Myeloid-derived suppressor cell mitochondrial fitness governs chemotherapeutic efficacy in hematologic malignancies.

Myeloid derived suppressor cells (MDSCs) are key regulators of immune responses and correlate with poor outcomes in hematologic malignancies. Here, we identify that MDSC mitochondrial fitness controls the efficacy of doxorubicin chemotherapy in a preclinical lymphoma model. Mechanistically, we show that triggering STAT3 signaling via ß2-adrenergic receptor (ß2-AR) activation leads to improved MDSC function through metabolic reprograming, marked by sustained mitochondrial respiration and higher ATP generation which reduces AMPK signaling, altering energy metabolism. Furthermore, induced STAT3 signaling in MDSCs enhances glutamine consumption via the TCA cycle. Metabolized glutamine generates itaconate which downregulates mitochondrial reactive oxygen species via regulation of Nrf2 and the oxidative stress response, enhancing MDSC survival. Using ß2-AR blockade, we target the STAT3 pathway and ATP and itaconate metabolism, disrupting ATP generation by the electron transport chain and decreasing itaconate generation causing diminished MDSC mitochondrial fitness. This disruption increases the response to doxorubicin and could be tested clinically.

Profession-based manual therapy nomenclature: exploring history, limitations, and opportunities.

OBJECTIVE: The International Consortium on Manual Therapies (ICMT) is a grassroots interprofessional association open to any formally trained practitioner of manual therapy (MT) and basic scientists promoting research related to the practice of MT. Currently, MT research is impeded by professions' lack of communication with other MT professions, biases, and vernacular. Current ICMT goals are to minimize these barriers, compare MT techniques, and establish an interprofessional MT glossary. METHODS: Practitioners from all professions with training in manual therapies were encouraged by e-mail and website to participate (www.ICMTConferene.org). Video conferences were conducted at least bimonthly for 2.5 years by profession-specific and interprofessional focus groups (FGs). Members summarized scopes of practice, technique descriptions, associated mechanisms of action (MOA), and glossary terms. Each profession presented their work to the interprofessional FG to promote dialogue, understanding and consensus. Outcomes were reported and refined at numerous public events. RESULTS: Focus groups with representatives from 5 MT professions, chiropractic, massage therapy, osteopathic, physical therapy and structural integration identified 17 targeting osseous structures and 49 targeting nonosseous structures. Thirty-two techniques appeared distinct to a specific profession, and 13 were used by more than 1. Comparing descriptions identified additional commonalities. All professions agreed on 4 MOA categories for MT. A glossary of 280 terms and definitions was consolidated, representing key concepts in MT. Twenty-one terms were used by all MT professions and basic scientists. Five terms were used by MT professions exclusive of basic scientists. CONCLUSION: Outcomes suggested a third to a half of techniques used in MT are similar across professions. Additional research is needed to better define the extent of similarity and how to consistently identify those approaches. Ongoing expansion and refinement of the glossary is necessary to promote descriptive clarity and facilitate communication between practitioners and basic scientists.

Predicting health-related quality of life change using natural language processing in thyroid cancer.

Background: Patient-reported outcomes (PRO) allow clinicians to measure health-related quality of life (HRQOL) and understand patients' treatment priorities, but obtaining PRO requires surveys which are not part of routine care. We aimed to develop a preliminary natural language processing (NLP) pipeline to extract HRQOL trajectory based on deep learning models using patient language. Materials and methods: Our data consisted of transcribed interviews of 100 patients undergoing surgical intervention for low-risk thyroid cancer, paired with HRQOL assessments completed during the same visits. Our outcome measure was HRQOL trajectory measured by the SF-12 physical and mental component scores (PCS and MCS), and average THYCA-QoL score.We constructed an NLP pipeline based on BERT, a modern deep language model that captures context semantics, to predict HRQOL trajectory as measured by the above endpoints. We compared this to baseline models using logistic regression and support vector machines trained on bag-of-words representations of transcripts obtained using Linguistic Inquiry and Word Count (LIWC). Finally, given the modest dataset size, we implemented two data augmentation methods to improve performance: first by generating synthetic samples via GPT-2, and second by changing the representation of available data via sequence-by-sequence pairing, which is a novel approach. Results: A BERT-based deep learning model, with GPT-2 synthetic sample augmentation, demonstrated an area-under-curve of 76.3% in the classification of HRQOL accuracy as measured by PCS, compared to the baseline logistic regression and bag-of-words model, which had an AUC of 59.9%. The sequence-by-sequence pairing method for augmentation had an AUC of 71.2% when used with the BERT model. Conclusions: NLP methods show promise in extracting PRO from unstructured narrative data, and in the future may aid in assessing and forecasting patients' HRQOL in response to medical treatments. Our experiments with optimization methods suggest larger amounts of novel data would further improve performance of the classification model.

Consideration of the importance of measuring thermal discomfort in biomedical research.

Core temperature stability is the result of a dynamically regulated balance of heat loss and gain, which is not reflected by a simple thermometer reading. One way in which these changes manifest is in perceived thermal comfort, 'feeling too cold' or 'feeling too hot', which can activate stress pathways. Unfortunately, there is surprisingly little preclinical research that tracks changes in perceived thermal comfort in response to either disease progression or various treatments. Without measuring this endpoint, there may be missed opportunities to evaluate disease and therapy outcomes in murine models of human disease. Here, we discuss the possibility that changes in thermal comfort in mice could be a useful and physiologically relevant measure of energy trade-offs required under various physiological or pathological conditions.

Chronic adrenergic stress and generation of myeloid-derived suppressor cells: Implications for cancer immunotherapy in dogs.

Recent studies have highlighted a key role played by the sympathetic nervous system (SNS) and adrenergic stress in mediating immune suppression associated with chronic inflammation in cancer and other diseases. The connection between chronic SNS activation, adrenergic stress and immune suppression is linked in part to the ability of catecholamines to stimulate the bone marrow release and differentiation of myeloid-derived suppressor cells (MDSC). Rodent model studies have revealed an important role for ß-adrenergic receptor signalling in suppression of cancer immunity in mice subjected to chronic stresses, including thermal stress. Importantly, therapeutic blockade of beta-adrenergic responses by drugs such as propranolol can partially reverse the generation and differentiation of MDSC, and partly restore tumour immunity. Clinical trials in both humans and dogs with cancer have demonstrated that propranolol blockade can improve responses to radiation therapy, cancer vaccines and immune checkpoint inhibitors. Thus, the SNS stress response has become an important new target to relieve immune suppression in cancer and other chronic inflammatory conditions.

Galectin-3 expression in donor T cells reduces GvHD severity and lethality after allogeneic hematopoietic cell transplantation.

Abundant donor cytotoxic T cells that attack normal host organs remain a major problem for patients receiving allogeneic hematopoietic cell transplantation (allo-HCT). Despite an increase in our knowledge of the pathobiology of acute graft versus host disease (aGvHD), the mechanisms regulating the proliferation and function of donor T cells remain unclear. Here, we show that activated donor T cells express galectin-3 (Gal-3) after allo-HCT. In both major and minor histocompatibility-mismatched models of murine aGvHD, expression of Gal-3 is associated with decreased T cell activation and suppression of the secretion of effector cytokines, including IFN-γ and GM-CSF. Mechanistically, Gal-3 results in activation of NFAT signaling, which can induce T cell exhaustion. Gal-3 overexpression in human T cells prevents severe disease by suppressing cytotoxic T cells in xenogeneic aGvHD models. Together, these data identify the Gal-3-dependent regulatory pathway in donor T cells as a critical component of inflammation in aGvHD.

Modelling growth of Bacillus cereus in paneer by one-step parameter estimation.

Bacillus cereus phylogenetic group III and IV strains are commonly associated with food products and cause toxin mediated foodborne diseases. These pathogenic strains have been identified from milk and dairy products, such as reconstituted infant formula and several cheeses. Paneer is a fresh, soft cheese originating from India that is prone to foodborne pathogen contamination, such as by Bacillus cereus. However, there are no reported studies of B. cereus toxin formation in paneer or predictive models quantifying growth of the pathogen in paneer under different environmental conditions. This study assessed enterotoxin-producing potential of B. cereus group III and IV strains, isolated from dairy farm environments, in fresh paneer. Growth of a four-strain cocktail of toxin-producing B. cereus strains was measured in freshly prepared paneer incubated at 5-55 °C and modelled using a one-step parameter estimation combined with bootstrap re-sampling to generate confidence intervals for model parameters. The pathogen grew in paneer between 10 and 50 °C and the developed model fit the observed data well (R2 = 0.972, RMSE = 0.321 log10 CFU/g). The cardinal parameters for B. cereus growth in paneer along with the 95% confidence intervals were: µopt 0.812 log10 CFU/g/h (0.742, 0.917); Topt is 44.177 °C (43.16, 45.49); Tmin is 4.405 °C (3.973, 4.829); Tmax is 50.676 °C (50.367, 51.144). The model developed can be used in food safety management plans and risk assessments to improve safety of paneer while also adding to limited information on B. cereus growth kinetics in dairy products.

Circadian Rhythm Disruption Increases Tumor Growth Rate and Accumulation of Myeloid-Derived Suppressor Cells.

Circadian rhythm disruption is implicated in the initiation and progression of many diseases, including cancer. External stimuli, such as sunlight, serve to synchronize physiological processes and cellular functions to a 24-h cycle. The immune system is controlled by circadian rhythms, and perturbation of these rhythms can potentially alter the immune response to infections and tumors. The effect of circadian rhythm disruption on the immune response to tumors remains unclear. Specifically, the effects of circadian disruption (CD) on immunosuppressive cell types within the tumor, such as myeloid-derived suppressor cells (MDSCs), are unknown. In this study, a shifting lighting schedule is used to disrupt the circadian rhythm of mice. After acclimation to lighting schedules, mice are inoculated with 4T1 or B16-F10 tumors. Tumor growth is increased in mice housed under circadian disrupting lighting conditions compared to standard lighting conditions. Analysis of immune populations within the spleen and tumor shows an increased accumulation of MDSCs within these tissues, suggesting that MDSC mediated immunosuppression plays a role in the enhanced tumor growth caused by circadian disruption. This paves the way for future studies of the effects of CD on immunosuppression in cancer.

Isolation of human and mouse myeloid-derived suppressor cells for metabolic analysis.

Metabolic reprogramming is associated with myeloid-derived suppressor cell (MDSC) immunosuppressive function. Here, we outline the process for acquiring MDSCs from human and murine sources for subsequent analysis of fatty acid oxidation, oxidative phosphorylation, and glycolysis using the Seahorse XFe 96 Analyzer. Murine MDSCs can be isolated directly from tumor-bearing mice or derived through IL-6 and GM-CSF culture of bone marrow cells from non-tumor-bearing mice. To generate human MDSCs, peripheral blood mononuclear cells (PBMCs) can be cultured with IL-6 and GM-CSF. For complete details on the use and execution of this protocol, please refer to Mohammadpour et al. (2021).

Conservative management of De Quervain's tendinopathy with an orthopedic manual physical therapy approach emphasizing first CMC manipulation: a retrospective case series.

De Quervain's tendinopathy (DQT) is a musculoskeletal disorder that limits hand function of affected individuals. Management of DQT can include splinting, activity modification, medications, corticosteroid injections, physical therapist management, and surgery. There is limited evidence to support the combination of manual therapy and exercise interventions within an Orthopedic Manual Physical Therapy (OMPT) approach when managing patients with DQT. Three patients identified with DQT underwent a multi-modal treatment regimen including carpometacarpal (CMC) thrust and non-thrust manipulation, end range radiocarpal mobilization, mobilization with movement (MWM), strengthening exercises, and grip proprioception training. Outcomes were assessed using the numeric pain rating scale (NPRS), Jamar hand dynamometer grip strength, and the Quick Disabilities of the Arm, Shoulder, and Hand (Quick DASH) questionnaire. These measures were administered at baseline and discharge. Each patient demonstrated improvements in all outcome measures and required ten visits or less to reach a satisfactory outcome. The NPRS improved by a mean of 7.1 points on a 0-10 scale, Quick DASH improved by an average of 37.1%, and grip strength improved by a mean of 27.6 pounds. Each patient was able to return to daily tasks without pain and all improvements were maintained at six month follow-up. An impairment based OMPT management approach was effective in managing three patients with DQT. The inclusion of first CMC manipulation within this multi-modal approach may enhance conservative management of patients with DQT. Because a cause and effect relationship cannot be inferred from a case series, further research is recommended to investigate the efficacy of this management approach.

An Implementation Assessment of the Virtual Acute Care for Elders Program From the Perspective of Key Stakeholders.

OBJECTIVE: The aim of this study was to obtain feedback from key stakeholders and end users to identify program strengths and weaknesses to plan for wider dissemination and implementation of the Virtual Acute Care for Elders (Virtual ACE) program, a novel intervention that improves outcomes for older surgical patients. BACKGROUND: Virtual ACE was developed to deliver evidence-based geriatric care without requiring daily presence of a geriatrician. Previous work demonstrated that Virtual ACE increased mobility and decreased delirium rates for surgical patients. METHODS: We conducted semi-structured interviews with 30 key stakeholders (physicians, nurses, hospital leadership, nurse managers, information technology staff, and physical/occupational therapists) involved in the implementation and use of the program. RESULTS: Our stakeholders indicated that Virtual ACE was extremely empowering for bedside nurses. The program helped nurses identify older patients who were at risk for a difficult postoperative recovery. Virtual ACE also gave them skills to manage complex older patients and more effectively communicate their needs to surgeons and other providers. Nurse managers felt that Virtual ACE helped them allocate limited resources and plan their unit staffing assignments to better manage the needs of older patients. The main criticism was that the Virtual ACE Tracker that displayed patient status was difficult to interpret and could be improved by a better design interface. Stakeholders also felt that program training needed to be improved to accommodate staff turnover. CONCLUSIONS: Although respondents identified areas for improvement, our stakeholders felt that Virtual ACE empowered them and provided effective tools to improve outcomes for older surgical patients.

Time Heals Most Wounds - Perceptions of Thyroidectomy Scars in Patients With Thyroid Cancer.

BACKGROUND: Patients understandably have concerns about thyroidectomy scars. This study aimed to characterize patients' perceptions of their thyroidectomy scar before and up to 1-y after surgery. METHODS: Patients with papillary thyroid cancer (n = 83) completed semi-structured interviews before and at 2-wks, 6-Wk, 6-mo, and 1-y post-thyroidectomy. Interviews probed about scar concerns and appearance. Content analysis was used to identify themes. RESULTS: The majority of participants did not express concerns about scar appearance. When expressed, preoperative concerns often stemmed from previous surgery experiences or unease with neck incisions. Postoperatively, concerns about scar appearance decreased over time throughout the healing period with most patients being satisfied with their scar appearance by 6-mo after surgery. CONCLUSIONS: Patients with papillary thyroid cancer express few concerns about scar thyroidectomy appearance. Surgeons can reassure patients who have preoperative concerns that most patients are satisfied with their scar appearance by 6-mo after surgery.

Ultrasonographic Validation for Needle Placement in the Tibialis Posterior Muscle.

BACKGROUND: The tibialis posterior (TP) muscle plays an important role in normal foot function. Safe, efficacious therapeutic approaches addressing this muscle are necessary; however, the location of the muscle in the deep posterior compartment can create challenges. PURPOSE: The purpose of this study was to assess the accuracy of needle placement in the TP muscle and determine the needle placement in relation to the neurovascular structures located within the deep compartment. DESIGN: Cross Sectional Study. METHODS: Needle placement and ultrasound imaging were performed on 20 healthy individuals. A 50 mm or 60 mm needle was inserted between 30 - 50% of the tibial length measured from the medial tibiofemoral joint. The needle was inserted in a medial to lateral direction into the right extremity with the patient in right side lying. Placement of the needle into the TP muscle was verified with ultrasound imaging, and the shortest distance from the needle to the posterior tibial artery and tibial nerve was measured. The depth from the skin to the superficial border of the TP muscle was also measured. RESULTS: Ultrasonography confirmed the needle filament was inserted into the TP muscle in all 20 individuals and did not penetrate the neurovascular bundle in any individual. The mean distance from the needle to the tibial nerve and posterior tibial artery was 10.0 + 4.7 mm and 10.2 + 4.7 mm respectively. The superficial border of the TP muscle from the skin was at a mean depth of 25.8 + 4.9 mm. CONCLUSION: This ultrasound imaging needle placement study supports placement of a solid filament needle into the TP muscle with avoidance of the neurovascular structures of the deep posterior compartment when placed from a medial to lateral direction at 30-50% of the tibial length. LEVEL OF EVIDENCE: 2b.

ß2-adrenergic receptor signaling regulates metabolic pathways critical to myeloid-derived suppressor cell function within the TME.

Myeloid-derived suppressor cells (MDSCs) impede antitumor immunity; however, the precise mechanisms that regulate their suppressive function remain unresolved. Identifying these mechanisms could lead to therapeutic interventions to boost cancer immunotherapy efficacy. Here, we reveal that ß2 adrenergic receptor (ß2-AR) expression on MDSCs increases with tumor growth and that the ß2-AR stress pathway drives the immune suppressive activity of MDSCs by altering their metabolism. We show that ß2-AR signaling decreases glycolysis and increases oxidative phosphorylation and fatty acid oxidation (FAO). It also increases expression of the fatty acid transporter CPT1A, which is necessary for the FAO-mediated immunosuppressive function of MDSCs. Moreover, we show that ß2-AR signaling increases autophagy and activates the arachidonic acid cycle, both required for increasing the release of the immunosuppressive mediator, PGE2. Our data reveal that ß2-AR signaling triggered by stress is an important physiological regulator of key metabolic pathways in MDSCs, driving their immunosuppressive function.

Evaluating the relationship between citation set size, team size and screening methods used in systematic reviews: a cross-sectional study.

BACKGROUND: Standard practice for conducting systematic reviews (SRs) is time consuming and involves the study team screening hundreds or thousands of citations. As the volume of medical literature grows, the citation set sizes and corresponding screening efforts increase. While larger team size and alternate screening methods have the potential to reduce workload and decrease SR completion times, it is unknown whether investigators adapt team size or methods in response to citation set sizes. Using a cross-sectional design, we sought to understand how citation set size impacts (1) the total number of authors or individuals contributing to screening and (2) screening methods. METHODS: MEDLINE was searched in April 2019 for SRs on any health topic. A total of 1880 unique publications were identified and sorted into five citation set size categories (after deduplication): < 1,000, 1,001-2,500, 2,501-5,000, 5,001-10,000, and > 10,000. A random sample of 259 SRs were selected (~ 50 per category) for data extraction and analysis. RESULTS: With the exception of the pairwise t test comparing the under 1000 and over 10,000 categories (median 5 vs. 6, p = 0.049) no statistically significant relationship was evident between author number and citation set size. While visual inspection was suggestive, statistical testing did not consistently identify a relationship between citation set size and number of screeners (title-abstract, full text) or data extractors. However, logistic regression identified investigators were significantly more likely to deviate from gold-standard screening methods (i.e. independent duplicate screening) with larger citation sets. For every doubling of citation size, the odds of using gold-standard screening decreased by 15 and 20% at title-abstract and full text review, respectively. Finally, few SRs reported using crowdsourcing (n = 2) or computer-assisted screening (n = 1). CONCLUSIONS: Large citation set sizes present a challenge to SR teams, especially when faced with time-sensitive health policy questions. Our study suggests that with increasing citation set size, authors are less likely to adhere to gold-standard screening methods. It is possible that adjunct screening methods, such as crowdsourcing (large team) and computer-assisted technologies, may provide a viable solution for authors to complete their SRs in a timely manner.

Psychosocial stress and immunosuppression in cancer: what can we learn from new research?

It is generally believed that the physiological consequences of stress could contribute to poor outcomes for patients being treated for cancer. However, despite preclinical and clinical evidence suggesting that stress promotes increased cancer-related mortality, a comprehensive understanding of the mechanisms involved in mediating these effects does not yet exist. We reviewed 47 clinical studies published between 2007 and 2020 to determine whether psychosocial stress affects clinical outcomes in cancer: 6.4% of studies showed a protective effect; 44.6% showed a harmful effect; 48.9% showed no association. These data suggest that psychosocial stress could affect cancer incidence and/or mortality, but the association is unclear. To shed light on this potentially important relationship, objective biomarkers of stress are needed to more accurately evaluate levels of stress and its downstream effects. As a potential candidate, the neuroendocrine signalling pathways initiated by stress are known to affect anti-tumour immune cells, and here we summarise how this may promote an immunosuppressive, pro-tumour microenvironment. Further research must be done to understand the relationships between stress and immunity to more accurately measure how stress affects cancer progression and outcome.

Qualitative Analysis of Single-Site Headache Surgery: Is It Different From Multiple-Site Surgery?

BACKGROUND: Migraine surgery has been shown to be efficacious, but nuanced effects of surgery on pain and individuals' lives remain incompletely understood. Surgery may be performed at a single or multiple "primary" sites. The aims of this study were to investigate patient perceptions following single-site surgery and compare themes in patients undergoing single-site surgery with those from a previously published conceptual framework generated with patients undergoing multisite surgery. METHODS: Patients who underwent single-site headache surgery participated in open-ended interviews at least 1 year after surgery. Participants (n = 14) had undergone either occipital, temporal, or nasoseptal site surgery. A multidisciplinary team analyzed transcripts. Recurring themes were identified and compared and contrasted to those observed in patients who underwent multiple-site surgery (n = 15) in a previous study (Plast Reconstr Surg 2019;144(4):956-964). RESULTS: Similar recurring themes emerged from the single-site cohort, and the conceptual framework was applicable to all participants. Two new themes emerged from the single-site analysis. First, 5 of 14 participants described being "migraine-free" postoperatively, a finding not observed in the multisite group. Second, several individuals described financial benefits after surgery, via decreased prescription medication requirements, raises at work, and improved productivity. CONCLUSIONS: Single-site headache surgery appears to positively impact patients' lives in ways that support and expand upon previously published outcomes. Patients undergoing surgery at a single site may be more likely to experience a "pain-free" state, which may relate to the underlying pathophysiology of chronic headache. The effect of surgery on finances appears to be an outcome of interest to patients, which should be explored further.

Chronic Adrenergic Stress Contributes to Metabolic Dysfunction and an Exhausted Phenotype in T Cells in the Tumor Microenvironment.

Metabolic dysfunction and exhaustion in tumor-infiltrating T cells have been linked to ineffectual antitumor immunity and the failure of immune checkpoint inhibitor therapy. We report here that chronic stress plays a previously unrecognized role in regulating the state of T cells in the tumor microenvironment (TME). Using two mouse tumor models, we found that blocking chronic adrenergic stress signaling using the pan ß-blocker propranolol or by using mice lacking the ß2-adrenergic receptor (ß2-AR) results in reduced tumor growth rates with significantly fewer tumor-infiltrating T cells that express markers of exhaustion, with a concomitant increase in progenitor exhausted T cells. We also report that blocking ß-AR signaling in mice increases glycolysis and oxidative phosphorylation in tumor-infiltrating lymphocytes (TIL), which associated with increased expression of the costimulatory molecule CD28 and increased antitumor effector functions, including increased cytokine production. Using T cells from Nur77-GFP reporter mice to monitor T-cell activation, we observed that stress-induced ß-AR signaling suppresses T-cell receptor (TCR) signaling. Together, these data suggest that chronic stress-induced adrenergic receptor signaling serves as a "checkpoint" of immune responses and contributes to immunosuppression in the TME by promoting T-cell metabolic dysfunction and exhaustion. These results also support the possibility that chronic stress, which unfortunately is increased in many patients with cancer following their diagnoses, could be exerting a major negative influence on the outcome of therapies that depend upon the status of TILs and support the use of strategies to reduce stress or ß-AR signaling in combination with immunotherapy.

Normative Parameters of Gastrocnemius Muscle Stiffness and Associations with Patient Characteristics and Function.

BACKGROUND: Quantifying muscle stiffness may aid in the diagnosis and management of individuals with muscle pathology. Therefore, the primary purpose of this study was to establish normative parameters and variance estimates of muscle stiffness in the gastrocnemius muscle in a resting and contracted state. A secondary aim was to identify demographic, anthropometric, medical history factors, and biomechanical factors related to muscle stiffness. METHODS: Stiffness of the gastrocnemius muscle was measured in both a resting and contracted state in 102 asymptomatic individuals in this cross-sectional study. Differences based on muscle state (resting vs contracted) and sex (female vs male) were assessed using a 2 X 2 analysis of variance (ANOVA). Associations between muscle stiffness and sex, age, BMI, race, exercise frequency, exercise duration, force production, and step length were assessed using correlation analysis. RESULTS: Gastrocnemius muscle stiffness significantly increased from a resting to a contracted state [mean difference: 217.5 (95% CI: 191.3, 243.8), p < 0.001]. In addition, muscles stiffness was 35% greater for males than females in a resting state and 76% greater in a contracted state. Greater muscle stiffness in a relaxed and contracted state was associated with larger plantarflexion force production (r = .26, p < 0.01 and r = .23, p < 0.01 respectively). CONCLUSION: Identifying normative parameters and variance estimates of muscle stiffness in asymptomatic individuals may help guide diagnosing and managing individuals with aberrant muscle function. LEVEL OF EVIDENCE: 2b Individual Cohort Study. CLINICAL RELEVANCE: What is known about the subject: Muscle stiffness has been shown to be related to individuals with pathology such as Achilles tendinopathy; however, research is sparse regarding normative values of muscle stiffness. Measuring muscle stiffness may also be a way to potentially predict individuals prone to injury or to monitor the effectiveness of management strategies.What this study adds to existing knowledge: This study establishes defined estimates of muscle stiffness of the gastrocnemius in both a relaxed and contracted state in healthy individuals. Myotonometry measures of muscle stiffness demonstrated an increase in stiffness during contraction that varies by sex. Greater gastrocnemius muscle stiffness was associated with increased plantarflexion force production.