Which may decrease as a result of chronic aerobic training?

Oxygen consumption at a given absolute submaximal workrate does not meaningfully decrease after training - the primary adaptation is that the same VO2 now represents a lower percentage of VO2max, not a reduction in absolute oxygen cost.

Regular aerobic exercise upregulates lipoprotein lipase activity, which accelerates the breakdown and clearance of triglycerides from the bloodstream. This results in significantly reduced fasting plasma triglyceride concentrations, a well-established metabolic benefit of chronic aerobic training. Lowering triglycerides is one of the most consistent lipid-related adaptations and contributes to reduced cardiovascular disease risk.

Chronic aerobic training increases HDL levels, not decreases them - elevated HDL is a beneficial lipid adaptation associated with improved cardiovascular health.

The lactate threshold increases with aerobic training, meaning the body can sustain higher exercise intensities before significant lactate accumulation, so it does not decrease.