One of the cons to running as an aerobic activity is that it may a. be too repetitive and boring for some individuals. b. require a learning curve for beginners. c. cause back strain if not performed correctly. d. lead to frequent, chronic injuries to muscles and joint

It is A because if you use it repetitively it can get boring and dull. so it's A

One of the cons to running as an aerobic activity is that it may

the answer is    C
lead to frequent, chronic injuries to muscles and joints.

Ibelieve the answer is c.

Well if you pick a machine to work on and that's gonna be your exercise if you don't stick to that machine your muscle strength your muscle mass rather will change because you haven't been doing it you change something in your exercise routine which changes your body's form of dealing with things for example you might become weaker or stronger depending on what kind of exercises you do in whether or not the machine you picked actually your muscles grow.