Real-world upper-limb use from bilateral wrist accelerometry

The field-standard free-living performance metrics for arm use – the sensor counterpart to a clinic upper-limb capacity test. From the affected (or dominant) and unaffected (or non-dominant) wrist activity it computes the Use Ratio, the Magnitude Ratio, the Bilateral Magnitude, the hours of use per arm and a laterality index. Maps to ICF d445 (hand and arm use), the performance substrate of the d5 self-care activities.

Usage

upperLimbUse(
  affected,
  unaffected,
  sampling_rate = NULL,
  epoch_sec = 5,
  active_threshold = 2
)

Arguments

affected, unaffected: The two arms' data: each an n x 3 acceleration matrix (g units) or a numeric vector of per-epoch ENMO (mg).
sampling_rate: Sampling rate in Hz (required for raw accel input).
epoch_sec: Epoch length in seconds (default 5).
active_threshold: ENMO (mg) above which an epoch counts as active (default 2).

Value

an upper_limb_use list: icf_code, use_ratio (affected/unaffected active time; 1 = symmetric, <1 = affected used less), magnitude_ratio (median log activity ratio, capped +/-7; 0 = symmetric, negative = unaffected dominant), bilateral_magnitude (median combined activity, mg), hours_affected/hours_unaffected, and laterality_index ((aff-unaff)/(aff+unaff)).

References

Uswatte (2005); Bailey (2014); Lang (2017).

Examples

# affected arm active half as often as the unaffected arm (per-epoch ENMO, mg)
set.seed(1)
unaff <- c(rep(10, 100), rep(0.5, 100))
aff   <- c(rep(10, 50),  rep(0.5, 150))
upperLimbUse(aff, unaff)$use_ratio        # ~ 0.5
#> [1] 0.5