Growth hormone (GH) treatment in GH-deficient adults: effects on muscle size, strength and neural activation

The Use and Abuse of Human Growth Hormone in Sports

CONTEXT

Recombinant human growth hormone (rHGH) has become a target of abuse in the sporting world. Conversely, sports medicine clinicians may encounter athletes using rHGH to achieve normalcy in the context of growth hormone (GH) deficiency.

EVIDENCE ACQUISITION

Medline and PubMed databases were queried using the following keywords: GH, GH physiology, GH deficiency, acromegaly, GH athlete, GH sports, GH athletic performance, and GH deficiency concussion. Articles focusing on GH physiology, deficiency, excess, and its effects in both deficient and healthy patients were included.

STUDY DESIGN

Clinical review.

LEVEL OF EVIDENCE

Level 3.

RESULTS

GH is a naturally occurring hormone with important roles in human physiology. Patients with GH deficiency (GHD) present variably, and GHD has numerous etiologies. rHGH treatment has substantial therapeutic benefits for patients with GHD. The benefits of rHGH treatment in otherwise-healthy adults are uncertain. GH excess may cause health problems such as acromegaly. Professional, collegiate, and international sports leagues and associations have banned rHGH use to maintain athlete health, safety, and fair play. Athletes misusing GH may face prolonged suspensions from competition. Implementing GH abuse testing is challenging, but new methods, such as the biomarker testing procedure, are being finalized.

CONCLUSION

rHGH is not only an important therapeutic agent for GH-deficient patients but also a target of abuse in competitive athletics. Its benefits in a healthy, adult population are uncertain. A safe exercise and competition plan, developed with a physician knowledgeable of GH use, physiology, and abuse potential, should be of benefit to a longitudinal clinician-patient relationship.

Specific force of the vastus lateralis in adults with achondroplasia

Achondroplasia is a clinical condition defined by shorter stature and disproportionate limb length. Force production in able-bodied individuals (controls) is proportional to muscle size, but given the disproportionate nature of achondroplasia, normalizing to anatomical cross-sectional area (ACSA) is inappropriate. The aim of this study was to assess specific force of the vastus lateralis (VL) in 10 adults with achondroplasia (22 ± 3 yr) and 18 sex-matched controls (22 ± 2 yr). Isometric torque (iMVCτ) of the dominant knee extensors (KE) and in vivo measures of VL muscle architecture, volume, activation, and patella tendon moment arm were used to calculate VL physiological CSA (PCSA), fascicle force, and specific force in both groups. Achondroplasic muscle volume was 53% smaller than controls (284 ± 36 vs. 604 ± 102 cm³, P < 0.001). KE iMVCτ was 63% lower in achondroplasia compared with controls (95 ± 24 vs. 256 ± 47 N⋅m, P < 0.001). Activation and moment arm length were similar between groups ( P > 0.05), but coactivation of bicep femoris of achondroplasic subjects was 70% more than controls (43 ± 20 vs. 13 ± 5%, P < 0.001). Achondroplasic subjects had 58% less PCSA (43 ± 10 vs. 74.7 ± 14 cm², P < 0.001), 29% lower fascicle force (702 ± 235 vs. 1704 ± 303 N, P < 0.001), and 29% lower specific force than control subjects (17 ± 6 vs. 24 ± 6 N⋅cm^-2, P = 0.012). The smaller VL specific force in achondroplasia may be attributed to infiltration of fat and connective tissue, rather than to any difference in myofilament function. NEW & NOTEWORTHY The novel observation of this study was the measurement of normalized force production in a group of individuals with disproportionate limb length-to-torso ratios.

Sex steroids and the GH axis: Implications for the management of hypopituitarism

Growth hormone (GH) regulates somatic growth, substrate metabolism and body composition. Sex hormones exert profound effect on the secretion and action of GH. Estrogens stimulate the secretion of GH, but inhibit the action of GH on the liver, an effect that occurs when administered orally. Estrogens suppress GH receptor signaling by stimulating the expression proteins that inhibit cytokine receptor signaling. This effect of estrogens is avoided when physiological doses of estrogens are administered via a non-oral route. Estrogen-like compounds, such as selective estrogen receptor modulators, possess dual properties of inhibiting the secretion as well as the action of GH. In contrast, androgens stimulate GH secretion, driving IGF-1 production. In the periphery, androgens enhance the action of GH. The differential effects of estrogens and androgens influence the dose of GH replacement in patients with hypopituitarism on concomitant treatment with sex steroids. Where possible, a non-oral route of estrogen replacement is recommended for optimizing cost-benefit of GH replacement in women with GH deficiency. Adequate androgen replacement in conjunction with GH replacement is required to achieve the full anabolic effect in men with hypopituitarism.

Growth hormone (GH) enhances anaerobic capacity: impact on physical function and quality of life in adults with GH deficiency

CONTEXT

Anaerobic capacity is impaired in adults with GH deficiency (GHD), adversely affecting physical function and quality of life (QoL).

OBJECTIVE

To investigate whether GH replacement improves anaerobic capacity, physical function and QoL in adults with GHD.

DESIGN

One-month double-blind placebo-controlled crossover study of GH (0·5 mg/day), followed by a 6-month open phase.

PATIENTS

A total of 18 adults with GHD.

MEASUREMENTS

Anaerobic power (watts) was assessed by the 30-s Wingate test, and aerobic capacity by the VO2 max (l/min) test. Physical functional was assessed by the stair climb test, chair stand test, 7-day pedometry and QoL by the AGHDA questionnaire. Lean body mass (LBM) was quantified by dual-energy X-ray absorptiometry.

RESULTS

GH replacement normalized IGF-1 levels during both study phases. During the 1-month placebo-controlled study, improvement in stair climb and chair stand performance was observed during GH and placebo treatment; however, there were no significant GH effects observed in any outcome measure compared to placebo. Six months of GH treatment significantly increased anaerobic power (P < 0·05), chair stand repetitions (P < 0·0001), daily step count (P < 0·05) and QoL scores (P < 0·001) compared to baseline measurements. GH treatment did not significantly improve VO2 max. Improvement in anaerobic power independently predicted an improvement in energy and vitality domain of QoL (P = 0·03).

CONCLUSIONS

GH replacement improves anaerobic capacity, physical function and QoL in a time-dependent manner in adults with GHD. Improvement in the anaerobic but not aerobic energy system is likely to underlie the improvement in QoL in patients with GHD during GH replacement.

Action of GH on skeletal muscle function: molecular and metabolic mechanisms

Skeletal muscle is a target tissue of GH. Based on its anabolic properties, it is widely accepted that GH enhances muscle performance in sports and muscle function in the elderly. This paper critically reviews information on the effects of GH on muscle function covering structure, protein metabolism, the role of IGF1 mediation, bioenergetics and performance drawn from molecular, cellular and physiological studies on animals and humans. GH increases muscle strength by enhancing muscle mass without affecting contractile force or fibre composition type. GH stimulates whole-body protein accretion with protein synthesis occurring in muscular and extra-muscular sites. The energy required to power muscle function is derived from a continuum of anaerobic and aerobic sources. Molecular and functional studies provide evidence that GH stimulates the anaerobic and suppresses the aerobic energy system, in turn affecting power-based functional measures in a time-dependent manner. GH exerts complex multi-system effects on skeletal muscle function in part mediated by the IGF system.

Growth hormone and physical performance

There has been limited research and evidence that GH enhances physical performance in healthy adults or in trained athletes. Even so, human growth hormone (GH) is widely abused by athletes. In healthy adults, GH increases lean body mass, although it is possible that fluid retention contributes to this effect. The most recent data indicate that GH does not enhance muscle strength, power, or aerobic exercise capacity, but improves anaerobic exercise capacity. In fact, there are adverse effects of long-term GH excess such that sustained abuse of GH can lead to a state mimicking acromegaly, a condition with increased morbidity and mortality. This review will examine GH effects on body composition and physical performance in health and disease.

The effect of growth hormone (GH) replacement on muscle strength in patients with GH-deficiency: a meta-analysis

CONTEXT/OBJECTIVES

GH replacement increases muscle mass and reduces body fat in growth hormone deficiency (GHD) adults. A recent meta-analysis has demonstrated that this improvement in body composition is associated with improved exercise performance. The current meta-analysis was carried out to determine whether high-quality evidence exists to support a beneficial effect of GH replacement on strength.

DESIGN/METHODS

An extensive Medline search/literature review identified eight studies with utilizable, robust data, involving 231 patients in nine cohorts. Previously unpublished data were sought from authors and obtained in two cases. All studies included were randomized, double-blind, placebo-controlled, of parallel or cross-over design and of an average 6.7 months duration. Information was retrieved in uniform format, with data pertaining to patient numbers, study-design, GH-dose, mean age, IGF-I levels and muscle strength measurements (isometric or isokinetic quadriceps strength) recorded. Data were analysed using a fixed-effects model, utilizing continuous data measured on different scales. A summary effect measure (d(s)) was derived for individual strength variables, whereas an overall summary effect was derived from the sum of all studies incorporating different variables; 95% CIs were calculated from the weighted variances of individual study effects.

RESULTS

Analysis revealed no significant improvement, neither when all studies were combined (d(s) = +0.01 +/- 0.26) nor when measured individually (isometric quadriceps strength, d(s) = +0.02 +/- 0.32 and isokinetic quadriceps strength, d(s) = 0.00 +/- 0.45).

CONCLUSIONS

Evidence from short-term controlled studies fails to support a benefit on muscle strength of GH replacement in GHD patients, which is likely to occur over a longer time-course, as seen in open-label studies.

Growth hormone administration: is it safe and effective for athletic performance

Human growth hormone (GH) is widely abused by athletes; however, there is little evidence that GH improves physical performance. Replacement of GH in GH deficiency improves some aspects of exercise capacity. There is evidence for a protein anabolic effect of GH in healthy adults and for increased lean body mass following GH, although fluid retention likely contributes to this increase. The evidence suggests that muscle strength, power, and aerobic exercise capacity are not enhanced by GH administration, however GH may improve anaerobic exercise capacity. There are risks of adverse effects of long-term abuse of GH. Sustained abuse of GH may lead to a state mimicking acromegaly, a condition with increased morbidity and mortality.

Muscle strength and power, maximum oxygen consumption, and body composition in middle-aged short-stature adults with childhood-onset growth hormone deficiency

BACKGROUND

Growth hormone (GH) replacement in adult GH-deficient (GHD) patients is reported to have a long-term beneficial effect on muscle mass and function, these effects being greater in young males and in adult-onset compared with those with childhood-onset GHD. To date, more discordant data are reported on the degree of muscle impairment in untreated GHD patients, due to the large heterogeneity of this syndrome.

METHODS

Muscle maximum total isotonic strength (ST), lower limb maximum power output (W), maximum aerobic capacity (VO(2)max) and body composition (by tetrapolar bio-impedentiometry) were evaluated in seven short-stature adults with childhood-onset GHD and in seven age-matched normal-stature controls with comparable lifestyle and daily physical activity.

RESULTS

Significant differences were found in body composition between control subjects and GHD patients, who presented higher adiposity (mean BMI+/-SD: GHD, 27.8+/-5.8 kg/m(2); controls, 22.1+/-0.8 kg/m(2); p=0.047), larger fat mass (GHD, 21.8+/-10.7 kg; controls, 8.8+/-3.5 kg; p=0.008), and lower fat-free mass (GHD, 65.8+/-11.4 %; controls, 87.0+/-6.5 %; p=0.002). In absolute terms, GHD patients attained significantly lower values in ST (GHD, 2479+/-493 N; controls, 4578+/-1476 N; p=0.008), W (GHD, 1092+/-452 W; controls, 1910+/-781 W; p=0.035) and VO(2)max (GHD, 1.68+/-0.40 l/min; controls, 2.67+/-0.84 l/min; p=0.035) than those attained by controls. The differences were still evident when the results were normalized by unit body mass, whereas they disappeared when the parameters were expressed per unit fat-free mass, suggesting for these patients the presence of an intrinsic muscle function in the same range as that of control subjects.

CONCLUSIONS

Middle-aged and short-stature adults with childhood-onset GHD, who received discontinuous pit-GH substitution therapy only during childhood and have uncorrected long-lasting GHD, still retain a normal intrinsic muscle capability in attaining isotonic strength, generating anaerobic power as well as accomplishing oxidative processes. Nonetheless, it is not known which age-dependent evolution in motor dysfunction could be expected in this subgroup of GHD patients, when ageing processes add up to hormonal deficiencies.

The influence of growth hormone status on physical impairments, functional limitations, and health-related quality of life in adults

The availability of recombinant human GH and somatostatin analogs has resulted in widespread treatment for adults with GH deficiency (GHD) and those with GH excess (acromegaly). Despite being at opposite ends of the spectrum in terms of their GH/IGF-I axis, both of these populations experience overlapping somatic impairments. Adults with untreated GHD have low circulating levels of IGF-I that manifest as altered body composition with increased fat and reduced lean body and skeletal muscle mass. At the other end of the spectrum, adults with GH excess, who have elevated levels of IGF-I, also have altered body composition. Impairments that result from disorders of either GHD or GH excess are both associated with increased functional limitations, such as reduced ability to walk quickly for prolonged periods, and poorer health-related quality of life (HR-QoL). Adults with untreated GHD and GH excess both commonly complain of excessive fatigue that seems to be associated more with impaired aerobic than muscular performance. Several studies have documented that administration of GH or somatostatin analogs to adults with GHD or GH excess, respectively, ameliorates abnormal biochemical profile and the associated somatic impairments. However, whether these improvements translate into improved physical function in adults with GHD or GH excess remains largely unknown, and their impact on HR-QoL controversial. Review of placebo-controlled trials to date suggests that GH and somatostatin analogs have greater effects on gas exchange and aerobic performance than as anabolic agents on skeletal muscle mass and function. Future investigations should include dose-response studies to establish the optimal combination of pharmacological agents plus exercise required to improve not only biochemical markers but also physical function and HR-QoL in adults with GHD or GH excess.

Continuation of growth hormone (GH) replacement in GH-deficient patients during transition from childhood to adulthood: a two-year placebo-controlled study

Previous studies have demonstrated beneficial effects of GH replacement, in adults with GH deficiency (GHD), on body composition, physical fitness, and quality of life. These studies, however, concern patients with adult-onset GHD or childhood-onset (CO) patients enrolled several years after withdrawal of initial therapy. So far, the effects of continuation of GH-administration in patients with CO-GHD have not been examined. We studied a group of nineteen young adults (13 males + 6 females; 16-26 yr old; mean age, 20.2 +/- 0.65 yr) with CO-GHD, in a randomized, parallel, double-blind, placebo-controlled trial for 1 yr, followed by an open phase with GH for 1 yr. All patients received GH therapy at the start of study, and trial medication (GH/placebo) was given in a similar dose. Patients randomized to continued GH treatment exhibited no significant changes in any parameters tested, but intra- and interindividual variations in insulin-like growth factor (IGF)-I levels could suggest compliance problems. Discontinuation of GH for 1 yr resulted in a decrease in serum IGF-I, from 422.0 +/- 56.8 to 147.8 +/- 33.4 microg/L, in the placebo group (P = 0.003). After discontinuation of GH for 1 yr, an increase in total body fat (TBF, kg), measured by dual-energy x-ray absorptiometry scan, was seen [placebo: 22.7 +/- 2.7 to 26.5 +/- 2.5 (P = 0.01); GH: 16.2 +/- 2.1 to 17.2 +/- 2.1 (not significant)]. Resumption of GH after placebo was followed by increments in serum IGF-I (microg/L) [from 147.8 +/- 33.4 to 452 +/- 76 (P = 0.001)] and IGF-binding protein 3, as well as in fasting glucose (mmol/L) [4.9 +/- 0.2 vs. 5.3 +/- 0.2 (P = 0.03)]. After resumption of GH lean body mass (kg) increased [52.4 +/- 4.9 vs. 60.7 +/- 5.6 (P = 0.006)]. Likewise, resumption of GH therapy increased thigh muscle volume and thigh muscle/fat ratio, as assessed by computed tomography [muscle volume (cm2/10 mm): 118.2 +/- 11.7 vs. 130.0 +/- 10.9 (P = 0.002); muscle/fat ratio: 1.33 +/- 0.24 vs. 1.69 +/- 0.36 (P = 0.02)]. In conclusion, discontinuation of GH treatment in GHD patients, during the transition from childhood to adulthood, induces significant and potentially unfavorable changes in IGF-I and body composition, both of which are reversed after resumption of GH treatment. By contrast, continuation of GH therapy results in unaltered IGF-I and body composition. We recommend continuation of GH therapy in these patients, to be undertaken in collaboration between pediatricians and adult endocrinologists.

Maximum anaerobic performance of childhood-onset GH-deficient adults

To date, physical capacity of adults with GH deficiency (GHD) has been studied in terms of muscle strength, contractile properties and aerobic performance. As a result, scanty data are available regarding the maximum anaerobic performance of these patients with reference to healthy controls. Therefore, the objective of this study was to evaluate maximum anaerobic power of adults with GHD and of age-matched controls by two methods, one testing lactacid power (w.;(c)) through a 15-s-maximal bout on a bicycle ergometer, the other testing alactic power (w.;(j)) through a vertical jump on a force platform. Absolute w.;(c)and w.;(j)values were both found to be 35% lower(P<0.04) in GHD patients than in controls. Similarly, peak pedalling velocity (V(peak)) was 21% lower (P<0.04) in patients. When w.;(c)and w.;(j)were respectively normalized for thigh and lower limb muscle plus bone volumes and V(peak)for muscle length, differences between patients and controls were no longer significant. Furthermore, the rate of power loss during the cycling bout was approximately 35% in both groups. This observation was in line with similar delta (peak minus baseline) lactate capillary blood concentrations, being 6.3 mM/l in patients and 7.5 mM/l in controls (NS). Lactacid capacity, which represents the energy extracted from lactate metabolism, normalized for body mass was similar in the two groups. In conclusion, the maximum anaerobic power that can be developed by short-statured childhood-onset GHD adults is significantly lower in terms of absolute values, but not different from that of controls once appropriately normalized. Therefore, the changes in maximum anaerobic power of GH deficient patients seem to be a consequence of their smaller muscle mass.

Human skeletal muscle architecture studied in vivo by non-invasive imaging techniques: functional significance and applications

The internal architecture plays an essential role in determining the functional features of skeletal muscle. Both length-force and force-velocity relationships depend on the spatial arrangement of muscle fibres in skeletal muscle. The degree of muscle pennation determines both the amount of contractile tissue packed along the tendons and fibre length, and is reflected by the force-generating capacity and shortening velocity of the muscle and by the elastic properties of the muscle-tendon complex. Until recently, knowledge on human muscle architecture was based on measurements performed on cadavers, whose muscle fibres were often shrunk by the preserving medium and by age. With the introduction of non-invasive imaging techniques, it has become possible to study muscle architecture in vivo at rest and the changes thereof upon contraction. This paper discusses the applications of these techniques, namely ultrasonography and nuclear magnetic resonance imaging, and their relevance in physiology and biomechanics.

One-year treatment with recombinant human growth hormone of children with meningomyelocele and growth hormone deficiency: a comparison of supine length and arm span

Growth retardation and precocious puberty are frequently found in children with meningomyelocele (MMC). Lower limb contractions, spasticity and kyphoscoliosis may lead to disproportionate short stature. Most of these patients have structural brain defects or hydrocephalus which can cause growth hormone deficiency. In this study, 19 children aged between 3.5 and 12.8 years with MMC and growth hormone (GH) deficiency were treated with recombinant human GH for a period of 12 months. Supine length, arm span and growth velocity were compared before, and after 6 and 12 months of treatment with rhGH (daily dose 2.0 IU/m2 BSA s.c.). Mean supine length standard deviation score (SDS) increased by +0.8 SDS after 6 months and +1.2 SDS after 12 months of therapy. Mean arm span standard deviation score increased by +0.9 SDS and +1.3 SDS. Growth velocity increased in supine length from 3.3 cm/yr (-2.1 SDS) to 8.4 cm/yr (+2.4 SDS) and in arm span from 4.8 cm/yr (-1.3 SDS) to 8.6 cm/yr (+3.1 SDS) in the first 6 months and was 8.1 cm/yr (+2.4 SDS) and 8.3 cm/yr (+2.6 SDS) after 12 months of therapy. Linear correlation between SDS growth velocity supine length and SDS growth velocity arm span during one year of treatment was excellent (r = 0.65, p < 0.0025). We surmise that body proportions do not deteriorate when growth velocity is stimulated in MMC patients. Both supine length and arm span measurements are necessary to document growth in children with spinal dysraphism.

Adults with childhood-onset growth hormone deficiency: effects of growth hormone treatment on cardiac structure

OBJECTIVES

To evaluate the effects of growth hormone deficiency (GHD) and of growth hormone (GH) therapy on cardiac structure in adults with childhood-onset GHD.

SETTING

Out-patient clinic in the Italian Institute for Auxology, Milan.

SUBJECTS

Eight adults with childhood-onset GHD and eight healthy controls, matched for sex, age, exercise and body mass index.

INTERVENTIONS

Recombinant GH (Saizen Serono, Italy), administered in a conventional dose of 0.5 IU kg-1 week-1 for 6 months.

MAIN OUTCOME MEASURES

Cardiac structure parameters, evaluated by two-dimensional, M-mode and Doppler echocardiograms, and stress test, by means of a modified Bruce protocol with a bicycle ergometer, were determined before and after 6 months GH therapy.

RESULTS

Before treatment, mean (+/- SE) intraventricular septal thickness (IVST: 7.1 +/- 0.2 mm), LV posterior wall thickness (LVPT: 5.2 +/- 0.1 mm), LV mass (LVM: 94.6 +/- 5.0 g), LV mass index (LVM/body surface area, LVMI: 65.1 +/- 3.0 g m-2) and left ventricular end-diastolic diameter (LVED: 41.4 +/- 0.6 mm) of patients were significantly lower (P < 0.01) than in controls, whilst LV end-systolic diameter (LVES) of patients (25.5 +/- 0.7 mm) was similar to controls (27.5 +/- 0.7). GH treatment significantly (P < 0.01) increased LVPT (6.8 +/- 0.2 mm), LVM (111.6 +/- 4.6 g) and LVMI (80.5 +/- 3.5 g m-2); no significant changes were observed in LVED, LVES and IVST values. The stress test showed a significant improvement of cardiac performance, as demonstrated by the reduction of blood pressure x heart rate product at the same workload (basal: 32,722.5 +/- 897.4 vs. after: 25,574.6 +/- 439.7).

CONCLUSIONS

GH plays a role in the maintenance of a normal cardiac structure in adulthood. The present study suggests that GH treatment might be able to improve the cardiac structure of patients with childhood-onset GHD.

Effects of recombinant growth hormone (GH) treatment on bone mineral density and body composition in adults with childhood onset growth hormone deficiency

Lumbar spine, whole proximal femur and total body bone mineral density (BMD, g/cm2) and the regional soft tissue composition were measured with dual energy X-ray absorptiometry (Hologic QDR 1000/W) in eight adults with childhood onset GHD, before and after 6 months of recombinant GH treatment (0.5 IU/kg/week). Data obtained from patients were compared with those recorded in an age and sex matched control group. Before treatment, lumbar (L2-L4) spine BMD (mean +/- SD: 0.811 +/- 0.159 g/cm2), whole proximal femur BMD (0.739 +/- 0.094 g/cm2) and total body BMD (0.946 +/- 0.087 g/cm2) of patients were significantly (p < 0.001, 0.01 and 0.001, respectively) lower than those recorded in an age- and sex-matched control group (1.077 +/- 0.155 g/cm2, 0.968 +/- 0.166 g/cm2 and 1.168 +/- 0.058 g/cm2, respectively), although three patients showed BMD values at the lower limit of the normal range. Mean lumbar spine BMD, whole proximal femur BMD and total body BMD did not significantly change alter 6 months' GH treatment (-1.4 +/- 3.7%, +2.7 +/- 3.7% and -1.1 +/- 5.0% vs basal values, respectively). On the other hand, trochanteric subregion showed a significant 4.8 +/- 5.3% increase (vs basal, p < 0.05), while other hip subregions did not show significant changes. GH therapy caused marked effects on body composition; in fact, a significant decrease (p < 0.01) of trunk fat (-25.2 +/- 15.0%) and a marked increase (p < 0.01) of limbs lean mass (+10.0 +/- 5.3%), resulting in a significant (p < 0.02) reduction (-16.5 +/- 13.5%) of the axial to peripheral fat ratio (APFR), were clearly evident after six months of therapy. In conclusion, our study shows that six months of GH treatment do not exert relevant effects on the BMD of adults with childhood onset GHD. On the contrary, the effects of GH therapy on body composition are more marked, being clearly appreciable after six months of treatment.