How repeatable are BSXInsight SmO2 measurements?

BSXInsight is sensitive to its physical location and the physiological condition of the athlete being monitored. This leads to the following question: what is the expected SmO2 reading repeatability of the BSXInsight device?

When considering repeatability, two types are of importance: baseline and dynamic. Baseline repeatability is defined as the SmO2 readings when the device is worn at rest while dynamic repeatability is defined as the recorded variation in SmO2 when athletes perform the same physical activity under the same initial conditions (e.g., starting from a rest state).

In a study with 10 volunteers we demonstrate that the BSXInsight has a baseline repeatability with a standard deviation of 2.8pts, the main contributor to change being the expected at-rest physiological variations that take place from day-to-day within a 13-day time period, as listed in Table 6.

Table 6: Expected long-term contributions to baseline variation when the device is carefully repositioned in the same position, same calf, over multiple days.

 

Independent sources of variation

Value (% pts)

Device-induced variation

0.05

Small placement-to-placement variation

1.53

Expected multi-day physiological variation

2.31

Expected long-term baseline std. dev.

2.77

 

Note that if the device is worn by someone else the expected person-to-person SmO2 variation is 7.2pts, but don’t worry: it is still 2.8pts when worn by the same person.

In another study with 5 volunteers we demonstrate that the BSXInsight has, on average, a multi-day (13-day) dynamic repeatability with a standard deviation of 2.7pts after recovery from high-intensity exercise. The exercise protocol is listed in Table 2 and the plot in Figure 10 shows an example of overlapped SmO2 values for a given athlete in a total time-period spanning 13 days, showing good correlation in SmO2 values from run-to-run.

Table 2: Timing of events during SmO2 variation experiment.

Time

Event

0 min

Baseline collection (start data collection and sit still)

1 min

Start warmup

4 min

Start All Out

5:30 min

Start Active Recovery

8:30 min

Passive recovery (stay still in the bike)

10:30 min

Stop data collection

 

Figure 10: Example of overlapped SmO2 plots captured from the same volunteer during the SmO2 variation experiment, showing good correlation from trial to trial.


[1] BSXInsight 2.0 User Manual. Austin, TX: BSX Athletics.

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