Kickureface...@ 17.5 to answer your question it really depends on a number of factors, the load your are lifting and frequency of training sessions, how physical mature your (ie when did you enter puberty), quality of yor nutrition etc...
I would suggest doing higher rep sets, really focusing on good form. I don't think you need to do 8 sets of squats, perhaps 2-3 sets x 12-15 reps @ a 20 Rep Max (RM) level is a good idea. You have many decades to spend in the sports, so be patient and build a good foundation. Make sure someone who has good form evaluates your form with all exercises.
I believe most of US are in agreement that this young man at 15 should not be doing squats...
I agree with you Skillz Staz 100%
Spesmilitis, you are correct long bone growth occurs at the end of epiphyseal plates...I also agree with your prescription.
What I think many of US are missing is the neurohormonal response to exercise...Growth Hormone, Insulin, DHT, Cortisol are all very potent modulaters of tissue remodeling. How the do your think your muscles increase in size with training? Most of it occurs through hormone signaling. (ok you can argue the mechanical loading of the muscle does effect signal transduction events mediated by the muscle cytoskeleton).
Insulin and Cortisol have intracellular effects mediated through different signal transduction pathways...affecting protein turnover in a cell plus they can also active certain transcription factors to turn/on off certain genes.
GH & DHT work at the level of the DNA by turning on/off certain genes, leading to changes in protien levels.
These signal are all intergrated by the cell. Different tissues do have different effect by the same hormones.
What I was saying is that @ 15 his hormonal status is in state of flux. Their are things that we are not aware of him as an individual. We should be aware that one training modality that works for one population might not be the best approach to use in a different populations. Think about the differences in the the young, the old, the untrained but college aged, the trained, and the elite/pro athlete. Each population is different. We are just begining to understand the differences in these population. What is know is that most studies have used college age individuals as they are easy to find, have the time etc. Bottom line we need to collect more data through well designed studies...
I'm suggesting that a conservative approach is prudent, by telling him to wait. I have trained many under 19 athletes in endurance sports...the ones that are the best are not the young superstars, but the ones who dedicate themselves in patient manner to achive their longterm goals.
Not all scientists drink pepsi in white lab coats. Some can squat 2.6x our BW. Lets not generalize here. We try out best to design good studies with limited money resources. It is not easy to design experiments that take into account all variables...
Yes, us scientists can also learn from the althetes. It gives us ideas to test. Most scientists are VERY open minded by nature.
I suggest you look through the scientific literature. Use Review papers to Start. Read alot. Come up with your own conclusions, but I would encourge your to start with the ideas that have been tested, rather than take and idea out from some forum or some big guy at the gym.
RD