The exercise-induced growth hormone response in athletes

Impacto da atividade física e esportes sobre o crescimento e puberdade de crianças e adolescentes

OBJETIVO: Apresentar revisão atualizada e crítica sobre o impacto do esporte e da atividade física no crescimento, desenvolvimento puberal e mineralização óssea de crianças e adolescentes. FONTES DE DADOS: Pesquisa bibliográfica nos bancos de dados Medline e Lilacs (1987-2007), selecionando os artigos escritos em inglês, português ou espanhol, a partir dos descritores "esportes" e "exercícios", em combinação com "crescimento", "puberdade" e "mineralização óssea". Foram examinados 252 artigos e 48 deles selecionados. SÍNTESE DOS DADOS: Diferentes modalidades esportivas não aumentam ou diminuem a estatura. Ocorre um viés de seleção, no qual fatores constitucionais determinam a seleção de biótipos privilegiados para determinados esportes. O exercício físico leve a moderado estimula o crescimento e deve ser incentivado. A atividade física extenuante, principalmente quando associada à restrição dietética, afeta o crescimento, o desenvolvimento puberal, a função reprodutiva e a mineralização óssea. A musculação praticada por jovens pré-púberes pode ser prejudicial, se não for realizada sob supervisão, já que há um potencial risco de lesão na cartilagem de crescimento. Entretanto, quando bem supervisionada, pode levar a um aumento de força e resistência muscular. CONCLUSÕES: Os efeitos deletérios dos esportes sobre o crescimento e desenvolvimento só foram observados em atletas de elite submetidos a treinamento intensivo e restrição alimentar. Alterações hormonais e de citocinas inflamatórias são parte da fisiopatologia desse processo. É necessário que estudos longitudinais avaliem as repercussões da atividade física recreacional sobre a estatura final.

Effect of hydration state on resistance exercise-induced endocrine markers of anabolism, catabolism, and metabolism

Hypohydration (decreased total body water) exacerbates the catabolic hormonal response to endurance exercise with unclear effects on anabolic hormones. Limited research exists that evaluates the effect of hypohydration on endocrine responses to resistance exercise; this work merits attention as the acute postexercise hormonal environment potently modulates resistance training adaptations. The purpose of this study was to examine the effect of hydration state on the endocrine and metabolic responses to resistance exercise. Seven healthy resistance-trained men (age = 23 ± 4 yr, body mass = 87.8 ± 6.8 kg, body fat = 11.5 ± 5.2%) completed three identical resistance exercise bouts in different hydration states: euhydrated (EU), hypohydrated by ∼2.5% body mass (HY25), and hypohydrated by ∼5.0% body mass (HY50). Investigators manipulated hydration status via controlled water deprivation and exercise-heat stress. Cortisol, epinephrine, norepinephrine, testosterone, growth hormone, insulin-like growth factor-I, insulin, glucose, lactate, glycerol, and free fatty acids were measured during euhydrated rest, immediately preceding resistance exercise, immediately postexercise, and during 60 min of recovery. Body mass decreased 0.2 ± 0.4, 2.4 ± 0.4, and 4.8 ± 0.4% during EU, HY25, and HY50, respectively, supported by humoral and urinary changes that clearly indicated subjects achieved three distinct hydration states. Hypohydration significantly 1) increased circulating concentrations of cortisol and norepinephrine, 2) attenuated the testosterone response to exercise, and 3) altered carbohydrate and lipid metabolism. These results suggest that hypohydration can modify the hormonal and metabolic response to resistance exercise, influencing the postexercise circulatory milieu.

Growth hormone isoform responses to GABA ingestion at rest and after exercise

Oral administration of the amino acid/inhibitory neurotransmitter gamma aminobutyric acid (GABA) reportedly elevates resting serum growth hormone (GH) concentrations.

PURPOSE

To test the hypothesis that GABA ingestion stimulates immunoreactive GH (irGH) and immunofunctional GH (ifGH) release at rest and that GABA augments the resistance exercise-induced irGH/ifGH responses.

METHODS

Eleven resistance-trained men (18-30 yr) participated in this randomized, double-blind, placebo-controlled, crossover study. During each experimental bout, participants ingested either 3 g of GABA or sucrose placebo (P), followed either by resting or resistance exercise sessions. Fasting venous blood samples were acquired immediately before and at 15, 30, 45, 60, 75, and 90 min after GABA or P ingestion and were assayed for irGH and ifGH.

RESULTS

At rest, GABA ingestion elevated both irGH and ifGH compared with placebo. Specifically, peak concentrations of both hormones were elevated by about 400%, and the area under the curve (AUC) was elevated by about 375% (P < 0.05). Resistance exercise (EX-P) elevated time-point (15-60 min) irGH and ifGH concentrations compared with rest (P < 0.05). The combination of GABA and resistance exercise (EX-GABA) also elevated the peak, AUC, and the 15- to 60-min time-point irGH and ifGH responses compared with resting conditions (P < 0.05). Additionally, 200% greater irGH (P < 0.01) and 175% greater ifGH (P < 0.05) concentrations were observed in the EX-GABA than in the EX-P condition, 30 min after ingestion. GABA ingestion did not alter the irGH to ifGH ratio, and, under all conditions, ifGH represented approximately 50% of irGH.

CONCLUSIONS

Our data indicate that ingested GABA elevates resting and postexercise irGH and ifGH concentrations. The extent to which irGH/ifGH secretion contributes to skeletal muscle hypertrophy is unknown, although augmenting the postexercise irGH/ifGH response may improve resistance training-induced muscular adaptations.

Effect of resistance exercise training combined with relatively low vascular occlusion

Previous studies have demonstrated that a low-intensity resistance exercise, combined with vascular occlusion, results in a marked increase in muscular size and strength. We investigated the optimal pressure for reduction of muscle blood flow with resistance exercise to increase the muscular strength and endurance. Twenty-one subjects were randomly divided into four groups by the different application of vascular occlusion pressure at the proximal of thigh: without any pressure (0-pressure group), with a pressure of 50mmHg (50-pressure group), with a pressure of 150mmHg (150-pressure group), and with a pressure of 250mmHg (250-pressure group). The isokinetic muscle strength at angular velocities of 60 and 180 degrees /s, total muscle work, and the cross-sectional knee extensor muscle area were assessed before and after exercise. Exercise was performed three times a week over an 8-week period at an intensity of approximately 20% of one-repetition maximum for straight leg raising and hip joint adduction and maximum force for abduction training. A significant increase in strength at 180 degrees /s was noted after exercise in all subjects who exercised under vascular occlusion. Total muscle work increased significantly in the 50- and 150-pressure groups (P<0.05, P<0.01, respectively). There was no significant increase in cross-sectional knee extensor muscle area in any groups. In conclusion, resistance exercise with relatively low vascular occlusion pressure is potentially useful to increase muscle strength and endurance without discomfort.

Young elite athletes of different sport disciplines present with an increase in pulsatile secretion of growth hormone compared with non-elite athletes and sedentary subjects

Acute exercise is a well-known stimulus for GH secretion but the effect of chronic training on GH secretion still remains equivocal. The aim of our study was to analyse spontaneous pulsatile GH secretion (during a period of 2 hours in the morning) in a group of young elite athletes (EA) compared with non-elite athletes (NEA), and sedentary subjects (SS). Mean and peak GH levels proved significantly higher in EA than in NEA and SS (p=0.0004 and p<0.0001, respectively). The same differences in mean and peak GH levels were also demonstrated in males and females when considered separately (males: p=0.0062 and p=0.0025; females: p=0.0056 and p=0.0032). In addition, GH levels (mean and peak) were higher in females than in males in SS while no differences were demonstrated between the 2 sexes in the EA and NEA groups. IGF-I levels were within the normal range for age in all the subjects with no difference between the 3 groups. Body mass index (BMI) exhibited no difference between groups, while EA showed higher lean mass (p=0.0063) and lower fat mass (p=0.0139) than NEA and SS measured by dual-energy x-ray absorptiometry. A strong positive correlation between GH levels (mean and peak) and hours of training a week was demonstrated (p=0.0101; r2=0.1184; p=0.0022; r2=0.1640, respectively). In conclusion, GH levels were higher in EA than NEA and SS without any modification of IGF-I levels; a strong positive correlation was present between GH levels and intensity of training. An increase in the knowledge of the effect of chronic training on GH secretion could improve the training programme to elicit the greatest exercise- induced GH response.

Activation or inactivation of cardiac Akt/mTOR signaling diverges physiological from pathological hypertrophy

Cardiomyocyte hypertrophy differs according to the stress exerted on the myocardium. While pressure overload-induced cardiomyocyte hypertrophy is associated with depressed contractile function, physiological hypertrophy after exercise training associates with preserved or increased inotropy. We determined the activation state of myocardial Akt signaling with downstream substrates and fetal gene reactivation in exercise-induced physiological and pressure overload-induced pathological hypertrophies. C57BL/6J mice were either treadmill trained for 6 weeks, 5 days/week, at 85-90% of maximal oxygen uptake (VO(2max)), or underwent transverse aortic constriction (TAC) for 1 or 8 weeks. Total and phosphorylated protein levels were determined with SDS-PAGE, and fetal genes by real-time RT-PCR. In the physiologically hypertrophied heart after exercise training, total Akt protein level was unchanged, but Akt was chronically hyperphosphorylated at serine 473. This was accompanied by activation of the mammalian target of rapamycin (mTOR), measured as phosphorylation of its two substrates: the ribosomal protein S6 kinase-1 (S6K1) and the eukaryotic translation initiation factor-4E binding protein-1 (4E-BP1). Exercise training did not reactivate the fetal gene program (beta-myosin heavy chain, atrial natriuretic factor, skeletal muscle actin). In contrast, pressure overload after TAC reactivated fetal genes already after 1 week, and partially inactivated the Akt/mTOR pathway and downstream substrates after 8 weeks. In conclusion, changes in opposite directions of the myocardial Akt/mTOR signal pathway appears to distinguish between physiological and pathological hypertrophies; exercise training associating with activation and pressure overload associating with inactivation of the Akt/mTOR pathway.

Neuroendocrine responses to an acute bout of eccentric-enhanced resistance exercise

PURPOSE

The purpose of this study was to compare the total testosterone (TT), bioavailable testosterone (BT), growth hormone (GH), lactate, and ratings of perceived exertion (RPE) responses between a single bout of traditional (TRAD) and eccentric-enhanced resistance exercise (ECC+) of matched training volumes.

METHODS

Twenty-two previously untrained males (21.9+/-0.8 yr) completed one familiarization and one baseline 1RM testing bout, for the bench press and squat exercises, and then two exercise bouts. During exercise bout 1, all subjects completed a TRAD protocol (four sets of six reps at 52.5% 1RM), and the subsequent exercise bout consisted of either a TRAD or an ECC+ protocol (three sets of six reps at 40% 1RM concentric and 100% 1RM eccentric) for the bench press and squat exercises. Blood samples acquired at rest, immediately after (T1), and 15, 30, 45, and 60 min after exercise were assessed for serum TT, BT, GH, and blood lactate concentrations.

RESULTS

Resting and postexercise TT, BT, and GH were not significantly different between groups. Postexercise TT was not elevated during either bout or in either group, whereas BT increased 15-16% at T1 in both groups during bout 2. Postexercise GH concentrations were elevated 500-7000% above baseline after both protocols. Postexercise lactate accumulation and RPE were greater with ECC+ than TRAD.

CONCLUSION

TRAD and ECC+ show similar neuroendocrine and differing metabolic responses during the early phase of resistance exercise in untrained, college-age men.

Effects of a multi-nutrient supplement on exercise performance and hormonal responses to resistance exercise

The purpose of this study was to determine the influence of a comprehensive multi-component nutritional supplement on performance, hormonal, and metabolic responses to an acute bout of resistance exercise. Nine healthy subjects ingested either Muscle Fuel (MF) or a matched placebo (PL) for 7 days. Subjects then reported to the laboratory, ingested the corresponding supplement, and performed two consecutive days of heavy resistance exercise testing with associated blood draws. MF supplementation improved vertical jump (VJ) power output and the number of repetitions performed at 80% of one repetition maximum (1RM). Additionally, MF supplementation potentiated growth hormone (GH), testosterone, and insulin-like growth factor-1 responses to exercise. Concentrations of circulating myoglobin and creatine kinase (CK) were attenuated immediately following resistance exercise during the MF trial, indicating that MF partially mediated some form of exercise-induced muscle tissue damage. In summary MF enhanced performance and hormonal responses associated with an acute bout of resistance exercise. These responses indicate that MF supplementation augments the quality of an acute bout of resistance exercise thereby increasing the endocrine signaling and recovery following heavy resistance exercise.

[Increase of muscle mass and strength with hormones and other drugs, combined with physical training]

Increasing muscle mass and strength is the aim of some body builders and sportsmen, and is a therapeutic target in hormonal deficiencies, as well as in many clinical situations, when muscle devastation is a life-limiting factor. Human growth hormone, insulin-like growth factor, anabolic-androgen steroids and regulating proteins influencing muscle development and differentiation are used also for delaying the aging processes. Some of the practices are hailed by several myths, mainly because doping cases in certain competitive sports. Physiology, and therapeutic experiences with these substances are reviewed with special reference to physical exercise and to some frail conditions.

Hormonal responses to a long duration exploration in a cave of 700 m depth

We studied the hypothalamus-pituitary adrenocortical, hypothalamus-pituitary and hypothalamus-pituitary thyroid system responses to a long duration activity (about 20 h) practiced in a demanding environment, characterized by darkness, low temperature and high humidity, namely alpine potholing. We performed four blood drawings in five elite potholers: (1) the morning before the performance, (2) at the bottom of the cave (-700 m), (3) at the end of the ascent, and (4) after 24 h of recovery. Two blood drawings as controls were performed on the same potholers, at the same resting time and with the same experimental procedures as the previous ones. Friedman two-way ANOVA test evidenced significant changes through the different time intervals for detrended (i.e., test values minus control values) growth hormone (GH) (P = 0.003), detrended cortisol (P = 0.004) and FT4 (P = 0.002), while this was not true for TSH and FT3. Successively pairwise comparisons were done both through the different time intervals and between test and control values. The rise of GH values during the performance underlines the great intensity and long duration characteristic of potholing as well as the possibility that the climbing sit harness can cause problems due to vascular hypo-perfusion. Cortisol data, peaking before entering the cave, suggest that there was a marked anticipatory stress reaction followed by less stressing phase during the performance. Finally, the rise of FT4 is likely due to the typical increase of free fatty acids that usually occurs during endurance exercise.

Growth hormone and muscle function responses to skeletal muscle ischemia

We examined the effects of ischemia (ISC) alone and with low-intensity exercise (ISC+EX) on growth hormone (GH) and muscle function responses. Nine men (22 +/- 0.7 yr) completed 3 study days: an ISC day (thigh cuff inflated five times, 5 min on, 3 min off), an ISC+EX day [knee extension at 20% maximal voluntary contraction (MVC) with ISC], and a control day. MVCs and submaximal contraction tasks (15 and 30% MVC) were performed before and following the perturbations. Surface electromyogram signals were collected from thigh muscles and analyzed for median frequency and root mean square alterations. Blood samples were collected every 10 min (190 min total) and analyzed for GH concentrations. Peak GH concentrations and GH area under the curve were highest (P < 0.01) on the ISC+EX day (7.5 microg/l and 432 microg.l(-1).min(-1), respectively) compared with the ISC (0.9 microg/l and 76.4 microg.l(-1).min(-1)), and CON (1.1 microg/l and 83.8 microg.l(-1).min(-1)) days. A greater GH pulse amplitude, mass/pulse, and production rate were also observed on the ISC+EX day (P < 0.05). Following the intervention, force production decreased on the ISC and ISC+EX days by 16.1 and 55.8%, respectively, and did not return to baseline values within 5 min of recovery. During the submaximal contractions, median frequency shifted to lower frequencies for most of the muscles examined, and root mean square electromyogram was consistently elevated for ISC+EX day. In conclusion, ISC coupled with resistance exercise acutely increases GH levels and reduces MVC, whereas ISC alone decreases force capacity, without alterations in GH levels.

Effects of resistance exercise and growth hormone administration at low doses on lipid metabolism in middle-aged female rats

hGH (human growth hormone) is a key factor for metabolism as well as for growth. Lack of hGH usually increases LDL (low-density lipoprotein) while impairing exercise capacity and cardiac function [Amato G., Carella C., Fazio S., La Montagna G., Cittadini A., Sabatini D., Marciano-Mone C., Sacca L., and Bellastella A., 1993. Body composition, bone metabolism, and heart structure and function in growth hormone (GH)-deficient adults before and after GH replacement therapy at low doses. J. Clin. Endocrinol. Metab. 77, 1671-1676.]. It is still unclear, however, whether the administration of hGH to humans or animals has a synergic effects on body composition and the desired metabolic parameters with endurance resistance exercise. Therefore, the present study seeks to establish whether or not lipid metabolism is altered by both recombinant GH (growth hormone) and X (resistance exercise) in middle-aged female rats. GH administration resulted in greater weight gain compared with control and exercised animals, but the effect was reduced when combined with exercise. The increased body weight was largely due to increased muscle mass. Exercise did not result in any additional effect of GH on muscle mass. In the exercise group, hepatic HDL (high density lipoprotein) increased compared to the C (control group). The GX (growth hormone+exercise) group's serum and X group's kidney IGF-I (Insulin-like growth factor-I) concentration increased compared to the C group. In G and GX groups, serum insulin and leptin concentrations were higher than in the control, suggesting that GH may induce an insulin resistant state. Any gains in muscle mass were minimal and were not synergistic with exercise. These results suggest that hGH may not be useful for increasing performance in athletes and may induce and acquired insulin resistance.

Growth hormone 1 (GH1) gene and performance and post-race rectal temperature during the South African Ironman triathlon

BACKGROUND

Some studies have suggested that the insertion allele of the ACE gene is associated with endurance performance, including the Ironman triathlon. It is possible that this association is due to genetic linkage between the ACE I/D locus and the T/A variant in intron 4 of the neighbouring GH1 gene. The A variant is associated with lower levels of growth hormone production. Growth hormone has multiple effects, especially on metabolism during exercise and recovery from exercise. Its production during exercise has also been shown to stimulate sweat rate and heat loss.

OBJECTIVE

To determine whether the GH1 gene is associated with the performance and/or post-race rectal temperatures of competitors in the South African Ironman triathlon.

METHODS

A total of 169 of the fastest finishing white male triathletes who completed the 2000 and/or 2001 South African Ironman triathlon and 155 control subjects were genotyped for the T/A variant in the GH1 gene. Post-race rectal temperature was also determined in 103 of these triathletes.

RESULTS

There was no significant difference in the frequency of this polymorphism in the GH1 gene when the fastest finishing triathletes were compared with the control subjects. Post-race rectal temperatures were, however, significantly higher in those triathletes with an AA genotype (mean (SD) 37.7 (0.8) degrees C) compared with those with a TT genotype (37.2 (0.8) degrees C) (p = 0.019).

CONCLUSIONS

The T/A polymorphism in intron 4 of the GH1 gene was not associated with performance of the fastest finishers of the South African Ironman triathlon. Post-race rectal temperatures were, however, significantly higher in the fastest finishing athletes, who were homozygous for a GH1 genotype associated with lower growth hormone production.

GH secretion in acute exercise may result in post-exercise lipolysis

Exercise is a potent stimulator of growth hormone (GH) secretion. We hypothesised that after a short bout of intense exercise GH may increase lipolysis during recovery. In 7 moderately trained young male subjects (21.8 +/- 0.5 years) and 7 moderately trained older male subjects (56.0 +/- 1.0 years) [(2)H(5)] glycerol was infused for 370min to measure glycerol production rate (R(a)), a measure of lipolysis. At 130 min subjects exercised on a cycle ergonometer for 20 min at 70% V(O2 max), followed by rest for 220 min. On a separate occasion the study was repeated in the young subjects with a 1h GH infusion (4microgkg(-1)h(-1)) at 130 min instead of exercise. In response to exercise, catecholamines (p < 0.02) and glycerol R(a) (p < 0.01) increased, peaking during exercise. GH concentration increased in response to exercise (p < 0.01), peaking after exercise (150-160 min) in both groups with no significant difference in peak response between groups. A post-exercise rise in glycerol R(a) was demonstrated in both groups peaking at 265-295 min in the older group (p < 0.002, peak vs. basal) and continuing to rise until 370 min in the young group (p < 0.01, peak vs. basal). The timing and magnitude of this was reproduced with the GH infusion. There was a significant correlation between the peak GH response to exercise and the post-exercise rise in glycerol R(a) measured as area under the curve (r=0.57, p < 0.04). In conclusion, this study provides evidence that the GH response to acute exercise may increase lipolysis during recovery.

Effect of training on GH and IGF-1 responses to a submaximal exercise in football players

To study the effects of regular football training on basal and exercise induced levels of growth hormone (GH) and insulin-like growth factor (IGF-1), 13 young football players were investigated by a submaximal exercise at the beginning of the sporting season in October (S1), at the middle of the season in January (S2) and at the end in May (S3). At each session, an exercise test on an ergogycle was performed for 25 min, beginning with an incremental exercise to reach 90% of theoretical maximal heart, which was maintained for the last 10 min of the test. Venous blood samples were collected at rest, at the end of the exercise and at 30 and 60 min during the recovery period. Plasma lactate and glucose concentrations increased during exercise with no difference found between sessions. GH level increased with exercise at each session but the response was significantly higher in S1 than in S2 and S3 (P<0.01). The GH area under the curve decreased significantly all along the football season (P<0.01); the IGF-1 level did not significantly change during exercise nor with training. Basal insulin-like growth factor binding protein-3 (IGFBP3) remained stable during the three sessions. Football training decreased significantly the exercise-stimulated GH levels all along the football season but did not have any significant effect on IGF-1 levels or on basal IGFBP3 levels.

Hemodynamic and hormonal responses to a short-term low-intensity resistance exercise with the reduction of muscle blood flow

We investigated the hemodynamic and hormonal responses to a short-term low-intensity resistance exercise (STLIRE) with the reduction of muscle blood flow. Eleven untrained men performed bilateral leg extension exercise under the reduction of muscle blood flow of the proximal end of both legs pressure-applied by a specially designed belt (a banding pressure of 1.3 times higher than resting systolic blood pressure, 160-180 mmHg), named as Kaatsu. The intensity of STLIRE was 20% of one repetition maximum. The subjects performed 30 repetitions, and after a 20-seconds rest, they performed three sets again until exhaustion. The superficial femoral arterial blood flow and hemodynamic parameters were measured by using the ultrasound and impedance cardiography. Serum concentrations of growth hormone (GH), vascular endothelial growth factor (VEGF), noradrenaline (NE), insulin-like growth factor (IGF)-1, ghrelin, and lactate were also measured. Under the conditions with Kaatsu, the arterial flow was reduced to about 30% of the control. STLIRE with Kaatsu significantly increased GH (0.11+/-0.03 to 8.6+/-1.1 ng/ml, P < 0.01), IGF-1 (210+/-40 to 236+/-56 ng/ml, P < 0.01), and VEGF (41+/-13 to 103+/-38 pg/ml, P < 0.05). The increase in GH was related to neither NE nor lactate, but the increase in VEGF was related to that in lactate (r = 0.57, P < 0.05). Ghrelin did not change during the exercise. The maximal heart rate (HR) and blood pressure (BP) in STLIRE with Kaatsu were higher than that without Kaatsu. Stroke volume (SV) was lower due to the decrease of the venous return by Kaatsu, but, total peripheral resistance (TPR) did not change significantly. These results suggest that STLIRE with Kaatsu significantly stimulates the exercise-induced GH, IGF, and VEGF responses with the reduction of cardiac preload during exercise, which may become a unique method for rehabilitation in patients with cardiovascular diseases.

Contraction-induced increases in Na+-K+-ATPase mRNA levels in human skeletal muscle are not amplified by activation of additional muscle mass

The present study tested the hypothesis that exercise with a large compared with a small active muscle mass results in a higher contraction-induced increase in Na(+)-K(+)-ATPase mRNA expression due to greater hormonal responses. Furthermore, the relative abundance of Na(+)-K(+)-ATPase subunit alpha(1), alpha(2), alpha(3), alpha(4), beta(1), beta(2), and beta(3) mRNA in human skeletal muscle was investigated. On two occasions, eight subjects performed one-legged knee extension exercise (L) or combined one-legged knee extension and bilateral arm cranking (AL) for 5.00, 4.25, 3.50, 2.75, and 2.00 min separated by 3 min of rest. Leg exercise power output was the same in AL and L, but heart rate at the end of each exercise interval was higher in AL compared with L. One minute after exercise, arm venous blood lactate was higher in AL than in L. A higher level of blood epinephrine and norepinephrine was evident 3 min after exercise in AL compared with L. Nevertheless, none of the exercise-induced increases in alpha(1), alpha(2), beta(1), and beta(3) mRNA expression levels were higher in AL compared with L. The most abundant Na(+)-K(+)-ATPase subunit at the mRNA level was beta(1), which was expressed 3.4 times than alpha(2). Expression of alpha(1), beta(2), and beta(3) was less than 5% of the alpha(2) expression, and no reliable detection of alpha(3) and alpha(4) was possible. In conclusion, activation of additional muscle mass does not result in a higher exercise-induced increase in Na(+)-K(+)-ATPase subunit-specific mRNA.

Muscle-bone interactions in dystrophin-deficient and myostatin-deficient mice

We have investigated muscle-bone interactions using two mouse mutants that are known to differ from normal mice in skeletal muscle growth and development: mice lacking myostatin (GDF8) and mice lacking dystrophin (mdx). Myostatin-deficient mice show increased muscle size and strength compared to normal mice, whereas the mdx mouse is a well-established animal model for Duchenne muscular dystrophy. The mdx mice have significantly larger hindlimb muscles than controls, and histological sections of the quadriceps muscles show dystrophic changes with extensive fibrosis. Femoral bone mineral density (BMD) and fracture strength (Fu) are significantly greater in mdx mice than controls, and these variables are more strongly correlated with quadriceps muscle mass than with body mass. In contrast, mdx mice do not shower high bone mineral density in the spine relative to controls, whereas myostatin-deficient mice have significantly increased BMD in the lumbar spine compared to normal mice. Both mdx mice and myostatin-deficient mice have expanded femoral trochanters for attachment of large hindlimb muscles, and both mutant strains show increased cross-sectional area moments of inertia mediolaterally (Iyy) but not anteroposteriorly (Ixx) compared to normal mice. These data suggest that lean (muscle) mass is a significant determinant of bone mineral density and strength in the limb skeleton, even when accompanied by a dystrophic phenotype. Likewise, increased muscle mass produces a marked increase in the external dimensions of muscle attachment sites, even when increased muscle size is accompanied by extensive fibrosis and muscle weakness.

Neurocognitive aging and cardiovascular fitness: recent findings and future directions

In the first century, ce, the Roman satirist Juneval famously observed Orandum est, ut sit mens sana in corpore sano, or "A sound mind in a sound body is something to be prayed for." This implicit link between mental and physical health, also paralleled by Eastern philosophies and practices such as tai chi, has survived the millennia since Juneval and his contemporaries. More recently, controlled examinations of the effects of physical fitness on cognitive performance have shown that improving cardiovascular fitness (CVF) can help to reduce the deleterious effects of age on cognition and brain structure. Thus, as we age, it may well be the case that a sound mind is a natural concomitant of a sound body. Numerous cross-sectional and longitudinal studies have examined the effects of aerobic exercise on cognitive performance in aging humans since earlier studies, which found that physically fit older adults performed better on simple cognitive tasks than their less-fit counterparts. This base of knowledge recently has been furthered through examinations of cortical structure (Colcombe et al., 2003) and neurocognitive function in aging humans via functional and structural magnetic resonance imaging techniques. In this manuscript, we will briefly review some of our recent research on the effects of CVF on brain function, structure, and behavior in older adults. We will then outline some of our current and future directions in this area.

O exercício físico potencializa ou compromete o crescimento longitudinal de crianças e adolescentes? Mito ou verdade?

A sociedade atual tem valorizado de forma significativa a aparência alta e esbelta. Essa constituição física tem sido reforçada desde a infância e atinge a população adolescente, que deseja enquadrar-se nos estereótipos, particularmente aqueles veiculados pela mídia. Nesse sentido, profissionais de saúde são questionados rotineiramente sobre os efeitos positivos que o exercício físico exerce sobre o crescimento longitudinal de crianças e adolescentes. Procurou-se revisar a literatura especializada a respeito dos principais efeitos que o exercício físico exerceria sobre a secreção e atuação do hormônio de crescimento (GH) nos diversos tecidos corporais, durante a infância e adolescência. Através dessa revisão, foi possível verificar que o exercício físico induz a estimulação do eixo GH/IGF-1. Embora muito se especule quanto ao crescimento ósseo ser potencializado pela prática de exercícios físicos, não foram encontrados na literatura científica específica estudos bem desenvolvidos que forneçam sustentação a essa afirmação. No tocante aos efeitos adversos advindos do treinamento físico durante a infância e adolescência, aparentemente, esses foram independentes do tipo de esporte praticado, porém resultantes da intensidade do treinamento. A alta intensidade do treinamento parece ocasionar uma modulação metabólica importante, com a elevação de marcadores inflamatórios e a supressão do eixo GH/IGF-1. Entretanto, é importante ressaltar que a própria seleção esportiva, em algumas modalidades, recruta crianças e/ou adolescentes com perfis de menor estatura, como estratégia para obtenção de melhores resultados, em função da facilidade mecânica dos movimentos. Através dessa revisão, fica evidente a necessidade de realização de estudos longitudinais, nos quais os sujeitos sejam acompanhados antes, durante e após sua inserção nas atividades esportivas, com determinação do volume e da intensidade dos treinamentos, para que conclusões definitivas relativas aos efeitos sobre a estatura final possam ser emanadas.

Ageing, growth hormone and physical performance

Human ageing is associated to a declining activity of the GH/IGF-I axis and to several changes in body composition, function and metabolism which show strict similarities with those of younger adults with pathological GH deficiency. The age-related changes of the GH/IGF-I axis activity are mainly dependent on age-related variations in the hypothalamic control of somatotroph function, which is also affected by changes in peripheral hormones and metabolic input. The term "somatopause" indicates the potential link between the age-related decline in GH and IGF-I levels and changes in body composition, structural functions and metabolism which characterise ageing. Physical exercise is an important environmental regulator of the GH/IGF-I axis activity. Increased physical fitness and regular training increase GH production in adults, while the GH response to aerobic or resistance exercise is reduced with age. In older subjects regular exercise has the potential to improve overall fitness and quality of life and is also associated to decreased morbidity and increased longevity. Similar effects are seen following GH therapy in adult deficiency. This assumption led to clinical trials focusing on rhGH and/or rhlGF-I as potential anabolic drug interventions in elderly subjects. To restore the activity of GH/IGF-I axis with anabolic, anti-ageing purposes, attention has been also paid to GH-releasing molecules such as GHRH, orally active synthetic GH-secretagogues (GHS) and, more recently, to the endogenous natural GHS, ghrelin, which exerts several important biological actions, including the regulation of metabolic balance and orexigenic effects. At present, however, there is no definite evidence that "frail" elderly subjects really benefit from restoring GH and IGF-I levels within the young adult range by treatment with rhGH, rhlGF-I, GHRH or GHS. In this article the alteration of the GH/IGF-I axis activity during ageing is revised taking into account the role of physical activity as a regulator of the axis function and considering the effects of the restoration of GH and IGF-I circulating levels on body composition and physical performance.