Several submaximal exercise tests are reliable, valid and acceptable in people with chronic pain, fibromyalgia or chronic fatigue: a systematic review

Relationship between subjectively-rated and objectively-tested physical function across six different medical diagnoses

OBJECTIVE

To quantify and compare associations and relationships between self-rated and tested assessments of mainly mobility-related physical function in different diagnoses.

DESIGN

Six longitudinal cohort studies before and after inpatient rehabilitation.

PATIENTS

Patients with whiplash-associated disorder (n = 71), low back pain (n = 121), fibromyalgia (n = 84), lipoedema (n = 27), lymphoedema (n = 78), and post-acute coronary syndrome (n = 64).

METHODS

Physical function was measured with the self-rated Short-Form 36 Physical functioning (SF-36 PF) and with the tested 6-Min Walk Distance (6MWD) and assessed by correlation coefficients. Across the 6 cohorts, the relationship between the 2 scores was compared using the ratio between them.

RESULTS

The correlations between the 2 scores were mostly moderate to strong at baseline (up to r = 0.791), and weak to moderate for the changes to follow-up (up to r = 0.408). The ratios SF-36 PF to 6MWD were 1.143-1.590 at baseline and 0.930-3.310 for the changes, and depended on pain and mental health.

CONCLUSION

Moderate to strong cross-sectional and moderate to weak longitudinal correlations were found between the 6MWD and the SF-36 PF. Pain and mental health should be considered when interpreting physical function. For a comprehensive assessment in clinical practice and research, the combination of self-rated and tested physical function measures is recommended.

Effect of Mobile Internet Technology in Health Management of Heart Failure Patients Guiding Cardiac Rehabilitation

In this paper, we are going to explore the effect of mobile Internet technology in health management for the heart failure patients with cardiac rehabilitation. To implement and evaluate its effects in real environment, a total of 60 heart failure patients were divided, preferably in random fashion, into two groups of 30 cases, i.e., control and observation groups. The former group has received the routine home cardiac rehabilitation after discharge, and the latter group, i.e., observation, has received home cardiac rehabilitation based on mobile medical technical guidance after discharge. The 6 min walking test, Minnesota Cardiac Dysfunction Quality of Life Scale score, cardiac function index, and cardiac rehabilitation training compliance were matched between these groups specifically before and after the intervention. After 12 weeks of intervention, the 6 min walking test, Minnesota Cardiac Dysfunction Quality of Life Scale score, B-type natriuretic peptide of N-terminal, end-diastolic diameter preferably left ventricular, left ventricular ejection fraction, and compliance of training, specifically in the observation group, were better than the control group whereas statistically significant differences were observed, i.e., P < 0.01. Home cardiac rehabilitation guided by mobile Internet technology can improve the function of cardiac, exercise tolerance, life's quality, and compliance of patients with heart failure.

Pain-Related Worrying and Goal Preferences Determine Walking Persistence in Women with Fibromyalgia

Physical activity and exercise are relevant behaviors for fibromyalgia health outcomes; however, patients have difficulties undertaking and maintaining an active lifestyle. With a cross-sectional design, this study explored the role of pain-related worrying and goal preferences in the walking persistence of women with fibromyalgia. The sample included 111 women who attended a tertiary health setting. We adapted the Six-Minute Walk Test where participants decided either to stop or continue walking in five voluntary 6 min bouts. Women who were categorized higher in pain-related worrying reported higher preference for pain avoidance goals (t = -2.44, p = 0.02) and performed worse in the walking task (LongRank = 4.21; p = 0.04). Pain avoidance goal preference increased the likelihood of stopping after the first (OR = 1.443), second (OR = 1.493), and third (OR = 1.540) 6 min walking bout, and the risk of ending the walking activity during the 30 min task (HR = 1.02, [1.0-1.03]). Influence of pain-related worrying on total walking distance was mediated by goal preferences (ab = -3.25). In interventions targeting adherence in physical activity and exercise, special attention is needed for women who are particularly worried about pain to help decrease their preference for short-term pain avoidance goals relative to long-term goals such as being active through walking.

Maximal cardiopulmonary exercise test in patients with chronic low back pain: feasibility, tolerance and relation with central sensitization. An observational study

PURPOSE

To analyze the feasibility of and pain-related tolerance to a maximal cardiopulmonary exercise test (CPET), and the relationship between the aerobic capacity and central sensitization (CS) in patients with chronic low back pain (CLBP).

METHODS

An observational study, combining a cross-sectional and a prospective 24-hour follow-up was performed. Participants underwent a maximal CPET on a cycle ergometer and were assessed with three measures of CS (CS Inventory, quantitative sensory testing and heart rate variability). Before the CPET, immediately afterwards and 24 h after, the Pain Response Questionnaire (PRQ) was filled out. The CPET was considered feasible when >80% performed maximally, and tolerable when <20% reported relevant pain increase, body reactions and additional pain medication use in the PRQ. Multiple regression analyses were applied to assess the relationship between the aerobic capacity (VO2max) and CS measures, corrected for confounders.

RESULTS

74 patients with CLBP participated of which 30 were male, mean age was 40.4 years (SD: 12.4) and median VO2max was 23.9 ml/kg/min (IQR: 18.2-29.4). CPET was completed by 92%. No serious adverse events occurred. A relevant pain increase was reported in the upper legs by 40% immediately after CPET and by 28% 24 h afterwards, 27% reported body reactions after 24 h, and 22% increased pain medication use 24 h after CPET. Very weak and not significant relations (r_partial=-0.21 to 0.05; p > 0.10) were observed between aerobic capacity and CS measures.

CONCLUSIONS

A maximal CPET is feasible in patients with CLBP. Most, but not all, tolerated it well. CS was not related to aerobic capacity.Implications for rehabilitationMaximal CPET is feasible in patients with CLBP and well tolerated by most patients.Maximal CPET can be safely applied to assess the aerobic capacity of patients with CLBP.Aerobic capacity is unrelated to central sensitization.Outcomes of a maximal CPET and the pain response to straining activity can be used to provide valid information for the decision-making of exercise therapy.

Aerobic Physical Exercise for Pain Intensity, Aerobic Capacity, and Quality of Life in Patients With Chronic Pain: A Systematic Review and Meta-Analysis

BACKGROUND

Currently, chronic pain is a disabling condition that is difficult to manage, which generates a high burden on health systems. The objective is to determine the effects of aerobic physical exercise in adults with chronic pain.

METHODS

A systematic review of searches in databases including MEDLINE, LILACS, ScienceDirect, PEDro, OTseeker, The Cochrane Library, EBSCO, and Google Scholar was conducted. The search process was carried out until July 31, 2020, and the study selection process was independently carried out through a criteria analysis for each phase. Outcome measures were chosen: aerobic capacity, physical function, quality of life, and pain.

RESULTS

Twenty-seven studies were included in which aerobic exercise was considered as an option to treat chronic pain. These studies showed significant results compared with other treatment options in terms of pain measurements (-0.22 [-0.42 to -0.03]) and aerobic capacity. For quality of life, there were significant improvements in the physical function component over the mental health component evaluated with the short form health survey-36/12.

CONCLUSION

Aerobic exercise is a nonpharmacological therapeutic option for treatment. Also, aerobic capacity and endurance improved when this type of exercise was prescribed, thus resulting in a substantial improvement in the quality of life of people suffering from chronic pain.

Physical activity in the treatment of fibromyalgia

International treatment recommendations for fibromyalgia (FM) highlight the importance of adapted physical activity (APA) combined with patient education. Cognitive and behavioral therapies as well as an interdisciplinary approach can be proposed for more complex or severe clinical situations, with a biopsychosocial vision of rehabilitation. To personalize the rehabilitation's therapeutic approach, a clinician can use simple and validated instruments for measuring physical performance that will highlight levels of physical conditioning, which range from low to very low in FM patients. Several systematic reviews and meta-analyses have found strong evidence that supervised aerobic and resistance-training programs reduce the pain intensity and significantly improve the quality of life and the physical and psychological functioning of female FM subjects. These therapeutic approaches appear safe and promising in terms of cost-effectiveness and should be the subject of more randomized controlled trials among male FM subjects and adolescents.

Reliability and Validity of Physical Tools and Measurement Methods to Quantify Hand Swelling: A Systematic Review

OBJECTIVE

Hand swelling may result from injury or trauma. Various physical assessment tools and measurement methods can be used to quantify the volume or size of the hand or fingers; however, the reliability and validity of each tool and measurement method have not been evaluated. The purpose of this study was to evaluate the reliability and validity of physical assessment tools and methods used to quantify hand and finger volume orsize.

METHODS

MEDLINE, CINAHL, EMBASE, Web of Science, and Scopus were searched using key terms related to swelling, edema, volume, size, hand, measures, reliability, and validity. Cross-sectional or longitudinal studies that assessed reliability and/or validity of physical assessment tools or measurement methods to quantify hand swelling were included. Two examiners independently extracted data from the included articles and appraised the articles' quality using the Consensus-Based Standards for the Selection of Health Measurement Instruments methodology. Data extracted from studies analyzing reliability and validity were grouped by type of assessment tool and measurement method.

RESULTS

Five physical assessment tools used for quantification of hand swelling were evaluated, including tape measure, water volumeter, bioimpedance spectroscopy, ring gauge, 3-dimensional techniques. All assessment tools had good to excellent reliability (ICC = 0.74 - 0.99), and moderate to high validity (Pearson coefficient = 0.58 - 0.99), for quantification of the volume or size of the hand or fingers.

CONCLUSION

All measurement methods with these tools had good to excellent reliability and moderate to high validity. The evidence underpinning the figure-of-eight technique, which uses a tape measure, was the highest. Because these physical assessment tools and measurement methods assess different aspects and regions of the hand, which one is selected depends on the region of interest for assessment and the availability of tools.

IMPACT

Reliable tools and measurement methods are available to measure the size or volume of the hand and fingers, either together or separately. The best tool will depend on the aim of assessment and tool availability.

LAY SUMMARY

Hand swelling can occur with injuries, burns, or lymphedema. This review shows that tools are available to accurately measure swelling in any part of thehand.

Effects of physical exercise on the prevention of stem cells senescence

Regular physical activity is essential for maintaining wellbeing; physical inactivity, on the contrary, is considered by the World Health Organization (WHO) as one of the most important risk factors for global mortality. During physical exercise different growth factors, cytokines and hormones are released, which affect positively the functions of heart, bone, brain and skeletal muscle. It has been reported that physical activity is able to stimulate tissue remodeling. Therefore, in this scenario, it is important to deepen the topic of physical activity-induced effects on stem cells.

A Clinical Method for Estimation of VO2max Using Seismocardiography

The purpose of this study was to investigate the correlation between the seismocardiogram and cardiorespiratory fitness. Cardiorespiratory fitness can be estimated as VO₂max using non-exercise algorithms, but the results can be inaccurate. Healthy subjects were recruited for this study. Seismocardiogram and electrocardiogram were recorded at rest. VO₂max was measured during a maximal effort cycle ergometer test. Amplitudes and timing intervals were extracted from the seismocardiogram and used in combination with demographic data in a non-exercise prediction model for VO₂max. 26 subjects were included, 17 females. Mean age: 38.3±9.1 years. The amplitude following the aortic valve closure derived from the seismocardiogram had a significant correlation of 0.80 (p<0.001) to VO₂max. This feature combined with age, sex and BMI in the prediction model, yields a correlation to VO₂max of 0.90 (p<0.001, 95% CI: 0.83-0.94) and a standard error of the estimate of 3.21 mL·kg^-1·min^-1 . The seismocardiogram carries information about the cardiorespiratory fitness. When comparing to other non-exercise models the proposed model performs better, even after cross validation. The model is limited when tracking changes in VO₂max. The method could be used in the clinic for a more accurate estimation of VO₂max compared to current non-exercise methods.

Energy System Assessment in Survivors of Breast Cancer

BACKGROUND

Survivors of breast cancer commonly report functional limitations, including cancer-related fatigue (CRF) and decreased aerobic capacity. One key gap is addressing the 3 energy systems (aerobic, anaerobic lactic, and alactic), requiring assessment to establish a baseline exercise intensity and duration.

OBJECTIVE

This study examined the feasibility of energy system-based assessment, also providing descriptive values for assessment performance in this population.

DESIGN

This was a cross-sectional study.

METHODS

Seventy-two posttreatment survivors of breast cancer were recruited. Following a baseline musculoskeletal assessment, women attempted 3 energy system assessments: submaximal aerobic (multistage treadmill), anaerobic alactic (30-second sit-to-stand [30-STS]), and anaerobic lactic (adapted burpees). Heart rate (HR) and rating of perceived exertion (RPE) were recorded. Secondary outcomes included body composition, CRF, and upper- and lower-limb functionality.

RESULTS

Seventy of 72 participants performed the 30-STS and 30 completed the adapted burpees task. HR and RPE specific to each task were correlated, reflecting increased intensity. Women reported low-moderate levels of CRF scores (3% [2.1]) and moderate-high functionality levels (upper-limb: 65.8% [23.3]; lower-limb: 63.7% [34.7]).

LIMITATIONS

All survivors of breast cancer had relatively low levels of CRF and moderate functioning. Additionally, on average, participants were classified as "overweight" based on BMI.

CONCLUSION

This study is the first to our knowledge to demonstrate feasibility of energy system assessment in survivors of breast cancer. Using a combination of HR and RPE, as well as baseline assessment of each energy system, clinicians may improve ability to prescribe personalized exercise and give patients greater ability to self-monitor intensity and progress.

Molecular and Lifestyle Factors Modulating Obesity Disease

Obesity adversely affects bone health by means of multiple mechanisms, e.g., alterations in bone-regulating hormones, inflammation, and oxidative stress. Substantial evidence supports the relationship between adiposity and bone disorders in overweight/obese individuals. It is well known that the balance between mutually exclusive differentiation of progenitor cells into osteoblasts or adipocytes is controlled by different agents, including growth factors, hormones, genetic and epigenetic factors. Furthermore, an association between vitamin D deficiency and obesity has been reported. On the other hand, regular physical activity plays a key role in weight control, in the reduction of obesity-associated risks and promotes osteogenesis. The aim of this review is to highlight relevant cellular and molecular aspects for over-weight containment. In this context, the modulation of progenitor cells during differentiation as well as the role of epigenetics and microbiota in obesity disease will be discussed. Furthermore, lifestyle changes including an optimized diet as well as targeted physical activity will be suggested as strategies for the treatment of obesity disease.

Assessing chronic fatigue syndrome: Self-reported physical functioning and correlations with physical testing

The pathophysiology of chronic fatigue syndrome (CFS) remains unclear; no biomarkers have thus far been identified or physical tests designed to underpin its diagnosis. Assessment mainly uses Fukuda's criteria and is based on the exclusion of symptoms related to other diseases/syndromes, subjective self-reporting, and outcomes of self-report questionnaires. In order to improve the baseline assessment and progress evaluation of individuals suspected of CFS and using an association-oriented research strategy and a cross-correlational design, this study investigates possible associations between the performance on two physical tests, i.e. 'Timed Loaded Standing' (TLS), assessing trunk-arm endurance, and the 'Stops Walking with Eyes Closed while performing a secondary Cognitive Task' (SWECCT), measuring impaired automaticity of gait, and the results of two self-report questionnaires, the Checklist Individual Strength (CIS, total score and fatigue subscale score) and the physical functioning and vitality subscales of the Short Form Health Survey (SF-36) to gauge the participants' subjective feelings of fatigue and beliefs regarding their abilities to perform daily-life activities. Comparisons of the outcomes obtained in 27 female patients with a confirmed diagnosis of CFS revealed that trunk-arm endurance as measured with the TLS correlated with the SF-36 physical functioning subscale only (raw p value: 0.004). None of the other correlations were statistically significant. It is concluded that the TLS may have potential as an objective assessment tool to support the diagnosis and monitoring of treatment effects in CFS.

Functional Capacity Evaluation in Different Societal Contexts: Results of a Multicountry Study

Purpose To examine factors associated with Functional Capacity Evaluation (FCE) results in patients with painful musculoskeletal conditions, with focus on social factors across multiple countries. Methods International cross-sectional study was performed within care as usual. Simple and multiple multilevel linear regression analyses which considered measurement's dependency within clinicians and country were conducted: FCE characteristics and biopsychosocial variables from patients and clinicians as independent variables; and FCE results (floor-to-waist lift, six-minute walk, and handgrip strength) as dependent variables. Results Data were collected for 372 patients, 54 clinicians, 18 facilities and 8 countries. Patients' height and reported pain intensity were consistently associated with every FCE result. Patients' sex, height, reported pain intensity, effort during FCE, social isolation, and disability, clinician's observed physical effort, and whether FCE test was prematurely ended were associated with lift. Patient's height, Body Mass Index, post-test heart-rate, reported pain intensity and effort during FCE, days off work, and whether FCE test was prematurely ended were associated with walk. Patient's age, sex, height, affected body area, reported pain intensity and catastrophizing, and physical work demands were associated with handgrip. Final regression models explained 38‒65% of total variance. Clinician and country random effects composed 1-39% of total residual variance in these models. Conclusion Biopsychosocial factors were associated with every FCE result across multiple countries; specifically, patients' height, reported pain intensity, clinician, and measurement country. Social factors, which had been under-researched, were consistently associated with FCE performances. Patients' FCE results should be considered from a biopsychosocial perspective, including different social contexts.

The Siconolfi step test: a valid and reliable assessment of cardiopulmonary fitness in older men with prostate cancer

BACKGROUND

Assessing fitness and promoting regular physical activity can improve health outcomes and early recovery in prostate cancer. This is however, underutilised in clinical practice. The cardiopulmonary exercise test (CPET) is increasingly being used pre-treatment to measure aerobic capacity and peak oxygen consumption (VO2peak - a gold standard in cardiopulmonary fitness assessment). However, CPET requires expensive equipment and may not always be appropriate. The Siconolfi step test (SST) is simpler and cheaper, and could provide an alternative.The aim of this study was to evaluate the validity and reliability of SST for predicting cardiopulmonary fitness in men with prostate cancer. Men were recruited to this two-centre study (Surrey and Newcastle, United Kingdom) after treatment for locally advanced prostate cancer. They had one or more of three risk factors: elevated blood pressure, overweight (BMI > 25), or androgen deprivation therapy (ADT). Cardiopulmonary fitness was measured using SST and cycle ergometry CPET, at two visits three months apart. The validity of SST was assessed by comparing it to CPET. The VO2peak predicted from SST was compared to the VO2peak directly measured with CPET. The reliability of SST was assessed by comparing repeated measures. Bland-Altman analysis was used to derive limits of agreement in validity and reliability analysis.

RESULTS

Sixty-six men provided data for both SST and CPET. These data were used for validity analysis. 56 men provided SST data on both visits. These data were used for reliability analysis. SST provided valid prediction of the cardiopulmonary fitness in men > 60 years old. The average difference between CPET and SST was 0.64 ml/kg/min with non-significant positive bias towards CPET (P = 0.217). Bland-Altman 95% limits of agreement of SST with CPET were ± 7.62 ml/kg/min. SST was reliable across the whole age range. Predicted VO2peak was on average 0.53 ml/kg/min higher at Visit 2 than at Visit 1 (P = 0.181). Bland-Altman 95% limits of agreement between repeated SST measures were ± 5.84 ml/kg/min.

CONCLUSIONS

SST provides a valid and reliable alternative to CPET for the assessment of cardiopulmonary fitness in older men with prostate cancer. Caution is advised when assessing men 60 years old or younger because the VO2peak predicted with SST was significantly lower than that measured with CPET.

Chronotropic Intolerance: An Overlooked Determinant of Symptoms and Activity Limitation in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome?

Post-exertional malaise (PEM) is the hallmark clinical feature of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). PEM involves a constellation of substantially disabling signs and symptoms that occur in response to physical, mental, emotional, and spiritual over-exertion. Because PEM occurs in response to over-exertion, physiological measurements obtained during standardized exertional paradigms hold promise to contribute greatly to our understanding of the cardiovascular, pulmonary, and metabolic states underlying PEM. In turn, information from standardized exertional paradigms can inform patho-etiologic studies and analeptic management strategies in people with ME/CFS. Several studies have been published that describe physiologic responses to exercise in people with ME/CFS, using maximal cardiopulmonary testing (CPET) as a standardized physiologic stressor. In both non-disabled people and people with a wide range of health conditions, the relationship between exercise heart rate (HR) and exercise workload during maximal CPET are repeatable and demonstrate a positive linear relationship. However, smaller or reduced increases in heart rate during CPET are consistently observed in ME/CFS. This blunted rise in heart rate is called chronotropic intolerance (CI). CI reflects an inability to appropriately increase cardiac output because of smaller than expected increases in heart rate. The purposes of this review are to (1) define CI and discuss its applications to clinical populations; (2) summarize existing data regarding heart rate responses to exercise obtained during maximal CPET in people with ME/CFS that have been published in the peer-reviewed literature through systematic review and meta-analysis; and (3) discuss how trends related to CI in ME/CFS observed in the literature should influence future patho-etiological research designs and clinical practice.

Determining the Minimal Clinically Important Difference for 6-Minute Walk Distance in Fibromyalgia

OBJECTIVE

The aim of this study was to estimate the minimal clinically important difference (MCID) for 6-min walk distance (6MWD) in patients with fibromyalgia.

DESIGN

Data from a recently completed trial that included 187 patients who completed the 6-min walk test, Fibromyalgia Impact Questionnaire (FIQ), and Short-Form 36 (SF36) at 12 and 36 wks were used to examine longitudinal changes in 6MWD. An anchor-based approach that used linear regression analyses was used to determine the MCID for 6MWD, using the total FIQ score (FIQ-Total) and SF36-physical function domain as clinical anchors.

RESULTS

The mean (SD) change in 6MWD from baseline to week 36 was 34.4 (65.2) m (P < 0.001). The anchor-based MCIDs for the 6MWD were 156 and 167 m for the FIQ and SF36-physical function domain, respectively. These MCIDs correspond with clinically meaningful improvements in FIQ (14% reduction) and SF36-physical function domain (10-point increase).

CONCLUSION

The MCID for 6MWD in patients with fibromyalgia was 156 to 167 m. These findings provide the first evidence of the change in 6MWD that is perceived by patients to be clinically meaningful. Further research using other MCID calculation methods is needed to refine estimates of the MCID for 6MWD in patients with fibromyalgia.

Application of a Web-Enabled Leg Training System for the Objective Monitoring and Quantitative Analysis of Exercise-Induced Fatigue

Background

Sustained cardiac rehabilitation is the key intervention in the prevention and treatment of many human diseases. However, implementation of exercise programs can be challenging because of early fatigability in patients with chronic diseases, overweight individuals, and aged people. Current methods of fatigability assessment are based on subjective self-reporting such as rating of perceived exertion or require specialized laboratory conditions and sophisticated equipment. A practical approach allowing objective measurement of exercise-induced fatigue would be useful for the optimization of sustained delivery of cardiac rehabilitation to improve patient outcomes.

Objectives

The objective of this study is to develop and validate an innovative approach, allowing for the objective assessment of exercise-induced fatigue using the Web-enabled leg rehabilitation system.

Methods

MedExercise training devices were equipped with wireless temperature sensors in order to monitor their usage by temperature rise in the resistance unit (Δt°). Since Δt° correlated with the intensity and duration of exercise, this parameter was used to characterize participants’ leg work output (LWO). Personal smart devices such as laptop computers with wireless gateways and relevant software were used for monitoring of self-control training. Connection of smart devices to the Internet and cloud-based software allowed remote monitoring of LWO in participants training at home. Heart rates (HRs) were measured by fingertip pulse oximeters simultaneously with Δt° in 7 healthy volunteers.

Results

Exercise-induced fatigue manifested as the decline of LWO and/or rising HR, which could be observed in real-time. Conversely, training at the steady-state LWO and HR for the entire duration of exercise bout was considered as fatigue-free. The amounts of recommended daily physical activity were expressed as the individual Δt° values reached during 30-minute fatigue-free exercise of moderate intensity resulting in a mean of 8.1°C (SD 1.5°C, N=7). These Δt° values were applied as the thresholds for sending automatic notifications upon taking the personalized LWO doses by self-control training at home. While the mean time of taking LWO doses was 30.3 (SD 4.1) minutes (n=25), analysis of times required to reach the same Δt° by the same participant revealed that longer durations were due to fatigability, manifesting as reduced LWO at the later stages of training bouts. Typically, exercising in the afternoons associated with no fatigue, although longer durations of evening sessions suggested a diurnal fatigability pattern.

Conclusions

This pilot study demonstrated the feasibility of objective monitoring of fatigue development in real-time and online as well as retrospective fatigability quantification by the duration of training bouts to reach the same exercise dose. This simple method of leg training at home accompanied by routine fatigue monitoring might be useful for the optimization of exercise interventions in primary care and special populations.