Extracellular and cellular Hsp72 differ as biomarkers in acute exercise/environmental stress and recovery.

Stress-inducible Hsp72 is a potential biomarker to track risk of exertional heat illness during exercise/environmental stress. Characterization of extracellular (eHsp72) vs cellular Hsp72 (iHsp72) responses is required to define the appropriate use of Hsp72 as a reliable biomarker. In each of four repeat visits, participants (n = 6 men, 4 trials; total n = 24): (a) passively dehydrated overnight, (b) exercised (2 h) with no fluid in a hot, humid environmental chamber, (c) rested and rehydrated (1 h), (d) maximally exercised for 0.5 h, and (e) returned after 24 h of at-home recovery and rehydration. We measured rectal temperature, hydration status (% body mass loss, urine markers, serum osmolality), and Hsp72 (ELISA, flow cytometry. eHsp72 (circulating) and iHsp72 (CD3+ PBMCs) correlated (P < 0.05) with markers of heat, exercise, and dehydration stresses. eHsp72 immediately post-exercise (>15% above baseline, P < 0.05) decreased back to baseline levels by 1 h post-exercise, but iHsp72 expression continued to rise and remained elevated 24 h post-exercise (~2.5-fold baseline, P < 0.05). These data suggest that in addition to the classic physiological biomarkers of exercise heat stress, using cellular Hsp72 as an indicator of lasting effects of stress into recovery may be most appropriate for determining long-term effects of stress on risk for exertional heat illness.

Muscle conduction velocity, strength, neural activity, and morphological changes after eccentric and concentric training.

This study compared the effects of concentric and eccentric training on neuromuscular adaptations in young subjects. Twenty-two men and women were assigned to one of two groups: concentric (CON, n = 11) and eccentric (ECC, n = 11) training. Training consisted of 6 weeks of isokinetic exercise, performed twice weekly, starting with two sets of eight repetitions, and progressing to five sets of 10 repetitions. Subjects were tested in strength variables [concentric, eccentric, and isometric peak torque (PT), and rate of force development (RFD)], muscle conduction velocity (CV), neuromuscular activity, vastus lateralis (VL) muscle thickness, and echo intensity as determined by ultrasonography. There were similar increases in the concentric and eccentric PTs in both the CON and ECC groups (P < 0.01), but only the ECC group showed an increase in isometric PT (P < 0.001). Similarly, both groups exhibited increased VL muscle thickness, CV, and RFD, and reduced VL echo intensity (P < 0.05). Significant correlations were observed among the relative changes in the neuromuscular outcomes and training variables (e.g., total work, average PT) (r = 0.68-0.75, P < 0.05). The results showed that both training types similarly improved dynamic PT, CV, RFD, and muscle thickness and quality during the early weeks of training.

Neuromuscular adaptations to constant vs. variable resistance training in older men.

This study examined the effects of constant or variable external resistance training on neuromuscular adaptations in the lower limbs of older men. 37 subjects (age 65±4 year) were quasi-randomly assigned to the constant or variable training group, or a non-training control group. Training consisted of a 20-week medium-intensity, high volume resistance training program. Maximum bilateral concentric and isometric force production of the leg extensors as well as repetitions-to-failure test were performed pre-, mid- and post-training. Vastus lateralis muscle cross-sectional area was assessed by ultrasound and lean leg mass was assessed by dual-energy x-ray absorptiometry. Both training groups significantly increased force production of the leg extensors (variable: 26 kg, 95% CI=12-39, P<0.01; constant: 31 kg, 95% CI=19-43, P<0.01) and VL cross-sectional area (variable: 1.5 cm2, 95% CI=0.03-3.1, P=0.046; constant: 3 cm2, 95% CI=1.2-4.8, P=0.002). However, only the variable training group significantly improved repetitions to failure performance (704 kg, 95% CI=45-1 364, P=0.035). Only the variable resistance training group improved fatigue-resistance properties, which may be an important adaptation to maintain exercise and functional capacity in older individuals.

Peripheral QCT sector analysis reveals early exercise-induced increases in tibial bone mineral density.

OBJECTIVES: The purpose of this controlled trial was to determine whether subtle changes in mineralization and geometry of the tibia were evident following short term exercise interventions. METHODS: Fifty-seven female volunteers (age 20.1±1.6) were randomized to one of four, 13-week training groups: sedentary control, resistance training, aerobic training, or combined aerobic-resistance. A pQCT image analysis software was developed and used to analyze images taken at sites 4%, 38% and 66% from the distal tibia at baseline and at completion of training. Parameters of bone mineral density, geometry and strength were determined for the entire scan cross-section and for each of six 60° polar sectors. Repeated-measures ANOVA and Fisher's LSD post hoc tests analyzed the effects of training over time. RESULTS: Trabecular density (TrDn) at the 4% site increased from 279.8±37.1 to 283.1±36.0 mg/cm(3) in the aerobic group, and from 285.1±24.6 to 287.5±22.9 mg/cm(3) in the combined group over the study period (P≤0.001). Regional sector analyses revealed that impact exercises resulted in localized changes to the medial aspect of the tibia. Small increases in total bone area were observed in the diaphysis (38% site) (P<0.05). CONCLUSIONS: Subtle, regional increases in trabecular density may be an early measurable manifestation of bone quality changes.

Molecular signaling in muscle is affected by the specificity of resistance exercise protocol.

Mammalian target of rapamycin and mitogen-activated protein kinase (MAPK) signaling pathways have been highlighted as important for muscle adaptations and thus, they may distinguish adaptations to different exercises. Typically, resistance exercise designed for muscle hypertrophy has moderate intensity (60-80% of one repetition maximum, 1 RM) while one prioritizing maximal strength with minor hypertrophy has a higher intensity (≥90% of 1 RM). Eight untrained men (28.4 ± 3.7 years) conducted two different bilateral leg press exercise protocols: hypertrophic (5 × 10 RM) and pure maximal strength (15 × 1 RM) in a counterbalanced, cross-over design with 1 week between exercises. Vastus lateralis muscle biopsies were taken before and 0.5 h after resistance exercise, or in six controls (26.5 ± 3.6 years) who rested. The phosphorylation of p70S6K (Thr(421) /Ser(424) ), rpS6 (Ser(240/244) and Ser(235/236) ) and MAPK p38 as increased (∼2-16 fold) after both exercise protocols. However, the phosphorylation of MAPK Erk1/2 and p70S6K at Thr(389) increased only after 5 × 10 RM. The increase in the phosphorylation of p70S6K (Thr(421) /Ser(424) ), rpS6 (Ser(235/236) ) and Erk1/2 were higher after 5 × 10 RM (P<0.05). No changes were seen in controls. In conclusion, MAPK signaling is greater after hypertrophic than maximal strength exercise protocol. This may mediate adaptations specific to these different types of training regimens.

Effects of strength, endurance and combined training on muscle strength, walking speed and dynamic balance in aging men.

The aim of this study was to examine effects of 21-week twice weekly strength (ST), endurance (ET) and combined (ST + ET 2 + 2 times a week) (SET) training on neuromuscular, endurance and walking performances as well as balance. 108 healthy men (56.3 ± 9.9 years) were divided into three training (ST; n = 30, ET; n = 26, SET; n = 31) groups and controls (C n = 21). Dynamic 1RM and explosive leg presses (1RMleg, 50%1RMleg), peak oxygen uptake using a bicycle ergometer (VO(2peak)), 10 m loaded walking time (10WALK) and dynamic balance distance (DYND) were measured. Significant increases were observed in maximal 1RMleg of 21% in ST (p < 0.001) and 22% in SET (p < 0.001) and in explosive 50%1RMleg of 7.5% in ST (p = 0.005) and 10.2% in SET (p < 0.001). VO(2peak) increased by 12.5% in ET (p = 0.001) and 9.8% in SET (p < 0.001). Significant decreases occurred in 10WALK in ST (p < 0.001) and SET (p = 0.003) and also in DYND of -10.3% in ST (p = 0.002) and -8% in SET (p = 0.028). The changes in C remained minor in all variables. In conclusion, ST and SET training produced significant improvements in maximal and explosive strength, walking speed and balance without any interference effect in SET. Significant but moderate relationships were observed between strength and dynamic balance and walking speed, while no corresponding correlations were found in the ET group.

A novel, noninvasive transdermal fluid sampling methodology: IGF-I measurement following exercise.

This study tested the hypothesis that transdermal fluid (TDF) provides a more sensitive and accurate measure of exercise-induced increases in insulin-like growth factor-I (IGF-I) than serum, and that these increases are detectable proximal, but not distal, to the exercising muscle. A novel, noninvasive methodology was used to collect TDF, followed by sampling of total IGF-I (tIGF-I) and free IGF-I (fIGF-I) in TDF and serum following an acute bout of exercise. Experiment 1: eight men (23 ± 3 yrs, 79 ± 7 kg) underwent two conditions (resting and 60 min of cycling exercise at 60% Vo(2)(peak)) in which serum and forearm TDF were collected for comparison. There were no significant changes in tIGF-I or fIGF-I in TDF obtained from the forearm or from serum following exercise (P > 0.05); however, the proportion of fIGF-I to tIGF-I in TDF was approximately fourfold greater than that of serum (P ≤ 0.05). These data suggest that changes in TDF IGF-I are not evident when TDF is sampled distal from the working tissue. To determine whether exercise-induced increases in local IGF-I could be detected when TDF was sampled directly over the active muscle group, we performed a second experiment. Experiment 2: fourteen subjects (22 ± 4 yr, 68 ± 11 kg) underwent an acute plyometric exercise condition consisting of 10 sets of 10 plyometric jumps with 2-min rest between sets. We observed a significant increase in TDF tIGF-I following exercise (P ≤ 0.05) but no change in serum tIGF-I (P > 0.05). Overall, these data suggest that TDF may provide a noninvasive means of monitoring acute exercise-induced changes in local IGF-I when sampled in proximity to exercising muscles. Moreover, our finding that the proportion of free to tIGF-I was greater in TDF than in serum suggests that changes in local IGF-I may be captured more readily using this system.

Effects of combined endurance and strength training on muscle strength, power and hypertrophy in 40-67-year-old men.

Both strength and endurance training have several positive effects on aging muscle and physical performance of middle-aged and older adults, but their combination may compromise optimal adaptation. This study examined the possible interference of combined strength and endurance training on neuromuscular performance and skeletal muscle hypertrophy in previously untrained 40-67-year-old men. Maximal strength and muscle activation in the upper and lower extremities, maximal concentric power, aerobic capacity and muscle fiber size and distribution in the vastus lateralis muscle were measured before and after a 21-week training period. Ninety-six men [mean age 56 (SD 7) years] completed high-intensity strength training (S) twice a week, endurance training (E) twice a week, combined training (SE) four times per week or served as controls (C). SE and S led to similar gains in one repetition maximum strength of the lower extremities [22 (9)% and 21 (8)%, P<0.001], whereas E and C showed minor changes. Cross-sectional area of type II muscle fibers only increased in S [26 (22)%, P=0.002], while SE showed an inconsistent, non-significant change [8 (35)%, P=0.73]. Combined training may interfere with muscle hypertrophy in aging men, despite similar gains in maximal strength between the strength and the combined training groups.

Serum basal hormone concentrations, nutrition and physical fitness during strength and/or endurance training in 39-64-year-old women.

We examined effects of 21 weeks of strength and/or endurance training and nutrition on serum hormones and physical fitness in 39-64-year-old women. Subjects (n=79) were randomized into the endurance group (E), strength group (S), combined group (SE) and controls (C). Total body strength training and high-intensity bicycle training were used. Average energy and nutrient intake remained the same in all groups. Body fat (dual energy X-ray absorptiometry) decreased significantly in all training groups and body mass index in E, SE and C. Only SE increased total body lean mass (2.2%, p=0.001), between groups p=0.044. Maximal cycling power increased more in E (16%) and SE (17%) than in S (8%)(all p<0.001), between groups p<0.001. Knee extension strength increased only in S (7%, p=0.006) and SE (11%, p<0.001). The changes in serum hormones did not differ between the groups, except insulin-like growth factor-1 (p=0.028), characterized by an 8% (p=0.097) increase in SE and a 7% (p=0.074) decrease in C. In women combined training led to marked improvements in physical fitness and body composition. Energy and protein intake was sufficient to ensure training-induced adaptations in muscle mass and physical fitness in response to both endurance and strength training, even though the energy balance was slightly negative in the endurance-trained groups.

Strength training in endurance runners.

This study examined effects of periodized maximal versus explosive strength training and reduced strength training, combined with endurance training, on neuromuscular and endurance performance in recreational endurance runners. Subjects first completed 6 weeks of preparatory strength training. Then, groups of maximal strength (MAX, n=11), explosive strength (EXP, n=10) and circuit training (C, n=7) completed an 8-week strength training intervention, followed by 14 weeks of reduced strength training. Maximal strength (1RM) and muscle activation (EMG) of leg extensors, countermovement jump (CMJ), maximal oxygen uptake (VO(2MAX)), velocity at VO(2MAX) (vVO(2MAX)) running economy (RE) and basal serum hormones were measured. 1RM and CMJ improved (p<0.05) in all groups accompanied by increased EMG in MAX and EXP (p<0.05) during strength training. Minor changes occurred in VO(2MAX), but vVO(2MAX) improved in all groups (p<0.05) and RE in EXP (p<0.05). During reduced strength training 1RM and EMG decreased in MAX (p<0.05) while vVO(2MAX) in MAX and EXP (p<0.05) and RE in MAX (p<0.01) improved. Serum testosterone and cortisol remained unaltered. Maximal or explosive strength training performed concurrently with endurance training was more effective in improving strength and neuromuscular performance and in enhancing vVO (2MAX) and RE in recreational endurance runners than concurrent circuit and endurance training.

Weakness Is Associated with Time to Incident Chronic Heart Failure in Aging Americans.

OBJECTIVE: Handgrip strength is considered a biomarker of nutritional status and strength capacity, which are both linked to heart complications. However, it is not well understood how weakness, as measured by handgrip strength, factors into common heart conditions seen in aging adults such as chronic heart failure (CHF). The purpose of this study was to determine the association between weakness and incident CHF for aging Americans. DESIGN: Longitudinal-Panel. SETTING: Physical measures were completed during enhanced face-to-face interviews. The core interview was typically conducted over the telephone. PARTICIPANTS: Data from 17,431 adults aged at least 50 years who identified as Black or White, completed interviews without a proxy, and participated in at least one wave of the 2006-2014 waves of the Health and Retirement Study were included. MEASUREMENTS: Handgrip strength was measured with a hand-held dynamometer. Healthcare provider diagnosed CHF was self-reported at each wave. Sex- and race-specific maximal handgrip strength cut-points were used for determining weakness (Black men: <40-kilograms, Black women: <31-kilograms, White men: <35-kilograms, White women: <22-kilograms). A covariate-adjusted Cox model analyzed the association between weakness and incident CHF. RESULTS: Of those included, 5,397 (31.0%) were weak and 327 (1.9%) developed CHF during the mean follow-up of 4.7±2.7 years. Those who were weak had a 35% higher risk (hazard ratio: 1.35; 95% confidence interval: 1.05, 1.74) of developing CHF, compared to those who were not-weak. CONCLUSION: Measures of handgrip strength should be utilized by healthcare providers for assessing age-related weakness, nutritional status, and CHF risk. Likewise, interventions aiming to prevent or treat CHF in aging adults should incorporate measures of handgrip strength for helping to determine efficacy of intervention programs.

Endogenous opioids modify dyspnoea during treadmill exercise in patients with COPD.

Exogenous opioid drugs, such as morphine, relieve breathlessness. The present study hypothesis was that endogenous opioids, released during the stress of exercise, modify dyspnoea in patients with chronic obstructive pulmonary disease. After familiarisation, patients performed an incremental treadmill exercise test followed by constant work on the treadmill for 10 min. At subsequent visits (2 to 3 days apart), patients received two puffs of albuterol, had a catheter placed in an arm vein for removal of blood to measure beta-endorphin immunoreactivity, received normal saline or 10 mg of naloxone intravenously in randomised order, and then performed high-intensity constant work rate exercise on the treadmill. The mean+/-sd age of the 17 patients (eight females and nine males) was 63+/-7 yrs, and post-bronchodilator forced expiratory volume in one second was 50+/-17% predicted. In both conditions, beta-endorphin levels increased three-fold from rest to end-exercise. The regression slope of breathlessness as a function of oxygen consumption (primary outcome), mean ratings of breathlessness throughout exercise and peak ratings of breathlessness were significantly higher with naloxone than normal saline. There were no differences in physiological responses throughout exercise between conditions. In conclusion, endogenous opioids modify dyspnoea during treadmill exercise in patients with chronic obstructive pulmonary disease by apparent alteration of central perception.

Neuromuscular fatigue after resistance training.

This study examined the effects of heavy resistance training on dynamic exercise-induced fatigue task (5 x 10RM leg-press) after two loading protocols with the same relative intensity (%) (5 x 10RM(Rel)) and the same absolute load (kg) (5 x 10RM(Abs)) as in pretraining in men (n=12). Maximal strength and muscle power, surface EMG changes [amplitude and spectral indices of muscle fatigue], and metabolic responses (i.e.blood lactate and ammonia concentrations) were measured before and after exercise. After training, when the relative intensity of the fatiguing dynamic protocol was kept the same, the magnitude of exercise-induced loss in maximal strength was greater than that observed before training. The peak power lost after 5 x 10RM(Rel) (58-62%, pre-post training) was greater than the corresponding exercise-induced decline observed in isometric strength (12-17%). Similar neural adjustments, but higher accumulated fatigue and metabolic demand were observed after 5 x 10RM(Rel). This study therefore supports the notion that similar changes are observable in the EMG signal pre- and post-training at fatigue when exercising with the same relative load. However, after training the muscle is relatively able to work more and accumulate more metabolites before task failure. This result may indicate that rate of fatigue development (i.e. power and MVC) was faster and more profound after training despite using the same relative intensity.

Strength, [corrected] endurance or combined training elicit diverse skeletal muscle myosin heavy chain isoform proportion but unaltered androgen receptor concentration in older men.

We investigated whether the myosin heavy chain (MyHC) proportion and androgen receptor (AR) concentration in skeletal muscle differ following 21 weeks of strength, endurance and combined training in untrained older men. Strength (S) and endurance (E) groups trained twice per week and combined (S+E) group trained four times per week (two strength and two endurance). Muscle biopsies were obtained before and after the training period from m. vastus lateralis (VL) and AR mRNA and protein concentration and MyHC proportion were determined. 1RM increased during the training period in S, S+E and E but the changes were greater in S and S+E than in E. Statistically significant increases were observed only in S and S+E in maximal isometric force as well as in VL thickness. VO (2max) increased significantly only in E. MyHCIIa proportion increased in S, while MyHCIIa proportion decreased and MyHCI increased (p<0.05) in E. No statistically significant changes were observed in serum testosterone and in AR mRNA or protein concentrations. The present results indicate that 21 weeks of strength, endurance or combined training changed MyHC proportion according to the training method but did not have an effect on AR mRNA or protein expression in skeletal muscle at rest.

Hormonal responses to a 160-km race across frozen Alaska.

BACKGROUND: Severe physical and environmental stress seems to have a suppressive effect on the hypothalamic-pituitary-gonadal (HPG) axis in men. Examining hormonal responses to an extreme 160-km competition across frozen Alaska provides a unique opportunity to study this intense stress. OBJECTIVE: To examine hormonal responses to an ultra-endurance race. METHODS: Blood samples were obtained from 16 men before and after racing and analyzed for testosterone, interleukin-6 (IL-6), growth hormone (GH) and cortisol. Six subjects (mean (SD) age 42 (7) years; body mass 78.9 (7.1) kg; height 1.78 (0.05) m raced by bicycle (cyclists) and 10 subjects (age 35 (9) years; body mass 77.9 (10.6) kg; height, 1.82 (0.05) m) raced by foot (runners). Mean (SD) finish times were 21.83 (6.27) and 33.98 (6.12) h, respectively. RESULTS: In cyclists there were significant (p< or =0.05) mean (SD) pre-race to post-race increases in cortisol (254.83 (135.26) to 535.99 (232.22) nmol/l), GH (0.12 (0.23) to 3.21 (3.33) microg/ml) and IL-6 (2.36 (0.42) to 10.15 (3.28) pg/ml), and a significant decrease in testosterone (13.81 (3.19) to 5.59 (3.74) nmol/l). Similarly, in runners there were significant pre-race to post-race increases in cortisol (142.09 (50.74) to 452.21 (163.40) ng/ml), GH (0.12 (0.23) to 3.21 (3.33) microg/ml) and IL-6 (2.42 (0.68) to 12.25 (1.78) pg/ml), and a significant decrease in testosterone (12.32 (4.47) to 6.96 (3.19) nmol/l). There were no significant differences in the hormonal levels between cyclists and runners (p>0.05). CONCLUSIONS: These data suggest a suppression of the hypopituitary-gonadal axis potentially mediated by amplification of adrenal stress responses to such an ultra-endurance race in environmentally stressful conditions.

Nutritional aspects of women strength athletes.

Strength training elicits sports related and health benefits for both men and women. Although sexual dimorphism is observed in exercise metabolism, there is little information outlining the specific nutritional needs of women strength athletes. Many women athletes restrict energy intake, specifically fat consumption, in order to modify body composition, but this nutritional practice is often counter-productive. Compared to men, women appear to be less reliant on glycogen during exercise and less responsive to carbohydrate mediated glycogen synthesis during recovery. Female strength athletes may require more protein than their sedentary and endurance training counterparts to attain positive nitrogen balance and promote protein synthesis. Therefore, women strength athletes should put less emphasis on a very high carbohydrate intake and more emphasis on quality protein and fat consumption in the context of energy balance to enhance adaptations to training and improve general health. Attention to timing of nutrient ingestion, macronutrient quality, and dietary supplementation (for example, creatine) are briefly discussed as important components of a nutritionally adequate and effective strength training diet for women.

Effects of prolonged combined strength and endurance training on physical fitness, body composition and serum hormones in women with rheumatoid arthritis and in healthy controls.

OBJECTIVE: The effects of a 21-week combined strength and endurance training period on physical fitness, serum hormone concentrations, and subcutaneous fat in 23 women with rheumatoid arthritis (RA) and in 12 matched healthy subjects was studied. METHODS: The measurements included leg extension forces and EMG activity, muscle and fat thickness on thigh, maximal oxygen uptake (VO2max) and serum concentrations of testosterone, free testosterone, growth hormone, insulin-like growth factor-I (IGF-I), dehydroepiandrosterone sulphate (DHEAS), and cortisol. RESULTS: During the training period significant increases took place in VO2max, muscle strength and EMG activity in both groups. The increases of the quadriceps femoris thickness were 6.5% (p < 0.001) in the healthy controls and 7.4% (p < 0.001) in the RA cases. The decreases in subcutaneous fat thicknesses were 9.9% (p < 0.001) and 12.3% (p < 0.001), respectively. No significant changes were found in serum hormone concentrations, but RA women showed lower levels of IGF-I during the whole follow-up. CONCLUSIONS: In RA women with stable disease the combined strength and endurance training increases physical fitness. Further the training increases muscle mass and decreases subcutaneous fat. It may decrease risks of cardiovascular diseases in RA patients. The intensive training had minor effects on serum hormone concentrations.

Effect of resistance training on resting metabolic rate and its estimation by a dual-energy X-ray absorptiometry metabolic map.

BACKGROUND/OBJECTIVES: Fat-free mass (FFM) is the major predictor of resting metabolic rate (RMR). As protein supplementation during resistance training may augment gains in FFM, we investigated the effects of resistance training combined with protein supplementation on RMR and whether RMR responses could be estimated by a dual-energy X-ray absorptiometry (DXA) metabolic map. SUBJECTS/METHODS: Healthy adults completed a whole-body periodized resistance training program consisting of 96 workouts (~9 months). Participants were randomly assigned to supplement with whey protein (whey; n=18), soy protein (soy; n=21) or carbohydrate (carb; n=22). RMR was measured using indirect calorimetry (RMR(IC)) and estimated by DXA metabolic mapping (RMR(MM)) pretraining and posttraining. RESULTS: RMR(IC) increased from pretraining to posttraining in the whole cohort (1653±302 to 1726±291 kcal/day, P=0.001) without differences between the groups. Delta RMR(IC) and RMR(MM) (73±158 vs 52±41 kcal/day were not significantly different by t-test (P=0.303), although they were not significantly correlated (r=0.081; P=0.535). Stepwise regression identified 43% of the shared variance in delta RMR(IC) using total serum thyroxine, RMR(IC) and FFM at baseline (P=0.009). CONCLUSIONS: These results indicate that 9 months of resistance training significantly increased RMR ~5% on average, but there was wide variability between individuals, which can be partially accounted for by changes in FFM and thyroid hormones.

Endurance and resistance exercise induce muscle fiber type specific responses in androgen binding capacity.

This study examined the effects of different exercise training programs on androgen receptor content and receptor affinity to dihydrotestosterone in fast glycolytic (FG) and slow oxidative (SO) skeletal muscle fibers in rats. Twenty-four male Sprague-Dawley rats were equally divided into three groups: control, endurance exercise trained and resistance exercise trained. After the exercise programs were completed, the extensor digitorum longus (EDL), predominantly a FG muscle, and the soleus, predominantly a SO muscle, were isolated, weighted and both androgen receptor content and affinity to dihydrotestosterone were determined. Resistance training evoked a significant (P < 0.05) hypertrophic response in the soleus but not the EDL. Endurance training was not associated with any significant hypertrophy in either the soleus or the EDL. Neither the endurance nor the resistance training program resulted in changes in androgen receptor affinity to dihydrotestosterone. However, alterations in androgen receptor content were noted. The endurance training program resulted in a significant increase in androgen receptor content in the soleus, but no significant difference in the EDL. The resistance training program elicited a significant decrease in androgen receptor content in the soleus, and a significant increase in the EDL. These results indicate that different exercise stimuli induce changes in androgen receptor content that are specific to skeletal muscle fiber type.

Basal concentrations and acute responses of serum hormones and strength development during heavy resistance training in middle-aged and elderly men and women.

Effects of 6 months of heavy resistance training combined with explosive exercises on both basal concentrations and acute responses of total and free testosterone, growth hormone (GH), dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEAS), cortisol and sex hormone-binding globulin (SHBG), as well as voluntary neural activation and maximal strength of knee extensors were examined in 10 middle-aged men (M40; 42 +/- 2 years), 11 middle-aged women (W40; 39 +/- 3 years), 11 elderly men (M70; 72 +/- 3 years), and in 10 elderly women (W70; 67 +/- 3 years). The maximal integrated electromyographic (iEMG) and 1 repetition maximum (RM) knee-extension values remained unaltered in all groups during a 1-month control period with no strength training. During the 6-month training the 1RM values increased in M40 by 27 +/- 9% (p < .001), in M70 by 16 +/- 6% (p < .001), in W40 by 28 +/- 11% (p < .001), and in W70 by 24 +/- 10% (p < .001). The iEMGs of the vastus lateralis and medialis muscles increased(p < .05-.001) in M40, M70, W40, and W70. No systematic changes occurred during the experimental period in the mean concentrations of serum total and free testosterone, DHEA, DHEAS, GH, cortisol, or SHBG. However, the mean levels of individual serum free testosterone in W70 and serum testosterone in the total group of women correlated with the individual changes recorded in strength during the training (r = .55,p <.05; and r = .43,p <.05). The single exercise session both before and after the training resulted in significant responses in serum total and free testosterone concentrations in both male groups (p <.05-.01), but not in the female groups, as well as in serum GH levels in all groups (p <.05-.01) except W70 (ns). In summary, the present strength training led to great increases in maximal strength not only in middle-aged but also in elderly men and women. The strength gains were accompanied by large increases in the maximal voluntary activation of the trained muscles. None of the groups showed systematic changes in the mean serum concentrations of hormones examined. However, a low level of testosterone, especially in older women, may be a limiting factor in strength development and testosterone could mediate interactions with the nervous system contributing to strength development. The physiological significance of the lack of acute responsiveness of serum GH to heavy resistance exercise in older women for their trainability during prolonged strength training requires further examination.