I have been so bweidelred in the past but now it all makes sense!
I thought I was big and snrtog until I held pads for a (much smaller) high level kickboxer for an hour. The next day my muscles were so sore that I honestly wished he would have accidentally missed a pad and knocked me out early in the training session. If shown/done correctly as in this video; holding pads can be as much of a workout as striking.
I was so cofnuesd about what to buy, but this makes it understandable.