve muscle strength and physical performance in these patients. This study assessed this possibility. METHODS: Twelve MHD patients performed incremental and constant work rate cycle exercise tests to determine peak work rate, VO(2)peak and endurance time (ET). Lower extremity strength, power and fatigability, stair-climbing time, 10 m walk time and a timed up-and-go were assessed before and after 8.6+/-2.3 weeks of thrice weekly, progressive, semi-recumbent, leg-cycle training during haemodialysis. Initial training intensity and duration targets were set at 50% peak work rate (WR) and 20 min, respectively, with a goal of progressing to 40 min at the highest WR tolerable. Non-exercising MHD patients and healthy volunteers with similar age, gender and race/ethnicity served as comparison groups. RESULTS: None of the subjects tolerated the initial target intensity. Therefore, WR was reduced to 19+/-9 watts (30% of peak WR) for 19.9 min/session. At end of training, subjects cycled at 29+/-25 watts (46% initial peak WR; P = 0.01) for 38+/-8 min (P<0.001). VO(2)peak and ET improved 22% (P = 0.018) and 144% (P = 0.001), respectively. Quadriceps strength, power and fatigability improved 16% (P = 0.002), 15% (P = 0.115) and 43% (P = 0.029), respectively. The three measures of physical performance improved by 14-17% (P<0.031). Total work performed in training increased by 5.5+/-21.1 kJ/week (17%); a 165% increase during the study period. CONCLUSIONS: Nine weeks of leg-cycling during haemodialysis in MHD patients improves not only cardiopulmonary fitness and endurance but also muscle strength, power, fatigability and physical function. These data underscore the value of endurance training in MHD.

Adult↗

PubMed2005

Dose-dependent effects of testosterone on sexual function, mood, and visuospatial cognition in older men.

CONTEXT: The relationships between testosterone dose and its effects on sexual function, mood, and visuospatial cognition are poorly understood. OBJECTIVE: To elucidate testosterone dose-response relationships in older men, we examined the effects of graded testosterone doses on sexual function, mood, and visuospatial cognition in healthy, older men (age, 60-75 yr). SETTING: This study was performed at the General Clinical Research Center. INTERVENTION/METHODS: Subjects each received a long-acting GnRH agonist to suppress endogenous testosterone production and were randomized to receive one of five doses (25, 50, 125, 300, and 600 mg) of testosterone enanthate weekly for 20 wk. Questionnaires were used to evaluate sexual function. Scores for overall sexual function as well as subcomponents of sexual function (libido, sexual activity, and erectile function) were calculated. RESULTS: Changes in overall sexual function (P = 0.003) and waking erections (P = 0.024) differed by dose. An interaction between libido and being sexually active was observed, such that libido changed by testosterone dose only among men who reported being sexually active at the beginning of the study (P = 0.009). Men's log-transformed free testosterone levels during treatment were positively correlated with overall sexual function (P = 0.001), waking erections (P = 0.040), spontaneous erections (P = 0.047), and libido (P = 0.027), but not with intercourse frequency (P = 0.428) or masturbation frequency (P = 0.814). No effects of testosterone dose were observed on two measures of mood: Hamilton's Depression Inventory (P = 0.359) and Young's Mania Scale (P = 0.851). The number of trials completed on a computer-based test of visuospatial cognition differed by dose (P = 0.042), but the number of squares correctly completed on this task did not differ by dose (P = 0.159). CONCLUSIONS: Different aspects of male behavior respond differently to testosterone. When considered together with previous data from young men, these data indicate that testosterone dose-response relationships for sexual function and visuospatial cognition differ in older and young men.

Affect↗

PubMed2005

Skeletal muscle mRNA for IGF-IEa, IGF-II, and IGF-I receptor is decreased in sedentary chronic hemodialysis patients.

BACKGROUND: Maintenance hemodialysis patients often display evidence for protein-energy malnutrition, inflammation, and sarcopenia. We therefore investigated whether sedentary maintenance hemodialysis patients have decreased skeletal muscle mRNA levels and muscle and serum protein concentrations of certain growth factors. METHODS: Fifty-one clinically stable maintenance hemodialysis patients (32 men and 19 women), and 21 normal adults (16 men and five women) of similar age, gender mix, racial/ethnic backgrounds, serum albumin, body composition, and level of sedentary activity were studied. Individuals underwent biopsy of the right vastus lateralis muscle, and real-time polymerase chain reaction (PCR) amplification of mRNAs for insulin-like growth factor-I (IGF-I), IGF-II, IGF-I receptor (IGF-IR), IGF-IIR, and myostatin (44 patients) was performed. Serum and muscle IGF-I and IGF-II, serum proinflammatory cytokines, and leg muscle strength, power, and fatigability were measured. RESULTS: Maintenance hemodialysis patients displayed significantly reduced mRNA levels for IGF-IEa mRNA (P < 0.05), IGF-II (P < 0.001), and IGF-IR (P < 0.001), and no difference in mRNAs for IGF-IEc, IGF-IIR, or myostatin as compared to normal controls. Muscle mRNA levels, in general, followed the same pattern in male and female maintenance hemodialysis patients considered separately. In the maintenance hemodialysis patients, muscle IGF-I protein, serum IGF-II and tumor necrosis factor-alpha (TNF-alpha) were each increased, whereas serum C-reactive protein (CRP) and interleukin-6 (IL-6) were normal. Muscle strength and power, but not fatigability, were reduced in the maintenance hemodialysis patients. CONCLUSION: In sedentary, clinically stable maintenance hemodialysis patients as compared to sedentary normal individuals, the mRNA levels for IGF-IEa, IGF-II, and the IGF-I receptor are decreased in vastus lateralis muscle. Protein levels for muscle IGF-I and serum IGF-II are increased.

Adult↗

PubMed2004

Older men are as responsive as young men to the anabolic effects of graded doses of testosterone on the skeletal muscle.

Although testosterone levels and muscle mass decline with age, many older men have serum testosterone level in the normal range, leading to speculation about whether older men are less sensitive to testosterone. We determined the responsiveness of androgen-dependent outcomes to graded testosterone doses in older men and compared it to that in young men. The participants in this randomized, double-blind trial were 60 ambulatory, healthy, older men, 60-75 yr of age, who had normal serum testosterone levels. Their responses to graded doses of testosterone were compared with previous data in 61 men, 19-35 yr old. The participants received a long-acting GnRH agonist to suppress endogenous testosterone production and 25, 50, 125, 300, or 600 mg testosterone enanthate weekly for 20 wk. Fat-free mass, fat mass, muscle strength, sexual function, mood, visuospatial cognition, hormone levels, and safety measures were evaluated before, during, and after treatment. Of 60 older men who were randomized, 52 completed the study. After adjusting for testosterone dose, changes in serum total testosterone (change, -6.8, -1.9, +16.1, +49.5, and +101.9 nmol/liter at 25, 50, 125, 300, and 600 mg/wk, respectively) and hemoglobin (change, -3.6, +9.9, +20.9, +12.6, and +29.4 g/liter at 25, 50, 125, 300, and 600 mg/wk, respectively) levels were dose-related in older men and significantly greater in older men than young men (each P < 0.0001). The changes in FFM (-0.3, +1.7, +4.2, +5.6, and +7.3 kg, respectively, in five ascending dose groups) and muscle strength in older men were correlated with testosterone dose and concentrations and were not significantly different in young and older men. Changes in fat mass correlated inversely with testosterone dose (r = -0.54; P < 0.001) and were significantly different in young vs. older men (P < 0.0001); young men receiving 25- and 50-mg doses gained more fat mass than older men (P < 0.0001). Mood and visuospatial cognition did not change significantly in either group. Frequency of hematocrit greater than 54%, leg edema, and prostate events were numerically higher in older men than in young men. Older men are as responsive as young men to testosterone's anabolic effects; however, older men have lower testosterone clearance rates, higher increments in hemoglobin, and a higher frequency of adverse effects. Although substantial gains in muscle mass and strength can be realized in older men with supraphysiological testosterone doses, these high doses are associated with a high frequency of adverse effects. The best trade-off was achieved with a testosterone dose (125 mg) that was associated with high normal testosterone levels, low frequency of adverse events, and significant gains in fat-free mass and muscle strength.

Adult↗

PubMed2004

Delta-4-androstene-3,17-dione binds androgen receptor, promotes myogenesis in vitro, and increases serum testosterone levels, fat-free mass, and muscle strength in hypogonadal men.

Previous studies of Delta 4-androstene-3,17-dione (4-androstenedione) administration in men have not demonstrated sustained increments in testosterone levels, fat-free mass (FFM), and muscle strength, and failure to demonstrate androstenedione's androgenic/anabolic effects has stifled efforts to regulate its sales. To determine whether 4-androstenedione has androgenic/anabolic properties, we evaluated its association with androgen receptor (AR) and its effects on myogenesis in vitro. Additionally, we studied the effects of a high dose of 4-androstenedione on testosterone levels, FFM, and muscle strength in hypogonadal men. We determined the dissociation constant (K(d)) for 4-androstenedione using fluorescence anisotropy measurement of competitive displacement of fluorescent androgen from AR ligand-binding domain. AR nuclear translocation and myogenic activity of androstenedione were evaluated in mesenchymal, pluripotent C3H10T1/2 cells, in which androgens stimulate myogenesis through an AR pathway. We determined effects of a high dose of androstenedione (500 mg thrice daily) given for 12 wk on FFM, muscle strength, and hormone levels in nine healthy, hypogonadal men. 4-Androstenedione competitively displaced fluorescent androgen from AR ligand-binding domain with a lower affinity than dihydrotestosterone (K(d), 648 +/- 21 and 10 +/- 0.4 nm, respectively). In C3H10T1/2 cells, 4-androstenedione caused nuclear translocation of AR and stimulated myogenesis, as indicated by a dose-dependent increase in myosin heavy chain II+ myotube area and up-regulation of MyoD protein. Stimulatory effects of 4-androstenedione on myosin heavy chain II+ myotubes and myogenic determination factor expression were attenuated by bicalutamide, an AR antagonist. Administration of 1500 mg 4-androstenedione daily to hypogonadal men significantly increased serum androstenedione, total and free testosterone, estradiol, and estrone levels and suppressed SHBG and high-density lipoprotein cholesterol levels. 4-androstenedione administration was associated with significant gains in FFM (+1.7 +/- 0.5 kg; P = 0.012) and muscle strength in bench press (+4.3 +/- 3.1 kg; P = 0.006) and leg press exercises (+18.8 +/- 17.3 kg; P = 0.045). 4-androstenedione is an androgen that binds AR, induces AR nuclear translocation, and promotes myogenesis in vitro, with substantially lower potency than dihydrotestosterone. 4-androstenedione administration in high doses to hypogonadal men increases testosterone levels, FFM, and muscle strength, although at the dose tested, the anabolic effects in hypogonadal men are likely because of its conversion to testosterone.

3T3 Cells↗

PubMed2004

Effects of testosterone and resistance training in men with chronic obstructive pulmonary disease.

Dysfunction of the muscles of ambulation contributes to exercise intolerance in chronic obstructive pulmonary disease (COPD). Men with COPD have high prevalence of low testosterone levels, which may contribute to muscle weakness. We determined effects of testosterone supplementation (100 mg of testosterone enanthate injected weekly) with or without resistance training (45 minutes three times weekly) on body composition and muscle function in 47 men with COPD (mean FEV(1) = 40% predicted) and low testosterone levels (mean = 320 ng/dl). Subjects were randomized to 10 weeks of placebo injections + no training, testosterone injections + no training, placebo injections + resistance training, or testosterone injections + resistance training. Testosterone injections yielded a mean increase of 271 ng/dl in the nadir serum testosterone concentration (to the middle of the normal range for young men). The lean body mass (by dual-energy X-ray absorptiometry) increase averaged 2.3 kg with testosterone alone and 3.3 kg with combined testosterone and resistance training (p < 0.001). Increase in one-repetition maximum leg press strength averaged 17.2% with testosterone alone, 17.4% with resistance training alone, and 26.8% with testosterone + resistance training (p < 0.001). Interventions were well tolerated with no abnormalities in safety measures. Further studies are required to determine long-term benefits of adding testosterone supplementation and resistance training to rehabilitative programs for carefully screened men with COPD and low testosterone levels.

Aged↗

PubMed2003

Development of models to predict anabolic response to testosterone administration in healthy young men.

Considerable heterogeneity exists in the anabolic response to androgen administration; however, the factors that contribute to variation in an individual's anabolic response to androgens remain unknown. We investigated whether testosterone dose and/or any combination of baseline variables, including concentrations of hormones, age, body composition, muscle function, and morphometry or polymorphisms in androgen receptor could explain the variability in anabolic response to testosterone. Fifty-four young men were treated with a long-acting gonadotropin-releasing hormone (GnRH) agonist and one of five doses (25, 50, 125, 300, or 600 mg/wk) of testosterone enanthate (TE) for 20 wk. Anabolic response was defined as a change in whole body fat-free mass (FFM) by dual-energy X-ray absorptiometry (DEXA), appendicular FFM (by DEXA), and thigh muscle volume (by magnetic resonance imaging) during TE treatment. We used univariate and multivariate analysis to identify the subset of baseline measures that best explained the variability in anabolic response to testosterone supplementation. The three-variable model of TE dose, age, and baseline prostate-specific antigen (PSA) level explained 67% of the variance in change in whole body FFM. Change in appendicular FFM was best explained (64% of the variance) by the linear combination of TE dose, baseline PSA, and leg press strength, whereas TE dose, log of the ratio of luteinizing hormone to testosterone concentration, and age explained 66% of the variation in change in thigh muscle volume. The models were further validated by using Ridge analysis and cross-validation in data subsets. Only the model using testosterone dose, age, and PSA was a consistent predictor of change in FFM in subset analyses. The length of CAG tract was only a weak predictor of change in thigh muscle volume and lean body mass. Hence, the anabolic response of healthy, young men to exogenous testosterone administration can largely be predicted by the testosterone dose.

Absorptiometry, Photon↗

PubMed2003

Androgen effects on body composition.

Androgens are known to have a role in the body fat, muscle size, muscle performance and physical function differences seen between hypogonadal and eugonadal men. The results of investigations into effects of testosterone on body composition, fat metabolism and muscle anabolism are reviewed here. Testosterone dose-response relationships are presented in studies of the effects of physiologic and supraphysiologic doses with and without exercise in young hypogonadal men, older men with low testosterone levels and in chronic illness states.

Adipose Tissue↗

PubMed2003

Testosterone dose-dependently increases maximal voluntary strength and leg power, but does not affect fatigability or specific tension.

Testosterone supplementation in men increases fat-free mass, but whether measures of muscle performance, such as maximal voluntary strength, power, fatigability, or specific tension, are improved has not been determined. Furthermore, the extent to which these measures of muscle performance are related to testosterone dose or circulating concentration is unknown. To examine the relationship between testosterone dose and muscle performance, 61 healthy, eugonadal young men (aged 18-35 yr) were randomized to 1 of 5 groups, each receiving a long-acting GnRH agonist to suppress endogenous testosterone production plus weekly injections of 25, 50, 125, 300, or 600 mg testosterone enanthate for 20 wk. These doses produced mean nadir testosterone concentrations of 253, 306, 542, 1345, and 2370 ng/dl, respectively. Maximal voluntary muscle strength and fatigability were determined by a seated leg press exercise. Leg power was measured using a validated leg power instrument. Specific tension was estimated by the ratio of one repetition maximum muscle strength to thigh muscle volume determined by magnetic resonance imaging. Testosterone administration was associated with a dose-dependent increase in leg press strength and leg power, but muscle fatigability did not change significantly during treatment. Changes in leg press strength were significantly correlated with total (r = 0.46; P = 0.0005) and free (r = 0.38; P = 0.006) testosterone as was leg power (total testosterone: r = 0.38; P = 0.007; free testosterone: r = 0.35; P = 0.015), but not muscle fatigability. Serum IGF-I concentrations were not significantly correlated with leg strength, power, or fatigability. Specific tension did not change significantly at any dose. We conclude that the effects of testosterone on muscle performance are specific; it increases maximal voluntary strength and leg power, but does not affect fatigability or specific tension. The changes in leg strength and power are dependent on testosterone dose and circulating testosterone concentrations and exhibit a log-linear relationship with serum total and free testosterone. Failure to observe a significant testosterone dose relationship with fatigability suggests that testosterone does not affect this component of muscle performance and that different components of muscle performance are regulated by different mechanisms.

Adolescent↗

PubMed2002

Ventilatory efficiency during exercise in healthy subjects.

When evaluating dyspnea in patients with heart or lung disease it is useful to measure the quantity of ventilation needed to eliminate metabolically produced CO2 (i.e., the ventilatory efficiency). Mathematically, the relationship between ventilation (VE) and CO2 output is determined by the arterial CO2 pressure and the physiologic dead space-tidal volume ratio. We decided to determine how age, sex, size, fitness, and the type of ergometer influenced ventilatory efficiency in normal subjects. Three methods were compared for expressing this relationship: (1) the VE versus CO2 output slope below the ventilatory compensation point, commonly used by cardiologists for estimating the severity of heart failure; (2) the VE/CO2 output ratio at the anaerobic threshold, commonly used by pulmonologists; and (3) the lowest VE/CO2 output ratio during exercise, the latter parameter not previously reported. We studied 474 healthy adults, between 17 and 78 years of age during incremental cycle and treadmill cardiopulmonary exercise tests at three test sites, correcting the total VE for the equipment dead space. The lowest VE/CO2 output ratio was insignificantly different from the ratio at the anaerobic threshold, less variable than that for the slope relationship, and unaffected by the site, ergometer, and gas exchange measurement systems. The regression equation for the lowest VE/CO2 output ratio was 27.94 + 0.108 x age + (0.97 = F, 0.0 = M) - 0.0376 x height, where age is in years and height is in centimeters. We conclude that the lowest VE/CO2 output ratio is the preferred noninvasive method to estimate ventilatory inefficiency.

Adult↗

PubMed2002

Effects of an oral androgen on muscle and metabolism in older, community-dwelling men.

To determine whether oxymetholone increases lean body mass (LBM) and skeletal muscle strength in older persons, 31 men 65-80 yr of age were randomized to placebo (group 1) or 50 mg (group 2) or 100 mg (group 3) daily for 12 wk. For the three groups, total LBM increased by 0.0 +/- 0.6, 3.3 +/- 1.2 (P < 0.001), and 4.2 +/- 2.4 kg (P < 0.001), respectively. Trunk fat decreased by 0.2 +/- 0.4, 1.7 +/- 1.0 (P = 0.018), and 2.2 +/- 0.9 kg (P = 0.005) in groups 1, 2, and 3, respectively. Relative increases in 1-repetition maximum (1-RM) strength for biaxial chest press of 8.2 +/- 9.2 and 13.9 +/- 8.1% in the two active treatment groups were significantly different from the change (-0.8 +/- 4.3%) for the placebo group (P < 0.03). For lat pull-down, 1-RM changed by -0.6 +/- 8.3, 8.8 +/- 15.1, and 18.4 +/- 21.0% for the groups, respectively (1-way ANOVA, P = 0.019). The pattern of changes among the groups for LBM and upper-body strength suggested that changes might be related to dose. Alanine aminotransferase increased by 72 +/- 67 U/l in group 3 (P < 0.001), and HDL-cholesterol decreased by -19 +/- 9 and -23 +/- 18 mg/dl in groups 2 and 3, respectively (P = 0.04 and P = 0.008). Thus oxymetholone improved LBM and maximal voluntary muscle strength and decreased fat mass in older men.

Absorptiometry, Photon↗

PubMed2002

Lower reference limit for maximal oxygen uptake in men and women.

Maximal oxygen uptake (VO2max) is an important measure of exercise tolerance and low values may have clinical significance. Our purpose was to develop the necessary statistics--prediction equations and standard errors of estimate (SEE)--so that the lower reference limit for VO2max can be predicted for men and women. The subjects were healthy, non-smoking, sedentary men (n = 115) and women (n = 115) aged 20-70 years who performed 15 W min-1 cycle ergometer exercise tests. Three equations were developed for each gender using multiple linear regression with the non-exercise predictor variables of age and height, age and mass, and age and fat-free mass (FFM). The assumptions of regression analysis were examined and the predicted residual sum of squares (PRESS) method was used to cross-validate each equation. Healthy and diseased individual subject data from the literature were used to externally validate our lower reference limit statistics. The equations developed meet the assumptions of regression analysis and have an accuracy similar to the non-exercise prediction equations in the literature with R2 values of approximately 0.581. The PRESS method revealed that the equations are generalizable, i.e. may be used in future studies without a significant loss of accuracy. The lower reference limit predictions for the healthy and diseased individual subject data from the literature produced few miscategorizations unless the subjects were obese and mass was used as a predictor variable. In conclusion, the equations and SEE generated in this study can be used to predict an accurate and valid VO2max lower reference limit for a given subject.

Adult↗

PubMed2002

Testosterone-induced increase in muscle size in healthy young men is associated with muscle fiber hypertrophy.

Administration of replacement doses of testosterone to healthy hypogonadal men and supraphysiological doses to eugonadal men increases muscle size. To determine whether testosterone-induced increase in muscle size is due to muscle fiber hypertrophy, 61 healthy men, 18-35 yr of age, received monthly injections of a long-acting gonadotropin-releasing hormone (GnRH) agonist to suppress endogenous testosterone secretion and weekly injections of 25, 50, 125, 300, or 600 mg testosterone enanthate (TE) for 20 wk. Thigh muscle volume was measured by magnetic resonance imaging (MRI) scan, and muscle biopsies were obtained from vastus lateralis muscle in 39 men before and after 20 wk of combined treatment with GnRH agonist and testosterone. Administration of GnRH agonist plus TE resulted in mean nadir testosterone concentrations of 234, 289, 695, 1,344, and 2,435 ng/dl at the 25-, 50-, 125-, 300-, and 600-mg doses, respectively. Graded doses of testosterone administration were associated with testosterone dose and concentration-dependent increase in muscle volume measured by MRI (changes in vastus lateralis volume, -4, +7, +15, +32, and +48 ml at 25-, 50-, 125-, 300-, and 600-mg doses, respectively). Changes in cross-sectional areas of both type I and II fibers were dependent on testosterone dose and significantly correlated with total (r = 0.35, and 0.44, P < 0.0001 for type I and II fibers, respectively) and free (r = 0.34 and 0.35, P < 0.005) testosterone concentrations during treatment. The men receiving 300 and 600 mg of TE weekly experienced significant increases from baseline in areas of type I (baseline vs. 20 wk, 3,176 +/- 186 vs. 4,201 +/- 252 microm(2), P < 0.05 at 300-mg dose, and 3,347 +/- 253 vs. 4,984 +/- 374 microm(2), P = 0.006 at 600-mg dose) muscle fibers; the men in the 600-mg group also had significant increments in cross-sectional area of type II (4,060 +/- 401 vs. 5,526 +/- 544 microm(2), P = 0.03) fibers. The relative proportions of type I and type II fibers did not change significantly after treatment in any group. The myonuclear number per fiber increased significantly in men receiving the 300- and 600-mg doses of TE and was significantly correlated with testosterone concentration and muscle fiber cross-sectional area. In conclusion, the increases in muscle volume in healthy eugonadal men treated with graded doses of testosterone are associated with concentration-dependent increases in cross-sectional areas of both type I and type II muscle fibers and myonuclear number. We conclude that the testosterone induced increase in muscle volume is due to muscle fiber hypertrophy.

Adolescent↗