Kelley used to do three sets of squats one time per week. after three weeks she noticed she was less sore than when she started this exercise. which principle is at work?

The principle underlying this change is called progression. This principle tells us that when your fitness level improves, your body has adjusted to your regular routine; thus, you will feel less sore than when you started the squats three weeks ago. During this time, your muscles have developed and your body has adopted to the stress brought about by your exercise. 

the right side of the picture going down is:

polymerase

protein

transport vesicle

modified protein

the left side of the picture going down is:

dna helix

single-stranded rna

endoplasmic reticulum

ribosome

golgi apparatus

protein released from vesicle

click to let others know, how is it

read more on -

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".