Intensity is a measure of effort put in by an individual during exercise. Intensity, in terms of weight training, could be purely judged by the maximum repetitions you are able to do with a given poundage in a set.
Suppose you squat 315lbs and are able to do only 4 repetitions, it means that the set was quite difficult or very intense for you. But, if the same poundage is lifted by an elite power lifter, he would perform 15 plus repetition easily with the same weight. This means it was a low intensity set for him. Intensity can’t be judged by how much weight you lift. It purely depends on how many reps you could do with that weight. The more repetitions you are capable of doing, the lower the intensity is, irrespective of the weight & the lesser repetitions the weight restricts you to, the higher the intensity, irrespective of the weight.
Many a times a low intensity set that is carried on for a large volume of repetitions gets the person out of breath & that is mistakenly considered by the person to be a High Intensity Set. Cardiovascular Fatigue, hyperventilation are not indicators of high intensity, they are indicators of high volume.
As a universal principle, Intensity & Volume are inversely proportionate. Higher the intensity, the more restricted the volume & higher volumes demand a drop in intensity.
In strength training Intensity should determine volume & in Endurance training, volume dictates intensity.
A couple of examples to elaborate upon the relationship between Intensity & Workload as it pertains to Strength Training – Example I A male & a female train together as training partners and are doing squats. Both are at the advanced level of training. Both decide to lift weights that restrict them to no more than 4 repetitions. The Male goes up to 405lbs for 4 reps & the Female manages 185lbs for 4 repetitions. In the above case the Male has managed a much higher workload than the female, but their Intensity (Level of effort put in by them individually) is the same. In this case they are said to be training in the heavy range & their Intensity would be specified as a 4-Repetition Maximum or a 4 Rep-Max or 4RM.
A male & a female train together as training partners and are doing squats.
Both decide to lift the exact same weight of 185lbs & do the maximum reps they can.
The male goes up to 20 repetitions, but the female can only do 4 with maximum effort.
Here again the Workload of the male (185 X 20) is higher than the female (185 X 4) but the male is working out at a 20RM intensity & the female is working out at a 4RM intensity.
Thus though the male is accomplishing a greater workload than the female, his intensity for this particular workout was way lesser than the females.
Thus it is now clear that Workload is simply the AMOUNT OF WORK DONE & Intensity is a measure of the level of effort needed to accomplish a given workload.
Intensity is measured as a REP-MAX (RM).