Training thresholds refer to the level of intensity needed in order to stress the body enough to cause an adaptation or improvement in performance. Training thresholds are measured by intensity and can be either a % MHR or % VO2max. %MHR is used most frequently so will be the focus here. There are generally two training thresholds: the aerobic threshold and the anaerobic threshold.
The aerobic threshold is the intensity needed in order to produce an adaptation that will improve someone’s aerobic capacity or VO2max. The aerobic training threshold is normally between 65% and 70% MHR.
The anaerobic threshold is the intensity needed in order to produce an adaptation that will improve someone’s anaerobic capacity, normally be increasing the speed of lactate removal. The anaerobic training threshold is normally between 80% and 85% MHR.
The intensities between the two thresholds are called the aerobic training zone and include the intensities that should be trained at in order to improve aerobic performance. The higher the training intensity within this zone the greater the adaptations. This is the same for the intensities above the anaerobic training threshold, these are called the anaerobic training zone and the higher the intensity the greater the gains.
Resistance training usually uses repetition maximum to speak about the intensity being used. Within resistance training there are a number of goals that can be achieved and the threshold required varies depending on the goal. Studies suggest that the best maximal strength and power gains can be made using 1-6RM. Training between 8-12RM has been shown to produce significant increases in strength and is the most effective intensity in order to produce muscular hypertrophy. Training between 12-15RM is the best range to significantly improve local muscular endurance. All of this resistance training develops the anaerobic systems, with the higher intensities developing the alactacid system and the lower intensities developing the lactic acid system, though these are not completely isolated from one another. Higher RMs has been shown to be negligible.
 Fleck, S. J. and Kraemer, W. J. Designing Resistance Training Programs (3rd Edition) Lower Mitcham, Human Kinetics, p. 167.