Depressive symptom heterogeneity among older adults after hip fracture.

OBJECTIVE: to evaluate patterns of depressive symptoms after hip fracture and examine their impact on functional recovery. METHODS: participants (n = 304) included older adults from the Baltimore Hip Studies 7th cohort who experienced a hip fracture. Depressive symptoms were measured at baseline or 2-, 6- or 12-month post-hip fracture using the 20-item Center for Epidemiologic Studies Depression scale. Gait speed was measured after hip fracture at 2-, 6- or 12-month follow-up. Latent class analysis was used to identify individuals with similar patterns of depressive symptoms after hip fracture. Item response probabilities characterised symptom profiles, and posterior probability estimates were used to assign participants to a baseline depressive symptom subtype. Weighted estimated equations compared post-fracture gait speed between baseline symptomatic and asymptomatic groups. RESULTS: four patterns of depressive symptoms were identified: asymptomatic (50.8%), somatic (28.6%), melancholic (11.4%) and anhedonic (9.2%). The somatic subtype was characterised by difficultly concentrating and reduced energy and movement, whereas anhedonic symptoms were associated with the inability to experience pleasure. Melancholic symptoms corresponded to anhedonia, decreased physical activity and other psychological and somatic complaints. Compared with the asymptomatic group, somatic symptoms were consistently associated with slower gait speed, -0.03 metres per second (m/s) and between-group differences for melancholic symptomology were as large as -0.05 m/s, but the associations were not statistically significant. CONCLUSION: findings demonstrate unique depressive symptom subtypes in older adults after hip fracture and provide confirmatory evidence of unique clinical phenotypes; however, their impact on functional recovery after hip fracture remains unclear.

Exchange of Sex for Drugs or Money in Adolescents and Young Adults: An Examination of Sociodemographic Factors, HIV-Related Risk, and Community Context.

The goal of this research was to examine associations among sociodemographic factors, HIV risk, and community context (e.g., economic insecurity, job training, housing instability, crime victimization, and perceived community norms) in adolescents and young adults who ever exchanged sex for drugs or money. Anonymous survey data were collected using ACASIs at community venues where adolescents and young adults congregate in resource-challenged, STI prevalent, urban, US neighborhoods. Conventional descriptive statistics, Fisher's exact tests, and generalized estimating equations approaches were used to examine associations. Participants (1818, 95.5 % of those screened eligible) were, on average, aged 21.0 years; 42.2 % were males, and 4.6 % were transgender. Almost one-third (32.1 %) identified as gay or lesbian, 18.1 % identified as bisexual; 66.2 % were Black and 21.0 % were Hispanic; 1.3 % was 'living on the street'. A sizeable proportion reported HIV-related risk: 16.3 % exchanged sex, 12.6 % had sex with someone they knew to be HIV-infected, 7.8 % had sex with someone who injected drugs, and 1.3 % injected drugs. Multivariate comparisons identified a number of variables (e.g., being male or transgender, homelessness, sex with a partner who has HIV, STI history, unemployment, job training access, housing instability, crime victimization, perceived community norms) that were significantly associated with exchange of sex (p < 0.05). This research contributes to the knowledge-base regarding exchange of sex among adolescents and young adults, particularly as it relates to community context. Longitudinal studies to describe the trajectory of social, health, and physical risks and consequences are needed for development of effective evidence-based prevention strategies.

Adult-onset immunodeficiency in Thailand and Taiwan.

BACKGROUND: Autoantibodies against interferon-γ are associated with severe disseminated opportunistic infection, but their importance and prevalence are unknown. METHODS: We enrolled 203 persons from sites in Thailand and Taiwan in five groups: 52 patients with disseminated, rapidly or slowly growing, nontuberculous mycobacterial infection (group 1); 45 patients with another opportunistic infection, with or without nontuberculous mycobacterial infection (group 2); 9 patients with disseminated tuberculosis (group 3); 49 patients with pulmonary tuberculosis (group 4); and 48 healthy controls (group 5). Clinical histories were recorded, and blood specimens were obtained. RESULTS: Patients in groups 1 and 2 had CD4+ T-lymphocyte counts that were similar to those in patients in groups 4 and 5, and they were not infected with the human immunodeficiency virus (HIV). Washed cells obtained from patients in groups 1 and 2 had intact cytokine production and a response to cytokine stimulation. In contrast, plasma obtained from these patients inhibited the activity of interferon-γ in normal cells. High-titer anti-interferon-γ autoantibodies were detected in 81% of patients in group 1, 96% of patients in group 2, 11% of patients in group 3, 2% of patients in group 4, and 2% of controls (group 5). Forty other anticytokine autoantibodies were assayed. One patient with cryptococcal meningitis had autoantibodies only against granulocyte-macrophage colony-stimulating factor. No other anticytokine autoantibodies or genetic defects correlated with infections. There was no familial clustering. CONCLUSIONS: Neutralizing anti-interferon-γ autoantibodies were detected in 88% of Asian adults with multiple opportunistic infections and were associated with an adult-onset immunodeficiency akin to that of advanced HIV infection. (Funded by the National Institute of Allergy and Infectious Diseases and the National Institute of Dental and Craniofacial Research; ClinicalTrials.gov number, NCT00814827.).

College Students' Perceptions of Depressed Mood: Exploring Accuracy and Associations.

College is a time of high risk for depressed mood. Theories about depression (i.e. Cognitive Theory and Depressive Realism theory) are well researched, but suggest different venues of understanding the cognitive underpinnings of mood. In addition, much research is available about normative perceptions around substance use and how those perceptions relate to behaviors. However, there are no studies examining normative perceptions around depressed mood nor how these perceptions may relate to students' own well-being. Undergraduates (N=1577) ages 18-24 responded to an online survey as part of a larger study on drinking and depressed mood. The survey assessed symptoms of depression and feelings of sadness, depression and suicidal ideation experienced in the past 2 weeks, as well as students' perceptions of the prevalence of these feelings among other students. Rates of sadness and depression reported in the sample were relatively high; whereas rates of reported suicidal ideation were low. Most students under-estimated the prevalence of sadness and depression experienced by other students; a finding that was especially true for male students. Conversely, most students over-estimated the prevalence of suicidal ideation. Students who reported experiencing a given feeling in the past two weeks perceived greater rates of the feeling among other students. Depression symptoms were associated with both greater perceived prevalence of sadness, depression and suicidal ideation, as well as correct and over-estimates of the prevalence of sadness and depression. Implications for future directions in prevention and interventions efforts are discussed.

Undiagnosed obstructive sleep apnea increases risk of hospitalization among a racially diverse group of older adults with comorbid cardiovascular disease.

STUDY OBJECTIVES: Undiagnosed obstructive sleep apnea (OSA) is associated with increased risk for subsequent cardiovascular events, hospitalizations, and mortality. The primary objective of this study was to determine the association between undiagnosed OSA and subsequent hospitalizations among older adults with preexisting cardiovascular disease (CVD). A secondary objective was to determine the risk of 30-day hospital readmission associated with undiagnosed OSA among older adults with CVD. METHODS: This was a retrospective cohort study of a 5% sample of Medicare administrative claims data for years 2006-2013. Beneficiaries aged 65 years and older diagnosed with CVD were included. Undiagnosed OSA was defined as the 12-month period prior to OSA diagnosis. A similar 12-month period among beneficiaries not diagnosed with OSA was used for the comparison group (no OSA). Our primary outcome was the first all-cause hospital admission. Among beneficiaries with a hospital admission, 30-day readmission was assessed for the first hospital admission only. RESULTS: Among 142,893 beneficiaries diagnosed with CVD, 19,390 had undiagnosed OSA. Among beneficiaries with undiagnosed OSA, 9,047 (46.7%) experienced at least 1 hospitalization whereas 27,027 (21.9%) of those without OSA experienced at least 1 hospitalization. Following adjustment, undiagnosed OSA was associated with increased risk of hospitalization (odds ratio 1.82; 95% confidence interval 1.77, 1.87) relative to no OSA. Among beneficiaries with ≥ 1 hospitalization, undiagnosed OSA was associated with a smaller but significant effect in weighted models (odds ratio 1.18; 95% confidence interval 1.09, 1.27). CONCLUSIONS: Undiagnosed OSA was associated with significantly increased risk of hospitalization and 30-day readmissions among older adults with preexisting CVD. CITATION: Kirk J, Wickwire EM, Somers VK, Johnson DA, Albrecht JS. Undiagnosed obstructive sleep apnea increases risk of hospitalization among a racially diverse group of older adults with comorbid cardiovascular disease. J Clin Sleep Med. 2023;19(7):1175-1181.

A comparison of MVP and MSVT performance among a diverse clinical pediatric sample.

The Memory Validity Profile (MVP) and Medical Symptom Validity Test (MSVT) are performance validity tests (PVTs) used to identify potential noncredible test performance during psychological evaluations. This study sought to examine the agreement between MVP and MSVT pass rates, as well as to determine if there are differences in MVP pass rates when using the cutoff score in the MVP professional manual compared with the experimental cutoff score of <31. Via retrospective review of records, 106 clients at a private neuropsychological clinic who had been given the MVP and the MSVT were identified. Results indicated that only one client met the manual cutoff scores, compared to 20 clients who failed the MSVT, raising concerns regarding the sensitivity of the MVP. Utilizing the receiver operator characteristic (ROC), curve analyses indicated fair discriminability of the MVP for the 106 participants (AUC = .717) with acceptable sensitivity (.50) and specificity (.92) for an MVP total score cutoff of <31. These findings support the utility of the experimental cut score in improving the sensitivity while maintaining adequate specificity in a clinically mixed population.

A review of performance and symptom validity testing with pediatric populations.

Growing recognition and concerns of non-credible performance in pediatric populations have led clinicians to investigate the utility of performance and symptom validity tests (PVT/SVTs) among children and adolescents. Yet current research has indicated that a minority of clinicians routinely utilize a free-standing PVT in pediatric neuropsychological evaluations. The current article investigates the rationale for using PVT/SVTs, and the impact that failure of such exams have on other neurocognitive tests. A review of common adult PVTs and their appropriateness for use with specific pediatric clinical populations is presented, as well as empirical evidence for evaluating embedded validity indicators. The limited literature on SVTs with youth is also reviewed and provides additional insight into symptom exaggeration. There are various reasons children would provide noncredible performance, many of which are different from adults. A review of how the clinician should handle this behavior in pediatric evaluations is provided and what patient populations may present with a higher base rate of failure. Finally, various approaches are offered on how to explain these results to children and their caregivers.

Estimating relationships between phenotypes and subjects drawn from admixed families.

BACKGROUND: Estimating relationships among subjects in a sample, within family structures or caused by population substructure, is complicated in admixed populations. Inaccurate allele frequencies can bias both kinship estimates and tests for association between subjects and a phenotype. We analyzed the simulated and real family data from Genetic Analysis Workshop 19, and were aware of the simulation model. RESULTS: We found that kinship estimation is more accurate when marker data include common variants whose frequencies are less variable across populations. Estimates of heritability and association vary with age for longitudinally measured traits. Accounting for local ancestry identified different true associations than those identified by a traditional approach. Principal components aid kinship estimation and tests for association, but their utility is influenced by the frequency of the markers used to generate them. CONCLUSIONS: Admixed families can provide a powerful resource for detecting disease loci, as well as analytical challenges. Allele frequencies, although difficult to adequately estimate in admixed populations, have a strong impact on the estimation of kinship, ancestry, and association with phenotypes. Approaches that acknowledge population structure in admixed families outperform those which ignore it.

The effects of perennial ryegrass and alfalfa on microbial abundance and diversity in petroleum contaminated soil.

Enhanced rhizosphere degradation uses plants to stimulate the rhizosphere microbial community to degrade organic contaminants. We measured changes in microbial communities caused by the addition of two species of plants in a soil contaminated with 31,000 ppm of total petroleum hydrocarbons. Perennial ryegrass and/or alfalfa increased the number of rhizosphere bacteria in the hydrocarbon-contaminated soil. These plants also increased the number of bacteria capable of petroleum degradation as estimated by the most probable number (MPN) method. Eco-Biolog plates did not detect changes in metabolic diversity between bulk and rhizosphere samples but denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified partial 16S rDNA sequences indicated a shift in the bacterial community in the rhizosphere samples. Dice coefficient matrices derived from DGGE profiles showed similarities between the rhizospheres of alfalfa and perennial ryegrass/alfalfa mixture in the contaminated soil at week seven. Perennial ryegrass and perennial ryegrass/alfalfa mixture caused the greatest change in the rhizosphere bacterial community as determined by DGGE analysis. We concluded that plants altered the microbial population; these changes were plant-specific and could contribute to degradation of petroleum hydrocarbons in contaminated soil.

Overview of the evaluation, diagnosis, and management of urinary tract infections in infants and children.

Urinary tract infection (UTI) is the most common serious bacterial infection in infants and children. UTI is an infection of the lower urinary tract, the upper urinary tract, or both. The diagnosis is dependent on the collection and analysis of an uncontaminated urine specimen. It is the combination of bacterial virulence, and host factors that are closely interrelated, which lead to the development of a UTI. Management of UTI in infants and children requires prompt diagnosis, treatment, and resolution of symptoms followed by appropriate radiologic evaluation. The ultimate goal is the preservation of kidney function.

Methods of studying soil microbial diversity.

Soil microorganisms, such as bacteria and fungi, play central roles in soil fertility and promoting plant health. This review examines and compares the various methods used to study microbial diversity in soil.

Systematic review of the effect of pneumococcal conjugate vaccine dosing schedules on vaccine-type invasive pneumococcal disease among young children.

BACKGROUND: Pneumococcal conjugate vaccines (PCV) are being implemented globally using a variety of different schedules. The optimal schedule to maximize protection of vaccinated children against vaccine-type invasive pneumococcal disease (VT-IPD) is not known. METHODS: To assess the relative benefit of various PCV dosing schedules, we conducted a systematic review of studies published in English from 1994 to 2010 (supplemented post hoc with studies from 2011) on PCV effectiveness against VT-IPD among children targeted to receive vaccine. Data on 2-dose and 3-dose primary series, both with and without a booster ("2+0," "2+1," "3+0" and "3+1"), were included. For observational studies using surveillance data or case counts, we calculated percentage reduction in VT-IPD before and after PCV introduction. RESULTS: Of 4 randomized controlled trials and 31 observational studies reporting VT-IPD among young children, none evaluated a 2+0 complete series, 7 (19%) evaluated 2+1, 4 (11%) 3+0 and 27 (75%) 3+1. Most (86%) studies were from North America or Europe. Only 1 study (observational) directly compared 2 schedules (3+0 vs. 3+1); results supported the use of a booster dose. In clinical trials, vaccine efficacy ranged from 65% to 71% with 3+0 and 83% to 94% with 3+1. Surveillance data and case counts demonstrate reductions in VT-IPD of up to 100% with 2+1 (6 studies) or 3+1 (17 studies) schedules and up to 90% with 3+0 (2 studies). Reductions were observed as early as 1 year after PCV introduction. CONCLUSIONS: These data support the use of 2+1, 3+0 and 3+1 schedules, although most data of PCV impact on VT-IPD among young children are from high-income countries using 3+1. Differences between schedules for impact on VT-IPD are difficult to discern based on available data.

Systematic review of the effect of pneumococcal conjugate vaccine dosing schedules on prevention of pneumonia.

BACKGROUND: Pneumonia is the leading cause of morbidity and mortality among children <5 years of age globally. Pneumococcal conjugate vaccines (PCVs) are known to provide protection against vaccine serotype pneumococcal pneumonia; uncertainty exists regarding the optimum PCV dosing schedule. METHODS: We conducted a systematic review of studies published from 1994 to 2010 (supplemented post hoc with studies from 2011) documenting the effect of PCV dosing schedules on clinical and radiologically confirmed pneumonia, pneumococcal pneumonia and empyema among children of ages targeted to receive vaccine. Data on 2- and 3-dose schedules were included. Percent change of pneumonia incidence rates from baseline to most recent year post-PCV introduction was calculated. RESULTS: We identified 42 primary citations that evaluated PCV schedules and pneumonia. Thirty-seven (88%) were from North America, Europe or Australia; 37 (88%) evaluated PCV7 and 1 (2%) PCV10. Two studies (both observational) compared multiple schedules within the study. We found evidence of reduced clinical and radiologically confirmed pneumonia incidence for all schedules, including 2+1 (1 nonrandomized trial, 5 observational studies), 3+0 (5 randomized trials, 2 observational studies) and 3+1 (5 clinical trials, 24 observational studies) schedules. The magnitude of disease impact did not differ among schedules. Evidence for impact on pneumococcal pneumonia and empyema varied. CONCLUSIONS: All schedules (2+1, 3+0 and 3+1) reduced clinical and radiologically confirmed pneumonia. Quantifying differences in pneumonia disease impact between schedules was difficult due to heterogeneity among studies in design, case definition and population. These findings support World Health Organization recommendations for 3-dose schedules administered as either 3+0 or 2+1 regimens. Pneumonia impact data are still needed on expanded serotype PCV products, developing country settings and the role for a booster dose.

Systematic review of the effect of pneumococcal conjugate vaccine dosing schedules on vaccine-type nasopharyngeal carriage.

BACKGROUND: Pneumococcal conjugate vaccines (PCV) reduce nasopharyngeal carriage of vaccine type (VT) pneumococci, an important driver of vaccine programs' overall benefits. The dosing schedule that best reduces carriage is unclear. METHODS: We performed a systematic review of English language publications from 1994 to 2010 (supplemented post hoc with studies from 2011) reporting PCV effects on VT carriage to assess variability in effect by dosing schedule. RESULTS: We identified 32 relevant studies (36 citations) from 12,980 citations reviewed. Twenty-one (66%) evaluated PCV7; none used PCV10 or PCV13. Five studies evaluated 2 primary doses and 13 three primary doses. After the first year of life, 14 evaluated 3-dose primary series with PCV booster (3+1), seven 3 doses plus 23-valent polysaccharide booster "3+1PPV23," five "3+0," four "2+1," three "2+1PPV23" and two "2+0." Four studies directly compared schedules. From these, 3 primary doses reduced VT carriage more than 2 doses at 1-7 months following the series (1 study significant; 2 borderline). In a study, the 2+1 schedule reduced VT carriage more than 2+0 at 18, but not at 24 months of age. One study of a 23-valent pneumococcal polysaccharide vaccine booster showed no effect. All 16 clinical trials with unvaccinated controls and 11 observational studies with before-after designs showed reduction in VT carriage. CONCLUSIONS: The available literature demonstrates VT-carriage reduction for 2+0, 2+1, 3+0 and 3+1 PCV schedules, but not for 23-valent pneumococcal polysaccharide vaccine booster. Comparisons between schedules show that 3 primary doses and a 2+1 schedule may reduce carriage more than 2 primary doses and a 2+0 schedule, respectively.

Systematic review of the indirect effect of pneumococcal conjugate vaccine dosing schedules on pneumococcal disease and colonization.

BACKGROUND: To aid decision making for pneumococcal conjugate vaccine (PCV) use in infant national immunization programs, we summarized the indirect effects of PCV on clinical outcomes among nontargeted age groups. METHODS: We systematically reviewed the English literature on infant PCV dosing schedules published from 1994 to 2010 (with ad hoc addition of 2011 articles) for outcomes on children >5 years of age and adults including vaccine-type nasopharyngeal carriage (VT-NP), vaccine-type invasive pneumococcal disease (VT-IPD) and syndromic pneumonia. RESULTS: Of 12,980 citations reviewed, we identified 21 VT-IPD, 6 VT-NP and 9 pneumonia studies. Of these 36, 21 (58%) included 3 primary doses plus PCV or pneumococcal polysaccharide vaccine (PPV23) booster schedule (3+1 or 3+PPV23), 5 (14%) 3+0, 9 (25%) 2+1 and 1 (3%) 2+0. Most (95%) were PCV7 studies. Among observational VT-IPD studies, all schedules (2+1, 3+0 and 3+1) demonstrated reductions in incidence among young adult groups. Among syndromic pneumonia observational studies (2+1, 3+0 and 3+1), only 3+1 schedules showed significant indirect impact. Of 2 VT-NP controlled trials (3+0 and 3+1) and 3 VT-NP observational studies (2+1, 3+1 and 3+PPV23), 3+1 and 3+PPV23 schedules showed significant indirect effect. The 1 study to directly compare between schedules was a VT-NP study (2+0 vs. 2+1), which found no indirect effect on older siblings and parents of vaccinated children with either schedule. CONCLUSIONS: Indirect benefit of a 3+1 infant PCV dosing schedule has been demonstrated for VT-IPD, VT-NP and syndromic pneumonia; 2+1 and 3+0 schedules have demonstrated indirect effect only for VT-IPD. The choice of optimal infant PCV schedule is limited by data paucity on indirect effects, especially a lack of head-to-head studies and studies of PCV10 and PCV13.

Methods for a systematic review of pneumococcal conjugate vaccine dosing schedules.

BACKGROUND: Streptococcus pneumoniae causes a considerable amount of morbidity and mortality in children <5. However, pneumococcal conjugate vaccines (PCVs) can prevent much of this burden. Until recently, PCVs were mostly available only in developed countries using a variety of dosing schedules. As more lower income countries make decisions to introduce PCV into their national immunization programs, an optimal schedule with which to administer PCV has become a key policy question. METHODS: We performed a systematic review of English literature published from 1994 to 2010 on the effects of PCV dosing schedules on immunogenicity, nasopharyngeal carriage, invasive pneumococcal disease and pneumonia. Data were independently double abstracted and cleaned for analysis. Descriptive analyses were performed. RESULTS: We identified 12,980 citations from the literature search (12,976) and secondary means (44). Double review of titles and abstracts yielded 769 articles that underwent full data abstraction. Of these, 350 were further analyzed and are presented in separate reports in this supplement. CONCLUSIONS: This article presents the methods utilized in our systematic review. Because of the heterogenity of the study methods of the reports identified by this review, we did not conduct formal meta-analyses. However, these methods allow us to present a full landscape of the literature on PCV dosing schedules.

Current and future uses of real-time polymerase chain reaction and microarrays in the study of intestinal microbiota, and probiotic use and effectiveness.

Probiotics are defined as live microorganisms that confer a health benefit to the host when administered in adequate amounts. In addition to human health benefits, probiotics can improve various aspects of growth and performance in livestock and poultry, as well as control undesirable microorganisms in food animals. Studies indicate that probiotics can prevent or treat certain conditions, including atopic disease in infants, food allergy, infection after surgery, acute diarrhea, and symptoms associated with irritable bowel syndrome. Understanding the complete mechanism, effectiveness, and potential use of probiotics is limited by the availability and sensitivity of current methods (i.e., culturing techniques). In recent years, real-time polymerase chain reaction (PCR) and microarrays have become prominent and promising methods to examine quantitative changes of specific members of the microbial community and the influence of probiotics on the structure and function of human and animal intestinal ecosystems. Culture-independent studies have established that only a fraction of organisms present in feces are cultivable, therefore, results obtained by cultivation are limited. Conversely, in-depth knowledge of microbial genomes has enabled real-time PCR and microarrays to be more sensitive and has resulted in precise methods for comprehensive analysis of the complex gut microbiota. Additionally, these technologies can assess the influence of intestinal microorganisms on host metabolism, nutrient status, and disease. This paper reviews method technologies and applications of real-time PCR and microarray assays as they relate to the effect and use of probiotics on the intestinal microbiota and gastrointestinal disease.

Effect of push frequency and strategy variations on economy and perceived exertion during wheelchair propulsion.

Wheelchair locomotion is a cyclical activity and participants are free to select any push frequency-propulsion strategy combination that suits their needs at a given power output. The aim of the study was to examine the physiological effects of varying push frequency and strategy on pushing economy. Twelve male, able-bodied participants completed four, randomly assigned, 5-min bouts of submaximal exercise at 32 W on a wheelchair ergometer. Each bout of exercise combined two different push frequencies (40 and 70 push min(-1)), with one of two different push strategies [synchronous (SYN): both arms pushing together, and asynchronous: one arm applying force to the wheel at a time). Physiological measures included oxygen uptake ( VO(2)), heart rate (HR) and blood lactate [La](b )concentration. Differentiated ratings of perceived exertion (RPE) were also recorded (overall, local and central). Separate ANOVA were used for VO(2), HR, [La](b) and RPE as the dependent variables. Where significant differences were identified, a Bonferroni post hoc test was used. The main effect for push frequency by strategy was significant for VO(2) ( P<0.01). Scrutiny of the HR values showed that the SYN 40 condition was significantly less stressful than all other frequency-strategy combinations ( P<0.01). RPE data supported these findings although they were found to be non-significant. When looking at [La](b,) both of the main effects were also significant showing the concentration was lower on average when the push rate was 40 as opposed to 70 (1.65 vs 2.14 mmol l(-1); P<0.01). This study provides further evidence that a low push frequency provides the most economical form of wheelchair propulsion especially when combined with a SYN strategy.