I expect you will find that with so few reps that much of your leg exercise was anaerobic, and your capacity for anaerobic exercise using your legs is much greater than for anaerobic exercise with your arms - due to muscle bulk and the ability of muscles to store glycogen.
The smaller the muscles, the sooner you would need to go into aerobic operation, and the sooner that this will show up on breathing and pulse rate.
As soon as you start aerobic movement with the large muscle groups you’ll find your pulse rate rises very rapidly, and you will also find a rapid rise in temperature - and so this will give rise to sweating.
How about increasing your reps and reducing the weight, and working for longer period? I bet your pulse will rise much more on the heavier muscle groups - instead of being repetition bound training, try do go for number of reps within a given period of time, try out maybe 5 minutes of repeats - in other words you are going for rate rather than repetitions.
This type of circuit training is very useful developing power rather than strength. The idea is to set a time, find the number of repeats you can do with a certain weight, and then train to improve that number.
For example, half squats - do it with 30 pounds for 5 minutes - see what you can achieve, rest, rinse and repeat until your performance drops below 80% of that number.I expect a reasonably fit person to be able to handle 150 to 200 repeats of such an exercise.
Once you can keep to within 80% across 3 circuits, add another 10 pounds.
You can do this across other muscle groups, adjusting weights and times according to the particular muscle group.
I have seen this done using recovery times instead of numbers of repetitions, in this case you work out you maximum aerobic pulse rate, and exercise to around 90% of that. You then rest until you recover to around 50% of maximum and go at it again, and you stop when it takes more than 5 minutes to recover to 50%.
There are many variations of this, such as increasing weight whilst decreasing the number of repetitions, to reaching a point where you go up to being only able to do 10 repeats, and then you work your way back down again in weight, and up again in repetitions.
Rowers and cyclists have equipment available - though very expensive - that can directly measure power output, which is a much more objective measure of performance, other sportspersons have the means to make such calculations - such as swimmers but its very much more complex.
This sort of training lends itself very well to charts and measurement, you can schedule your performance much better, work out how to break up the training better so you concentrate on differant muscle groups on differant days - but you will not end up with the huge bodybuilder type physique - its much more suited to athletes