9.1 Physical Activity vs Exercise: Assessment Instruments, Logs & Wearables

9.1 Physical Activity vs Exercise: Assessment Instruments, Logs & Wearables

[!NOTE] Blueprint anchors: Domain 9 (Physical Activity Counseling), tasks 9.4, 9.5, and 9.6 — Differentiate between physical activity and exercise; Evaluate and interpret physical activity assessment results; and Identify subjective (e.g., activity logs, DASI, IPAQ) and objective (e.g., activity trackers/wearable devices) methods to assess physical activity.

A patient can complete every supervised session and still be profoundly sedentary for the other 165 hours of the week. Measuring what happens outside the gym is a distinct competency from prescribing what happens inside it.

---

The Definitional Distinction

[!IMPORTANT] The exam tests this hierarchy directly. Gardening, carrying groceries, and walking the dog are physical activity but not exercise. A structured 30-minute treadmill session is both. Sedentary behavior is a separate construct — a patient can meet the 150-minute exercise guideline and still accumulate 11 hours of daily sitting, which carries independent cardiovascular risk.

---

Subjective (Self-Report) Instruments

Duke Activity Status Index (DASI)

A 12-item questionnaire asking whether the patient can perform specific activities — personal care, walking indoors, climbing a flight of stairs, running a short distance, heavy housework, moderate recreational activities. Each item carries a weight reflecting its metabolic cost, and the summed score estimates peak oxygen uptake:

$\text{VO}_2\text{peak (mL/kg/min)} \approx 0.43 \times \text{DASI} + 9.6$

Dividing by 3.5 converts to METs. Its value is that it produces a functional capacity estimate with no physical testing at all, making it usable for patients who decline or cannot perform a walk test, for telephone or telehealth intake, and for tracking change over time.

International Physical Activity Questionnaire (IPAQ)

Available in short (7-item) and long forms, the IPAQ asks about the previous 7 days across walking, moderate activity, vigorous activity, and sitting time. Output is expressed in MET-minutes per week, with classification into low, moderate, or high activity categories. Its inclusion of sitting time makes it one of the few self-report tools that captures sedentary behavior alongside activity.

Physical Activity Vital Sign (PAVS)

Two questions, designed for routine clinical use:

1. On average, how many days per week do you engage in moderate to vigorous physical activity?
2. On those days, how many minutes do you engage in activity at that level?

Multiplying gives weekly minutes, directly comparable to the 150-minute guideline. Brief enough to repeat at every visit.

Activity logs and diaries

A patient-maintained record of mode, duration, intensity, and symptoms. Logs suffer from recall bias and reactivity, but that reactivity is therapeutically useful: self-monitoring is itself a behavior change intervention, and the act of recording increases activity independent of the data's precision.

The limitation common to all self-report

Self-report systematically overestimates activity, particularly moderate-intensity activity, and underestimates sitting time. Social desirability and recall difficulty both push in the same direction. Interpret self-reported minutes as an upper bound.

---

Objective (Device-Based) Methods

Interpreting step counts

[!IMPORTANT] The 10,000-step figure originated as a marketing target, not a clinical threshold. In older adults, mortality benefit accrues steeply from very low counts and largely plateaus around 6,000 to 8,000 steps per day. For a patient averaging 2,400 steps, a goal of 4,500 is both achievable and clinically meaningful; prescribing 10,000 sets them up to fail. Set step goals as a percentage increase over the patient's own measured baseline — commonly 10% to 20% — rather than against a population number.

---

Combining the Two Categories

Subjective and objective methods answer different questions and should be used together. A device tells you how much the patient moved; a questionnaire tells you what they did, in what context, and what they believe about it. A patient whose accelerometer shows minimal activity but who reports swimming three times a week is not necessarily lying — the device simply does not capture swimming.

Re-administer the same instrument at baseline, at the 30-day reassessment, and at discharge, since physical activity is an AACVPR core outcome and only identical-method comparisons are valid.

---

Realistic Clinical Scenario

Scenario: A 69-year-old man completes 24 CR sessions. On the Physical Activity Vital Sign he reports 5 days per week at 45 minutes, which computes to 225 weekly minutes — apparently well above guideline. His wearable, however, averages 3,100 steps per day including session days, and he reports about 10 hours of daily sitting. He declines a treadmill test; his DASI score is 28.

Analysis: The discrepancy is the finding. His self-report almost certainly counts light household movement as moderate-intensity activity, a classic overestimation pattern, while 3,100 steps per day places him firmly in the sedentary category. His DASI of 28 estimates VO₂peak at roughly 0.43 × 28 + 9.6 = 21.6 mL/kg/min, about 6.2 METs — a usable functional capacity estimate obtained without any physical test. His 10 hours of sitting is an independent risk factor requiring its own target, separate from his exercise prescription.

Plan: Address the discrepancy without accusation — review with him what he counted as moderate activity and use the talk test to recalibrate what moderate intensity actually feels like. Set a step goal anchored to his own baseline, roughly 3,700 to 4,200 per day initially rather than 10,000, progressing by increments. Add a distinct sedentary-behavior goal such as standing and moving for a few minutes each hour, since reducing sitting is a separate target from meeting the exercise guideline. Record DASI, PAVS, and average daily steps as the baseline triad and repeat all three by identical method at discharge to document physical activity as an AACVPR core outcome.