Associations of Google Pixel Watch 3 Daily Readiness with Autonomic Physiology and Self-Reported Wellness: An Exploratory 14-Day Repeated-Measures Study

Consumer smartwatch readiness scores summarise physiological and sleep data, but their relationships with independently measured physiology and self-reported wellness remain uncertain. This exploratory 14-day repeated-measures observational study examined Google Pixel Watch 3 Daily Readiness in 38 participants (410 participant-days; 220 with recorded readiness scores). Morning heart rate variability was measured independently using Polar H10 and Kubios, and daily questionnaires assessed fatigue, stress, body soreness, and sleep quality. Mixed-effects models separated within-person and episode-mean associations; participant-grouped cross-validation tested incremental wellness prediction. Within participants, each 10-point increase in readiness relative to the episode mean was associated with 6.2% higher root mean square of successive differences (95% CI 2.7–11.7%), a 0.15-unit higher parasympathetic index (0.08–0.23), a 0.12-unit lower sympathetic index (−0.25 to −0.05), and 0.99 beats/min lower heart rate (−1.91 to −0.42). Respiratory rate was not associated. Higher readiness was associated with more favourable fatigue (odds ratio 1.19, 95% CI 1.03–1.38) and stress (1.26, 1.08–1.47) ratings, but not body soreness or sleep quality after multiplicity correction. No episode-mean association survived correction, although estimates were imprecise. Daily Readiness did not improve out-of-sample prediction. These findings show convergence with one physiological input domain but do not validate the composite or assess its use alongside load metrics.