Muscle strain and soreness is more likely if

When you don't exercise enough, don't exercise at all  or if you just don't exercise properly. This is because the muscles need training and if they are not used in a while, then will get the idea that they are not needed. that is why, when exercising, the body needs to be pumped up so that the muscles are too.   

If you exercise or are active without stretching before hand

If it's a smaller child or infant, place one on the middle of the chest and on the child's back. (if it is a bigger child with enough room for two, place one on the upper right/your left of the chest, and one on the lower left/your right) the pads should never touch each other. 

Number one is kayaking number two is communication skills