HR	heart rate
HRV	heart rate variability
HRVT	heart rate variability threshold
CPET	cardiopulmonary exercise test
ECG	electrocardiography
AerT	aerobic threshold
AnT	anaerobic threshold
ANS	autonomic nervous system
S	sympathetic activity
PS	parasympathetic activity
CSI	cardiac stress index
SD1	standard deviation of instantaneous beat-to-beat interval variability
SD2	standard deviation of continuous long-term R–R interval variability
DFA	detrended fluctuation analysis
ApEn	approximate entropy
RQA	recurrence quantification analysis
DET	percent of determinism
FFT	fast Fourier transform
HF	high frequencies
LF	low frequencies
VO2	oxygen consumption
Ln(rMSSD)	natural logarithm of root mean square standard deviation
BLa	blood lactate production