Increased Grip Strength Research Articles

Effect of submaximal isometric wrist extension training on grip strength

Gripping force is produced by co-contraction of forearm flexors and extensors. Activation of extensors is important for stabilizing the wrist during gripping. However, forearm muscle function is complicated and the neurophysiological mechanism responsible for the gain in gripping force is unclear. Therefore, the purpose of this study was to investigate whether increasing forearm extensor activation with isometric wrist extension training has an effect on gripping force. Thirteen healthy subjects participated in this study. Maximal voluntary contraction of gripping was measured using a piezosensor (MVC(grip)) and EMG of forearm muscles at every wrist angle (from 70° flexion to 80° extension with 10° intervals) were measured simultaneously at baseline, 4 weeks, and 8 weeks after training. Training consisted of 30 repetitions equal to 70% MVC of isometric wrist extension for 8 weeks (5/week) on the right side. Gripping force was measured on both sides using a grip dynamometer without wrist angle restriction. Gripping force, EMG, maximal wrist extension force, and wrist angle-gripping force curve were investigated after training. After training, maximal wrist extension force increased significantly. Gripping force on the trained side also increased significantly. The training changed wrist angle at peak of MVC(grip). EMG activation of forearm extensors increased and that of flexors decreased during gripping. These results suggest that wrist extension training leads to an increase in gripping force and changes the balance of EMG activation between forearm flexors and extensors during gripping. Therefore, this training method should be useful as a therapeutic strategy for increasing grip strength.

Akt Deficiency Attenuates Muscle Size and Function but Not the Response to ActRIIB Inhibition

BackgroundAkt is a critical mediator of developmental skeletal muscle growth. Treatment with a soluble ActRIIB fusion protein (ActRIIB-mFc) increases skeletal muscle mass and strength by inhibiting myostatin and related peptides. Recent in vitro studies have suggested that Akt signaling is necessary for the ability of ActRIIB inhibition to induce muscle hypertrophy. Thus, we hypothesized that mice deficient in either Akt1 or Akt2 would not respond to in vivo inhibition of ActRIIB with ActRIIB-mFc treatment.Methodology and Principal FindingsWe analyzed body composition and muscle parameters in wild-type C57BL/6J and Akt1 and Akt2 knockout mice, and compared the responses to blockade of ActRIIB signaling via ActRIIB-mFc treatment. Mice lacking Akt1 or Akt2 had reduced muscle mass, grip strength and contractile force. However, deficiency of Akt1 or Akt2 did not prevent the ability of ActRIIB-mFc treatment to induce muscle hypertrophy, or increase grip strength and contractile force. Akt1 and Akt2 deficient mice responded similarly as wild type mice to ActRIIB-mFc treatment by increasing fiber size.Conclusions and SignificanceAkt1 and Akt2 are important for the regulation of skeletal muscle mass and function. However, these Akt isoforms are not essential for the ability of ActRIIB inhibition to regulate muscle size, fiber type, strength or contractile force.

Characterization of Developmental Neurotoxicity of As, Cd, and Pb Mixture: Synergistic Action of Metal Mixture in Glial and Neuronal Functions

Neurotoxicity of individual metals is well investigated but that of metal mixture (MM), an environmental reality, in the developing brain is relatively obscure. We investigated the combinatorial effect of arsenic (As), cadmium (Cd), and lead (Pb) on rat brain development, spanning in utero to postnatal development. MM was administered by gavage to pregnant and lactating rats, and to postweaning pups till 2 months. The pups exhibited behavioral disturbances characterized by hyperlocomotion, increased grip strength, and learning-memory deficit. Disruption of the blood-brain barrier (BBB) was associated with dose-dependent increase in deposition of the metals in developing brain. Astrocytes were affected by MM treatment as evident from their reduced density, area, perimeter, compactness, and number of processes, and increased apoptosis in cerebral cortex and cerebellum. The metals induced synergistic reduction in glial fibrillary acidic protein (GFAP) expression during brain development; however, postweaning withdrawal of MM partially restored the levels of GFAP in adults. To characterize the toxic mechanism, we treated rat primary astrocytes with MM at concentrations ranging from lethal concentration (LC)(10) to LC(75) of the metals. We observed synergistic downregulation in viability and increase in apoptosis of the astrocytes, which were induced by proximal activation of extra cellular signal-regulated kinase (ERK) signaling and downstream activation of Jun N-terminal kinase (JNK) pathway. Furthermore, rise in intracellular calcium ion ([Ca(2+)](i)) and reactive oxygen species generation promoted apoptosis in the astrocytes. Taken together, these observations are the first to show that mixture of As, Cd, and Pb has the capacity to induce synergistic toxicity in astrocytes that may compromise the BBB and may cause behavioral dysfunction in developing rats.

Evaluation of Systemic Follistatin as an Adjuvant to Stimulate Muscle Repair and Improve Motor Function in Pompe Mice

Due to the lack of acid alpha-glucosidase (GAA) activity, Pompe mice develop glycogen storage pathology and progressive skeletal muscle dysfunction with age. Applying either gene or enzyme therapy to reconstitute GAA levels in older, symptomatic Pompe mice effectively reduces glycogen storage in skeletal muscle but provides only modest improvements in motor function. As strategies to stimulate muscle hypertrophy, such as by myostatin inhibition, have been shown to improve muscle pathology and strength in mouse models of muscular dystrophy, we sought to determine whether these benefits might be similarly realized in Pompe mice. Administration of a recombinant adeno-associated virus serotype 8 vector encoding follistatin, an inhibitor of myostatin, increased muscle mass and strength but only in Pompe mice that were treated before 10 months of age. Younger Pompe mice showed significant muscle fiber hypertrophy in response to treatment with follistatin, but maximal gains in muscle strength were achieved only when concomitant GAA administration reduced glycogen storage in the affected muscles. Despite increased grip strength, follistatin treatment failed to improve rotarod performance. These findings highlight the importance of treating Pompe skeletal muscle before pathology becomes irreversible, and suggest that adjunctive therapies may not be effective without first clearing skeletal muscle glycogen storage with GAA.

Non-invasive Optical Imaging of Muscle Pathology in mdx Mice Using Cathepsin Caged Near-Infrared Imaging

PurposeTo develop a reliable live-animal imaging method for monitoring muscle pathology in mouse models of myopathy.ProceduresA caged near-infrared Cathepsin B (CTSB) substrate, ProSense 680, is evaluated in the dystrophin deficient mdx mice, a genetic homologue of Duchenne muscular dystrophy via optical imaging.ResultsWe show high levels of infrared signal in dystrophic muscle relative to healthy muscle at 24 h post-injection. Imaging for CTSB presence revealed localization to inflammatory infiltrates and regenerating muscle fibers. A time series myotoxin-induced muscle injury experiment showed that CTSB activity and its mRNA levels peaked at the interface between inflammation and myoblast fusion stage of recovery. Prednisone treatment in mdx mice resulted in decreased CTSB activity and increased grip strength in forelimbs and hindlimbs.ConclusionsOptical imaging of CTSB activity is an ideal method to sensitively monitor inflammation, regeneration, and response to therapy in myopathic skeletal muscle.Electronic supplementary materialThe online version of this article (doi:10.1007/s11307-010-0376-z) contains supplementary material, which is available to authorized users.

Thyroid Function within the Upper Normal Range Is Associated with Reduced Bone Mineral Density and an Increased Risk of Nonvertebral Fractures in Healthy Euthyroid Postmenopausal Women

The relationship between thyroid function and bone mineral density (BMD) is controversial. Existing studies are conflicting and confounded by differences in study design, small patient numbers, and sparse prospective data. We hypothesized that variation across the normal range of thyroid status in healthy postmenopausal women is associated with differences in BMD and fracture susceptibility. The Osteoporosis and Ultrasound Study (OPUS) is a 6-yr prospective study of fracture-related factors. We studied a population-based cohort from five European cities. A total of 2374 postmenopausal women participated. Subjects with thyroid disease and nonthyroidal illness and those receiving drugs affecting thyroid status or bone metabolism were excluded, leaving a study population of 1278 healthy euthyroid postmenopausal women. There were no interventions. We measured free T(4) (fT4) (picomoles/liter), free T(3) (fT3) (picomoles/liter), TSH (milliunits/liter), bone turnover markers, BMD, and vertebral, hip, and nonvertebral fractures. Higher fT4 (beta = -0.091; P = 0.004) and fT3 (beta = -0.087; P = 0.005) were associated with lower BMD at the hip, and higher fT4 was associated with increasing bone loss at the hip (beta = -0.09; P = 0.015). After adjustment for age, body mass index, and BMD, the risk of nonvertebral fracture was increased by 20% (P = 0.002) and 33% (P = 0.006) in women with higher fT4 or fT3, respectively, whereas higher TSH was protective and the risk was reduced by 35% (P = 0.028). There were independent associations between fT3 and pulse rate (beta = 0.080; P = 0.006), increased grip strength (beta = 0.171; P<0.001), and better balance (beta = 0.099; P < 0.001), indicating that the relationship between thyroid status and fracture risk is complex. Physiological variation in normal thyroid status is related to BMD and nonvertebral fracture.

The effects of Mulligan mobilisation with movement and taping techniques on pain, grip strength, and function in patients with lateral epicondylitis

Abstract This experimental design study investigated the effect of a combination of Mulligan techniques and traditional treatment compared with that of traditional treatment alone in patients with lateral epicondylitis. The applied Mulligan techniques included mobilisation with movement and taping, and were aimed to reduce pain, increase grip strength, and improve activities of daily living. A total of 34 patients aged between 16 and 69 years underwent 11 sessions of a combination of Mulligan techniques and traditional treatment (experimental group, n = 17) or traditional treatment only (control group, n = 17). They were evaluated before the treatment, and after 4 weeks, using visual analogue scale, maximum grip strength, and Patient-Rated Tennis Elbow Evaluation. Analysis showed statistically significant improvement in all outcomes in both the experimental and the control groups. In addition, the mean improvement in visual analogue scale and maximum grip strength was significantly greater in the experimental group than that in the control group. This study showed that the combination of Mulligan techniques with traditional treatment leads to better outcomes in treatment of lateral epicondylitis than traditional treatment alone.

Examining the effect of the Flextend Orthotic Device® on grip strength: A pilot study

Strengthening exercises like those used to treat carpal tunnel syndrome have been recommended for prevention however their effectiveness when used in this manner are not known. The purpose of this study was to determine the effects of the Flextend Orthotic Device on grip strength of dental hygiene students. This study used a convenience sample of 24 (n=24) first year dental hygiene students. Students were randomly assigned to either the Flextend Orthotic Exercise glove group or a control group. A series of grip strength measurements were taken periodically throughout the study using a hydraulic hand dynamometer. In a repeated measures analysis of covariance there were no significant effects for study group (p=0.812) time (p=0.954), nor was there a significant interaction between group and time (p=0.858). Use of the Flextend Orthotic Device did not additionally increase grip strength among dental hygiene students over the eight week time period. In none of the weeks post baseline was there a significant difference between the Flextend Orthotic Device group and control groups.

Osteotomy of distal radius fracture malunion using a fast remodeling bone substitute consisting of calcium sulphate and calcium phosphate

Malunion after a distal radius fracture can be treated with an osteotomy of the distal radius. Autologous iliac crest bone graft is often used to fill the gap, but the procedure is associated with donor site morbidity. In this study a novel fast resorbing biphasic bone substitute consisting of a mixture of calcium sulphate and calcium phosphate is used (Cerament BoneSupport AB, Sweden). Fifteen consecutive patients, with a mean age of 52 (27-71) years were included. All had a malunion after a distal radius fracture and underwent an osteotomy. A fragment specific fixation system, TriMed (TriMed, Valencia, CA), consisting of a Buttress Pin and a Radial Pin Plate were used for fixation and a calcium sulphate and calcium phosphate mixture as bone substitute. The patients were followed for 1 year. Grip strength increased from 61 (28-93)% of the contralateral hand to 85 (58-109)%, p < 0.001. DASH scores decreased from 37 (22-61) to 24 (2-49) p = 0.003. Radiographically all osteotomies healed. An increase of ulnar variance was noted during healing from 1.8 mm immediately postoperatively to 2.6 mm at final follow up. Osteotomy can increase grip strength and decease disability after a malunited fracture. In the present series the bone substitute was replaced by bone, but a minor loss of the achieved radiographic correction was noted in some patients during osteotomy healing. A more rigid fixation may improve the radiographic outcome with this kind of bone substitute.

A randomized single blind crossover trial comparing leather and commercial wrist splints for treating chronic wrist pain in adults

BackgroundTo compare the effectiveness of a custom-made leather wrist splint (LS) with a commercially available fabric splint (FS) in adults with chronic wrist pain.MethodsParticipants (N = 25, mean age = 54) were randomly assigned to treatment order in a 2-phase crossover trial. Splints were worn for 2 weeks, separated by a one-week washout period. Outcomes were assessed at baseline and after each splint phase using the Australian/Canadian Osteoarthritis Hand Index (AUSCAN), the Canadian Occupational Performance Measure (COPM) and Jamar dynamometer by an observer blinded to treatment allocation.ResultsBoth styles of wrist splint significantly reduced pain (effect size LS 0.79, FS 0.43), improved hand function and increased grip strength compared to baseline (all p < 0.05) with no increase in wrist stiffness. There was a consistent trend for the LS to be superior to the FS but this was statistically significant only for patient perceived occupational performance (p = 0.008) and satisfaction (p = 0.015). Lastly, 72% of patients preferred the custom-made leather splint compared to the commercially available splint.ConclusionLeather wrist splints were superior to a commercially available fabric splint for the short-term relief of pain and dysfunction.

Effects of progesterone administration on infarct volume and functional deficits following permanent focal cerebral ischemia in rats

Recent experimental evidence indicates that progesterone (PROG) protects against various models of brain injury, including ischemic stroke. Most human studies of pharmacologic treatments for acute cerebral stroke have failed despite initial success in animal models. To simulate better the typical human stroke without reperfusion, the present study was conducted to examine the efficacy of PROG on infarct volume and functional outcome in a permanent model of stroke, using direct cauterization of the middle cerebral artery (MCA). Twenty-four male adult Sprague–Dawley rats underwent pMCAO by electro-coagulation and sham operation. After induction of permanent MCA occlusion (pMCAO), the rats received an initial intraperitoneal injection of PROG (8 mg/kg) or vehicle at 1 h post-occlusion followed by subcutaneous injections at 6, 24 and 48 h. Functional deficits were tested on the rotarod and grip-strength meter at 24, 48 and 72 h after pMCAO. The rats were killed 72 h after surgery and isolated brain was sectioned into coronal slices and stained with 2, 3, 5-triphenyltetrazolium chloride (TTC). PROG-treated rats showed a substantial reduction (54.05%) in the volume of the infarct (% contralateral hemisphere) compared to vehicle controls. In addition there was a significant improvement in ability to remain on an accelerating rotarod and increased grip strength observed in the pMCAO rats treated with PROG compared to vehicle. Taken together, these data indicate that PROG is beneficial in one of the best-characterized models of stroke, and may warrant further testing in future clinical trials for human stroke.

P27 Antiangiogenic activity of combining gefitinib and rapamycin in a panel of pancreas cancer cell lines

PURPOSE: Pancreatic ductal adenocarcinoma (PDAC) is the third leading cause of cancer death in the United States. This study was aimed at evaluating the efficacy of AR-42 (formerly OSU-HDAC42), a novel histone deacetylase (HDAC) inhibitor currently in clinical trials, in suppressing tumor growth and/or cancer-induced muscle wasting in murine models of PDAC. EXPERIMENTAL DESIGN: The in vitro antiproliferative activity of AR-42 was evaluated in six human pancreatic cancer cell lines (AsPC-1, COLO-357, PANC-1, MiaPaCa-2, BxPC-3, SW1990). AsPC-1 subcutaneous xenograft and transgenic KPfl/flC (LSL-KrasG12D;Trp53flox/flox;Pdx-1-Cre) mouse models of pancreatic cancer were used to evaluate the in vivo efficacy of AR-42 in suppressing tumor growth and/or muscle wasting. RESULTS: Growth suppression in AR-42–treated cells was observed in all six human pancreatic cancer cell lines with dose-dependent modulation of proliferation and apoptotic markers, which was associated with the hallmark features of HDAC inhibition, including p21 upregulation and histone H3 hyperacetylation. Oral administration of AR-42 at 50 mg/kg every other day resulted in suppression of tumor burden in the AsPC-1 xenograft and KPfl/flC models by 78% and 55%, respectively, at the end of treatment. Tumor suppression was associated with HDAC inhibition, increased apoptosis, and inhibition of proliferation. Additionally, AR-42 as a single agent preserved muscle size and increased grip strength in KPfl/flC mice. Finally, the combination of AR-42 and gemcitabine in transgenic mice demonstrated a significant increase in survival than either agent alone. CONCLUSIONS: These results suggest that AR-42 represents a therapeutically promising strategy for the treatment of pancreatic cancer.

Arthroscopic Repair of Triangular Fibrocartilage Complex Tears

The objective of this study was to investigate the clinical results and functional outcomes of patients with peripheral triangular fibrocartilage complex (TFCC) lesions repaired by arthroscopic technique and to describe the pathology of dorsal tears of the TFCC, which was not described in Palmer's classification. Thirty-five patients with arthroscopic repair of TFCC tears were reviewed. There were 22 males and 13 females. The average age was 33 years (range, 13 to 51 years). The average follow-up was 39 months (range, 4 to 82 months). TFCC tears were classified by the Palmer classification as follows: IB (11), IC (5), and ID (1). The remaining 18 were not classified according to the Palmer classification. Functional results were evaluated using the ADL (activities of daily living) score and the Modified Mayo Wrist Score. A dorsal peripheral tear found in 18 wrists does not fulfill the Palmer classification of traumatic TFCC injuries. Seventy-four percent of patients had reduction in pain after surgery, with improvement in grip strength and daily activities (P < .05). The Modified Mayo Wrist score was excellent in 54%, good in 20%, fair in 12%, and poor in 14%. Nineteen of 28 working patients returned to their original work. Ulnar nerve dorsal branch neuritis occurred in 17%. A "second-look" arthroscopy was performed on 9 patients with healing shown in 7. Additional procedures were performed on 10 patients (29%) to improve functional outcome. Arthroscopic repair of peripheral TFCC tears can provide satisfactory results. Seventy-four percent of our patients achieved good to excellent results, had significant pain relief, had increased grip strength, and had an increased capacity to perform daily activities. The Palmer classification does not completely classify all peripheral TFCC tears. Level IV, therapeutic case series.

Sclerosing polidocanol injections in chronic painful tennis elbow-promising results in a pilot study

Sclerosing polidocanol injections targeting the area with neovessels (vascularity) have been demonstrated to give promising clinical results in patients with chronic painful Achilles and patellar tendinosis. Recently, we demonstrated vascularity in the extensor origin in patients with chronic painful tennis elbow, but not in controls with pain-free elbows. In this pilot study, 11 patients (four men and seven women, mean age 46 years) with the diagnosis of tennis elbow in altogether 13 elbows, were included. All patients had a long duration of pain symptoms (mean 23 months), and ultrasonography (US) + colour Doppler (CD) examination showed structural tendon changes with hypo-echoic areas, and a vascularity, corresponding to the painful area in the extensor origin. All patients were treated with US- and CD-guided injections of the sclerosing substance polidocanol, targeting the area with vascularity. At 8-month follow-up after treatment, there was a good clinical result in 11/13 elbows. Extensor origin pain during wrist loading activities (recorded on a VAS-scale) was significantly reduced (mean VAS from 75 to 34; P < 0.003), and maximal grip strength was significantly increased (from 29 to 40 kg; P < 0.025). Our findings indicate that one treatment with sclerosing polidocanol injections, targeting the area with vascularity in the extensor origin, has a potential to reduce the tendon pain and increase grip strength, in patients with chronic painful tennis elbow.

Hypnosis for rehabilitation after stroke: six case studies

This report presents qualitative accounts from a pilot clinical study of six chronic stroke subjects. Our hypothesis was that a hypnotic procedure would help overcome learned nonuse, which is thought to contribute to impaired motor function of the paretic upper limb in chronic stroke patients. The hypnotic procedure involved selecting motor tasks that would challenge each subject, then (1) imagined practice of the challenging motor task revivified from prior to the stroke alternated with imagined practice in the present; (2) imagined practice in the present alternated with imagined practice during active-alert hypnosis; and (3) active-alert imagined practice alternated with actual physical performance. We observed qualitative improvements in motor function related to increased range of motion, increased grip strength, and reduced spasticity of the paretic upper limb. Subjects consistently reported an improved outlook, increased motivation, as well as greater awareness of and decreased effort to perform motor tasks with the paretic limb. Copyright © 2006 British Society of Experimental & Clinical Hypnosis. Published by John Wiley & Sons, Ltd.

Enhanced function in nerve-injured hands after contralateral deafferentation

To explore whether contralateral deafferentation by tourniquet-induced anaesthesia can improve function in a nerve-injured hand, we investigated 14 patients with median or ulnar nerve injuries at wrist level. Deafferentation of the contralateral forearm and hand resulted in significantly improved tactile discrimination, threshold for perception of touch in the injured nerve area and in the area corresponding to the intact nerve in the injured hand, and significantly increased grip strength. Improvements lasted at least 15 min. The results show that hand function after peripheral nerve injury can be temporarily enhanced by manipulation of the process of brain plasticity. Our results may have practical applications in the rehabilitation of peripheral nerve-injured patients.

Riluzole slows the progression of neuromuscular dysfunction in the wobbler mouse motor neuron disease

In the wobbler mouse motor neuron disease (MND), we firstly evaluated the effect of riluzole, the only approved drug for amyotrophic lateral sclerosis, and compared it with that of brain-derived neurotrophic factor (BDNF). Wobbler mice received either daily subcutaneous treatment with BDNF (5, 20, and 40 mg/kg) or oral riluzole in drinking water (100 and 200 μg/ml), beginning immediately after the clinical onset of MND. We examined motor functions, such as grip strength and rota-rod walking performance, weekly, and the amplitude of the compound muscle action potential (CMAP) in the forelimb biceps at the end of treatment. BDNF treatment slowed the disease progression maximally at a dose of 20 mg/kg, consistent to the previous evidence. Only high-dose riluzole treatment increased grip strength at weeks 1 (P=0.0023) and 2 (P=0.021), time before falling in the rota-rod test throughout all 4 weeks of treatment (P=0.0022 to 0.0282), and CMAP amplitude (P=0.0069) at the end of treatment, compared with the vehicle. Furthermore, the riluzole treatment increased the number of the cervical cord anterior horn neurons that were immunoreactive for SMI-32, a specific motor neuron marker, by the end of treatment (P=0.0063), although it did not affect the vacuolar degeneration on the SMI-32-positive neurons. This study demonstrated that riluzole was comparable to BDNF in slowing the progression of neuromuscular dysfunction in the wobbler mouse MND, which may provide a useful model for examining the mechanisms of selective motor neuron degeneration.

Intravenous regional administration of corticosteroids in juvenile chronic arthritis.

Treatment of juvenile chronic arthritis patients with longstanding multiple joint or tendon involvement that is resistant to medication remains a challenge. For 20 years, we have been treating these severely ill patients with intravenous regional glucocorticoids (a modified Bier's block). Since 1996, all juvenile chronic arthritis patients have been followed prospectively by an occupational therapist who has registered the grip strength and range of motion at an average of 6 months after treatment. In 22/40 wrists and hands, increased grip strength was recorded. The mean grip strength increased for the whole group from 47 to 59 N and the flexion lag decreased. The effect of intravenous regional steroid treatment may be limited from a long-term perspective, but in our series, half of the patients showed a considerable improvement after 6 months. Surgical synovectomy can be postponed and perhaps even be omitted.

Dorsal Intercarpal Augmentation Ligamentoplasty for Scapholunate Dissociation

Carpal instability secondary to scapholunate ligament tears can lead to significant disability of the wrist. Disruption of the ligamentous stabilizers of the scaphoid causes rotatory subluxation of the scaphoid and subsequent abnormal loads across the radioscaphoid joint. Arthritic changes involving the radioscaphoid and midcarpal joint will develop if the wrist is untreated. Treatment of scapholunate ligament tears has varied widely in the literature. Today, most surgeons perform either a soft tissue reconstruction using local tissue or a limited fusion. Motion of the wrist favors soft tissue reconstructions. Also, the relative intercarpal motion with a more flexible carpus may prevent abnormal load patterns that are associated with a rigid radial column and limited fusions. We have reconstructed flexible subacute (>3 weeks) and chronic (>2 months) scapholunate dissociations with a radial-based dorsal intercarpal ligament. Clinical results have demonstrated increased grip strength, decreased pain, and improved intercarpal alignment.

Inhibition of myostatin in adult mice increases skeletal muscle mass and strength

A human therapeutic that specifically modulates skeletal muscle growth would potentially provide a benefit for a variety of conditions including sarcopenia, cachexia, and muscular dystrophy. Myostatin, a member of the TGF-β family of growth factors, is a known negative regulator of muscle mass, as mice lacking the myostatin gene have increased muscle mass. Thus, an inhibitor of myostatin may be useful therapeutically as an anabolic agent for muscle. However, since myostatin is expressed in both developing and adult muscles, it is not clear whether it regulates muscle mass during development or in adults. In order to test the hypothesis that myostatin regulates muscle mass in adults, we generated an inhibitory antibody to myostatin and administered it to adult mice. Here we show that mice treated pharmacologically with an antibody to myostatin have increased skeletal muscle mass and increased grip strength. These data show for the first time that myostatin acts postnatally as a negative regulator of skeletal muscle growth and suggest that myostatin inhibitors could provide a therapeutic benefit in diseases for which muscle mass is limiting.