Reliability Of A Vagal Modulation Index In Different Conditions: 1266 Board #28 May 30 9:30 AM - 11:00 AM

Previous studies conducted with athletes have suggested a minimum of 3 days are required for identifying training induced adaptations in supine, morning, resting heart rate variability (HRV). However, there are no studies evaluating the minimum days required for appropriate reliability of HRV measures in non-athletes, and during different conditions of evaluation. PURPOSE: 1) To evaluate the reliability of a prominent HRV measure, the root mean square of the successive differences of R-R intervals (RMSSD), during different conditions in non-athletes; 2) to identify the minimum number of days required for weekly (5-day) evaluations of RMSSD. METHODS: Thirty-four young, physically active individuals (22.2±3.6 years) completed daily 4-min R-R recordings during supine, seated, standing and walking (5 km/h) conditions over 5 days. Relative (intraclass correlation coefficients, ICC) and absolute (technical error of measurement, TEM; coefficient of variation, %CV) reliability, and bias were calculated for 1, 2, 3, and 4 days, and compared with weekly (5 days) assessments. RESULTS: Excellent reliability was identified for all conditions over 4 days (ICC≥0.986, CV≤2.8%) that was diminished when examined over 3 (ICC≥0.970, CV≤3.4%), 2 (ICC≥0.932, CV≤5.7%) and 1 (ICC≥0.804, CV≤10.2%) day. When compared with weekly recordings, 2 day recordings demonstrated excellent and similar reliability values for all conditions examined, with better values observed for supine vs. seated vs. standing vs. walking conditions. CONCLUSIONS: From the current results, daily assessment of RMSSD is highly reliable with a minimum of 2 days of recordings recommended for determination of weekly HRV in non-athletes, regardless of the condition.