Objectively measuring physical activity: Research and clinical applications of accelerometers
Matthew Cox, Ph.D.
Instructor
Duncan Family Institute Mentored Junior Fellow in Cancer
Prevention Research
Department of Behavioral Science
University of Texas, MD Anderson Cancer Center
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• Benefits of physical activity (PA)
• PA recommendations
• Measuring PA
• How accelerometers work
• Current levels of PA in U.S.
• Pros and cons of measuring PA
• How to choose measurement tool
2

Benefit of physical activity (PA) for cancer prevention/survivorship
• Decreased all-cause mortality risk
• Decreased risk of cardiovascular disease and type II diabetes
• Decreased risk of breast, kidney, lung, endometrial, colon, and prostate cancer
• During cancer therapy
– Improved physical functioning
– Decreased fatigue
– Decreased anxiety
– Decreased sleep disturbances
• Posttreatment
– Improved fitness levels
– Decreased body fat and waist circumference
– Decrease risk of reoccurrence
• Benefits moderated by type, frequency, intensity, and duration
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Review of efficacy and safety for exercise in cancer survivors
ACSM Roundtable on Exercise Guidelines for Cancer Survivors, 2010
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• ACSM Recommendations for healthy 18-65 yrs:
– 30 minutes, five days a week of moderate-intensity aerobic physical activity OR 20 minutes three days a week of vigorous-intensity aerobic activity.
– Can benefit from incorporating resistance training for all large muscle groups at least twice a week
– Moderate-intensity = noticeably elevated hear rate (e.g., brisk walk)
– Vigorous-intensity = substantially increased heart rate (e.g., jogging)
• ACSM Recommendations for cancer survivors is the same
– Without cancer site-specific contraindications
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• Diary
• International Physical Activity Questionnaire
(IPAQ)
• Godin Leisure Time Exercise Questionnaire
(Godin/GLTEQ)
• Physical Activity Recall (PAR)
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• Doubly Labeled Water
• Indirect calorimetry
• Heart rate
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• Pedometers
• Accelerometers
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• Gold standard for research
• Uniaxial or triaxial
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• Accelerometers count the gravitational units (g) sampling at a frequency of 100Hz or 100 samples per second.
• Counts are usually aggregated at the minute level
• The higher the counts the more intense the activity.
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• Formulas to determine cut points for low, moderate and, vigorous physical activity
– Cut points vary by population
– Sedentary behavior is less than 100 counts per minute
• Formulas can convert counts into metabolic equivalent units (METs)
• No feedback to participants
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• Number of minutes of PA and sedentary behavior
• Bouts of PA and sedentary behavior
• Intensity of PA behavior
• Posture (sitting and standing)
• Can use accelerometer data to calculate:
– Energy expenditure
– Adherence to PA guidelines
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Can accelerometers really be that great?
• No
• Provider/Researcher needs to specify
– Spurious wear
– Non-wear
– Minimum wear time
– PA and sedentary cut points
– How many days of consecutive wear
20

• We’ve created free software for processing accelerometry data
– Package ‘acc’ in R
• PROSPR shared resource rents accelerometers!
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Current Levels of PA in cancer survivors (self-report)
• Breast Cancer Survivors
(Irwin et al., Med Sci Sport Exer 2004)
– 32% of Breast cancer survivors meet current recommended levels
– Obese breast cancer survivors less likely to meet recommendations than others
• PA levels tend to decline after diagnosis
(Blanchard et al.,
2003)
– Doesn’t return to prediagnosis levels
22

Current Levels of PA in cancer survivors (accelerometers)
• Non cancer patients
(Tucker et al., Am J Prev Med 2011)
– Estimates may be much lower with objective measures
• 62% meeting ASCM recommendations for self report
• 5%-9.6% using accelerometers (Troiano et al., Med Sci Sport Exer
2008)
• Cancer survivors
– Breast cancer survivors
(Johnson-Kozlow et al., IJBNPA 2006)
• IPAQ overestimates PA in breast cancer survivors by 247%
• PAR over estimate by 13%
– Colon cancer survivors
(Boyle et al., Support Care Cancer 2015)
• Mean daily MVPA minutes with GLTEQ = 26
• Mean daily MVPA minutes with accelerometers = 12 23

Pros
• Easy to administer
• Fast
• Cheap
Cons
• Not accurate/valid (maybe)
• Different measures may not be comparable
Rogers, Phys Ther Rev 2010 24

•
•
Pros
Accurate
Measures sedentary behavior
Cons
• Measurement limited to ambulatory activity
• Pricing
• Technical
• PA cut points not developed for all cancer diagnoses
Broderick et al., Support Care Cancer 2015
• Statistical consideration
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• Research
– It depends
– Accelerometers
– Alternative exercise testing protocols
• Clinical
– It depends
– www.exerciseismedicine.org
– Fitbits?
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Looking towards the future of measuring PA
• Wearables that measure more than walking/running
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• PA is a proxy for other health outcomes
– Cardiorespiratory fitness
– Energy expenditure
– Muscle strength
– Biomarkers
• How do new wearables relate to outcomes?
30

Pooled effects of supervised exercise training, compared with usual care (control), on cardiorespiratory fitness (peak oxygen consumption, VO2peak) by treatment status.Abbreviations: CI, confidence interval; SD, standard deviation.
Lee W. Jones et al. The Oncologist 2011;16:112-120
©2011 by AlphaMed Press

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Modeling
Intervention
Social
Support
Somatic
Sensations
Bandura 1986
Self-Efficacy
Time
Self-
Regulation
Outcome
Expectations
Physical
Activity
33

Physical
Activity
Energy
Expenditure
Quality of
Life
CRF
Biomarkers Biomarkers
Time
Health
Outcomes
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• Use accelerometers if you can
– Know the limitations
• Measurement of PA is constantly changing
• Be mindful of the target outcomes
– Clinical vs Research
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