Despite the appeal of ultra-short-term heart rate variability (HRV) methods of
analysis applied in the clinical and research settings, the number of studies
that have investigated HRV by analyzing R-R interval (RRi) recordings shorter
than 5 min is still limited. Moreover, ultra-short-term HRV analysis has not
been extensively validated during exercise and, currently, no indications exist
for its applicability during resistance exercise. The aim of the present study
was to compare ultra-short-term HRV analysis with standard short-term HRV
analysis during low-intensity, dynamic, lower limb resistance exercise in
healthy elderly subjects. Heart rate (HR) and RRi signals were collected from 9
healthy elderly men during discontinuous incremental resistance exercise
consisting of 4-min intervals at low intensities (10, 20, 30, and 35% of
1-repetition maximum). The original RRi signals were segmented into 1-, 2-, and
3-min sections. HRV was analyzed in the time domain (root mean square of the of
differences between adjacent RRi, divided by the number of RRi, minus one
[RMSSD]), RRi mean value and standard deviation [SDNN] (percentage of
differences between adjacent NN intervals that are greater than 50 ms [pNN50]),
and by non-linear analysis (short-term RRi standard deviation [SD1] and
long-term RRi standard deviation [SD2]). No significant difference was found at
any exercise intensity between the results of ultra-short-term HRV analysis and
the results of standard short-term HRV analysis. Furthermore, we observed
excellent (0.70 to 0.89) to near-perfect (0.90 to 1.00) concordance between
linear and non-linear parameters calculated over 1- and 2-min signal sections
and parameters calculated over 3-min signal sections. Ultra-short-term HRV
analysis appears to be a reliable surrogate of standard short-term HRV analysis
during resistance exercise in healthy elderly subjects.