Standardizing moderate- and vigorous-intensity exercise doses – considerations from acute responses

Background Current approaches to prescribing exercise intensity may not standardize physiological strain across individuals, potentially affecting training outcomes. Whether exercise guidelines applying a 1:2 duration ratio between moderate (MOD) and vigorous (VIG) activity equalize physiological strain is unclear. This study compared physiological strain and its variance across two intensities and three prescription methods. Methods Thirteen habitually active males performed an incremental treadmill test as well as 40-min MOD and 20-min VIG sessions prescribed by: (1) absolute metabolic equivalents (ABS), (2) relative maximal oxygen uptake (VO _2max ) (REL), and (3) lactate thresholds (LT). Physiological strain was estimated using excess post-exercise oxygen consumption, individualized training impulse, post-exercise heart rate variability (HRV), blood lactate, and session rating of perceived exertion (sRPE). Results Except for sRPE, estimated physiological strain was greater during VIG than MOD (p < 0.05) across all prescription methods. A general linear mixed model indicated that equivalent strain for most outcomes would have required MOD > 55% and VIG < 72% of VO _2max . According to modified Levene’s test, variance in physiological strain did not differ between prescription methods in MOD. In blood lactate, the variance was higher in VIG _REL than VIG _LT (p = 0.025), and HRV variance was greater in VIG _ABS than VIG _LT (p = 0.041). Conclusion The 1:2 duration ratio underestimated physiological strain of current VIG sessions regardless of prescription method. When comparing exercises, the significant influence of intensity levels within MOD and VIG should also be acknowledged. Despite some differences, variance in strain was mostly comparable across prescription methods, highlighting the heterogeneity of responses even with LT-based prescription.