Overnight Cardiac Chronotropy Assessed By Wrist-worn Device On Markers Of Allostatic Load In Marines

Allostatic load (AL) reflects the cumulative physiological demands that trigger recurrent autonomic responses elicited by heightened stress and engender a gradual disruption of biological systems if unmanaged. Overnight cardiac chronotropy (OCC) reflects the basal autonomic activity during sleep assessed by heart rate that responds to AL. Understanding the suitability of OCC on markers of AL assessed by wrist-worn device in Marines may help manage AL in this populace. PURPOSE Assess the relation between OCC and markers of AL from a wrist-worn device in Marines enduring a military training course. METHODS 82 Marines (men: n = 59, 22 [21, 26] y, 177.5 [172, 183.2] cm, 81.7 [72.7, 87.2] kg; women: n = 23, 24 [21, 27] y, 166 [163.4, 171.4] cm, 68.7 [59.8, 73.3] kg) participated. Wrist-worn devices (Garmin Instinct Solar, Garmin, Ltd., Olathe, KS) assessed OCC and markers of AL over 30 d including active kilocalories (kcal), steps, distance (m), moderate intensity (min), vigorous intensity (min), total sleep (min), deep sleep (min), light sleep (min), REM sleep (min), awake time during sleep (min) and sleep phase (%). Wear time ≥ 10 h/d over ≥1 wk was analyzed. Data were shown as median [Q1, Q3]. Spearman’s correlations (rs) assessed associations between OCC and AL. Strength of correlation coefficients was based on 0.8-1.0 very strong, 0.6-0.79 moderate, 0.3-0.59 fair and 0.1-0.29 poor. RESULTS 64 Marines (19 women) were included. Wear time was 24 [23.8, 24] h/d over 21 [16, 23] d. OCC (50 [44, 55] bpm) showed poor to fair correlations with AL: kcal (rs = 0.173 [0.12, 0.23] p < 0.001), steps (rs = -0.127 [-0.18, -0.07] p < 0.001), distance (rs = -0.180 [-0.24, -0.12] p < 0.001), moderate intensity (rs = 0.319 [0.25, 0.39] p < 0.001), vigorous intensity (rs = 0.198 [0.12, 0.27] p < 0.001), deep sleep (rs = 0.010 [0.02, 0.17] p = 0.011), % deep sleep (rs = 0.128 [0.05, 0.20] p < 0.001), REM sleep (rs = -0.149 [-0.22, -0.07] p < 0.001), % REM sleep (rs = -0.140 [-0.21, -0.06] p < 0.001), % awake time during sleep (rs = 0.090 [0.01, 0.16] p = 0.018) and total sleep (rs = -0.068 [-0.13, -0.01] p = 0.018). Light sleep (p = 0.328), % light sleep (p = 0.639) and awake time during sleep (p = 0.063) were not correlated. CONCLUSION OCC captured by a wrist-worn device may be unsuitable to assess AL in Marines as more sensitive markers or devices are warranted. ONRN00014-20-C2020