Exploring Field-Expedient Readiness Monitoring in a Tactical Athlete: Relationships Among HRV, Resting Heart Rate, Grip Strength, and Sleep

Background: Tactical athletes may require practical readiness-monitoring methods when direct heart rate variability (HRV) assessment is unavailable or operationally impractical. This retrospective observational exploratory pilot study examined daily relationships among autonomic, cardiovascular, sleep, and neuromuscular measures and explored whether grip strength or resting heart rate (RHR) warrant further investigation as field-expedient adjuncts to HRV. Materials and methods: One adult male tactical athlete completed 22 consecutive days of monitoring. HRV, RHR, sleep duration, and proprietary Sleep Score were obtained using a Garmin fēnix 8 smartwatch, while dominant-hand isometric grip strength was measured using digital dynamometry. Relationships were evaluated using Pearson correlations, Spearman sensitivity analyses, and Benjamini-Hochberg false discovery rate correction. Results: Grip strength demonstrated a strong positive association with HRV (r = .674; ρ = .690), while RHR demonstrated strong inverse associations with HRV (r = −.655; ρ = −.629) and grip strength (r = −.711; ρ = − .754). Sleep Score demonstrated a strong positive association with HRV (r = .624; ρ = .682). Its association with grip strength was moderate and nonsignificant using Pearson correlation (r = .404) but significant using Spearman sensitivity analysis (ρ = .531). Sleep duration demonstrated negligible relationships with HRV, RHR, and grip strength. Conclusion: These preliminary within-participant findings support further investigation of RHR and grip strength as complementary field-expedient measures when HRV monitoring is unavailable. Larger studies incorporating independent performance and readiness criteria are required before substitution or readiness-monitoring validity can be established.