How much harder are the courses compared to first year?
I want to take chem 1a03 during next year but i heard biomechanics and muscle physiology are heavy courses...and I dont want to kill myself taking them together

It's definitely do-able. I did it this year! I found the kin courses to be fine this year, I enjoy math so biomechanics wasn't as bad as people were saying and I loved musculoskeletal too(this course is TONS of work!). I did find it difficult only because I hate chemistry and chem was taking up all my time. So if you like chemistry, it may not be as bad as people are saying. Besides, you tend to have better study habits in upper years, so even if the courses are harder, you are able to manage them better.

How are you at math? Chem can be a bit mathy and thus having it with biomechanics might be a bit of a load if you are not at all mathematically inclined. If you are decent mathematically/have some high school physics, biomechanics should not be much of a problem if at all. Neuromuscular is one of the toughest kin courses out there, mainly because the tests really do test you. That said it is not necessarily all that more work. For volume of work, the main course will be MSK. My advice would be if you are worried about biomechanics, chem and neuromuscular is to schedule MSK in whichever term has the fewest. (Probably second, but I'm not sure what semesters, health psych, biomechanics and growth will be in). I personally found Growth and Cardio are the courses that require the least work out of the second year courses, so throwing in MSK with them might be best if you can pull it off.

first year chem is a pretty light courseload imo. lots of high school review and i, along with many, found that all you need to do to do well was listen in class, know the slides, and do tutorial and old tests. it really doesnt take much to study for chem in first year. and lots of it is review anyways.

I found 2nd year a lot easier. First year I had a bunch of 4's a 6 and some other bs marks. And 2nd year my lowest mark was a 9 which happened to be biomechanics. Biomechanics is actually not bad at all, just read the questions carefully!! I also put the least amount of time into biomechanics so that probably played a factor. Muslce physiology is simply memorizing whats on the slides and spitting it out onto your scantron. MSK is simply how much you study. if you study 80% of the material thats what you'll get, if you only know half the material your getting a 50, there are no trick questions.