# Presentation: 020393

## Step Activity Monitor (SAM)

- Barbara Resnick, PhD,CRNP
- Denise Orwig, Phd
- Sheryl Zimmerman, PhD
- Jay Magaziner, PhD

## SAM

- The Step Activity Monitor (SAM) (Prosthetics Research Study, Seattle, WA) is a new type of step counter that was developed by Smith et al (1991) in order to improve on the previously available monitors.

## Advantages of the SAM

-  The goal was to develop a device that was easy to use, accurate, unobtrusive for the wearer, and able to store a continuous collection of data.

## Advantages of the SAM

- Detects and counts steps for a wide variety of gait styles.
- The monitor, which is 6.5cm high, 5.0 cm wide, and 1.5cm thick, weighs 65 grams and includes a sensor, surface mount electronics, and a battery and is sealed in a urethane case.

## Advantages to the SAM

- The device is placed on the right lateral malleolus or left medial malleolus.  The SAM  is curved with a 50 mm radius, and is strapped to the leg by two elastic attachment straps.  Alternatively, the SAM can be placed in a ankle band that fits around the ankle and holds the SAM in place.
- It is comfortable!

## Advantages of the SAM

- The sensitivity of the sensor to movement can be adjusted through a software control called the “threshold” setting.
- The sensitivity of the sensor for step counting can also be adjusted by varying two electronic filtering parameters, the “cadence” and the “motion” settings.

## Advantages of the SAM

- The cadence setting limits the frequency with which steps are detected.
- At the lower settings very high or frequent steps will be accurately identified, and at higher settings slower or less frequent steps will be accurately evaluated.
- Accuracy is maximized.

## Advantages of the SAM

- The SAM can store up to 16,128 intervals of data as 8-bit integers.  The maximum time limit for monitoring is determined by this memory capacity and the duration of the selected recording interval.
- The SAM records data in many short consecutive time intervals (usually 1 minute intervals).

## Advantages to the SAM

- Accuracy
- Large amounts of data can be collected
- Can establish periods of high and low activity

## How to Use the SAM

- The SAM is used in conjunction with a personal computer and a small, battery-powered docking unit to set up the SAM for monitoring and to transfer the data to a computer file after monitoring.

## How to Use the SAM

- The SAM is programmed by selecting the desired cadence and motion settings and activating the monitor.
- Once testing is completed the same software is used to transfer the data from the SAM to a statistical program for analysis.

## Psychometrics of the SAM

- In a study of 45 subjects with diabetic peripheral neuropathy there was evidence of test-retest reliability.
- Average age of participants was 65.
- Two accuracy trials were conducted by having participants walk over the same course separated by a 2-week period.

## Psychometrics of the SAM

- The average step count at trial 1 was 134 and in trial 2 it was 135.
- In addition there was an average deviation of only .54% at trial 1 and .65% at trial 2 between the steps recorded by the SAM and those counted by a researcher using a hand-held tally counter.

## Pilot Testing with Older Adults

- A total of 30  subjects were included in the study with an average age of 86 _+_ 6.1
- twenty two (60%) used an  assistive device to ambulate
- three (10%) had Parkinson’s disease
- ten (30%) had sustained hip fractures previously.

## Pilot Test

- The participant was asked to walk on a carpeted level surface for one minute, rest for two minutes, and then ambulate over the same path for another minute.
- In twenty of the walks two observers counted steps during both walks.

## Reliability

- Reliability was based on statistically significant correlations between the two readings of the SAM done two minutes apart.

## Validity

- Validity, or accuracy of the SAM, was based on statistically significant correlations between the mean of the two counters and the results of the SAM at each testing interval

## Validity

- The average deviation between the SAM and the mean of the two counters.
- The average deviation was calculated by summing the absolute value of the percent error/ by the number of  walks completed.
- The percent error = the actual number of steps taken (i.e. the mean of the two counters) minus the number of steps recorded by the SAM / the actual number of steps taken.

## Validity

- Validity of the SAM was also considered by having four subjects wear the SAM from 6 to 48 hours and comparing that against an activity diary to determine if there was a relationship between the diary and recorded periods of activity on the SAM.

## Results

- 	   A total of 60 one-minute walks were completed

## Results

- There was a statistically significant correlation between the two recordings of the SAM (r=.80, p<.05) completed 2 minutes apart.
- There was a strong and statistically significant relationship between the SAM and the mean of the two counters (r=.95, p<.05).

## Results

- The average deviation was 5.1 and the overall step counting accuracy for walking was 95 percent.
- The lowest accuracy recorded was 88 %, and only 5% of the 60 walks recorded resulted in accuracy readings of less than 90%.

## Results

- In 16 (27%) of the cases the SAM undercounted compared with the human counter, in 31 (51%) of the cases the SAM overcounted, and in 13 (22%) of the cases there was no difference between the human counter and the SAM.

## Results

- Two individuals wore the SAM for 6  hours, one individual wore the SAM for 8 hours, and one individual wore the device for 48 hours.

## Results

- The four individuals all reported the SAM to be very comfortable and generally forgot that they were wearing anything.
- In all cases the activity levels based on the SAM matched the activity diaries.

## Product Information

- Available from Prosthetic Research Study (206-903-8136)
- email:  info@prs-research.org
- Cost:
- 800 per SAM
- 1,000 for software (initial cost only)
- Must have an Apple