Commentary: one small step

Physical performance analysis: A new approach to assessing free-living physical activity in musculoskeletal pain and mobility-limited populations

Background

Accurate measurement of physical performance in individuals with musculoskeletal pain is essential. Accelerometry is a powerful tool for this purpose, yet the current methods designed to evaluate energy expenditure are not optimized for this population. The goal of this study is to empirically derive a method of accelerometry analysis specifically for musculoskeletal pain populations.

Methods

We extracted data from 6,796 participants in the 2003–4 National Health and Nutrition Examination Survey (NHANES) including: 7-day accelerometry, health and pain questionnaires, and anthropomorphics. Custom macros were used for data processing, complex survey regression analyses, model selection, and statistical adjustment. After controlling for a multitude of variables that influence physical activity, we investigated whether distinct accelerometry profiles accompany pain in different locations of the body; and we identified the intensity intervals that best characterized these profiles.

Results

Unique accelerometry profiles were observed for pain in different body regions, logically clustering together based on proximity. Based on this, the following novel intervals (counts/minute) were identified and defined: Performance Sedentary (PSE) = 1–100, Performance Light 1 (PL1) = 101–350, Performance Light 2 (PL2) = 351–800, Performance Light 3 (PL3) = 801–2500, and Performance Moderate/Vigorous (PMV) = 2501–30000. The refinement of accelerometry signals into these new intervals, including 3 distinct ranges that fit inside the established light activity range, best captures alterations in real-life physical performance as a result of regional pain.

Discussion and conclusions

These new accelerometry intervals provide a model for objective measurement of real-life physical performance in people with pain and musculoskeletal disorders, with many potential uses. They may be used to better evaluate the relationship between pain and daily physical function, monitor musculoskeletal disease progression, gauge disease severity, inform exercise prescription, and quantify the functional impact of treatments. Based on these findings, we recommend that future studies of pain and musculoskeletal disorders analyze accelerometry output based on these new “physical performance” intervals.

Determinants of physical activity in America: a first characterization of physical activity profile using the National Health and Nutrition Examination Survey (NHANES)

OBJECTIVES

To develop and implement methodologies for characterizing accelerometry-derived patterns of physical activity (PA) in the United States in relation to demographics, anthropometrics, behaviors, and comorbidities using the National Health and Nutrition Examination Survey (NHANES) dataset.

DESIGN

Retrospective analysis of nationally representative database.

SETTING

Computer-generated modeling in silico.

PARTICIPANTS

A total of 6329 adults in the United States from the NHANES 2003-2004 database.

METHODS

To discover subtle multivariate signal in the dynamic and noisy accelerometry data, we developed a novel approach, termed discretized multiple adaptive regression and implemented the algorithm in SAS 9.2 (SAS Institute, Cary, NC).

MAIN OUTCOME MEASUREMENTS

Demographic, anthropometric, comorbidity, and behavioral variables.

RESULTS

The intensity of PA decreased with both increased age and increased body mass index. Both greater education and greater income correlate with increased activity over short durations and reduced activity intensity over long durations. Numerous predictors demonstrated effects within activity ranges that may be masked by use of the standard activity intensity intervals. These include age, one of the most robust variables, where we discovered decreasing activities inside the moderate activity range. It also includes gender, where women compared with men have increased proportions of active times up to the center of light activity range, and income greater than $45,000, where a complex effect is seen with little correspondence to existing cut-points.

CONCLUSIONS

The results presented in this study suggest that the method of multiple regression and heat map visualization can generate insights otherwise hidden in large datasets such as NHANES. A review of the provided heat maps reveals the trends discussed previously involving demographic, anthropometric, comorbidity, and behavioral variables. It also demonstrates the power of accelerometry to expose alterations in PA. Ultimately, this study provides a US population-based norm to use in future studies of PA.

Commentary: more or less satisfied?

Hazard RG, Spratt KF, McDonough CM, et al. Patient-centered evaluation of outcomes from rehabilitation for chronic disabling spinal disorders: the impact of personal goal achievement on patient satisfaction. Spine J 2012;12:1132-7 (in this issue).

Changes in objectively measured physical activity (performance) after epidural steroid injection for lumbar spinal stenosis

OBJECTIVE

To examine changes in objectively measured physical activity (performance) at 1 week following epidural steroid injection for lumbar spinal stenosis.

DESIGN

Prospective cohort.

SETTING

University spine program.

PARTICIPANTS

Individuals (N=17) who were undergoing fluoroscopically guided epidural steroid injection for symptomatic lumbar spinal stenosis (mean age ± SD, 70.1±6.7; 47% women).

INTERVENTION

Fluoroscopically guided epidural injection.

MAIN OUTCOME MEASURE(S)

The 2 primary outcomes, measured with accelerometers, were total activity (performance) measured over 7 days and maximum continuous activity (capacity). Walking capacity was also assessed with the Self-Paced Walking Test, and subjects completed the Oswestry Disability Index, Swiss Spinal Stenosis Questionnaire, Medical Outcomes Study 36-Item Short-Form Health Survey, visual analog pain scales, and body diagrams.

RESULTS

At 1 week postinjection, 58.8% of the subjects demonstrated increased total activity and 53% had increased maximum continuous activity, although neither change was statistically significant. Significant improvements were observed in a number of the self-report instruments, including the Physical Function Scale of the Swiss Spinal Stenosis Questionnaire, general health (Medical Outcomes Study 36-Item Short-Form Health Survey), role-limitation emotional (Medical Outcomes Study 36-Item Short-Form Health Survey), leg pain intensity (visual analog pain scales), and presence of leg weakness.

CONCLUSIONS

While patients perceived improvements in pain and function following injection, these improvements were not reflected in significant changes in performance or capacity. Future studies will continue to find value in subjective measures of pain and quality of life. However, with modern technology, performance is no longer a subjective variable. Use of activity monitors to objectively measure performance can result in more rigorous validation of treatment effects, while simultaneously highlighting the potential need for additional postinjection rehabilitation aimed at improving performance.