Experience with an Ambulatory Physical Activity Meter

We are currently undertaking pilot work with an advanced physical activity meter (Fig. 2), the activPAL™ professional 'physical activity logger' (PAL Technologies, Glasgow, Scotland). This records the time that is spent lying/sitting, standing and stepping. In addition it will display the number of up-down/down-up transitions, the stepping cadence and estimated energy expenditure. From this estimated energy expenditure it is possible to derive an estimated PAL (the estimated energy expenditure function has not yet been validated against standard methodologies, e.g. doubly labelled water). The lightweight device is about the size of a matchbox and worn on the front of the thigh. It can record about a week of data, which is downloaded onto a computer, analysed by proprietary software and displayed (Fig. 3).

Table 1 shows preliminary results from nine cachectic patients with upper GI cancer (varying primary sites) who wore the activPAL™ meter for 1 week. Many of the patients were receiving palliative chemotherapy at the time of activity assessment. Their physician-assigned WHO performance status was recorded at the beginning of the week. The total time spent upright (stationary or moving) was combined and used to derive a figure for the average proportion of an idealised 16-hour waking day spent in the vertical position. This was done to allow a provisional comparison to the performance status score. A WHO performance status of 0-2 suggests that the patient is up and about for more than 50% of the waking day; however, from the meter data it appears that patients have a very low level of physical activity, spending on average only about 20% of an idealised day in the vertical position. The estimated PAL is also extremely low. This is only a first-order estimate. Whilst this may reflect a true reduction in physical activity, it might also suggest that this parameter (derived from meter information) may require calibration

Fig. 2. The activPAL™ professional physical activity logger attached to the front of the thigh

Summary of recording period.

Start date, SIT/UE STAND ST time and day. If default display/analysis is for "calendar day" then start time is 12 midnight, otherwise start time reflects the recording start time.

Summary of recording period.

Summary lay 16 01-1-1--19 PM to May 26 03-112-31 PM

Time spent sitting or lying is plotted in yellow and falls below the axis (sit to stand movements per day in italics).

Summary

SMJe 134.7h Stand IMh Step tK*>

Hours spent in each activity (sedentary activities plotted down axis, upright activities plotted up axis),Stall lime mmA

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Time spent standing (green) and stepping (red) is plotted above the axis (with steps per day In italics).

SMJe 134.7h Stand IMh Step tK*>

stuf ittei ^ 39195 steps

Time in *eideiitärv adit 1 r'> |huvi/il<iyl „''.'t!<> k! 5jrr.'>'<-iH¿w

Fig.3. An example of data from the activPAL™ meter. (Reproduced with permission)

from gold-standard measurements using doubly labelled water/indirect calorimetry. Further study is clearly required; however, despite these reserva tions, the preliminary data raise the suggestion that patients with cancer cachexia may be less active than we realise.

Table 1. Performance status and activity assessment in a group of patients with upper gastrointestinal cancer and cachexia

Age

Sex

%WL

WHO

%UP

ePAL

pPAL

43a

M

10

0

28

1.23

1.5

46a

M

26

1

32

1.15

1.5

47a

F

7

0

23

1.15

1.5

55a

M

39

2

18

1.1

1.5

59a

M

19

2

36

1.23

1.5

62

M

19

2

10

1.08

1.5

65a

F

6

2

2

1.01

1.5

69

F

44

2

17

1.09

1.5

70a

M

9

2

12

1.09

1.5

aReceiving chemotherapy (not all patients were receiving the same regimen or had their activity recorded at the same point in their treatment schedule)

%WL, per cent of'usual' weight lost; WHO, physician-assigned World Health Organisation performance status; %UP, Proportion (in per cent) of an 'idealised' 16-h waking day spent upright (either moving about or stationary); ePAL, estimated physical activity level derived from meter information; pPAL, predicted physical activity level; a PAL of 1.5 is typical of a healthy, sedentary adult aReceiving chemotherapy (not all patients were receiving the same regimen or had their activity recorded at the same point in their treatment schedule)

%WL, per cent of'usual' weight lost; WHO, physician-assigned World Health Organisation performance status; %UP, Proportion (in per cent) of an 'idealised' 16-h waking day spent upright (either moving about or stationary); ePAL, estimated physical activity level derived from meter information; pPAL, predicted physical activity level; a PAL of 1.5 is typical of a healthy, sedentary adult

There remain appreciable challenges in developing physical activity meter technology. These include determining the acceptability, reliability and practicality of the equipment, deciding which variables should be reported, the appropriate timing, frequency and duration of data collection and how the information should be presented and interpreted. In addition, devices such as the activPAL™ need to be 'tested' in populations with differing levels of activity. As with all assessment tools, it is conceivable that in setting out to measure a variable, its level is inadvertently changed. However, these devices measure activity objectively over a prolonged period of time, which is likely to increase the chances of obtaining an accurate reflection of contemporary activity. The initial experience suggests that the device is acceptable to patients.

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